Synthesis and In-vitro antibacterial activity of 5-substituted 1-methyl-4-nitro-1H-imidazoles

Article abstract of DOI:10.1002/ardp.200800022

A series of 5-substituted 1-methyl-4-nitro-1H-imidazole derivatives were synthesized and evaluated for in-vitro antibacterial activity against a panel of microorganisms including Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Esherichia coli, Klebsiella pneumonia, Entrobacter aerogenes, and Helicobacter pylori using conventional agar dilution method. Among the test compounds, 1-methyl-4-nitro-5-(phenylsulfonyl)-1H-imidazole was the most potent against Gram-positive bacteria, with a MIC value of ≤8 μg/mL. All compounds showed no significant activity against Gram-negative bacteria at concentrations ≤64 μg/mL The MIC values against 15 clinical isolates of H. pylori indicated that compounds 10 and 11 were the most active compounds in this series in terms of inhibiting the growth of H. pylori (MIC = 2 μg/mL). It was also demonstrated that their corresponding activities were four times larger than that of metronidazole.

Full text of DOI:10.1002/ardp.200800022

Arch. Pharm. Chem. Life Sci. 2008, 341, 497–501
B. Letafat et al.
497
Full Paper
Synthesis and In-Vitro Antibacterial Activity of 5-Substituted
1-Methyl-4-nitro-1H-imidazoles
Bahram Letafat1, Saeed Emami2, Alireza Aliabadi3, Negar Mohammadhosseini1, 3, Mohammad
Hassan Moshafi4, Ali Asadipour4, Abbas Shafiee3, and Alireza Foroumadi3, 4
1 Department of Chemistry and Islamshar Young Researchers Club, Islamic Azad University, Islamshahr-
Branch, Tehran, Iran
2 Department of Medicinal Chemistry, Faculty of Pharmacy, Mazandaran University of Medical Sciences,
Sari, Iran
3 Department of Medicinal Chemistry, Faculty of Pharmacy and Pharmaceutical Sciences Research Center,
Tehran University of Medical Sciences, Tehran, Iran
4 Kerman Neuroscience Research Center and Department of Microbiology, Faculty of Pharmacy, Kerman
University of Medical Sciences, Kerman, Iran
A series of 5-substituted 1-methyl-4-nitro-1H-imidazole derivatives were synthesized and eval-
uated for in-vitro antibacterial activity against a panel of microorganisms including Staphylococ-
cus aureus, Staphylococcus epidermidis, Bacillus subtilis, Esherichia coli, Klebsiella pneumonia, Entro-
bacter aerogenes, and Helicobacter pylori using conventional agar dilution method. Among the test
compounds, 1-methyl-4-nitro-5-(phenylsulfonyl)-1H-imidazole was the most potent against Gram-
positive bacteria, with a MIC value of f8 lg/mL. All compounds showed no significant activity
against Gram-negative bacteria at concentrations f64 lg/mL The MIC values against 15 clinical
isolates of H. pylori indicated that compounds 10 and 11 were the most active compounds in this
series in terms of inhibiting the growth of H. pylori (MIC = 2 lg/mL). It was also demonstrated
that their corresponding activities were four times larger than that of metronidazole.
Keywords: Antimicrobial activity / Helicobacter pylori / 4-Nitroimidazole / Synthesis /
Received: February 15, 2008; accepted: March 27, 2008
DOI 10.1002/ardp.200800022
lymphoid tissue (MALT)-type gastric carcinoma; its eradi-
cation is strongly recommended for patients with these
diseases and those with unexplained iron-deficiency ane-
mia [2]. Clinical evidences also demonstrated that the
eradication of H. pylori can reduce the risk of ulcer
relapse and may be an effective method to prevent gastric
cancer [3]. Hence, our research efforts are directed toward
the discovery of new chemical entities that are effective
as antimicrobial agents (especially against staphylococci
and Helicobacter pylori) and the optimization of their
structures.
