Synthesis and biological activity of some triazole-bearing benzimidazole derivatives

Article abstract of DOI:10.2298/JSC100301029A

A number of N'-(arylmethylidene)-2-(2-methyl-1H-benzimidazol- -1-yl)acetohydrazide and 4-aryl-5-[(2-methyl-1H-benzimidazol-1-yl)methyl]- -4H-1,2,4-triazole-3-thiol derivatives were synthesized by incorporating various aromatic and heterocyclic substituents on 2-methyl-1H-benzimidazole. The structures of all the synthesized compounds were elucidated based on their elemental analyses and spectral data. The in vitro activities of these compounds against bacteria and fungi were evaluated by the disc diffusion and the minimum inhibitory concentration (MIC) methods. Some of the synthesized derivatives were found to be as active as kanamycin (standard drug).

Full text of DOI:10.2298/JSC100301029A

J. Serb. Chem. Soc. 76 (3) 341–352 (2011)
UDC 542.913+57–188:547.79+547.53
JSCS–4122
Original scientific paper
Synthesis and biological activity of some triazole-bearing
benzimidazole derivatives
*
K. F. ANSARI, C. LAL and R. K. KHITOLIYA
Department of Chemistry, Harcourt Butler Technological Institute, Kanpur-208002, India
(Received 1 March 2010)
Abstract: A number of N’-(arylmethylidene)-2-(2-methyl-1H-benzimidazol-
-1-yl)acetohydrazide and 4-aryl-5-[(2-methyl-1H-benzimidazol-1-yl)methyl]-
-4H-1,2,4-triazole-3-thiol derivatives were synthesized by incorporating vari-
ous aromatic and heterocyclic substituents on 2-methyl-1H-benzimidazole. The
structures of all the synthesized compounds were elucidated based on their ele-
mental analyses and spectral data. The in vitro activities of these compounds
against bacteria and fungi were evaluated by the disc diffusion and the mini-
mum inhibitory concentration (MIC) methods. Some of the synthesized deriva-
tives were found to be as active as kanamycin (standard drug).
Keywords: benzimidazole; triazole; antimicrobial activity; ampicillin; kanamy-
cin; amphotericin B.
INTRODUCTION
The benzimidazole nucleus, which is a useful structure for research and
development of new pharmaceutical molecules, has received much attention in
the last decade. Due to their antimicrobial activities, new benzimidazoles have
been synthesized and investigated for medical applications. As resistance to
antimicrobial drugs is widespread; there is an increase necessity for the iden-
tification of novel structures which could lead to the design of new, potent and
less toxic antimicrobial agents. Numerous attempts have been made to develop
new structural prototypes to search for more effective antimicrobials. The benz-
imidazoles still remain one of the most versatile classes of compounds against
microbes and, therefore, are useful substructures for further molecular explora-
tion. They exhibit a range of biological activities. Specifically, this ring system is
1,2
3,4
5–8
14
present in numerous antioxidants,
antiparasitic,
antimicrobial,
anticonvulsant, antineo-
anthel-
9,10
11
12,13
mintic,
plastic,
antiproliferative, anti-inflammatory,
antihypertensive anti HIV agents. Owing to the immense impor-
15,16
17
18
tance and varied biological activities exhibited by the benzimidazoles, efforts
*Corresponding author. E-mail: c_lal12@rediffmail.com
doi: 10.2298/JSC100301029A
341
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342
ANSARI, LAL and KHITOLIYA
have been made periodically to generate libraries of these compounds and screen
them for their potential biological activities. In addition, it is well documented
that the triazole nucleus is associated with a variety of pharmacological activities.
19,20
21
22
It displays pronounced antimicrobial,
anti-inflammatory and analgesic
activities. The effectiveness of the benzimidazole and triazole moieties towards
various microbes prompted the synthesis of some new benzimidazole derivatives
bearing the triazole nucleus and the screening of their potential biological acti-
vities. In continuation of studies on biologically active benzimidazole deriva-
23–25
tives,
the results of the synthesis of some new benzimidazole derivatives
having a triazole nucleus are reported herein.
