Synthesis, physicochemical properties and antimicrobial activity of some new benzimidazole derivatives

Article abstract of DOI:10.1016/j.ejmech.2009.04.037

Some derivatives of benzimidazole were synthesized by nucleophilic substitution of 2-substituted-1H-benzimidazole. The resulting ethyl (2-substituted-1H-benzimidazol-1-yl) acetate on treatment with hydrazine hydrate yielded 2-(2-substituted-1H-benzimidazol-1-yl) acetohydrazide, which on further reaction with one equivalent of different aliphatic or aromatic carboxylic acids in the presence of phosphoryl chloride afforded the corresponding target compounds, 2-substituted-1-[{(5-substituted alkyl/aryl)-1,3,4-oxadiazol-2-yl} methyl]-1H-benzimidazole. The structures of the synthesized compounds were evaluated by spectral and elemental methods of analyses. All the synthesized compounds were screened for their antimicrobial activities. All of the derivatives showed good activity towards Gram-positive bacteria and negligible activity towards Gram-negative bacteria. Some of the synthesized compounds showed moderate activity against tested fungi.

Full text of DOI:10.1016/j.ejmech.2009.04.037

European Journal of Medicinal Chemistry 44 (2009) 4028–4033
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, physicochemical properties and antimicrobial activity
of some new benzimidazole derivatives
*
K.F. Ansari, C. Lal
Department of Chemistry, Harcourt Butler Technological Institute, Nawabganj, Kanpur 208002, Uttar Pradesh, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Some derivatives of benzimidazole were synthesized by nucleophilic substitution of 2-substituted-1H-
benzimidazole. The resulting ethyl (2-substituted-1H-benzimidazol-1-yl) acetate on treatment with
hydrazine hydrate yielded 2-(2-substituted-1H-benzimidazol-1-yl) acetohydrazide, which on further
reaction with one equivalent of different aliphatic or aromatic carboxylic acids in the presence of
phosphoryl chloride afforded the corresponding target compounds, 2-substituted-1-[{(5-substituted
alkyl/aryl)-1,3,4-oxadiazol-2-yl} methyl]-1H-benzimidazole. The structures of the synthesized
compounds were evaluated by spectral and elemental methods of analyses. All the synthesized
compounds were screened for their antimicrobial activities. All of the derivatives showed good activity
towards Gram-positive bacteria and negligible activity towards Gram-negative bacteria. Some of the
synthesized compounds showed moderate activity against tested fungi.
Received 3 September 2008
Received in revised form
16 April 2009
Accepted 23 April 2009
Available online 5 May 2009
Keywords:
Benzimidazole
Antimicrobial activity
Antifungal activity
Lipophilicity
Ó 2009 Elsevier Masson SAS. All rights reserved.
1,3,4-Oxadiazole
1. Introduction
derivatives bearing oxadiazole moiety and screen them for poten-
tial biological activities. We have previously reported the synthesis
Benzimidazoles are remarkably effective compounds both with
respect to their inhibitory activity and their favorable selectivity
ratio. Extensive biochemical and pharmacological studies have
confirmed that benzimidazole molecules are effective against
various strains of microorganisms [1–8]. Benzimidazoles are
regarded as a promising class of bioactive heterocyclic compounds
that exhibit a range of biological activities. Specifically, this nucleus
is a constituent of vitamin-B12 [9]. This ring system is present in
numerous antioxidant [10–12], antiparasitic [13,14], antihelmintics
[15], antiproliferative [16], anti-HIV [17], anticonvulsant [18], anti-
inflammatory [19–22], antihypertensive [23,24], antineoplastic
[25,26], and antitrichinellosis [27] activities. Owing to the immense
importance and varied bioactivities exhibited by benzimidazoles,
efforts have been made from time to time to generate libraries of
these compounds and screened them for potential biological
activities. Also it is well documented that oxadiazole nucleus is
associated with a variety of pharmacological actions [28,29]. It
displays pronounced anticonvulsant [30], antifungal [31] and
antimycobacterial [32] activities. Looking at the importance of
benzimidazole and oxadiazole nucleus, it was thought that it would
be worthwhile to design and synthesize some new benzimidazole
of some new biologically active benzimidazoles [33]. In continua-
tion of our work on biologically active benzimidazoles, we have
synthesized some 1-{[5-(alkyl/aryl)-1,3,4-oxadiazol-2-yl]methyl}-
2-alkyl-1H-benzimidazoles for their antimicrobial activities.
2. Results and discussion
2.1. Chemistry
The reaction sequence for different title compounds is outlined in
Scheme 1. The starting material 2-substituted-1H-benzimidazole 2
was prepared according to a reported procedure through the reac-
tion of o-phenylenediamine with appropriate carboxylic acid [34].
