Synthesis and Antifungal Activity of Substituted 2-Aryl Benzimidazoles Derivatives

Article abstract of DOI:10.1002/jhet.3639

Benzimidazole fungicides were among the early systemic fungicides developed and used for controlling a wide variety of plant diseases. During the course of our screening process for active compounds, two 2-aryl benzimidazoles derivatives bearing sulfoxide group (6b and 6c) have been demonstrated to exhibit good inhibition activity against high-resistant isolate of Botrytis cinerea compared with carbendazim, and the inhibition rates are up to 46.67% and 51.11% at the concentration of 10 μg/mL, which might be considered as the active framework for the discovery of novel fungicide to high-resistant isolate of B. cinerea.

Full text of DOI:10.1002/jhet.3639

Month 2019
Synthesis and Antifungal Activity of Substituted 2-Aryl Benzimidazoles
Derivatives
*
Daye Huang, Fang Qiu, Zhigang Zhang, Liqiao Shi, Chunxia Cao, and Shaoyong Ke
National Biopesticide Engineering Research Centre, Hubei Biopesticide Engineering Research Centre, Hubei Academy of
Agricultural Sciences, Wuhan 430064, China
*E-mail: keshaoyong@163.com
Received March 19, 2019
DOI 10.1002/jhet.3639
Published online 00 Month 2019 in Wiley Online Library (wileyonlinelibrary.com).
Benzimidazole fungicides were among the early systemic fungicides developed and used for controlling a
wide variety of plant diseases. During the course of our screening process for active compounds, two 2-aryl
benzimidazoles derivatives bearing sulfoxide group (6b and 6c) have been demonstrated to exhibit good in-
hibition activity against high-resistant isolate of Botrytis cinerea compared with carbendazim, and the inhi-
bition rates are up to 46.67% and 51.11% at the concentration of 10 μg/mL, which might be considered as
the active framework for the discovery of novel fungicide to high-resistant isolate of B. cinerea.
J. Heterocyclic Chem., 00, 00 (2019).
INTRODUCTION
discovery of novel agrochemicals or drugs. In addition,
two 2-aryl benzimidazoles derivatives bearing sulfoxide
group have been indicated to exhibit good inhibition
activity against high-resistant isolate of B. cinerea during
the course of our screening process for active compounds.
So, in the present study, we would like to present the
synthesis of several functional 2-aryl benzimidazoles
derivatives (Fig. 2), and the in vitro fungicidal activities
of target derivatives towards benzimidazoles-sensitive
and high-resistant isolates of B. cinerea were
Benzimidazole fungicides were among the early
systemic fungicides developed and extensively used
worldwide for controlling a variety of plant diseases
[1,2]. These fungicides were known as a specific inhibitor
of microtubule assembly by binding to the β-subunit of
β-tubulin and interfering with microtubule formation
during mitosis of cell division [3,4]. Even though they
were initially proved to be very effective, their life was
often cut short by the appearance and spread of
benzimidazole-resistant strains [5]; it has been reported
that many of fungal species were resistant to
benzimidazole fungicides. In most cases, the resistance is
due to the mutations in β-tubulin gene, causing the
changes of amino acid sequences [6].
investigated, which can provide
a
certain useful
information for the development of potential antifungal
agents against high-resistant isolates of B. cinerea.
RESULTS AND DISCUSSION
Gray mold, caused by Botrytis cinerea, is an important
disease of horticultural crops in the worldwide, which
causes vast economic losses every year [7].
Benzimidazole fungicides, such as carbendazim, were
used in controlling gray mold; however, with the
frequency used in controlling this disease, resistant
isolates soon appeared [8–18].
Meanwhile, organosulfur compounds have received
considerable attention in the field of drug discovery [19–
22]. Many sulfur-containing molecules have been
developed as agrochemicals such as fosthiazate [23],
fluensulfone [24], clothianidin [25], thiamethoxam [26],
and isotianil [27] (Fig. 1), which also demonstrate that
sulfur-containing group will be an important
pharmacophore that binds to receptor proteins for the
In this work, several multisubstituted benzimidazoles
mainly including sulfur-containing benzimidazoles (5a–c
and 6b,c) were designed and synthesized via sequence
simple synthetic method. The general process for these
benzimidazoles derivatives is described in Scheme 1.
Firstly, the easily available 4-(methylthio)benzaldehyde
1 was used as a reactant, which was converted into
corresponding sodium hydroxy(4-(methylthio)phenyl)
methanesulfonate 2 via nucleophilic addition reaction. On
the other hand, substituted nitroanilines 3a–c have been
reduced to the substituted o-phenylenediamines 4a–c.
Subsequently, the intermediate 2 condense with the
corresponding 4a–c to obtain the sulfur-containing
benzimidazole 5a–c. Then the treatment of various 5a–c
© 2019 Wiley Periodicals, Inc.

