Synthesis, biological evaluation, and molecular docking studies of 2-chloropyridine derivatives possessing 1,3,4-oxadiazole moiety as potential antitumor agents

Article abstract of DOI:10.1016/j.bmc.2010.09.051

A series of new 2-chloropyridine derivatives possessing 1,3,4-oxadiazole moiety were synthesized. Antiproliferative assay results indicated that compounds 6o and 6u exhibited the most potent activity against gastric cancer cell SGC-7901, which was more potent than the positive control. Especially, compound 6o exhibited significant telomerase inhibitory activity (IC ₅₀ = 2.3 ± 0.07 μM), which was comparable to the positive control ethidium bromide. Docking simulation was performed to position compound 6o into the active site of telomerase (3DU6) to determine the probable binding model.

Full text of DOI:10.1016/j.bmc.2010.09.051

Bioorganic & Medicinal Chemistry 18 (2010) 7836–7841
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis, biological evaluation, and molecular docking studies
of 2-chloropyridine derivatives possessing 1,3,4-oxadiazole moiety
as potential antitumor agents
⇑
⇑
Qing-Zhong Zheng, Xiao-Min Zhang, Ying Xu, Kui Cheng, Qing-Cai Jiao , Hai-Liang Zhu
State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of new 2-chloropyridine derivatives possessing 1,3,4-oxadiazole moiety were synthesized. Anti-
proliferative assay results indicated that compounds 6o and 6u exhibited the most potent activity against
gastric cancer cell SGC-7901, which was more potent than the positive control. Especially, compound 6o
Received 19 August 2010
Revised 19 September 2010
Accepted 21 September 2010
Available online 25 September 2010
exhibited significant telomerase inhibitory activity (IC50 = 2.3 0.07 lM), which was comparable to the
positive control ethidium bromide. Docking simulation was performed to position compound 6o into
the active site of telomerase (3DU6) to determine the probable binding model.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Synthesis
2-Chloropyridine
1,3,4-Oxadiazole
Molecular docking
Antitumor
1. Introduction
and esters, which can contribute substantially in increasing phar-
macological activity by participating in hydrogen bonding interac-
Telomerase remains active in the early stages of life maintain-
ing telomere length and the chromosomal integrity of frequently
dividing cells. It turns dormant in most somatic cells during adult-
hood.1 In cancer cells, however, telomerase gets reactivated and
works tirelessly to maintain the short length of telomeres of rap-
idly dividing cells, leading to their immortality.2 The essential role
of telomerase in cancer and ageing makes it an important target for
the development of therapies to treat cancer and other age-associ-
ated disorders. Telomere and telomerase are closely related to the
occurrence and development of gastric cancer.3
tions with the receptors.17,18
In view of above mentioned facts and an attempt to achieve
new potent antitumor agents with good bioavailability and low
toxicity, herein, we describe the synthesis and the SAR of a series
of new 2-chloropyridine derivatives possessing 1,3,4-oxadiazole
moiety (Fig. 1) as potential antitumor agents. Docking simulations
were performed using the X-ray crystallographic structure of the
telomerase in complex with an inhibitor to explore the binding
modes of these compounds at the active site.
Pyridine derivatives have attracted significant interest in phar-
maceutical and agrochemical fields.4,5 Furthermore, 2-pyridone, a
small bioactive molecule, is an important pharmacophore that
can form hydrogen bonded structures similar to those encountered
with the base-pairing mechanism in DNA and RNA.6,7 Besides,
1,3,4-oxadiazoles are an important class of heterocyclic com-
pounds. The widespread use of them as a scaffold in medicinal
chemistry establishes this moiety as a member of the privileged
structures class.8 They possess a variety of biological activities.9–
2. Results and discussion
2.1. Chemistry
The synthetic route for the preparation of new 2-chloropyridine
derivatives 6a–6u is outlined in Scheme 1. The synthesis of these
13
In particular, a few differently substituted 1,3,4-oxadiazoles
have been found to exhibit anticancer activities.14–16 Further,
1,3,4-oxadiazole heterocycles are very good bioisosteres of amides
⇑
Corresponding authors. Tel./fax: +86 25 8359 2672 (H.-L.Z.).
E-mail address: zhuhl@nju.edu.cn (H.-L. Zhu).
Figure 1. The skeleton of target compounds.
