Synthesis and fungicidal activity of novel imidazole-based ketene dithioacetals

Article abstract of DOI:10.1016/j.bmc.2018.02.051

Novel imidazole-based ketene dithioacetals show impressive in planta activity against the economically important plant pathogens Alternaria solani, Botryotinia fuckeliana, Erysiphe necator and Zymoseptoria tritici. Especially derivatives of the topical antifungal lanoconazole, which bear an alkynyloxy or a heteroaryl group in the para-position of the phenyl ring, exhibit excellent control of the mentioned phytopathogens. These compounds inhibit 14α -demethylase in the sterol biosynthesis pathway of the fungi. Synthesis routes starting from either benzaldehydes or acetophenones as well as structure-activity relationships are discussed in detail.

Full text of DOI:10.1016/j.bmc.2018.02.051

Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and fungicidal activity of novel imidazole-based ketene
dithioacetals
a
Stephane Jeanmart a, Julien Gagnepain a, Pulakesh Maity b, Clemens Lamberth a, , Fredrik Cederbaum ,
⇑
Ramya Rajan b, Olivier Jacob a, Mathias Blum a, Stephane Bieri a
a Syngenta Crop Protection AG, Chemical Research, Schaffhauserstr. 101, CH-4332 Stein, Switzerland
b Syngenta Biosciences Pvt. Ltd, Research & Technology Centre, Santa Monica Works, Corlim, Ilhas, Goa 403 110, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel imidazole-based ketene dithioacetals show impressive in planta activity against the economically
important plant pathogens Alternaria solani, Botryotinia fuckeliana, Erysiphe necator and Zymoseptoria trit-
ici. Especially derivatives of the topical antifungal lanoconazole, which bear an alkynyloxy or a heteroaryl
group in the para-position of the phenyl ring, exhibit excellent control of the mentioned phytopathogens.
Received 10 January 2018
Revised 23 February 2018
Accepted 28 February 2018
Available online xxxx
These compounds inhibit 14a -demethylase in the sterol biosynthesis pathway of the fungi. Synthesis
routes starting from either benzaldehydes or acetophenones as well as structure-activity relationships
are discussed in detail.
Keywords:
Dithiolane
Imidazole
Ó 2018 Elsevier Ltd. All rights reserved.
C14-demethylase inhibitor
Fungicide
Crop protection
1. Introduction
atom of the heme cofactor in the active site of CYP51. Most of these
active ingredients are either triazole derivatives (e.g. the pharma-
14
a
-Demethylase (CYP51) belongs to the family of cytochrome
ceutical antimycotics voriconazole and fluconazole as well as the
agrochemical fungicides difenoconazole and epoxiconazole) or imi-
dazole derivatives (e.g. the pharmaceutical antimycotics clotrima-
zole and ketoconazole as well as the agrochemical fungicides
prochloraz and oxpoconazole), but also other heterocycles have
been used as pharmacophore of DMI’s, such as pyridines and
pyrimidines.
P450 enzymes and facilitates the transformation of 24-
methylenedihydrolanosterol (eburicol) to 4,4-dimethylergosta-
8,14,24(28)-trien-3b-ol within the biosynthesis pathway from the
acyclic terpenoid squalene to the tetracyclic ergosterol, the major
cellular membrane component of fungi and protozoans. The inhibi-
tionof thisenzymeleadstotheformationofabnormalamountsof14
a
-methylated sterol precursors and consequently to a depletion of
ergosterol important for fungal tissue development. Inhibitors of
14 -demethylase (also called DeMethylase Inhibitors, DMI’s) found
The development of resistance did not spare the DMI’s, of which
the first commercialized examples entered the pharmaceutical and
agrochemical markets in the 19700s. The shift of sensitivity based
on point mutations in the amino acid sequence of the CYP51 gene
is different for the different pathogens and also impacts the diverse
active ingredients not in the same manner as there are different
cross-resistance patterns existing.10,11 In addition some of the
commercialized DMI’s are under regulatory pressure because of
potential off-target effects, such as endocrine disruption or liver
toxicity based on the inhibition of other hepatic CYP enzymes.
Therefore there is a constant need for new structure types amongst
the DMI’s with improved properties regarding environmental and
toxicological safety and resistance profile. We became interested
in the introduction of the ketene dithioacetal scaffold, which is part
of the modern antifungal agents lanoconazole (2) and luliconazole
(3),12,13 as novel structure motif into an agrochemical fungicide.
Lanoconazole and luliconazole are modern topical antimycotics
a
ample application in the prevention and treatment of fungal
infections of human1,2 and plants,3,4 but recently also against
leishmaniasis and trypanosomiasis,5,6 such as sleeping sickness
(Trypanosoma brucei) and Chagas disease (Trypanosoma cruzi).7–9
Interestingly, inhibition of 14
a -demethylase is the only mode of
action which is used for the control of fungal pathogens of both
human (e.g. Aspergillus fumigatus and Candida albicans) and plants
(e.g. Puccinia recondita and Zymoseptoria tritici). A whole arsenal of
DMI’s, the conazoles, has entered the agrochemical and pharmaceu-
tical market, in which a ring nitrogen of a heterocyclic pharma-
cophore is forming the essential competitive binding to the iron
⇑
Corresponding author.