D. Huang, F. Qiu, Z. Zhang, L. Shi, C. Cao, and S. Ke
Vol 000
Figure 1. Commercial sulfur-containing agrochemicals.
compounds 5c and 6c appear to be compatible with their
structures. In addition, the corresponding MS analyses
can also confirm the obvious molecular peak [M + H]+
with relative abundance in the corresponding MS
spectrum.
The in vitro fungicidal activities of target 2-aryl
benzimidazoles derivatives towards benzimidazoles-
sensitive and high-resistant isolates of B. cinerea were
screened, and the results from the tests were described in
Table 1.
Figure 2. Design strategies for multisubstituted 2-aryl benzimidazoles
derivatives. [Color figure can be viewed at wileyonlinelibrary.com]
with appropriated oxidation agents such as oxone formed
sulfonyl
group-containing
benzimidazoles
6b–c.
Furthermore, a benzimidazole bearing carboxylic group
10 has also been prepared to explore the effect of
different fragments on activity. The structures of all
synthesized benzimidazole derivatives in this work were
elucidated on the basis of spectral analysis. The
As the results indicated in Table 1, some of these
compounds exhibited moderate inhibition against
benzimidazoles-sensitive and high-resistant isolate of
B. cinerea at the concentration of 10 μg/mL. However,
compounds 5a–c containing methylthio group are
inactive against the sensitive and high-resistant isolate of
B. cinerea, which demonstrated that the sulfoxide group
will be favorable for increasing the inhibition activity. In
particular, the inhibition activity of compounds 6b and 6c
to sensitive and high-resistant isolate was similar, and the
inhibition ratio of compounds 6b and 6c was decreased
to sensitive isolates and was increased to high-resistant
isolate compared with the control carbendazim. The
commercial carbendazim showed almost no inhibitory
activity against high-resistant isolate of B. cinerea at the
same condition. It is important to note that compounds
6b and 6c can be explored as lead scaffold for the
discovery of novel fungicide to high-resistant isolate of
B. cinerea.
1
representative H NMR spectrum for compounds 5c and
6c was indicated in Figs S1 and S2, and the
corresponding analyses data were given in the
Experimental section.
1
For the H NMR studies of compound 5c, the typical
signal for proton of methyl attached sulfur atom was
resonated as a singlet at 2.57 ppm, the methyl on benzene
ring was assigned on the signal at 2.55 ppm, and the
1
other signals that emerged in their H NMR spectrum in
the range 8.15–6.98 ppm were assigned to the protons of
aryl units. However, the signal peak for the methyl group
linked sulfone group in compound 6c is very difference,
1
which present at 3.30 ppm in the corresponding H NMR
spectrum. From these analyses, the characterizations of
Scheme 1. Synthetic route for multisubstituted benzimidazole derivatives.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

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Synthesis and Antifungal Activity of Substituted 2-Aryl Benzimidazoles
Derivatives
Table 1
The fungicidal activity for target compounds against Botrytis cinerea.
Fungal inhibition (%) (conc. in 10 μg/mL)
Sensitive isolate High-resistant isolate
Entry
1
Compound no.
Structure
5a
0
0
2
3
5b
5c
0
0
0
0
4
5
6b
6c
41.33
53.33
46.67
51.11
6
7
10
0
0
0
Carbendazim
100
CONCLUSION
absorption spectra were recorded on a Thermo Nicolet
FT-IR Avatar 330 instrument in KBr discs and were
1
Several substituted 2-aryl benzimidazoles derivatives
were synthesized and evaluated as potential fungicidal
agents. The in vitro fungicidal activities indicated that
compounds 6b and 6c bearing sulfoxide group exhibited
good inhibition activity against high-resistant isolate of
B. cinerea compared with carbendazim, which could be
further optimized as lead scaffold for the discovery of
novel fungicide to high-resistant isolate of B. cinerea.
reported in cmÀ1. H NMR and 13C NMR were tested on
a Bruker Avance III 600 MHz FT-NMR spectrometer
using DMSO-d6 as solvent and tetramethylsilane as
internal standard. Mass spectra were determined on a
Waters ACQUITY UPLC H-CLASS PDA (Waters)
instrument. Thin-layer chromatography (TLC) was
carried out on precoated silica gel plates GF254, and
spots were visualized with ultraviolet light.
Sodium hydroxy(4-(methylthio)phenyl)methanesulfonate
2.
A 5-mL aqueous of sodium bisulfite (1.25 g,
EXPERIMENTAL
12 mmol) was added to a solution of 4-(methylthio)
benzaldehyde 1 (1.52 g, 10 mmol) in ethanol (20 mL),
and the reaction mixture was stirred at ambient
temperature and detected by TLC. Then the solution was
concentrated to obtain white solid as crude product 2,
which was used for the next step transformation without
further purification.
Instrumentation and chemicals. All starting materials
and reagents commercially available were used without
further purification, unless otherwise specified. All
melting points (mp) were obtained using a digital model
X-5 apparatus and were uncorrected. The infrared
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

