Synthesis and antimicrobial activities of some new benzimidazole derivatives

Article abstract of DOI:10.1016/S0014-827X(03)00190-3

Some benzimidazolylbenzamides were synthesized and their antimicrobial activities against Staphylococcus aureus, Streptococcus faecalis, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans evaluated. It was shown that the compound 14 exhibited the best activity against B. subtilis, P. aeruginosa and C. albicans.

Full text of DOI:10.1016/S0014-827X(03)00190-3

Il Farmaco 58 (2003) 1345ꢀ1350
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www.elsevier.com/locate/farmac
Short communication
Synthesis and antimicrobial activities of some new benzimidazole
derivatives
Gulgun Ayhan-K lc gil a,*, Nurten Altanlar b
ı ı
¨ ¨
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Ankara University, 06100 Tando˘gan, Ankara, Turkey
b Department of Microbiology, Faculty of Pharmacy, Ankara University, 06100 Tando˘gan, Ankara, Turkey
Received 3 January 2003; accepted 12 June 2003
Abstract
Some benzimidazolylbenzamides were synthesized and their antimicrobial activities against Staphylococcus aureus, Streptococcus
faecalis, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans evaluated. It was shown that the
compound 14 exhibited the best activity against B. subtilis, P. aeruginosa and C. albicans.
´
# 2003 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: Benzimidazoles; Benzamides; Antimicrobial activity
1. Introduction
In some previous papers [1ꢀ
compounds 2ꢀ11. 2-(3-Nitrophenyl)-1H-benzimidazole
/
(12) was prepared via oxidative condensation of o-
phenylenediamine, 3-nitrobenzaldehyde and sodium
metabisulfite [5]. Treatment of 2-(3-nitrophenyl)-1H-
benzimidazole with iodomethane in K2CO3/dry acetone
gave the N-methylated product, 2-(3-nitrophenyl)-1-
methyl-1H-benzimidazole (13). The reduction of 13
with H2, Pd/C produced 14. Acylation of 14 with
chloroacetylchloride in dry acetone afforded 2-
chloro-N-[3-(1-methyl-1H-benzimidazol-2-yl)-phenyl]-
acetamide (15) [6]. Compound 15 was reacted with
thiophenol and few drops of piperidine in dry benzene
to give N-[3-(1-methyl-1H-benzimidazol-2-yl)-phenyl]-
2-phenylthio-acetamide (16) [7]. Some physico-chemical
properties and spectral findings are given in Table 1.
/
4], we reported the
synthesis and antimicrobial activity of some benzimida-
zole-5(6)-carboxamido and 4-(1H-benzimidazol-2-
yl)benzamide derivatives. Among them, compounds I,
II, III and IV exhibited good antimicrobial activity. In
this investigation, as a continuation on the synthesis of
antimicrobial benzimidazoles, it was planned to modify
the amide group to the anilide on the 2-phenyl
benzimidazole moiety.
2. Chemistry
For the synthesis of the target compounds the
reaction sequences outlined in the Scheme 1 are
followed. 2-(4-Aminophenyl)-1H-benzimidazol (1) was
prepared by heating of o-phenylenediamine with p-
aminobenzoic acid in polyphosphoric acid (PPA).
Arylcarboxylic acids were converted into acyl chlorides
with SOCl2 and their reaction with 2-(4-aminophenyl)-
1H-benzimidazol (1) in NaHCO3/ether/H2O gave the
3. Experimental
Melting points were determined with a Buchi SMP-20
¨
and Electrothermal melting point apparatus and are
1
uncorrected. H NMR spectra were measured with a
Bruker GmbH DPX-400, 400 MHz instrument using
TMS internal standard and DMSO-d6. All chemical
shifts were reported as d (ppm) values. EI MS were
obtained with a VG Platform II, Micromass spectro-
meter with ionization energy maintained at 70 eV.
Elemental analyses (C, H, and N) were determined on
* Corresponding author.
E-mail address: kilcigil@pharmacy.ankara.edu.tr (G. Ayhan-
K lc gil).
ı ı
´
0014-827X/03/$ - see front matter # 2003 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
doi:10.1016/S0014-827X(03)00190-3