Structure of compound 2 was confirmed by comparison of its
physical and spectral data with the reported ones [35]. Nucleophilic
substitution of compound 2 yielded ethyl (2-substituted-1H-benzi-
midazol-1-yl) acetate 3. The structure of compound 3 was confirmed
by its IR, 1H NMR as well as elemental analysis. The IR spectra of
compound 3a showed broad band at 1745 cmꢀ1 (–C]O ester) and at
1632 cmꢀ1 (–C]N).1H NMR spectra revealed the multiplet at
d 7.72–
7.90 corresponding to the four aromatic protons. Mass spectrum of
compound 3b revealed the molecular ion peak Mþ at m/z 218
(R ¼ Me) (100%), corresponding to molecular mass of this compound.
Compound 3 on treatment with hydrazine hydrate resulted in the
* Corresponding author. Tel.: þ91 9450333851; fax: þ91 512 2533812.
E-mail address: c_lal12@rediffmail.com (C. Lal).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.04.037

K.F. Ansari, C. Lal / European Journal of Medicinal Chemistry 44 (2009) 4028–4033
4029
Scheme 1. Synthesis of benzimidazole derivatives.
formation
drazide 4. IR spectrum of compound 4a showed a broad band at
1682 cmꢀ1 (–C]O amide) and C]N stretching at 1640 cmꢀ1
Compound 4 on treatment with different aliphatic or aromatic
carboxylic acids in the presence of phosphoryl chloride yielded the
2-methyl-1-[(5-substituted-1,3,4-oxadiazol-2-yl)methyl]-1H-benz-
imidazole 5–26. All the spectral data of compounds 2a, 2b, 3a, 3b, 4a,
4b and 5–26 were in accordance with assumed structures. The purity
of the synthesized compounds was monitored by TLC. Physical and
analytical data of compounds 5–26 are shown in Table 1.
of
2-(2-substituted-1H-benzimidazol-1-yl)acetohy-
Bacillus subtilis (MTCC 121) and Streptococcus mutans (MTCC 890)
and Gram-negative bacteria including Escherichia coli (ATCC 25922),
Pseudomonas aeruginosa (MTCC 741) and Salmonella typhi (MTCC
733). Yeast including Candida albicans (MTCC 1637), and fungi
Aspergillus flavus (AIIMS) and Aspergillus niger (AIIMS) were used to
test the antifungal activity. To evaluate the activity of synthesized
compounds against bacteria minimum inhibitory concentrations
(MICs) were determined and for yeast and fungi zone of inhibition
was determined. Known antibiotics like Ciprofloxacin and Ampi-
cillin (the reference antibacterial drugs) and Amphotericin B (the
reference antifungal drug) were used for comparison.
.
By comparing the antimicrobial activity of the synthesized
compounds, it was found that the tested compounds are more
effective against the Gram-positive bacteria. It is believed that the
strong lipophilic character of the molecule plays an essential role in
2.2. Antimicrobial evaluation
The in vitro antibacterial activity was performed against Gram-
positive bacteria including Staphylococcus aureus (ATCC 29213),
Table 1
Physical and analytical data of compounds 5–26.
Compounds
R
R1
Yield (%)
M.p. (ꢁC)
Mol. formula
Analysis % calculated (Found)
C
H
N
5
6
7
8
H
H
H
H
H
H
H
H
–CH3
–C2H5
–CH2Cl
–CH2CH2Cl
–C6H5
2-ClC6H4
4-ClC6H4
2-OHC6H4
4-OHC6H4
2-OCH3C6H4
4-OCH3C6H4
–CH3
–C2H5
–CH2Cl
–CH2CH2Cl
–C6H5
2-ClC6H4
4-ClC6H4
2-OHC6H4
4-OHC6H4
2-OCH3C6H4
4-OCH3C6H4
79
81
76
87
80
83
80
84
88
72
71
84
68
75
69
77
81
75
76
65
79
82
181–83
187–89
176–78
172–74
176–78
197–99
165–67
166–68
158–60
153–55
167–69
178–80
167–69
194–99
172–74
191–93
182–84
174–76
156–58
150–52
178–80
167–69
C11H10N4O
61.67 (61.65)
63.15 (63.12)
53.13 (53.11)
54.87 (54.84)
69.55 (69.52)
61.84 (61.81)
61.84 (61.81)
65.75 (65.72)
65.75 (65.73)
66.66 (66.63)
66.66 (66.64)
63.15 (63.12)
64.45 (64.42)
54.87 (54.84)
56.42 (56.40)
70.33 (70.30)
62.87 (62.84)
62.87 (62.85)
66.66 (66.63)
66.66 (66.63)
67.49 (67.46)
67.49 (67.47)
4.71 (4.69)
5.30 (5.28)
3.65 (3.64)
4.22 (4.20)
4.38 (4.35)
3.57 (3.56)
3.57 (3.54)
4.14 (4.12)
4.14 (4.11)
4.61 (4.59)
4.61 (4.59)
5.30 (5.28)
5.82 (5.81)
4.22 (4.20)
4.74 (4.72)
4.86 (4.83)
4.03 (4.00)
4.03 (4.01)
4.61 (4.60)
4.61 (4.59)
5.03 (5.02)
5.03 (5.01)
26.15 (26.12)
24.55 (24.52)
22.53 (22.51)
21.33 (21.30)
20.28 (20.26)
18.03 (18.02)
18.03 (18.00)
19.17 (19.15)
19.17 (19.16)
18.29 (18.26)
18.29 (18.26)
24.55 (24.53)
23.13 (23.11)
21.33 (21.30)