0968-0896/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2010.09.051

Q.-Z. Zheng et al. / Bioorg. Med. Chem. 18 (2010) 7836–7841
7837
Scheme 1. Synthesis of compounds 6a–6u. Reagents and conditions: (a) H2SO4 (concd), ethanol, reflux, 8–12 h; (b) NH2NH2ꢀH2O (85%), ethanol, reflux, 8–12 h; (c) (1) CS2/
KOH, ethanol (95%), reflux, 24 h; (2) HCl, pH 5–6; (d) NaOH, acetonitrile, reflux, 8–24 h.
derivatives started from 5-substituted-2-mercapto-1,3,4-oxadiaz-
oles 4 and 2-chloro-5-(chloromethyl)pyridine 5.19 The key inter-
mediates 4 were prepared in three steps. Esterification of the
carboxylic acids 1 with ethanol and concentrated sulfuric acid
afforded the corresponding esters 2. The aroyl hydrazides 3 were
obtained by reaction of the esters 2 with 85% hydrazine monohy-
drate in ethanol. Treatment of the hydrazides 3 with carbon disul-
fide in the presence of KOH and 95% ethanol under reflux gave the
key intermediates 4. The synthesis of compounds 6a–6u were
accomplished by refluxing compounds 4 with 2-chloro-5-(chloro-
methyl)pyridine 5 in the presence of NaOH in acetonitrile. All the
target compounds 6a–6u were reported for the first time.
All of the synthetic compounds gave satisfactory analytical and
spectroscopic data, which were in full accordance with their de-
picted structures. Additionally, the structure of compound 6d
was further confirmed by X-ray diffraction. Its crystal data are pre-
sented in Table 1, and Figure 2 gives a perspective view of this
compound together with the atomic labeling system.
Table 1
Crystallographical and experimental data for compound 6d
Compound
6d
Formula
Mr
Crystal system
C
15H12ClN3O2S
333.79
Orthorhombic
P bca
Space group
0
12.311(3)
a (AÅ)
0
8.123(2)
b (AÅ)
0
29.956(6)
c (AÅ)
a
(°)
b (°)
(°)
90
90
90
2995.7(1)
8
1.480
0.404
1376
c
Volume (Å3)
Z
Dc (g/cm3)
l
(mmꢁ1)
F(0 0 0)
Crystal size (mm3)
T (K)
0.28 ꢂ 0.22 ꢂ 0.16
293(2)
h Range (°)
1.36/25.31
ꢁ14/14, 0/9, 0/35
2730/1514
1514/0/200
1.023
0.0696/0.1613
0.1361/0.1940
0.427/ꢁ0.530
2.2. Biological activity
Index range (h, k, l)
Reflections collected/unique
Data/restraints/parameters
Goodness-of-fit on F2
All the synthesized 2-chloropyridine derivatives 6a–6u were
evaluated for their ability to antiproliferative activity against gas-
tric cell SGC-7901. The results were summarized in Table 2. A num-
ber of 2-chloropyridine derivatives possessing 1,3,4-oxadiazole
moiety showed remarkable effects on antiproliferative activity.
For compounds 6a–6f, it could be observed that compounds with
electron-donating groups on the ortho position of benzene ring
(e.g., 6a, 6c, 6e) displayed less inhibitory activity than those with
the same groups on the para position (e.g., 6b, 6d, 6f). Meanwhile,
a comparison of the substitution on benzene ring demonstrated
that para position-halogen-substituted derivatives (e.g., 6h, 6j)
have more potent activity than that of ortho position-halogen-
substituted derivatives (e.g., 6g, 6i), and the potency order is
Cl < F. Moreover, a free hydroxyl group at the para position of C-
5 phenyl ring of 1,3,4-oxadiazole ring was detrimental for the
R1, wR2 [I > 2
r
(I)]a
a
R1, wR2
0
(D
q)
max, (
D
q)
min
(e/ÅA3)
a
R1
=
R
||Fo| ꢁ |Fc||/
R
|Fo|, wR2 = [
R
w(|Fo| ꢁ |Fc|)2/
R .
w(|Fo|2]1/2
activity as evident from the activity of compound 6k. Compared
to the 2-Me analogue 6a, compound 6l with a p-i-Pr substituent
displayed relatively good activity (IC50 = 4.32 0.21
bly, 3,4-dimethoxyl group was well tolerated (6p; IC50 = 4.48
0.26 g/mL). Besides, introduction of 4-amino, 4-dimethamino, or
lg/mL). Nota-
l
3,4,5-trimethoxyl group to C-5 phenyl ring of 1,3,4-oxadiazole
gives compound 6m, 6n or 6q with reduced activity. Furthermore,

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Q.-Z. Zheng et al. / Bioorg. Med. Chem. 18 (2010) 7836–7841
Figure 2. Molecular structure of compound 6d.
