Synthesis and evaluation of in vitro anti-microbial and anti-tubercular activity of 2-styryl benzimidazoles

Article abstract of DOI:10.1016/j.ejmech.2009.05.021

A new series of novel 5-(nitro/bromo)-styryl-2-benzimidazoles (1-12) has been synthesized by simple, mild and efficient synthetic protocol by attempted condensation of 5-(nitro/bromo)-o-phenylenediamine with trans-cinnamic acids in ethylene glycol. Screen

Full text of DOI:10.1016/j.ejmech.2009.05.021

European Journal of Medicinal Chemistry 44 (2009) 4244–4248
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and evaluation of in vitro anti-microbial and anti-tubercular activity
of 2-styryl benzimidazoles
*
Ramya V. Shingalapur, Kallappa M. Hosamani , Rangappa S. Keri
P. G. Department of Studies in Chemistry, Karnataka University, Pavate Nagar, Dharwad 580 003, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of novel 5-(nitro/bromo)-styryl-2-benzimidazoles (1–12) has been synthesized by simple,
mild and efficient synthetic protocol by attempted condensation of 5-(nitro/bromo)-o-phenylenediamine
with trans-cinnamic acids in ethylene glycol. Screening for in vitro anti-tubercular activity against Myco-
bacterium tuberculosis H37 Rv, anti-bacterial activity against Staphylococcus aureus, Escherichia coli,
Enterococcus faecalis, Klebsiella pneumoniae bacterial strains and anti-fungal activity against Candida
albicans and Asperigillus fumigatus fungal strains were carried out. Compounds 5, 7, 8, 9, 11 showed higher
Received 15 February 2009
Received in revised form
13 May 2009
Accepted 20 May 2009
Available online 28 May 2009
anti-tubercular activity and compounds 7, 8, 10, 11, 12 have proved to be effective with MIC (mg/ml) and
Keywords:
Styryl benzimidazole
Ethylene glycol
Anti-microbial activity
Anti-tubercular activity
emerged as lead molecules showing excellent activities against a panel of microorganisms. All synthesized
compounds were characterized using IR, 1H, 13C NMR, GC–MS and elemental analysis.
Ó 2009 Elsevier Masson SAS. All rights reserved.
1. Introduction
multidrug-resistant microorganisms have reached an alarming
level in many countries around the world. Resistance to a number
Tuberculosis (TB), a contagious infection caused by Mycobacte-
rium tuberculosis (MTB), still remains the leading cause of the
worldwide death among the infectious disease [1,2]. The WHO has
estimated that every year about eight million new cases of tuber-
culosis occur, and up to three million individuals die due to this
disease (one person dies every 10 s) [3]. It is also estimated that
between 2002 and 2020, approximately a billion people will be
newly infected, more than 150 million people will get sick, and 36
million will die of TB. This is also a leading cause of death amongst
people who are HIV-positive (13% of AIDS deaths worldwide) [4].
The synergy between tuberculosis and the AIDS epidemic as well as
the surge of multidrug-resistant isolates of M. tuberculosis has
reaffirmed tuberculosis as a primary public health threat. The
current threat in TB treatment lies in the emergence of strains
resistant to two of the best anti-tubercular drugs, isoniazid (INH)
and rifampicin (RIF). The current TB treatment comprises of 3–4
drugs for a period of 6–9 months. Novel drugs are urgently required
which can shorten this long-treatment period and target multi-
drug-resistant strains of TB.
of anti-microbial agents (
b-lactam antibiotics, macrolides, quino-
lones, and vancomycin) among variety of clinically significant
species of bacteria is becoming increasingly important global
problem. Also a number of recent clinical reports describe the
increasing occurrence of Methicillin Resistant Staphylococcus
Aureus (MRSA) which is most disturbing cause of nosocomial
infections in developed countries [5,6]. Infections caused by these
microorganisms pose
a serious challenge to the medicinal
community and the need for an effective therapy has led to search
for novel anti-microbial agents. In particular, increasing drug
resistance among gram-positive bacteria such as Staphylococci,
Enterococci and Streptococci is a significant health matter [7]. This
has stimulated the scientists for the development of novel mole-
cules to combat these illnesses.