20.25 (20.22)
19.30 (19.27)
17.25 (17.23)
17.25 (17.22)
18.29 (18.26)
18.29 (18.27)
17.49 (17.48)
17.49 (17.47)
C12H12N4O
C11H9N4OCl
C12H11N4OCl
C16H12N4O
C16H11N4OCl
C16H11N4OCl
C16H12N4O2
C16H12N4O2
C17H14N4O2
C17H14N4O2
C12H12N4O
C13H14N4O
C12H11N4OCl
C13H13N4OCl
C17H14N4O
C17H13N4OCl
C17H13N4OCl
C17H14N4O2
C17H14N4O2
C18H16N4O2
C18H16N4O2
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
H
H
H
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3
–CH3

4030
K.F. Ansari, C. Lal / European Journal of Medicinal Chemistry 44 (2009) 4028–4033
Table 3
producing antimicrobial effect. These properties are seen as an
important parameter related to membrane permeation in biolog-
ical system. Many of the processes of drug disposition depend on
the capability to cross membranes and hence there is a high
correlation with measures of lipophilicity. Hydrophobic drugs
with high partition coefficients are preferentially distributed to
hydrophobic compartments such as lipid bilayers of cells while
hydrophilic drugs (low partition coefficients) preferentially are
found in hydrophilic compartments such as blood serum. Hydro-
phobicity/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 excreted. In
this context the presence of the 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 the compounds, expressed as log P, explains
the main predictor for the activity. The octanol/water partition
coefficient C log P being a measure of hydrophobicity/lipophilicity
was calculated using ChemDraw Ultra 11.0 software integrated
with Cambridgesoft Software (Cambridgesoft Corporation) [36].
The results obtained are given in Table 2. The calculated values of
log P for 2-methyl-1-(1,3,4-oxadiazol-2-ylmethyl)-1H-benzimid-
azole derivatives 16–26 were about 0.27 higher than for the cor-
Antibacterial activity of compounds 5–26 (MIC in mg/mL).
Compounds
Microorganisms
S. aureus B. subtilis S. mutans E. coli P. aeruginosa S. typhi
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
16
32
16
16
16
32
32
32
NT
16
16
4
16
32
32
16
16
16
32
NT
16
16
32
4
16
16
16
NT
32
16
16
NT
32
NT
16
8
16
16
NT
NT
64
>128
>128
32
32
NT
32
64
64
64
>128
32
NT
16
NT
NT
32
16
32
>128
16
64
>128 NT
32
64
32
32
64
64
32
16
32
32
NT
64
64
>128
32
64
>128
NT
NT
NT
4
16
4
8
16
8
4
32
8
8
8
8
21
22
23
24
25
26
NT
2
NT
8
8
2
NT
4
16
8
4
8
16
4
8
4
8
4
2
NT
>128 NT
>128 NT
32
NT
32
NT
16
16
32
NT
>128 NT
64
16
4
ꢂ1
64
64
>128
NT
Ampicillin
Ciprofloxacin ꢂ1
2
2
ꢂ1
>128
NT
responding
1-(1,3,4-oxadiazol-2-ylmethyl)-1H-benzimidazole
NT ¼ Not tested.
derivatives. The lipophilic power of compounds increased with
increasing log P. The activity observed for compounds 16–26,
having higher values of log P was slightly higher than that of the
corresponding compounds 5–15 having no methyl group at C-2
position of benzimidazole.
Regarding the correlation of the antimicrobial activity of
substituted benzimidazoles with the planarity of their molecules,
the ortho-substitution on benzene ring of 2-substituted-1-
(1,3,4-oxadiazol-2-ylmethyl)-1H-benzimidazole generates steric
hindrance, hence it is less active than the corresponding para-
substitution on same nucleus which shows marginal steric effect.
The molar refractivity (MR), which represents size and polariz-
ability 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 2, it can be inferred that
the higher value of molar refractivity favors the activity ratio.
The values of the MIC against microorganisms tested are
reported in Table 3. The investigations showed significant inhibi-
tory effects, with the majority of the compounds with the
MIC values 4–64
mg/mL. The antibacterial data indicated that
1-{[5-(4-chlorophenyl)-1,3,4-oxadiazol-2-yl]methyl}-2-methyl-1H-
benzimidazole 22 and 1-{[5-(4-methoxyphenyl)-1,3,4-oxadiazol-2-
yl]methyl}-2-methyl-1H-benzimidazole 26 illustrated appreciable
antibacterial activity (MIC 2 mg/mL) against S. aureus. All the
synthesized compounds showed significant antibacterial activity
against all the Gram-positive strains of bacteria. Among them
Table 2
Calculated log P and molar refractivity of compounds 3a, b, 4a, b and 5–26.