During recent years, there have been intense investiga-
tions of different classes of 1,3,4-thiadiazole- and nitroi-
midazole-containing compounds, many of which are
known to possess biological properties such as antituber-
culosis and anti-H. pylori activities [4–6]. The use of nitro-
heterocycles as antibacterial, antiviral, antiprotozoal,
anticancer, and radiosensitizing agents is well estab-
Introduction
The emergence of multi-drug resistant Gram-positive bac-
teria, such as Staphylococcus aureus has made the treat-
ment of infectious diseases difficult and has, over the last
decades, become a serious medical problem. As patho-
genic bacteria continuously evolve mechanisms of resist-
ance to currently used antibacterial drugs, the discovery
of novel and potent antibacterial agents is the best way
to overcome bacterial resistance and develop effective
therapies [1]. On the other hand, Helicobacter pylori is now
a well-recognized cause of active chronic gastritis, peptic
ulcer disease, gastric carcinoma, and mucosa-associated
Correspondence: Dr. Alireza Foroumadi, Faculty of Pharmacy and
Pharmaceutical Sciences Research Center, Tehran University of Medical
Sciences, Tehran 14174, Iran.
E-mail: aforoumadi@yahoo.com
Fax: +98 21 6646 1178
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498
B. Letafat et al.
Arch. Pharm. Chem. Life Sci. 2008, 341, 497–501
9 by m-CPBA in dichloromethane gave 1,3,4-thiadiazole
sulfone 12. Phenylsulfone derivatives 5–7 obtained
directly from the reaction of 3 with sodium phenylsulfi-
nates in refluxing DMF.
Antibacterial activity
The synthesized compounds 4–12 were assessed for their
antibacterial activity against a panel of Gram-positive
(Staphylococcus aureus, Staphylococcus epidermidis, and
Bacillus subtilis) and Gram-negative (Kelebsiella pneumo-
niae, Escherichia coli, and Enterobacter aerogenes) bacteria
using a conventional agar-dilution method. The MIC
(minimum inhibitory concentration) values were deter-
mined and compared to norfloxacin as standard antibac-
terial drug. In addition, this series of compounds were
tested in vitro against 15 clinical isolates of Helicobacter
pylori in comparison to metronidazole as standard anti-
H. pylori drug. The MIC values (lg/mL) obtained for com-
pounds 4–12 are presented in Table 1.
Reagents and conditions: (a) CH2N2, dry ether; (b) sodium thiophenolate, EtOH,
reflux; (c) DMF, reflux; (d) KOH, EtOH, reflux; (e) m-CPBA, CH2Cl2.
MIC values of the tested derivatives indicate that com-
pounds 5–8 showed a higher antibacterial activity
against Gram-positive rather than Gram-negative bacte-
ria. Indeed, the latter compounds had respectable in-vitro
activity against staphylococci and B. subtilis (MIC = 4–
64 lg/mL), but were less active than the reference drug
norfloxacin. Compound 5 was the most potent against
Gram-positives, with MIC value of 4-8 lg/mL. None of the
compounds showed significant activity against Gram-
negative bacteria at concentrations =64 lg/mL. Gener-
ally, compounds containing phenyl ring showed better
activity than compounds with the 1,3,4-thiadiazole ring
system.
As is evident from the data, compounds 10 and 11 were
the most active in terms of inhibiting the growth of H.
pylori (MIC = 2 lg/mL), and their activities were found to
be four times better than metronidazole. When 5-nitroi-
midazole 10 compared to 5-nitrofuran 11, both com-
pounds had similar in-vitro activities against clinical iso-
lates of H. pylori, but the susceptibility against Gram-posi-
tive bacteria was reduced in 5-nitroimidazole 10. Surpris-
ingly, the susceptibility against Gram-negatives was lost
in both compounds. The remaining compounds 5–9
showed weak activity against H. pylori strains (MIC = 32–
64 lg/mL).
Scheme 1. Synthesis of 5-substituted 1-methyl-4-nitro-1H-imi-
dazoles 4–12.
lished [7–12]. In our previous studies some new com-
pounds containing 5-nitroheterocycles and 1,3,4-thiadia-
zole with different substituents at the C2-position of the
thiadiazole ring were synthesized and evaluated for
activity against several bacterial species [13]. In continua-
tion to our ongoing research work on nitroheterocyclic
derivatives, herein, we describe the synthesis and in-vitro
antibacterial activity of new 5-substituted 1-methyl-4-
nitro-1H-imidazole derivatives 4–12 against a panel of
Gram-positive and Gram-negative bacteria including Heli-
cobacter pylori.