Benzimidazole and its derivatives are reported to be physio-
logically and pharmacologically active and find applications in the
treatment of several diseases like epilepsy, diabetes, anti-fertility
[8,9]. It is an important pharmacophore and privileged structure in
medicinal chemistry [10,11] encompassing a diverse range of bio-
logical activities including anti-bacterial [12], anti-inflammatory,
analgesic [13,14], anti-histamine [15], anti-ulcerative [16], anti-
oxidant [17], anti-proliferative [18,19], anti-allergic [20,21], anti-
tumour [22,23], anti-kinase [24,25], anti-cancer activities [26–30],
cytotoxicity [31] and anti-HIV-1 [32,33]. Owing to the importance
and in continuation of our ongoing project benzimidazole [34,35],
now we wish to describe simple, novel and environmentally benign
Infectious microbial disease remains
a pressing problem
worldwide, because microbes have resisted prophylaxis or therapy
longer than any other form of life. In recent decades, problems of
* Corresponding author. Tel.: þ91 836 2215286; fax: þ91 836 2747884,2771275.
E-mail address: dr_hosamani@yahoo.com (K.M. Hosamani).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.05.021

R.V. Shingalapur et al. / European Journal of Medicinal Chemistry 44 (2009) 4244–4248
4245
approach towards the synthesis of 2-styryl benzimidazole deriva-
tives and in vitro screening results of anti-microbial and anti-
tubercular activities.
temperature was very essential as it led to a gelatinous substance
due to the reduced temperature. An appreciable yield of 75–82% is
obtained. Postulated structures of the newly synthesized
compounds are in agreement with their IR, 1H NMR, 13C NMR, GC–
MS and elemental analysis data. In FT-IR of compound (1), a broad
peak at 3421.3 cmꢁ1 was due to –NH of the benzimidazole moiety.
The 1H NMR shows a broad peak at 12.2 ppm due to –NH proton
which is also D2O exchangeable. Sharp doublet was found for
vicinal protons at 8.03 ppm with a coupling constant of 16.84 Hz. In
13C NMR the peaks at 114.4, 117.8, 128.54, and 157.4 ppm confirm
the formation of benzimidazole moiety. The mass spectrum of
compound (1) shows the molecular ion peak at m/z 265 (70%) and
[M þ 1] peak at m/z 266 (6%).
2. Chemistry
The general synthetic strategy employed to obtain the title
compounds in excellent yield is depicted in Scheme 1. The cyclo-
condensation of 5-(nitro/bromo)-substituted-o-phenylenediamine
with various cinnamic acids in ethylene glycol for 6 h at around
200 ꢀC led to the formation of 5-(nitro/bromo) substituted-2-styryl
benzimidazoles. This eco-friendly method for the preparation of
styryl benzimidazoles is particularly attractive because it specifi-
cally generates crystalline products. All the newly synthesized
compounds were characterized using IR, 1H NMR, 13C NMR, GC–MS
and elemental analysis.
4.2. Anti-bacterial activity assay
3. Bioevaluations
MIC values for the in vitro anti-bacterial studies of the
compounds (1–12) and the standard are represented in Table 1. The
anti-bacterial activity of all the compounds against S. aureus and E.
faecalis as Gram (þ), K. pneumoniae and E. coli as Gram (ꢁ) bacteria
showed good potencies compared to control drug ciprofloxacin.
From the results it is apparent that among the synthesized
All the compounds prepared herein were screened for their
potential biological activities such as anti-bacterial, anti-fungal and
anti-tubercular activities. Anti-tubercular activity was carried out
against M. tuberculosis H37 Rv (ATCC-27294) by Alamar Blue Assay.
Bacterial strains Staphylococcus aureus [ATCC-25923] and Entero-
coccus faecalis [ATCC-29212] as gram positive, Klebsiella pneumo-
niae [ATCC-13883] and Escherichia coli [ATCC-25922] as gram
negative and Candida albicans [ATCC-10145], Asperigillus fumigatus
as fungal strains are used for the in vitro study. The in vitro anti-
microbial activity of the compounds was tested by the tube dilution
technique [36]. Each of the test compounds and standards cipro-
compounds 1, 7, 8, 9, 11, 12 showed MIC value of 16–1
Compound 12 showed excellent activity with an MIC of 1 g/ml and
g/ml against Gram (þ) and Gram (ꢁ), respectively, which are
comparable with ciprofloxacin. Compound 8 exhibited MIC of 2 g/
ml against Gram (þ) and 8 g/ml against K. pneumoniae. Compound
7 was also comparable with standard against S. aureus with an MIC
of 2 g/ml.