Table 2
Inhibition (IC50
SGC-7901 and guide further SAR studies, molecular docking of
) of SGC-7901 cells proliferation by
the potent inhibitor 6o into ATP binding site of telomerase was
performed on the binding model based on the telomerase structure
(3DU6.pdb). The binding models of compound 6o and telomerase
are depicted in Figures 3 and 4. In the binding model, compound
6o is nicely bound to telomerase with its hydroxyl group project
toward the amino group of LYS 249, with the hydroxyl group form-
ing a more optimal H-bond (N–Hꢀ ꢀ ꢀO: 2.290 Å, 121.1°) interaction,
and the hydrogen atom of hydroxyl group of 6o also forms hydro-
gen bond (O–Hꢀ ꢀ ꢀO: 1.993 Å, 147.7°) with oxygen atom of ASP 344.
Meanwhile, the oxygen atom of methoxy group of 6o forms an-
other hydrogen bond (N–Hꢀ ꢀ ꢀO: 2.248 Å, 134.3°) with amino
hydrogen of GLY 391. The enzyme assay data and the molecular
docking results suggested that compound 6o was potential inhibi-
tor of telomerase.
compounds 6a–6u
Compound
SGC-7901 (IC50 SD, lg/mL)
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
8.51 0.56
3.62 0.21
8.20 0.48
3.50 0.13
10.28 0.67
4.97 0.27
9.12 0.55
3.67 0.20
13.45 1.0
8.62 0.63
>20
4.32 0.21
8.48 0.38
8.90 0.41
1.61 0.06
4.48 0.26
10.2 0.75
12.6 0.92
14.3 1.1
15.1 1.3
2.56 0.11
7.36 0.55
3. Conclusion
6q
6r
6s
6t
A
series of new 2-chloropyridine derivatives possessing
1,3,4-oxadiazole moiety were synthesized. Antiproliferative assay
results indicated that compounds 6o and 6u exhibited the most
potent activity against gastric cancer cell SGC-7901. In particular,,
compound 6o exhibited significant telomerase inhibitory activity
6u
5-Fluorouracila
a
Used as a positive control.
(IC50 = 2.3 0.07 lM), which was comparable to the positive con-
trol ethidium bromide. Docking simulation was performed to posi-
tion compound 6o into the active site of telomerase (3DU6) to
determine the probable binding model. The enzyme assay data
and the molecular docking results suggested that compound 6o
was potential inhibitor of telomerase.
variation of the aromatic ring moiety was also explored. As for
compounds 6r–6u, compared with compound 6o, compound 6u
with a 1-naphthyl group was compatible with the most potent
inhibitory activity. That is to say, compounds 6o and 6u exhibited
the most potent activity (as for 6o, IC50 = 1.61 0.06
lg/mL; as for
4. Experimental
6u, IC50 = 2.56 0.11 g/mL), which was more potent than the po-
l
sitive control. Subsequently, these two compounds 6o and 6u
which had the most potent inhibitory activity were selected to
be evaluated for their ability to inhibit telomerase by a modified
TRAP (telomere repeat amplification protocol). The results (Table
3) indicated that compounds 6o exhibited significant telomerase
inhibitory activity (IC50 = 2.3 0.07 lM), which was comparable
to the positive control ethidium bromide (IC50 = 2.5 0.23 lM).
4.1. Chemistry general
All chemicals and reagents used in current study were of analyt-
ical grade. The reactions were monitored by thin layer chromatog-
raphy (TLC) on Merck pre-coated silica GF254 plates. Melting
points (uncorrected) were determined on a XT4MP apparatus (Tai-
ke Corp., Beijing, China). ESI mass spectra were obtained on a Mar-
iner System 5304 mass spectrometer, and 1H NMR spectra were
collected on a Bruker DPX500 or DPX300 spectrometer at room
temperature with TMS and solvent signals allotted as internal stan-
dards. Chemical shifts are reported in ppm (d). Elemental analyses
were performed on a CHN–O-Rapid instrument, and were within
0.4% of the theoretical values.