Results and discussion
Chemistry
The synthesis of 5-substituted-1-methyl-4-nitro-1H-imida-
zole derivatives 4–12 was achieved with an efficient syn-
thetic route outlined in Scheme 1. The starting material
5(4)-bromo-4(5)-nitroimidazole 1 was prepared according
to the literature method [14]. The reaction of 1 with
diazomethane in dry diethyl ether afforded 1-methyl-5-
bromo-4-nitro-1H-imidazole 3 as major product. Com-
pound 3 could be also prepared from nitration of 5-
bromo-1-methyl-1H-imidazole [15]. Treatment of 3 with
sodium thiophenolate or appropriate arylthiols in the
presence of potassium hydroxide afforded the desired
sulfides 4 and 8–11, respectively. Oxidation of compound
In summary, we have synthesized and evaluated the
antibacterial activities of a series of 1-methyl-4-nitro-1H-
imidazoles containing different arylthio- or arylsulfonyl-
groups at the 5-position. Several compounds with 5-(phe-
nylsulfonyl)-residue on the general scaffold have shown
promising antibacterial activities against several types of
Gram-positive bacteria including Staphylococcus aureus,
Staphylococcus epidermidis, and Bacillus subtilis. A few tar-
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Arch. Pharm. Chem. Life Sci. 2008, 341, 497–501
5-Substituted methylnitro-imidazoles
499
Table 1. In vitro antibacterial activities of compounds 4–12 against selected strainsa).
Compound
R
n
0
S. a.a)
S. e. a)
B. s.a)
64
K. p.a)
E. c.a)
E. a.a)
H. p.a)
4
A64c)
64
A64
A64
A64
A64
5
6
2
2
8
4
8
4
A64
A64
A64
A64
A64
A64
32 (16 to A64)c)
32 (16 to A64)c)
32
16
7
8
2
0
16
32
32
8
8
A64
A64
A64
A64
A64
A64
64 (16 to A64)c)
64 (16 to A64)c)
64
9
0
0
16
64
64
A64
A64
A64
A64
A64
A64
A64
A64
64 (16 to A64)c)
10
A64
2 (0.5 to 8)c)
11
12
0
2
4
32
64
A64
A64
A64
A64
A64
A64
2 (0.5 to 8)c)
A64
A64
A64
A64
8 (4 to A64)c)
Norfloxacin
Metronidazole
1
1
0.13
0.25
0.13
0.13
a)
S. a. = Staphylococcus aureus ATCC 6538p; S. e. = Staphylococcus epidermidis ATCC 12228; B. s. = Bacillus subtilis PTCC 1023; K. p. =
Kelebsiella pneumoniae ATCC 10031; E. c. = Escherichia coli ATCC 8739; E. a. = Enterobacter aerogenes PTCC 1221, and 15 clinical iso-
lates of H. p. = H. pylori were used for determination of MIC.
(MICs in lg/mL)
The MIC range is in the parenthesis.
b)
c)
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Arch. Pharm. Chem. Life Sci. 2008, 341, 497–501
7.38 (d, 2H, phenyl, JAB = 8.0 Hz), 4.06 (s, 3H, N-CH3), 2.45 (s, 3H,
CH3). MS: m/z (%) 281 [M+] (18), 200 (43), 146 (28), 139 (42), 111
(90), 107 (100), 79 (85), 65 (95), 42 (87).
get compounds 10 and 11 were also found to be effective
against Helicobacter pylori. The structures of these com-
pounds and the structure-activity relationship observed
from this series of compounds can be used to further
optimize the structures to obtain potent novel antimicro-
bial drugs.
1-Methyl-4-nitro-5-[4-acetamido(phenylsulfonyl)]-1H-
imidazole 7
Yield 93%; m.p. 129–1318C (m.p. 125–1278C, Lit. [17]); 1H-NMR
(CDCl3) d: 8.06 (d, 2H, phenyl, JAB = 8.8 Hz), 7.74 (d, 2H, phenyl, JAB
= 8.8 Hz), 7.45 (br s, 1H, imidazole and 1H, NH), 4.07 (s, 3H, N-
CH3), 2.22 (s, 3H, CH3CO). MS: m/z (%) 324 [M+] (15), 282 (25), 150
(21), 111 (90), 108 (100), 43 (15).
The authors have declared no conflict of interest.