RESULTS AND DISCUSSION
Chemistry
The physical, analytical and spectral data are given in Supplementary mate-
rial.
The key intermediate used for the synthesis of both series of the final com-
pounds was 2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazide (3), which in turn
was prepared by the reaction of 2-methyl-1H-benzimidazole (1) with ethyl chlo-
23
roacetate in the presence of anhydrous potassium carbonate as a base, followed
24
by the reaction with hydrazine hydrate (Scheme 1). The reaction of compound
3 with different arylaldehyde and acetophenones in absolute ethanol gave the
desired N’-[(aryl)methylidene]-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazi-
des 4a–v. The N-(aryl)-2-[(2-methyl-1H-benzimidazol-1-yl)acetyl]hydrazinecar-
bothioamides 5a–k were prepared by condensing compound 3 with appropriate
phenyl isothiocyanates. Cyclization of compounds 5a–i in 2 M NaOH solution
under reflux finally gave the 4-(aryl)-5-[(2-methyl-1H-benzimidazol-1-yl)me-
thyl]-4H-1,2,4-triazole-3-thiols 6a–k. The purity of the synthesized compounds
was monitored by TLC and the structures of all the derivatives were supported by
1
13
spectral data. The IR, H-NMR, C-NMR and mass spectra are in agreement
with the proposed structures. The structures of all the compounds were esta-
blished based on analysis of the spectral data. The compounds 4a–v showed the
–1
1
–CONH group band between 1657–1679 cm in their IR spectra. The H-NMR
spectra of these compounds showed the signal of the –CONH proton between δ
9.00–9.27. In compounds 5a–k, the appearance of a new band between 1220–
–1
1
–1246 cm showed the formation of thiosemicarbazide and the H-NMR signal
for the –NH– proton peak appeared between δ 7.04–9.03, depending on the type
of substitution at the benzene ring. Compounds 6a–k showed the –N–N– group
band between 1253–1275 cm and S–H group band between 2545–2562 cm ,
which indicate the formation of the triazole ring. In the H-NMR spectra of com-
–1
–1
1
pounds 6a–k, a sharp peak between δ 12.90–12.92 showed the presence of the
C–SH proton and the –N–CH proton signal appeared between δ 6.00–6.18. The
2
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SYNTHESIS AND BIOLOGICAL ACTIVITY OF BENZIMIDAZOLE DERIVATIVES
343
mass spectra of compounds 6a–k exhibited molecular ion peaks at m/z 321, 351,
337, 355, 444 and 336 together with their fragmentation peaks, which indicated
the formation of triazole derivatives.
Scheme 1. Reagents and conditions: i) ClCH2COOC2H5/dry acetone, K2CO3; RT: 10 h,
ii) NH2NH2.H2O/dry methanol; RT: 4–5 h, iii) substituted arylaldehyde or actophe-
none/absolute ethanol; RT: 5 h, iv) substituted phenyl isothiocyanate/absolute
ethanol; RT: 1 h and v) 2NaOH; RT: 4 h.
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ANSARI, LAL and KHITOLIYA
Antimicrobial evaluation
The in vitro antimicrobial activity against different strains of bacteria and
fungi was screened using the disc diffusion and the minimum inhibitory con-
centration (MIC) methods. Ampicillin, nalidixic acid and kanamycin were used
as the positive controls for the bacteria and amphotericin B for the fungi.
By comparing the antimicrobial activity of the synthesized compounds, it
was found that the tested compounds were more effective against the Gram po-
sitive bacteria. It is believed that the strong lipophilic character of a molecule
plays an essential role in producing antimicrobial effects. These properties are
seen as an important parameters related to membrane permeation in biological
systems. Many of the processes of drug disposition depend on the capability of a
drug to cross membranes and hence there is a high correlation with measures of
lipophilicity. Hydrophobic drugs with high partition coefficients are preferen-
tially distributed to hydrophobic compartments, such as lipid bilayers of cells,
while hydrophilic drugs (low partition coefficients) are found preferentially in
hydrophilic compartments, such as blood serum. Hydrophobicity/lipophilicity
play a major role in determining where drugs are distributed within the body after
adsorption and as a consequence in how rapidly they are metabolized and ex-
creted. In this context, the presence of a hydrophobic moiety would be important
for such activity. Moreover, many of the proteins involved in drug disposition
have hydrophobic binding sites, further adding to the importance of lipophilicity.