E-mail address: clemens.lamberth@syngenta.com (C. Lamberth).
https://doi.org/10.1016/j.bmc.2018.02.051
0968-0896/Ó 2018 Elsevier Ltd. All rights reserved.
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2
S. Jeanmart et al. / Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
which show potent activity against candidiasis,14 onychomyco-
sis,15 Malassezia-associated skin diseases16 and dermatophytosis
induced by Trichophyton spp.17 Their design has been probably
influenced by the older agrochemical fungicide buthiobate (1), a
pyridine-based DMI which has been specialized on the control of
powdery mildew diseases, e.g. caused by Sphaerotheca fuliginea
on cucumber.18,19 In this paper we report how we modified the
imidazole-based ketene dithioacetals lanoconazole (2) and luli-
conazole (3) to obtain new experimental fungicides such as 4
and 5, which show an impressive efficacy against a broad spectrum
of phytopathogens (Fig. 1).
2. Results and discussion
2.1. Chemistry
Although there are two imidazole-based ketene dithioacetal
antimycotics on the market, the synthesis of compounds with such
a scaffold is not well described in the scientific literature. So far
only V. J. Ram from the Indian Central Drug Research Institute
reported the synthesis of imidazole-linked ketene dithioacetals in
two publications 20 years ago.20,21 Therefore we would like to
describe in detail how to access such compounds.
1
Buthiobate,
For the synthesis of 4, a thienyl analog of luliconazole (3), we
started with 2,5-dichlorothiophene (6) which was transformed
an agrochemical fungicide specialized
on powdery mildew diseases
into the
cetyl chloride.22 In the case of several other – mainly phenyl – ana-
logs, such -chloro or bromo-ketones were easily obtained by
halogenation of the corresponding acetophenones. Then the
a-chloroketone 7 by Friedel-Crafts acylation with chloroa-
a
a-
chloroketone 7 was reduced with sodium borohydride to the
chlorohydrin 8. Hereby, the reaction time has to be kept as short
as possible to avoid the formation of epoxide side products. Mesy-
lation of the chlorohydrin 8 delivered the interesting thiophene
derivative 9 with two different leaving groups. This building block
reacts with the dipotassium dithiolate intermediate 12, which was
obtained in two steps by alkylation of imidazole (10) with bro-
moacetonitrile and subsequent transformation of the resulting
imidazolylacetonitrile 11 with carbon disulfide and potassium
hydroxide. Both reactive intermediates, the b-chloromesylate 9
and the dipotassium dithiolate 12 furnish the desired imidazole-
based ketene dithioacetal as a mixture of the E-isomer 4 and the
Z-isomer 13 which can be separated by chromatography
(Scheme 1).
3
2
Luliconazole
Lanoconazole
two pharmaceutical antifungal agents for topical application
If the above shown route is not possible, e.g. the Friedel-Crafts
acylation with chloroacetyl chloride would fail for regioselectivity
reasons and an appropriate aryl or heteroaryl methyl ketone is not
available, imidazole-based ketene dithioacetals are also available
from aromatic aldehydes. This approach is demonstrated by the
4
5
two experimental agrochemical broad-spectrum fungicides
Fig. 1. Evolution of ketene dithioacetal antifungals and fungicides.
ClCH2COCl, AlCl3,
CS2, 16 h, rt
MsCl, NEt3,
NaBH4,
MeOH, 2 h, rt
EtOAc, 30 min, 0 o
C
91 %
100 %
91 %
9
6
7
8
_
K
_
BrCH2CN, K2CO3,
MeCN, reflux, 3h
K
CS2, KOH,
DMSO, 2 h, rt
10
11
12
KOH, MeCN, 3 h, rt
4
13
38 %
23 %
Scheme 1. Friedel-Crafts acylation-type synthesis of ketene dithioacetal fungicide 4.
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S. Jeanmart et al. / Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
3
Br,
CHCl3, Ca(OH)2,
iPrMgCl.LiCl,
K2CO3, 4 h, 50 o
C
K2CO3, 2 h, 65 o
C
ICH2Cl, 8 h, -78 o
C
34 %
47 %
82 %
14
15
16
17
MsCl, NEt3,
100 %
1 h, 0 o
C
11
CS2, KOH,
DMSO, 16 h, rt
19
17 %
5
18
23 %
Scheme 2. Turbo-Grignard-type synthesis of ketene dithioacetal fungicide 5.