mg/ml.
m
4
m
m
m
m
floxacin and fluconazole were dissolved in DMSO initially at 250
ml and then were serially diluted in culture medium as follows:
125, 62.5, 31.250, 16, 8, 4, 2, 1 g/ml concentrations. The minimum
mg/
m
inhibitory concentrations (MICs) were defined as the lowest
concentrations of the compounds that prevented visible growth. It
was determined that the solvent had no anti-microbial activity
against any of the test microorganisms.
4.3. Anti-fungal activity assay
MIC values for the in vitro anti-fungal studies of the compounds
(1–12) and the standard are represented in Table 1. Among test
compounds, most interesting activities were found for compounds
7, 8, 9 and 12 against C. albicans and A. fumigatus compared to
control fluconazole. Compound 8 was promising with MIC values of
4. Results and discussion
4.1. Chemistry
1 and 2 mg/ml, respectively, against both the fungi. Anti-fungal
activity indicated that some of the derivatives possessed a broad
spectrum of activity against tested fungi; however, compound 8
showed a better spectrum of activity than the reference drug.
The synthetic strategy involves the reaction of 5-(nitro/bromo)-
substituted-o-phenylenediamine with variously substituted cin-
namic acids. The cyclocondendensation of the reactants in ethylene
glycol for 6 h at around 200 ꢀC leads to the formation of 5-(nitro/
Table 1
bromo)-2-styryl benzimidazoles. Maintenance of
a
high
Anti-microbial activity of synthesized compounds (1–12).
MIC (mg/ml)
H
NH2
NH2
HO
Comp.
S. aureus E. faecalis K.
E. coli
C. albicans A.
R
(25923)a (29212)
pneumonia (25922) (10145)a
fumigatus
+
R'
O
(13883)
H
Ethylene
glycol
1
2
3
4
5
6
7
8
8.0
31.250
4.0
31.250
31.250
4.0
2.0
2.0
31.250
8.0
16.125
1.0
31.250
31.250
16.125
31.250
31.250
31.250
16.125
2.0
31.250
31.250
8.0
1.0
0.70
4.0
16.125
16.125
62.5
62.5
31.250
31.250
8.0
8.0
16.125
2.0
4.0
0.19
31.250 16.125
31.250 16.125
16.125
31.250
31.250
16.125
31.250
62.5
8.0
2.0
8.0
6 hrs
62.5
31.250 16.125
62.5 16.125
31.250 31.250
31.250
H
N
R
R'
N
H
16.125
31.250
16
8.0
1.0
4.0
H
(1 - 12)
9
10
11
12
31.250 31.250
31.250 31.250
31.250
16.125
8.0
R, a = -NO2, b = -Br
R', a = H , b = 3,4 (OCH3) , c = 4- CH3 , d = 3,4- (CH2)O2 , e = 2,4-(Cl) , f = 3 - OH
4.0
4.0
Ciprofloxacin 0.78
0.19
–
–
Fluconazole
–
–
–
–
2.0
2.0
Scheme 1. Synthesis of 5-(nitro/bromo)-2-styryl benzimidazoles from
rated acids.
a, b-unsatu-
a
ATCC number.

4246
R.V. Shingalapur et al. / European Journal of Medicinal Chemistry 44 (2009) 4244–4248
4.4. Anti-tubercular activity assay
used. All the compounds gave C, H and N analysis within ꢃ0.5%
of the theoretical values.
MIC values for the in vitro anti-tubercular studies of the
compounds (1–12) and the standard are represented in Table 2.
The data of the anti-tubercular activity screening reveals that the
compounds 7, 8, 9 and 11 showed good activity against M. tubercu-
losis strain, whereas compound 5 showed moderate activity.
Encouraging activity was found for the bromo derivatives; however,
the nitro derivatives did not show any considerable activity.