Compounds
C log P
MR
Table 4
3a
3b
4a
4b
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
1.88
2.15
ꢀ0.12
0.15
0.07
0.59
0.36
0.31
1.89
2.39
2.64
1.21
1.52
1.41
1.97
0.34
0.87
0.63
0.58
2.16
2.66
2.91
1.49
1.79
1.68
2.24
55.96
60.34
52.54
56.92
60.24
64.87
64.76
69.36
80.92
85.52
85.52
82.73
82.73
88.14
88.17
64.65
69.25
69.14
73.74
85.30
89.90
89.90
87.11
87.11
92.55
92.55
Antifungal activity of compounds 5–26.
Compoundsa
Microorganisms
C. albicans
A. niger
A. flavus
5
6
7
8
14
15
16
17
18
19
21
22
24
25
26
þþ
þ
þþ
ꢀ
þþ
þ
þþ
þþ
þþ
þþ
þþþ
þþ
þ
þ
þ
þþ
ꢀ
þ
ꢀ
ꢀ
ꢀ
þþ
þ
þþ
þþ
þ
þþ
þ
þþ
þþ
þþþ
þþþ
þþ
þþþ
þþþ
þ
þþ
þ
þþ
þþþ
þþ
þþ
þþ
þþþ
þþ
þþ
þþ
þþþ
Amphotericin Ba
Symbols: zone diameter of growth inhibition: (ꢀ) ¼ inactive (<10 mm);
(þ) ¼ weakly active (10–15 mm); (þþ) ¼ moderately active (16–21 mm);
(þþþ) ¼ highly active (22–28 mm); (þþþ) ¼ amphotericin B.
a
Amphotericin
B
(10
mg/disc) was used as positive reference; synthesized
compounds (300
mg/disc).

K.F. Ansari, C. Lal / European Journal of Medicinal Chemistry 44 (2009) 4028–4033
4031
compounds 16, 17, 19, 20, 22, 24, 25 and 26 were found to be more
potent. As shown in Table 3, none of the compounds have inhibitory
effect against E. coli. Less activity was noted against P. aeruginosa
and S. typhi. According to the investigations, 2-methyl benzimid-
azole derivatives having para-substituted benzene ring on oxadia-
zole moiety yielded increased activity.
The in vitro antifungal activity of the derivatives of 2-methyl-1-
(1,3,4-oxadiazol-2-ylmethyl)-1H-benzimidazole 5–15 and 1-(1,3,4-
oxadiazol-2-ylmethyl)-1H-benzimidazole 16–26 is characterized in
Table 4. Some of the synthesized compounds tested were endowed
with a medium activity against A. flavus. Of these, 1-{[5-(4-chlor-
ophenyl)-1,3,4-oxadiazol-2-yl]methyl}-2-methyl-1H-benzimidazole
22 was found to be most potent. The compounds with para-
substitution on the benzene ring of 1-{[5-(4-substituted phenyl)-
1,3,4-oxadiazol-2-yl]methyl}-2-methyl-1H-benzimidazole (22, 24
and 26) also showed better activity against C. albicans. For A. niger,
the tested compounds showed low to moderate antifungal activity.
The compounds which have no antifungal activity are not included
in the table.
IR (KBr): 1148 (–C–N), 1670 (–C]N ester) cmꢀ1; 1H NMR (CDCl3)
d
ppm: 2.51 (s, 3H, –CH3), 5.0 (s, 1H, –NH), 7.22–7.59 (m, 4H, Ar–H);
EI-MS: 119 (Mþ þ 1).
4.1.2. Synthesis of 2-methyl-1H-benzimidazole (2b)
Heat together the mixture of 0.03 mol of o-phenylenediamine
dihydrochloride, 20 mL of water and 0.09 mol of acetic acid under
reflux for 45 min, make the cooled reaction mixture distinctly basic
by gradual addition of conc. ammonia solution, collect the precip-
itate product and recrystallized it from 10% aqueous ethanol. Yield
60%, mp 176–178 ꢁC (Found: C, 72.68; H, 6.08; N, 21.17. Calcd for
C8H8N2: C, 72.70; H, 6.10; N, 21.20%).
IR (KBr): 1150 (–C–N), 1675 (–C]N ester) cmꢀ1; 1H NMR (CDCl3)
d
ppm: 2.51 (s, 3H, –CH3), 5.0 (s, 1H, –NH), 7.22–7.59 (m, 4H, Ar–H);
EI-MS: 133 (Mþ þ 1).