The lipophilicity of compounds, expressed as log P, represents the main pre-
dictor for activity. The octanol/water partition coefficient, Clog P, being a mea-
sure of hydrophobicity/ lipophilicity was calculated using ChemDraw Ultra 11.0
software integrated with Cambridgesoft Software (Cambridgesoft Corpora-
26
tion). The results obtained are given in Table I. The calculated values of log P
for the N’-(arylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides
4a–v were lower than for the corresponding 4-aryl-5-[(2-methyl-1H-benzimida-
zol-1-yl)methyl]-4H-1,2,4-triazole-3-thiols 6a–k. The lipophilic power of the
compounds increased with increasing log P. The activity observed for com-
pounds 6a–k, having higher values of log P was slightly higher than that of the
corresponding compounds 4a–v, which shows that incorporation of triazole nuc-
leus on benzimidazole derivatives did not favor antimicrobial activity.
Regarding the correlation of the antimicrobial activity of substituted benz-
imidazoles with the planarity of their molecules, the ortho-substitution in the
benzene nucleus of the N’-(arylmethylidene)-2-(2-methyl-1H-benzimidazol-1-
-yl)acetohydrazides 4a–v, N-aryl-2-[(2-methyl-1H-benzimidazol-1-yl)acetyl]-
hydrazinecarbothioamides 5a–k and 4-aryl-5-[(2-methyl-1H-benzimidazol-1-
-yl)methyl]-4H-1,2,4-triazole-3-thiols 6a–k generates steric hindrance, hence
they were less active than the corresponding para-substituted derivatives, thereby
showing a marginal steric effect. The molar refractivity (MR), which represents
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SYNTHESIS AND BIOLOGICAL ACTIVITY OF BENZIMIDAZOLE DERIVATIVES
345
the size and polarizability of a molecule describing steric effects, was calculated
(using ChemDraw Ultra 11.0 software) to explain the activity behavior of the
synthesized compounds. From Table I, it can be inferred that a slightly lower
value of the molar refractivity favored the activity ratio.
TABLE I. Calculated log P and molar refractivity of compounds 4a–4v, 5a–5k and 6a–6k
(calculated from ACD/Labs software, v.12.0 (Advanced Chemistry Development, Inc.))
Compound
X
C log P
MR
4a
4b
4c
4d
4e
4f
4g
4h
4i
–
2-CH3
2-CH2CH3
2-CH2CH2CH3
2-OH
2.626
2.858
2.754
3.283
3.225
2.595
2.415
2.845
2.739
3.339
1.999
3.485
3.984
4.513
5.042
2.818
2.818
3.404
3.404
4.198
4.198
2.258
1.978
2.477
3.006
3.535
1.311
1.311
1.897
1.897
2.691
2.691
0.751
3.455
3.954
4.483
5.012
3.160
3.160
85.62
91.58
96.12
100.72
87.44
87.44
92.87
92.87
90.23
90.23
90.45
89.72
95.62
100.21
104.81
91.53
91.53
96.97
96.97
94.32
94.32
94.54
96.49
102.39
106.99
111.59
98.31
98.31
103.74
103.74
101.10
101.10
101.32
93.15
99.05
103.65
108.25
94.97
94.97
4-OH
2-OCH3
4-OCH3
2-Cl
4-Cl
4-NH2
4j
4k
4l
–
4m
4n
4o
4p
4q
4r
4s
4t
4u
4v
5a
5b
5c
5d
5e
5f
2-CH3
2-CH2CH3
2-CH2CH2CH3
2-OH
4-OH
2-OCH3
4-OCH3
2-Cl
4-Cl
4-NH2
–
2-CH3
2-CH2CH3
2-CH2CH2CH3
2-OH
4-OH
5g
5h
5i
2-OCH3
4-OCH3
2-Cl
4-Cl
4-NH2
5j
5k
6a
6b
6c
6d
6e
6f
–
2-CH3
2-CH2CH3
2-CH2CH2CH3
2-OH
4-OH
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ANSARI, LAL and KHITOLIYA
TABLE I. Continued
Compound
X
C log P
MR
6g
6h
6i
6j
6k
2-OCH3
4-OCH3
2-Cl
4-Cl
4-NH2
3.434
3.434
4.171