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a Leco CHNS 932 instrument (St. Joseph, USA), and
were within 90.4% of the theoretical values. All
instrumental analysis were performed at Scientific and
reagents used in synthesis were purchased from E.
Merck (Darmstadt, FRG) and Aldrich (Milwaukee,
USA). Column chromatography was accomplished on
/
Technical Research Council of Turkey. The chemical
silica gel 60 (230ꢀ400 mesh ASTM). 2-(4-aminophe-
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Scheme 1. Synthesis of the compounds 1ꢀ
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16. Reagents: (a) PPA (b) corresponding acylchlorides (c) NaHSO3 (d) CH3IꢀK2CO3 (e) H2, Pd/C.
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Table 1
Some physico-chemical properties and spectral findings of compounds 3ꢀ
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11

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nyl)benzimidazole (1) (m.p.: 237 8C (Lit. [8] m.p.:
240 8C), N-[4-(1H-benzimidazol-2-yl)-phenyl]-benza-
3.4. Synthesis of the 2-chloro-N-[3-(1-methyl-1H-
benzimidazol-2-yl)-phenyl]-acetamide (15)
mide (2) (m.p.: 335 8C (Lit. [8] m.p.: 333 8C), 2-(3-
nitrophenyl)benzimidazole (12) (m.p.: 209 8C (Lit. [9]
0.673 mmol 3-(1-methyl-1H-benzimidazol-2-yl)-phe-
nylamine was dissolved in 2 ml of dry acetone and
treated drop by drop, with stirring, 0.026 ml chloroace-
tylchloride. 0.24 ml 2 N NaOH was then added and the
mixture treated further with 0.026 ml chloroacetylchlo-
ride. The mixture was stirred for 1 h period at room
temperature, made acidic with 1 N HCl, then extracted
with EtOAc. The extract was washed with water, dried
over Na2SO4 and evaporated. Residue was recrystallized
from EtOH. M.p.: 339 8C, yield 52%.
m.p.: 207ꢀ
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208 8C) and 2-(3-nitrophenyl)-1-methylbenzi-
midazole (13) (m.p.: 154 8C (Lit. [10] m.p.: 151ꢀ
/
154 8C)
were prepared in our laboratory. ATCC strains of the
microorganism used in this study were obtained from
the culture collection of Refik Saydam Health Institu-
tion of Health Ministry, Ankara, Turkey.
3.1. General procedure for the preparation of the N-[4-
(1H-benzimidazol-2-yl)-phenyl]-benzamides (2ꢀ
/
10)
1H NMR (d ppm): 4.01 (s, 3H, Ã
CH2Ã); 7.59ꢀ8.00 (m, 7H, ArÃH); 8.29 (s, 1H, H-2?).
/NCH3); 4.37 (s, 2H,
Ã
/
/
/
/
Appropriate arylcarboxylic acids(1.5 mmol) were
refluxed in benzene (5 ml) with SOCl2 (5 ml) for 2 h at
80 8C. Then solvent and excess of SOCl2 were evapo-
rated completely and the residue was dissolved in ether
(10 ml). This mixture was added to an ice-cold mixture
of 2-(4-aminophenyl)benzimidazole (1.5 mmol),
NaHCO3 (3 mmol), ether (10 ml) and water (10 ml)
during 1 h period. The mixture was stirred overnight at
room temperature. The resultant precipitate was fil-
tered, washed with 1 N HCl and then water, and
purified by column chromatography using chloroform
(25):isopropanol (1) as eluent.
3.5. Synthesis of the N-[3-(1-methyl-1H-benzimidazol-
2-yl)-phenyl]-2-phenylthio-acetamide (16)
2-Chloro-N-[3-(1-methyl-1H -benzimidazol-2-yl)-
phenyl]-acetamide (0.33 mmol) was dissolved in dry
benzene (1 ml), and thiophenol (0.055 g, 0.50 mmol) and
few drops of piperidine were added. The reaction
mixture was refluxed for 6 h on a water bath, precipitate
was filtered off, washed with water, purified by column
chromatography using chloroform (4):isopropanol (1)
as eluent. M.p.: 158 8C, yield 10%.
1H NMR (d ppm): 3.89 (s, 3H, NÃ
COCH2); 7.21ꢀ7.71 (m, 12H, ArÃH); 8.11 (d, 1H, Jmꢁ
/CH3); 3.91 (s, 2H,
/
/
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3.2. Synthesis of the furan-2-carboxylic acid [4-(1H-
benzimidazol-2-yl)-phenyl]-amide (11)
1.62 Hz, H-2?); 10.29 (s, 1H, NHCO).
Mass (70 eV) m/z (%): 373 (Mꢂ) (57.60), 375
(Mꢂ2ꢂ) (2.97), 296(4.16), 264 (7.13), 250 (13.06), 222
(29.69), 207 (7.35), 123 (60.57), 108 (37.37), 77 (100), 63
(43.56), 43 (29.12), 41 (23.20).
Preparation was same as for 2ꢀ10, using furan-2-
/
carboxylic acid as starting carboxylic acid.
3.3. Synthesis of the 3-(1-methyl-1H-benzimidazol-2-
yl)-phenylamine (14)
4. Antimicrobial activity
The in vitro antimicrobial activity of the compounds
was tested by the tube dilution technique [11]. Each of
the test compounds and standards ampicillin trihydrate,
miconazole and fluconazole was dissolved in 12.5%
DMSO, at concentrations of 200 mg/ml, further dilutions
of the compounds and standards in the test medium
were prepared at the required quantities of 100, 50, 25,
12.5, 6.25, 3.12, 1.56, 0.78 mg/ml concentrations. The
final inoculum’s size was 105 CFU/ml. The minimum
inhibitory concentrations (MIC) were defined as the
lowest concentrations of the compounds that prevented
visible growth. It was determined that the solvent had
no antimicrobial activity against any of the test micro-
organism.
To the 2-(3-nitrophenyl)-1-methylbenzimidazole dis-
solved in EtOH (10 ml) was added 10% Pd/C (10 mg)
and the solution was hydrogenated at room temperature
at 40 psi. The reaction was stopped after cessation of H2
uptake. The catalyst was filtered through a bed of Celite,
washed with EtOH and concentrated. The residue was
purified by column chromatography using hexane
(1):EtOAc (1) as eluent. M.p.: 153 8C, yield 79%.
1H NMR (d ppm): 3.85 (s, 3H, NÃ
2H, NH2); 6.73 (d, 1H, Joꢁ7.96 Hz, H-4?); 6.92 (d, 1H,
Joꢁ7.53 Hz, H-6?); 7.03 (s, 1H, H-2?); 7.18ꢀ7.30 (m,
3H, H-5,6,5?); 7.59 (d, 1H, Joꢁ7.74 Hz, H-4); 7.64 (d,
1H, Joꢁ7.78 Hz, H-7).
/
CH3); 5.36 (br s,
/
/
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Mass (70 eV) m/z (%): 223 (Mꢂ) (61.21), 222 (100),
208 (1.24), 207 (2.02), 195 (2.86), 192 (1.29), 179 (1.31),
119 (8.76), 117 (33.18), 91 (23.13), 77 (59.35), 63 (40.65),
43 (29.91), 41 (31.78).
All the compounds were tested for their in vitro
growth inhibitory activity against Staphylococcus aureus
ATCC 25923, Streptococcus faecalis ATCC 19433 and
Bacillus subtilis ATCC 6633 as Gram positive, Escher-