D. Huang, F. Qiu, Z. Zhang, L. Shi, C. Cao, and S. Ke
Vol 000
Synthesis of substituted o-phenylenediamines 4a–c. The
4-Methyl-2-(4-(methylthio)phenyl)-1H-benzo[d]imidazole
5c.
This compound was yielded as off-white powder,
representative procedure for the preparation of substituted
o-phenylenediamines 4a–c is as follows: Substituted
nitroanilines 3a–c (5 mmol) was dissolved in ethyl
acetate (80 mL), and tinchloridedihydrate (25 mmol) was
added in batches. Then the reaction mixture was stirred at
ambient temperature and monitored by TLC. After
completion of the reaction, the mixture was adjusted to
pH 8 using saturated aqueous of sodium bicarbonate and
filtered under reduce pressure, the filtrate was treated by
conventional extraction, and the organic layer was dried
through Na2SO4 and concentrated to obtain the crude
product, which was recrystallized from methanol.
yield 76%, mp 187–188°C; IR (KBr, cmÀ1): υ 1600,
1475 cmÀ1; H NMR (600 MHz, DMSO-d6): δ = 12.75
1
(bs, 1H), 8.15 (d, J = 6 Hz, 2H), 7.43–7.41 (m, 3H), 7.08
(t, J = 9 Hz, 1H), 6.99 (d, J = 6 Hz, 1H), 2.57 (s, 3H),
2.55 (s, 3H); 13C NMR (150 MHz, DMSO-d6): δ
158.6, 147.2, 128.5, 124.8, 123.2, 121.2, 116.2, 18.3,
16.4; MS (ESI) m/z 255.35 (M + H)+, calcd for
C15H14N2S m/z = 254.09.
Synthesis of sulfonyl group-containing benzimidazoles
6b–c.
To a solution of sulfur-containing benzimida
zoles 5b,c (1 mmol) in 10 mL of methanol, the
aqueous containing oxone (4 mmol) was added, which
was stirred and heated to 60–70°C. After this, the
reaction mixture was poured into 50 mL of ice water
with stirring. Then the product was extracted with
EtOAc, and the organic layer was dried through
anhydrous Na2SO4 and concentrated to obtain the crude
product, which was recrystallized from ethanol to form
the target sulfonyl group-containing benzimidazoles 6b,
Benzene-1,2-diamine 4a. This compound was obtained
as gray crystal, yield 75%, mp 101–102°C; MS (ESI) m/z
108.21 (M + H)+, calcd for C6H8N2 m/z = 108.07.
4-Chlorobenzene-1,2-diamine 4b.
This compound
was produced as brown powder, yield 81%, mp 75–
77°C; MS (ESI) m/z 143.06 (M + H)+, calcd for
C6H7ClN2 m/z = 142.03.
3-Methylbenzene-1,2-diamine 4c.
This compound was
1
obtained as oil, yield 62%; MS (ESI) m/z 123.12
c. The target compounds were determined by H NMR
(M + H)+, calcd for C7H10N2 m/z = 122.08.
and ESI-MS spectroscopic data.
5-Chloro-2-(4-(methylsulfonyl)phenyl)-1H-benzo[d]
imidazole 6b. This compound was obtained as yellowish
Synthesis of sulfur-containing benzimidazoles 5a–c.
Sodium hydroxy(4-(methylthio)phenyl)methanesulfonate
2 (2 mmol) was dissolved in 10 mL of DMF, and the
equal amount of substituted o-phenylenediamines 4a–c
(2 mmol) was added, which were stirred and heated to
70°C and monitored by TLC. After this, the mixture was
poured into 50 mL of ice water with stirring. Then the
precipitate was filtered and dried to obtain a crude
product, which was purified by recrystallization from
methanol to the target sulfur-containing benzimidazoles
powder, yield 77%, mp 152–154°C; IR (KBr, cmÀ1): υ