6.1.1. General method for the synthesis of 5-(nitro/bromo)-2-styryl
benzimidazole
A mixture of 5-substituted-o-phenylenediamine (0.01 mol) and
cinnamic acid (0.01 mol) in ethylene glycol was stirred for 1 h and
then the mixture was refluxed at a temperature of 200 ꢀC for nearly
6 h. The completion of the reaction was monitored through TLC
technique. After cooling, the reaction mixture was poured in
crushed ice with stirring. The product separated out was filtered,
washed with water and dried to obtain 5-(nitro/bromo)-2-styryl-
benzimidazole. The compound obtained was chromatographed on
silica gel column using CHCl3. The remaining compounds are
synthesized in the similar manner.
5. Conclusion
The preliminary in vitro anti-bacterial, anti-fungal and anti-
tubercular screening results of novel 5-(nitro/bromo) substituted-
2-styryl benzimidazole derivatives reported here have emerged as
highly potent anti-bacterial, anti-fungal and anti-tubercular agents.
The possible improvements in the activity can be further achieved
by slight modifications in the substituents on the basic benzimid-
azole nucleus. The presence of the bromo group on the aromatic
ring has highly increased the activity of the compounds compared
to nitro substituent compounds. In the view of the above findings
and to identify new candidates that may value in designing new,
selective, less toxic anti-microbial and anti-tubercular agents who
might serve as new templates, we report the development of
6.1.1.1. 5-Nitro-2-styryl-1H-benzimidazole
(1). Brown crystals,
yield: 79.21%; m.p. 217–219 ꢀC; IR (KBr): ymax in cmꢁ1: 3421.3 (NH),
2921.7 (]C–H), 1629.6 (C]N), 1592.2 (C]C), {1339.8 (Sym), 1518.4
(Asymm)}(NO2); 1H NMR (DMSO-d6, 300 MHz)
d ppm: 7.5–8.3 (m,
3
5H, Ar–H), 8.03 (d, 2H, Vinylic, JH–H ¼ 16.84 Hz), 12.2 (b, 1H, NH-
benzimidazole); 13C NMR (DMSO-d6, 75 MHz)
d ppm: 39.7, 39.4,
111.9, 114.4, 117.8, 126.28, 128.54, 142.87, 157.4 (6 aryl carbons, 6
phenyl carbons, 2 vinylic carbons and 1 imidazole quaternary
carbon); MS (EI) m/z (%) 170 (100), 265 (Mþ, 70), 266 (M þ 1, 6), 188
(55), 163 (10), 143 (19), 110 (25), 108 (30), 77 (5), 46 (15); Anal.
Calcd. for C15H22N3O2: C, 67.92; H, 4.18; N, 15.84%. Found: C, 67.81;
H, 4.09; N, 15.69%.
potent therapeutics having MIC values ꢂ1
mg/ml. Our findings will
now have a very good impact on chemists and biochemists for
further investigations in this field of benzimidazoles selectively
being bromo substituted.
6.1.1.2. 2-[2-(3,4-Dimethoxy-phenyl)-vinyl]-5-nitro-1H-benzimidazole
(2). Brown crystals, yield: 82.32%; m.p. 184–186 ꢀC; IR (KBr): ymax in
cmꢁ1: 3281.1 (NH), 3000.3 (]C–H), 1712.5 (C]N),1628 (C]C),
6. Experimental protocols
6.1. Chemistry
1340.2, 1512.8 (NO2); 1H NMR (CDCl3, 300 MHz)
d
ppm: 6.4–8.4 (m, 3
3
aryl, 3 phenyl, 2 vinylic protons, JH–H ¼ 16.86 Hz), 2.71 (s, 6H, 2-
Melting points of the synthesized compounds were determined
in open capillaries and are uncorrected. Infrared spectra were
recorded using KBr pellets on Nicolet 5700 FT-IR instrument. The
1H NMR and 13C NMR spectra were recorded on Brucker Avance-
300 (300 MHz) model spectrophotometer in CDCl3 and DMSO as
solvent and TMSi as internal standard with 1H resonant frequency
of 300 MHz and 13C resonant frequency of 75 MHz. D2O exchange
was applied to confirm the assignment of the signals of NH protons.
OCH3), 10.9 (b, 1H, NH-benzimidazole); 13C NMR (CDCl3, 75 MHz)
d
ppm: 21.98, 24.11, 40.92, 108.4, 120.8, 121.85, 152.82, 154.8 (6 aryl
carbons, 6 phenyl carbons, 2 vinylic carbons, 1 imidazole quaternary
carbon and 2 methoxy carbons); MS (EI) m/z (%) 174 (100), 325 (Mþ,
79), 326 (M þ 1, 10), 188 (60), 163 (10), 138 (8), 143 (10), 77 (15), 28
(2); Anal. Calcd. for C18H19N3O4: C, 63.33; H, 5.61; N, 12.31%. Found:
C, 63.35; H, 5.45; N, 12.40%.
