2-Aryl benzazole derived new class of anti-tubercular compounds: Endowed to eradicate mycobacterium tuberculosis in replicating and non-replicating forms

Article abstract of DOI:10.1016/j.bioorg.2020.104170

The high mortality rate and the increasing prevalence of Mtb resistance are the major concerns for the Tuberculosis (TB) treatment in this century. To counteract the prevalence of Mtb resistance, we have synthesized 2-aryl benzazole based dual targeted molecules. Compound 9m and 9n were found to be equally active against replicating and non-replicating form of Mtb (MIC_(MABA) 1.98 and 1.66 μg/ml; MIC_(LORA) 2.06 and 1.59 μg/ml respectively). They arrested the cell division (replicating Mtb) by inhibiting the GTPase activity of FtsZ with IC₅₀ values 45 and 64 μM respectively. They were also capable of kill Mtb in non-replicating form by inhibiting the biosynthesis of menaquinone which was substantiated by the MenG inhibition (IC₅₀ = 11.62 and 7.49 μM respectively) followed by the Vit-K2 rescue study and ATP production assay.

Full text of DOI:10.1016/j.bioorg.2020.104170

BioorganicChemistry103(2020)104170
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
2-Aryl benzazole derived new class of anti-tubercular compounds: Endowed
to eradicate mycobacterium tuberculosis in replicating and non-replicating
forms
Anand Babu Velappana, Dhrubajyoti Dattab,1, Rui Mac, Shiwani Ranad, Kalyan Sundar Ghoshd,
⁎
Natarajan Harie, Scott G. Franzblauc, Joy Debnatha,
a Department of Chemistry, SCBT, SASTRA Deemed to be University, Tamilnadu 613401, India
b Department of Chemistry, Indian Institute of Science Education and Research, Pune, Maharashtra 411008, India
c Institute for Tuberculosis Research, College of Pharmacy, University of Illinois at Chicago, 833 S. Wood St., Chicago, IL 60612, USA
d Department of Chemistry, National Institute of Technology Hamirpur, Himachal Pradesh 177005, India
e NMR Laboratory, SCBT, SASTRA Deemed to be University, Tamilnadu 613401, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
The high mortality rate and the increasing prevalence of Mtb resistance are the major concerns for the
Tuberculosis (TB) treatment in this century. To counteract the prevalence of Mtb resistance, we have synthesized
2-aryl benzazole based dual targeted molecules. Compound 9m and 9n were found to be equally active against
replicating and non-replicating form of Mtb (MIC(MABA) 1.98 and 1.66 μg/ml; MIC(LORA) 2.06 and 1.59 μg/ml
respectively). They arrested the cell division (replicating Mtb) by inhibiting the GTPase activity of FtsZ with IC50
values 45 and 64 μM respectively. They were also capable of kill Mtb in non-replicating form by inhibiting the
biosynthesis of menaquinone which was substantiated by the MenG inhibition (IC50 = 11.62 and 7.49 μM re-
spectively) followed by the Vit-K2 rescue study and ATP production assay.
Benzazole
MenG enzyme
Tuberculosis
FtsZ enzyme
1. Introduction
endogenous resistance, which can be because of lower cell permeability
or increased efflux or up-regulation of the target enzyme. Thus, for the
Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) is the
single disease which causes an estimate of 1.5 million deaths according
to WHO Global Tuberculosis Report 2019 [1]. Despite the tremendous
effort it is difficult to control, as evidenced from the comparative da-
tabase of Global Tuberculosis Report 2018 [2] and 2019, where a de-
crease of only ~ 0.1 million mortality rate was observed. In Africa and
Asia, new TB incidences were found between 100,000 to 2,500,000 [1].
TB treatment itself is challenging regarding its early and accurate di-
agnosis, administration of effective drug regimen and resistant
screening. Moreover, the high tolerance of Mtb towards first line (e.g.,
Isoniazid, rifampicin, Pyrazinamide) [3–7] and second line antibiotics
(e.g., Streptomycin, Ethionamide, Ofloxacin) [8–10] are the major
concerns. Therefore, it is pertinent to revisit our drug designing strategy
for broadening the antibiotic spectrum against Mtb.
TB patients anti-tuberculosis drugs are used in combination with others
[12]. However, sometimes effectiveness of the combination therapy
over systematic monotherapy was found to get compromised with ne-
phrotoxicity and ototoxicity in several clinical studies [13]. The genetic
reason for the occurrence of high level of endogenous resistance against
a particular antibiotic is due to its single gene product target [14].
Alternatively, the probability of high level resistance is low for the
drugs which interacts with multiple biological targets, i.e., a product of
multiple genes. Hence, for a single targeted drug there is high chance
for single step mutation in the target enzyme or the target alteration
[15]. Therefore, multi-targeted drugs have an added advantage over the
single targeted drugs in prevention of target-based resistance develop-
ment.
Selection of a target is important for new drug development. It
needs to be pursued based on the significance of the target and un-
availability of the same in normal mammalian cell to minimize the
toxicity in host cell [16–21]. There are several promising targets for
The popular Direct Observation Therapy (DOT) fundamentally re-
lies on the combination therapy [11]. The antibiotics used in a sys-
tematic monotherapy have a greater possibility for the high-level of
⁎ Corresponding author.
E-mail address: joydebnath@scbt.sastra.edu (J. Debnath).
1 Present address: Alnylam Pharmaceuticals, Inc. 675 W Kendall St., Cambridge, MA 02142, USA.
https://doi.org/10.1016/j.bioorg.2020.104170
Received 19 May 2020; Received in revised form 30 July 2020; Accepted 2 August 2020
Availableonline27August2020
0045-2068/©2020ElsevierInc.Allrightsreserved.

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
new drug development against Mtb [22–24], and there are several
multi-targeting molecules reported in literature [25–27]. The designing
of those molecules are primarily based upon the incorporation of bio-
logically labile linkers [28] where two known drug molecules are
connected with each other, however, the success of this designing relies
on the abundance of the enzyme to cleave the linker. There is another
method of designing, in which the molecule can target several enzymes
in a particular metabolic pathway (series inhibition). However, it is
quite rare to design molecules (without a linker) in such a way that they
can interact simultaneously with two different targets.
methylbenzoate (Scheme 1).
The respective 2-arylbenzimidazole molecules (9a-n, 10a-n) were
prepared through oxidative cyclization of o-phenylenediamine with 7a-
n and 8a-n in the presence of 20% p-TsOH [37] (Scheme 2).
However, for 2-arylbenzoxazole the above mentioned methodology
did not work. Hence to synthesize the target molecules 14a-n, we
prepared their corresponding imine by treating 2-hydroxyaniline with
4-methoxybenzaldehyde in the presence of catalytic amount of acetic
acid followed by the cyclization in the presence of DDQ to form the
benzoxazole ring (12) [38]. Thereafter, the building blocks 3a-j and 6a-
d were attached with the benzoxazole moiety by an ester linkage
(Scheme 3). The failure of DDQ mediated oxidative cyclization of 3-
methoxybenzaldehyde is presumed because of the + R effect of the
–OH group. In an effort to overcome this problem we used 3-ni-
trobenzaldehyde and we obtained quantitative yield (15) during the
cyclization. Thereafter, the nitro group was converted to hydroxyl
through a series of reactions. The compounds (18a-n) were then finally
prepared by using the building blocks 3a-j and 6a-d in the presence of
EDC.HCl and DMAP with quantitative yield (Scheme 3).
Filamenting temperature-sensitive mutant Z (FtsZ) is functionally
similar to tubulin protein, which is an important enzyme for the bac-
terial cell division. FtsZ monomers self–assembled during the bacterial
cell division and form the Z-ring at the site of septum formation [29].
The whole process from assemble, organization and ring formation is
regulated by the binding of GTP and its hydrolysis [30]. Several studies
have identified FtsZ as a potential target for the inhibitor designing to
eradicate Mtb in its replicating form [31–34]. On the other hand, to kill
the pathogen in its non-replicating form it is important to stop their
ATP synthesis pathway by inhibiting certain enzymes involved in this
process. Menaquinone (MQ) is a lipid soluble electron carrier which
plays an important role to harness the required energy from ATP in its
non-replicating form. Therefore, inhibition of the MQ biosynthesis can
be an effective measure to kill Mtb in its non-replicating form. The
unavailability of the targets in eukaryotic cells makes them very much
attractive for different drug development program.
Similar to benzoimidazole, the 2-arylbenzothiazole molecules were
prepared by DDQ mediated oxidative cyclization between 2-ami-
nothiophenol and corresponding aldehydes (19a-n and 20a-g). Like the
meta isomers, we prepared the para isomers with higher alkyl and al-
kenyl chains (23a-g) by three steps (Scheme 4) [39,40].
2.2. Determination of antitubercular activity and cytotoxicity
Based on our pervious findings we have seen that aliphatic chains
with variable carbon numbers, especially prenyl groups play a sig-
nificant role to kill the Mtb in non-replicating form and also improves
the anti-tubercular activity [35,36]. It is most likely because of the
recognition of isoprenyl group by the membrane bound MenG, which
eventually converts demethylmenaquinone (having isoprenyl group) to
menaquinone. In this report we have prepared three sets of hybrid
molecules having benzimidazole, benzoxazole and benzothiazole moi-
eties (active scaffold against FtsZ) with the attachment of various ali-
phatic chains (Fig. 1). All these heteroaryl systems were functionalized
at their 2-position with substituted aromatic ring. Collectively, we had
synthesized eighty four molecules in multiple steps. The synthesized
molecules were tested against H37Rv, H37Ra strains in their replicating
and non-replicating form. We also investigated the mechanism of action
of the best active molecules.
The synthesized compounds were tested for their anti-tubercular
activity against Mtb strains H37Ra (non pathogenic) and H37Rv (pa-
thogenic). Minimum inhibitory concentration (MIC) values were de-
termined by two different methods, Microplate Alamar Blue assay
(MABA) [41] and Low-Oxygen-Recovery Assay (LORA) [42]. Mamma-
lian PBMC cell was used to determine their cytoxicity and the corre-
sponding IC50 values were calculated from their dose response curve
[43]. The anti-tubercular activity and cytotoxicity value of the syn-
thesized molecules are given in Table 1.
For 2-Aryl benzimidazole derivatives (9a-9n; para-derivatives), we
observed a decent increase of anti-tubercular activity with the elonga-
tion of alkyl chain length and for 9f with 6-carbon aliphatic chain it
reaches to the optimum value of 6.03 μg/ml (MIC against replicating)
and 31.46 μg/ml (MIC against non-replicating) against H37Rv, and for
H37Ra these values were 6.25 and 25.00 μg/ml respectively. The 5 fold
increase of its activity against non-replicating Mtb prompted us to in-
corporated alkenyl group in place of alkyl chain. Compounds 9k-9n
with alkenyl chain showed almost limiting activity (MIC 2.49–1.66 μg/
ml) against replicating Mtb, however, there activity against the non-
replicating Mtb was found to increased by 20 times (for 9n) compared
to 9f. With the increase of alkenyl chain length and number of double
bonds, activity remains almost the same against replicating Mtb but
improved against non-replicating Mtb for both R37Rv and R37Ra
strains. These observations clearly demonstrated the importance of al-
kenyl chain, typically prenyl group for diminishing Mtb in its non-re-
plicating form. Similarly, for the meta-isomers of the same (10a-10n),
we did not observe any increment in their activity with the increase of
alkyl chain length. The best activity was observed for 10a with methyl
group but it was inactive against non-replicating Mtb (for H37Rv and
H37Ra). However, compound 10h with 8-carbon chain, showed almost
comparable or better activity in both replicating and non-replicating
Mtb. In the event of 10k-10n with alkenyl chain, we observe im-
provement of their activity against replicating Mtb but unlike the para-
isomers they were comparatively less active against non-replicating
Mtb. This experimental data indicated that perhaps the conformation of
the meta-analogues was not preferred by the target responsible for the
killing of non-replicating Mtb.
2. Results and discussion
2.1. Synthesis of the target molecules
In this study we had prepared several benzazole derivatives com-
prising of three series viz., benzimidazole, benzoxazole and benzothia-
zole. For the synthesis of the benzazole derivatives we first prepared the
intermediates 7a-n and 8a-n. These intermediates 7a-n and 8a-n were
prepared from 4-hydroxybenzaldehyde and 4-hydroxymethylbenzoate.
To avoid syn dihydroxylation of the alkenyl chains (allyl, prenyl, ger-
anyl and farnesyl) during KMnO4 mediated oxidation of the aldehyde to
carboxylic acid, we prepared 6a-d through O-alkylation of 4-hydro-
xymethylbenzoate followed by the alkaline hydrolysis of
Fig. 1. General structure of the synthesized molecules: the heteroaromatic
Molecules belonging to 2-Aryl benzoxazole series did not show ap-
preciable activity against Mtb either in replicating or non-replicating
system is connected with the alkyl/alkenyl chain through a spacer.
2

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
Scheme 1. Reagents and conditions: (a) R1Cl/R2Cl, K2CO3 in DMF, 80 °C, 8–12 h; (b) KMnO4, NaH2PO4 in CAN-H2O (1:1), rt, 3 h; (c) NaOH in dioxane-H2O (1:1),
reflux, 15 h; (d) m-hydroxybenzaldehyde, DCC, DMAP in DMF, rt, 3–8 h; (e) p-hydroxybenzaldehyde, DCC, DMAP in DMF, rt, 3–8 h. *Starting material p-meth-
oxybenzaldehyde.
Scheme 2. Reagents and conditions: (a) p-TsOH in DMF, 80 °C, 3–6 h.
form. Only for compounds 14j and 14l we observed MIC value ~50 μg/
ml against replicating or non-replicating Mtb for both H37Rv and
H37Ra. However, for compounds 14m and 14n, we observed improved
anti-tubercular activity, attributed to geranyl and farnesyl group re-
spectively. Most importantly, we observed better activity for these
molecules against the non-replicating Mtb compared to replicating,
which was similar to the molecules of 2-Aryl benzimidazole series. For
the meta-isomers the profile was almost the same with higher MIC va-
lues compared to their para-isomers.
replicating Mtb. On the contrary, for the meta-isomers we found that the
activity decreased with the increase of the alkyl chain length against
replicating Mtb and the best activity was recorded for 20a with methyl
chain. Again, an improved anti-tubercular activity was found (< 50 μg/
ml) for the alkenyl chain. However, compounds 23e, 23f and 23g with
prenyl, geranyl and farnesyl groups respectively showed no significant
difference in their activity towards replicating and non-replicating Mtb.
From the comparative activity of the synthesized molecules it was
concluded that the conformation (meta or para) and presence of the
heteroatom in the heteroaromatic ring has a significant role in their
activity against replicating and non-replicating forms of Mtb.
In case of the 2-Aryl benzothiazole derivatives (19a-19n, 20a-20g
and 23a-23g), we observed anti-tubercular activity of 30.12 μg/ml for
19h (with 8-carbon chain) against replicating Mtb. On the other hand,
compound 19i with of 9-carbon alkyl chain was found to be the most
active against the non-replicating Mtb. For the molecules with geranyl
(19m) and farnesyl (19n) chains the MIC values were found within the
range of 56–32 μg/ml against replicating and 40–28 μg/ml against non-
2.3. Effect of the active molecules on cell morphology
The effect of the synthesized derivatives on the cell division of Mtb
(H37Ra), was evaluated by comparing the morphology of untreated
3

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
Scheme 3. Reagents and conditions: (a) p-Methoxybenzaldehyde or m-nitrobenzaldehyde, MeOH, AcOH (cat.), rt, 3 h; (b) DDQ in DCM, rt, 2 h; (c) HBr in AcOH,
80 °C, overnight; (d) EDC.HCl, DMAP in THF, rt, 4–5 h; (e) NiCl2·6H2O, NaBH4 in MeOH, rt, 1 h; (f) i. NaNO2, HCl, 5 °C; ii. Heating at 80 °C for 6 h.
bacilli with treated bacilli under fluorescence microscope. Fluorescein
diacetate (FDA) was used as the fluorophore. Best three molecules were
selected with MIC < 4 μg/ml against the replicating Mtb. The elon-
gation in the morphology of the treated bacilli compared to the control
bacilli attributes to the inhibition of bacterial cell division by the
compounds 9k, 9l and 9m (Fig. 2). The elongation in the bacterial
morphology occurs due to decrease of cross linking of the pepti-
doglycan region of the cell wall so that the surface area of the cell in-
creased [44]. In the presence of compound 9k we observed maximum
elongation (> 10 μm) compared to 9l and 9m (≥5 μm) and it was
Scheme 4. Reagents and conditions: (a) CAN, H2O2, grinding, 3–10 min; (b) HBr in AcOH, 80 °C, 6 h; (c) EDC.HCl, DMAP in THF, rt, 3–5 h.
4

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
Table 1
Table 1 (continued)
The anti-tubercular activity and cytotoxicity values of the synthesized mole-
cules.
Comp.
MIC (μg/ml)
Cytotoxicity IC50 (μg/ml)
Comp.
MIC (μg/ml)
Cytotoxicity IC50 (μg/ml)
H37Rv
H37Ra
MABA**
LORA***
MABA**
LORA***
H37Rv
H37Ra
MABA**
LORA***
MABA**
LORA***
19n
20a
20b
20c
20d
20e
20f
31.49
29.51
35.87
98.67
> 100
> 100
> 100
> 100
> 100
> 100
> 100
52.37
43.52
30.29
35.42
0.40
27.81
70.42
82.69
> 100
nd*
25.00
25.00
50.00
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
50.00
50.00
25.00
50.00
0. 39
25.00
50.00
100.00
nd*
162.49
135.62
167.15
189.76
140.61
158.43
153.15
179.08
184.52
165.09
153.55
149.39
180.47
181.07
142.59
73.09
9a
24.39
19.70
21.18
17.52
9.47
80.24
68.31
72.51
41.94
30.64
31.46
nd*
25.00
25.00
25.00
12.50
12.50
6.25
100.00
50.00
50.00
50.00
50.00
25.00
nd*
131.52
149.31
160.89
170.18
147.17
158.32
180.49
197.83
183.57
163.91
157.11
103.42
179.30
162.97
153.08
171.01
108.34
121.98
142.37
150.06
167.81
183.49
156.03
191.54
161.06
142.11
169.31
158.09
162.39
157.55
168.81
141.43
159.35
168.38
157.02
160.52
182.39
136.41
148.32
165.11
178.21
161.54
159.08
121.39
159.45
182.05
171.56
168.39
151.15
168.30
189.13
172.58
176.31
172.45
168.91
159.37
134.02
153.15
128.62
157.52
163.47
169.07
168.04
121.04
129.06
134.48
149.32
133.07
145.51
9b
9c
nd*
9d
nd*
nd*
9e
nd*
nd*
9f
6.03
20g
23a
23b
23c
23d
23e
23f
nd*
nd*
9g
> 100
> 100
> 100
> 100
2.49
100.00
100.00
> 100
> 100
3.13
nd*
nd*
9h
nd*
nd*
nd*
nd*
9i
nd*
nd*
nd*
nd*
9j
nd*
nd*
43.11
49.12
28.73
21.02
> 100
0.04
50.00
50.00
25.00
25.00
> 100
0.08
9k
24.36
6.47
2.06
1.59
> 100
70.07
nd*
25.00
6.25
3.13
1.56
50.00
100.00
100.00
nd*
9l
2.16
3.13
9m
9n
1.98
3.13
23g
INHa
RIFb
1.66
6.25
10a
10b
10c
10d
10e
10f
10g
10h
10i
10j
10k
10l
10m
10n
14a
14b
14c
14d
14e
14f
14g
14h
14i
14j
14k
14l
14m
14n
18a
18b
18c
18d
18e
18f
18g
18h
18i
18j
18k
18l
18m
18n
19a
19b
19c
19d
19e
19f
19g
19h
19i
19j
19k
19l
19m
23.85
41.87
> 100
> 100
> 100
> 100
82.78
41.61
> 100
> 100
> 100
11.74
7.22
25.00
50.00
50.00
> 100
> 100
> 100
100.00
50.00
> 100
> 100
> 100
12.50
6.25
0.01
0.02
63.15
* Not determined.
nd*
** Microplate Alamer Blue Assay (for replicating form of Mtb).
*** Low Oxygen Recovery Assay (for non-replicating form of Mtb).
nd*
nd*
nd*
nd*
a
b
INH: Isoniazid.
78.24
31.04
nd*
nd*
RIF: Rifampin.
25.00
nd*
nd*
nd*
nd*
nd*
20.00
12.91
13.25
91.46
> 100
nd*
25.00
12.50
12.50
100.00
> 100
nd*
6.08
6.25
63.18
80.32
> 100
> 100
> 100
> 100
> 100
> 100
> 100
49.52
55.36
> 100
11.61
9.65
50.00
100.00
> 100
> 100
> 100
> 100
> 100
> 100
50.00
50.00
50.00
> 100
12.50
12.50
100.00
50.00
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
100.00
25.00
25.00
25.00
50.00
50.00
50.00
100.00
> 100
> 100
> 100
25.00
50.00
> 100
25.00
50.00
50.00
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
52.04
39.08
nd*
50.00
50.00
nd*
8.72
5.43
> 100
72.58
nd*
12.50
6.25
> 100
100.00
nd*
83.08
39.06
> 100
> 100
> 100
> 100
> 100
> 100
> 100
> 100
85.09
50.08
34.52
65.11
43.37
60.20
71.31
88.59
> 100
> 100
> 100
30.12
39.52
> 100
20.33
48.23
56.13
Fig. 2. Effect of the compounds 9k, 9l and 9m on the cell morphology (H37Ra).
Cells were grown for 7 days without any compound (control) and with 2xMIC of
9k, 9l and 9m. 10 μl of FDA solution was used to take fluorescence image.
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
nd*
longer than the untreated Mtb (2.5 – 3 μm). This finding was in well
agreement with their respective MIC values against replicating Mtb.
nd*
nd*
nd*
nd*
65.81
41.27
21.38
18.45
30.81
80.31
68.42
79.09
nd*
50.00
50.00
25.00
12.50
25.00
100.00
50.00
> 100
nd*
2.4. Gtpase activity of the FtsZ in the presence of active molecules
Cell division occurs through a septa formation at the division site,
which is formed through the polymerization of the FtsZ enzyme. FtsZ is
a GTPase enzyme, which converts GTP to GDP and thereby harnesses
the energy to generate the key constructive force for bacterial cell di-
vision. Therefore, we measured the GTPase activity of FtsZ (Mtb) in the
presence of our synthesized molecules to find out the reason (target) for
their anti-mycobacterium activity against replicating Mtb. Compounds
9k, 9l and 9m (MIC < 3 μg/ml against replicating Mtb) were selected
for this assay, where we quantified and compared the inorganic phos-
phate content in the presence of FtsZ with and without the synthesized
compounds. The best IC50 value was obtained for compound 9k
(32 μM), which indeed showed the optimum elongation of Mtb (Fig. 3).
nd*
nd*
nd*
nd*
47.31
40.63
nd*
50.00
50.00
nd*
43.12
nd*
50.00
nd*
40.09
50.00
5