4.171
2.576
100.4
100.4
97.76
97.76
97.98
Considering the structure of the compounds that exhibit antimicrobial acti-
vity, substituted methylidene and triazole may play a role for the antimicrobial
activity. From the results, which indicated that tested compounds were more ac-
tive against Gram-positive bacteria than Gram-negative bacteria, it may be con-
cluded that the antimicrobial activity of the compounds is related to cell wall
structure of the bacteria. This is possible because the cell wall is essential for the
survival of many bacteria and some antibiotics are able to kill bacteria by inhi-
biting a step in the synthesis of peptidoglycan. Gram positive bacteria possess a
thick cell wall containing many layers of peptidoglycan and teichoic acids, but in
contrast, Gram negative bacteria have a relatively thin cell wall consisting of a
few layers of peptidoglycan surrounded by a second lipid membrane containing
lipopolysachharides and lipoproteins. These differences in cell wall structure can
produce differences in the antibacterial susceptibility and some antibiotics that
can kill only Gram-positive bacteria are ineffective against Gram negative bac-
27
teria.
Antibacterial activity
The results of the preliminary testing of the antibacterial activity of the final
compounds are given in Table II. The results revealed that the majority of the
synthesized compounds show varying degrees of inhibition against the tested
microorganisms. In general, the inhibitory activity against the Gram-positive bac-
teria was higher than against the Gram-negative bacteria. The triazole derivatives
6a–k displayed the lowest activity. Compounds 4a, 4b, 4e, 4f, 4k and 4l showed
excellent activity against the Gram-positive bacteria. None of the compounds
tested in this study displayed any effect against Escherichia coli and Salmonella
typhi and only an insignificant effect against Pseudomonas aeruginosa (except
compound 4a, which showed the same activity as the standard drug against P.
aeruginosa).
The values of the minimum inhibitory concentration (MIC) against the mic-
roorganism susceptible in the preliminary test are reported in Table III. The
results showed significant inhibitory effects, with the majority of the compounds
–1
tested having MIC values of 2–16 µg mL . This class of compounds presented
high activity against Staphylococcus aureus and Bacillus subtilis, especially com-
pounds 4a, 4b, 4f, 4h, 4j, 4l, 4s, 4u, 5f and 5j showed good antibacterial activity
against these two microorganisms. For Streptococcus mutans, these compounds
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SYNTHESIS AND BIOLOGICAL ACTIVITY OF BENZIMIDAZOLE DERIVATIVES
347
–1
were as active as the standard kanamycin (MIC = 4 µg mL ), but less active than
ampicillin. Activity compared to ampicillin was also encountered for 4a, 4f, 4k,
and 4v against B.subtilis and for 4a, 4b, 4f, 4l, 4s, 4v and 5j against P. aeru-
ginosa.
TABLE II. Inhibitory zone diameter of compounds against bacterial strains using the disc dif-
fusion method (Sa – S. aureus, Bs – B. subtilis, Sm – S. mutans, Ec – E. coli, Pa – P. aerugi-
nosa and St – S. typhi)
Mean zone inhibition, mma
Compd.