The chemical shifts were measured in
d
ppm downfield from
6.1.1.3. 5-Nitro-2-(2-p-tolyl-vinyl)-1H-benzimidazole
(3). Light
internal standard TMSi at
d
¼ 0. The TLC was performed on alumina
brown crystals, yield: 76.25%; m.p. 192–194 ꢀC; IR (KBr): ymax in
cmꢁ1: 3561.7 (NH), 2994.7 (]C–H), 1679.5 (C]N), 1626.6 (C]C),
silica gel 60 F254 (Merck). The mobile phase was ethyl acetate and n-
hexane (1:1) and detection was made using UV light and iodine.
The resulting compounds were purified bycolumn chromatography.
For column chromatography Merck silica gel (0.040–0.063 mm) was
1515.4, 1338.8 (NO2); 1H NMR (CDCl3, 300 MHz)
d ppm: 6.9–8.2 (m,
3 aryl, 4 phenyl, 2 vinylic protons, 3JH–H ¼ 16.25 Hz), 3.4 (s, 3H, CH3),
10.5 (b, 1H, NH-benzimidazole); 13C NMR (CDCl3, 75 MHz)
d ppm:
24.15, 55.8, 110.25, 112.8, 119.5, 154.59, 150.20 (1 methane carbon, 6
aryl carbons, 6 phenyl carbons, 2 vinylic carbons and 1 imidazole
quaternary carbon); MS (EI) m/z (%) 165 (100), 279 (Mþ, 77), 280
(M þ 1, 10), 188 (59), 118 (20), 110 (18), 92 (55), 77(12), 28 (5); Anal.
Calcd. for C16H13N3O2: C, 68.81; H, 4.69; N, 15.05%. Found: C, 68.85;
H, 4.55; N, 15.00%.
Table 2
Anti-tubercular activity of synthesized compounds (1–12).
Comp
R
R1
MIC (mg/ml)
1
2
3
4
5
6
7
8
–NO2
–NO2
–NO2
–NO2
–NO2
–NO2
–Br
–Br
–Br
–Br
–Br
H
>7.25
>7.25
>7.25
>7.25
>7.25 (45)
>7.25
>7.25 (83)
>7.25 (54)
>7.25 (63)
>7.25
>7.25 (76)
>7.25
3,4-OCH3
4-CH3
3,4-O2CH2
2,4-Cl
3-OH
6.1.1.4. 2-(2-Benzo [1, 3] dioxol-5-yl-vinyl)-5-nitro-1H-benzimid-
azole (4). Light brown crystals, yield: 75.32%; m.p. 214–216 ꢀC; IR
(KBr): ymax in cmꢁ1: 3411.3 (NH), 2961.0 (]C–H), 1679.3 (C]N),
–H
1618.9 (C]C),1397.9,1542.4(NO2);1HNMR(CDCl3, 300 MHz)
dppm:
3,4-OCH3
4-CH3
3,4-O2CH2
2,4-Cl
3-OH
9
6.7–7.8 (m, 3 aryl, 3 phenyl, 2 vinylic protons, 3JH–H ¼ 16.41 Hz), 2.6 (s,
10
11
12
2H, CH2), 11.1 (b, 1H, NH-benzimidazole); 13C NMR (CDCl3, 75 MHz)
d
ppm: 15.29, 115.85, 116.02, 117.91, 126.02, 137.53, 140.5, 152.26 (1
–Br
dioxy methylene carbon, 6 aryl carbons, 6 phenyl carbons, 2 vinylic
carbons and 1 imidazole quaternary carbon); MS (EI) m/z (%) 169
(100), 309 (Mþ, 77), 310 (M þ 1, 7), 187 (52), 163 (11), 147 (28), 122
Standard: streptomycin (100% inhibition).
All compounds tested at concentration of 7.25
The active compounds are marked in bold letters.
m
g/ml.