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
IC50 = 64.1 3.9 µM
IC50 = 46.2 3.7 µM
IC50 = 32.0 4.1 µM
Fig. 3. Concentration-response curve of GTPase activity for FtsZ (Mtb) in the presence of comp. 9k (A), 9l (B) and 9m (C). Assay composition: 3.5 µM FtsZ with
varying concentrations of the 9k, 9l and 9m (5–100 µM) in 50 µM MOPS buffer for 10 min at 25 °C, followed by the addition of 500 µM GTP in 5 µM MgCl2 and
200 µM KCl. Each point represents the mean of three independent assays, and the vertical bars show the standard derivation of the mean.
2.5. Docking study with Mtb-FtsZ with 9k, 9l and 9n
thiophosphate, although the guanine and benzoimidazole moieties
were found to get projected at perpendicular with each other (Fig. 4B).
On the other hand, in the docked conformation of 9l and 9n we ob-
served that the benzoimidazole moiety of these compounds resided
remarkably close to T6 loop like guanine (for GTPγS) (Fig. 4C and D).
Nevertheless, the alkenyl chains of these molecules were found to get
exposed in an opposite direction compared to the γ-thiophosphate (T1-
T4 loop), which is presumably because of the increase of hydro-
phobicity of the flanking chain. Therefore, we observed a decreased
After the FtsZ inhibition assay we proceeded for the docking study
with 9k, 9l and 9n to visualize their binding conformation within the
protein. This docking study revealed that all the three molecules bind at
the active site (GTPase domain) of FtsZ protein. However, their modes
of bindings were quite different with each other. Compared to the
conformation of GTPγS in FtsZ (PDB ID: 1RLU) [45], the alkenyl chain
of 9k was found to occupy the same pocket (T1 to T4 loops) as for the γ-
Fig. 4. Docking conformation and comparison of GTPγS binding with 9k, 9l and 9m. (A) Conformations of GTPγS, 9k, 9l and 9m together in Mtb-FtsZ. (B) Relative
conformation between GTPγS (white) and 9k (Yellow); (C) Relative conformation between GTPγS (white) and 9l (Red); (D) Relative conformation between GTPγS
(white) and 9n (Cyan). Energy minimization and docking was performed using AutoDock software. (For interpretation of the references to colour in this figure
legend, the reader is referred to the web version of this article.)
6

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
Fig. 5. The IC50 curve for the MenG inhibition assay by synthesized compound; (A) Comp. 9l, (B) Comp. 9m, (C) Comp. 9n, (D) Comp. 10m, (E) Comp. 10n and (F)
Comp. 14n, using H37Ra membrane fraction. Substrate A (500 μM) was mixed with 500 μM SAM and 100 μl membrane fraction and incubated for 3 h at 37 °C. Each
point represents the mean of three independent assays, and the vertical bars show the standard derivation of the mean.
activity of compound 9l and 9n compared with compound 9k on FtsZ,
and it is in well corroboration with our previous observation (change in
cell morphology).
The substrate and the product were prepared separately (SI-I)
[35,48] for calibration and identification purpose. The retention times
for substrate (comp. A) and product (comp. B) were 5.713 min and
6.400 min respectively, which was found good to determine the IC50
value using HPLC system. The membrane fraction (according to the
reported protocol) [49] of Mtb (H37Ra) was used as a source of mem-
brane bound MenG. Representative IC50 profiles for effective com-
pounds are shown in Fig. 5 (and SI-I). The IC50 calculation was based on
the conversion of A with respect to the control set (without inhibitor
molecule) and given in Table 2.
2.6. Effect of the synthesized molecules on MenG
To understand the plausible reason of their activity against non-
replication Mtb, we tested the active molecules against the respiratory
system, as it remains active in the dormant state. Hence, our synthe-
sized molecules have structural resemblance with MenG substrate;
therefore, we performed the MenG inhibition study with compounds 9l,
9m, 9n, 10m, 10n, 14m, 14n and 18n (LORA MIC ≤ 12.5 μg/ml;
MABA MIC ≤ 25 μg/ml against H37Ra). The MenG inhibition values
(IC50) were determined by HPLC based assay, which is quite similar to
the MenA inhibition assay except the use of DMMQ and SAM (methyl
transferring agent) [46]. MenG is the final enzyme in the menaquinone
biosynthesis pathway, which converts the DMMQ to MQ in the presence
of SAM. The MQ accepts two electrons from NADH and get converted to
its reduced form, finally it again reversibly converted to MQ by trans-
ferring these electrons to the other electron acceptors present in the
electron transport system. Therefore, inhibition of this enzyme is ex-
pected to perturb the respiratory system of Mtb through which it har-
nesses its required energy in the latent or non-replicating state [47].
In this assay the conversion of the model substrate (comp. A;
DMMQ) by MenG (from H37Ra) to the corresponding product (Comp.
B; MQ) was monitored at 250 nm (by HPLC) in the presence of 6 dif-
ferent concentrations of the synthesized molecules and the corre-
sponding IC50 values were calculated by non-linear regression analysis
(Table 2).
The best activity was observed for compound 9n (IC50 7.49 μM)
with farnesyl side chain. However, comparative activity of 9n, 10n,
14n and 18n against MenG showed that it was not only the farnesyl
group but the presence of heteroatom in the benzazole ring and the
overall orientation (meta or para) of the molecule played a decisive role
for inhibition of MenG activity.
To find out the consequence of MQ biosynthesis inhibition in the
dormant state of Mtb, we prepared the dormant H37Ra following the
reported protocol [50] and performed the Vit-K2 rescue experiment.
Vit-K2 (MQ) is the only quinone present in the electron transport chain
of Mtb. Thus, inhibition of the MQ synthesis is expected to affect the
energy harnessing process in its non-replicating state. Whereas, co-
culture of Mtb with Vit-K2 is used to provide the electron carrier ex-
ternally and by virtue of this supplement Mtb becomes able to convert
ATP to ADP despite the inhibition of the MQ biosynthesis. In the pre-
sence of Vit-K2 (1 mM), the growth of the H37Ra (dormant form) did
not significantly affected after 10 days exposure (Fig. 6; left panel).
However, when they were incubated with 9l, 9m, 9n and 14n (20 μg/
ml) the growth was diminished to 5.3, 4.1, 2.6 and 4.8 log10CFU/ml
respectively compared to the set with 1 mM Vit-K2 (Fig. 6; right panel).
Table 2
Effect of the synthesized molecules on the MenG inhibition.
Compound
Men G Inhibition; IC50 (μM) H37Ra
9l
12.59
11.62
7.49
0.49
0.21
9m
9n
0.37
10m
10n
14m
14n
18n
23.29
21.37
32.53
16.57
36.61
1.03
0.71
0.14
0.09
1.23
7

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
Fig. 6. Effect of the comp. 9l, 9m, 9n and 14n against non-replicating H37Ra: Growth of the non-replicating H37Ra in absence and in the presence of Vit-K2 (1 mM)
at 0th and 10th day (Left panel); Growth of the non-replicating H37Ra in absence and in the presence of Vit-K2 (1 mM) and comp. 9l, 9m, 9n and 14n at 20 μg/ml on
10th day followed by 27 days after CFU counting on 7H10 agar plate (Right panel). Each point represents the mean of three independent assays, and the vertical bars
show the standard derivation of the mean.
This provided unambiguous evidence of molecules inhibiting the bio-
synthesis of MenG and in turn reduced their growth in dormant state by
blocking the respiratory chain of H37Ra.
Table 3
The MIC values of the compounds 9l, 9m, 9n and 14n against H37Rv drug
resistance strains.
Entry Strains
Thereafter, the production of ATP was measured in presence of our
best molecule 9n (MICLORA < 2 μg/ml and IC50 (MenG) < 10 μM).
The ATP/ADP ratio was varied in the range of 1.04–1.34 for the control
set from day 3 to day 9 (Fig. 7). For the co-culture of the dormant
H37Ra with comp. 9n (10, 25 and 50 μg/ml), we observed continuous
reduction in their ATP production level which confirms that the comp.
9n eradicates Mtb in the dormant state by inhibiting the MenG bio-
synthesis and as a whole by reducing its ATP production.
MIC (μg/ml) against replicating Mtb
9l
9m
9n
14n
INHa
RIFb
1
2
H37Rv (ATCC 27294)
2.16
1.04
3.54
2.13
4.66
1.42
9.65
3.27
0.4
0.01
0.03
H37Rv-INH-R(ATCC
35822)
> 8
3
H37Rv-RIF-R (ATCC
35838)
1.57
1.94
1.06
4.14
0.25
> 2
a
b
INH: Isoniazid.
RIF: Refampin, The MIC value were calculated by agar plate dilution
2.7. Effect on resistant strains of Mtb
method.
Finally, we tested the best molecules 9l, 9m, 9n and 14n (MABA
and LORA MIC < 10 μg/ml) against the isoniazide and refampin re-
sistant H37Rv strains (ATCC-35822 and ATCC-35838 respectively).
Both these compounds showed slightly better MIC values against the
resistance strains as compared to the non-resistance strain (Table 3).
3. Conclusion
In conclusion, 84 molecules were designed and synthesized to target
the cell division and the respiratory system of Mtb simultaneously.
Compounds with alkenyl chain, typically geranyl and farnesyl group
showed the best activity against replicating and non-replicating Mtb.
Out of the three heterocyclic systems, it was observed that the ben-
zoimidazole was the most preferred one. The anti-tubercular activity for
the best active molecules against replicating form was found because of
the inhibition of GTPase activity of FtsZ enzyme, which was system-
atically substantiated by the morphological change of Mtb and reduc-
tion of GTPase activity of FtsZ enzyme in the presence of active mole-
cules. Comparative activity of molecules with small aliphatic chain and
prenyl group showed that the heterocyclic ring was mainly responsible
for their activity against replication Mtb. The presence of aliphatic
chain has a role in their activity to some extent as observed from the
docking conformations. On the other hand, for the molecules with
prenyl groups we observed a significant improvement in their activity
against non-replicating Mtb, which is attributed to their better re-
cognition by MenG enzyme. The best molecule (9n) against non-re-
plicating Mtb showed IC50 value as 7.49 μM for in MenG inhibition
assay. The Vit-K2 rescue study for comp. 9n with farnesyl group clearly
showed the best inhibitory effect on the electron transport system at
20 μg/ml concentration which gets revived in the presence of Vit-K2.
Similarly, the ATP/ADP ratio got diminished in the presence of 9n,
which plausibly confirms that these molecules (with prenyl chain)
eradicate the Mtb in its non-replication form by affecting its electron
transport system. The dual-targeted best molecules 9l, 9m, 9n and 14n
Fig. 7. Effect of Comp. 9n on the ATP synthesis against non-replicating H37Ra
on 3rd, 6th and 9th day at 10, 25 and 50 μg/ml. Each point represents the mean
of two independent assays, and the vertical bars show the standard derivation
of the mean.
8

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
were also found to be active against INH and RIF resistant strains. This
work shows that by customizing the molecular design we can perturb
more than one target of Mtb, to counteract the emergence of resistant
strain.
4.3. General procedure for 4-alkoxy benzoic acids (6a-6d)
4-alkenyloxy methyl benzoate (28.0 mmol) was dissolved in 1, 4-
dioxane in water (1:1) followed by the addition of sodium hydroxide
(84.0 mmol) and maintained under reflux for 24–30 h. After completion
of reaction, volatiles were evaporated and the aqueous mass neutralized
with concentrated hydrochloric acid. The white solid thus formed was
filtered, washed thoroughly with water and dried to afford the benzoic
acids.
4. Experimental
4.1. Reagents and instrumentation
All the reagents were purchased from Sigma-Aldrich, Alfa-Aesar and
Merck chemicals. Solvents were dried according to the standard pro-
tocols. TLC were performed on Merck silica gel 60, f254 pre-coated
aluminium plates. Spots were visualized under UV lamp or stained
using 10% PMA in Ethanol, 5% Sulfuric acid in methanol or Iodine.
Column chromatographic separations were performed using silica gel
(100–200 mesh). NMR spectra were run on Bruker AVANCE II instru-
ment using TMS as internal standard for 1H (300 and 400 MHz) and
solvent as internal standard for 13C (75 and 100 MHz) experiments.
Chemical shifts were given in ppm (δ scale) UV–vis measurements were
made using a Perkin Elmer UV–vis spectrophotometer (Model Lambda
25). Mass spectra had been recorded using Waters Mass Spectrometer
(model XevoG2QTof). HPLC experiments were performed using an
Agilent 1200 infinity series with DAD detector with silica C18 column
(4.6x250mm) and 5 μm.
4.3.1. 4-(allyloxy)benzoic acid (6a)
Yield- 85.4%; white solid; m.p- 142–144 °C; 1H NMR (400 MHz,
CDCl3): δ 4.64 (d, J = 5.4 Hz, 2H), 5.34–5.37 (m, 1H), 5.46–5.48 (m,
1H), 6.05–6.11 (m, 1H), 6.99 (d, J = 6.8 Hz, 2ArH), 8.09 (d,
J = 6.8 Hz, 2ArH). HRMS (ESI+): m/z calculated for C10H10O3 [M
+H]+: 178.0630; found: 178.0633.
4.3.2. 4-((3-methylbut-2-en-1-yl)oxy)benzoic acid (6b)
Yield- 81.4%; white solid; m.p- 136–138 °C; 1H NMR (400 MHz,
CDCl3): δ 1.79 (s, 3H), 1.84 (s, 3H), 4.62 (d, J = 5.4 Hz, 2H), 5.52 (t,
J = 6.4 Hz, 1H), 6.98 (d, J = 6.8 Hz, 2ArH), 8.09 (d, J = 6.8 Hz,
2ArH). HRMS (ESI+): m/z calculated for C12H14O3 [M+H]+:
206.0943; found: 206.0947.
4.3.3. (E)-4-((3,7-dimethylocta-2,6-dien-1-yl)oxy)benzoic acid (6c)
Yield- 82.5%; white solid; m.p- 108–110 °C; 1H NMR (400 MHz,
CDCl3): δ 1.61 (s, 3H), 1.68 (s, 3H), 1.76 (s, 3H), 2.06–2.15 (m, 4H)
4.62 (d, J = 6.6 Hz, 2H), 5.07–5.10 (m, 1H), 5.47–5.51 (m, 1H), 6.96
(dd, J = 2.4, 9.0 Hz, 2ArH), 8.05 (d, J = 8.7 Hz, 2ArH), 9.87 (s, 1H
COOH). HRMS (ESI+): m/z calculated for C17H22O3 [M+H]+:
274.1569; found: 274.1574.
4.2. General procedure for methyl 4-alkenyloxy benzoates (5a-5d)
4-Hydroxy methyl benzoate (5.0 g, 32.9 mmol) was dissolved in
DMF and to that Potassium carbonate (11.4 g, 82.25 mmol) was added
under stirring. Finally the corresponding alkenyl halide (39.5 mmol)
was added and maintained at 80 °C for 8–12 h. After completion of
reaction, the reaction mass was poured into water and extracted with
ethyl acetate (3x150 ml). Combined organic layer was thoroughly
washed with water followed by brine solution. The organic portion was
evaporated and purified by column chromatography (silica gel 100–200
mesh) using ethyl acetate in hexanes to afford the compounds.
4.3.4. 4-(((2E,6E)-3,7,11-trimethyldodeca-2,6,10-trien-1-yl)oxy)benzoic
acid (6d)
Yield- 68.8%; white solid; m.p- 56–58 °C; 1H NMR (400 MHz,
CDCl3): δ 1.60 (s, 6H), 1.68 (s, 3H), 1.75 (s, 3H) 1.81–2.18 (m, 8H),
4.61 (d, J = 6.6 Hz, 2H), 5.09–5.11 (m, 2H), 5.48–5.51 (m, 1H), 6.95
(d, J = 9.0 Hz, 2ArH), 8.04 (d, J = 8.7 Hz, 2ArH). HRMS (ESI+): m/z
calculated for C22H30O3 [M+H]+: 342.2195; found: 342.2198.
4.2.1. Methyl 4-(allyloxy)benzoate (5a)
Yield- 85.7%; colorless liquid; 1H NMR (300 MHz, CDCl3): δ 3.88 (s,
3H), 4.59 (dt, J = 1.5, 5.4 Hz, 2H), 5.32 (dq, J = 1.5, 10.5 Hz, 1H),
5.42 (dq, J = 1.5, 17.4 Hz, 1H), 5.99–6.12 (m, 1H), 6.90–6.95 (m,
2ArH), 7.96–8.01 (m, 2ArH). HRMS (ESI+): m/z calculated for
4.3.5. General procedure for the synthesis of aldehyde scaffolds 7a-7n and
8a-8n
3-Hydroxybenzaldehyde (for 7a-7n) or 4-hydroxybenzaldehyde (for
8a-8n) (1.0 g, 8.19 mmol), DMAP (0.05 g, 0.4 mmol) and the corre-
sponding 4-alkoxy benzoic acid (8.19 mmol) were dissolved in DMF
and stirred at room temperature for 15 min. Then DCC (2.0 g,
9.83 mmol) was added drop wise to the reaction mixture. After com-
pletion of reaction, the reaction mixture was diluted with ethyl acetate
and filtered through celite. The filtrate was washed with water and
brine solution. The organic portion was dried over sodium sulfate and
concentrated under reduced pressure. The crude was then purified by
column chromatography (silica gel 100–200 mesh) using ethyl acetate
in hexanes to obtain the product.
C
11H12O3 [M+H]+: 192.0786; found: 1925.0790.
4.2.2. Methyl 4-((3-methylbut-2-en-1-yl)oxy)benzoate (5b)
Yield- 87.5%; colorless liquid; 1H NMR (300 MHz, CDCl3): δ 1.76 (s,
3H), 1.81 (s, 3H), 3.88 (s, 3H), 4.56 (d, J = 6.9 Hz, 2H), 5.48 (tt,
J = 1.5, 6.9 Hz, 1H), 6.89–6.95 (m, 2ArH) 7.96–8.01 (m, 2ArH). HRMS
(ESI+): m/z calculated for C13H16O3 [M+H]+: 220.1099; found:
220.1101.
4.2.3. Methyl-4-((3,7-dimethylocta-2,6-dien-1-yl)oxy)benzoate (5c)
Yield- 83.2%; colorless liquid; 1H NMR (300 MHz, CDCl3): δ 1.61 (s,
3H), 1.68 (s, 3H), 1.75 (s, 3H), 2.05–2.14 (m, 4H), 3.88 (s, 3H), 4.59 (d,
J = 6.3 Hz, 2H), 5.06–5.11 (m, 1H), 5.48 (td, J = 1.2, 6.6 Hz, 1H),
6.90–6.95 (m, 2ArH), 7.96–8.01 (m, 2ArH). HRMS (ESI+): m/z calcu-
lated for C18H24O3 [M+H]+: 288.1725; found: 288.1729.
4.3.6. Synthesis of 3-formylphenyl 4-methoxybenzoate (7a)
Yield: 1.65 g, 78.6%, white solid, m.p: 78–80 °C, 1H NMR (400 MHz,
CDCl3): δ 3.91 (s, 3H), 7.01 (dd, J = 2.0, 6.8 Hz, 2ArH), 7.48–7.51 (m,
1ArH), 7.60 (t, J = 7.6 Hz, 1ArH), 7.75 (d, J = 2.0 Hz, 1ArH),
7.79–7.81 (m, 1ArH), 8.17 (dd, J = 2.0, 6.8 Hz, 2ArH), 10.04 (s, 1H
CHO). HRMS (ESI+): m/z calculated for C15H13O4 [M+H]+: 257.0814;
found: 257.0815.
4.2.4. Methyl 4-((-3,7,11-trimethyldodeca-2,6,10-trien-1-yl)oxy)benzoate
(5d)
Yield- 81.6%; colorless liquid; 1H NMR (400 MHz, CDCl3): δ 1.60 (s,
6H), 1.67 (s, 3H), 1.74 (s, 3H), 1.81–2.11 (m, 8H), 3.88 (s, 3H), 4.59 (d,
J = 6.4 Hz, 2H), 5.09–5.12 (m, 2H), 5.48–5.51 (m, 1H), 6.87–6.93 (m,
2ArH), 7.93–7.99 (m, 2ArH). HRMS (ESI+): m/z calculated for
4.3.7. Synthesis of 3-formylphenyl 4-ethoxybenzoate (7b)
Yield: 1.83 g, 82.8%, white solid, m.p: 76–78 °C, 1H NMR (400 MHz,
CDCl3): δ 1.47 (t, J = 7.2 Hz, 3H), 4.14 (q, J = 7.2 Hz, 2H), 6.98 (dd,
J = 2.0, 6.8 Hz, 2ArH), 7.50 (dd, J = 1.2, 2.4 Hz, 1ArH) 7.60 (t,
C
23H32O3 [M+H]+: 356.2351; found: 356.2352.
9