Experimental
General procedure for the synthesis of sulfides 8–11
Melting points were determined on a Kofler hot stage apparatus
and are uncorrected (C. Reichert, Vienna, Austria). 1H-NMR spec-
tra were recorded using a Bruker AC-80 spectrometer (Bruker,
Germany), and chemical shifts are expressed as d (ppm) with tet-
ramethylsilane as internal standard. The mass spectra were run
on a Finnigan TSQ-70 spectrometer (Finnigan, USA) at 70 eV. Ele-
mental analyses were carried out on a CHN-O-rapid elemental
analyzer (Foss-Heraeus GmbH, Germany) for C, H and N, and the
results are within l 0.4% of the theoretical values. The purity of
the synthesized compounds was confirmed by thin-layer chro-
matography (TLC) using various solvents of different polarities.
Merck silica gel 60 F254 plates were applied for analytical TLC
(Merck, Germany).
A
mixture of 1-methyl-5-bromo-4-nitro-1H-imidazole
3
(1.0 mmol),
2-mercapto-5-substituted-1,3,4-thiadiazole
(1.0 mmol), and potassium hydroxide (1.0 mmol) in 10 mL etha-
nol, was refluxed for two hours. After cooling, water (20 mL) was
added and the precipitate was filtered and washed with water
and dried to give a solid which was recrystallized from ethanol
affording compounds 8–11.
2-[(1-Methyl-4-nitro-5-imidazolyl)thio]-5-acetamido-1,3,4-
thiadiazole 8
Yield 76%; m.p. 250–2538C; 1H-NMR (DMSO-d6) d: 8.19 (br s, 1H,
NH), 7.60 (s, 1H, imidazole), 3.77 (s, 3H, N-CH3), 2.15 (s, 3H,
CH3CO). MS: m/z (%) 301 [M+ + 1] (85), 254 (100), 212 (22), 159 (18),
142 (23), 43 (20). Anal. Calcd. for C8H8N6O3S2: C, 31.99; H, 2.68; N,
27.98. Found: C, 32.12; H, 2.66; N, 28.14.
Chemistry
1-Methyl-4-nitro-5-(phenylthio)-1H-imidazole 4
A
mixture of 1-methyl-5-bromo-4-nitro-1H-imidazole
3
(1.0 mmol) and sodium thiophenolate (1.0 mmol) in 10 mL etha-
nol was refluxed for two hours. The reaction mixture was
cooled, poured into 20 mL of water, and extracted with chloro-
form. The extracts were washed with water, dried, and evapo-
rated under vacuum. The residue is recrystallized from ethanol
affording compound 4 in 81% yield. M.p. 75–768C (m.p. 77–
2-[(1-Methyl-4-nitro-5-imidazolyl)thio]-5-(4-
methoxyphenyl)-1,3,4-thiadiazole 9
1
Yield 66%; m.p. 159–1618C; H-NMR (CDCl3) d: 7.81 (d, 2H, phe-
nyl, JAB = 9.6 Hz), 7.66 (s, 1H, imidazole), 6.96 (d, 2H, phenyl, JAB
=
9.6 Hz), 3.92 (s, 3H, N-CH3), 3.86 (s, 3H, OCH3). MS: m/z (%) 349 [M+]
(63), 303 (45), 170 (18), 135 (15), 151 (100). Anal. Calcd. for
C13H11N5O3S2 : C, 44.69; H, 3.17; N, 20.04. Found: C, 44.91; H, 3.28;
N, 19.92.
1
788C, Lit. [16]); H-NMR (CDCl3) d: 7.60 (s, 1H, imidazole), 7.36–
7.16 (m, 5H, phenyl), 3.62 (s, 3H, CH3). MS: m/z (%) 236 [M+ + 1]
(100), 235 [M+] (37), 218 (94), 185 (18), 154 (18), 142 (30), 109 (30),
43 (18).
General procedure for the synthesis of phenylsulfone
2-[(1-Methyl-4-nitro-5-imidazolyl)thio]-5-(1-methyl-5-
nitro-2-imidazolyl)-1,3,4-thiadiazole 10
derivatives 5–7
A
mixture of 1-methyl-5-bromo-4-nitro-1H-imidazole
3
Yield 71%; m.p. 188–1908C; 1H-NMR (CDCl3) d: 8.05 (s, 1H, 5-nitro-
imidazole), 7.74 (s, 1H, 4-nitroimidazole), 4.51 (s, 3H, N-CH3 of 5-
nitroimidazole), 3.91 (s, 3H, N-CH3 of 4-nitroimidazole). MS: m/z
(%) 401 [M+ + 1] (25), 385 (20), 369 (60), 322 (100), 285 (20), 247
(22), 201 (20), 170 (75), 142 (25), 83 (60), 67 (20). Anal. Calcd. for
C10H8N8O4S2: C, 32.61; H, 2.19; N, 30.42. Found: C, 32.48; H, 2.23;
N, 30.54.
(1.0 mmol) and sodium arylsulfinate (1.0 mmol) in 10 mL DMF
was refluxed for three hours. After cooling, water (15 mL) was
added and the precipitate was filtered, washed with water, and
dried to give a solid which was recrystallized from ethanol.
1-Methyl-4-nitro-5-(phenylsulfonyl)-1H-imidazole 5
Yield 61%; m.p. 138–1398C (m. p. 137–1388C, Lit. [16]); 1H-NMR
(CDCl3) d: 8.18–8.06 (m, 2H, phenyl), 7.67–7.48 (m, 1H, imida-
zole and 3H, phenyl), 4.08 (s, 3H, CH3). MS: m/z (%) 267 [M+] (15),
203 (10), 141 (10), 133 (22), 110 (22), 83 (40), 77 (100), 42 (40).
2-[(1-Methyl-4-nitro-5-imidazolyl)thio]-5-(5-nitrofuran-2-
yl)-1,3,4-thiadiazole 11
Yield 61%; m.p. 198–2008C; 1H-NMR (CDCl3) d: 7.73 (s, 1H, imida-
zole), 7.50–7.28 (m, 2H, furyl), 3.92 (s, 3H, CH3). MS: m/z (%) 354
[M+] (10), 275 (18), 210 (100), 194 (21), 155 (83), 139 (30), 108 (55),
105 (100), 77 (95), 65 (70), 51 (38). Anal. Calcd. for C10H6N6O5S2 : C,
33.90; H, 1.71; N, 23.72. Found: C, 33.99; H, 1.68; N, 23.70.
1-Methyl-4-nitro-5-(4-methylphenylsulfonyl)-1H-
imidazole 6
1
Yield 65%; m.p.128–1308C (m.p. 130–1328C, Lit. [16]); H-NMR
(CDCl3) d: 7.99 (d, 2H, phenyl, JAB = 8.0 Hz), 7.46 (s, 1H, imidazole),
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Arch. Pharm. Chem. Life Sci. 2008, 341, 497–501
5-Substituted methylnitro-imidazoles
501
a turbidity equivalent to the 0.5 McFarland standards. The plates
were inoculated and incubated at 378C for 72 h under micro-
aerobic conditions (10% CO2 in a gas incubator). The MIC was
defined as the lowest concentration capable of inhibiting any
visible bacterial growth.
2-[(1-Methyl-4-nitro-5-imidazolyl)sulfonyl]-5-(4-
methoxyphenyl)-1,3,4-thiadiazole 12
A mixture of 9 (1.0 mmol), m-chloroperbenzoic acid (3.0 mmol),
and NaHCO3 (3.0 mmol) in 15 mL of dichloromethane was
stirred for three days. The reaction mixture was monitored by
TLC. After consumption of the starting material, water (15 mL)
was added and the organic phase was separated. The aqueous
phase was extracted with dichloromethane (2615 mL). The com-
bined organic phases were washed with water and dried
(Na2SO4). Evaporation of the solvent gave a solid which was
recrystallized from ethanol. Yield 78%; m.p. 181–1838C; 1H-NMR
(CDCl3) d: 7.91 (d, 2H, phenyl, JAB = 8.8 Hz), 7.59 (s, 1H, imidazole),
7.00 (d, 2H, phenyl, JAB = 8.8 Hz), 4.15 (s, 3H, N-CH3), 3.88 (s, 3H,
OCH3). MS: m/z (%) 381 [M+] (20), 366 (10), 349 (23), 303 (38), 151
(80), 133 (100), 83 (27). Anal. Calcd. for C13H11N5O3S: C, 49.21; H,
3.49; N, 22.07. Found: C, 49.42; H, 3.33; N, 21.96.
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