R.V. Shingalapur et al. / European Journal of Medicinal Chemistry 44 (2009) 4244–4248
4247
(42), 77 (8), 28 (5); Anal. Calcd. for C18H17N3O4: C, 63.71; H, 5.05; N,
12.38%. Found: C, 64.00; H, 5.10; N, 12.22%.
6.1.1.10. 2-(2-Benzo [1, 3] dioxol-5-yl-vinyl)-5bromo-1H-benzimid-
azole (10). Light brown crystals, yield: 81.32%; m.p. 210–212 ꢀC; IR
(KBr): ymax in cmꢁ1: 3424.2 (NH), 2924.2 (]C–H), 1664.8 (C]N),
6.1.1.5. 2-[2-(2, 4-Dichloro-phenyl)-vinyl]-5-nitro-1H-benzimidazole
(5). Brown crystals, yield: 70.12%; m.p. 212–214 ꢀC; IR (KBr): ymax in
cmꢁ1: 3430.4 (NH), 2922.7 (]C–H), 1631.8 (C]N), 1590.6 (C]C),
1627.5 (C]C); 1H NMR (CDCl3, 300 MHz)
d ppm: 6.45–7.55 (m, 4
aryl, 3 phenyl, 2 vinylic protons, 3JH-H ¼ 16.35 Hz), 2.52 (s, 2H, CH2),
11.02 (b, 1H, NH-benzimidazole); 13C NMR (CDCl3, 75 MHz)
d ppm:
1340.2, 1545.0 (NO2); 1H NMR (DMSO-d6, 300 MHz)
d
ppm: 7.2–8.5
15.05, 115.4, 115.9, 117.00, 125.08, 128.24, 140.85, 152.09, 152.7 (1
dioxy methylene carbon, 6 aryl carbons, 6 phenyl carbons, 2 vinylic
carbons and 1 imidazole quaternary carbon); MS (EI) m/z (%) 158
(100), 342 (Mþ, 77), 343 (M þ 1, 12), 344 (M þ 2, 5), 222 (45), 147
(26), 124 (32), 110 (20); Anal. Calcd. for C16H11BrN2O2: C, 56.00; H,
3.23; N, 8.16%. Found: C, 55.99; H, 3.55; N, 8.25%.
(m, 3 aryl, 3 phenyl, 2 vinylic protons, 3JH–H ¼ 16.28 Hz), 11.9 (b, 1H,
NH-benzimidazole); 13C NMR (DMSO-d6, 75 MHz)
d ppm: 30.42,
51.82, 55.4,111.4,118.25,119.7,121.2,152.71 (6 aryl carbons, 6 phenyl
carbons, 2 vinylic carbons and 1 imidazole quaternary carbon); MS
(EI) m/z (%) 174 (100), 333 (Mþ, 85), 334 (M þ 1, 2), 335 (M þ 2, 4),190
(21),174 (16),164 (9),145 (28), 30 (7); Anal. Calcd. for C16H15N3O3: C,
53.92; H, 2.71; N, 12.58%. Found: C, 53.95; H, 2.80; N, 12.57%.
6.1.1.11. 2-[2-(2, 4-Dichloro-phenyl)-vinyl]-5-bromo-1H-benzimid-
azole (11). Pale yellow crystals, yield: 72.23%; m.p. 204–206 ꢀC; IR
(KBr): ymax in cmꢁ1: 3479.9 (NH), 2924.3 (]C–H), 1638.2 (C]N),
6.1.1.6. 3-[2-(5-Nitro-1H-benzimidazole-2-yl)-vinyl]-phenol (6). Brown
crystals, yield: 82.24%; m.p. 228–230 ꢀC; IR (KBr): ymax in cmꢁ1
:
1590.6 (C]C); 1H NMR (DMSO-d6, 300 MHz)
d
ppm: 7.00–7.6 (m, 3
3
3515.90 (OH), 3464.2 (NH), 2923.0 (]C–H), 1674.3 (C]N), 1628.1
aryl, 3 phenyl, 2 vinylic protons, JH–H ¼ 16.19 Hz), 11.9 (b, 1H, NH-
(C]C), 1339.4, 1517.4 (NO2); 1H NMR (DMSO-d6, 300 MHz)
d
ppm:
benzimidazole); 13C NMR (DMSO-d6, 75 MHz)
d ppm: 51.55, 55.20,
7.18 - 8.54 (m, 3 aryl, 4 phenyl, 2 vinylic protons, 3JH–H ¼ 16.88 Hz),
111.89, 115.28, 118.24, 119.00 (6 aryl carbons, 6 phenyl carbons, 2
vinylic carbons and 1 imidazole quaternary carbon); MS (EI) m/z (%)
154 (100), 265 (Mþ, 82), 266 (M þ 1, 9), 267 (M þ 2, 5), 192 (31), 169
(24),148 (62),118 (20),104(22), 77 (15); Anal. Calcd. for C15H9BrCl2N2:
C, 48.95; H, 2.46; N, 7.61%. Found: C, 48.55; H, 2.37; N, 7.55%.