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
J = 7.6 Hz, 1ArH), 7.74–7.80 (m, 2ArH), 8.15 (dd, J = 2.0, 6.8 Hz,
2ArH), 10.03 (s, 1H CHO). HRMS (ESI+): m/z calculated for C16H15O4
[M+H]+: 271.0970; found: 271.0973.
[M+H]+: 369.2066; found: 369.2067.
4.3.15. Synthesis of 3-formylphenyl 4-(decyloxy)benzoate (7j)
Yield: 2.68 g, 85.6%, white solid, m.p: 38–40 °C, 1H NMR (400 MHz,
CDCl3): δ 0.89 (t, J = 6.8 Hz, 3H), 1.28–1.38 (m, 12H), 1.48 (sextet,
J = 6.8 Hz, 2H), 1.81 (quintet, J = 6.8 Hz, 2H), 4.05 (t, J = 6.4 Hz,
2H), 6.99 (dd, J = 2.0, 6.8 Hz, 2ArH), 7.48–7.51 (m, 1H), 7.60 (t,
J = 7.6 Hz, 1ArH), 7.74 (t, J = 2.0 Hz, 1ArH), 7.79 (dt, J = 1.2,
7.6 Hz, 1ArH), 8.15 (dd, J = 2.0, 6.8 Hz, 2ArH), 10.03 (s, 1H CHO).
HRMS (ESI+): m/z calculated for C24H31O4 [M+H]+: 383.2222; found:
383.2224.
4.3.8. Synthesis of 3-formylphenyl 4-propoxybenzoate (7c)
Yield: 2.10 g, 90.1%, white solid, m.p: 72–74 °C, 1H NMR (300 MHz,
CDCl3): δ 1.07 (t, J = 7.5 Hz, 3H), 1.85 (sextet, J = 7.2 Hz, 2H) 4.02 (t,
J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH), 7.49 (dq, J = 1.2, 8.1 Hz,
1ArH), 7.60 (t, J = 7.8 Hz, 1ArH), 7.74 (t, J = 1.5 Hz, 1ArH), 7.80 (dt,
J = 1.2, 7.5 Hz, 1ArH), 8.12–8.17 (m, 2ArH) 10.03 (s, 1H CHO). HRMS
(ESI+): m/z calculated for C17H17O4 [M+H]+: 285.1127; found:
285.1128.
4.3.16. Synthesis of 3-formylphenyl 4-(allyloxy)benzoate (7k)
Yield: 2.1 g, 90.9%, white solid, m.p: 58–60 °C, 1H NMR (400 MHz,
CDCl3): δ 4.64 (dt, J = 1.2, 5.6 Hz, 2H), 5.33–5.37 (m, 1H), 5.43–5.48
(m, 1H), 6.04–6.11 (m, 1H), 7.02 (dd, J = 2.0, 6.8 Hz, 2ArH),
7.48–7.51 (m, 1ArH), 7.60 (t, J = 7.6 Hz, 1ArH), 7.74 (t, J = 2.0 Hz,
1ArH), 7.80 (dt, J = 1.2, 7.6 Hz, 1ArH), 8.16 (dd, J = 2.0, 6.8 Hz,
2ArH), 10.03 (s, 1H CHO). HRMS (ESI+): m/z calculated for C17H15O4
[M+H]+: 283.0970; found: 283.0973.
4.3.9. Synthesis of 3-formylphenyl 4-butoxybenzoate (7d)
Yield: 2.11 g, 86.5%, white solid, m.p: 66–68 °C, 1H NMR (400 MHz,
CDCl3): δ 0.98 (t, J = 7.2 Hz, 3H), 1.52 (sextet, J = 7.2 Hz, 2H), 1.82
(quintet, J = 6.4 Hz, 2H), 4.06 (t, J = 6.4 Hz, 2H), 6.99 (dd, J = 2.0,
6.8 Hz, 2ArH), 7.48–7.51 (m, 1ArH), 7.60 (t, J = 7.6 Hz, 1ArH), 7.74 (t,
J = 2.0 Hz, 1ArH), 7.79 (d, J = 7.6 Hz, 1ArH), 8.15 (dd, J = 2.0,
6.8 Hz, 2ArH), 10.03 (s, 1H CHO). HRMS (ESI+): m/z calculated for
C
18H19O4 [M+H]+: 299.1283; found: 299.1288.
4.3.17. Synthesis of 3-formylphenyl 4-((3-methylbut-2-en-1-yl)oxy)
benzoate (7l)
4.3.10. Synthesis 3-formylphenyl 4-(pentyloxy)benzoate (7e)
Yield: 2.18 g, 85.2%, white solid, m.p: 60–62 °C, 1H NMR (300 MHz,
CDCl3): δ 0.95 (t, J = 7.2 Hz, 3H), 1.40–1.49 (m, 4H), 1.84 (quintet,
J = 7.5 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH),
7.46–7.54 (m, 1ArH), 7.60 (t, J = 1.5 Hz, 1ArH), 7.74 (t, J = 1.5 Hz,
1ArH), 7.80 (dt, J = 1.2, 7.5 Hz, 1ArH), 8.12–8.16 (m, 2ArH), 10.03 (s,
1H CHO). HRMS (ESI+): m/z calculated for C19H21O4 [M+H]+:
313.1440; found: 313.1445.
Yield: 2.23 g, 87.8%, white solid, m.p: 72–74 °C, 1H NMR (400 MHz,
CDCl3): δ1.78 (s, 3H), 1.82 (s, 3H), 4.62 (d, J = 6.8 Hz, 2H), 5.49–5.53
(m, 1H), 7.01 (dd, J = 2.0, 6.8 Hz, 2ArH), 7.50 (d, J = 1.2 Hz, 1ArH),
7.58 (t, J = 7.6 Hz, 1ArH), 7.74 (d, J = 2.0 Hz, 1ArH), 7.80 (d,
J = 7.6 Hz, 1ArH), 8.15 (dd, J = 2.0, 4.8 Hz, 2ArH), 10.03 (s, 1H
CHO). HRMS (ESI+): m/z calculated for C19H19O4 [M+H]+: 311.1283;
found: 311.1284.
4.3.11. Synthesis of 3-formylphenyl 4-(hexyloxy)benzoate (7f)
Yield: 2.23 g, 83.5%, white solid, m.p: 56–58 °C, 1H NMR (400 MHz,
CDCl3): δ 0.92 (t, J = 6.8 Hz, 3H), 1.35–1.37 (m, 4H), 1.45–1.51 (m,
2H), 1.83 (quintet, J = 6.4 Hz, 2H), 4.05 (t, J = 6.4 Hz, 2H), 6.99 (d,
J = 8.8 Hz, 2ArH), 7.49 (dd, J = 1.2, 8.0 Hz, 1ArH), 7.60 (t,
J = 8.0 Hz, 1ArH), 7.75 (t, J = 1.6 Hz, 1ArH), 7.79 (d, J = 7.6 Hz,
1ArH), 8.14 (d, J = 8.8 Hz, 2ArH), 10.03 (s, 1H CHO). HRMS (ESI+):
m/z calculated for C20H23O4 [M+H]+: 327.1596; found: 327.1599.
4.3.18. Synthesis of 3-formylphenyl −4-((3,7-dimethylocta-2,6-dien-1-yl)
oxy)benzoate (7m)
Yield: 2.86 g, 92.3%, pale yellow liquid, 1H NMR (400 MHz, CDCl3):
δ 1.62 (s, 3H), 1.69 (s, 3H), 1.77 (s, 3H), 2.12–2.15 (m, 4H), 4.65 (d,
J = 7.2 Hz, 2H), 5.06–5.10 (m, 1H), 5.47–5.50 (m, 1H), 7.00 (d,
J = 8.8 Hz, 2ArH), 7.48–7.50 (m, 1ArH), 7.60 (t, J = 8.0 Hz, 1ArH),
7.74–7.81 (m, 2ArH), 8.15 (d, J = 8.8 Hz, 2ArH), 10.03 (s, 1H CHO).
HRMS (ESI+): m/z calculated for C24H27O4 [M+H]+: 379.1909; found:
379.1910.
4.3.12. Synthesis of 3-formylphenyl 4-(heptyloxy)benzoate (7g)
Yield: 2.35 g, 84.2%, white solid, m.p: 48–50 °C, 1H NMR (400 MHz,
CDCl3): δ 0.91 (t, J = 6.8 Hz, 3H), 1.30–1.40 (m, 6H), 1.46–1.48 (m,
2H), 1.83 (t, J = 6.8 Hz, 2H), 4.05 (t, J = 6.8 Hz, 2H), 6.99 (dd,
J = 2.0, 6.8 Hz, 2ArH), 7.50 (q, J = 1.2 Hz, 1ArH), 7.60 (t, J = 8.0 Hz,
1ArH), 7.74 (t, J = 2.0 Hz, 1ArH), 7.78–7.80 (m, 1ArH), 8.15 (dd,
J = 2.0, 6.8 Hz, 2ArH), 10.03 (s, 1H CHO). HRMS (ESI+): m/z calcu-
lated for C21H25O4 [M+H]+: 341.1753; found: 341.1754.
4.3.19. Synthesis of 3-formylphenyl 4-((3,7,11-trimethyldodeca-2,6,10-
trien-1-yl)oxy)benzoate (7n)
Yield: 3.20 g, 87.4%, pale yellow liquid, 1H NMR (400 MHz, CDCl3):
δ 1.60–1.61 (m, 6H), 1.68–1.69 (s, 3H), 1.77 (s, 3H), 1.96–2.17 (m,
8H), 4.60–4.65 (m, 2H), 5.10–5.11 (m, 2H), 5.50 (t, J = 4.5 Hz, 1H),
7.01 (d, J = 6.3 Hz, 2ArH), 7.49 (dd, J = 0.9, 6.0 Hz, 1ArH), 7.60 (t,
J = 6.0 Hz, 1ArH), 7.74 (s, 1ArH), 7.79 (d, J = 5.7 Hz, 1ArH), 8.15 (d,
J = 6.6 Hz, 2ArH) 10.03 (s, 1H CHO). HRMS (ESI+): m/z calculated for
C29H35O4 [M+H]+: 447.2535; found: 447.2536.
4.3.13. Synthesis of 3-formylphenyl 4-(octyloxy)benzoate (7h)
Yield: 2.46 g, 84.8%, white solid, m.p: 38–40 °C, 1H NMR (400 MHz,
CDCl3): δ 0.90 (t, J = 6.8 Hz, 3H), 1.30–1.39 (m, 8H), 1.47 (sextet,
J = 7.2 Hz, 2H), 1.83 (quintet, J = 6.8 Hz, 2H), 4.05 (t, J = 6.4 Hz,
2H), 6.99 (dd, J = 2.0, 6.8 Hz, 2ArH), 7.48–7.51 (m, 1ArH), 7.60 (t,
J = 7.6 Hz, 1ArH), 7.74 (t, J = 2.0, 1ArH), 7.79 (dt, J = 1.2, 7.6 Hz,
1ArH), 8.15 (dd, J = 2.0, 6.8 Hz, 2ArH), 10.03 (s, 1H CHO). HRMS
(ESI+): m/z calculated for C22H27O4 [M+H]+: 355.1909; found:
355.1911.
4.3.20. Synthesis of 4-formylphenyl 4-methoxybenzoate (8a)
Yield: 1.59 g, 75.7%, white solid, m.p: 78–80 °C, 1H NMR (300 MHz,
CDCl3): δ 3.91 (s, 3H), 6.99–7.03 (m, 2ArH), 7.39–7.42 (m, 2ArH),
7.95–7.99 (m, 2ArH), 8.14–8.19 (m, 2ArH), 10.03 (s, 1H CHO). HRMS
(ESI+): m/z calculated for C15H13O4 [M+H]+: 257.0814; found:
257.0817.
4.3.14. Synthesis of 3-formylphenyl 4-(nonyloxy)benzoate (7i)
Yield: 2.65 g, 88.3%, white solid, m.p: 38–40 °C, 1H NMR (300 MHz,
CDCl3): δ 0.89 (t, J = 6.9 Hz, 3H), 1.29–1.33 (m, 10H), 1.46–1.51 (m,
2H), 1.83 (quintet, J = 6.6 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 6.96–7.01
(m, 2ArH), 7.47–7.51 (m, 1ArH), 7.60 (t, J = 7.8 Hz, 1ArH), 7.74 (t,
J = 1.8 Hz, 1ArH), 7.50 (dd, J = 1.2, 5.1 Hz, 1ArH), 8.12–8.17 (m,
2ArH), 10.03 (s, 1H CHO). HRMS (ESI+): m/z calculated for C23H29O4
4.3.21. Synthesis of 4-formylphenyl 4-ethoxybenzoate (8b)
Yield: 1.74 g, 78.7%, white solid, m.p: 78–80 °C, 1H NMR (400 MHz,
CDCl3): δ 1.49 (t, J = 6.8 Hz, 3H), 4.16 (q, J = 6.4 Hz, 2H), 6.99–7.03
(m, 2ArH), 7.41–7.44 (m, 2ArH), 7.97–8.01 (m, 2ArH), 8.15–8.19 (m,
2ArH), 10.05 (s, 1H CHO). HRMS (ESI+): m/z calculated for C16H15O4
[M+H]+: 271.0970; found: 271.0974.
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4.3.22. Synthesis of 4-formylphenyl 4-propoxybenzoate (8c)
Yield: 1.89 g, 87.1%, white solid, m.p: 72–74 °C, 1H NMR (400 MHz,
CDCl3): δ 1.07 (t, J = 6.8 Hz, 3H), 1.82–1.91 (m, 2H), 4.02 (t,
J = 6.8 Hz, 2H), 6.99 (d, J = 8.8 Hz, 2ArH), 7.40 (d, J = 8.4 Hz,
2ArH), 7.97 (d, J = 8.4 Hz, 2ArH), 8.14 (d, J = 8.8 Hz, 2ArH), 10.02 (s,
1H CHO). HRMS (ESI+): m/z calculated for C17H17O4 [M+H]+:
285.1127; found: 285.1130.
[M+H]+: 383.2222; found: 383.2223.
4.3.30. Synthesis of 4-formylphenyl 4-(allyloxy)benzoate (8k)
Yield: 1.89 g, 81.8%, white solid, m.p: 86–88 °C, 1H NMR (400 MHz,
CDCl3): δ 4.63–4.65 (m, 2H), 5.3–5.37 (m, 1H), 5.43–5.48 (m, 1H),
6.04–6.11 (m, 1H), 7.01 (dd, J = 2.0, 5.2 Hz, 2ArH), 7.40 (dd, J = 2.0,
5.2 Hz, 2ArH), 7.95–7.98 (m, 2ArH), 8.13–8.17 (m, 2ArH), 10.02 (s, 1H
CHO). HRMS (ESI+): m/z calculated for C17H15O4 [M+H]+: 283.0970;
found: 283.0972.
4.3.23. Synthesis of 4-formylphenyl 4-butoxybenzoate (8d)
Yield: 1.98 g, 81.2%, white solid, m.p: 70–72 °C, 1H NMR (400 MHz,
CDCl3): δ 1.00 (t, J = 7.2 Hz, 3H), 1.53 (sextet, J = 7.6 Hz, 2H), 1.82
(quintet, J = 7.6 Hz, 2H), 4.06 (t, J = 6.8 Hz, 2H), 6.99 (dd, J = 1.6,
6.8 HZ, 2ArH), 7.40 (dd, J = 1.6, 6.8 Hz, 2ArH), 7.97 (dd, J = 1.6,
6.4 Hz, 2ArH), 8.14 (dd, J = 2.0, 6.8 Hz, 2ArH), 10.02 (s, 1H CHO).
HRMS (ESI+): m/z calculated for C18H19O4 [M+H]+: 299.1283; found:
299.1287.
4.3.31. Synthesis of 4-formylphenyl 4-((3-methylbut-2-en-1-yl)oxy)
benzoate (8l)
Yield: 2.10 g, 82.7%, white solid, m.p: 108–110 °C. 1H NMR
(400 MHz, CDCl3): δ 1.78 (s, 3H), 1.82 (s, 3H), 4.61 (d, J = 6.8 Hz, 2H),
5.49–5.52 (m, 1H), 7.00 (d, J = 8.8 Hz, 2ArH), 7.40 (d, J = 8.4 Hz,
2ArH), 7.97 (d, J = 8.4 Hz, 2ArH), 8.14 (d, J = 8.8 Hz, 2ArH), 10.02 (s,
1H CHO). HRMS (ESI+): m/z calculated for C19H19O4 [M+H]+:
311.1283; found: 311.1284.
4.3.24. Synthesis of 4-formylphenyl 4-(pentyloxy)benzoate (8e)
Yield: 2.05 g, 80.1%, white solid, m.p: 64–66 °C, 1H NMR (400 MHz,
CDCl3): δ 0.95 (t, J = 7.2 Hz, 3H), 1.38–1.51 (m, 4H), 1.84 (quintet,
J = 6.4 Hz, 2H), 4.05 (t, J = 6.4 Hz, 2H), 6.97–7.00 (m, 2ArH),
7.39–7.42 (m, 2ArH), 7.95–7.98 (m, 2ArH), 8.12–8.16 (m, 2ArH),
10.02 (s, 1H CHO). HRMS (ESI+): m/z calculated for C19H21O4 [M
+H]+: 313.1440; found: 313.1441.
4.3.32. Synthesis of 4-formylphenyl-4-((3,7-dimethylocta-2,6-dien-1-yl)
oxy)benzoate (8m)
Yield: 2.78 g, 89.7%, white solid, m.p: 44–46 °C. 1H NMR (400 MHz,
CDCl3): δ 1.64 (s, 3H), 1.71 (s, 3H), 1.79 (s, 3H), 2.11–2.1 (m, 4H), 4.67
(d, J = 7.2 Hz, 2H),5.10–5.12 (m, 1H), 5.50–5.54 (m, 1H), 7.03 (d,
J = 6.8 Hz, 2ArH), 7.43 (d, J = 6.8 Hz, 2ArH), 7.99 (d, J = 6.8 Hz,
2ArH), 8.17 (d, J = 6.4 Hz, 2ArH), 10.05 (s, 1H CHO). HRMS (ESI+):
m/z calculated for C24H27O4 [M+H]+: 379.1909; found: 379.1911.
4.3.25. Synthesis of 4-formylphenyl 4-(hexyloxy)benzoate (8f)
Yield: 2.10 g, 78.7%, white solid, m.p: 52–54 °C, 1H NMR (400 MHz,
CDCl3): δ 0.92 (t, J = 7.2 Hz, 3H), 1.35–1.38 (m, 4H), 1.49 (sextet,
J = 7.2 Hz, 2H), 1.83 (quintet, J = 6.8 Hz, 2H), 4.05 (t, J = 6.8 Hz,
2H), 6.99 (dd, J = 2.0, 7.2 Hz, 2ArH), 7.40 (dd, J = 1.6, 6.8 Hz, 2ArH),
7.97 (dd, J = 2.0, 6.4 Hz, 2ArH), 8.14 (dd, J = 2.0, 6.8 Hz, 2ArH),
10.02 (s, 1H CHO). HRMS (ESI+): m/z calculated for C20H23O4 [M
+H]+: 327.1596; found: 327.1598.
4.3.33. Synthesis of 4-formylphenyl −4-((3,7,11-trimethyldodeca-2,6,10-
trien-1-yl)oxy)benzoate (8n)
Yield: 3.33 g, 90.1%, pale yellow liquid. 1H NMR (400 MHz, CDCl3):
δ 1.61 (s, 6H), 1.69 (s, 3H), 1.77 (s, 3H), 1.96–2.17 (m, 8H), 4.64 (d,
J = 6.4 Hz, 2H), 5.09–5.11 (m, 2H), 5.50 (t, J = 6.4 Hz, 1H), 7.00 (d,
J = 8.4 Hz, 2ArH), 7.40 (d, J = 8.4 Hz, 2ArH), 7.97 (d, J = 8.4 Hz,
2ArH), 8.14 (d, J = 8.4 Hz, 2ArH), 10.02 (s, 1H CHO). HRMS (ESI+):
m/z calculated for C29H35O4 [M+H]+: 447.2535; found: 447.2538.
4.3.26. Synthesis of 4-formylphenyl 4-(heptyloxy)benzoate (8g)
Yield: 2.20 g, 78.9%, white solid, m.p: 50–52 °C, 1H NMR (400 MHz,
CDCl3): δ 0.95 (t, J = 7.2 Hz, 3H), 1.30–1.40 (m, 6H), 1.46–1350 (m,
2H), 1.81–1.85 (m, 2H), 4.05 (t, J = 6.4 Hz, 2H), 6.97–7.00 (m, 2ArH),
7.40–7.41 (m, 2ArH), 7.85–7.98 (m, 2ArH), 8.14 (dd, J = 2.0, 4.8 Hz,
2ArH), 10.02 (s, 1H CHO). HRMS (ESI+): m/z calculated for C21H25O4
[M+H]+: 341.1753; found: 341.1756.
4.3.34. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-methoxybenzoate (9a)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7a (0.118 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.113 g, 71.5%, pale brown
solid, m.p: 156–158 °C. 1H NMR (300 MHz, CDCl3): δ 3.92 (s, 3H),
6.96–7.02 (m, 2ArH), 7.23–7.29 (m, 3ArH), 7.42 (t, J = 7.5 Hz, 1ArH),
7.61 (bs, 2ArH), 7.85–7.90 (m, 2ArH), 8.13–8.18 (m, 2ArH), 10.10 (bs,
1 NeH). 13C NMR (75 MHz, CDCl3): δ 55.5, 113.9, 120.2, 121.2, 122.9,
123.2, 124.0, 130.0, 131.4, 132.4, 150.8, 151.3, 164.1, 165.4. HRMS
(ESI) m/z calculated for C21H17N2O3 (M+H)+: 345.1239; found:
345.1240.
4.3.27. Synthesis of 4-formylphenyl 4-(octyloxy)benzoate (8h)
Yield: 2.20 g, 75.9%, white solid, m.p: 50–52 °C, 1H NMR (400 MHz,
CDCl3): δ 0.90 (t, J = 6.8 Hz, 3H), 1.30–1.36 (m, 8H), 1.48 (sextet,
J = 7.2 Hz, 2H), 1.83 (quintet, J = 7.2 Hz, 2H), 4.05 (t, J = 6.4 Hz,
2H), 6.98 (dd, J = 1.6, 6.8 Hz, 2ArH), 7.40 (dd, J = 1.6, 6.8 Hz, 2ArH),
7.97 (dd, J = 2.0, 6.8 Hz, 2H), 8.14 (dd, J = 2.0, 6.8 Hz, 2ArH), 10.02
(s, 1H CHO). HRMS (ESI+): m/z calculated for C22H27O4 [M+H]+:
355.1909; found: 355.1912.
4.3.28. Synthesis of 4-formylphenyl 4-(nonyloxy)benzoate (8i)
Yield: 2.40 g, 80.0%, white solid, m.p: 52–54 °C, 1H NMR (400 MHz,
CDCl3): δ 0.89 (t, J = 6.8 Hz, 3H), 1.30–1.39 (m, 10H), 1.44–1.49 (m,
2H), 1.83 (quintet, J = 7.2 Hz, 2H), 4.05 (t, J = 6.8 Hz, 2H), 6.98 (dd,
J = 2.0, 6.8 Hz, 2ArH), 7.40 (dd, J = 1.6, 6.8 Hz, 2ArH), 7.97 (dd,
J = 2.0, 6.8 Hz, 2ArH), 8.14 (dd, J = 2.0, 6.8 Hz, 2ArH), 10.02 (s, 1H,
CHO). HRMS (ESI+): m/z calculated for C23H29O4 [M+H]+: 369.2066;
found: 369.2069.
4.3.35. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-ethoxybenzoate (9b)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7b (0.124 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction(TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography on silica gel (100–200
mesh) using 28% ethyl acetate in hexanes. Yield: 0.128 g, 78.0%, pale
brown solid, m.p: 186–188 °C. 1H NMR (300 MHz, CDCl3 + acetoned6):
δ 1.48 (t, J = 7.2 Hz, 3H), 4.14 (q, J = 6.9 Hz, 2H), 6.96–6.99 (m,
2ArH), 7.24–7.29 (m, 4ArH), 7.43 (t, J = 7.8 Hz, 1ArH), 7.78 (bs,
4.3.29. Synthesis of 4-formylphenyl 4-(decyloxy)benzoate (8j)
Yield: 2.45 g, 78.3%, white solid, m.p: 52–54 °C, 1H NMR (300 MHz,
CDCl3): δ 0.91 (t, J = 6.6 Hz, 3H), 1.28–1.45 (m, 12H), 1.48–1.50 (m,
2H), 1.83 (quintet, J = 6.6 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 6.91–7.01
(m, 2ArH), 7.38–7.42 (m, 2ArH), 7.95–7.99 (m, 2ArH), 8.12–8.17 (m,
2ArH), 10.02 (s, 1H CHO). HRMS (ESI+): m/z calculated for C24H31O4
11

