Ring-substituted imidazoles as a new class of anti-tuberculosis agents

Article abstract of DOI:10.1016/j.ejmech.2004.05.005

We describe in vitro anti-Mycobacterium tuberculosis activities of ring-substituted-1H-imidazole-4-carboxylic acid derivatives (1-6), and 3-(2-alkyl-1H-imidazol-4-yl)-propionic acid derivatives (7-13) against drug-sensitive and drug-resistant M. tuberculosis H37Rv strains. The most effective analogues, 2f (R=R₁=c-C₅H₉), and 2h (R=R₁=c-C₆H₁₁) have produced >90% inhibition at a concentration of <6.25 μg/ml in the drug-sensitive screen. Upon further evaluation against drug-resistant strains, both analogues 2f and 2h produced an MIC value of 25.0 μg/ml. The observation of significant anti-tuberculosis activity in some of these analogues describes the discovery of novel ring-substituted-1H-imidazole-4-carboxylic acid ethyl esters as a new class of anti-tuberculosis agents.

Full text of DOI:10.1016/j.ejmech.2004.05.005

European Journal of Medicinal Chemistry 39 (2004) 805–814
www.elsevier.com/locate/ejmech
Preliminary communication
Ring-substituted imidazoles as a new class of anti-tuberculosis agents
Preeti Gupta, Shahul Hameed, Rahul Jain *
Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research, Sector 67, S.A.S. Nagar, Punjab 160 062, India
Received 19 March 2004; received in revised form 19 May 2004; accepted 27 May 2004
Available online 28 July 2004
Abstract
We describe in vitro anti-Mycobacterium tuberculosis activities of ring-substituted-1H-imidazole-4-carboxylic acid derivatives (1–6), and
3-(2-alkyl-1H-imidazol-4-yl)-propionic acid derivatives (7–13) against drug-sensitive and drug-resistant M. tuberculosis H37Rv strains. The
most effective analogues, 2f (R=R1=c-C5H9), and 2h (R=R1=c-C6H11) have produced >90% inhibition at a concentration of <6.25 µg/ml in the
drug-sensitive screen. Upon further evaluation against drug-resistant strains, both analogues 2f and 2h produced an MIC value of 25.0 µg/ml.
The observation of significant anti-tuberculosis activity in some of these analogues describes the discovery of novel ring-substituted-1H-
imidazole-4-carboxylic acid ethyl esters as a new class of anti-tuberculosis agents.
© 2004 Elsevier SAS. All rights reserved.
Keywords: Tuberculosis; Homolytic free radical reaction; Ring-substituted-1H-imidazole-4-carboxylic acid derivatives; 3-(2-Alkyl-1H-imidazol-4-yl)-
propionic acid derivatives
1. Introduction
introduced specifically to combat tuberculosis in the past
40 years. Thus, there is an urgent need to discover drugs,
preferably belonging to new structural classes to combat
drug-resistant cases, and to assist in decreasing the duration
of therapy [5]. In pursuit of this goal, our research efforts are
directed towards discovery of new chemical entities that are
effective as anti-tuberculosis agents, and to optimize the
structure to display the potent efficacy [6–7]. In continuing
our anti-tuberculosis drug discovery program, this prelimi-
nary communication describes the synthesis and hitherto
unknown in vitro anti-M. tuberculosis activities of new
structural class of ring-substituted-1H-imidazole-4-carboxy-
lic acid derivatives (Series 1, Fig. 1), and 3-(2-alkyl-1H-
imidazol-4-yl)-propionic acid derivatives (Series 2, Fig. 1).
Tuberculosis is a devastating worldwide problem, whose
control is complicated by a number of confounding factors
including development of multi-drug-resistant (MDR)
strains to commonly used drugs, substantially long course of
therapy, and lack of affordable cheap drugs in the cases
involving patients suffering due to MDR tuberculosis [1–3].