12.8 (s, 1H, OH) 11.85 (b, 1H, NH-benzimidazole); 13C NMR (DMSO-
d6, 75 MHz)
d ppm: 50.6, 110.27, 118.21, 120.85, 121.7, 151.94 (6 aryl
carbons, 6 phenyl carbons, 2 vinylic carbons and 1 imidazole
quaternary carbon); MS (EI) m/z (%) 174 (100), 281 (Mþ, 82), 282
(M þ 1, 7), 185 (26), 120 (32), 95 (26), 77 (17), 29 (15); Anal. Calcd.
for C16H15N3O3: C, 64.64; H, 5.09; N, 14.13%. Found: C, 63.52; H,
5.10; N, 14.25%.
6.1.1.12. 3-[2-(5-Bromo-1H-benzimidazole-2-yl)-vinyl]-phenol (12).
Light brown crystals, yield: 75.32%; m.p. 99–101 ꢀC; IR (KBr): ymax
in cmꢁ1: 3510.40 (OH), 3423.03 (NH), 2925.3 (]C–H), 1635.6
(C]N), 1581.0 (C]C); 1H NMR (DMSO-d6, 300 MHz)
d ppm: 6.5–
6.1.1.7. 5-Bromo-2-styryl-1H-benzimidazole (7). Pale yellow crys-
tals, yield: 82.12%; m.p. 198–200 ꢀC; IR (KBr): ymax in cmꢁ1: 3430.0
(NH), 2924.5 (]C–H),1680.9 (C]N),1620.3 (C]C); 1H NMR (CDCl3,
7.85 (m, 3 aryl, 4 phenyl, 2 vinylic protons, 3JH–H ¼ 16.81 Hz), 12.43
(b, 1H, OH), 10.40 (b, 1H, NH-benzimidazole); 13C NMR (DMSO-d6,
75 MHz)
d ppm: 39.7, 56.90, 113.9, 114.14, 115.32, 115.9, 118.17,
300 MHz)
d ppm: 7.32–7.42 (m, 3 aryl, 5 phenyl, 2 vinylic protons,
3JH–H ¼ 16.82 Hz), 12.18 (b, 1H, NH-benzimidazole); 13C NMR
122.09, 124.71, 153.70, 158.58 (6 aryl carbons, 6 phenyl carbons, 2
vinylic carbons and 1 imidazole quaternary carbon); MS (EI) m/z (%)
128 (100), 315 (Mþ, 90), 396 (M þ 1, 9), 397 (M þ 2, 4), 220 (14), 192
(18), 95 (27), 77 (12), 29 (14), 20 (5); Anal. Calcd. for C15H11BrN2O: C,
57.16; H, 3.52; N, 8.89%. Found: C, 57.25; H, 3.47; N, 8.95%.
(CDCl3, 75 MHz) d ppm: 76.99, 115.72, 125.90, 128.62, 143.8, 152.7 (6
aryl carbons, 6 phenyl carbons, 1 imidazole quaternary carbon and
2 vinylic carbons); MS (EI) m/z (%) 155 (100), 298 (Mþ, 83), 299
(M þ 1, 11), 300 (M þ 2, 2), 220 (41), 195 (28), 142 (19), 104 (22), 76
(25); Anal. Calcd. for C15H11BrN3: C, 60.22; H, 3.71; N, 9.36%. Found:
C, 60.00; H, 3.85; N, 9.25%.