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BioorganicChemistry103(2020)104170
1ArH), 7.86 (dd, J = 1.2, 8.7 Hz, 1ArH), 7.90 (t, J = 2.1 Hz, 1ArH),
8.13–8.16 (m, 2ArH), 9.99 (bs, 1 NeH). 13C NMR (75 MHz, CDCl3): δ
14.6, 63.8, 114.3, 120.2, 121.2, 122.7, 123.2, 123.9, 129.9, 131.6,
132.2, 150.9, 151.5, 163.5, 164.8.HRMS (ESI) m/z calculated for
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.156 g, 82.1%, pale brown
solid, m.p:142–144 °C. 1H NMR (300 MHz, CDCl3): δ 0.93 (t,
J = 6.9 Hz, 3H), 1.35–1.40 (m, 4H), 1.45–1.55 (m, 2H), 1.84 (quintet,
J = 6.9 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.96–7.00 (m, 2ArH),
7.23–7.29 (m, 3ArH), 7.42 (t, J = 7.8 Hz, 2ArH), 7.79 (bs, 1ArH), 7.85
(dt, J = 1.2, 7.8 Hz, 1ArH), 7.90 (t, J = 2.1 Hz, 1ArH), 8.12–8.17 (m,
2ArH), 9.98 (bs, 1 NeH). 13C NMR (75 MHz, CDCl3 + DMSO‑d6): δ
13.5, 22.0, 25.0, 28.4, 30.9, 67.8, 113.8, 120.5, 121.7, 121.8, 127.5,
131.7, 150.8, 151.6, 163.1, 164.1. HRMS (ESI) m/z calculated for
C26H27N2O3 (M+H)+: 415.2022; found: 415.2023.
C
22H19N2O3 (M+H)+: 359.1396; found:359.1399.
4.3.36. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-propoxybenzoate (9c)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7c (0.131 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.115 g, 67.2%, pale brown
solid, m.p: 154–156 °C. 1H NMR (300 MHz, CDCl3): δ 1.00 (t,
J = 7.5 Hz, 3H), 1.73–1.85 (m, 2H), 4.08 (t, J = 6.6 Hz, 2H), 7.00–7.12
(m, 1ArH), 7.14–7.17 (m, 2ArH), 7.22–7.27 (m, 2ArH), 7.40–7.43 (m,
1ArH), 7.56–7.59 (m, 1ArH), 7.65–7.68 (m, 2ArH), 8.05–8.08 (m,
1ArH), 8.13 (d, J = 9.0 Hz, 2ArH), 13.00 (s, 1 NeH). 13C NMR
(75 MHz, CDCl3): δ 10.8, 22.4, 69.9, 115.1, 120.4, 121.1, 123.9, 124.3,
130.7, 132.1, 132.5, 132.6, 150.8, 151.6, 163.8, 164.7. HRMS (ESI) m/
z calculated for C23H21N2O3 (M+H)+: 373.1552; found: 373.1554.
4.3.40. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(heptyloxy)benzoate (9g)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7g (0.157 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.148 g, 75.1%, pale brown
solid, m.p: 128–130 °C. 1H NMR (300 MHz, CDCl3): δ 0.91 (t,
J = 6.6 Hz, 3H), 1.33–1.49 (m, 8H), 1.84 (quintet, J = 6.6 Hz, 2H),
4.05 (t, J = 6.6 Hz, 2H), 6.97 (d, J = 8.4 Hz, 2ArH), 7.21–7.23 (m,
3ArH), 7.37 (t, J = 8.1 Hz, 1ArH), 7.60 (bs, 2ArH), 7.84 (d, J = 7.2 Hz,
1ArH), 7.90 (s, 1ArH), 8.12 (d, J = 8.4 Hz, 2ArH). 13C NMR (75 MHz,
CDCl3): δ 14.1, 22.6, 26.0, 29.0, 29.1, 31.8, 68.4, 114.4, 120.2, 121.0,
122.9, 123.2, 123.9, 130.0, 131.4, 132.4, 150.7, 151.4, 163.8, 165.4.
HRMS (ESI) m/z calculated for C27H29N2O3 (M+H)+: 429.2178; found:
429.2179.
4.3.37. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-butoxybenzoate (9d)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7d (0.137 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.122 g, 68.5%, pale brown
solid, m.p: 118–120 °C. 1H NMR (300 MHz, CDCl3): δ 0.99 (t,
J = 6.9 Hz, 3H), 1.52 (quintet, J = 6.6 Hz, 2H), 1.82 (sextet,
J = 6.6 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.92–6.94 (2ArH), 7.04–7.15
(m, 1ArH), 7.22–7.41 (m, 3ArH), 7.45–7.54 (m, 1ArH), 7.54–7.60 (m,
1ArH), 7.84–7.87 (m, 1ArH), 7.90 (t, J = 1.8 Hz, 1ArH), 8.05–8.14 (m,
2ArH), 10.31 (bs, 1 NeH).13C NMR (75 MHz, CDCl3): δ 13.9, 19.2,
31.2, 68.1, 114.3, 120.2, 121.5, 123.0, 126.2, 131.1, 150.7, 151.3,
162.4, 163.7, 164.8, 165.2. HRMS (ESI) m/z calculated for C24H23N2O3
(M+H)+: 387.1709; found: 387.1711.
4.3.41. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(octyloxy)benzoate (9h)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7h (0.163 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.154 g, 75.5%, pale brown
solid, m.p: 112–114 °C. 1H NMR (300 MHz, CDCl3): δ 0.90 (t,
J = 6.3 Hz, 3H), 1.31–1.49 (m, 10H), 1.79–1.88 (m, 2H), 4.05 (t,
J = 6.6 Hz, 2H), 6.97 (d, J = 9.0 Hz, 2ArH), 7.20–7.25 (m, 3ArH), 7.36
(t, J = 8.1 Hz, 1ArH), 7.60 (bs, 2ArH), 7.82 (d, J = 7.8 Hz, 1ArH), 7.89
(t, J = 1.8 Hz, 1ArH), 8.13 (d, J = 9.0 Hz, 2ArH), 10.16 (bs, 1 NeH).
13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.4, 29.7, 31.8,
68.2, 113.8, 120.0, 121.6, 121.7, 122.0, 123.0,130.1, 131.3,132.4,
150.7, 151.4, 163.8, 165.4. HRMS (ESI) m/z calculated for C28H31N2O3
(M+H)+: 443.2335; found: 443.2338.
4.3.38. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(pentyloxy)benzoate (9e)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7e (0.144 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.099 g, 53.8%, off white
solid, m.p: 148–150 °C. 1H NMR (300 MHz, CDCl3): δ 0.96 (t,
J = 6.9 Hz, 3H), 1.41–1.49 (m, 4H), 1.82–1.84 (m, 2H), 4.05 (t,
J = 6.6 Hz, 2H), 6.92–6.98 (m, 2ArH), 7.21–7.30 (m, 4ArH), 7.34–7.40
(m, 1ArH), 7.60–7.61 (m, 1ArH), 7.83–7.87 (m, 1ArH), 7.90 (t,
J = 1.8 Hz, 1ArH), 8.05–8.14 (m, 2ArH) 13C NMR (75 MHz,
CDCl3 + DMSO‑d6): δ 13.0, 21.3, 27.0, 27.6, 67.2, 113.4, 120.3, 121.4,
122.1, 128.8, 131.2, 150.2, 150.5, 162.6, 163.5. HRMS (ESI) m/z cal-
culated for C25H25N2O3 (M+H)+: 401.1865; found: 401.1866.
4.3.42. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(nonyloxy)benzoate (9i)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7i (0.169 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.148 g, 70.5%, pale brown
solid, m.p: 128–130 °C. 1H NMR (300 MHz, CDCl3): δ 0.90 (t,
J = 6.9 Hz, 3H), 1.30–1.44 (m, 10H), 1.47–1.51 (m, 2H), 1.82 (quintet,
J = 6.6 Hz, 2H), 4.05 (t, J = 6.6 Hz, 2H), 6.97 (dd, J = 1.2, 9.0 Hz,
2ArH), 7.19–7.28 (m, 3ArH), 7.32–7.42 (m, 1ArH), 7.61 (bs, 2ArH),
7.83 (t, J = 6.9 Hz, 1ArH), 7.89 (s, 1ArH), 8.13 (dd, J = 2.4, 9.0 Hz,
4.3.39. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(hexyloxy)benzoate (9f)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7f (0.150 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
12

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
2ArH), 10.16 (bs, 1 NeH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7,
26.0, 29.1, 29.3, 29.4, 29.6, 31.9, 68.4, 114.4, 115.3, 120.2, 120.9,
123.0, 123.3, 123.9, 130.1, 131.1, 132.4, 138.8, 150.6, 151.4, 163.8,
165.5. HRMS (ESI) m/z calculated for C29H33N2O3 (M+H)+: 457.2491;
found: 457.2491.
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 22% ethyl acetate in hexanes. Yield: 0.165 g, 76.7%, pale brown
solid, m.p: 112–114 °C. 1H NMR (300 MHz, CDCl3): δ 1.63 (s, 3H), 1.69
(s, 3H), 1.78 (s, 3H), 2.13–2.15 (m, 4H), 4.65 (d, J = 6.6 Hz, 2H),
5.09–5.11 (m, 1H), 5.49–5.53 (m, 1H), 6.99–7.03 (m, 2ArH), 7.27–7.30
(m, 3ArH), 7.48 (t, J = 8.1 Hz, 2ArH), 7.80 (bs, 1ArH), 7.88–7.91 (m,
2ArH), 8.16–8.18 (m, 2ArH), 9.89 (bs, 1 NeH). 13C NMR (75 MHz,
CDCl3 + DMSO‑d6): δ 16.2, 17.2, 25.2, 25.7, 64.7, 114.1, 115.2, 118.2,
119.9, 120.7, 122.0, 122.6, 123.2, 123.6, 129.3, 131.2, 131.4, 131.7,
141.4, 150.5, 151.0, 162.9, 164.2.HRMS (ESI) m/z calculated for
4.3.43. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(decyloxy)benzoate (9j)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7j (0.176 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.125 g, 57.8%, pale brown
solid, m.p: 96–98 °C. 1H NMR (300 MHz, CDCl3): δ 0.89 (t, J = 6.9 Hz,
3H), 1.25–1.49 (m, 12H), 1.44–1.49 (m, 2H), 1.84 (quintet, J = 6.3 Hz,
2H), 4.05 (t, J = 6.6 Hz, 2H), 6.96–6.99 (m, 2ArH), 7.23–7.29 (m,
4ArH), 7.41 (t, J = 8.1 Hz, 1ArH), 7.61 (bs, 2ArH), 7.86 (d, J = 7.8 Hz,
1ArH), 7.89 (t, J = 1.8 Hz, 1ArH), 8.12–8.15 (m, 2ArH). 13C NMR
(75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3, 29.4, 29.6, 29.7, 31.9,
68.4, 114.4, 120.2, 121.0, 123.0, 123.3, 123.9, 130.1, 131.2, 132.4,
150.6, 151.4, 163.8, 165.4. HRMS (ESI) m/z calculated for C30H35N2O3
(M+H)+: 471.2648; found: 471.2651.
C
30H31N2O3 (M+H)+: 467.2335; found: 467.2336.
4.3.47. 3-(1H-benzo[d]imidazol-2-yl)phenyl
4-(((2E,6E)-3,7,11-
trimethyldodeca-2,6,10-trien-1-yl)oxy)benzoate (9n)
o-phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7n (0.205 g,
0.46 mmol) and p-Toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 22% ethyl acetate in hexanes. Yield: 0.154 g, 62.8%, pale brown
solid, m.p: 154–156 °C, 1H NMR (300 MHz, CDCl3): δ 1.61–1.62 (m,
6H), 1.69 (s, 3H), 1.84 (s, 3H), 2.01–2.14 (m, 8H), 4.61–4.66 (m, 2H),
5.10–5.12 (m, 2H), 5.51 (t, J = 6.6 Hz, 1H), 6.96–7.02 (m, 2ArH),
7.26–7.30 (m, 4ArH), 7.46 (t, J = 7.8 Hz, 1ArH), 7.61–7.62 (m, 1ArH),
7.87–7.91 (m, 2ArH), 8.12–8.17 (m, 2ArH). 13C NMR (75 MHz, CDCl3):
δ 16.1, 16.8, 17.7, 25.7, 26.1, 26.7, 39.6, 39.9, 65.2, 114.6, 118.7,
120.2, 121.0, 122.9, 123.1, 123.6, 124.0, 130.0, 131.3, 131.7, 132.4,
135.6, 142.1, 150.8, 151.3, 163.6, 165.6. HRMS (ESI) m/z calculated
for C35H39N2O3 (M+H)+: 535.2961; found: 535.2963.
4.3.44. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-(allyloxy)benzoate (9k)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7k (0.130 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 30% ethyl acetate in hexanes. Yield: 0.096 g, 56.5%, off white
solid, m.p:, 1H NMR (300 MHz, CDCl3): δ 4.64 (td, J = 1.5, 8.4 Hz, 2H),
5.26 (dd, J = 1.2, 10.5 Hz, 1H), 5.49 (dd, J = 1.5, 15.9 Hz, 1H),
6.02–6.15 (m, 1H), 6.96–7.02 (m, 2ArH), 7.19–7.26 (m, 3ArH), 7.35 (t,
J = 7.8 Hz, 1ArH), 7.60 (bs, 2ArH), 7.82 (d, J = 8.1 Hz, 1ArH), 7.89 (t,
J = 1.8 Hz, 1ArH), 8.09–8.15 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ
68.6, 114.3, 117.9, 120.1, 121.3, 122.2, 122.8, 123.8, 129.5, 131.7,
131.9, 132.1, 150.7, 151.1, 162.7, 164.4. HRMS (ESI) m/z calculated
for C23H19N2O3 (M+H)+: 371.1396; found: 371.1399.
4.3.48. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-methoxybenzoate (10a)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8a (0.118 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 35% ethyl acetate in hexanes. Yield: 0.096 g, 60.7%, pale brown
solid, m.p: 216–218 °C. 1H NMR (300 MHz, CDCl3): δ 3.92 (s, 3H),
6.99–7.03 (m, 2ArH), 7.27–7.33 (m, 4ArH), 7.64 (q, J = 3.0 Hz, 2ArH),
8.04–8.07 (m, 2ArH), 8.15–8.19 (m, 2ArH). 13C NMR (75 MHz,
CDCl3 + DMSO‑d6): δ 54.6, 113.0, 120.3, 121.3, 121.4, 127.0, 131.3,
150.3, 151.2, 163.1, 163.5. HRMS (ESI) m/z calculated for C21H17N2O3
(M+H)+: 345.1239; found: 345.1241.
4.3.45. 3-(1H-benzo[d]imidazol-2-yl)phenyl 4-((3-methylbut-2-en-1-yl)
oxy)benzoate (9l)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7l (0.143 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC) the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 30% ethyl acetate in hexanes. Yield: 0.129 g, 70.5%, brown solid,
4.3.49. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-ethoxybenzoate compound
(10b)
1
m.p: 106–108 °C. H NMR (300 MHz, CDCl3): δ 1.79 (s, 3H), 1.83 (s,
3H), 4.62 (d, J = 6.9 Hz, 2H), 5.50–5.54 (m, 1H), 6.96–7.01 (m, 2ArH),
7.22–7.29 (m, 3ArH), 7.41 (t, J = 7.8 Hz, 1ArH), 7.61 (bs, 2ArH), 7.84
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8b (0.124 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 35% ethyl acetate in hexanes. Yield: 0.121 g, 73.3%, pale brown
solid, m.p: 218–220 °C. 1H NMR (300 MHz, CDCl3): δ 1.48 (t,
J = 6.9 Hz, 3H), 4.14 (q, J = 6.9 Hz, 2H), 6.99 (d, J = 9.0 Hz, 2ArH),
7.28–7.30 (m, 2ArH), 7.31–7.36 (m, 2ArH), 7.50 (bs, 1ArH), 7.82 (bs,
1ArH), 8.06–8.09 (m, 2ArH), 8.14–8.18 (m, 2ArH), 9.74 (bs, 1 NeH).
(d, J = 7.8 Hz, 1ArH), 7.89 (t, 2.1 Hz, 1ArH), 8.13–8.16 (m, 2ArH). 13
C
NMR (75 MHz, CDCl3): δ 17.7, 25.7, 65.2, 114.6, 118.7, 120.1, 121.1,
123.0, 123.3, 123.6, 123.9, 124.3, 124.4, 130.1, 131.4, 131.7, 132.4,
135.6, 135.8, 142.1, 150.6, 151.4, 163.6, 165.4. HRMS (ESI) m/z cal-
culated for C25H23N2O3 (M+H)+: 399.1709; found: 399.1711.
4.3.46. 3-(1H-benzo[d]imidazol-2-yl)phenyl
(E)-4-((3,7-dimethylocta-
2,6-dien-1-yl)oxy)benzoate (9m)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 7m (0.174 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
13

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
13C NMR (75 MHz, CDCl3): δ 14.3, 63.5, 114.0, 120.9, 121.9, 122.0,
127.7, 132.0, 151.0, 151.9, 163.1, 164.3. HRMS (ESI) m/z calculated
for C22H19N2O3 (M+H)+: 359.1396; found: 359.1398.
sulfate and purified by column chromatography (silica gel 100–200
mesh) using 28% ethyl acetate in hexanes. Yield: 0.123 g, 64.7%, pale
1
brown solid, m.p: 184–186 °C, H NMR (300 MHz, CDCl3): δ 0.92 (t,
J = 6.9 Hz, 3H), 1.35–1.38 (m, 4H), 1.49–1.52 (m, 2H), 1.83 (quintet,
J = 6.9 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.01 (m, 2ArH),
7.26–7.30 (m, 2ArH), 7.31–7.36 (m, 2ArH), 7.61–7.89 (bs, 2ArH),
8.07–8.10 (m, 2ArH), 8.14–8.18 (m, 2ArH), 9.83 (bs, 1 NeH). 13C NMR
(75 MHz, CDCl3 + DMSO‑d6): δ 13.4, 21.9, 24.9, 28.3, 30.8, 67.7,
113.7, 120.4, 121.6, 121.8, 127.1, 127.4, 131.6, 150.6, 151.6, 163.0,
163.9. HRMS (ESI) m/z calculated for C26H27N2O3 (M+H)+: 415.2022;
found: 415.2024.
4.3.50. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-propoxybenzoate (10c)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8c (0.131 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 35% ethyl acetate in hexanes. Yield: 0.112 g, 65.5%, pale brown
solid, m.p: 172–174 °C, 1H NMR (300 MHz, DMSO‑d6): δ 1.01 (t,
J = 7.2 Hz, 3H), 1.75–1.82 (m, 2H), 4.06 (q, J = 6.6 Hz, 2H), 7.11 (d,
J = 9.0 Hz, 2ArH), 7.13–7.27 (m, 2ArH), 7.48 (d, J = 9.0 Hz, 2ArH),
7.55 (d, J = 7.2 Hz, 1ArH), 7.69 (d, J = 6.9 Hz, 1ArH), 8.03 (d,
4.3.54. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(heptyloxy)benzoate (10g)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8g (0.157 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.131 g, 66.5%, pale brown
solid, m.p: 192–194 °C, 1H NMR (300 MHz, CDCl3): δ 0.91 (t,
J = 6.6 Hz, 3H), 1.32–1.50 (m, 6H), 1.51–1.53 (m, 2H), 1.84 (quintet,
J = 6.6 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.98–7.01 (m, 2ArH),
7.28–7.31 (m, 2ArH), 7.33–7.36 (m, 2ArH), 7.49 (bs, 1ArH), 7.81 (bs,
1ArH), 8.05–8.08 (m, 2ArH), 8.14–8.18 (m, 2ArH), 9.81 (bs, 1 NeH).
13C NMR (75 MHz, CDCl3): δ 14.0, 25.5, 25.9, 28.9, 29.0, 31.7, 68.3,
114.3, 121.1, 122.2, 128.0, 128.1, 132.2, 151.3, 152.2, 163.7, 164.7.
HRMS (ESI) m/z calculated for C27H29N2O3 (M+H)+: 429.2178; found:
429.2180.
J = 8.7 Hz, 2ArH), 8.26 (d, J = 8.7 Hz, 2ArH), 12.97 (s, 1 NeH). 13
C
NMR (75 MHz, DMSO‑d6 + CDCl3): δ 9.2, 21.0, 68.4, 113.2, 119.7,
121.0, 121.1, 121.2, 125.9, 126.7, 129.1, 130.8, 130.9, 149.9, 150.9,
162.3, 163.1. HRMS (ESI) m/z calculated for C23H21N2O3 (M+H)+:
373.1552; found: 373.1552.
4.3.51. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-butoxybenzoate (10d)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8d (0.137 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.118 g, 66.3%, pale brown
solid, m.p: 220–222 °C. 1H NMR (300 MHz, CDCl3 + DMSO‑d6): δ 1.00
(t, J = 7.2 Hz, 3H), 1.47–1.57 (m, 2H), 1.82 (quintet, J = 6.9 Hz, 2H),
4.07 (t, J = 6.6 Hz, 2H), 6.95–7.02 (m, 2ArH), 7.19 (s, 1ArH),
7.27–7.31 (m, 2ArH), 7.34–7.37 (m, 2ArH), 7.74–7.89 (m, 1ArH),
8.06–8.11 (m, 2ArH), 8.14–8.18 (m, 2ArH), 11.30 (bs,1N-H). 13C NMR
(75 MHz, CDCl3 + DMSO‑d6): δ 12.9, 18.2, 30.1, 63.8, 113.5, 120.8,
121.4, 121.9, 127.1, 131.3, 151.1, 151.8, 163.3, 163.5.HRMS (ESI) m/z
calculated for C24H23N2O3 (M+H)+: 387.1709; found: 387.1710.
4.3.55. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(octyloxy)benzoate (10h)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8h (0.163 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography on silica gel (100–200
mesh) using 25% ethyl acetate in hexanes. Yield: 0.136 g, 67.0%, pale
1
brown solid, m.p: 108–110 °C, H NMR (300 MHz, CDCl3): δ 0.89 (t,
4.3.52. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(pentyloxy)benzoate (10e)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8e (0.144 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel (100–200 mesh)
using 28% ethyl acetate in hexanes. Yield: 0.132 g, 71.7%, brown solid,
J = 6.3 Hz, 3H), 1.26–1.33 (m, 8H), 1.42–1.48 (m, 2H), 1.83 (quintet,
J = 6.3 Hz, 2H), 4.05 (t, J = 6.3 Hz, 2H), 6.95–7.00 (m, 2ArH), 7.19 (s,
1ArH), 7.28–7.37 (m, 3ArH), 7.61 (bs, 1ArH), 7.75 (d, J = 8.7 Hz,
1ArH), 7.88 (d, J = 7.5 Hz, 1ArH), 8.06–8.11 (m, 1ArH), 8.15 (dd,
J = 1.5, 9.0 Hz, 2ArH), 10.13 (bs, 1 NeH). 13C NMR (75 MHz, CDCl3):
δ 14.1, 22.7, 26.0, 29.1, 29.2, 29.3, 31.8, 68.4, 114.4, 121.0, 122.4,
123.0, 127.2, 128.0, 132.3, 150.6, 151.0, 152.5, 163.8, 165.0. HRMS
(ESI) m/z calculated for C28H31N2O3 (M+H)+: 443.2335; found:
443.2336.
1
m.p: 108–110 °C, H NMR (300 MHz, CDCl3): δ 0.96 (t, J = 6.9 Hz,
3H), 1.41–1.49 (m, 4H), 1.82–1.84 (m, 2H), 4.05 (t, J = 6.6 Hz, 2H),
6.92–6.98 (m, 2ArH), 7.21–7.30 (m, 4ArH), 7.34–7.40 (m, 1ArH),
7.60–7.61 (m, 1ArH), 7.83–7.87 (m, 1ArH), 7.90 (t, J = 1.8 Hz, 1ArH),
8.05–8.14 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 14.0, 22.5, 28.1,
28.8, 68.4, 114.3, 1207, 121.2, 121.5, 127.0, 127.3, 128.8, 130.5,
136.0, 136.9, 137.6, 143.0, 151.1, 152.5, 163.6, 165.2. HRMS (ESI) m/
z calculated for C25H25N2O3 (M+H)+: 401.1865; found: 401.1868.
4.3.56. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(nonyloxy)benzoate (10i)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8i (0.169 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.126 g, 60.0%, pale brown
solid, m.p:, 1H NMR (300 MHz, CDCl3): δ 0.89 (t, J = 6.9 Hz, 3H),
1.20–1.30 (m, 10H), 1.44–1.48 (m, 2H), 1.78–1.88 (m, 2H), 4.05 (t,
J = 6.3 Hz, 2H), 6.95–7.00 (m, 2ArH), 7.18–7.33 (m, 5ArH), 7.30–7.60
(m, 1ArH), 8.03–8.06 (m, 2ArH), 8.14–8.18 (m, 2ArH). 13C NMR
(75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3, 29.4, 29.5, 31.9, 68.4,
114.5, 121.0, 122.4, 122.9, 127.6, 128.0, 132.4, 151.2, 152.3, 163.9,
4.3.53. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(hexyloxy)benzoate (10f)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8f (0.150 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction by TLC, the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium
14

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
165.2. HRMS (ESI) m/z calculated for C29H33N2O3 (M+H)+: 457.2491;
using 25% ethyl acetate in hexanes. Yield: 0.124 g, 57.7%, pale brown
solid, m.p: 128–130 °C. 1H NMR (300 MHz, CDCl3): δ 1.62 (s, 3H), 1.69
(s, 3H), 1.77 (s, 3H), 2.09–2.21 (m, 4H), 4.65 (d, J = 6.6 Hz, 2H),
5.08–5.11 (m, 1H), 5.50 (t, J = 5.4 Hz, 1H), 6.97–7.03 (m, 2ArH),
7.24–7.29 (m, 4ArH), 7.61 (bs, 2ArH), 8.04 (d, J = 7.8 Hz, 2ArH),
8.14–8.18 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 16.8, 17.7, 25.7,
26.3, 39.5, 65.2, 114.7, 115.1, 118.7, 121.1, 122.6, 123.4, 123.7,
128.1, 132.0, 132.4, 142.1, 150.5, 152.8, 163.6, 164.9. HRMS (ESI) m/
z calculated for C30H31N2O3 (M+H)+: 467.2335; found: 467.2339.
found: 457.2494.
4.3.57. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(decyloxy)benzoate (10j)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8j (0.176 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.130 g, 60.2%, pale brown
solid, m.p: 142–144 °C. 1H NMR (300 MHz, CDCl3): δ 0.89 (t,
J = 6.9 Hz, 3H), 1.29–1.34 (m, 12H), 1.42–1.48 (m, 2H), 1.83 (quintet,
J = 6.6 Hz, 2H), 4.05 (t, J = 6.3 Hz, 2H), 6.97 (d, J = 9.0 Hz, 2ArH),
4.3.61. 4-(1H-benzo[d]imidazol-2-yl)phenyl
4-(((2E,6E)-3,7,11-
trimethyldodeca-2,6,10-trien-1-yl)oxy)benzoate (10n)
o-phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8n (0.205 g,
0.46 mmol) and p-Toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 25% ethyl acetate in hexanes. Yield: 0.105 g, 42.9%, pale brown
solid, m.p:, 1H NMR (300 MHz, CDCl3): δ 1.61 (s, 6H), 1.69 (s, 3H),
1.77 (s, 3H), 1.98–2.18 (m, 8H), 4.65 (d, J = 6.3 Hz, 2H), 5.11 (d,
J = 6.3 Hz, 2H), 5.53 (t, J = 6.6 Hz, 1H), 6.97–7.02 (m, 2ArH),
7.16–7.19 (m, 1ArH), 7.27–7.42 (m, 3ArH), 7.63–7.66 (m, 2ArH), 8.06
(d, J = 8.7 Hz, 2ArH), 8.13–8.18 (m, 2ArH). 13C NMR (75 MHz,
CDCl3): δ 16.1, 16.8, 17.7, 26.6, 65.2, 114.7, 118.7, 121.2, 122.5,
123.1, 123.5, 124.3, 124.4, 127.3, 127.9, 128.8, 131.4, 132.4, 135.6,
142.1, 150.8, 152.6, 163.6, 164.9.HRMS (ESI) m/z calculated for
7.25–7.28 (m, 4H), 7.64–7.67 (m, 2ArH), 8.09–8.13 (m, 4ArH).13
C
NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3, 29.4, 29.6, 29.7,
31.9, 68.4, 114.5, 115.2, 121.0, 122.4, 123.0, 127.3, 128.0, 132.4,
139.0, 151.1, 152.4, 163.9, 165.2. HRMS (ESI) m/z calculated for
C
30H35N2O3 (M+H)+: 471.2648; found: 471.2649.
4.3.58. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-(allyloxy)benzoate (10k)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8k (0.130 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 30% ethyl acetate in hexanes. Yield: 0.106 g, 62.3%, pale brown
solid, m.p:, 1H NMR (300 MHz, CDCl3): δ 4.62–4.66 (m, 2H), 5.32–5.34
(m, 1H), 5.42–5.51 (m, 1H), 6.03–6.09 (m, 1H), 6.98–7.03 (m, 2ArH),
7.19 (s, 1ArH), 7.28–7.36 (m, 3ArH), 7.66 (bs, 1ArH), 7.76 (d,
J = 8.7 Hz, 1ArH), 7.87 (d, J = 8.7 Hz, 1ArH), 8.07–8.18 (m, 3ArH).
13C NMR (75 MHz, CDCl3 + DMSO‑d6): δ 68.3, 114.0, 117.6, 120.9,
121.6, 121.7, 121.9, 122.6, 126.4, 127.4, 129.7, 131.6, 131.7, 133.0,
135.4, 142.4, 149.9, 150.7, 162.3, 162.4, 163.8. HRMS (ESI) m/z cal-
culated for C23H19N2O3 (M+H)+: 371.1396; found: 371.1397.
C
35H39N2O3 (M+H)+: 535.2961; found: 535.2964.
4.3.62. Synthesis of compound 2-((4-methoxybenzylidene)amino)phenol
(11a)
2-Aminophenol (5 g, 45.82 mmol) and p-anisaldehyde (6.24 g,
45.82 mmol) were dissolved in methanol and stirred at room tem-
perature in the presence of catalytic amount of acetic acid for 3 h. The
solid thus formed was filtered and washed with cold methanol and air
dried to get compound 11a (8.43 g, 81.0%) as yellow solid, m.p:
80–82 °C. 1H NMR (300 MHz, CDCl3): δ 3.89 (s, 3H), 6.90 (td, J = 1.5,
7.8 Hz, 1ArH), 7.01 (dd, J = 1.8, 9.0 Hz, 3ArH), 7.17 (td, J = 1.5,
9.0 Hz, 1ArH), 7.29 (d, J = 1.2 Hz, 1ArH), 7.88 (dd, J = 2.4, 11.4 Hz,
2ArH), 8.63 (s, 1H). HRMS (ESI+): m/z calculated for C17H22O3 [M
+H]+: 274.1569; found: 274.1574.
4.3.59. 4-(1H-benzo[d]imidazol-2-yl)phenyl 4-((3-methylbut-2-en-1-yl)
oxy)benzoate (10l)
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8l (0.143 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
using 30% ethyl acetate in hexanes. Yield: 0.103 g, 56.3%, brown solid,
4.3.63. Synthesis of compound 2-((3-nitrobenzylidene)amino)phenol
(11b)
2-Aminophenol (5 g, 45.8 mmol) and m-nitrobenzaldehyde (6.92 g,
45.82 mmol) were dissolved in methanol and stirred at room tem-
perature in the presence of catalytic amount of acetic acid for 3 h. The
solid thus formed was filtered and washed with cold methanol and air
dried to get compound 11b (9.3 g, 84.5%) as yellow solid, m.p:
118–120 °C. The compound was used as such for the next step. 1H NMR
(300 MHz, CDCl3): δ 6.95 (td, J = 1.2, 8.1 Hz, 1ArH), 7.06 (dd, J = 1.2,
8.1 Hz, 1ArH), 7.16 (s, 1O-H), 7.24–7.30 (m, 1ArH), 7.35 (dd, J = 1.2,
8.1 Hz, 1ArH), 7.69 (t, J = 8.1 Hz, 1ArH), 8.26 (d, J = 7.8 Hz, 1ArH),
8.35 (dq, J = 1.2, 8.1 Hz, 1ArH), 8.75 (t, J = 1.8 Hz, 1ArH), 8.79 (s,
1H). HRMS (ESI+): m/z calculated for C13H8N2O3 [M+H]+: 240.0535;
found: 240.0539.
1
m.p: 202–204 °C. H NMR (300 MHz, CDCl3): δ 1.78 (s, 3H), 1.82 (s,
3H), 4.62 (d, J = 6.3 Hz, 2H), 5.49–5.53 (m, 1H), 6.97–7.02 (m, 2ArH),
7.18–7.34 (m, 4ArH), 7.60–7.62 (m, 2ArH), 8.03–8.06 (m, 2ArH),
8.14–8.17 (m, 2ArH). 13C NMR (75 MHz, CDCl3 + DMSO‑d6): δ 17.5,
25.0, 64.3, 113.8, 118.2, 120.3, 121.6, 122.5, 129.6, 131.4, 138.0,
150.5, 151.5, 162.6, 163.8. HRMS (ESI) m/z calculated for C25H23N2O3
(M+H)+: 399.1709; found: 399.1710.
4.3.60. 4-(1H-benzo[d]imidazol-2-yl)phenyl
(E)-4-((3,7-dimethylocta-
2,6-dien-1-yl)oxy)benzoate (10m)
4.3.64. Synthesis of compound 2-(4-methoxyphenyl)benzo[d]oxazole (12)
Compound 11 (8.0 g, 35.2 mmol) was dissolved in DCM and to that
DDQ (8.79 g, 38.7 mmol) was added and stirred at room temperature
for 2 h. After completion of reaction, the mass was diluted with DCM
and washed with water. Aqueous layer again extracted with DCM
(3x150 mL). Combined organic layer was washed with water followed
by brine solution. The organic portion was dried over sodium sulfate
and concentrated under reduced pressure. The crude was then purified
o-Phenylenediamine (0.05 g, 0.46 mmol), aldehyde 8m (0.174 g,
0.46 mmol) and p-toluenesulfonic acid (0.044 g, 0.23 mmol) were
dissolved in DMF and maintained at 80 °C for 4 h. After completion of
reaction (TLC), the reaction mass was diluted with ethyl acetate and
partitioned with water (2 times). Combined organic layer was washed
with water and brine. The organic portion was dried over sodium sul-
fate and purified by column chromatography (silica gel 100–200 mesh)
15

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
by column chromatography (silica gel 100–200 mesh) using ethyl
acetate in hexanes (25%) to afford compound 12 (6.7 g, 84.5%) as pale
brown solid, m.p: 86–88 °C. 1H NMR (400 MHz, CDCl3): δ 3.90 (s, 3H),
7.04 (d, J = 9.2 Hz, 2ArH), 7.32–7.36 (m, 2ArH), 7.55–7.57 (m, 1ArH),
7.73–7.75 (m, 1ArH), 8.20 (dd, J = 1.6, 8.8 Hz, 2ArH). HRMS (ESI+):
m/z calculated for C14H11NO2 [M+H]+: 225.0790; found: 225.0795.
7.33–7.37 (m, 4ArH), 7.57–7.59 (m, 1ArH), 7.72–7.77 (m, 2ArH), 9.15
(bs, 1O-H). HRMS (ESI+): m/z calculated for C13H9NO2 [M+H]+:
211.0633; found: 211.0636.
4.3.69. 4-(Benzo[d]oxazol-2-yl)phenyl 4-methoxybenzoate (14a)
To a stirred solution of 4-methoxybenzoic acid (0.072 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.125 g, 77.1%, white solid, m.p: 144–146 °C,
1H NMR (300 MHz, CDCl3): δ 3.91 (s, 3H), 6.98–7.03 (m, 2ArH),
7.34–7.42 (m, 4ArH), 7.57–7.63 (m, 1ArH), 7.76–7.81 (m, 1ArH),
8.15–8.20 (m, 2ArH), 8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3):
δ 55.6, 110.6, 114.0, 120.0, 121.4, 122.5, 124.7, 125.2, 129.0, 132.4,
142.1, 150.8, 153.7, 162.4, 164.1, 164.5. HRMS (ESI) m/z calculated
for C21H16NO4 (M+H)+: 346.1079; found: 346.1081.
4.3.65. Synthesis of compound 4-(benzo[d]oxazol-2-yl)phenol (13)
Compound 12 (6 g, 26.6 mmol) was suspended in hydrobromic acid
(50% in acetic acid) and maintained at 80 °C for 12 h. After completion
of reaction the mass was poured into water and the solid was filtered.
The solid thus obtained was dissolved in ethyl acetate and washed with
10% sodium carbonate solution. The organic layer was further washed
with water, brine solution and dried over sodium sulfate. The organic
portion was then concentrated and purified by column chromatography
(silica gel 100–200 mesh) using ethyl acetate in hexanes (32%) to af-
ford compound 13 (4.4 g, 78.3%) as off white solid, m.p: > 200 °C. 1H
NMR (400 MHz, CDCl3): δ 5.52 (bs, 1O-H), 6.97 (d, J = 8.8, 2ArH),
7.32–7.34 (m, 2ArH), 7.55–7.57 (m, 1ArH), 7.73–7.75 (m, 1ArH),
8.15–8.22 (m, 2ArH). HRMS (ESI+): m/z calculated for C13H9NO2 [M
+H]+: 211.0633; found: 211.0634.
4.3.66. Synthesis of compound 2-(3-nitrophenyl)benzo[d]oxazole (15)
Compound 11b (9.0 g, 37.2 mmol) was dissolved in DCM and to
that DDQ (9.29 g, 40.9 mmol) was added and stirred at RT for 2 h. After
completion of reaction, the mass was diluted with DCM and washed
with water. Aqueous layer was again extracted with DCM (3x150 mL).
Combined organic layer was washed with water followed by brine so-
lution. The organic portion was dried over sodium sulfate and con-
centrated under reduced pressure. The crude was purified by column
chromatography (silica gel 100–200 mesh) using ethyl acetate in hex-
anes (25%) to afford compound 15 (7.64 g, 85.5%) as pale yellow solid,
m.p: 168–170 °C. 1H NMR (300 MHz, CDCl3): δ 7.38–7.45 (m, 2ArH),
7.62–7.68 (m, 1ArH), 7.74 (t, J = 7.8 Hz, 1ArH), 7.80–7.85 (m, 1ArH),
8.39 (dq, J = 0.9, 8.1 Hz, 1ArH), 8.60 (dt, J = 1.2, 7.8 Hz, 1ArH), 9.11
(s, 1ArH). HRMS (ESI+): m/z calculated for C13H8N2O3 [M+H]+:
240.0535; found: 240.0539.
4.3.70. 4-(Benzo[d]oxazol-2-yl)phenyl 4-ethoxybenzoate (14b)
To a stirred solution of 4-ethoxybenzoic acid (0.079 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.139 g, 82.2%, white solid, m.p: 170–172 °C,
1H NMR (300 MHz, CDCl3): δ 1.47 (t, J = 6.9 Hz, 3H), 4.14 (q,
J = 6.9 Hz, 2H), 6.97–7.01 (m, 2 ArH), 7.34–7.42 (m, 4 ArH),
7.57–7.63 (m, 1ArH), 7.75–7.81 (m, 1 ArH), 8.14–8.19 (m, 2ArH),
8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 14.7, 63.9, 110.6,
114.4, 120.0, 121.2, 122.5, 124.7, 125.2, 129.0, 132.4, 142.1, 150.8,
153.7, 162.4, 163.6, 164.5. HRMS (ESI) m/z calculated for C22H18NO4
(M+H)+: 360.1236; found: 360.1239.
4.3.67. Synthesis of compound 3-(benzo[d]oxazol-2-yl)aniline (16)
Compound 15 (7 g, 29.14 mmol) was dissolved in methanol and
°
chlroform (3:2) and cooled to 0–5 C and then Nickel chloride hex-
ahydrate (0.345 g, 1.46 mmol) was added and stirred for 10 min. Then
sodium borohydride (3.31 g, 87.42 mmol) was added in 5 lots over a
period of 30 min and stirred at room temperature for another 1 h. Then
the reaction mixture was then filtered through celite bed and the bed
washed with warm methanol. The filtrate was evaporated and parti-
tioned between ethyl acetate and water (3x200 mL). Combined organic
layer washed with water and then with brine. The organic portion was
dried over sodium sulfate and concentrated under reduced pressure to
get the product 16 (5.45 g, 88.9%) as brown solid, m.p: 162–164 °C. 1H
NMR (400 MHz, CDCl3): δ 3.25 (bs, 2 NH), 6.84–6.86 (m, 1ArH),
7.31–7.36 (m, 3ArH), 7.59–7.60 (m, 2ArH), 7.66–7.68 (m, 1ArH),
7.82–7.85 (m, 1ArH). HRMS (ESI+): m/z calculated for C13H10N2O [M
+H]+: 210.0793; found: 210.0791.
4.3.71. 4-(Benzo[d]oxazol-2-yl)phenyl 4-propoxybenzoate (14c)
To a stirred solution of 4-propoxybenzoic acid (0.085 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.118 g, 67.2%, white solid, m.p: 170–172 °C,
1H NMR (300 MHz, CDCl3): δ 1.08 (t, J = 7.5 Hz, 3H), 1.87 (sextet,
J = 7.5 Hz, 2H), 4.03 (t, J = 6.6 Hz, 2H), 7.00 (td, J = 1.8, 4.8 Hz,
2H), 7.36–7.39 (m, 2H), 7.41 (dd, J = 0.9, 4.8 Hz, 1H), 7.57–7.62 (m,
2H), 7.75–7.81 (m, 1H), 8.13 (t, J = 1.8 Hz, 1H), 8.17 (td,
J = 1.8,5.1 Hz, 3H). 13C NMR (75 MHz, CDCl3): δ 10.5, 22.5, 69.8,
110.6, 114.4, 120.0, 121.1, 122.5, 124.7, 125.2, 129.0, 132.4, 142.1,
150.8, 153.7, 162.5, 163.8, 164.5. HRMS (ESI) m/z calculated for
4.3.68. Synthesis of compound 3-(benzo[d]oxazol-2-yl)phenol (17)
Compound 16 (5 g, 23.8 mmol) was dissolved in 5% aqueous HCl
(30 mL) and cooled to 5 °C for 15 min. Then aqueous solution of sodium
nitrite (1.97 g, 28.5 mmol) was added drop wise to the reaction mass
and stirred for 15 min. It was heated to 80 °C, and maintained for 6 h.
After completion of the reaction by TLC the aqueous phase was ex-
tracted with ethyl acetate (3x150). Combined organic layer was washed
with water and then with brine. Evaporated and purified by column
chromatography (silica gel 100–200 mesh) using 15% ethyl acetate in
hexanes to get the product 17 (3.9 g, 77.5%) as pale brown solid m.p:
196–198 °C. 1H NMR (400 MHz, DMSO‑d6): δ 7.03–7.06 (m, 1ArH),
C
23H20NO4 (M+H)+: 374.1392; found: 374.1395.
4.3.72. 4-(Benzo[d]oxazol-2-yl)phenyl 4-butoxybenzoate (14d)
To a stirred solution of 4-butoxybenzoic acid (0.091 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
16

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
ethyl acetate in hexanes. Yield: 0158 g, 78.2%, white solid, m.p:
1
106–108 °C, H NMR (300 MHz, CDCl3): δ 0.91 (t, J = 6.9 Hz, 3H),
1.33–1.37 (m, 6H), 1.40–1.51 (m, 2H), 1.84 (quintet, J = 6.6 Hz, 2H),
4.06 (t, J = 6.6 Hz, 2H), 6.98–7.01 (m, 2ArH), 7.34–7.42 (m, 4ArH),
7.57–7.62 (m, 1ArH), 7.76–7.82 (m, 1ArH), 8.14–8.18 (m, 2ArH),
8.31–8.35 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.6, 26.0,
29.0, 29.1, 31.8, 68.4, 110.6, 114.4, 120.0, 121.1, 122.5, 124.7, 125.2,
129.0, 132.4, 142.1, 150.8, 153.7, 162.5, 163.8, 164.5. HRMS (ESI) m/
z calculated for C27H28NO4 (M+H)+: 430.2018; found:430.2020.
1
acetate in hexanes. Yield: 0.142 g, 77.2%, white solid, m.p:, H NMR
(300 MHz, CDCl3): δ 1.00 (t, J = 7.5 Hz, 3H), 1.54 (sextet, J = 7.5 Hz,
2H), 1.82 (quintet, J = 7.8 Hz, 2H), 4.07 (t, J = 6.6 Hz, 2H), 6.97–7.02
(m, 2ArH), 7.32–7.42 (m, 4ArH), 7.55–7.63 (m, 1ArH), 7.73–7.81 (m,
1ArH), 8.14–8.22 (m, 2ArH), 8.31–8.35 (m, 2ArH). 13C NMR (75 MHz,
CDCl3): δ 18.8, 19.2, 31.1, 68.1, 110.6, 114.4, 120.0, 121.1, 122.5,
124.7, 125.2, 129.0, 132.4, 142.1, 150.8, 153.7, 162.5, 163.8, 164.5.
HRMS (ESI) m/z calculated for C24H22NO4 (M+H)+: 388.1549; found:
388.1551.
4.3.76. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(octyloxy)benzoate (14h)
To a stirred solution of 4-octyloxybenzoic acid (0.118 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.163 g, 78.4%, appearance, m.p:
4.3.73. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(pentyloxy)benzoate (14e)
To a stirred solution of 4-pentoxybenzoic acid (0.098 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.151 g, 79.9%, white solid, m.p: 120–122 °C,
1H NMR (300 MHz, CDCl3): δ 0.95 (t, J = 6.9 Hz, 3H), 1.42–1.48 (m,
4H), 1.82–1.86 (m, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH),
7.34–7.42 (m, 4ArH), 7.57–7.63 (m, 1ArH), 7.76–7.81 (m, 1ArH),
8.14–8.19 (m, 2ArH), 8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3):
δ 14.0, 22.5, 28.1, 28.8, 68.4, 110.6, 114.4, 120.0, 121.1, 122.5, 124.6,
125.2, 129.0, 132.4, 142.1, 150.8, 153.7, 162.4, 163.8, 164.5. HRMS
(ESI) m/z calculated for C25H24NO4 (M+H)+: 402.1705; found:
402.1706.
1
118–120 °C, H NMR (300 MHz, CDCl3): δ 0.90 (t, J = 6.6 Hz, 3H),
1.30–1.35 (m, 8H), 1.60–1.61 (m, 2H), 1.83 (quintet, J = 6.6 Hz, 2H),
4.06 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH), 7.34–7.42 (m, 4ArH),
7.57–7.63 (m, 1ArH), 7.76–7.81 (m, 1ArH), 8.14–8.18 (m, 2ArH),
8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0,
29.1, 29.2, 29.3, 31.8, 68.4, 110.6, 114.4, 120.0, 121.1, 122.5, 124.6,
125.2, 129.0, 132.4, 142.1, 150.8, 153.7, 162.5, 163.8, 164.5. HRMS
(ESI) m/z calculated for
C
28H30NO4 (M+H)+: 444.2175;
found:444.2177.
4.3.77. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(nonyloxy)benzoate (14i)
To stirred solution of 4-nonyloxybenzoic acid (0.124 g,
a
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.187 g, 87.0%, white solid, m.p:
84–86 °C, 1H NMR (300 MHz, CDCl3): δ 0.89 (t, J = 6.6 Hz, 3H),
1.26–1.39 (m, 10H), 1.46–1.48 (m, 2H), 1.83 (quintet, J = 6.6 Hz, 2H),
4.05 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH), 7.33–7.41 (m, 4ArH),
7.54–7.63 (m, 1ArH), 7.73–7.81 (m, 1ArH), 8.14–8.22 (m, 2ArH),
8.31–8.35 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0,
29.1, 29.3, 29.4, 29.5, 31.9, 68.4, 110.6, 114.4, 120.0, 121.9, 122.5,
124.7, 125.2, 129.0, 129.4, 132.4, 142.1, 150.8, 153.7, 162.5, 163.8,
164.5. HRMS (ESI) m/z calculated for C29H32NO4 (M+H)+: 458.2331;
found: 458.2333.
4.3.74. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(hexyloxy)benzoate (14f)
To
a stirred solution of 4-hexyloxybenzoic acid (0.104 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.163 g, 83.6%, white solid, m.p:
1
118–120 °C, H NMR (300 MHz, CDCl3): δ 0.92 (t, J = 6.9 Hz, 3H),
1.33–1.39 (m, 4H), 1.46–1.51 (m, 2H), 1.83 (quintet, J = 6.9 Hz, 2H),
4.06 (t, J = 6.3 Hz, 2H), 6.98–7.02 (m, 2ArH), 7.31–7.41 (m, 4ArH),
7.58–7.63 (m, 1ArH), 7.77–7.81 (m, 1ArH), 8.14–8.19 (m, 2ArH),
8.31–8.36 (m, 2ArH) 13C NMR (100 MHz, CDCl3): δ 14.1, 22.6, 25.7,
29.1, 31.6, 68.4, 110.6, 114.4, 120.0, 121.1, 122.5, 124.7, 125.2,
129.0, 129.4, 132.4, 142.1, 15.08, 153.7, 162.5, 163.8, 164.5. HRMS
(ESI) m/z calculated for C26H26NO4 (M+H)+: 416.1862; found:
416.1866.
4.3.78. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(decyloxy)benzoate (14j)
To a stirred solution of 4-decyloxybenzoic acid (0.131 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.183 g, 82.4%, white solid, m.p: 96–98 °C,
1H NMR (300 MHz, CDCl3): δ 0.89 (t, J = 6.9 Hz, 3H), 1.25–1.34 (m,
12H), 1.43–1.49 (m, 2H), 1.83 (quintet, J = 6.9 Hz, 2H), 4.06 (t,
J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH), 7.34–7.42 (m, 4ArH), 7.56–7.63
4.3.75. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(heptyloxy)benzoate (14g)
To
a stirred solution of 4-heptyloxybenzoic acid (0.111 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
17

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
(m, 1ArH), 7.74–7.82 (m, 1ArH), 8.14–8.19 (m, 2ArH), 8.31–8.36 (m,
2ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3, 29.4,
29.6, 29.7, 31.9, 68.4, 110.6, 114.4, 120.0, 121.1, 122.5, 124.7, 125.2,
129.0, 132.4, 142.1, 150.8, 153.7, 162.5, 163.8, 164.5. HRMS (ESI) m/
z calculated for C30H34NO4 (M+H)+: 472.2488; found: 472.2450.
(M+H)+: 468.2175; found: 468.2178.
4.3.82. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)oxy)benzoate (14n)
To a stirred solution of 4-farnesyloxybenzoic acid (0.161 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.205 g, 81.3%, pale yellow solid, m.p:
60–62 °C, 1H NMR (300 MHz, CDCl3): δ 1.62 (s, 6H), 1.68 (s, 3H), 1.77
(s, 3H), 1.98–2.18 (m, 8H), 4.65 (d, J = 6.6 Hz, 2H), 5.07–5.09 (m,
2H), 5.51 (t, J = 6.6 Hz, 1H), 6.99–7.02 (m, 2ArH), 7.34–7.41 (m,
4ArH), 7.57–7.63 (m, 1ArH), 7.76–7.81 (m, 1ArH), 8.16 (t, J = 8.7 Hz,
2ArH), 8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 16.1, 16.8,
17.7, 23.4, 26.1, 26.2, 32.0, 39.5, 39.7, 65.2, 110.6, 114.6, 118.7,
120.0, 121.2, 122.5, 123.6, 124.3, 124.3, 124.7, 125.2, 129.0, 131.4,
132.4, 135.6, 142.1, 150.8, 153.7, 162.5, 163.5, 164.5. HRMS (ESI) m/
z calculated for C35H38NO4 (M+H)+: 536.2801; found: 536.2805.
4.3.79. 4-(Benzo[d]oxazol-2-yl)phenyl 4-(allyloxy)benzoate (14k)
To a stirred solution of 4-allyloxybenzoic acid (0.084 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.152 g, 87.4%, white solid, m.p: 128–130 °C,
1H NMR (300 MHz, CDCl3): δ 4.65 (dt, J = 1.5, 5.4 Hz, 2H), 5.33–5.37
(m, 1H), 5.42–5.50 (m, 1H), 6.04–6.13 (m,1H), 7.01–7.05 (m, 2ArH),
7.36–7.42 (m, 4ArH), 7.59–7.62 (m, 1ArH), 7.77–7.80 (m, 1ArH),
8.15–8.20 (m, 2ArH), 8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3):
δ 69.0, 110.6, 114.7, 118.3, 120.0, 121.5, 122.5, 124.6, 124.7, 125.2,
129.0, 132.4, 142.1, 150.8, 153.7, 162.4, 163.1, 164.4. HRMS (ESI) m/
z calculated for C23H18NO4 (M+H)+: 372.1236; found: 372.1239.
4.3.83. 3-(Benzo[d]oxazol-2-yl)phenyl 4-methoxybenzoate (18a)
To a stirred solution of 4-methoxybenzoic acid (0.072 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.124 g, 76.5%, white solid, m.p: 138–140 °C,
1H NMR (300 MHz, CDCl3): δ 3.92 (s, 3H), 6.99–7.04 (m, 2ArH),
7.34–7.38 (m, 2ArH), 7.39–7.43 (m, 1ArH), 7.57–7.62 (m, 2ArH),
7.77–7.80 (m, 1ArH), 8.13 (t, J = 1.8 Hz, 1ArH), 8.16–8.20 (m, 3ArH).
13C NMR (75 MHz, CDCl3): δ 55.6, 110.7, 114.0, 120.2, 121.2, 121.5,
124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.4, 142.0, 150.8, 151.5,
162.2, 164.1, 164.7. HRMS (ESI) m/z calculated for C21H16NO4 (M
+H)+: 346.1079; found: 346.1082.
4.3.80. 4-(Benzo[d]oxazol-2-yl)phenyl
4-((3-methylbut-2-en-1-yl)oxy)
benzoate (14l)
To
a stirred solution of 4-prenyloxybenzoic acid (0.097 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.148 g, 78.7%, pale yellow solid, m.p:
1
148–150 °C, H NMR (300 MHz, CDCl3): δ 1.78 (s, 3H), 1.83 (s, 3H),
4.62 (d, J = 6.6 Hz, 2H), 5.49–5.54 (m, 1H), 6.99–7.03 (m, 2ArH),
7.34–7.41 9 (m, 4ArH), 7.57–7.63 (m, 1ArH), 7.76–7.81 (m, 1ArH),
8.14–8.19 (m, 2ArH), 8.31–8.35 (m, 2ArH). 13C NMR (75 MHz, CDCl3):
δ 18.3, 25.9, 65.1, 110.6, 114.6, 118.9, 120.0, 121.2, 122.5, 124.7,
125.2, 129.0, 132.4, 139.1, 142.1, 150.8, 153.7, 162.4, 163.5, 164.5.
HRMS (ESI) m/z calculated for C25H22NO4 (M+H)+: 400.1549; found:
400.1550.
4.3.84. 3-(Benzo[d]oxazol-2-yl)phenyl 4-ethoxybenzoate (18b)
To a stirred solution of 4-ethoxybenzoic acid (0.079 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.118 g, 69.8%, white solid, m.p: 80–82 °C,
1H NMR (300 MHz, CDCl3): δ 1.48 (t, J = 6.9 Hz, 3H), 4.14 (q,
J = 6.9 Hz, 2H), 6.98–7.02 (m, 2 ArH), 7.34–7.43 (m, 2 ArH),
7.48–7.58 (m, 2 ArH), 7.92 (d, J = 8.1 Hz, 1 ArH), 7.96–7.99 (m, 2
ArH), 8.07 (d, J = 8.1 Hz, 1 ArH), 8.06–8.20 (m, 2 ArH). 13C NMR
(75 MHz, CDCl3): δ 14.7, 63.9, 114.4, 120.9, 121.3, 121.7, 123.4,
124.5, 124.9, 125.4, 126.4, 130.0, 132.4, 135.1, 151.6, 154.0, 163.5,
164.7, 166.9. HRMS (ESI) m/z calculated for C22H18NO4 (M+H)+:
360.1236; found: 360.1237.
4.3.81. 4-(Benzo[d]oxazol-2-yl)phenyl (E)-4-((3,7-dimethylocta-2,6-dien-
1-yl)oxy)benzoate (14m)
To a stirred solution of 4-geranyloxybenzoic acid (0.129 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 13 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.165 g, 75.0%, pale yellow solid, m.p:
1
110–112 °C, H NMR (300 MHz, CDCl3): δ 1.62 (s, 3H), 1.69 (s, 3H),
1.77 (s, 3H), 2.12–2.14 (m, 4H), 4.65 (d, J = 6.3 Hz, 2H), 5.10 (t,
J = 1.5 Hz, 1H), 5.50 (t, J = 1.2 Hz, 1H), 6.99–7.03 (m, 2ArH),
7.34–7.42 (m, 4ArH), 7.57–7.63 (m, 1ArH), 7.75–7.81 (m, 1ArH),
8.15–8.19 (m, 2ArH), 8.31–8.36 (m, 2ArH). 13C NMR (75 MHz, CDCl3):
δ 16.8, 17.7, 25.7, 26.3, 39.5, 65.2, 110.6, 114.7, 118.7, 120.0, 121.2,
122.5, 123.7, 124.7, 125.2, 129.0, 132.0, 132.4, 142.1, 142.1, 150.8,
153.7, 162.5, 163.5, 164.5. HRMS (ESI) m/z calculated for C30H30NO4
4.3.85. 3-(Benzo[d]oxazol-2-yl)phenyl 4-propoxybenzoate compound
(18c)
To a stirred solution of 4-propoxybenzoic acid (0.085 g, 0.47 mmol)
18

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.139 g, 79.0%, white solid, m.p: 116–118 °C,
1H NMR (300 MHz, CDCl3): δ 1.08 (t, J = 7.5 Hz, 3H), 1.83 (sextet,
J = 7.2 Hz, 2H), 4.03 (t, J = 6.6 Hz, 2H), 6.98–7.03 (m, 2ArH),
7.34–7.38 (m, 2ArH), 7.39–7.43 (m, 1ArH), 7.57–7.59 (m, 1ArH),
7.60–7.62 (m, 1ArH), 7.75–7.81 (m, 1ArH), 8.13 (t, J = 1.8 Hz, 1ArH),
8.15–8.20 (m, 3ArH). 13C NMR (75 MHz, CDCl3): δ 10.5, 22.5, 69.8,
110.7, 114.4, 120.2, 121.2, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1,
132.4, 142.0, 150.8, 151.5, 162.2, 163.7, 164.7.HRMS (ESI) m/z cal-
culated for C23H20NO4 (M+H)+: 374.1392; found: 374.1393.
evaporated and the crude mass was partitioned between ethyl acetate
and 10% sodium bicarbonate solution (2 times). Combined organic
layer was washed with water and brine. Dried over sodium sulfate and
purified by column chromatography (silica gel 100–200 mesh) using
15% ethyl acetate in hexanes. Yield: 0.158 g, 81.0%, white solid, m.p:
1
106–108 °C, H NMR (300 MHz, CDCl3): δ 0.93 (t, J = 7.2 Hz, 3H),
1.37 (sextet, J = 3.6 Hz, 4H), 1.45–1.54 (m, 2H), 1.84 (pentet,
J = 6.6 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH),
7.34–7.38 (m, 2ArH), 7.39–7.42 (m, 1ArH), 7.56–7.62 (m, 2ArH),
7.75–7.81 (m, 1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.15–8.19 (m, 3ArH).
13C NMR (75 MHz, CDCl3): δ 14.0, 22.6, 25.7, 29.1, 31.6, 68.4, 110.7,
114.4, 120.2, 121.2, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.4,
142.0, 150.8, 151.5, 162.2, 163.7, 164.7. HRMS (ESI) m/z calculated
for C26H26NO4 (M+H)+: 416.1862; found: 416.1865.
4.3.89. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(heptyloxy)benzoate compound
(18g)
To
a stirred solution of 4-heptyloxybenzoic acid (0.111 g,
4.3.86. 3-(Benzo[d]oxazol-2-yl)phenyl
4-butoxybenzoate
compound
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.162 g, 80.1%, appearance, m.p:
90–92 °C, 1H NMR (300 MHz, CDCl3): δ 0.91 (t, J = 6.6 Hz, 3H),
1.33–1.41 (m, 6H), 1.46–1.49 (m, 2H), 1.81 (pentet, J = 6.6 Hz, 2H),
4.06 (t, J = 6.6 Hz, 2H), 6.97–7.01 (m, 2ArH), 7.34–7.43 (m, 3ArH),
7.56–7.62 (m, 2ArH), 7.75–7.81 (m, 1ArH), 8.12 (t, J = 1.5 Hz, 1ArH),
8.15–8.21 (m, 3ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.6, 26.0,
29.0, 29.1, 31.8, 68.4, 110.7, 114.4, 120.2, 121.2, 124.7, 124.9, 125.1,
125.4, 128.6, 130.1, 132.4, 142.0, 150.8, 151.5, 162.2, 163.7, 164.7.
HRMS (ESI) m/z calculated for C27H28NO4 (M+H)+: 430.2018; found:
430.2021.
(18d)
To a stirred solution of 4-butoxybenzoic acid (0.091 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.134 g, 73.6%, white solid, m.p: 102–104 °C,
1H NMR (300 MHz, CDCl3): δ 0.98 (t, J = 6.9 Hz, 3H), 1.47–1.57 (m,
2H), 1.78–1.87 (m, 2H), 4.07 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH),
7.34–7.38 (m, 2ArH), 7.39–7.43 (m, 1ArH), 7.57–7.62 (m, 2ArH),
7.75–7.81 (m, 1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.15–8.20 (m, 3H).
13C NMR (75 MHz, CDCl3): δ 13.8, 19.2, 31.2, 68.1, 110.7, 114.4,
120.2, 121.2, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.4, 142.0,
150.8, 151.5, 162.2, 163.7, 164.7.HRMS (ESI) m/z calculated for
C
24H22NO4 (M+H)+: 388.1549; found: 388.1551.
4.3.90. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(octyloxy)benzoate (18h)
To a stirred solution of 4-octyloxybenzoic acid (0.118 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.157 g, 75.5%, white solid, m.p: 78–80 °C,
1H NMR (300 MHz, CDCl3): δ 0.90 (t, J = 6.9 Hz, 3H), 1.31–1.35 (m,
8H), 1.46–1.49 (m, 2H), 1.82 (pentet, J = 6.9 Hz, 2H), 4.06 (t,
J = 6.6 Hz, 2H), 6.98–7.01 (m, 2ArH), 7.34–7.43 (m, 3ArH), 7.56–7.62
(m, 2ArH), 7.75–7.81 (m, 1ArH), 8.12 (t, J = 1.5 Hz, 1ArH), 8.15–8.18
(m, 3ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.2,
29.3, 31.8, 68.4, 110.7, 114.4, 120.2, 121.2, 124.9, 125.1, 125.4,
128.6, 130.1, 132.4, 142.0, 150.8, 151.3, 162.2, 163.7, 164.7. HRMS
(ESI) m/z calculated for C28H30NO4 (M+H)+: 444.2175; found:
444.2175.
4.3.87. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(pentyloxy)benzoate compound
(18e)
To a stirred solution of 4-pentoxybenzoic acid (0.098 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.145 g, 76.7%, white solid, m.p: 95–97 °C,
1H NMR (300 MHz, CDCl3): δ 0.96 (t, J = 6.9 Hz, 3H), 1.43–1.48 (m,
4H), 1.85 (quintet, J = 6.9 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.01
(m, 2ArH), 7.34–7.43 (m, 3ArH), 7.56–7.62 (m, 2ArH), 7.75–7.81 (m,
1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.16–8.19 (m, 3ArH). 13C NMR
(75 MHz, CDCl3): δ 14.0, 22.5, 28.2, 28.8, 68.4, 110.7, 114.4, 120.2,
121.2, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.4, 142.0, 150.8,
151.5, 162.2, 163.7, 164.7. HRMS (ESI) m/z calculated for C25H24NO4
(M+H)+: 402.1705; found: 402.1708.
4.3.91. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(nonyloxy)benzoate (18i)
To
a stirred solution of 4-nonyloxybenzoic acid (0.124 g,
4.3.88. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(hexyloxy)benzoate (18f)
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
To
a stirred solution of 4-hexyloxybenzoic acid (0.104 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles
19

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.174 g, 80.9%, white solid, m.p:
84–86 °C, 1H NMR (300 MHz, CDCl3): δ 0.90 (t, J = 6.9 Hz, 3H),
1.30–1.34 (m, 10H), 1.46–1.49 (m, 2H), 1.83 (pentet, J = 6.9 Hz, 2H),
4.06 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH), 7.34–7.43 (m, 3ArH),
7.56–7.62 (m, 2ArH), 7.75–7.81 (m, 1ArH), 8.12 (t, J = 2.1 Hz, 1ArH),
8.16–8.18 (m, 3ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0,
29.1, 29.3, 29.4, 29.5, 31.9, 68.4, 110.7, 114.4, 120.2, 121.2, 124.7,
125.1, 128.6, 130.1, 132.4, 142.0, 150.8, 151.5, 162.2, 163.7, 164.7.
HRMS (ESI) m/z calculated for C29H32NO4 (M+H)+: 458.2331; found:
458.2335.
ethyl acetate in hexanes. Yield: 0.132 g, 70.6%, pale yellow solid, m.p:
1
118–120 °C, H NMR (300 MHz, CDCl3): δ 1.79 (s, 3H), 1.83 (s, 3H),
4.62 (d, J = 6.9 Hz, 2H), 5.49–5.55 (m, 1H), 6.99–7.04 (m, 2ArH),
7.34–7.38 (m,2H), 7.39–7.43 (m, 1ArH), 7.57–7.62 (m, 2ArH),
7.75–7.81 (m, 1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.15–8.17 (m, 3ArH).
13C NMR (75 MHz, CDCl3): δ 18.3, 25.9, 65.1, 110.7, 114.6, 118.9,
120.2, 121.2, 121.3, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.4,
139.1, 142.0, 150.8, 151.5, 162.2, 163.4, 164.7. HRMS (ESI) m/z cal-
culated for C25H22NO4 (M+H)+: 400.1549; found: 400.1553.
4.3.95. 3-(Benzo[d]oxazol-2-yl)phenyl (E)-4-((3,7-dimethylocta-2,6-dien-
1-yl)oxy)benzoate (18m)
To a stirred solution of 4-geranyloxybenzoic acid (0.129 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.168 g, 76.7%, pale yellow solid, m.p:
90–92 °C, 1H NMR (300 MHz, CDCl3): δ 1.62 (s, 3H), 1.69 (s, 3H), 1.78
(s, 3H), 2.09–2.20 (m, 4H), 4.65 (d, J = 6.6 Hz, 2H), 5.09–5.11 (m,
1H), 5.51 (t, J = 6.6 Hz, 1H), 6.70–7.03 (m, 2ArH), 7.36–7.38 (m, 2H),
7.39–7.43 (m, 1ArH), 7.57–7.62 (m, 2ArH), 7.77–7.80 (m, 1ArH), 8.12
(t, J = 1.8 Hz, 1ArH), 8.15–8.19 (m, 3ArH). 13C NMR (75 MHz, CDCl3):
δ 16.8, 17.7, 25.7, 26.3, 39.6, 65.2, 110.7, 114.6, 118.7, 120.2, 121.2,
121.3, 123.7, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.0, 132.4,
142.0, 142.1, 150.8, 151.5, 162.2, 163.5, 164.7. HRMS (ESI) m/z cal-
culated for C30H30NO4 (M+H)+: 468.2175; found: 468.2176.
4.3.92. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(decyloxy)benzoate compound
(18j)
To a stirred solution of 4-decyloxybenzoic acid (0.131 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.185 g, 83.7%, white solid, m.p: 76–78 °C,
1H NMR (300 MHz, CDCl3): δ 0.89 (t, J = 6.9 Hz, 3H), 1.29–1.34 (m,
12H), 1.44–1.49 (m, 2H), 1.84 (pentet, J = 6.6 Hz, 2H), 4.06 (t,
J = 6.3 Hz, 2H), 6.98–7.00 (m, 2ArH), 7.34–7.42 (m, 3ArH), 7.56–7.62
(m, 2ArH), 7.75–7.80 (m, 1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.16–8.18
(m, 3ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3,
29.4, 29.6, 68.4, 110.7, 114.4, 120.2, 121.2, 124.9,125.1, 125.4, 128.6,
130.1, 132.4, 142.0, 150.8, 151.5, 162.2, 163.7, 164.7. HRMS (ESI) m/
z calculated for C30H34NO4 (M+H)+: 472.2488; found: 472.2491.
4.3.96. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)oxy)benzoate (18n)
4.3.93. 3-(Benzo[d]oxazol-2-yl)phenyl 4-(allyloxy)benzoate compound
(18k)
To a stirred solution of 4-farnesyloxybenzoic acid (0.161 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
ethyl acetate in hexanes. Yield: 0.189 g, 75.3%, pale yellow solid, m.p:
52–54 °C, 1H NMR (300 MHz, CDCl3): δ 1.61–1.62 (m, 6H), 1.69 (s,
3H), 1.78 (s, 3H), 1.96–2.18 (m, 8H), 4.65 (d, J = 6.3 Hz, 2H),
5.08–5.12 (m, 2H), 5.51 (t, J = 6.3 Hz, 1H), 7.01 (dd, J = 2.4, 9.0 Hz,
2ArH), 7.34–7.43 (m, 3ArH), 7.56–7.62 (m, 2ArH), 7.75–7.81 (m,
1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.16–8.19 (m, 3ArH). 13C NMR
(75 MHz, CDCl3): δ 16.1, 16.8, 23.4, 26.1, 26.2, 32.0, 39.6, 39.7, 65.2,
110.7, 114.6, 118.8, 120.2, 121.2, 121.3, 123.6, 124.3, 124.4, 124.7,
124.9, 125.1, 125.4, 128.6, 130.1, 131.4, 131.6, 132.4, 135.6, 142.0,
150.8, 151.5, 162.2, 163.5, 164.7. HRMS (ESI) m/z calculated for
To a stirred solution of 4-allyloxybenzoic acid (0.084 g, 0.47 mmol)
in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl (0.118 g,
0.62 mmol) were added and stirred at room temperature for 15 min.
Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at room
temperature. After completion of reaction (TLC), volatiles evaporated
and the crude mass was partitioned between ethyl acetate and 10%
sodium bicarbonate solution (2 times). Combined organic layer was
washed with water and brine. Dried over sodium sulfate and purified by
column chromatography (silica gel 100–200 mesh) using 15% ethyl
acetate in hexanes. Yield: 0.128 g, 73.6%, white solid, m.p: 120–122 °C,
1H NMR (300 MHz, CDCl3): δ 4.65 (dt, J = 1.5, 5.4 Hz, 2H), 5.35 (dd,
J = 1.2, 10.5 Hz, 1H), 5.46 (dd, J = 1.5, 17.4 Hz, 1H), 6.02–6.15 (m,
1H), 7.00–7.05 (m, 2ArH), 7.34–7.43 (m, 3ArH), 7.56–7.62 (m, 2ArH),
7.75–7.81 (m, 1ArH), 8.12 (t, J = 1.8 Hz, 1ArH), 8.16–8.20 (m, 3ArH).
13C NMR (75 MHz, CDCl3): δ 69.0, 110.7, 114.7, 118.3, 120.2, 121.1,
121.6, 124.7, 124.9, 125.1, 125.4, 128.6, 130.1, 132.4, 132.4, 142.0,
150.8, 151.5, 162.2, 163.1, 164.6. HRMS (ESI) m/z calculated for
C
23H18NO4 (M+H)+: 372.1236; found: 372.1238.
C
35H38NO4 (M+H)+: 536.2801; found: 536.2803.
4.3.94. 3-(Benzo[d]oxazol-2-yl)phenyl
4-((3-methylbut-2-en-1-yl)oxy)
4.3.97. 2-(4-Methoxyphenyl)benzo[d]thiazole (21)
benzoate (18l)
2-Aminothiophenol (4 g, 31.95 mmol), p-anisaldehyde (4.35 g,
31.95 mmol) were mixed thoroughly in a mortar with pestle for 5 min.
Then ceric ammonium nitrate (0.088 g, 0.16 mmol) was added and
ground well. To that 30% Hydrogen peroxide (3 mL) was added and
further ground for 10 min. Reaction mass dissolved with ethyl acetate
and washed thoroughly with water. Then washed with brine solution
and dried over Sodium sulfate. It was then purified by column chro-
matography using ethyl acetate in hexanes (8%) to afford the product
21 (5.30 g, 89.2%) as pale yellow solid, m.p: 104–106 °C. 1H NMR
(400 MHz, CDCl3): δ 3.89 (s, 3H), 7.01 (dd, J = 2.0, 4.8 Hz, 2ArH),
To
a stirred solution of 4-prenyloxybenzoic acid (0.097 g,
0.47 mmol) in THF, DMAP (0.005 g, 0.047 mmol) and EDC.HCl
(0.118 g, 0.62 mmol) were added and stirred at room temperature for
15 min. Then 17 (0.1 g, 0.47 mmol) was added and stirred for 3 h at
room temperature. After completion of reaction (TLC), volatiles eva-
porated and the crude mass was partitioned between ethyl acetate and
10% sodium bicarbonate solution (2 times). Combined organic layer
was washed with water and brine. Dried over sodium sulfate and pur-
ified by column chromatography (silica gel 100–200 mesh) using 15%
20

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
7.35–7.45 (m, 1ArH), 7.47 (t, J = 7.2 Hz, 1ArH), 7.88 (d, J = 7.6 Hz,
1ArH), 8.02–8.06 (m, 3ArH). HRMS (ESI+): m/z calculated for
CDCl3): δ 1.08 (t, J = 7.5 Hz, 3H), 1.87 (sextet, J = 7.2 Hz, 2H), 4.03
(t, J = 6.6 Hz, 2H), 6.98–7.01 (m, 2ArH), 7.35–7.38 (m, 1ArH),
7.40–7.43 (m, 1ArH), 7.48–7.51 (m, 1ArH), 7.53–7.58 (m, 1ArH), 7.92
(dq, J = 0.9,6.0 Hz, 1ArH) 7.96 (t, J = 0.9 Hz, 1ArH) 7.98–7.99
(m,1ArH) 8.08 (dq, J = 0.6,6.6 Hz, 1ArH) 8.16–8.19 (m, 2ArH). 13C
NMR (75 MHz, CDCl3): δ 10.5, 22.5, 69.8, 114.4, 120.9, 121.2, 121.7,
123.4, 124.5, 124.9, 125.4, 126.4, 130.1, 132.4, 135.1, 135.1, 151.6,
154.1, 163.7, 164.8, 166.9. HRMS (ESI) m/z calculated for C23H20NO3S
(M+H)+: 390.1164; found: 390.1165.
C
14H12NOS [M+H]+: 242.0640; found: 242.0642.
4.3.98. 4-(Benzo[d]thiazol-2-yl)phenol (22)
Compound 21 (4 g, 16.6 mmol) was suspended in hydrobromic acid
(33% in acetic acid) and maintained at 80 °C for 12 h. After completion
of reaction the mass was poured into water and was filtered. The solid
thus obtained was dissolved in ethyl acetate and washed with 10%
sodium carbonate solution. The organic layer was washed with water
and then with brine solution. It was then dried over sodium sulfate,
concentrated and purified by column chromatography (silica gel
100–200 mesh) using ethyl acetate in hexanes (25%) to afford com-
pound 22 (2.8 g, 74.3%) as off white solid, 200–202 °C. 1H NMR
(400 MHz, DMSO‑d6): δ 6.94–6.97 (m, 2 ArH), 7.31–7.45 (m, 1ArH),
7.44–7.45 (m, 1ArH), 7.86 (dd, J = 2.4, 5.6 Hz, 1ArH), 7.92–7.96 (m,
2ArH), 8.00 (dd, J = 2.4, 5.6 Hz, 1ArH), 9.32 (s, 1O-H). HRMS (ESI+):
m/z calculated for C13H10NOS [M+H]+: 228.0483; found: 228.0487.
4.3.102. 3-(Benzo[d]thiazol-2-yl)phenyl 4-butoxybenzoate (19d)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7d (0.119 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.138 g, 85.7%, pale yellow solid, m.p: 106–108 °C. 1H NMR (300 MHz,
CDCl3): δ 1.01 (t, J = 7.5 Hz, 3H) 1.47–1.57 (m, 2H), 1.78–1.87 (m,
2H), 4.07 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH), 7.35–7.38 (m,
1ArH), 7.40–7.43 (m, 1ArH), 7.48–7.52 (m, 1ArH), 7.53–7.58 (m,
1ArH), 7.91–7.93 (m, 1ArH), 7.96–7.99 (m, 2ArH), 8.06–8.09 (m,
1ArH) 8.15–8.20 (m,2ArH). 13C NMR (75 MHz, CDCl3): δ 13.8, 19.2,
31.2, 68.1, 114.4, 120.9, 121.2, 121.7, 123.4, 124.5, 124.9, 125.4,
126.4, 130.0, 132.4, 135.1, 135.1, 151.6, 154.1, 163.7, 164.8, 166.9.
HRMS (ESI) m/z calculated for C24H22NO3S (M+H)+: 404.1320;
found: 404.1323.
4.3.99. 3-(Benzo[d]thiazol-2-yl)phenyl 4-methoxybenzoate (19a)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7a (0.103 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.114 g, 79.2%, white solid, m.p: 116–118 °C. 1H NMR (300 MHz,
CDCl3): δ 3.91 (s, 3H), 6.99–7.03 (m, 2ArH), 7.35–7.38 (m, 1ArH),
7.40–7.43 (m, 1ArH), 7.48–7.51 (m, 1ArH), 7.53–7.58 (m, 1ArH),
7.90–7.93 (m, 1ArH), 7.96–7.99 (m, 2ArH), 8.08 (td, J = 0.6, 6.9 Hz,
1ArH), 8.16–8.21 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 55.6, 113.9,
120.9, 121.5, 121.7, 123.4, 124.5, 124.9, 125.4, 126.4, 130.1, 132.4,
135.1, 135.1, 151.6, 154.0, 164.1, 164.7, 166.9. HRMS (ESI) m/z cal-
culated for C21H16NO3S (M+H)+: 362.0851; found: 362.0853.
4.3.103. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(pentyloxy)benzoate (19e)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7e (0.125 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.133 g, 79.6%, pale yellow solid, m.p: 112–114 °C. 1H NMR (300 MHz,
CDCl3): δ 0.96 (t, J = 6.9 Hz, 3H), 1.42–1.46 (m, 4H), 1.82–1.84 (m,
2H), 4.06 (t, J = 6.6 Hz, 2H), 6.98–7.02 (m, 2ArH), 7.34–7.43 (m,
2ArH), 7.48–7.58 (m, 2ArH), 7.90–7.93 (m, 1ArH), 7.96–7.99 (m,
2ArH), 8.06–8.09 (m, 1ArH), 8.15–8.19 (m, 2ArH). 13C NMR (75 MHz,
CDCl3): δ 14.0, 22.5, 28.2, 28.8, 68.4, 114.4, 120.9, 121.2, 121.7,
123.4, 124.5, 124.9, 125.4, 126.4, 130.0, 132.4, 135.1, 135.1, 151.6,
154.0, 163.7, 164.8, 166.9, HRMS (ESI) m/z calculated for C25H24NO3S
(M+H)+: 418.1477; found: 418.1477.
4.3.100. 3-(Benzo[d]thiazol-2-yl)phenyl 4-ethoxybenzoate (19b)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7b (0.108 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.124 g, 82.7%, white solid, m.p: 124–126 °C. 1H NMR (300 MHz,
CDCl3): δ 1.48 (t, J = 6.9 Hz, 3H), 4.14 (q, J = 6.9 Hz, 2H), 6.97–7.02
(m, 2ArH), 7.34–7.38 (m, 1ArH), 7.40–7.43 (m, 1ArH), 7.48–7.52 (m,
1ArH), 7.53–7.58 (m, 1ArH), 7.92 (dd, J = 0.6, 8.1 Hz, 1ArH),
7.96–7.99 (m, 2ArH), 8.07 (d, J = 8.1 Hz, 1ArH), 8.15–8.20 (m, 2ArH).
13C NMR (75 MHz, CDCl3): δ 14.7, 63.9, 114.4, 120.9, 121.3, 121.7,
123.4, 124.5, 124.9, 125.4, 126.4, 130.1, 132.4, 135.1, 135.1, 151.6,
154.0, 151.6, 154.0, 163.5, 164.7, 166.9HRMS (ESI) m/z calculated for
4.3.104. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(hexyloxy)benzoate (19f)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7f (0.130 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.142 g, 82.1%, pale yellow solid, m.p: 96–98 °C. 1H NMR (300 MHz,
CDCl3): δ 0.93 (t, J = 6.9 Hz,3H), 1.35–1.38 (m, 4H), 1.49–1.59 (m,
2H), 1.84 (quintet, J = 6.9 HZ, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.98–7.02
(m, 2ArH), 7.35–7.43 (m, 2ArH), 7.48–7.52 (m, 1ArH), 7.53–7.58 (m,
1ArH), 7.92 (d, J = 7.2 Hz, 1ArH), 7.96–7.99 (m, 2ArH), 8.07 (t,
J = 7.8 Hz, 1ArH), 8.15–8.19 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ
14.1, 22.6, 25.7, 29.1, 31.6, 68.4, 114.4, 120.9, 121.2, 121.7, 123.4,
124.5, 124.9, 125.4, 126.4, 130.0, 132.4, 135.1, 151.6, 154.1, 163.7,
C
22H18NO3S (M+H)+: 376.1007; found: 376.1009.
4.3.101. 3-(Benzo[d]thiazol-2-yl)phenyl 4-propoxybenzoate (19c)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7c (0.114 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.12 g, 76.9%, white solid, m.p: 108–110 °C. 1H NMR (300 MHz,
21

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
164.8, 166.9. HRMS (ESI) m/z calculated for C26H26NO3S (M+H)+:
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.142 g, 72.8%, white solid, m.p: 92–94 °C. 1H NMR (300 MHz, CDCl3):
δ 0.89 (t, J = 6.9 Hz, 3H), 1.25–1.33 (m, 14H), 1.81–1.83 (m, 2H), 4.06
(t, J = 6.3 Hz, 2H), 6.98–7.02 (m, 2ArH), 7.34–7.38 (m, 1ArH),
7.40–7.43 (m, 1ArH), 7.48–7.51 (m, 1ArH), 7.53–7.58 (m, 1ArH),
7.90–7.93 (m, 1ArH), 7.97–7.99 (m, 2ArH), 8.07–8.09 (m, 1ArH),
8.16–8.19 (m, 2ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0,
29.1, 29.3, 29.4, 29.6, 31.9, 68.4, 114.4, 120.9, 121.2, 121.7, 123.4,
124.5, 124.9, 125.4, 126.4, 130.0, 132.4, 135.1, 135.2, 151.6, 154.0,
163.7, 164.8, 166.9. HRMS (ESI) m/z calculated for C30H34NO3S (M
+H)+: 488.2259; found: 488.2260.
432.1633; found: 432.1637.
4.3.105. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(heptyloxy)benzoate (19g)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7g (0.136 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.145 g, 81.5%, white solid, m.p: 130–132 °C. 1H NMR (300 MHz,
CDCl3): δ 0.91 (t, J = 6.9 Hz, 3H), 1.33–1.37 (m, 6H), 1.40–1.58 (m,
2H), 1.81–1.86 (m, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH),
7.35–7.43 (m, 3ArH), 7.51 (dt, J = 1.2, 8.1 Hz, 1ArH), 7.91–7.93 (m,
1ArH), 8.07–8.09 (m, 1ArH), 8.15–8.18 (m, 4ArH). 13C NMR (75 MHz,
CDCl3): δ 14.1, 22.6, 26.0, 29.0, 29.1, 31.8, 68.4, 114.4, 121.2, 121.7,
122.5, 123.2, 125.2, 126.4, 128.8, 131.2, 132.4, 135.2, 153.3, 154.2,
163.8, 164.6, 167.1. HRMS (ESI) m/z calculated for C27H28NO3S (M
+H)+: 446.1790; found: 446.1793.
4.3.109. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(allyloxy)benzoate (19k)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7k (0.113 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.127 g, 81.9%, white solid, m.p: 122–124 °C. 1H NMR (300 MHz,
CDCl3): δ 4.65 (td, J = 1.5, 2.4 Hz, 2H), 5.35 (dd, J = 1.5, 9.3 Hz, 1H),
5.46 (dd, J = 1.5, 15.6 Hz, 1H), 6.04–6.14 (m, 1H), 7.00–7.05 (m,
2ArH), 7.34–7.43 (m, 2ArH), 7.48–7.58 (m, 2ArH), 7.92 (d, J = 7.8 Hz,
1ArH), 7.97–7.99 (m, 2ArH), 8.07 (d, J = 7.8 Hz, 1ArH), 8.16–8.21 (m,
2Ar-H). 13C NMR (75 MHz, CDCl3): δ 69.0, 114.6, 118.3, 120.8, 121.6,
121.7, 123.4, 124.5, 124.9, 125.4, 126.5, 130.1, 132.4, 132.4,
135.1,135.1,151.6, 154.0, 163.1, 164.7, 166.9.HRMS (ESI) m/z calcu-
lated for C23H18NO3S (M+H)+: 388.1007; found: 388.1009.
4.3.106. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(octyloxy)benzoate (19h)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7h (0.142 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.136 g, 74.3%, white solid, m.p: 88–90 °C. 1H NMR (300 MHz, CDCl3):
δ 0.90 (t, J = 6.9 Hz, 3H), 1.29–1.35 (m, 8H), 1.43–1.60 (m, 2H), 1.83
(quintet, J = 6.9 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m,
2ArH), 7.34–7.38 (m, 1ArH), 7.40–7.43 (m, 1ArH), 7.48–7.52 (m,
1ArH), 7.53–7.58 (m, 1ArH), 7.92 (dd, J = 0.6, 7.8 Hz, 1ArH),
7.96–7.99 (m, 2ArH), 8.07 (dd, J = 0.6, 7.8 Hz, 1ArH), 8.15–8.19 (m,
2ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3, 29.4,
31.8, 68.4, 114.4, 120.9, 121.2, 121.7, 123.4, 124.5, 124.9, 125.4,
126.4, 130.0, 132.4, 135.1, 135.1, 151.6, 154.1, 163.7, 164.8, 166.9.
HRMS (ESI) m/z calculated for C28H30NO3S (M+H)+: 460.1946;
found: 460.1947.
4.3.110. 3-(Benzo[d]thiazol-2-yl)phenyl 4-((3-methylbut-2-en-1-yl)oxy)
benzoate (19l)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7l (0.124 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.126 g, 75.9%, white solid, m.p: 96–98 °C. 1H NMR (300 MHz, CDCl3):
δ 1.79 (s, 3H), 1.83 (s, 3H), 4.62 (d, J = 6.9 Hz, 2H), 5.52 (t,
J = 6.6 Hz, 1H), 7.01 (d, J = 8.7 Hz, 2ArH), 7.35–7.43 (m, 2ArH),
7.48–7.58 (m, 2ArH), 7.92 (d, J = 7.5 Hz, 1ArH), 7.97–7.99 (m, 2ArH),
8.08 (d, J = 7.8 Hz, 1ArH), 8.18 (d, J = 9.0 Hz, 2ArH). 13C NMR
(75 MHz, CDCl3): δ 18.3, 25.9, 65.1, 114.6, 118.9, 120.9, 121.4, 121.7,
123.4, 124.5, 124.9, 125.4, 126.4, 130.1, 132.4, 135.1, 135.1, 139.1,
151.6, 154.0, 163.4, 164.7, 166.9. HRMS (ESI) m/z calculated for
4.3.107. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(nonyloxy)benzoate (19i)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7i (0.147 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.154 g, 81.5%, white solid, m.p: 72–74 °C. 1H NMR (300 MHz, CDCl3):
δ 0.89 (t, J = 6.9 Hz, 3H), 1.25–1.33 (m, 10H), 1.44–1.51 (m, 2H),
1.79–1.86 (m, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.98–7.00 (m, 2ArH),
7.34–7.43 (m, 2ArH), 7.48–7.58 (m, 2ArH), 7.90–7.93 (m, 1ArH),
7.96–7.98 (m, 2ArH), 8.06–8.09 (m, 1ArH), 8.15–819 (m, 2ArH). 13C
NMR (75 MHz, CDCl3): δ 14.1, 22.7, 26.0, 29.1, 29.3, 29.4, 29.5, 31.9,
68.4, 114.4, 120.9, 121.2, 121.7, 123.4, 124.5 124.9, 125.4, 126.4,
130.0, 132.4, 135.1, 135.1, 151.6, 154.1, 163.7, 164.8, 166.9. HRMS
(ESI) m/z calculated for C29H32NO3S (M+H)+: 474.2103; found:
474.2104.
C
25H22NO3S (M+H)+: 416.1320; found: 416.1322.
4.3.111. 3-(Benzo[d]thiazol-2-yl)phenyl
(E)-4-((3,7-dimethylocta-2,6-
dien-1-yl)oxy)benzoate (19m)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7m (0.151 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
4.3.108. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(decyloxy)benzoate (19j)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7j (0.153 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
22

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BioorganicChemistry103(2020)104170
0.142 g, 73.6%, off white solid, m.p: 42–44 °C. 1H NMR (300 MHz,
CDCl3): δ 1.62 (s, 3H), 1.69 (s, 3H), 1.78 (s, 3H), 2.13–2.14 (m, 4H),
4.65 (d, J = 6.3 Hz, 2H), 5.08–5.11 (m, 1H), 5.51 (t, J = 6.6 Hz, 1H),
7.00–7.03 (m, 2ArH), 7.34–7.43 (m, 2ArH), 7.49 (dd, J = 1.2,6.0 Hz,
1ArH), 7.55 (t, J = 6.3 Hz, 1ArH), 7.92 (td, J = 0.6,6.6 Hz, 1ArH),
7.96–7.99 (m, 2ArH), 8.08 (d, J = 7.5 Hz, 1ArH), 8.15–8.20 (m, 2ArH).
13C NMR (75 MHz, CDCl3): δ 16.8, 17.7, 25.7, 26.3, 39.6, 65.2, 114.6,
118.7, 120.9, 121.3, 121.7, 123.4, 123.7, 124.5, 125.4, 126.4, 130.1,
132.0, 132.4, 135.1, 135.1, 142.1, 151.6, 154.0, 163.4, 164.8, 166.9.
HRMS (ESI) m/z calculated for C30H30NO3S (M+H)+: 484.1946;
found: 484.1947.
135.1, 153.3, 154.1, 163.5, 164.6, 167.1. HRMS (ESI) m/z calculated
for C22H18NO3S (M+H)+: 376.1007; found: 376.1008.
4.3.115. 4-(Benzo[d]thiazol-2-yl)phenyl 4-propoxybenzoate (20c)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 8c (0.114 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.076 g, 48.7%, white solid, m.p: 92–94 °C. 1H NMR (300 MHz, CDCl3):
δ 1.07 (t, J = 7.5 Hz, 3H), 1.86 (sextet, J = 7.2 Hz, 2H), 4.02 (t,
J = 6.6 Hz, 2H), 6.99 (d, J = 8.7 Hz, 2ArH), 7.35–7.43 (m, 3ArH), 7.51
(td, J = 1.5, 8.4 Hz, 1ArH), 7.92 (d, J = 7.8 Hz, 1ArH), 8.08 (d,
J = 7.8 Hz, 1ArH), 8.16 (d, J = 8.7 Hz, 4ArH). 13C NMR (75 MHz,
CDCl3 + DMSO‑d6): δ 10.0, 21.9, 69.3, 113.9, 120.5, 121.2, 122.0,
122.6, 124.8, 125.9, 128.2, 130.5, 131.8, 134.5, 152.7, 153.6, 163.2,
164.0, 166.4. HRMS (ESI) m/z calculated for C23H20NO3S (M+H)+:
390.1164; found: 390.1167.
4.3.112. 3-(Benzo[d]thiazol-2-yl)phenyl 4-(((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)oxy)benzoate (19n)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 7n (0.179 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 10% ethyl acetate in hexanes. Yield:
0.168, 76.4%, pale yellow solid, m.p: 154–156 °C. 1H NMR (300 MHz,
CDCl3): δ 1.60 (d, J = 4.5 Hz,6H), 1.69 (s, 3H), 1.78 (s, 3H), 1.98–2.18
(m,8H), 4.60–4.66 (m, 2H), 5.10 (t, J = 6.9 Hz, 2H), 5.51 (t,
J = 6.6 Hz, 1H), 6.99–7.03 (m, 2ArH), 7.34–7.43 (m, 2ArH), 7.48–7.58
(m, 2ArH), 7.92 (dd, J = 0.6,7.2 Hz, 1ArH), 7.96–7.99 (m, 2ArH), 8.09
(dd, J = 0.6,7.2 Hz, 1ArH), 8.16–8.19 (m, 2ArH). 13C NMR (75 MHz,
CDCl3): δ 16.1, 16.8, 17.7, 25.7, 26.1, 26.7, 39.6, 39.8, 65.2, 114.6,
118.7, 121.3, 121.7, 123.4, 123.6, 124.3, 124.4, 124.5, 124.9, 125.4,
126.5, 130.1, 131.4, 132.4, 135.1, 135.6, 142.1, 151.6, 154.0, 163.4,
164.8, 166.9. HRMS (ESI) m/z calculated for C35H38NO3S (M+H)+:
552.2572; found: 552.2574.
4.3.116. 4-(Benzo[d]thiazol-2-yl)phenyl 4-butoxybenzoate (20d)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 8d (0.119 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.062 g, 38.5%, pale yellow solid, m.p: 170–172 °C. 1H NMR (300 MHz,
CDCl3): δ 1.00 (t, J = 7.5 Hz, 3H), 1.47–1.57 (m, 2H), 1.84 (quintet,
J = 6.9 Hz, 2H), 4.07 (t, J = 6.6 Hz, 2H), 6.97–7.02 (m, 2ArH),
7.34–7.39 (m, 2ArH), 7.40–7.43 (m, 1ArH), 7.48–7.54 9 m, 1ArH),
7.91–7.94 (m, 1ArH), 8.07–8.10 (m, 1ArH), 8.14–8.19 (m, 4ArH). 13C
NMR (100 MHz, CDCl3): δ 13.8, 19.2, 31.1, 68.1, 114.4, 121.1, 121.7,
122.5, 123.2, 125.3, 126.4, 128.8, 131.1, 132.4, 135.1, 153.3, 154.1,
163.8, 164.6, 167.2. HRMS (ESI) m/z calculated for C24H22NO3S (M
+H)+: 404.1320; found: 404.1321.
4.3.113. 4-(Benzo[d]thiazol-2-yl)phenyl 4-methoxybenzoate (20a)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 8a (0.103 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.121 g, 84.0%, white solid, m.p: 178–180 °C. 1H NMR (300 MHz,
CDCl3): δ 3.91 (s, 3H), 6.99–7.02 (m, 2ArH), 7.35–7.42 (m, 3ArH), 7.51
(t, J = 8.1 Hz, 1ArH), 7.92 (d, J = 8.1 Hz, 1ArH), 8.08 (d, J = 8.1 Hz,
1ArH), 8.15–8.19 (m, 4ArH). 13C NMR (75 MHz, CDCl3): δ 54.7, 113.1,
120.9, 121.7, 122.1, 124.4, 125.5, 127.7, 130.1, 131.4, 134.0, 152.2,
153.1, 163.2. 164.3, 167.2 HRMS (ESI) m/z calculated for C21H16NO3S
(M+H)+: 362.0851; found: 362.0852.
4.3.117. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(pentyloxy)benzoate (20e)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 8e (0.125 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.056 g, 33.5%, white solid, m.p: 158–160 °C. 1H NMR (300 MHz,
CDCl3): δ 0.95 (t, J = 7.2 Hz, 3H), 1.40–1.48 (m, 4H), 1.84 (quintet,
J = 6.9 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.99 (d, J = 9.0 Hz, 2ArH),
7.34–7.3 (m, 2ArH), 7.39–7.43 (m, 1ArH), 7.51 (td, J = 1.2, 7.2 Hz,
1ArH), 7.92 (d, J = 7.2 Hz, 1ArH), 8.08 (d, J = 7.8 Hz, 1ArH),
8.13–8.18 (m, 4ArH). 13C NMR (75 MHz, CDCl3): δ 14.0, 22.5, 28.1,
28.8, 68.4, 114.4, 121.2, 121.7, 122.5, 123.2, 125.3, 126.4, 128.8,
131.2, 132.4, 135.2, 153.3, 154.2, 163.8, 164.6, 167.1. HRMS (ESI) m/
z calculated for C25H24NO3S (M+H)+: 418.1477; found: 418.1478.
4.3.114. 4-(Benzo[d]thiazol-2-yl)phenyl 4-ethoxybenzoate (20b)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 8b (0.108 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
0.113 g, 75.3%, white solid, m.p: 168–170 °C. 1H NMR (300 MHz,
CDCl3): δ 1.47 (t, J = 6.9 Hz, 3H), 4.14 (q, J = 6.9 Hz, 2H), 6.98–7.00
(m, 2ArH), 7.36–7.39 (m, 2ArH), 7.43–7.49 (m, 1ArH), 7.52 (td,
J = 1.2, 8.4 Hz, 1ArH), 7.92 (d, J = 7.8 Hz, 1ArH), 8.10 (d, J = 8.1 Hz,
1ArH), 8.14–8.19 (m, 4ArH). 13C NMR (75 MHz, CDCl3): δ 14.7, 63.9,
114.4, 121.2, 121.7, 122.5, 123.2, 125.3, 126.4, 128.8, 131.1, 132.4,
4.3.118. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(hexyloxy)benzoate (20f)
2-Aminothiophenol (0.05 g, 0.40 mmol) and aldehyde 8f (0.125 g,
0.40 mmol) were crushed in a mortar and pestle for 5 min. To that CAN
(0.011 g, 0.02 mmol) and 30% H2O2 (0.5 mL) were added and crushed
for another 5 min. After completion of reaction (TLC), the crude mass
was partitioned between ethyl acetate and water (2 times). Combined
23