synthesis of the highly active compound 5. We started its synthesis
from 3-chloro-2-fluorophenol (14), which is transformed into the
trisubstituted benzaldehyde 15 by Reimer-Tiemann reaction with
dichlorocarbene generated from chloroform under basic condi-
tions. After alkylation of its phenol group with propargyl bromide,
the aldehyde function of the resulting 16 is directly transformed
into the chlorohydrin derivative 17 by reaction with
model is based on a Saccharomyces cerevisiae CYP51 X-ray structure
in complex with itraconazole (PDB code 5EQB).25 Docking and
homology modeling were performed with the Glide and Prime pro-
grams from Schrödinger.26
Figure 2 shows the possible binding mode of 5 in our Zymo-
spetoria tritici homology model. The nitrogen atom in imidazole
ring position 3 is bound to the iron atom of the heme. The propar-
gyloxy group and the fluorine atom, two substituents which
occupy positions in the phenyl ring in which lanoconazole bears
only hydrogen atoms, facilitate a better filling of the active site,
where they undergo extra hydrophobic interactions.
(chloromethyl)magnesium chloride-lithium chloride,
a mixed
lithium-magnesium carbenoid obtained from Knochel’s ‘‘turbo-
Grignard” reagent isopropylmagnesium chloride-lithium chloride
and chloro(iodo)methane.23,24 The mesylation of the benzylic alco-
hol of 17 delivered the reactive intermediate 18, which is equiva-
lent to the thiophene derivative 9 obtained on a different route.
The desired 1,3-dithiolane derivative 5 and its Z-isomer 19 are
obtained by the above discussed transformation of 18 with the
in situ prepared dipotassium dithiolate 12 (Scheme 2).
2.3. Structure-activity relationship
The first hypothesis we checked within the derivatization of
lanoconazole (2) was the replacement of its phenyl ring by an aro-
matic heterocycle. Therefore we prepared several different imida-
zole-based ketene dithioacetal derivatives, in which a five- or a
six-membered heterocycle is linked to the 1,3-dithiolane ring.
Table 1 shows the in planta activity of some examples with a chlo-
rinated thiophene (entry 1), pyrazole (entry 2) or pyrimidine (entry
3) in place of lanoconazole’s 2-chlorophenyl ring (entry 4) against
the deuteromycetes species Alternaria solani, causal agent of potato
and tomato early blight, and the three Ascomycota Botryotinia fuck-
eliana, causal agent of grey mold disease of several crops, Erysiphe
necator, causal agent of grape powdery mildew, and Zymoseptoria
tritici, causal agent of wheat leaf blotch. Although the 4-chloro-1-
methyl-5-trifluoromethylpyrazol-3-yl moiety of entry 2 was at
least as active as lanoconazole, the other thienyl and pyrimidinyl
derivatives were clearly weaker. Therefore we decided to stay with
the phenyl motif of the pharma lead compounds and to modify it
by the introduction of novel substituents.
2.2. Computational modeling
The design of novel analogs of lanoconazole and luliconazole
was supported by docking key derivatives into the active site of a
homology model of the Zymoseptoria tritici CYP51 enzyme. This
Because both alkyne groups27 and heterocyclic rings28 are espe-
cially well-known as privileged scaffolds in agrochemistry, we
introduced such functionalities either directly or via an oxygen lin-
ker into the para-position of lanoconazole’s phenyl ring. As shown
in Table 2, several of such derivatives showed very interesting
fungicidal activity, which was for some phytopathogens definitely
higher than the efficacy of lanoconazole. In the case of the two
derivatives with a CAC triple bond, the propargyloxy derivative
(entry 2) was clearly better than the cyclopropylethynylated com-
pound (entry 1) and convinced us especially regarding its interest-
ing spectrum. The two directly bonded pyrazole (entry 3) and
pyrimidine (entry 4) derivatives seem to have higher potency
against the four different phytopathogens than their oxygen-linked
pyridyl (entry 5), pyridazinyl (entry 6), pyrimidinyl (entry 7) and
pyrazinyl (entry 8) counterparts. Especially the methoxy-substi-
tuted pyridazine derivative (entry 6) showed a rather weak perfor-
mance. Overall the high potency and easy synthetically
accessibility of the propargyloxy derivative (entry 2) prompted
Fig. 2. Possible binding mode of 5 in the Zymoseptoria tritici CYP51 homology
model.
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S. Jeanmart et al. / Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
Table 1
Influence of the heterocyclic phenyl replacement on the fungicidal activity.a
Entry
R
Alternaria solani
Botryotinia fuckeliana
Erysiphe necator
Zymoseptoria tritici
(tomato early blight)
(tomato grey mold)
(grape powdery mildew)
(wheat leaf blotch)
1 (4)
63
36
96
10
2
97
96
100
75
3
42
93
38
91
96
99
35
40
4 (2)
a
Results are given in % activity at 60 ppm.