6.2. Bioassays
6.1.1.8. 5-Bromo-2-[2-(3, 4-dimethoxy-phenyl)-vinyl]-1H-benzimid-
azole (8). Yellow crystals, yield: 79.35%; m.p. 87–89 ꢀC; IR (KBr):
ymax in cmꢁ1: 3406.4 (NH), 2925.1 (]C–H), 1627.7 (C]N), 1544.1
6.2.1. Anti-bacterial assay
The cultures were obtained in Mueller–Hinton Broth (Difco) for
all the bacteria after 18–24 hrs of incubation at 37 ꢃ 1 ꢀC. Testing
was carried out in Mueller–Hinton Broth at pH 7.4 and twofold
dilution technique was applied. A set of tubes containing only
inoculated broth was kept as controls. After incubation for 18–24 h
at 37 ꢃ 1 ꢀC, the last tube with no growth of microorganism was
(C]C); 1H NMR (CDCl3, 300 MHz)
d ppm: 6.7–8.4 (m, 3 aryl, 3
3
phenyl, 2 vinylic protons, JH–H ¼ 16.85 Hz), 2.69 (s, 6H, 2-OCH3),
10.82 (b, 1H, NH-benzimidazole); 13C NMR (CDCl3, 75 MHz)
d ppm:
15.58, 41.85, 110.84, 120.2, 121.5, 153.11, 154.01 (2 methoxy carbons,
6 aryl carbons, 6 phenyl carbons, 2 vinylic carbons and 1 imidazole
quaternary carbon); MS (EI) m/z (%) 128 (100), 358 (Mþ, 75), 359
(M þ 1, 4), 360 (M þ 2, 6), 220 (40), 195 (20), 163 (28), 139 (22), 45
(12); Anal. Calcd. for C18H19BrN2O2: C, 57.61; H, 5.10; N, 7.47%.
Found: C, 57.60; H, 5.55; N, 7.50%.
recorded to represent MIC expressed in
used as standard drug.
mg/ml. Ciprofloxacin was
6.2.2. Anti-fungal assay
The yeasts were maintained in Sabouraud Dextrose Broth
(Difco) after incubation for 48 h at 25 ꢃ1 ꢀC. Testing was performed
in Sabouraud Dextrose Broth at pH 7.4 and the twofold dilution
technique was applied. A set of tubes containing only inoculated
broth was kept as controls. After incubation for 48 h at 25 ꢃ1 ꢀC,
the last tube with no growth of yeast was recorded to represent MIC
6.1.1.9. 5-Bromo-2-(2-p-tolyl-vinyl)-1H-benzimidazole
(9). Pale
yellow crystals, yield: 71.32%; m.p. 184–186 ꢀC; IR (KBr): ymax in
cmꢁ1: 3430.0 (NH), 2924.9 (]C–H), 1686.1 (C]N), 1621.4 (C]C);
1H NMR (DMSO-d6, 300 MHz)
d
ppm: 6.2–7.6 (m, 3 aryl, 4 phenyl, 2
3
vinylic protons, JH–H ¼ 16.20 Hz), 3.42 (s, 3H, CH3), 10.28 (b, 1H,
expressed in mg/ml. Fluconazole was used as standard drug.
NH-benzimidazole); 13C NMR (DMSO-d6, 75 MHz)
d ppm: 15.27,
55.85, 110.92, 111.99, 120.74, 129.45, 147.28, 154.04 (1 methane
carbon, 6 aryl carbons, 6 phenyl carbons, 2 vinylic carbons and 1
imidazole quaternary carbon); MS (EI) m/z (%) 174 (100), 313 (Mþ,
90), 314 (M þ 1, 11), 315 (M þ 2, 2), 225 (51), 194 (21), 118 (45), 104
(16), 92 (54), 20 (4); Anal. Calcd. for C16H13BrN2: C, 61.36; H, 4.18; N,
8.94%. Found: C, 61.25; H, 4.52; N, 8.85%.
6.2.3. Anti-tubercular assay
Primary screening was conducted at 7.25 mg/ml against M.
tuberculosis H37Rv (ATCC-27294) in BACTEC 12B [37,38] medium
using a broth micro dilution assay [39,40] the microplate Alamar
blue assay (MABA) [41]. Compounds exhibiting <90% inhibition in
the primary screen were not evaluated further. Compounds

4248
R.V. Shingalapur et al. / European Journal of Medicinal Chemistry 44 (2009) 4244–4248
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This research work is financially supported by the Department
of Science and Technology (DST), New Delhi 110 016 (Ref. No SR/S1/
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