G. Ayhan-K lc gil, N. Altanlar / Il Farmaco 58 (2003) 1345ꢀ
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Table 2
The in vitro antifungal activity of the compounds 2ꢀ
/11, 14, 16
Comp. No
S. aureus
S. faecalis
B. subtilis
E. coli
P. aeruginosa
C. albicans
2
100
50
100
50
50
25
50
50
25
25
50
25
50
50
50
25
50
50
25
25
25
25
3
12.5
25
4
50
50
50
50
50
50
5
100
50
100
50
25
50
6
50
50
50
50
7
25
50
25
25
8
100
50
100
50
50
25
100
25
9
10
25
25
50
50
50
50
25
50
50
50
11
14
25
6.25
25
50
50
50
50
12.5
25
25
50
16
Ampicillin
Fluconazole
Miconazole
3.125
6.25
6.25
3.125
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
ꢀ/
6.25
3.125
MIC, mg/ml.
ichia coli ATCC 23556 and Pseudomonas aeruginosa
ATCC 10145 as Gram negative bacteria and Candida
albicans ATCC 10231 as fungus. MIC values of the
compounds and the standards are presented in Table 2.
was comparable to ampicillin. Compound 14 exhibited
significant activity against B. subtilis with a 12.5 mg/ml.
Among the tested compounds, 14 and 3 showed good
antifungal activity against C. albicans with 6.25 and 12.5
mg/ml, respectively, which was comparable with fluco-
nazole (6.25 mg/ml) and close to miconazole (3.125 mg/
ml). As a result of antimicrobial activity, substitution of
amine function to anilide at the 2-phenyl moiety of
benzimidazole ring decreases the activity against B.
subtilis and C. albicans. It was also observed that sulfur
bearing compound (16) was found to be moderately
active against the tested microorganism.
4.1. Antibacterial activity assay
The cultures were obtained in Mueller-Hinton Broth
(Difco) for all the bacteria after 18ꢀ/24 h of incubation
at 3791 8C. 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
In conclusion, the similar antimicrobial activity
was kept as controls. After incubation for 18ꢀ
/24 h at
results for compounds 2ꢀ11 with the previously re-
/
3791 8C, the last tube with no growth of microorga-
/
ported 5 or 4? amides of benzimidazole (I, II, III and IV)
show that there is no important difference between the
position of amide and the transformation of amide to
nism was recorded to represent MIC expressed in mg/ml.
4.2. Antifungal activity assay
anilide (2ꢀ11).
/
The yeasts were maintained in Sabouraud Dextrose
Broth (Difco) after incubation for 48 h at 2591 8C.
/
Acknowledgements
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
This study was supported by the Research Organisa-
tion of the Ankara University, Turkey (No: 2001-08-03-
026).
as controls. After incubation for 48 h at 2591 8C, the
/
last tube with no growth of yeast was recorded to
represent MIC expressed in mg/ml.
References
5. Results and discussion
[1] H. Goker, E. Tebrizli, U. Abbasog˘lu, Synthesis of 1,2-disubsti-
¨
tuted benzimidazole-5(6)-carboxamides and evaluation of their
The antibacterial activity of all of the compounds
antimicrobial activity, Farmaco 51 (1996) 53ꢀ58.
/
[2] H. Goker, M. Tunc¸bilek, G. Ayhan, N. Altanlar, Synthesis of
¨
some new benzimidazolecarboxamides and evaluation of their
against S. aureus and S. faecalis as Gram (ꢂ
/
) and E.
coli as a Gram (ꢃ) bacteria showed lower potencies
/
antimicrobial activity, Farmaco 53 (1998) 415ꢀ
/420.
than the control drug ampicillin. Some of the com-
pounds (2, 3, 5, 9, 14 and 16) showed good activity with
a MIC value of 25 mg/ml against P. aeruginosa, which
[3] G. Ayhan-K lc gil, M. Tuncbilek, N. Altanlar, H. Goker, Synth-
¨
ı
ı
¸
esis and antimicrobial activity of some new benzimidazole
carboxylates and carboxamides, Farmaco 54 (1999) 562ꢀ565.
/