These factors combined with shortage of new structural
classes of drugs has made tuberculosis second leading infec-
tious cause of death in the world today behind only to
HIV/AIDS. Mycobacterium tuberculosis, the causative or-
ganism claims approximately three million human lives each
year. Recently, World Health Organization (WHO) reported
that the global figure of total deaths by infectious diseases is
17 million, of which tuberculosis accounts for approximately
20% of mortality. The gravity of the problem increases even
more by the fact that one new case of tuberculosis is reported
every 4 s, and one patient dies every 10 s [4]. It is commonly
known that M. tuberculosis has developed resistance to the
majority of the existing drugs, and no new drug has been
* Corresponding author. Tel.: +91-172-221-4682;
fax: +91-172-221-4692.
E-mail address: rahuljain@niper.ac.in (R. Jain).
Fig. 1. Ring-substituted imidazoles.
© 2004 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2004.05.005

806
P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
Scheme 1. Conditions: (i) RCO2H, AgNO3, (NH4)2S2O8, 10% H2SO4, 70–80 °C; (ii) NH2NH2, EtOH, reflux, 8 h; (iii) R2CHO, EtOH, reflux, 2 h; (iv) 6 N HCl,
100 °C, 8 h; (v) H-Gly-OMe, Et3N, DCC, DMF, 12 h.
2. Chemistry
ride (Gly-OMe) in the presence of 1,3-dicyclo-
hexylcarbodiimide (DCC) and triethylamine (Et3N) in dim-
ethylformamide (DMF) for 12 h at ambient temperature
afforded [(2-substituted/2,5-disubstituted-1H-imidazole-4-
carbonyl)amino]acetic acid methyl esters (6a–c) in good
yield (Scheme 1).
Commercially available 1H-imidazole-4,5-dicarboxylic
acid upon partial decarboxylation with refluxing aniline fol-
lowed by acidic hydrolysis with refluxing aqueous HCl, and
finally esterification with abs. ethanol in the presence of dry
HCl gas afforded desired starting material, 1H-imidazole-4-
carboxylic acid ethyl ester (1) in excellent yield as reported
earlier [8]. 1H-Imidazole-4-carboxylic acid ethyl ester (1)
upon homolytic free radical reaction with various commer-
cially available alkyl/cycloalkylcarboxylic acids in the pres-
ence of ammonium persulfate and catalytic amount of silver
nitrate in 10% sulfuric acid provided readily separable mix-
ture of 2-substituted and 2,5-disubstituted-1H-imidazole-4-
carboxylic acid ethyl esters (2a–j) in moderate yield
(Scheme 1). The reaction, as mentioned earlier is known to
proceed through a homolytic free radical mechanism, and
highly efficient in introducing otherwise difficult and previ-
ously unrealizable bulky alkyl/cycloalkyl groups directly
into the imidazole ring [9–12]. 2-Substituted/2,5-
disubstituted-1H-imidazole-4-carboxylic acid ethyl esters
(2a–j) upon reaction with hydrazine hydrate in refluxing
95% ethyl alcohol produced 2-substituted/2,5-disubstituted-
1H-4-imidazole carbohydrazides (3a–j) in quantitative
yields. The reaction of latter compounds (3a–j) with various
commercially available aromatic/aliphatic aldehydes at
80 °C for 2 h in 95% ethyl alcohol gave hydrazones (4a–f) in
excellent yields. On the other hand, 2-substituted/2,5-
disubstituted-1H-imidazole-4-carboxylic acid ethyl esters
(2a–j) upon acidic hydrolysis with refluxing 6 N HCl for 8 h
provided 2-substituted/2,5-disubstituted-1H-imidazole-4-
carboxylic acids (5a–j) as hydrochloride salts. Condensation
reaction of the acids (5) with glycine methyl ester hydrochlo-