2.3. Molecular docking study of compound 6o
In an effort to elucidate the possible mechanism by which the
title compounds can induce anticancer activity in the gastric cell
Table 3
4.2. General procedure for the preparation of target compounds
6a–6u
Telomerase inhibitory activity of compounds 6o and 6u
Compound
Telomerase (IC50 SD, lM)
To a stirred solution of 5-substituted-2-mercapto-1,3,4-oxadi-
azoles 4 (2 mmol) and sodium hydroxide (2 mmol) in acetonitrile
(20 mL) was added dropwise acetonitrile (5 mL) containing
6o
6u
2.3 0.07
4.2 0.15
Ethidium bromidea 2.5 0.23
a
2-chloro-5-(chloromethyl)pyridine
5
(2 mmol, 0.324 g). The
Used as a positive control.

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7839
Figure 3. Molecular docking modeling of compound 6o with telomerase: compound 6o is nicely bound to the telomerase with its hydroxyl group project toward the amino
group of LYS 249, with the hydroxyl group forming a more optimal H-bond (N–Hꢀ ꢀ ꢀO: 2.290 Å, 121.1°) interaction, and the hydrogen atom of hydroxyl group of 6o also forms
hydrogen bond (O–Hꢀ ꢀ ꢀO: 1.993 Å, 147.7°) with oxygen atom of ASP 344. Meanwhile, the oxygen atom of methoxy group of 6o forms another hydrogen bond (N–Hꢀ ꢀ ꢀO:
2.248 Å, 134.3°) with amino hydrogen of GLY 391.
the organic phase was dried over anhydrous Na2SO4, filtered, and
removed in vacuo. The purification of the residue by recrystalliza-
tion from acetonitrile yielded the desired compounds 6a–6u.
4.2.1.2-Chloro-5-[[(5-(o-tolyl)-1,3,4-oxadiazol-2-yl)thio]methyl]
pyridine (6a)
White solid, yield 65.8%, mp: 80–81 °C. 1H NMR (300 MHz,
DMSO-d6) d: 2.55 (s, 3H), 4.59 (s, 2H), 7.38–7.43 (m, 2H), 7.46–
7.52 (m, 2H), 7.81 (d, J = 7.9 Hz, 1H), 7.98 (d, J = 8.2 Hz, 1H), 8.51
(s, 1H). MS (ESI): 318.0 (C15H13ClN3OS, [M+H]+). Anal. Calcd for
C15H12ClN3OS: C, 56.69; H, 3.81; N, 13.22. Found: C, 56.66; H,
3.78; N, 13.26.
4.2.2.2-Chloro-5-[[(5-(p-tolyl)-1,3,4-oxadiazol-2-yl)thio]methyl]
pyridine (6b)
Light yellow crystal, yield 65.1%, mp: 148–149 °C. 1H NMR
(500 MHz, DMSO-d6) d: 2.40 (s, 3H), 4.60 (s, 2H), 7.41 (d,
J = 8.0 Hz, 2H), 7.53 (d, J = 9.0 Hz, 1H), 7.84 (d, J = 8.0 Hz, 2H),
8.00 (d, J = 8.5 Hz, 1H), 8.52 (s, 1H). MS (ESI): 318.0 (C15H13ClN3OS,
[M+H]+). Anal. Calcd for C15H12ClN3OS: C, 56.69; H, 3.81; N, 13.22.
Found: C, 56.76; H, 3.75; N, 13.28.
Figure 4. 3D model of the interaction between compound 6o and telomerase
binding site. Telomerase is represented by molecular surface. Compound 6o is
depicted by sticks and balls.
4.2.3. 2-Chloro-5-[[(5-(o-methoxyphenyl)-1,3,4-oxadiazol-2-yl)
thio] methyl]pyridine (6c)
Light yellow crystal, yield 52.7%, mp: 73–74 °C. 1H NMR
(300 MHz, DMSO-d6) d: 3.88 (s, 3H), 4.57 (s, 2H), 7.11 (t,
J = 7.3 Hz, 1H), 7.26 (d, J = 8.4 Hz, 1H), 7.52 (d, J = 8.2 Hz, 1H),
7.60 (t, J = 7.3 Hz, 1H), 7.77 (d, J = 7.8 Hz, 1H), 7.98 (d, J = 8.3 Hz,
1H), 8.51 (s, 1H). MS (ESI): 334.0 (C15H13ClN3O2S, [M+H]+). Anal.
Calcd for C15H12ClN3O2S: C, 53.97; H, 3.62; N, 12.59. Found: C,
53.91; H, 3.55; N, 12.65.
resulting mixture was heated under reflux for 8–24 h and the reac-
tion was monitored by TLC. Afterwards the solution was cooled to
room temperature and the organic solvent was removed in vacuo.
The residue was dissolved in ethyl acetate and the organic layer
was washed with water and saturated brine, respectively. Then

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Q.-Z. Zheng et al. / Bioorg. Med. Chem. 18 (2010) 7836–7841
4.2.4. 2-Chloro-5-[[(5-(p-methoxyphenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6d)
10.35 (s, 1H). MS (ESI): 320.0 (C14H11ClN3O2S, [M+H]+). Anal. Calcd
for C14H10ClN3O2S: C, 52.59; H, 3.15; N, 13.14. Found: C, 52.66; H,
3.18; N, 13.17.
Light yellow crystal, yield 53.9%, mp: 120–121 °C. 1H NMR
(500 MHz, DMSO-d6) d: 3.85 (s, 3H), 4.58 (s, 2H), 7.13 (d,
J = 8.8 Hz, 2H), 7.51 (d, J = 8.2 Hz, 1H), 7.88 (d, J = 8.8 Hz, 2H),
7.98 (d, J = 8.2 Hz, 1H), 8.50 (s, 1H). MS (ESI): 334.0
(C15H13ClN3O2S, [M+H]+). Anal. Calcd for C15H12ClN3O2S: C, 53.97;
H, 3.62; N, 12.59. Found: C, 53.88; H, 3.53; N, 12.67.
4.2.12. 2-Chloro-5-[[(5-(p-isopropylphenyl)-1,3,4-oxadiazol-2-
yl)thio]methyl]pyridine (6l)
Yellow solid, yield 51.4%, mp: 195–197 °C. 1H NMR
(500 MHz, DMSO-d6) d: 1.24 (d, J = 7.0 Hz, 6H), 2.97–3.00 (m,
1H), 4.54 (s, 2H), 7.47 (d, J = 8.5 Hz, 2H), 7.53 (d, J = 8.5 Hz,
1H), 7.87 (d, J = 8.5 Hz, 2H), 8.00 (d, J = 8.0 Hz, 1H), 8.52 (s,
1H). MS (ESI): 346.1 (C17H17ClN3OS, [M+H]+). Anal. Calcd for
4.2.5. 2-Chloro-5-[[(5-(o-ethoxyphenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6e)
Brown crystal, yield 52.2%, mp: 87–88 °C. 1H NMR (500 MHz,
DMSO-d6) d: 1.33 (t, J = 6.5 Hz, 3H), 4.17 (q, J = 7.0 Hz, 2H), 4.58
(s, 2H), 7.11 (t, J = 8.0 Hz, 1H), 7.25 (d, J = 8.5 Hz, 1H), 7.54 (d,
J = 8.5 Hz, 1H), 7.57–7.60 (m, 1H), 7.78 (d, J = 7.5 Hz, 1H), 7.98 (d,
J = 8.5 Hz, 1H), 8.50 (s, 1H). MS (ESI): 348.0 (C16H15ClN3O2S,
[M+H]+). Anal. Calcd for C16H14ClN3O2S: C, 55.25; H, 4.06; N,
12.08. Found: C, 55.33; H, 4.01; N, 12.11.
C17H16ClN3OS: C, 59.04; H, 4.66; N, 12.15. Found: C, 59.07; H,
4.61; N, 12.21.
4.2.13. 2-Chloro-5-[[(5-(p-aminophenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6m)
Yellow solid, yield 58.9%, mp: 154–155 °C. 1H NMR (500 MHz,
DMSO-d6) d: 4.54 (s, 2H), 5.97 (s, 2H), 6.66 (d, J = 9.0 Hz, 2H),
7.52 (d, J = 8.5 Hz, 1H), 7.58 (d, J = 8.5 Hz, 2H), 7.96 (d, J = 8.0 Hz,
1H), 8.49 (s, 1H). MS (ESI): 319.0 (C14H12ClN4OS, [M+H]+). Anal.
Calcd for C14H11ClN4OS: C, 52.75; H, 3.48; N, 17.58. Found: C,
52.71; H, 3.50; N, 17.55.