Table 2
Influence of the substituent in the para-position of the phenyl ring on the fungicidal activity.a
Entry
1
R
Alternaria solani
(tomato early blight)
Botryotinia fuckeliana
(tomato grey mold)
Erysiphe necator
(grape powdery mildew)
Zymoseptoria tritici
(wheat leaf blotch)
69
4
25
40
2
3
97
68
91
94
100
94
70
55
4
5
93
79
97
44
99
67
90
70
6
7
8
29
96
62
38
94
31
0
10
55
80
Me
88
98
9 (2)
H
93
91
99
40
a
Results are given in % activity at 60 ppm.
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S. Jeanmart et al. / Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
5
us to put this structural motif into the focus of our further
optimization.
Therefore we decided to prepare and test further analogs with a
2-chloro-4-propargyloxy substituted phenyl ring (entry 1). First we
found out that the introduction of a methyl group either into the
pharmacophore is unsubstituted. Nevertheless we wanted to
assess information on the impact of substituents in the imidazole
ring on the fungicidal activity, because of the special ketene
dithioacetal scaffold the situation might be different. Therefore
we prepared those analogs of lanoconazole (entry 4), which carry
a methyl group in imidazole position 2 (entry 1), 4 (entry 2) or 5
(entry 3). The fungicidal screening of these compounds gave a very
clear picture which is fully in line with the molecular target bind-
ing: both derivatives with a methyl group in an adjacent position
of the ring nitrogen in imidazole position 3 (entries 1 and 2) are
completely inactive, as such a substitution pattern sterically hin-
ders the interaction of the neighbouring ring nitrogen with the iron
atom of the heme in CYP51. However, a methyl group introduced
into imidazole ring position 5 (entry 3) does not change at all the
strong fungicidal efficacy of lanoconazole (entry 4), which is
unsubstituted in this position (Table 4).
terminal position (entry 2) or the
a -position of the alkyne (entry
3) did clearly diminish the fungicidal activity against most of the
reported pathogens. Next we turned our attention to the phenyl
position 3. The introduction of a fluorine atom into this position
in between the chloro- and propargyloxy substituents resulted in
a highly and broadly active compound, which controlled all four
phytopathogens with 93% and higher efficacy at 60 ppm (entry
4). The replacement of this fluoro substituent by a second chlorine
(entry 5), a methyl group (entry 6) or a second propargyloxy func-
tion (entry 7) was less satisfactory. (Table 3).
Typically in all commercialized CYP51 inhibiting triazole and
imidazole antifungals and fungicides this five-membered ring
Table 3
Influence of the different substituents introduced into the 2-chloro-4-propargyloxyphenyl moiety on the fungicidal activity.a
Entry
R
Alternaria solani
Botryotinia fuckeliana
Erysiphe necator
Zymoseptoria tritici
(tomato early blight)
(tomato grey mold)
(grape powdery mildew)
(wheat leaf blotch)
1
R1 = H; R2 = H;
R3 = H
97
81
94
97
91
86
91
91
50
0
100
63
63
99
19
38
75
70
45
38
98
75
85
31
2
R
1 = CH3;
R2 = H; R3 = H
1 = H; R2 = CH3;
R3 = H
1 = H; R2 = H;
R3 = F
1 = H; R2 = H;
R3 = Cl
1 = H; R2 = H;
R3 = CH3
1 = H; R2 = H;
R3 = OCH2C„CH
3
R
4 (5)
R
93
75
99
6
5
6
7
R
R
R
a
Results are given in % activity at 60 ppm.
Table 4
Influence of a methyl substituent in the imidazole ring on the fungicidal activity.a
Entry
1
R
Alternaria solani
(tomato early blight)
Botryotinia fuckeliana
(tomato grey mold)
Erysiphe necator
(grape powdery mildew)
Zymoseptoria tritici
(wheat leaf blotch)
R1 = CH3; R2 = H;
R3 = H
0
0
0
0
2
3
R
1 = H; R2 = CH3; R3 = H
0
97
0
69
0
99
0
74
R1 = H; R2 = H;
R3 = CH3
4 (2)
R
1 = H; R2 = H;
93
91
99
40
R3 = H
a
Results are given in % activity at 60 ppm.
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6
S. Jeanmart et al. / Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
Regarding the E and Z isomers obtained in the cyclocondensa-
The organic layer was washed with water, dried over sodium sul-
fate and evaporated. The residue was purified by chromatography
on silica gel, using ethyl acetate and heptane 1:10 as eluents to
deliver 2-chloro-1-(2,5-dichloro-3-thienyl)ethanone (7, 2.1 g, 9.2
mmol, 91%). Mp 43–44 °C. 1H NMR (CDCl3): d = 4.59 (s, 2H), 7.12
(s, 1H). LC-MS: Rt = 1.65 min; MS: m/z = 230 [M+1]+.
tion step, a general trend observed for all the described compounds
is, that the E form was in most cases the predominantly formed
isomer and in all cases the isomer with the by far better fungicidal
activity. The potency of the Z-isomers 13 and 19 was too weak to
be tested in the same whole-plant assay, with which we have eval-
uated the efficacy of their E-counterparts 4 and 5. In addition, the
enantiomers of 5 have been obtained by separation on chiral HPLC,
their in vitro testing revealed that only one of them was highly
active, whereas the other enantiomer showed clearly lower effi-
cacy. Also here, a clean comparison in our whole-plant assay
between both enantiomers and the racemate 5 was not possible
because of too weak activity of this second enantiomer.