4.1.3. Synthesis of ethyl 1H-benzimidazol-1-ylacetate (3a)
A mixture of equimolar alkaline solution (0.5 mL, 4 N NaOH) of
1H-benzimidazole 2a (0.01 mol, 1.18 g) in MeOH (50 mL) and eth-
ylchloroacetate (0.01 mol, 1 mL) in MeOH (30 mL) was heated
gently on boiling water bath for 0.5 h. The solid thus obtained on
cooling was recrystallized from chloroform to give 3a. Yield 76%,
mp 178–180 ꢁC (Found: C, 64.67; H, 5.91; N, 13.70. Calcd for
C11H12N2O2: C, 64.69; H, 5.92; N, 13.72%).
3. Conclusions
In conclusion, several substituted 2-substituted-1-[{(5-subst
ituted alkyl/aryl)-1,3,4-oxadiazol-2-yl} methyl]-1H-benzimidazoles
5–26 were synthesized. The pharmacological study was undertaken
to evaluate the effects of substituents on the antibacterial and anti-
fungal activities. All the synthesized compounds exhibited good
antibacterial activity towards Gram-positive bacteria and some of
the synthesized compounds showed good to moderate antifungal
activity. These compounds however did not show any promising
activity towards Gram-negative bacteria. In conclusion, antimicro-
bial activity of the synthesized compounds increases with increasing
log P and molar refractivity. From Tables 2–4, it can be inferred that
as the number of carbon atom increases in side chain at 2-position of
oxadiazole heterocyclic ring causes an increase in the intensity of the
activity against S. aureus, B. subtilis and C. albicans and also the para-
substitution on benzene nucleus at oxadiazole moiety supports the
chemotherapeutic activity.
IR (KBr): 1632 (–C]N), 1150 (–C–N), 1745 (–C]O ester), 1460
(–N–CH2) cmꢀ1; 1H NMR (CDCl3)
d ppm: 3.70 (s, 2H, –N–CH2), 4.21
(q, 2H, –COOCH2CH3), 1.32 (t, 3H, –COOCH2CH3), 8.50 (s, 1H,
–N]CH), 7.72–7.90 (m, 4H, Ar–H); EI-MS: 205 (Mþ þ 1).
4.1.4. Synthesis of ethyl (2-methyl-1H-benzimidazol-1-yl)acetate (3b)
Ethylchloroacetate (0.01 mol, 1.06 mL) was added to a solution
of 2-methyl-1H-benzimidazole (0.01 mol, 1.32 g) in dry acetone
(20 mL). To that mixture, anhydrous K2CO3 (1 g) was added and the
reaction mixture was refluxed for 10 h. Acetone was removed after
completion of reaction and the residue crystallized from ethanol to
give compound 3b. Yield 78%, mp 184–186 ꢁC (Found: C, 66.01; H,
6.45; N, 12.81. Calcd for C12H14N2O2: C, 66.04; H, 6.47; N, 12.84%).
IR (KBr): 1624 (–C]N), 1145 (–C–N), 1730 (–C]O ester), 1455
(–N–CH2), 2850 (–C–CH3) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.67
4. Experimental section
(s, 2H, –N–CH2), 4.24 (q, 2H, –COOCH2CH3), 1.26 (t, 3H,
–COOCH2CH3), 2.25 (s, 3H, –CH3), 7.75–7.94 (m, 4H, Ar–H); EI-MS:
219 (Mþ þ 1).
All melting points were determined in open capillary tube and
are uncorrected. Infrared spectra were recorded in KBr on Perkin–
Elmer RX1 spectrophotometer. The 1H NMR spectra were
measured in dimethyl sulfoxide-d6 or CDCl3 solutions on a Brucker
400 MHz spectrometer using TMS as an internal reference
4.1.5. Synthesis of 2-(2-substituted-1H-benzimidazol-1-yl)
acetohy-drazides (4a) and (4b)
General method. To a solution of compounds 3a and 3b
(0.01 mol) dissolved in dry methanol (50 mL) 99% hydrazine
hydrate (1 mL) was added and the mixture was refluxed for 4–5 h.
The reaction mixture was cooled and the solid obtained was
filtered, washed with small quantity of cold methanol to give 4a
and 4b respectively.
(chemical shift in d ppm). The mass spectra were recorded on a Jeol
SX-102 instrument. All the synthesized compounds were micro-
analyzed satisfactorily for C, H and N by Elementar Vario EL III
elemental analyzer.
4.1. Methods of synthesis
4.1.5.1. 2-(1H-Benzimidazol-1-yl)acetohydrazide (4a). Yield 80%,
mp 200–202 ꢁC (Found: C, 56.82; H, 5.29; N, 29.43. Calcd for
C9H10N4O: C, 56.83; H, 5.30; N, 29.46%).