Gram-positive bacteria
Gram-negative bacteria
Sa
35
33
28
24
35
24
33
27
30
35
33
29
22
21
28
24
28
29
24
28
25
29
18
24
20
24
21
38
NT
Bs
25
24
23
23
25
19
28
18
25
–
Sm
Ec
–
–
Pa
18
16
17
14
17
13
16
12
16
16
16
16
15
14
17
–
17
17
10
16
14
17
–
St
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
NT
20
b
4a
20
19
18
16
19
15
18
14
20
16
19
17
16
16
18
15
18
20
–
17
17
19
–
20
12
18
18
22
NT
4b
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4p
4r
4s
4t
4u
4v
5a
5b
5d
5f
5g
5j
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
20
28
23
20
20
–
24
18
22
24
18
24
21
24
20
18
18
19
18
28
NT
15
10
12
16
NTd
18
6b
6f
6h
Ampicillinc
Nalidixic acidc
an = 3; indicates no sensitivity or mean inhibition zone diameter less than 7 mm; campicillin (10 µg/disc) and
b
nalidixic acid (30 µg/disc) used as positive reference, synthesized compounds, 300 µg/disc; dnot tested
Antifungal activity
The in vitro antifungal activities of the derivatives of N’-(arylmethylidene)-
-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazide (4a–v), N-aryl-2-[(2-methyl-
1H-benzimidazol-1-yl)acetyl]hydrazinecarbothioamide (5a–k) and 4-aryl-5-[(2-
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ANSARI, LAL and KHITOLIYA
-methyl-1H-benzimidazol-1-yl)methyl]-4H-1,2,4-triazole-3-thiol (6a–k) and of
amphotericin B as a reference drug on three fungi species are given in Table IV.
Some of the compounds tested were endowed with a good activity against Can-
dida albicans. Of these, 2-(2-methyl-1H-benzimidazol-1-yl)-N’-(phenylmethyl-
idene)acetohydrazide 4a and N’-[1-(4-aminophenyl)ethylidene]-2-(2-methyl-1H-
-benzimidazol-1-yl)acetohydrazide (4v) were found to be the most potent, show-
–1
ing an MIC value 4 µg mL , whereas the MIC value for compounds 4b, 4f, 4i,
–1
4k, 4v and 5a was 8 µg mL (Table III). Compounds with a para-substitution in
the benzene ring (4a, 4b, 4d, 4f, 4j, 4k, 4s, 4u, 5d and 5j) were also found to be
potent against Aspergillus flavus (inhibition zone 18–22 mm) with medium acti-
vity. All the other tested compounds exhibited insignificant chemotherapeutical
activity against the tested microorganism.
TABLE III. Antimicrobial activity of tested compounds expressed as MIC in µg mL-1 (Sa – S.
aureus, Bs – B. subtilis, Sm – S. mutans, Pa – P. aeruginosa and Ca – C. albicans)
Compd.
Sa
Bs
Sm
Pa
Ca
4a
4b
4d
4e
4
8
16
16
4
4
8
16
16
4
4
4
16
16
4
8
8
4
8
32
NT
8
NTa
16
8
4f
4g
4h
4i
4j
4k
4l
4m
4p
4r
4s
4t
4u
16
16
8
16
4
NT
8
8
32
4
8
16
16
32
8
NT
8
32
4
16
4
8
4
16
4
16
16
16
8
NT
32
16
8
16
16
8
32
16
8
16
8
16
16
32
16
16
NT
8
4
8
8
NT
16
8
16
8
16
16
4
32
4
4v
8
4
4
4
5a
5b
5d
5f
5g
5j
6b
6f
8
8
16
4
32
4
NT
8
8
2
2
16
16
16
8
32
8
NT
16
16
2
≤1
NT
8
8
8
4
64
4
16
16
32
≤1
4
16
32
16
NT
32
8
16
16
32
4
8
16
16
16
16
NT
32
NT
32
NT
NT
2
6h
Ampicillin
Kanamycin
Amphotericin B
2
NT
NT
NT
aNot tested
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SYNTHESIS AND BIOLOGICAL ACTIVITY OF BENZIMIDAZOLE DERIVATIVES
349
TABLE IV. Inhibitory zone of compounds against fungal strains using the disc diffusion me-
thod (Ca – C. albicans, An – A. niger and Af – A. flavus)
Mean zone of inhibition, mm (n = 3)
Compd.