4.1.2. 2-Chloro-1-(2,5-dichloro-3-thienyl)ethanol (8)
Sodium borohydride (93 mg, 2.4 mmol) was added at 0 °C to a
solution of 2-chloro-1-(2,5-dichloro-3-thienyl)ethanone (7, 2.0 g,
8.7 mmol) in 12 ml of methanol. The resulting suspension was stir-
red for 2 h at room temperature and then quenched by addition of
saturated aqueous ammonium chloride solution. This mixture was
extracted with methyl tert-butyl ether. The organic layer was
washed with brine, dried over sodium sulfate and evaporated
under reduced pressure. The residue was purified by chromatogra-
phy on silica gel, using ethyl acetate and heptane 1:8 as eluents to
deliver 2-chloro-1-(2,5-dichloro-3-thienyl)ethanol (8, 2.0 g, 8.6
mmol, 91%). 1H NMR (CDCl3): d = 2.64 (d, 1H, J = 3.7 Hz), 3.62
(dd, 1H, J = 8.4, 11.4 Hz), 3.74 (dd, 1H, J = 3.7, 11.4 Hz), 5.02 (dt,
1H, J = 3.7, 8.4 Hz), 6.92 (s, 1H). LC-MS: Rt = 1.44 min; MS: m/z =
232 [M+1]+.
3. Conclusions
Novel ketene dithioacetals bearing a 1,3-dithiolane core and an
imidazole pharmacophore have been evaluated as new scaffold for
agrochemical fungicides. As we found out, the phenyl ring of the
two similarly constructed, commercialized antifungal agents
lanoconazole (2) and luliconazole (3), can be replaced by an aro-
matic heterocycle or substituted by a heteroaryl ring or an alkyny-
loxy function with excellent results, delivering better fungicidal
activity than the mentioned lead compounds.
Some derivatives of lanoconazole, e.g. with a 2-pyrimidinyl ring
in position 4 of the phenyl ring (entry 4 of Table 2) and with a flu-
orine atom in position 3 and a propargyloxy function in position 4
(5, entry 4 of Table 3) display in whole-plant assays the strong con-
trol of more than 90% efficacy at 60 ppm against the four econom-
ically important plant pathogens Alternaria solani, Botryotinia
fuckeliana, Erysiphe necator and Zymoseptoria tritici.
4.1.3. [2-Chloro-1-(2,5-dichloro-3-thienyl)ethyl] methanesulfonate
(9)
Methanesulfonyl chloride (0.44 g, 3.9 mmol) was added at 0 °C
to a solution of 2-chloro-1-(2,5-dichloro-3-thienyl)ethanol (8, 0.9
g, 3.8 mmol) and triethylamine (0.43 g, 4.3 mmol) in 5 ml of ethyl
acetate. The reaction mixture was stirred for 30 min at 0 °C. The
resulting suspension was filtered, water was added to the filtrate
and it was extracted with ethyl acetate. After separation of the
phases, the organic layer was washed with brine, dried over
sodium sulfate and evaporated under reduced pressure to deliver
4. Experimental section
[2-chloro-1-(2,5-dichloro-3-thienyl)ethyl]methanesulfonate
(9,
1.2 g, 3.8 mmol, 100%) which was pure enough to be converted
in the next step without further purification. 1H NMR (CDCl3): d
= 3.04 (s,3H), 3.78 (dd, 1H, J = 5.0, 11.9 Hz), 3.85 (dd, 1H, 7.4,
11.9 Hz), 5.79 (dd, 1H, 5.0, 7.4 Hz), 6.91 (s, 1H). LC-MS: Rt = 1.71
min; MS: m/z = 214 [MꢀOMs]+.
4.1. Chemistry
All new compounds were characterized by standard spectro-
scopical methods. 1H NMR spectra were recorded on a Varian Unity
400 spectrometer at 400 MHz using CDCl3 as solvent and tetram-
ethylsilane as internal standard. Chemical shifts are reported in
ppm downfield from the standard (d = 0.00), coupling constants
in Hz. LC-MS spectra were determined using the following appara-
tus: ACQUITY UPLC from Waters, Phenomenex Gemini C18, 3 mm
particle size, 110 Angström, 30 x 3 mm column, 1.7 ml/min., 60 °C,
H2O + 0.05% HCOOH (95%)/CH3CN/MeOH 4:1 + 0.04% HCOOH (5%)
ꢀ 2 min ꢀ CH3CN/MeOH 4:1 + 0.04% HCOOH (5%) ꢀ 0.8 min;
ACQUITY SQD Mass Spectrometer from Waters, ionization method:
electrospray (ESI), Polarity: positive ions, Capillary (kV) 3.00, Cone
(V) 20.00, Extractor (V) 3.00, Source Temperature (°C) 150, Desol-
vation Temperature (°C) 400, Cone Gas Flow (L/Hr) 60, Desolvation
Gas Flow (L/Hr) 700. Analytical thin-layer chromatography (TLC)
was performed using silica gel 60 F524 precoated plates. Prepara-
tive flash chromatography was performed using silica gel 60 (40–
63 mm, E. Merck). Unless otherwise stated, all reactions were car-
ried out under anhydrous conditions in an inert atmosphere (nitro-
gen or argon) with dry solvents.