4.2.6. 2-Chloro-5-[[(5-(p-ethoxyphenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6f)
White solid, yield 57.1%, mp: 117–119 °C. 1H NMR (500 MHz,
DMSO-d6) d: 1.36 (t, J = 7.0 Hz, 3H), 4.13 (q, J = 6.5 Hz, 2H), 4.59
(s, 2H), 7.12 (d, J = 8.5 Hz, 2H), 7.53 (d, J = 8.0 Hz, 1H), 7.87 (d,
J = 9.0 Hz, 2H), 8.00 (d, J = 8.5 Hz, 1H), 8.52 (s, 1H). MS (ESI):
348.0 (C16H15ClN3O2S, [M+H]+). Anal. Calcd for C16H14ClN3O2S: C,
55.25; H, 4.06; N, 12.08. Found: C, 55.29; H, 4.05; N, 12.11.
4.2.14.2-Chloro-5-[[(5-(p-dimethaminophenyl)-1,3,4-oxadiazol-
2- yl)thio]methyl]pyridine (6n)
Yellow solid, yield 61.3%, mp: 151–153 °C. 1H NMR (500 MHz,
DMSO-d6) d: 3.02 (s, 6H), 4.56 (s, 2H), 6.82 (d, J = 9.0 Hz, 2H),
7.53 (d, J = 8.0 Hz, 1H), 7.72 (d, J = 8.5 Hz, 2H), 7.98 (d, J = 8.0 Hz,
1H), 8.50 (s, 1H). MS (ESI): 347.1 (C16H16ClN4OS, [M+H]+). Anal.
Calcd for C16H15ClN4OS: C, 55.41; H, 4.36; N, 16.15. Found: C,
55.48; H, 4.31; N, 16.18.
4.2.7. 2-Chloro-5-[[(5-(o-fluorophenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6g)
White crystal, yield 62.8%, mp: 109–110 °C. 1H NMR (300 MHz,
DMSO-d6) d: 4.60 (s, 2H), 7.40–7.53 (m, 3H), 7.65–7.73 (m, 1H),
7.95–8.01 (m, 2H), 8.52 (s, 1H). MS (ESI): 322.0 (C14H10ClFN3OS,
[M+H]+). Anal. Calcd for C14H9ClFN3OS: C, 52.26; H, 2.82; N,
13.06. Found: C, 52.21; H, 2.73; N, 13.12.
4.2.15. 2-Chloro-5-[[(5-(o-hydroxyl-p-methoxyphenyl)-1,3,4-
oxadiazol-2-yl)thio]methyl]pyridine (6o)
Yellow crystal, yield 73.5%, mp: 123–124 °C. 1H NMR (500 MHz,
DMSO-d6) d: 3.80 (s, 3H), 4.57 (s, 2H), 6.61 (s, 2H), 7.53 (d,
J = 8.0 Hz, 1H), 7.65 (d, J = 9.5 Hz, 1H), 7.99 (s, 1H), 8.52 (s, 1H),
10.30 (s, 1H). MS (ESI): 350.0 (C15H13ClN3O3S, [M+H]+). Anal. Calcd
for C15H12ClN3O3S: C, 51.51; H, 3.46; N, 12.01. Found: C, 51.40; H,
3.51; N, 11.97.
4.2.8. 2-Chloro-5-[[(5-(p-fluorophenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6h)
Light yellow crystal, yield 56.2%, mp: 132–133 °C. 1H NMR
(500 MHz, DMSO-d6) d: 4.61 (s, 2H), 7.45 (t, J = 8.5 Hz, 2H), 7.53
(d, J = 8.0 Hz, 1H), 7.99–8.04 (m, 3H), 8.53 (s, 1H). MS (ESI): 322.0
(C14H10ClFN3OS, [M+H]+). Anal. Calcd for C14H9ClFN3OS: C, 52.26;
H, 2.82; N, 13.06. Found: C, 52.33; H, 2.77; N, 13. 01.