Ca
28
24
22
20
24
–
25
16
18
26
24
–
18
12
18
12
18
28
18
17
15
16
12
16
17
18
18
28
An
24
23
22
20
22
–
10
14
23
22
20
13
17
14
24
14
18
20
–
10
22
18
12
20
14
14
16
32
Af
18
20
22
4a
4b
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4p
4r
4s
4t
4u
4v
5a
5b
5d
5f
5g
5j
a
–
22
10
12
–
20
22
17
15
10
13
18
–
18
–
12
12
20
12
10
22
10
10
15
28
6b
6f
6h
Amphotericin Bb
aNo sensitivity or mean inhibition zone diameter lower than 7 mm; bamphotericin B (30µg/disc) used as positi-
ve reference; synthesized compounds: 300µg/disc
EXPERIMENTAL
All melting points were determined in an open capillary tube and are uncorrected. Infra-
red spectra were recorded in KBr on Perkin-Elmer RX1 spectrophotometer. The 1H-NMR and
13C-NMR spectra were measured in CDCl3 solutions on a Bruker DRX-300 MHz spectro-
meter using TMS as an internal reference (chemical shift in δ / ppm). The mass spectra were
recorded on a Jeol SX-102 instrument. Elemental analyses were realized using an Elementar
Vario EL III elemental analyzer. Thin layer chromatography was performed on silica plates
pre-coated with Merck Silica Gel 60 F254 and column chromatography with silica gel.
Synthesis of N’-(arylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazides 4a–v
General procedure. An equimolar (0.001 mol) mixture of compound 3 and substituted
arylaldehyde or substituted acetophenone in absolute ethanol (50 ml) containing 2–3 drops of
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350
ANSARI, LAL and KHITOLIYA
glacial acetic acid was refluxed for 5 h and the solvent removed. The separated solid was fil-
tered and recrystallized from a suitable solvent to give compounds 4a–v.
Synthesis of N-aryl-2-[(2-methyl-1H-benzimidazol-1-yl)acetyl]hydrazinecarbothioamides 5a–k
General procedure. To a boiling solution of compound 3 (0.001 mol) in absolute ethanol
(30 ml) was added an appropriate substituted phenyl isothiocyanate (0.001 mol) and the reac-
tion mixture was refluxed for 1 h, concentrated and cooled. The separated solid was filtered
and recrystallized from an appropriate solvent to give 5a–k.
Synthesis of 4-aryl-5-[(2-methyl-1H-benzimidazol-1-yl)methyl]-4H-1,2,4-triazole-3-thiols 6a–k
General procedure. A solution of compound 5 (0.001 mol) in 2 M NaOH (20 ml) was re-
fluxed for 4 h, cooled, poured into ice cold water (50 ml) and neutralized with acetic acid. The
precipitate was filtered, washed with water and recrystallized from an appropriate solvent to
afford compounds 6a–k.
Antimicrobial activity test
All the synthesized compounds 4a–v and 6a–k were screened for their in vitro antimicro-
bial activity against the standard strains: Staphylococcus aureus (ATCC 29213), Bacillus sub-
tilis (MTCC 121), Streptococcus mutans (MTCC 890), Escherichia coli (ATCC 25922), Pseu-
domonas aeruginosa (MTCC 741) and Salmonella typhi (MTCC 733) and the fungi Candida
albicans (MTCC 1637), Aspergillus flavus (AIIMS) and Aspergillus niger (AIIMS).
The preliminary antimicrobial activity was reported using the disc diffusion method.28 In
this method, paper discs (6 mm) containing specific amounts of an antimicrobial agent (300
µg for the synthesized compounds) were placed on the surface of an agar plate inoculated with
a standardized suspension of the tested microorganisms. The plates were incubated at 35 °C
for 24 and 48 h, respectively, for the bacteria and fungi. Amphotericin B (30 µg) for the fungi,
ampicillin (10 µg) for the Gram-positive bacteria and nalidixic acid (30 µg) for the Gram-ne-
gative bacteria were used as standard drugs. Paper discs with only dimethyl sulfoxide (DMSO)
were utilized as the negative control.
The twofold serial dilution technique29,30 was followed to determine the MIC of the com-
pounds against the microorganisms susceptible in the preliminary tests (Gram positive bacte-
ria and fungi). The test compounds were dissolved in DMSO and then diluted with culture
medium (Mueller–Hinton agar medium for the bacteria and Sabouraud liquid medium for the
fungi), at the required final concentration, within the range 128–1.0 µg mL-1. A plate for the
bacteria and a tube for the fungi containing only culture medium and DMSO, in the same dilu-
tion as in the experiments, were used as negative controls.