4.1.1. Synthesis of 1H-benzimidazole (2a)
Take 0.24 mol of o-phenylenediamine in round-bottomed flask
and add 0.48 mol of 90% formic acid. Heat the mixture on water
bath at 100 ꢁC for 2 h. Cool, add 10% NaOH solution slowly with
constant rotation of the flask until the mixture is just alkaline to
litmus. Filter out the crude benzimidazole at the pump, wash with
ice-cold water. Dissolve the crude product in 400 mL of boiling
water, add 2 g of decolourizing carbon and digest for 15 min, filter,
cool the filtrate to about 10 ꢁC, filter off the benzimidazole, wash
with 25 mL of cold water and dry at 100 ꢁC. Yield 85%, mp
171–173 ꢁC (Found: C, 71.15; H, 5.10; N, 23.70. Calcd for C7H6N2:
C, 71.17; H, 5.12; N, 23.71%).
IR (KBr): 1640 (–C]N), 1122 (–C–N), 1682 (–C]O amide), 1461
(–N–CH2) cmꢀ1; 1H NMR (CDCl3)
d ppm: 3.66 (s, 2H, –N–CH2), 8.45
(s, 1H, –N]CH), 8.10 (m, 3H, –CONHNH2), 7.60–8.00 (m, 4H, Ar–H);
EI-MS: 191 (Mþ þ 1).
4.1.5.2. 2-(2-Methyl-1H-benzimidazol-1-yl)acetohydrazide (4b).
Yield 77%, mp 248–250 ꢁC (Found: C, 58.79; H, 5.90; N, 27.40. Calcd
for C10H12N4O: C, 58.81; H, 5.92; N, 27.43%).
IR (KBr): 1635 (–C]N), 1130 (–C–N), 1775 (–C]O amide), 1457
(–N–CH2), 2862 (–C–CH3) cmꢀ1; 1H NMR (CDCl3)
d ppm: 3.70 (s, 2H,

4032
K.F. Ansari, C. Lal / European Journal of Medicinal Chemistry 44 (2009) 4028–4033
–N–CH2), 2.25 (s, 3H, –CH3), 8.05 (m, 3H, –CONHNH2), 7.70–8.05
4.1.6.10. 1-{[5-(2-Methoxyphenyl)-1,3,4-oxadiazol-2-yl]methyl}-1H-
benzimidazole (14). IR (KBr): 1647 (–C]N), 1138 (–C–N), 1458 (–N–
(m, 4H, Ar–H); EI-MS: 205 (Mþ þ 1).
CH2), 2810 (–C–OCH3) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.59 (s, 2H,
–N–CH2), 8.61 (s, 1H, –N]CH), 3.73 (s, 3H, –OCH3), 6.61–7.85 (m,
4.1.6. Synthesis of 2-substituted-1-[{(5-substituted alkyl/aryl)-1,3,4-
oxadiazol-2-yl} methyl]-1H-benzimidazole (5–26)
8H, Ar–H); EI-MS: 307 (Mþ þ 1).
General method. An equimolar mixture of compound
4
4.1.6.11. 1-{[5-(4-Methoxyphenyl)-1,3,4-oxadiazol-2-yl]methyl}-1H-
benzimidazole (15). IR (KBr): 1650 (–C]N), 1135 (–C–N), 1455 (–N–
(0.001 mol) and substituted carboxylic acid in phosphoryl chloride
was refluxed for 10–16 h. Then reaction mixture was cooled,
poured into ice-cold water and neutralized with 20% NaHCO3
solution. The resultant solid was filtered, washed with water and
recrystallized from ethanol to give the title compounds.
CH2), 2816 (–C–OCH3) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.50 (s, 2H,
–N–CH2), 8.67 (s, 1H, –N]CH), 3.75 (s, 3H, –OCH3), 6.67–7.90 (m,
8H, Ar–H); EI-MS: 307 (Mþ þ 1).
4.1.6.12. 2-Methyl-1-[(5-methyl-1,3,4-oxadiazol-2-yl)methyl]-1H-
benzimidazole (16). IR (KBr): 1642 (–C]N), 1150 (–C–N), 1466
4.1.6.1. 1-[(5-Methyl-1,3,4-oxadiazol-2-yl)methyl]-1H-benzimidazole
(5). IR (KBr): 1680 (–C]N), 1134 (–C–N), 1457 (–N–CH2), 2870 (–C–
(–N–CH2), 2852 (–C–CH3) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.75
CH3) cmꢀ1; 1H NMR (CDCl3)
d ppm: 3.65 (s, 2H, –N–CH2), 4.10 (s,1H,
(s, 2H, –N–CH2), 2.22 (s, 3H, –CH3), 7.20–7.81 (m, 4H, Ar–H);
–N–CH), 2.30 (s, 3H, –CH3), 7.22–7.85 (m, 4H, Ar–H); EI-MS: 215
EI-MS: 229 (Mþ þ 1).
(Mþ þ 1).