On the other hand, intermediate 3-(1H-imidazol-4-
yl)propionic acid methyl ester (9) was obtained in two steps
from commercially available 3-(1H-imidazol-4-yl)acrylic
acid (7) (Scheme 2). The latter compound 9 upon homolytic
free radical reaction with various alkylcarboxylic acids in the
presence of ammonium persulfate and catalytic amount of
silver nitrate in 10% sulfuric acid provided 3-(2-alkyl-1H-
imidazol-4-yl)propionic acid methyl esters (10a–c) in mod-
erate yield.Acidic hydrolysis with 6 N HCl at reflux tempera-
ture produced 3-(2-alkyl-1H-imidazol-4-yl)propionic acids
(11a–c), which upon reaction with various primary amines in
the presence of DCC in dichloromethane (DCM) at ambient
temperature for 12 h provided 3-(2-alkyl-1H-imidazol-4-yl)-
N-alkyl-propionamides (12a–c) in good yield. Finally, 3-(2-
alkyl-1H-imidazol-4-yl)propionic acid methyl esters
(10a–c) upon reaction with hydrazine hydrate in refluxing
95% ethyl alcohol for 8 h produced 3-(2-alkyl-1H-imidazol-
4-yl)propionic acid hydrazides (13a–c) in quantitative yield
(Scheme 2).
3. Microbiology
In vitro activities of the synthesized compounds for tuber-
culosis inhibition against M. tuberculosis H37Rv strain
(ATCC 27294, susceptible both to rifampin and isoniazid)
were carried out using the Microplate Alamar Blue Assay
(MABA) [13]. Compounds exhibiting fluorescence were

P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
807
Scheme 2. Conditions: (i) CH3OH, HCl; (ii) Pd-C/H2, Et3N, RTP, 24 h; (iii) RCO2H, AgNO3, (NH4)2S2O8, 10% H2SO4, 70–80 °C; (iv) 6 N HCl, reflux, 8 h; (v)
R1NH2, DCC, DCM, 4 h; (vi) NH2NH2, EtOH, reflux, 8 h.
then tested in the BACTEC 460 radiometric system [13]
and/or in broth microdilution assay, and activities expressed
as minimum inhibitory concentration (MIC, µg/ml) are sum-
marized in Tables 1–2. Compounds demonstrating at least
90% inhibition are re-tested at lower concentrations in the
broth microdilution assay to determine the actual MIC, a
value defined as the lowest concentration inhibiting ~90% of
the inoculum relative to controls.
replacement of the ethyl ester group in the effective ana-
logues with long chain esters, and other electron-
withdrawing groups may impart additional information on
their role and provide inputs regarding most suitable group
required at the C-4 position of the imidazole ring. The most
effective analogues 2f (R=R1=c-C5H9), and 2h (R=R1=c-
C6H11) upon further evaluation against isoniazid and
rifampin resistant M. tuberculosis H37Rv strains exhibited
similar results and produced 90% inhibition at a concentra-
tion of 25.0 µg/ml (MIC = 25.0 µg/ml).
4. Results and discussion
At the same time, none of the 3-(2-alkyl-1H-imidazol-4-
yl)propionic acid analogues (7–13) exhibited significant
anti-tuberculosis activity (Table 2), thereby establishing the
fact that placement of any spacer between the ring-
substituted imidazole moiety and the ester functionality is
detrimental for enhancement in biological activity.
Among the ring-substituted-1H-imidazole-4-carboxylic
acid derivatives (1–6), esters 2f (R=R1=c-C5H9), and 2h
(R=R1=c-C6H11) produced highest efficacy and exhib-
ited >90% inhibition at a concentration of 6.25 µg/ml
(MIC < 6.25 µg/ml) (Table 1). On the other hand, analogue
3h (R=R1=c-C6H11) exhibited moderate activity
(MIC > 6.25 µg/ml) (see Table 1).