4.2.16. 2-Chloro-5-[[(5-(3,4-dimethoxylphenyl)-1,3,4-oxadiazol-
2-yl)thio]methyl]pyridine (6p)
White solid, yield 58.1%, mp: 123–124 °C. 1H NMR (500 MHz,
DMSO-d6) d: 3.85 (s, 6H), 4.59 (s, 2H), 7.16 (d, J = 8.5 Hz, 1H),
7.40 (s, 1H), 7.53 (d, J = 9.0 Hz, 2H), 7.99 (d, J = 8.0 Hz, 1H), 8.52
(s, 1H). MS (ESI): 364.0 (C16H15ClN3O3S, [M+H]+). Anal. Calcd for
4.2.9. 2-Chloro-5-[[(5-(o-chlorophenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6i)
White crystal, yield 58.4%, mp: 79–80 °C. 1H NMR (300 MHz,
DMSO-d6) d: 4.61 (s, 2H), 7.51–7.58 (m, 2H), 7.61–7.72 (m, 2H),
7.94 (d, J = 7.7 Hz, 1H), 7.99 (d, J = 8.2 Hz, 1H), 8.52 (s, 1H). MS
(ESI): 338.0 (C14H10Cl2N3OS, [M+H]+). Anal. Calcd for
C16H14ClN3O3S: C, 52.82; H, 3.88; N, 11.55. Found: C, 52.76; H,
3.91; N, 11.51.
C
14H9Cl2N3OS: C, 49.72; H, 2.68; N, 12.42. Found: C, 49.62; H,
4.2.17. 2-Chloro-5-[[(5-(3,4,5-trimethoxylphenyl)-1,3,4-oxadia-
zol-2-yl)thio]methyl]pyridine (6q)
2.60; N, 12.45.
Yellow crystal, yield 60.1%, mp: 119–120 °C. 1H NMR (500 MHz,
DMSO-d6) d: 3.75 (s, 3H), 3.88 (s, 6H), 4.60 (s, 2H), 7.18 (s, 2H), 7.54
(d, J = 8.5 Hz, 1H), 8.00 (d, J = 8.0 Hz, 1H), 8.54 (s, 1H). MS (ESI):
394.1 (C17H17ClN3O4S, [M+H]+). Anal. Calcd for C17H16ClN3O4S: C,
51.84; H, 4.09; N, 10.67. Found: C, 51.75; H, 4.08; N, 10.70.
4.2.10. 2-Chloro-5-[[(5-(p-chlorophenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6j)
White solid, yield 61.3%, mp: 147–148 °C. 1H NMR (300 MHz,
DMSO-d6) d: 4.61 (s, 2H), 7.52 (d, J = 8.2 Hz, 2H), 7.67 (d,
J = 8.4 Hz, 2H), 7.95–8.00 (m, 2H), 8.52 (s, 1H). MS (ESI): 338.0
(C14H10Cl2N3OS, [M+H]+). Anal. Calcd for C14H9Cl2N3OS: C, 49.72;
H, 2.68; N, 12.42. Found: C, 49.83; H, 2.61; N, 12.38.
4.2.18. 2-Chloro-5-[[(5-(pyridin-2-yl)-1,3,4-oxadiazol-2-yl)thio]
methyl]pyridine (6r)
White solid, yield 62.3%, mp: 135–136 °C. 1H NMR (500 MHz,
DMSO-d6) d: 4.63 (s, 2H), 7.53 (d, J = 8.5 Hz, 1H), 7.62–7.65 (m,
1H), 8.00–8.07 (m, 2H), 8.13 (d, J = 8.0 Hz, 1H), 8.54 (s, 1H), 8.77–
8.78 (m, 1H). MS (ESI): 305.0 (C13H10ClN4OS, [M+H]+). Anal. Calcd
for C13H9ClN4OS: C, 51.23; H, 2.98; N, 18.38. Found: C, 51.29; H,
2.95; N, 18.41.
4.2.11. 2-Chloro-5-[[(5-(p-hydroxyphenyl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6k)
Yellow crystal, yield 67.5%, mp: 198–200 °C. 1H NMR (500 MHz,
DMSO-d6) d: 4.58 (s, 2H), 6.93 (d, J = 9.0 Hz, 2H), 7.53 (d, J = 8.0 Hz,
1H), 7.78 (d, J = 8.5 Hz, 2H), 7.98 (d, J = 8.5 Hz, 1H), 8.50 (s, 1H),

Q.-Z. Zheng et al. / Bioorg. Med. Chem. 18 (2010) 7836–7841
7841
4.2.19. 2-Chloro-5-[[(5-(furan-2-yl)-1,3,4-oxadiazol-2-yl)thio]
methyl]pyridine (6s)
The absorbance at 570 nm of each well was measured on an ELISA
plate reader. The data represented the mean of three independent
experiments in triplicate and were expressed as means SD. The
IC50 value was defined as the concentration at which 50% of the
cells could survive. The results were summarized in Table 2.