4.1.4. (2E)-2-[4-(2,5-dichloro-3-thienyl)-1,3-dithiolan-2-ylidene]-2-
imidazol-1-yl-acetonitrile (4)
A mixture of potassium hydroxide (0.21 g, 3.2 mmol) in 6 ml of
dimethylsulfoxide was purged with argon and cooled to 10 °C. A
solution of 2-imidazol-1-ylacetonitrile (11, 0.16 g, 1.55 mmol)
and carbon disulfide (0.24 g, 3.23 mmol) in 1 ml of dimethylsulfox-
ide was then slowly added. The cooling bath was removed and the
resulting orange mixture was stirred for 10 min at room tempera-
ture.
A solution of [2-chloro-1-(2,5-dichloro-3-thienyl)ethyl]
methanesulfonate (9, 0.4 g, 1.3 mmol) in 3 ml of dimethylsulfoxide
was then added dropwise. The reaction mixture was stirred for 3 h
at room temperature and then poured on water. The phases were
separated, the aqueous phase was extracted with dichloro-
methane, the organic layer was washed with water, dried over
sodium sulfate and evaporated under reduced pressure. The resi-
due was purified by chromatography on silica gel, using ethyl acet-
ate and heptane 1:1 as eluents to deliver (2E)-2-[4-(2,5-dichloro-3-
thienyl)-1,3-dithiolan-2-ylidene]-2-imidazol-1-yl-acetonitrile (4,
0.18 g, 0.5 mmol, 38%) and (2Z)-2-[4-(2,5-dichloro-3-thienyl)-1,3-
dithiolan-2-ylidene]-2-imidazol-1-yl-acetonitrile (13, 0.11 g, 0.3
mmol, 23%). 4: 1H NMR (CDCl3): d = 3.64 (dd, 1H, J = 8.7, 11.9 Hz),
3.75 (dd, 1H, J = 5.2, 11.9 Hz), 5.40 (dd, 1H, J = 5.2, 8.7 Hz), 6.97
(s, 1H), 7.06 (t, 1H, J = 1.3 Hz), 7.19 (s, 1H), 7.64 (s, 1H). LC-MS:
Rt = 1. min; MS: m/z = 360 [M+1]+. M.p. 117–119 °C. 13: 1H NMR
(CDCl3): d = 3.72 (dd, 1H, J = 8.8, 12.1 Hz), 3.84 (dd, 1H, J = 5.1,
12.1 Hz), 5.33 (dd, 1H, J = 5.1, 8.8 Hz), 6.93 (s, 1H), 7.04 (s, 1H),
4.1.1. 2-Chloro-1-(2,5-dichloro-3-thienyl)ethanone (7)
2,5-Dichlorothiophene (6, 1.5 g, 10 mmol) was added to a mix-
ture of chloroacetyl chloride (1.3 g, 12 mmol) and aluminum
trichloride (1.5 g, 12 mmol) in 50 ml of carbon disulfide. The reac-
tion mixture was stirred for 16 h at room temperature, then heated
to reflux for 1 h and cooled to 0 °C. 1 N hydrochloric acid was
added under vigorous stirring, hereby the solid disappeared and
the reaction mixture formed two phases which were separated.
Please cite this article in press as: Jeanmart S., et al. Bioorg. Med. Chem. (2018), https://doi.org/10.1016/j.bmc.2018.02.051

S. Jeanmart et al. / Bioorganic & Medicinal Chemistry xxx (2018) xxx–xxx
7
7.16 (s, 1H), 7.61 (s, 1H). LC-MS: Rt = 1.38 min; MS: m/z = 360 [M
[2-chloro-1-(2-chloro-3-fluoro-4-prop-2-ynoxy-phenyl)ethyl]
+1]+.
methanesulfonate (18, 2.6 g, 6.4 mmol, 100%) which was pure
enough to be converted in the next step without further purifica-
tion. 1H NMR (CDCl3): d = 2.62 (t, 1H), 3.11 (s, 3H), 3.76–3.90 (m,
2H), 4.83 (d, 2H), 6.02–6.06 (m, 1H), 7.14 (t, 1H), 7.36 (d, 1H).
LC-MS: Rt = 1.47 min; MS: m/z = 342 [M+1]+.
4.1.5. 2-Chloro-3-fluoro-4-hydroxybenzaldehyde (15)
Calcium hydroxide (40.4 g, 0.54 mol) and potassium carbonate
(61.5 g, 0.44 mol) were suspended in 220 ml of water. Then 3-
chloro-2-fluorophenol (14, 14.7 g, 0.1 mol) was added and the
resulting mixture was heated to 65 °C. At this temperature chloro-
form (23.9 g, 0.2 mol) was added dropwise within 2 h. The reaction
mixture was stirred for further 2 h at 65 °C, then cooled to room
temperature, acidified to pH 2–3 by addition of concentrated
hydrochloric acid and diluted with ethyl acetate. The phases were
separated, the organic layer was washed with brine, dried over
sodium sulfate and concentrated under reduced pressure. The resi-
due was purified by chromatography on silica gel, using ethyl acet-
ate and heptane 1:1 as eluents to deliver 2-chloro-3-fluoro-4-
hydroxybenzaldehyde (15, 5.8 g, 33 mmol, 34%). 1H NMR (CDCl3):
d = 7.07 (t, 1H), 7.74 (d, 1H), 10.32 (s, 1H). LC-MS: Rt = 0.91 min;
MS: m/z = 175 [M+1]+.
4.1.9. (2E)-2-[4-(2-chloro-3-fluoro-4-prop-2-ynoxy-phenyl)-1,3-
dithiolan-2-ylidene]-2-imidazol-1-yl-acetonitrile (5)
Potassium hydroxide (0.9 g, 16 mmol) was added in portions to
a solution of 2-imidazol-1-ylacetonitrile (11, 1.0 g, 9.6 mmol) and
carbon disulfide (1.2 g, 16 mmol) in 10 ml of dimethylsulfoxide.
The resulting orange mixture was stirred for 30 min at room tem-
perature and then added dropwise to a solution of [2-chloro-1-(2-
chloro-3-fluoro-4-prop-2-ynoxy-phenyl)ethyl]methanesulfonate
(18, 2.4 g, 6.4 mmol) in 10 ml of dimethylsulfoxide was then added
dropwise. The reaction mixture was stirred for 16 h at room tem-
perature, then diluted with water and extracted with ethyl acetate.
The organic layer was washed with water, dried over sodium sul-
fate and evaporated under reduced pressure. The residue was puri-
fied by chromatography on silica gel, using ethyl acetate and
cyclohexane 7:3 as eluents to deliver (2E)-2-[4-(2-chloro-3-flu-
oro-4-prop-2-ynoxy-phenyl)-1,3-dithiolan-2-ylidene]-2-imidazol-
1-yl-acetonitrile (5, 0.56 g, 1.4 mmol, 23%) and (2Z)-2-[4-(2-
chloro-3-fluoro-4-prop-2-ynoxy-phenyl)-1,3-dithiolan-2-ylidene]-
2-imidazol-1-yl-acetonitrile (19, 0.43 g, 1.1 mmol, 17%). 5: 1H NMR
(CDCl3): d = 2.53 (t, 1H), 3.60 (dd, 1H, J = 8.7, 11.9 Hz), 3.79 (dd, 1H,
J = 5.2, 11.9 Hz), 4.73 (d, 2H), 5.58 (dd, 1H, J = 5.2, 8.7 Hz), 6.98–
7.10 (m, 2H), 7.33 (d, 1H), 7.59 (s, 1H). LC-MS: Rt = 1.35 min; MS:
m/z = 392 [M+1]+. 19: 1H NMR (CDCl3): d = 2.62 (t, 1H), 3.78 (dd,
1H, J = 8.7, 11.9 Hz), 3.99 (dd, 1H, J = 5.2, 11.9 Hz), 4.83 (d, 2H),
5.64 (dd, 1H, J = 5.2, 8.7 Hz), 7.07–7.19 (m, 2H), 7.35 (d, 1H), 7.66
(s, 1H). LC-MS: Rt = 1.33 min; MS: m/z = 392 [M+1]+.
4.1.6. 2-Chloro-3-fluoro-4-prop-2-ynoxy-benzaldehyde (16)
Potassium carbonate (2.3 g, 16.6 mmol) was added to a mixture
of 2-chloro-3-fluoro-4-hydroxybenzaldehyde (15, 2.9 g, 16.6
mmol) in 27 ml of methyl ethyl ketone. Then 3.9 ml of a solution
of propargyl bromide in toluene (35 mmol) was added dropwise
at room temperature. The reaction mixture was heated to 50 °C
for 4 h, then cooled to room temperature and filtered. The filtrate
was concentrated under reduced pressure. The residue was puri-
fied by chromatography on silica gel, using ethyl acetate and cyclo-
hexane 3:7 as eluents to deliver 2-chloro-3-fluoro-4-prop-2-
ynoxy-benzaldehyde (16, 1.7 g, 7.9 mmol, 47%). 1H NMR (CDCl3):
d = 2.65 (t, 1H), 4.90 (d, 2H), 7.16 (t, 1H), 7.79 (d, 1H), 10.35 (s,
1H). LC-MS: Rt = 1.34 min; MS: m/z = 213 [M+1]+.