5. Conclusions
These results clearly demonstrated that the presence of
two cycloalkyl groups at the imidazole ring cause improve-
ment in anti-tuberculosis activity. Most surprisingly, these
results are identical and in agreement with our earlier obser-
vation as in the case of ring-substituted quinolines that pres-
ence of two cycloalkyl groups in the ring is utmost important
for potent anti-tuberculosis activity [6]. Furthermore, ana-
logues (3–6) prepared by synthetic modification on the ethyl
ester group have exhibited decrease of activity. However,
To summarize, we have uncovered ring-substituted-1H-
imidazole-4-carboxylic acid ethyl esters as a new class of
anti-tuberculosis agents. The most effective analogues have
demonstrated good anti-tuberculosis activities against both
drug-sensitive and drug-resistant strains of M. tuberculosis,
and are easily synthesized through a simple single step reac-
tion. These properties make ring-substituted imidazole de-
rivatives interesting lead molecules for further synthetic and

808
P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
Table 1
In vitro antimycobacterial activity evaluation of ring-substituted-1H-4-imidazole carboxylic acid derivatives (1–6) against drug-sensitive M. tuberculosis
H37Rv strain
S. No.
1
2a
2b
2c
2d
2e
2f
R
R1
R2
(%) Inhibition
MIC (µg/ml)
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
<6.25
>6.25
<6.25
>6.25
>6.25
>6.25
ND
H
H
–
21
20
5
CH(CH3)2
CH(CH3)2
C(CH3)3
H
–
CH(CH3)2
–
H
–
0
C(CH3)3
C(CH3)3
–
0
c-C5H9
H
–
16
91
22
99
0
c-C5H9
c-C5H9
–
2g
2h
2i
c-C6H11
H
–
c-C6H11
c-C6H11
–
adamantan-1-yl
adamantan-1-yl
CH(CH3)2
CH(CH3)2
C(CH3)3
H
–
2j
Adamantan-1-yl
–
0
3a
3b
3c
3d
3e
H
–
0
CH(CH3)2
–
ND
10
20
1
H
–
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
ND
C(CH3)3
C(CH3)3
–
c-C5H9
H
–
3f
c-C5H9
c-C5H9
–
0
3g
3h
3i
c-C6H11
H
–
37
54
ND
ND
27
9
c-C6H11
c-C6H11
–
adamantan-1-yl
adamantan-1-yl
adamantan-1-yl
adamantan-1-yl
adamantan-1-yl
adamantan-1-yl
adamantan-1-yl
adamantan-1-yl
CH(CH3)2
CH(CH3)2
C(CH3)3
H
–
3j
adamantan-1-yl
–
ND
4a
4b
4c
4d
4e
H
CH(CH3)2
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
0.05
H
C6H5
H
p-OCH3-C6H4
11
5
H
C6F5
adamantan-1-yl
CH(CH3)2
0
4f
adamantan-1-yl
p-OCH3-C6H4
0
5a
5b
5c
5d
5e
H
–
–
–
–
–
–
–
–
–
–
–
–
–
3
CH(CH3)2
0
H
0
C(CH3)3
C(CH3)3
0
c-C5H9
H
0
5f
c-C5H9
c-C5H9
0
5g
5h
5i
c-C6H11
H
0
c-C6H11
c-C6H11
1
adamantan-1-yl
adamantan-1-yl
C(CH3)3
H
0
5j
adamantan-1-yl
0
6a
6b
6c
H
12
11
21
C(CH3)3
C(CH3)3
H
adamantan-1-yl
Isoniazid
ND, not done.
biological exploration. Additional studies on the role of ester
functionality and replacement of cycloalkyl group present at
the imidazole ring with substituted cycloalkyl groups are
currently underway in our laboratory. It can be concluded
that this class of compounds certainly hold great promise
towards pursuit to discover new structural class of anti-
tuberculosis agents.