Light yellow crystal, yield 59.3%, mp: 97–98 °C. 1H NMR
(300 MHz, DMSO-d6) d: 4.58 (s, 2H), 6.80 (s, 1H), 7.33 (s, 1H),
7.53 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 8.5 Hz, 1H), 8.06 (s, 1H), 8.51(s,
1H). MS (ESI): 294.0 (C12H9ClN3O2S, [M+H]+). Anal. Calcd for
C12H8ClN3O2S: C, 49.07; H, 2.75; N, 14.31. Found: C, 49.16; H,
4.5. Telomerase inhibitory assay
2.80; N, 14.25.
Compounds 6o and 6u were assayed for telomerase inhibition
by a modified TRAP assay, using a SGC-7901 cell extract. The telo-
merase assay methods used are the same as previously de-
scribed.22 The results were reported in Table 3.
4.2.20. 2-Chloro-5-[[(5-(thiophen-2-yl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6t)
White solid, yield 58.3%, mp: 93–94 °C. 1H NMR (300 MHz,
DMSO-d6) d: 4.58 (s, 2H), 7.27–7.30 (m, 1H), 7.52 (d, J = 8.2 Hz,
1H), 7.78–7.79 (m, 1H), 7.94–7.95 (m, 1H), 7.97–8.00 (m, 1H),
8.51(s, 1H). MS (ESI): 310.0 (C12H9ClN3OS2, [M+H]+). Anal. Calcd
for C12H8ClN3OS2: C, 46.52; H, 2.60; N, 13.56. Found: C, 46.48; H,
2.53; N, 13.62.
4.6. Molecular docking modeling
The GLIDE protocol (Schrodinger Inc.)23 was used to dock com-
pound 6o into ATP binding site of telomerase crystal structure
(3DU6.pdb, downloaded from the Protein Data Bank). No con-
straints were implemented during the docking calculation.
4.2.21. 2-Chloro-5-[[(5-(naphth-1-yl)-1,3,4-oxadiazol-2-yl)
thio]methyl]pyridine (6u)
Light yellow crystal, yield 61.4%, mp: 110–111 °C. 1H NMR
(500 MHz, DMSO-d6) d: 4.66 (s, 2H), 7.55 (d, J = 8.5 Hz, 1H), 7.66–
7.76 (m, 3H), 8.03 (d, J = 8.0 Hz, 1H), 8.10 (d, J = 7.5 Hz, 1H), 8.15
(d, J = 7.5 Hz, 1H), 8.22 (d, J = 8.5 Hz, 1H), 8.57 (s, 1H), 8.99 (d,
J = 9.0 Hz, 1H). MS (ESI): 354.0 (C18H13ClN3OS, [M+H]+). Anal. Calcd
for C18H12ClN3OS: C, 61.10; H, 3.42; N, 11.88. Found: C, 61.02; H,
3.37; N, 11.92.
Acknowledgment
This work was supported by Jiangsu National Science Founda-
tion (No. BK2009239).
References and notes
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4.3. Crystal structure determination
X-ray single-crystal diffraction data for compound 6d were col-
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0
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structures were solved by direct methods using the SHELXS program
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methods with SHELXL-97.20 All non-hydrogen atoms of compound
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The antiproliferative activity of the prepared compounds 6o–6u
against SGC-7901 gastric cancer cells was evaluated as described in
the literature21 with some modifications. Target tumor cells were
grown to log phase in RPMI 1640 medium supplemented with
10% fetal bovine serum. After reaching
a
dilution of
3 ꢂ 104 cells mLꢁ1 with the medium, 100
lL of the obtained cell
suspension was added to each well of 96-well culture plates. Sub-
sequently, incubation was performed at 37 °C in 5% CO2 atmo-
sphere for 24 h before the cytotoxicity assessment. Tested
samples at pre-set concentrations were added to six wells with
5-fluorouracil being employed as a positive reference. After 48 h
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Coviello, G. M.; Wright, W. E.; Weinrich, S. L.; Shay, J. W. Science 1994, 266,
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exposure period, 25
was added to each well. After 4 h, the medium was replaced by
150 L DMSO to dissolve the purple formazan crystals produced.
l
L of PBS containing 2.5 mg mLꢁ1 of MTT
23. Glide, version 5.6, Schrodinger, LLC: New York, NY, 2010.
l