4.1.6.13. 1-[(5-Ethyl-1,3,4-oxadiazol-2-yl)methyl]-2-methyl-1H-
benzimidazole (17). IR (KBr): 1650 (–C]N), 1139 (–C–N), 1451
4.1.6.2. 1-[(5-Ethyl-1,3,4-oxadiazol-2-yl)methyl]-1H-benzimidazole
(6). IR (KBr): 1672 (–C]N), 1155 (–C–N), 1473 (–N–CH2) cmꢀ1 1H
;
(–N–CH2), 2859 (–C–CH3) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.65 (s,
NMR (CDCl3) d ppm: 3.70 (s, 2H, –N–CH2), 8.42 (s, 1H, –N]CH), 4.12
2H, –N–CH2), 2.19 (s, 3H, –CH3), 4.45 (q, 2H, –CH2CH3), 1.00 (t, 3H,
(q, 2H, –CH2CH3), 1.02 (t, 3H, –CH2CH3), 7.22–7.89 (m, 4H, Ar–H); EI-
–CH2CH3), 7.25–7.84 (m, 4H, Ar–H); EI-MS: 243 (Mþ þ 1).
MS: 229 (Mþ þ 1).
4.1.6.14. 1-{[5-(Chloromethyl)-1,3,4-oxadiazol-2-yl]methyl}-2-methyl-
4.1.6.3. 1-{[5-(Chloromethyl)-1,3,4-oxadiazol-2-yl]methyl}-1H-benz-
imidazole (7). IR (KBr): IR (KBr): 1660 (–C]N), 1140 (–C–N), 1469
1H-benzimidazole (18). IR (KBr): 1657 (–C]N), 1150 (–C–N), 1442
(–N–CH2), 2822 (–C–CH3) 765 (–C–Cl) cmꢀ1 1H NMR (CDCl3)
;
(–N–CH2), 760 (–C–Cl) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.61 (s, 2H,
d
ppm: 3.71 (s, 2H, –N–CH2), 2.28 (s, 3H, –CH3), 4.20 (s, 2H, –CH2Cl),
–N–CH2), 8.55 (s, 1H, –N]CH), 5.25 (s, 2H, –CH2Cl), 7.35–7.92 (m,
7.52–8.00 (m, 4H, Ar–H); EI-MS: 263 (Mþ þ 1).
4H, Ar–H); EI-MS: 249 (Mþ þ 1).
4.1.6.15. 1-{[5-(2-Chloroethyl)-1,3,4-oxadiazol-2-yl]methyl}-2-methyl-
4.1.6.4. 1-{[5-(2-Chloroethyl)-1,3,4-oxadiazol-2-yl]methyl}-1H-benz-
imidazole (8). IR (KBr): 1662 (–C]N), 1160 (–C–N), 1463 (–N–
1H-benzimidazole (19). IR (KBr): 1648 (–C]N), 1145 (–C–N), 1457
(–N–CH2), 2830 (–C–CH3) 760 (–C–Cl) cmꢀ1; 1H NMR (CDCl3)
d ppm:
CH2), 752 (–C–Cl) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.59 (s, 2H,
3.75 (s, 2H, –N–CH2), 2.25 (s, 3H, –CH3), 4.13 (t, 2H, –CH2CH2Cl), 1.08
–N–CH2), 8.46 (s, 1H, –N]CH), 5.12 (q, 2H, –CH2CH3Cl), 5.36
(t, 3H, –CH2CH3Cl), 7.10–7.84 (m, 4H, Ar–H); EI-MS: 263
(Mþ þ 1).
(t, 2H, –CH2CH2Cl), 7.62–8.15 (m, 4H, Ar–H); EI-MS: 277 (Mþ þ 1).
4.1.6.16. 2-Methyl-1-[(5-phenyl-1,3,4-oxadiazol-2-yl)methyl]-1H-
benzimidazole (20). IR (KBr): 1660 (–C]N), 1152 (–C–N), 1439
4.1.6.5. 1-[(5-Phenyl-1,3,4-oxadiazol-2-yl)methyl]-1H-benzimidazole
(–N–CH2), 2828 (–C–CH3) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.69 (s,
(9). IR (KBr): 1670 (–C]N), 1152 (–C–N), 1475 (–N–CH2) cmꢀ1 1H
;
2H, –N–CH2), 2.27 (s, 3H, –CH3), 7.58–8.12 (m, 9H, Ar–H); EI-MS:
NMR (CDCl3)
d ppm: 3.69 (s, 2H, –N–CH2), 8.59 (s, 1H, –N]CH),
291 (Mþ þ 1).
6.69–7.50 (m, 9H, Ar–H); EI-MS: 277 (Mþ þ 1).