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
organic layer was washed with water and brine. The organic portion
was dried over sodium sulfate and purified by column chromatography
(silica gel 100–200 mesh) using 15% ethyl acetate in hexanes. Yield:
white solid, m.p: 144–146 °C. 1H NMR (300 MHz, CDCl3): δ 0.92 (t,
J = 6.9 Hz, 3H), 1.33–1.39 (m, 4H), 1.47–1.52 (m, 2H), 1.83 (pentet,
J = 6.9 Hz, 2H), 4.06 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH),
7.34–7.38 (m, 2ArH), 7.40 (dt, J = 0.9, 7.8 Hz, 1ArH), 7.51 (dt,
J = 1.2, 7.5 Hz, 1ArH), 7.92 (d, J = 7.8 Hz, 1ArH), 8.08 (d, J = 8.1 Hz,
1ArH), 8.15–8.18 (m, 4ArH). 13C NMR (75 MHz, CDCl3): δ 14.1, 22.6,
25.7, 29.1, 31.6, 68.4, 114.4, 121.2, 121.7, 122.5, 123.3, 125.3, 126.4,
128.8, 131.2, 132.4, 135.2, 153.3, 154.2, 163.8, 164.6, 167.1.HRMS
(ESI) m/z calculated for C26H26NO3S (M+H)+: 432.1633; found:
432.1635.
acetate in hexanes. Yield: 0.142 g, 68.3%, pale yellow solid, m.p:
1
118–120 °C. H NMR (300 MHz, CDCl3): δ 0.88 (t, J = 6.9 Hz, 3H),
1.29–1.48 (m, 10H), 1.50–1.58 (m, 2H), 1.83 (pentet, J = 6.6 Hz, 2H),
4.05 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH), 7.35–7.43 (m, 3ArH),
7.51 (dt, J = 1.2, 8.1 Hz, 1ArH), 7.92 (d, J = 8.1 Hz, 1ArH), 8.08 (d,
J = 8.1 Hz, 1ArH), 8.15–8.18 (m, 4ArH), 13C NMR (75 MHz, CDCl3): δ
14.1, 22.7, 26.0, 29.1, 29.3, 29.5, 29.7, 31.9, 68.4, 114.4, 121.1, 121.7,
122.5, 123.3, 125.3, 126.4, 128.8, 131.2, 132.4, 135.1, 153.3, 154.2,
163.8, 164.6, 167.1. HRMS (ESI) m/z calculated for C29H32NO3S (M
+H)+: 474.2103; found: 474.2105.
4.3.122. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(decyloxy)benzoate (23c)
To a stirred solution of decanoic acid (0.122 g, 0.44 mmol) in THF,
DMAP (0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were
added and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 20% ethyl
acetate in hexanes. Yield: 0.148 g, 69.2%, off white solid, m.p:
4.3.119. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(heptyloxy)benzoate (20g)
To a stirred solution of 8g (0.098 g, 0.44 mmol) in THF, DMAP
(0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were added
and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 20% ethyl
acetate in hexanes. Yield: 0.12 g, 63.1%, off white solid, m.p:
1
120–122 °C. H NMR (300 MHz, CDCl3): δ 0.89 (t, J = 6.9 Hz, 3H),
1.22–1.33 (m, 12H), 1.42–1.50 (m, 2H), 1.82 (pentet, J = 6.6 Hz, 2H),
4.05 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH), 7.35–7.43 (m, 3ArH),
7.51 (dt, J = 1.2, 8.1 Hz, 1ArH), 7.92 (d, J = 8.1 Hz, 1ArH), 8.08 (d,
J = 8.1 Hz, 1ArH), 8.15–8.18 (m, 4ArH).13C NMR (75 MHz, CDCl3): δ
14.1, 22.7, 26.0, 29.1, 29.3, 29.4, 29.6, 29.7, 31.9, 68.4, 114.4, 121.1,
121.7, 122.5, 123.3, 125.2, 126.4, 128.8, 131.2, 132.4, 135.2, 153.3,
154.2, 163.8, 164.6, 167.1.HRMS (ESI) m/z calculated for C30H34NO3S
(M+H)+: 488.2259; found: 488.2261.
1
136–138 °C. H NMR (300 MHz, CDCl3): δ 0.91 (t, J = 6.9 Hz, 3H),
1.33–1.43 (m, 6H), 1.46–1.51 (m, 2H), 1.81 (quintet, J = 6.6 Hz, 2H),
4.06 (t, J = 6.6 Hz, 2H), 6.99 (d, J = 8.7 Hz, 2ArH), 7.35–7.38 (m,
2ArH), 7.39–7.43 (m, 1ArH), 7.51 (dt, J = 1.5, 8.4 Hz, 1ArH), 7.92 (d,
J = 7.8 Hz, 1ArH), 8.08 (d, J = 7.8 Hz, 1ArH), 8.15–8.18 (m, 4ArH).
13C NMR (75 MHz, CDCl3): δ 14.1, 22.6, 26.0, 29.0, 29.1, 31.8, 68.4,
114.4, 121.2, 121.7, 122.5, 123.3, 125.2, 126.4, 128.8, 131.2, 132.4,
135.2, 153.3, 154.2, 163.8, 164.6, 167.1. HRMS (ESI) m/z calculated
for C27H28NO3S (M+H)+: 446.1790; found: 446.1791.
4.3.123. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(allyloxy)benzoate (23d)
To a stirred solution of 6a (0.078 g, 0.44 mmol) in THF, DMAP
(0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were added
and stirred at room temperature for 15 min. Then 22 (0.1 g, 0.44 mmol)
was added and stirred for 3 h at room temperature. After completion of
reaction (TLC), volatiles evaporated and the crude mass was partitioned
between ethyl acetate and 10% sodium bicarbonate solution (2 times).
Combined organic layer was washed with water and brine. The organic
portion was dried over sodium sulfate and purified by column chro-
matography (silica gel 100–200 mesh) using 15% ethyl acetate in
hexanes. Yield: 0.124 g, 73.0%, white solid, m.p: 148–150 °C. 1H NMR
(300 MHz, CDCl3): δ 4.63–4.66 (m, 2H), 5.33 (dd, J = 1.2, 10.5 Hz,
1H), 5.46 (dd, J = 1.2, 17.1 Hz, 1H), 6.02–6.14 (m, 1H), 7.00–7.03 (m,
2ArH), 7.34–7.43 (m, 3ArH), 7.51 (td, J = 1.2, 8.4 Hz, 1ArH),
7.91–7.93 (m, 1ArH), 8.07–8.10 (m, 1ArH), 8.14–8.19 (m, 4ArH). 13C
NMR (75 MHz, CDCl3): δ 69.0, 114.7, 118.3, 121.6, 121.7, 122.5,
123.3, 126.4, 128.8, 131.2, 132.4, 135.2, 153.2, 154.2, 163.1, 164.5,
167.1. HRMS (ESI) m/z calculated for C23H18NO3S (M+H)+: 388.1007;
found: 388.1010.
4.3.120. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(octyloxy)benzoate (23a)
To a stirred solution of octanoic acid (0.104 g, 0.44 mmol) in THF,
DMAP (0.005, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were
added and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 20% ethyl
acetate in hexanes. Yield: 0.128 g, 63.6%, off white solid, m.p:
1
132–134 °C. H NMR (300 MHz, CDCl3): δ 0.90 (t, J = 6.9 Hz, 3H),
1.30–1.35 (m, 8H), 1.42–1.50 (m, 2H), 1.83 (pentet, J = 6.6 Hz, 2H),
4.05 (t, J = 6.6 Hz, 2H), 6.97–7.00 (m, 2ArH), 7.34–7.43 (m, 3ArH),
7.51 (dt, J = 1.2, 8.4 Hz, 1ArH), 7.92 (d, J = 8.1 Hz, 1ArH), 8.08 (d,
J = 8.1 Hz, 1ArH), 8.15–8.18 (m, 4ArH). 13C NMR (75 MHz, CDCl3): δ
14.1, 22.7, 26.0, 29.1, 29.2, 29.4, 31.8, 68.4, 114.4, 121.1, 121.7,
122.5, 123.3, 125.3, 126.4, 128.8, 131.2, 132.4, 135.2, 153.3, 154.2,
163.8, 164.6, 167.1.HRMS (ESI) m/z calculated for C28H30NO3S (M
+H)+: 460.1946; found: 460.1948.
4.3.124. 4-(Benzo[d]thiazol-2-yl)phenyl 4-((3-methylbut-2-en-1-yl)oxy)
benzoate (23e)
To a stirred solution of 6b (0.091 g, 0.44 mmol) in THF, DMAP
(0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were added
and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 10% ethyl
acetate in hexanes. Yield: 0.105 g, 57.9%, white solid, m.p: 172–174 °C.
1H NMR (300 MHz, CDCl3): δ 1.78 (s, 3H), 1.83 (s, 3H), 4.62 (d,
J = 6.9 Hz, 2H), 5.49–5.54 (m, 1H), 6.99–7.03 (m, 2ArH), 7.34–7.39
4.3.121. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(nonyloxy)benzoate (23b)
To a stirred solution of nonanoic acid (0.106 g, 0.44 mmol) in THF,
DMAP (0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were
added and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 20% ethyl
24

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
(m, 2ArH), 7.40–7.43 (m, 1ArH), 7.48–7.54 (m, 1ArH), 7.91–7.93 (m,
1ArH), 8.07–8.09 (m, 1ArH), 8.14–8.19 (m, 4ArH). 13C NMR (100 MHz,
CDCl3): δ 18.4, 25.7, 65.1, 114.6, 118.7, 121.3, 121.7, 122.5, 123.2,
125.3, 126.4, 128.8, 131.2, 132.4, 135.3, 139.3, 153.2, 154.2, 163.5,
164.5, 167.1. HRMS (ESI) m/z calculated for C25H22NO3S (M+H)+:
416.1320; found: 416.1321.
excitation/emission wavelengths of 530/590 nm respectively. The MIC
was calculated as the lowest concentration effecting a reduction in
fluorescence (or luminescence) of 90% relative to controls. Isoniazid
and rifampin were run as the control experiments.
4.5. Drug susceptibility on non replicating M. tuberculosis H37Rv by LORA
assay
4.3.125. 4-(Benzo[d]thiazol-2-yl)phenyl
(E)-4-((3,7-dimethylocta-2,6-
dien-1-yl)oxy)benzoate (23f)
Low Oxygen Recovery Assay was used to determine the anti my-
cobacterial efficiency of a substance against the non replicating bacilli.
The strain used for LORA is a recombinant H37Rv strain pFCA-LuxAB
which makes direct luminescence measurements to determine the MIC.
Briefly the strain was cultured in 7H12 media under humidified at-
mosphere (37 °C, 5% CO2). Cultures were incubated in 200 μl medium
in 96-well plates evacuated in an anaerobic jar for producing hypoxic
environment using anaerobic gas mixture of 10% H2, 5% CO2 and 85%
N2 for 10 days at 37 °C. Then the culture was subjected to a recovery
phase in 5% CO2 and 95% humidity in a CO2 incubator. Then 1% n-
decanal was added and luminescence measured in a luminometer [29].
To a stirred solution of 6e (0.121 g, 0.44 mmol) in THF, DMAP
(0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were added
and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 10% ethyl
acetate in hexanes. Yield: 0.152 g, 72.6%, white solid, m.p: 130–132 °C.
1H NMR (300 MHz, CDCl3): δ 1.62 (s, 3H), 1.69 (s, 3H), 1.77 (s, 3H),
2.12–2.16 (m, 4H), 4.65 (d, J = 6.6 Hz, 2H), 5.10 (t, J = 1.2 Hz, 1H),
5.50–5.53 (m, 1H), 6.98–7.02 (m, 2ArH), 7.34–7.43 (m, 3ArH), 7.51(td,
J = 1.2, 8.1 Hz, 1ArH), 7.92 (dd, J = 0.6, 8.1 Hz, 1ArH), 8.09 (d,
J = 7.5 Hz, 1ArH), 8.14–8.19 (m, 4ArH). 13C NMR (75 MHz, CDCl3): δ
16.8, 17.7, 25.7, 26.3, 39.5, 65.2, 114.6, 118.7, 121.2, 121.7, 122.5,
123.2, 123.7, 125.3, 126.4, 128.8, 131.1, 132.0, 132.4, 135.1, 142.1,
153.3, 154.1, 163.5, 164.6, 167.1. HRMS (ESI) m/z calculated for
4.6. Drug susceptibility on replicating M. tuberculosis H37Ra by MABA
assay
The MIC evaluation of the synthesized molecules against replicating
H37Ra was performed by MABA assay. Briefly the bacteria were grown
using the 7H9 media supplemented with OADC. at 37 °C. For minimum
inhibitory concentration (MIC) testing, two fold serial dilutions of
compounds were prepared in 360 mL in optically clear, round bottom
96-well plates. An equivalent volume of mid loge phase H37Ra culture
(diluted to an optical density at 570 nm of 0.01 was added to achieve a
final drug concentration range of 100–0.78 μg/ml in 7H9 broth, with a
control. Plates were incubated in ambient air at 37 °C for 7 day, at
which Alamar Blue and Tween 80 were added and incubation was
continued for 24 h at 37 °C. Fluorescence was determined at excitation/
emission wavelengths of 530/590 nm respectively. The MIC was cal-
culated as the lowest concentration effecting a reduction in fluores-
cence (or luminescence) of 90% relative to controls. Isoniazid and ri-
fampin were run as the reference drug.
C
30H30NO3S (M+H)+: 484.1946; found: 484.1949.
4.3.126. 4-(Benzo[d]thiazol-2-yl)phenyl 4-(((2E,6E)-3,7,11-trimethyldodeca-
2,6,10-trien-1-yl)oxy)benzoate (23g)
To a stirred solution of 6f (0.137 g, 0.44 mmol) in THF, DMAP
(0.005 g, 0.04 mmol) and EDC.HCl (0.100 g, 0.53 mmol) were added
and stirred at room temperature for 15 min. Then 22 (0.100 g,
0.44 mmol) was added and stirred for 3 h at room temperature. After
completion of reaction (TLC), volatiles evaporated and the crude mass
was partitioned between ethyl acetate and 10% sodium bicarbonate
solution (2 times). Combined organic layer was washed with water and
brine. The organic portion was dried over sodium sulfate and purified
by column chromatography (silica gel 100–200 mesh) using 10% ethyl
acetate in hexanes. Yield: 0.163 g, 67.2%, white solid, m.p: 74–76 °C.
1H NMR (300 MHz, CDCl3): δ 1.57 (s, 3H), 1.61 (s, 3H), 1.68 (s, 3H),
1.78 (s, 3H), 1.96–2.19 (m, 8H), 4.65 (d, J = 6.6 Hz, 2H), 5.10 (t,
J = 6.6 Hz, 2H), 5.51 (t, J = 6.6 Hz, 1H), 6.99–7.02 (m, 2ArH), 7.36
(dd, J = 1.8, 6.9 Hz, 2ArH), 7.42 (dt, J = 1.2, 6.9 Hz, 1ArH), 7.51 (dt,
J = 1.2, 8.1 Hz, 1ArH), 7.92 (d, J = 8.1 Hz, 1ArH), 8.08 (d, J = 8.1 Hz,
1ArH), 8.14–8.18 (m, 4ArH).13C NMR (75 MHz, CDCl3): δ 16.1, 16.8,
17.7, 25.7, 26.2, 26.7, 39.6, 39.7, 65.2, 114.6, 118.7, 121.2, 121.7,
122.5, 123.6, 124.3, 125.3, 126.4, 128.8, 131.2, 131.4, 132.4, 135.2,
135.6, 142.1, 153.3, 154.2, 163.5, 164.6, 167.1. HRMS (ESI) m/z cal-
culated for C35H38NO3S (M+H)+: 552.2572; found: 552.2573.
4.7. Cytotoxicity study
Cytotoxicity studies were performed against the PBMC cells isolated
from blood. The PBMC cells were propagated in RPMI media in a hu-
midified incubator (37 °C, 5% CO2). After scrapping the cells with a cell
scraper, they were collected by centrifugation (1000 rpm for 5 min),
resuspended in fresh medium at ~1 × 106 cells/mL, dispensed into 96-
well microplates (100 μl/well) and incubated for 24 h at 37 °C before
being used for cytotoxicity assays. Test compounds were subsequently
added at concentrations ranging from 400 to 0.2 μg/mL and incubation
continued for another 72 h before the cytopathic effects of compounds
was determined using the MTT Cell Proliferation Assay (ATCC). The
cytotoxic IC50 defined as the concentration causing 50% reduction in
PBMC viability, was obtained from a dose–response curve plotted from
percentage activity versus log10 concentration.
4.4. Drug susceptibility on replicating M. tuberculosis H37Rv by MABA
assay
The MIC evaluation of the synthesized molecules against replicating
H37Rv was performed by MABA assay. The bacteria were grown using
the 7H12 media instead of the 7H9 + glycerol + casitone + OADC
supplement. Luciferase reporter strains [47] of H37Rv were used for
compounds with intrinsic background fluorescence and the in-
tracellular ATP levels measured. Compounds were used as a stock so-
lution in DMSO, and two fold serial dilutions of the compounds were
used for the assay. Cultures along with different compounds of varying
concentrations were incubated in 200 μl medium in 96-well plates for
7 days at 37 °C. Alamar Blue and Tween 80 were added and incubation
was continued for 24 h at 37 °C. Fluorescence was determined at
4.8. Whole cell based morphology assay
The effect of best molecules (9k, 9l and 9m) on the cell division of
the bacilli was evaluated by the comparison of its morphology between
the control set and the treated set. In brief Mtb (H37Ra) culture having
OD600 = 0.5 was incubated with a concentration of 2 times of the MIC
of the compounds 9k, 9l and 9m. After incubating for a period of
7 days, the culture was centrifuged and washed 3 times with PBS buffer
and then suspended in 20 μl of PBS. 10 μl of the culture was mixed with
10 μl of FDA solution and spread on a glass slide and fluorescence image
was recorded at a magnification of 100X. The elongation in the
25

A.B. Velappan, et al.
BioorganicChemistry103(2020)104170
morphology of the molecule treated set shows the influence of these
molecules on the bacterial cell division [51].
reaction mix (containing 10 μl ATP monitoring enzyme and 90 μl nu-
cleotide releasing buffer) with 10 μl of the solution containing ADP and
ATP and incubated for 2 min and take the reading using a plate reader.
Thereafter, 10 μl ADP converting enzyme was added and luminescence
was recorded using the plate reader. The ATP/ADP ratio was de-
termined according to the manufacturer protocol.
4.9. Gtpase activity
FtsZ being a GTPase utilises GTP and releases inorganic phosphate
and produces GDP. A quantification of inorganic phosphate is a direct
measure of a molecule’s GTPase activity. A molecule inhibiting FtsZ
leads to low inorganic phosphate content. A plot of molecule’s con-
centration to the GTPase activity can be utilized for evaluating the IC50
of that molecule for GTPase inhibition. Briefly 3.5 µM FtsZ (Mtb)
[32,52,53] was incubated with varying concentrations of the molecule
under investigation in 50 µM (MOPS) buffer for 10 min at 25 °C. Then
500 µM GTP in 5 µM MgCl2 and 200 µM KCl was added and incubated
for 30 min at 37 °C. Then 100 µl of cytophos reagent was added and the
OD at 650 nm was recorded. A plot of GTPase inhibition and compound
concentration gave the IC50 of that compound.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgements
J. D. thankful to SERB (DST), India for their financial support
Project No.: EMR-2016-005029/OC.
4.10. MenG inhibition assay
Appendix A. Supplementary material
The inhibitory activity of the synthesized molecules against MenG
was evaluated by a HPLC based assay by monitoring S-Adenosyl
Methionine (SAM) mediated methylation of Comp A (representative
molecule for DMMQ) in the presence of the molecule under investiga-
tion. In brief for 200 μl assay mixture, 500 μM Comp A (20 μl) was
incubated with 5 μM (20 μl) MgCl2, 5 mM DTT (20 μl) and 0.1% CHAPS
(20 μl) in 100 mM Tris buffer (pH = 8). To that 500 μM SAM (10 μl)
was added along with the inhibitor molecule with varying concentra-
tion (10 μl) and the reaction was initiated by adding 100 μl of H37Ra
membrane bound protein (obtained by disrupting H37Ra cell using
probe sonicator) separately. The mixture was incubated for 3 h and
then quenched by adding 0.1 M acetic acid in methanol. The reaction
mixture was then extracted with ether and injected to the HPLC
(Agilent) and quantified the conversion of Comp A to Comp B. The
same experiment was repeated with the synthesized molecules in in-
creasing concentrations (10, 25, 35, 50, 65 and 80 μM) and the corre-
sponding IC50 was determined from non-linear regression analysis. We
had used HyperClone 5 μm BDS C18 130 Å column from Phenomenex
(250 × 4.6 mm) with the solvent system ACN/Water (90:10) with
0.05% TFA. The flow rate was maintained at 1 mL/min.
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bioorg.2020.104170.
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