1350
G. Ayhan-K lc gil, N. Altanlar / Il Farmaco 58 (2003) 1345ꢀ1350
/
ı
ı
[4] H. Goker, M. Tuncbilek, S. Suzen, C. Kus, N. Altanlar, Synthesis
¨
¸ ¸
¨
and antimicrobial activity of some new 2-phenyl-N-substituted
carboxamido-1H-benzimidazole derivatives, Arch. Pharm.
[8] B. Miklaszewski, S. Niememtowski, Vergleichendes studium der
drei isomeren (b)-amino-phenylbenzimidazole, Chem. Ber. 34
(1901) 2953ꢀ
[9] F.F. Stephens, J.D. Bower, The preparation of benzimidazoles
and benzoxazoles from Schiff’s bases. Part I, (1949) 2971ꢀ2972.
[10] A.V. El’tsov, Kh. L. Muravich-Aleksandr, 1,2-dihydrobenzimi-
dazole derivatives I., Zh. Organ. Khim. 1(7) (1965) 1307ꢀ1314.
Ref. C.A: 63 (1965) 13238g.
/
2974.
Pharm. Med. Chem. 334 (2001) 148ꢀ152.
/
[5] H.F. Ridley, R.G.W. Spickett, G.M. Timmis, A new synthesis of
benzimidazoles and aza-analogs, J. Heterocyclic Chem. 2 (1965)
/
453ꢀ456.
/
/
[6] W.A. Jacobs, M. Heidelberger, I.P. Rolf, On certain aromatic
amines and chloroacetyl derivatives, J. Am. Chem. Soc. 41 (1919)
[11] D.F. Sahm, J.A. Washington, Antibacterial Suspectibility Tests,
Dilution Methods, in: A. Balowes, W.J. Hausler, K.L. Hermann,
H.D. Shadomy (Eds.), fifth ed. American Society for Microbio-
458ꢀ476.
/
[7] Z.M. Nofal, H.H. Fahmy, H.S. Mohamed, Synthesis, antimicro-
bial and molluscicidal activities of new benzimidazole derivatives,
logy, Washington, 1991, pp. 1105ꢀ1116.
/
Arch. Pharm. Res. 25 (2002) 28ꢀ38.
/