1628, 1510 cmÀ1 1H NMR (600 MHz, DMSO-d6):
;
δ = 13.12 (bs, 1H), 8.43 (dd, J = 6 Hz, 2H), 8.13 (dd,
J = 6 Hz, 2H), 7.72 (s, 1H), 7.67 (d, J = 12 Hz, 1H),
7.29 (q, J = 6 Hz, 1H), 3.74 (s, 3H); 13C NMR
(150 MHz, DMSO-d6): δ 160.9, 151.2, 129.6, 125.7,
123.1, 122.4, 118.4, 117.1, 49.8; MS (ESI) m/z 307.29
(M + H)+, calcd for C14H11ClN2O2S m/z = 306.02.
1
4-Methyl-2-(4-(methylsulfonyl)phenyl)-1H-benzo[d]
5a–c. The target molecules were elucidated by H NMR
and ESIMS spectroscopic data.
imidazole 6c.
This compound was produced as white
powder, yield 82%, mp 180–182°C; IR (KBr, cmÀ1): υ
1612, 1485 cmÀ1 1H NMR (600 MHz, DMSO-d6):
2-(4-(Methylthio)phenyl)-1H-benzo[d]imidazole 5a.
This
;
compound was produced as white powder, yield 84%,
δ = 13.14 (bs, 1H), 8.46 (s, 2H), 8.12–8.08 (m, 2H),
7.51–7.41 (m, 1H), 7.15 (t, J = 9 Hz, 1H), 7.06 (d,
J = 6 Hz, 1H), 3.30 (s, 3H), 2.60 (s, 3H); 13C NMR
(150 MHz, DMSO-d6): δ 158.1, 148.4, 127.3, 123.9,
123.3, 120.7, 114.6, 48.8, 17.5; MS (ESI) m/z 287.31
(M + H)+, calcd for C15H14N2O2S m/z = 286.08.
1
mp 225–227°C; IR (KBr, cmÀ1): υ 1610, 1480 cmÀ1; H
NMR (600 MHz, DMSO-d6): δ = 12.86 (bs, 1H), 8.12–
8.10 (m, 2H), 7.58 (bs, 2H), 7.44–7.41 (m, 2H), 7.21–
7.18 (m, 2H), 2.55 (s, 3H); 13C NMR (150 MHz,
DMSO-d6): δ 159.2, 148.8, 129.5, 123.4, 121.2, 116.7,
16.8; MS (ESI) m/z 241.49 (M + H)+, calcd for
Synthesis of benzimidazole derivative 10.
The
C14H12N2S m/z = 240.07.
benzimidazole bearing carboxylic group 10 has been
prepared using a similar procedure. The intermediate 8
(2 mmol) was dissolved in 10 mL of DMF, and the equal
amount of salicylaldehyde (2 mmol) was added, which
was stirred and heated to 80°C. After the completion of
transformation, the reaction mixture was poured into
50 mL of ice water with stirring. The precipitate was
filtered and dried to give the crude product, which was
purified by recrystallization from methanol to the target
2-(2-hydroxyphenyl)-1H-benzo[d]imidazole-4-carboxylic
5-Chloro-2-(4-(methylthio)phenyl)-1H-benzo[d]imidazole
5b. This compound was obtained as gray powder, yield
72%, mp 166–167°C; IR (KBr, cmÀ1):
υ 1620,
1
1495 cmÀ1; H NMR (600 MHz, DMSO-d6): δ = 13.08
(bs, 1H), 8.11–8.09 (m, 2H), 7.63 (s, 1H), 7.59 (d,
J = 6 Hz, 1H), 7.44–7.42 (m, 2H), 7.23–7.21 (dd,
J = 12 Hz, 1H), 2.55 (s, 3H); 13C NMR (150 MHz,
DMSO-d6): δ 160.3, 149.6, 130.2, 125.1, 123.8, 121.9,
117.8, 17.1; MS (ESI) m/z 275.24 (M + H)+, calcd for
C14H11ClN2S m/z = 274.03.
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Synthesis and Antifungal Activity of Substituted 2-Aryl Benzimidazoles
Derivatives
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acid 10 as off-white powder: yield 73%, mp >250°C; IR
(KBr, cmÀ1): υ 3388, 1596, 1495 cmÀ1 1H NMR
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Acknowledgments. This work was supported by the Hubei
Technical Innovation Special Project (2017ABA160) and the
Program for Leading Talents of Hubei Academy of Agricultural
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet