Synthesis and antitubercular screening of imidazole derivatives

Article abstract of DOI:10.1016/j.ejmech.2009.02.013

A series of imidazole based compounds were synthesized by reacting simple imidazoles with alkyl halides or alkyl halocarboxylate in presence of tetrabutylammonium bromide (TBAB). The compounds bearing carbethoxy group undergo amidation with different amines in the presence of DBU to give respective carboxamides. The synthesized compounds were screened against Mycobacterium tuberculosis where compound 17 exhibited very good in vitro antitubercular activity and may serve as a lead for further optimization.

Full text of DOI:10.1016/j.ejmech.2009.02.013

European Journal of Medicinal Chemistry 44 (2009) 3350–3355
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Preliminary communication
Synthesis and antitubercular screening of imidazole derivativesq
,
Jyoti Pandeya, Vinod K. Tiwari a 1, Shyam S. Verma a, Vinita Chaturvedi b, S. Bhatnagar b, S. Sinha b,
,
A.N. Gaikwad b, Rama P. Tripathi a
*
a Divisions of Medicinal and Process Chemistry, Central Drug Research Institute, Lucknow 226001, India
b Drug Target Discovery and Development, Central Drug Research Institute, Lucknow 226001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of imidazole based compounds were synthesized by reacting simple imidazoles with alkyl
halides or alkyl halocarboxylate in presence of tetrabutylammonium bromide (TBAB). The compounds
bearing carbethoxy group undergo amidation with different amines in the presence of DBU to give
respective carboxamides. The synthesized compounds were screened against Mycobacterium tuberculosis
where compound 17 exhibited very good in vitro antitubercular activity and may serve as a lead for
further optimization.
Received 7 June 2008
Received in revised form
29 January 2009
Accepted 12 February 2009
Available online 20 February 2009
Ó 2009 Elsevier Masson SAS. All rights reserved.
Keywords:
Tuberculosis
Imidazoles
Glycosyl amino ester
C-alkylation
C-Allyl imidazoles
1. Introduction
[14–16]. It is established that these compounds target the sterol
demethylase, a mixed-function oxidase involved in sterol synthesis
An increase in the global burden of tuberculosis with the
worldwide mortality rate of 23% is a major concern in the socio-
economic and health sectors [1–5]. The synergy of this disease with
HIV infection and the emergence of multi drug resistance and
extensively drug resistance tuberculosis (MDRTB and XDRTB) pose
a threatening global challenge [6–8]. Although a number of lead
molecules exist today to develop new drugs, no new chemical
entity has emerged for clinical use for over the last 45 years in the
treatment of this disease [9,10]. Therefore, there is an urgent need
to develop new drugs, acting through a novel mechanism of action
for the chemotherapy of tuberculosis.
in eukaryotic organisms [17]. The unraveling of Mycobacterium
genome sequence has revealed that a protein having homology to
one of the above mixed oxidase function is present in Mycobacte-
rium tuberculosis [18]. Nitroimidazole derivative such as nitro-
imidazopyran is in advanced stage of clinical trial for the treatment
of tuberculosis and it has been speculated that this compound is
active against both the replicating and the latent Mycobacterium
[19]. Keeping in mind the above facts, we were interested to see the
antitubercular potential in simple imidazole derivatives.
2. Results and discussion
Recently certain imidazole based compounds were reported to
possess antimicrobial activities [11]. It is believed that aryl–azolyl–
ethane moiety, present in many azole antifungal drugs serve as
pharmacophore in compounds having Mycobacterium killing
activity [12,13]. Many azole derivatives have also displayed inter-
esting antimycobacterial activity in addition to antifungal activity
Compounds 3–5 and 15–18 were synthesized starting from
simple imidazoles by reacting them with different alkyl halides
(viz. 3,4-dichlorobenzyl bromide, ethyl bromoacetate, ethyl bro-
mopropionate, 1,3-dibrompropane and 1,5-dibromopentane) in the
presence of NaH/TBAB (tetrabutylammonium bromide) in anhy-
drous DMF or THF (Table 1). Although few such alkylation methods
for the synthesis of 1-alkyl-, aralkyl imidazoles and bis-imidazolyl
alkanes were reported earlier [32–35], however our method of
alkylation of imidazole and 2-propylimidazole in the presence of
TBAB offers advantages over previous ones in terms of mild reac-
tion conditions along with shorter reaction time and better yield of
the products.
q
CDRI communication number: 7398.
* Corresponding author. Fax: þ91 522 2623405.
E-mail addresses: vtiwari@ucdavis.edu (V.K. Tiwari), rpt.cdri@yahoo.co.in,
rpt.cdri@gmail.com (R.P. Tripathi).
1
Present address: Department of Chemistry, Faculty of Science, Banaras Hindu
University, Varanasi 221005, India.
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.02.013

J. Pandey et al. / European Journal of Medicinal Chemistry 44 (2009) 3350–3355
3351
Table 1
Synthesis of substituted imidazoles and benzimidazoles (3–18).
N
N
Amines/DBU
Toluene/reflux
Compound
No.
Physical state
M.p. (ꢁC)
Known m.p.
(ꢁC) [Ref]
% Yield
R
R
N
N
3
4
Yellow semi solid
White solid
–
–
65
70
70
78
78
80
78
46
80
70
75
68
70
55
45
O
120–124
124 [32]
COOEt
5
6
7
8
Light brown solid
Viscous mass
Yellow semi solid
Yellow solid
165–168
–
–
–
–
[33]
–
4
NHR1
6: R=H, R1=n-butyl
7: R=H, R1=n-hexyl
8: R=H, R1=n-heptyl
9: R=H, R1=benzyl
74–76
9
Pale yellow semi solid
Colorless solid
Viscous mass
Pale yellow solid
Yellow solid
Yellow oil
Viscous mass
Colorless oil
–
–
10
11
13
14
15
16
17
18
37–39
–
116–118
138–140
–
–
–
–
36–40 [34]
–
–
–
[35]
–
–
LiAlH4/THF
N
N
Colorless oil
–
(i) CH3SO2Cl/Et3N/CH2Cl2
N
R
(ii) Benzylamine/4ÅMS/DBU
Toluene/reflux
N
H
Thus, reaction of imidazole (1) with 3,4-dichlorobenzyl
bromide, ethyl bromoacetate and ethyl bromopropionate sepa-
rately in THF in the presence of NaH/TBAB gave 1-(3,4-dichloro-
benzyl)-1H-imidazole (3), imidazol-1-yl-acetic acid ethyl ester (4)
and 3-imidazol-1-yl-propionic acid ethyl ester (5) respectively in
quantitative yield (Scheme 1).
N
Ph
OH
10
11
Scheme 2. Synthesis of imidazole derivatives.
Compounds (6–9) were prepared by reaction of compound 4
with different amines viz. n-butyl, n-hexyl, n-heptylamine, and
benzylamine under refluxing condition. LiAlH4 reduction of the
above compound 4 gave respective 1-(2-hydroxy ethyl)-1H-imid-
azole (10) in good yield. The latter, on mesylation with meth-
anesulphonyl chloride followed by reaction with benzyl amine in
presence of DBU and 4 Å molecular sieve gave 1-(2-benzyl amino
ethyl)-1H-imidazole (11) in quantitative yield (Scheme 2).
The structures of all the synthesized compounds were estab-
lished on the basis of spectroscopic data and analysis. The IR data
for compound 3 exhibited C]N and C]C stretching frequency at
ymax 1730 and 1642 cmꢀ1, respectively. In the 1H NMR spectrum of
the formation of compounds 15 and 16 respectively in good yields.
However, reacting 2 eq. of 2-propylimidazole with 1 eq. of
1,3-dibromopropane gave the expected 1,3-bis-(2-propylimidazol-
1-yl)-propane (17) as major product along with another unusual
minor product, 1-(4-allyl-2-propylimidazol-1-yl)-3-(2-propylimi-
dazol-1-yl)-propane (18) (Scheme 4). Formation of compound 18 is
speculated via electrophilic attack of carbocation generated from
allyl bromide which in turn formed via rearrangement of
1,3-dibromopropane. However, exact mechanism is yet to be
established.
Since glycosyl amino ester derivatives and other glyco-
conjugates bearing alkyl substitutents at the nitrogen atom [20–24]
have been found to possess antitubercular activity, we were
prompted to see the effect of imidazole ring at the C-5 of sugar
moiety on antitubercular activity profiles. Synthesis of imidazolyl
glycosyl uronoates (19–22, Fig. 1) in moderate yields was carried
out by us as reported earlier [25].
compound 3, appearance of a multiplet in the range of
corresponds to three imidazole and three phenyl protons and
a singlet at
5.09 corresponds to methylene protons. In the 13C
NMR spectrum, peaks at 142.7, 137.6, 136.8, 136.4, 134.5, 134.1,
132.2, 128.2 and 124.6 showed the presence of imidazole carbons
and aromatic carbons whereas peak at 54.3 showed the presence
d 7.56–6.89
d
d
d
The imidazole derivatives (3–22) were screened for their anti-
tubercular efficacy against M. tuberculosis using different test
models [26–29] and the results are shown in Table 2. The antitu-
bercular efficacy of these compounds were tested against avirulent
strain M. tuberculosis H37Ra and virulent strain M. tuberculosis
of methylene carbon. Finally, molecular ion peak at m/z 228
(M þ H)þ in MS spectrum confirms the structure of compound 3.
Similarly, compounds 13 and 14 were prepared by benzylation
of benzimidazole (12) with benzyl bromide and 3,4-dichlorbenzyl
bromide respectively (Scheme 3) and the structures were estab-
lished on the basis of spectroscopic data and analysis.
Compounds 15–18 were prepared by the reaction of imidazole
(1 or 2) with dibromoalkanes in presence of NaH and TBAB in THF
(Scheme 4). The reaction of 2 eq. of imidazole with 1 eq. of
1,3-dibromopropane and 1,5-1,5-dibromopentane separately led to
H37Rv at different concentrations ranging from 50
3.25 g/ml. As evident from Table 2 that most of the compounds
displayed antitubercular activity with MIC ranging from 25 to
>12.5 g/ml against either the avirulent strain M. tuberculosis
H37Ra or the virulent strain M. tuberculosis H37Rv. The only
mg/ml to
m
m
compound 17 showed MIC 6.25
mg/ml against virulent strain
R1
N
N
R1-X, THF
N
NaH/TBAB
N
ArCH2Br, THF
N
R2
NaH, / 0-30 °C
N
R
N
R
N
H
H
3: R= H, R1= 3,4-dichlorobenzyl
4: R= H, R1= CH2COOEt
5: R= H, R1= CH2CH2COOEt
12
1: R=H
2: R=Propyl
R1
13: R1= R2=H
14: R1= R2=Cl
Scheme 1. Synthesis of N-alkyl(aralkyl) imidazoles.
Scheme 3. Synthesis of benzimidazole derivatives.

3352
J. Pandey et al. / European Journal of Medicinal Chemistry 44 (2009) 3350–3355
R1
N
( )
1,3-dibromopropane or
1,5-dibromopentane
n
N
N
R
NaH/THF, TBAB, 0-30°C, 4h
N
R
R
N
H
N
1: R=H
15: n=1, R=R1=H
16: n=3, R=R1=H
2: R=C3H7
17: n=1, R=Propyl, R1=H
18: n=1, R=Propyl,R1=Allyl
Scheme 4. Synthesis of bis-imidazolyl derivatives.
were screened against avirulent and virulent strains of M. tuber-
culosis. One of the compounds offers potential for further optimi-
zation and development to new antituberculars.
N
R1
O
N
4. Experimental
O
O
4.1. Chemistry
OEt
Me2C
Commercially available reagent grade chemicals were used as
received. All reactions were followed by TLC on E. Merck Kieselgel
60 F254, with detection by UV light and/or spraying a 20% KMnO4
aq. soln. Column chromatography was performed on silica gel
(60–120 mesh, E. Merck). IR spectra were recorded as thin films or
O
OR
19: R=CH3; R1=H, 20: R=CH2Ph; R1=H, 21: R=CH3; R1=Propyl, 22: R=CH2Ph;
R1=Propyl
Fig. 1.
in chloroform soln. with
a Perkin–Elmer Spectrum RX-1
(4000–450 cmꢀ1) spectrophotometer. 1H and 13C NMR spectra
were recorded on a Brucker DRX-300 in CDCl3. Chemical shift
values are reported in ppm relative to SiMe4 as internal reference,
unless otherwise stated; s (singlet), d (doublet), t (triplet), m
(multiplet); J in hertz. FAB mass spectra were performed using
a mass Spectrometer Jeol SX-102 and ESI mass spectra with Quattro
II (Micromass). Elemental analyses were performed on a Perkin–
Elmer 2400 II elemental analyzer.
Table 2
Antitubercular activities of synthesized imidazole derivatives.
Compound no.
MIC (
mg/ml) using
MIC (mg/ml) using Agar
MABA method
microdilution method
3
4
5
6
7
8
9
10
11
13
14
15
16
17
18
19
20
21
22
>12.5
>12.5
nd
>12.5
25
>12.5
>12.5
>12.5
12.5
>12.5
>12.5
>12.5
>12.5
>12.5
>12.5
25
nd
>6.25
>12.5
>12.5
>12.5
>12.5
>12.5
>12.5
12.5
>12.5
>12.5
>12.5
>12.5
6.25þ
25
4.2. General procedure for the synthesis of N-substituted imidazole
or benzimidazoles (3–5, 13–14 and 15–18)
To the stirred slurry of NaH (0.21 g, 14.7 mmol) in dry THF (5 ml)
at 0 ꢁC, a solution of imidazole (1.0 g, 14.7 mmol) in THF was added
dropwise and the reaction mixture was stirred for half an hour. The
corresponding alkyl halide or alkyl haloacetate (14.7 mmol) was
added dropwise followed by addition of tetrabutylammonium
bromide and the reaction mixture was further stirred at 30 ꢁC till the
disappearance of starting material (TLC). The reaction mixture was
filtered through celite pad and filtrate thus obtained was evaporated
under reduced pressure to give a residual mass. The latter was
dissolved in CH2Cl2 and washed with water. The organic layer was
dried over Na2SO4 and the solvent was evaporated under reduced
pressure to give a crude product, which was purified by column
chromatography (SiO2) using methanol:chloroform (1:5) as eluent.
25
50
25
50
50
25
50
MIC, minimum inhibitory concentration; nd, not determined; MIC of the
compounds used as control: EMB 1.5–5.0
BACTEC method.
mg/ml, INH 0.65 m
g/ml; þMIC confirmed by
4.2.1. 1-(3,4-Dichloro-benzyl)-1H-imidazole (3)
M. tuberculosis H37Rv. The MIC for this compound was also
confirmed by using BACTEC assay and thus offers a prototype lead
for further optimization and development.
The reaction of 1 and 3,4-dichlorobenzyl bromide (2.1 ml,
14.1 mmol) as described above gave 3. FT-IR (KBr, cmꢀ1): 3424,
2968, 1730, 1642; ESMS: 228 (M þ H)þ. 1H NMR (200 MHz, CDCl3–
CCl4):
NMR (50 MHz, CDCl3–CCl4): d 142.7, 137.6, 136.8, 136.4, 134.5, 134.1,
d C
7.56–6.89 (m, 6H, Im–H and Ar–H), 5.09 (s, 2H, –CH2). 13
3. Conclusion
132.2, 128.2, 124.6, 54.3. Anal. Calcd for C10H8N2Cl2: C, 52.89; H,
3.55; N, 12.34; Found: C, 52.86; H, 3.57; N, 12.33.
In conclusion, we have synthesized simple imidazole derivatives
either by simple alkylation of imidazoles followed by further
manipulations or by conjugate addition of imidazoles to different
glycosyl olefinic esters. An unusual observation of introducing an
allyl moiety in 2-propylimidazole is also revealed. The compounds
4.2.2. Imidazol-1-yl-acetic acid ethyl ester (4) [32]
The reaction of 1 and ethyl bromo acetate (1.63 ml, 14.7 mmol)
as described above gave 4. FT-IR (KBr, cmꢀ1): 3436, 2989, 1743,

J. Pandey et al. / European Journal of Medicinal Chemistry 44 (2009) 3350–3355
3353
1637, 1514; ESMS: 155 (M þ H) þ. 1H NMR (200 MHz, CDCl3–CCl4):
4.2.7. 1-Benzyl-1H-benzimidazole (13)
d
7.60–6.92 (m, 3H, Im–H), 4.24 (m, 2H, –N–CH2), 4.16 (dd, J ¼ 7.1 Hz
The reaction of benzimidazole (12, 1.0 g, 8.47 mmol) and benzyl
bromide (1.0 ml, 8.47 mmol) in the slurry of NaH (0.3 g, 12.5 mmol)
as described above gave 13. FT-IR (KBr, cmꢀ1): 3286, 3018, 1672,
1510, 1405; ESMS: 209 (M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
and 7.3 Hz, 2H, –OCH2), 1.27 (m, 3H, –CH3). 13C NMR (50 MHz,
CDCl3–CCl4): 167.6, 138.1, 129.9, 120.2, 62.2, 48.3, 14.4. Anal. Calcd
d
for C7H10N2O2: C, 54.54; H, 6.54; N, 18.17; Found: C, 54.52; H, 6.53;
N, 18.15%.
d
7.87–7.11 (m, 10H, Im–H and Ar–H), 5.32 (s, 2H, CH2); 13C NMR
(50 MHz, CDCl3–CCl4):
d 144.4, 143.2, 135.9, 134.2, 129.3, 128.5,
4.2.3. 3-Imidazol-1-yl-propionic acid ethyl ester (5)
127.3, 123.3, 122.5, 120.9, 110.1, 49.07. Anal. Calcd for C14H12N2: C,
80.74; H, 5.81; N, 13.45; Found: C, 80.72; H, 5.83; N, 13.44%.
The reaction of
1 and ethyl bromo propionate (1.8 ml,
14.7 mmol) as described above gave 5. FT-IR (KBr, cmꢀ1): 3418,
2986, 1726, 1513; ESMS: 169 (M þ H). 1H NMR (200 MHz, CDCl3–
4.2.8. 1-(3,4-Dichloro-benzyl)-1H-benzimidazole (14)
CCl4):
d
7.52 (s, 1H, Im–H), 7.04 (s, 1H, Im–H), 6.93 (s, 1H, Im–H),
The reaction of 12 and 3,4-dichloro benzyl bromide (1.26 ml,
8.47 mmol) as described above gave 14. FT-IR (KBr, cmꢀ1): 3386,
3020, 1672, 1610, 1495; ESMS: 278 (M þ H)þ. 1H NMR (200 MHz,
4.27 (t, J ¼ 6.5 Hz, 2H, –N–CH2), 4.15 (dd, J ¼ 7.1 Hz and 7.1 Hz, 2H,
–OCH2), 2.77 (t, J ¼ 6.5 Hz, 2H, –CH2), 1.26 (m, 3H, –CH3); 13C NMR
(50 MHz, CDCl3–CCl4):
d
177.5, 142.3, 133.6, 124.5, 65.8, 47.8, 40.9,
CDCl3–CCl4): d 7.94–6.93 (m, 8H, Im–H and Ar–H), 5.30 (s, 2H,
19.3. Anal. Calcd for C8H12N2O2: C, 57.13; H, 7.19; N, 16.66; Found: C,
57.11; H, 7.20; N, 16.64%.
–CH2). 13C NMR (50 MHz, CDCl3–CCl4):
d 144.3, 143.4, 136.1, 133.9,
132.9, 131.4, 130.3, 129.3, 126.5, 123.8, 121.0, 112.41, 110.1, 48.0. Anal.
Calcd for C14H10N2Cl2: C, 60.67; H, 3.64; Cl, 25.58; N, 10.11; Found:
C, 60.65; H, 3.62; Cl, 25.56; N, 10.09%.
4.2.4. 1,3-Bis-(imidazol-1-yl)-propane (15) [35]
The reaction of 1 and 1,3- dibromo propane (1.53 ml,14.6 mmol)
as described above gave 15. FT-IR (KBr, cmꢀ1): 3381, 2965, 1733,
1458; ESMS (M þ H) ¼ 177. 1H NMR (200 MHz, CDCl3–CCl4):
4.2.9. Synthesis of 1-(2-hydroxy ethyl)-1H-imidazole (10) [34]
To the stirred slurry of LiAlH4 (0.34 g, 8.92 mmol) in dry THF
under nitrogen atmosphere, compound 4 (1.0 g, 8.92 mmol) was
added slowly at 0 ꢁC and the reaction mixture was further stirred
for 2 h at room temperature. The excess of the reducing agent was
quenched with saturated NH4Cl, filtered the reaction mixture on
celite pad, the filtrate was evaporated. Water was added to the
residue and the solution was extracted with CH2Cl2. The organic
layer was dried (Na2SO4) and the solvent was evaporated under
reduced pressure. The crude product was purified by column
chromatography using methanol:chloroform (1:5) as eluent gave
compound 10. FT-IR (KBr, cmꢀ1): 3447, 2925, 1713, 1594; ESMS: 113
d
7.64–6.69 (m, 6H, Im–H), 3.94–3.87 (m, 4H, 2 ꢂ –N–CH2),
2.32–2.19 (m, 2H, –CH2). 13C NMR (50 MHz, CDCl3–CCl4):
d 137.3,
128.3, 122.1, 119.8, 43.8, 32.2. Anal. Calcd for C9H12N4: C, 61.34; H,
6.86; N, 31.79; Found: C, 61.32; H, 6.88; N, 31.76%.
4.2.5. 1,5-Bis-(imidazol-1-yl)-pentane (16)
The reaction of 1 and 1,3-dibromo pentane (2.0 ml, 14.7 mmol)
as described above gave 16. FT-IR (KBr, cmꢀ1): 3435, 2989, 1743,
1636, 1513; ESMS: 205 (M þ H). 1H NMR (200 MHz, CDCl3–CCl4):
d
7.50–6.84 (m, 6H, Im–H), 3.91 (m, 4H, 2 ꢂ –N–CH2), 1.78 (m, 4H,
2 ꢂ –CH2), 1.27 (m, 2H, –CH2). 13C NMR (50 MHz, CDCl3–CCl4):
(M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
d 7.31 (s, 1H, Im–H), 6.89
d
137.2, 129.9, 118.9, 47.0, 30.9, 24.0. Anal. Calcd for C11H16N4: C,
(s, 1H, Im–H), 6.82 (s, 1H, Im–H), 3.98 (m, 2H, CH2), 3.78 (m, 2H,
64.68; H, 7.89; N, 27.43; Found: C, 64.68; H, 7.89; N, 27.42%.
CH2). 13C NMR (50 MHz, CDCl3–CCl4):
d 137.5, 128.5, 119.8, 61.5,
50.3. Anal. Calcd for C5H8N2O: C, 53.56; H, 7.19; N, 24.98; Found: C,
53.54; H, 7.20; N, 24.99%.
4.2.6. 1,3-Bis-(2-propyl-imidazol-1-yl)-propane (17) and 1,3-(4-
allyl-2-propyl-imidazol-1-yl)-(2-propyl-imidazol-1-yl)-propane
(18)
4.2.10. 1-(2-Benzyl amino ethyl)-1H-imidazole (11)
The reaction of 2-propylimidazole (2, 1.0 g, 8.26 mmol) and 1,3-
dibromopropane (0.86 ml, 8.26 mmol) in the slurry of NaH (0.3 g,
12.5 mmol) as described above gave the title compounds 17 and 18
in quantitative yield as in the ratio of 55:45 respectively.
A solution of the above compound 10 in anhydrous dichloro-
methane (20 ml) and triethyl amine was treated with meth-
anesulphonyl chloride and reaction mixture was stirred at room
temperature for 4 h. After the completion of the reaction, the
reaction mixture was poured over a mixture of crushed ice and
NaHCO3 and extracted with dichloromethane. Dichloromethane
layer was dried (anhydrous Na2SO4) and evaporated under reduced
pressure to give a crude methanesulphonyloxy derivative which
was used as such in the next step. The latter was refluxed with
benzyl amine (0.7 ml, 6.41 mmol) in toluene in presence of DBU
(5 mol%) and 4 Å molecular sieve for 4 h. The reaction mixture was
extracted with chloroform and washed with aqueous NaHCO3 fol-
lowed by water (2 ꢂ 25 ml), organic layer was dried (anhydrous
Na2SO4) and evaporated under reduced pressure to give compound
11. FT-IR (KBr, cmꢀ1): 3235, 3021, 1603, 1457; ESMS: 202 (M þ H)þ.
4.2.6.1. 1,3-Bis-(2-propyl-imidazol-1-yl)-propane (17). FT-IR (KBr,
cmꢀ1): 3381, 2965, 1733, 1458; ESMS: 261 (M þ H). 1H NMR
(200 MHz, CDCl3–CCl4):
d 7.64 (s, 1H, Im–H), 7.54 (s, 1H, Im–H),
6.95–6.75 (m, 2H, Im–H), 3.97 (t, J ¼ 6.5 Hz, 2H, –N–CH2), 3.83 (t,
J ¼ 7.0 Hz, 2H, –N–CH2), 2.70–2.48 (m, 4H, 2 ꢂ –CH2), 2.25 (t,
J ¼ 6.9 Hz, 2H, –CH2), 1.72 (m, 4H, 2 ꢂ –CH2), 0.97 (m, 6H, 2 ꢂ –CH3).
13C NMR (50 MHz, CDCl3–CCl4):
d 147.6, 126.5, 120.2, 117.6, 41.5,
30.9, 29.5, 27.6, 21.0, 20.4, 18.1, 13.0. Anal. Calcd for C15H24N4: C,
69.19; H, 9.29; N, 21.52; Found: C, 69.17; H, 9.30; N, 21.54%.
4.2.6.2. 1,3-(4-Allyl-2-propyl-imidazol-1-yl)-(2-propyl-imidazol-1-yl)-
1H NMR (200 MHz, CDCl3–CCl4):
d 7.33–7.25 (m, 8H, Im–H and
propane (18). FT-IR (KBr, cmꢀ1): 3381, 2965, 1733, 1458; ESMS: 302
Ar–H), 4.86 (bs, 1H, –NH), 4.31–4.24 (m, 2H, PhCH2), 2.82–2.70 (m,
4H, 2 ꢂ –CH2). Anal. Calcd for C12H15N3: C, 71.61; H, 7.51; N, 20.88;
Found: C, 71.59; H, 7.60; N, 20.86%.
(M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
d 8.48 (s, 1H, Im–H), 7.48
(s, 1H, Im–H), 7.31 (s, 1H, Im–H), 5.98–5.82 (m, 1H, –CH]CH2), 5.24
and 5.05 (two d, J ¼ 10.2 and 16.5 Hz, 2H, –CHA and –CHB), 4.48–4.45
(d, J ¼ 3.8 Hz, 2H, –CH]CH2), 2.98 (s, 2H, –N–CH2), 2.87 (s, 2H,
–CH2), 2.60 (t, J ¼ 7.4 Hz, 2H, –CH2), 1.82–1.67 (m, 2H, –CH2), 1.05–
4.3. General procedure for the synthesis of imidazol-1-yl-
acetamides (6–9)
0.92 (m, 3H, –CH3). 13C NMR (50 MHz, CDCl3–CCl4):
d 162.8, 148.6,
133.4, 127.5, 119.5, 117.7, 66.6, 48.4, 36.7, 31.7, 28.9, 21.6, 14.2. Anal.
Calcd for C18H28N4: C, 71.96; H, 9.39; N, 18.65; Found: C, 71.94; H,
9.41; N, 18.64%.
A mixture of imidazol-1-yl-acetic acid ethyl ester (4, 1.0 g,
6.4 mmol), DBU (5 mol%) and appropriate amine (6.4 mmol) in the
presence of 4 Å molecular sieve (1.0 g) in dry toluene (10 ml) was

3354
J. Pandey et al. / European Journal of Medicinal Chemistry 44 (2009) 3350–3355
stirred at room temperature for 10 min. The corresponding amine
was added and the reaction mixture was heated to 80 ꢁC for
10–18 h. After the completion of the reaction, it was cooled to
ambient temperature, followed by extraction with CH2Cl2. The
organic layer was dried (Na2SO4) and the solvent was evaporated
under reduced pressure. The crude product was purified by column
chromatography using methanol:chloroform (1:5) as eluent.
at 544 nm and emission frequency at 590 nm. The compounds,
which were found active (>90% inhibition as compared with
control) at this concentration were further tested at 6 serial dilu-
tions starting from 50 to 3.12 mg/ml.
4.4.2. Activity against M. tuberculosis H37Rv strain (Agar dilution
method)
Drug susceptibility and determination of MIC of the test
compounds against M. tuberculosis H37Rv was performed by agar
microdilution method [23,24] where twofold dilutions of each test
compound were added into 7H10 agar supplemented with OADC
and organism. A culture of M. tuberculosis H37Rv growing on L–J
medium was harvested in 0.85% saline with 0.05% Tween-80.
4.3.1. N-(n-Butyl)-2-imidazol-1-yl-acetamide (6)
The reaction of 4 and n-butylamine (0.64 ml, 6.45 mmol) as
described above gave 6. FT-IR (KBr, cmꢀ1): 3288, 2960, 1668, 1564;
ESMS: 182 (M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
¼ 7.50–6.97
d
(m, 3H, Im–H), 5.96 (bs, 1H, –NH), 4.64 (s, 2H, –COCH2), 3.28–3.19
(m, 2H, –NHCH2), 1.50–1.18 (m, 4H, 2 ꢂ –CH2), 0.89 (m, 3H, –CH3).
A solution of 1 mg/ml concentration of compounds was prepared in
13C NMR (50 MHz, CDCl3–CCl4):
d
167.1, 138.3, 130.3, 120.0, 50.4,
DMSO. This suspension was added to (in tubes) 7H10 middle
brook’s medium (containing 1.7 ml medium and 0.2 ml OADC
supplement) at different concentrations of compound keeping the
volume constant i.e. 0.1 ml. Medium was allowed to cool keeping
the tubes in slanting position. These tubes were then incubated at
37 ꢁC for 24 h followed by streaking of M. tuberculosis H37Rv
(5 ꢂ104 bacilli per tube). These tubes were then incubated at 37 ꢁC.
Growth of bacilli was seen after 30 days of incubation. Tubes having
the compounds were compared with control tubes where medium
alone was incubated with H37Rv. The concentration at which
complete inhibition of colonies occurred was taken as active
concentration of test compound.
39.8, 31.6, 20.3, 14.0. Anal. Calcd for C9H15N3O: C, 59.64; H, 8.34; N,
23.19; Found: C, 59.62; H, 8.35; N, 23.18%.
4.3.2. N-(n-Hexyl)-2-imidazol-1-yl-acetamide (7) [33]
The reaction of 4 and n-hexylamine (0.85 ml, 6.49 mmol) as
described above gave 7. FT-IR (KBr, cmꢀ1): 3307, 2933, 2361, 1669,
1570. ESMS: 210 (M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
d
7.27–6.83 (m, 3H, Im–H), 5.40 (bs, 1H, –NH), 4.55 (s, 2H, –COCH2),
3.23 (m, 2H, –NHCH2), 2.61 (m, 2H, –CH2), 1.77 (m, 2H, –CH2),
1.46–0.99 (m, 7H, 2 ꢂ –CH2 and –CH3); 13C NMR (50 MHz, CDCl3–
CCl4):
d 167.2, 149.3, 128.9, 119.9, 49.5, 39.9, 31.7, 29.6, 28.8, 26.7,
22.8, 21.4, 14.3. Anal. Calcd for C11H19N3O: C, 63.13; H, 9.15; N,
20.08; Found: C, 63.12; H, 9.17; N, 20.10%.
4.4.3. BACTEC method
Stock solution of the test compounds prepared in DMSO at 1 mg/
4.3.3. N-(n-Heptyl)-2-imidazol-1-yl-acetamide (8)
ml was sterilized by passage through 0.22 mm filters. 50 ml were
The reaction of 4 and n-heptylamine (0.97 ml, 6.52 mmol) as
described above gave 8. FT-IR (KBr, cmꢀ1): 3300, 2933, 2360, 1669,
1569; ESMS: 224 (M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
added to 4 ml radiometric 7H12Broth (BACTEC 12B; Becton Dick-
inson Diagnostic Instrument System US) to achieve final concen-
trations. Controls received 50 ml DMSO. Ofloxacin, streptomycin and
d
7.51–6.93 (m, 3H, Im–H), 5.82 (bs, 1H, –NH), 4.64 (s, 2H, –COCH2),
rifampicin (Sigma Chemical Co. St. Louis, MO) were included as
positive drug control. In BACTEC method, M. tuberculosis H37 Rv was
scraped from fresh Lowenstein–Jensen slants resuspended in 3 ml
diluting fluid and homogenized with glass beads (2 mm). Homog-
enous supernatant was taken; turbidity was adjusted to mc Farland
1 with diluting fluid and 0.1 ml injected into a BACTEC 12B vial
which was used as a primary inoculum after growth index (GI) of
0 reached 500–700. 0.1 ml of this suspension was used to inoculate
4 ml fresh BACTEC 12B broth containing the test compounds. An
additional control vial was included which received a further 1:100
inoculum. Cultures were incubated at 37 ꢁC and the GI determined
daily. When the GI of 1:100 control vials reached 30, the test was
read for an additional day and then terminated. If the drug differ-
3.24 (m, 2H, –NHCH2), 1.43 (m, 2H, –CH2), 1.24 (s, 8H, 4 ꢂ –CH2),
0.87 (m, 3H, –CH3). 13C NMR (50 MHz, CDCl3–CCl4):
d
167.0, 138.4,
130.9, 120.1, 50.5, 40.1, 32.0, 29.6, 29.2, 27.1, 22.9, 14.9. Anal. Calcd
for C12H21N3O: C, 64.54; H, 9.48; N, 18.82; Found: C, 64.52; H, 9.50;
N, 18.84%.
4.3.4. N-Benzyl-2-imidazol-1-yl-acetamide (9)
The reaction of 4 and benzylamine (0.7 ml, 6.41 mmol) as
described above gave 9. FT-IR (KBr, cmꢀ1): 3212, 2940, 1683, 1597;
ESMS: 216 (M þ H)þ. 1H NMR (200 MHz, CDCl3–CCl4):
d 7.46–6.94
(m, 8H, Im–H and Ar–H), 6.32 (bs, 1H, –NH), 4.66 (s, 2H, –COCH2),
4.41 (m, 2H, –CH2). 13C NMR (50 MHz, CDCl3–CCl4):
d 167.1, 138.3,
130.1, 129.1, 128.0, 120.3, 50.3, 43.9. Anal. Calcd for C12H13N3O: C,
66.96; H, 6.09; N, 19.52; Found: C, 66.94; H, 6.10; N, 19.50%.
ence in the GI values from the previous day (called
DGI) in case of
drug containing vials was less than GI of the 1:100 control, then
D
the bacteria was defined as 1 ꢀ (GI of the test sample/GI of con-
trol) ꢂ 100. Assays were completed in 5–8 days and were carried
out according to procedure reported earlier [29–31].
4.4. Biology
4.4.1. Activity against M. tuberculosis H37Ra strain (microplate
alamar blue assay – MABA method)
Acknowledgements
The compounds were evaluated against M. tuberculosis H37Ra at
concentration ranging from 50 mg/ml to 3.12 mg/ml using twofold
dilutions in the initial screen. Log phase culture of M. tuberculosis
H37Ra was diluted so as to give final OD550nm of 0.05 in Sauton’s
medium. In 96 well white plates 190 ml of culture was dispensed in
each well. A dimethyl sulfoxide solution of test compounds was
dispensed to 96 well plates so as to make final test concentration
Authors are thankful to ICMR and DBT New Delhi for financial
assistance as grant-in-aid and CSIR, New Delhi for award of SRF and
JRF to JP and SSV respectively. We also thank SAIF CDRI for spectral
data and microanalysis of our synthesized compounds. We
sincerely thank Dr. Ranjana Srivastava for BACTEC screening of one
of the compounds.
25
mg/ml (5 mg test compound was dispensed in 10 ml of DMSO).
Then the plate was incubated at 37 ꢁC/5% CO2 for 5 days. On 5th day
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