4.1.7. 2-Chloro-1-(2-chloro-3-fluoro-4-prop-2-ynoxy-phenyl)ethanol
(17)
4.2. Biology
9 ml of a 1.3 M solution of isopropylmagnesium chloride-
lithium chloride complex in tetrahydrofuran (11.7 mmol) were
added dropwise at – 78 °C to a mixture of chloro(iodo)methane
(3.4 g, 19.5 mmol) in 10 ml of tetrahydrofuran. The resulting mix-
ture was stirred for 15 min at – 78 °C, then a solution of 2-chloro-
3-fluoro-4-prop-2-ynoxy-benzaldehyde (16, 1.7 g, 7.9 mmol) in 9
ml of tetrahydrofurane was slowly added at this temperature.
The reaction mixture was stirred for 8 h at – 78 °C, then quenched
by addition of 10 ml of a saturated aqueous ammonium chloride
solution and warmed to room temperature. The phases were sep-
arated and the aqueous phase was extracted with ethyl acetate.
The combined organic layer was washed with brine, dried over
sodium sulfate and evaporated under reduced pressure. The resi-
due was purified by chromatography on silica gel, using ethyl acet-
ate and heptane 1:10 as eluents to deliver 2-chloro-1-(2-chloro-3-
fluoro-4-prop-2-ynoxy-phenyl)ethanol (17, 1.7 g, 6.4 mmol, 82%).
1H NMR (CDCl3): d = 2.61 (t, 1H), 3.53–3.60 (m, 1H), 3.87–3.92
(m, 1H), 4.81 (d, 2H), 5.25–5.30 (m, 1H), 7.13 (t, 1H), 7.40 (d,
1H). LC-MS: Rt = 1.34 min; MS: m/z = 264 [M+1]+.
4.2.1. Alternaria solani/tomato (activity against early blight on
tomato)
4-week old tomato plants cv. Roter Gnom are sprayed in a spray
chamber with the formulated test compound diluted in water. The
test plants are inoculated by spraying them with a spore suspen-
sion two days after application. The inoculated test plants are incu-
bated at 22/18 °C (day/night) and 95% rh in a greenhouse and the
percentage leaf area covered by disease is assessed when an appro-
priate level of disease appears on untreated check plants (5–7 days
after application).
4.2.2. Botryotinia fuckeliana/tomato (activity against grey mold on
tomato)
4-week old tomato plants cv. Roter Gnom are sprayed in a spray
chamber with the formulated test compound diluted in water. The
test plants are inoculated by spraying them with a spore suspen-
sion two days after application. The inoculated test plants are incu-
bated at 20 °C and 95% rh in a greenhouse and the percentage leaf
area covered by disease is assessed when an appropriate level of
disease appears on untreated check plants (3–5 days after
application).
4.1.8. [2-Chloro-1-(2-chloro-3-fluoro-4-prop-2-ynoxy-phenyl)ethyl]
methanesulfonate(18)
Methanesulfonyl chloride (0.74 g, 6.4 mmol) was added at 0 °C
to a solution of 2-chloro-1-(2-chloro-3-fluoro-4-prop-2-ynoxy-
phenyl)ethanol (17, 1.8 g, 6.4 mmol) and triethylamine (0.7 g, 7.0
mmol) in 8 ml of ethyl acetate. The reaction mixture was stirred
for 1 h min at 0 °C. The resulting suspension was filtered and the
filtrate was concentrated under reduced pressure. The remainder
was taken up in ethyl acetate, the organic layer was dried over
sodium sulfate and evaporated under reduced pressure to deliver
4.2.3. Erysiphe necator/grape (activity against powdery mildew on
grape)
5-week old grape seedlings cv. Gutedel are sprayed in a spray
chamber with the formulated test compound diluted in water.
The test plants are inoculated by shaking plants infected with
grape powdery mildew above them one day after application.
The inoculated test plants are incubated at 24/22 °C (day/night)
and 70% rh under a light regime of 14/10 h (light/dark) and the
Please cite this article in press as: Jeanmart S., et al. Bioorg. Med. Chem. (2018), https://doi.org/10.1016/j.bmc.2018.02.051

8
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priate level of disease appears on untreated check plants (7–9 days
after application).
4.2.4. Zymoseptoria tritici/wheat (activity against leaf blotch on
wheat)
2-week old wheat plants cv. Riband are sprayed in a spray
chamber with the formulated test compound diluted in water.
The test plants are inoculated by spraying a spore suspension on
them one day after application. After an incubation period of 4
days at 22 °C/21 °C (day/night) and 95% rh, the inoculated test
plants are kept at 22 °C/21 °C (day/night) and 70% rh in a green-
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Please cite this article in press as: Jeanmart S., et al. Bioorg. Med. Chem. (2018), https://doi.org/10.1016/j.bmc.2018.02.051