4.1.6.17. 1-{[5-(2-Chlorophenyl)-1,3,4-oxadiazol-2-yl]methyl}-2-
4.1.6.6. 1-{[5-(2-Chlorophenyl)-1,3,4-oxadiazol-2-yl]methyl}-1H-benz-
imidazole (10). IR (KBr): 1665 (–C]N), 1138 (–C–N), 1453 (–N–CH2),
methyl-1H-benzimidazole (21). IR (KBr): 1662 (–C]N), 1148 (–C–
N), 1435 (–N–CH2), 2832 (–C–CH3), 767 (–C–Cl) cmꢀ1 1H NMR
;
792 (–C–Cl) cmꢀ1; 1H NMR (CDCl3)
d ppm: 3.67 (s, 2H, –N–CH2), 8.40
(CDCl3):
d ppm: 3.73 (s, 2H, –N–CH2), 2.20 (s, 3H, –CH3), 7.64–8.15
(s, 1H, –N]CH), 6.65–7.74 (m, 8H, Ar–H); EI-MS: 311 (Mþ þ 1).
(m, 8H, Ar–H); EI-MS: 325 (Mþ þ 1).
4.1.6.7. 1-{[5-(4-Chlorophenyl)-1,3,4-oxadiazol-2-yl]methyl}-1H-
benzimidazole (11). IR (KBr): 1645 (–C]N), 1145 (–C–N), 1446
4.1.6.18. 1-{[5-(4-Chlorophenyl)-1,3,4-oxadiazol-2-yl]methyl}-2-
methyl-1H-benzimidazole (22). IR (KBr): 1670 (–C]N), 1132 (–C–
(–N–CH2), 780 (–C–Cl) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.65 (s, 2H,
N), 1440 (–N–CH2), 2839 (–C–CH3) 782 (–C–Cl) cmꢀ1 1H NMR
;
–N–CH2), 8.54 (s, 1H, –N]CH), 6.62–7.78 (m, 8H, Ar–H); EI-MS:
(CDCl3):
d ppm: 3.70 (s, 2H, –N–CH2), 2.24 (s, 3H, –CH3), 7.60–8.11
311 (Mþ þ 1).
(m, 8H, Ar–H); EI-MS: 325 (Mþ þ 1).
4.1.6.8. 2-[5-(1H-Benzimidazol-1-ylmethyl)-1,3,4-oxadiazol-2-yl]phe-
nol (12). IR (KBr): 1660 (–C]N), 1140 (–C–N), 1452 (–N–CH2), 3384
4.1.6.19. 2-{5-[(2-Methyl-1H-benzimidazol-1-yl)methyl]-1,3,4-oxa-
diazol-2-yl}phenol (23). IR (KBr): 1672 (–C]N), 1145 (–C–N), 1457
(–C–OH aromatic) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.64 (s, 2H, –N–
(–N–CH2), 2852 (–C–CH3), 3350 (–C–OH aromatic) cmꢀ1 1H NMR
;
CH2), 8.62 (s,1H, –N]CH), 5.50 (s,1H, Ar–OH), 6.78–7.93 (m, 8H, Ar–
(CDCl3)
d ppm: 3.68 (s, 2H, –N–CH2), 2.19 (s, 3H, –CH3), 5.58 (s, 1H,
H); EI-MS: 293 (Mþ þ 1).
Ar–OH), 7.61–8.12 (m, 8H, Ar–H); EI-MS: 307 (Mþ þ 1).
4.1.6.9. 4-[5-(1H-Benzimidazol-1-ylmethyl)-1,3,4-oxadiazol-2-yl]phe-
nol (13). IR (KBr): 1667 (–C]N), 1130 (–C–N), 1457 (–N–CH2), 3360
4.1.6.20. 4-{5-[(2-Methyl-1H-benzimidazol-1-yl)methyl]-1,3,4-oxa-
diazol-2-yl}phenol (24). IR (KBr): 1665 (–C]N), 1132 (–C–N), 1449
(–C–OH aromatic) cmꢀ1 1H NMR (CDCl3)
; d ppm: 3.67 (s, 2H, –N–
(–N–CH2), 2847 (–C–CH3), 3362 (–C–OH aromatic) cmꢀ1 1H NMR
;
CH2), 8.65 (s,1H, –N]CH), 5.50 (s,1H, Ar–OH), 6.78–7.93 (m, 8H, Ar–
(CDCl3)
d ppm: 3.62 (s, 2H, –N–CH2), 2.15 (s, 3H, –CH3), 5.62 (s, 1H,
H); EI-MS: 293 (Mþ þ 1).
Ar–OH), 7.58–8.11 (m, 8H, Ar–H); EI-MS: 307 (Mþ þ 1).

K.F. Ansari, C. Lal / European Journal of Medicinal Chemistry 44 (2009) 4028–4033
4033
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placed on the surface of an agar plate inoculated with a standard-
ized suspension of the microorganisms tested. The plates were
incubated at 28 ꢃ 2 ꢁC for 7 days for evaluating antifungal activity.
The diameters of inhibition zones (in mm) of triplicate sets were
measured and the results are reported in Table 3. Paper discs with
dimethyl sulfoxide (DMSO) only were utilized as negative controls.
Acknowledgement
Authors are thankful to Head, RSIC, Central Drug Research
Institute, Lucknow for providing spectral and analytical data of the
compounds.
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