The final amount applied was of 104 CFU/plate for the bacteria and 103 CFU/tube for the
fungi. The MIC values were read after incubation at 35 °C for a period of 20 (bacteria) and 48
h (fungi). The lowest concentration of the test substance that completely inhibited growth of
the microorganism was recorded as the MIC, expressed in µg mL-1. Ampicillin and kanamy-
cin for the bacteria and amphotericin B for the fungi were used as standard drugs. All expe-
riments were performed in triplicate.
CONCLUSIONS
In conclusion, several benzimidazole derivatives were synthesized starting
with 2-methylbenzimidazole. A microbiological study was undertaken to eva-
luate the effect of the synthesized compounds on different bacteria and fungal
strains. With regards to the structure–activity relationship of the derivatives of
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SYNTHESIS AND BIOLOGICAL ACTIVITY OF BENZIMIDAZOLE DERIVATIVES
351
N’-(arylmethylidene)-2-(2-methyl-1H-benzimidazol-1-yl)acetohydrazide 4a–v,
N-aryl-2-[(2-methyl-1H-benzimidazol-1-yl)acetyl]hydrazinecarbothioamide 5a–k
and 4-aryl-5-[(2-methyl-1H-benzimidazol-1-yl)methyl]-4H-1,2,4-triazole-3-thiol
6a–k, the group with a substituent on para-position exhibited enhanced anti-
microbial activity in comparison to ortho-substitution on the same ring. More-
over, para substituted hydroxy and chloro derivatives produced activity equal to
that of ampicillin for S. aureus. Similarly, in the case of the antifungal activity,
para hydroxy and para chloro substituted derivatives were proved to be the most
active compounds and their activity was equal to that of amphotericin B. These
differences in activity depended on the substitution of different reactive group on
the benzimidazole moiety. Based on the observations, it may be concluded that
the order of inhibitory effect against S. aureus was influenced by the type of
substitution present at para position, i.e., the derivatives with chloro and hyd-
roxyl groups showed maximum activity in comparison to those with a methyl
group, which in turn were more reactive than the methoxy derivatives.
More extensive studies are required to confirm these preliminary results and
studies involving the mechanism of action are necessary for a complete under-
standing of their antimicrobial activity, as well as structural modifications on the
final investigated compounds to improve their biological activity.
SUPPLEMENTARY MATERIAL
The physical, analytical and spectral data of synthesized compounds are available elec-
tronically from http://www.shd.org.rs/JSCS/, or from the corresponding author on request.
Acknowledgement. The authors are thankful to the Head, RSIC, Central Drug Research
Institute, Lucknow, India, for providing the spectral and analytical data of the compounds.
Authors are thankful to the University Grants Commission, New Delhi, India, for providing fi-
nancial grant vide F. No. 37-494/2009 (SR).
И З В О Д
СИНТЕЗА И БИОЛОШКА АКТИВНОСТ НЕКИХ ТРИАЗОЛСКИХ ДЕРИВАТА КОЈИ
САДРЖЕ БЕНЗИМИДАЗОЛНИ СТРУКТУРНИ СЕГМЕНТ
K. F. ANSARI, C. LAL и R. K. KHITOLIYA
Department of Chemistry, Harcourt Butler Technological Institute, Kanpur – 208002, India
Синтетисани су бројни деривати N’-(супституисани фенилметилиден)-2-(2-метил-1H-
-бензимидазол-1-ил)ацетохидразида и 4-(супституисани фенил)-5-[(2-метил-1H-бензимида-
зол-1-ил)метил]-4H-1,2,4-триазол-3-тиола који садрже различите ароматичне и хетероаро-
матичне супституенте на 2-метил-1H-бензимидазолу. Структуре синтетисаних једињења ут-
врђене су на основу елементалне анализе и спектралних података. Испитане су in vitro ак-
тивности једињења према бактеријама и гљивама диск-дифузионом методом и методом ми-
нималних инхибиторних концентрација. Нека од испитиваних једињења активна су у истој
мери као и стандардни лек канамицин.
(Примљено 1. марта 2010)
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352
ANSARI, LAL and KHITOLIYA
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