spectra were recorded on 300 MHz Bruker FT-NMR (Avance
DPX300) spectrometer using tetramethylsilane as internal
standard and the chemical shifts are reported in d units. Mass
spectra were recorded on either GCMS (Shimadzu QP
5000 spectrometer) auto sampler/direct injection (EI/CI) or
HRMS (Finnigan Mat LCQ spectrometer) (APCI/ESI). IR
spectra (kmax in cm–1) were recorded on a Nicolet spectrom-
eter. Elemental analyses were recorded on Elementar Vario
EL spectrometer. All chromatographic purification was per-
formed with silica gel 60 (230–400 mesh), whereas all TLC
(silica gel) development was performed on silica gel coated
(Merck Kiesel 60 F254, 0.2 mm thickness) sheets. All chemi-
cals were purchased fromAldrich Chemical Ltd (Milwaukee,
6. Experimental
6.1. Chemistry
Melting points were recorded on Mettler DSC 851 or
1
capillary melting point apparatus and are uncorrected. H

P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
809
Table 2
solution and extracted with ethyl acetate (3 × 50 ml). The
combined extracts were washed with brine (2 × 10 ml), and
dried (Na2SO4). The solvent was removed under reduced
pressure to afford oil, which upon chromatography over
silica using ethyl acetate/hexanes (4:6) first eluted 2,5-
dialkyl followed by 2-alkyl-1H-4-imidazole carboxylic acid
ethyl esters in 9–33% yield.
In vitro antimycobacterial activity evaluation of 3-(2-alkyl-1H-imidazol-4-
yl)-propionic acid derivatives (7–13) against drug-sensitive M. tuberculosis
H37Rv strain
S. No.
R
R1
(%)
Inhibition
MIC (µg/ml)
7
8
9
–
–
–
–
–
–
–
–
–
–
22
0
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
0.05
–
–
24
0
8.1. 2-Isopropyl-1H-4-imidazole carboxylic acid ethyl
ester (2a)
10a
10b
10c
11a
11b
11c
12a
12b
12c
13a
13b
13c
Isoniazid
c-C5H9
c-C6H11
adamantan-1-yl
c-C5H9
2
21
0
1
Yield: 9%; m.p. 166–168 °C; IR (KBr): 1709 cm–1; H
NMR (CDCl3): d 7.61 (s, 1H, 5-H), 4.34 (q, 2H, J = 7.1 Hz,
CH2), 3.11 (m, 1H, CH), 1.36 (m, 6H, 2 × CH3), 1.35 (t, 3H,
J = 7.1 Hz, CH3); APCIMS: m/z 183 (M + 1); Anal.
C9H14N2O2 (C, H, N).
c-C6H11
adamantan-1-yl
0
2
adamantan-1-yl (CH2)4CH3
adamantan-1-yl (CH2)5CH3
adamantan-1-yl (CH2)6CH3
25
23
8
8.2. 2,5-Diisopropyl-1H-4-imidazole carboxylic acid ethyl
ester (2b)
c-C5H9
–
–
–
20
21
14
c-C6H11
adamantan-1-yl
Yield: 11%; m.p. 135–136 °C; IR (KBr): 1705 cm–1; 1H
NMR (CDCl3): d 4.34 (q, 2H, J = 7.1 Hz, CH2), 3.11 (m, 1H,
CH), 1.70 (m, 1H, CH), 1.33 (m, 6H, 2 × CH3), 1.27 (m, 9H,
3 × CH3); APCIMS: m/z 225 (M + 1); Anal. C12H20N2O2 (C,
H, N).
WI, USA). Solvents used for the chemical synthesis acquired
from commercial sources were of analytical grade, and were
used without further purification unless otherwise stated.
8.3. 2-tert-Butyl-1H-4-imidazole carboxylic acid ethyl
ester (2c)
7. Synthesis of 1H-imidazole-4-carboxylic acid ethyl
ester (1)
Yield: 24%; m.p. 185–186 °C; IR (KBr): 1717 cm–1; 1H
NMR (CDCl3): d 7.59 (s, 1H, 5-H), 4.34 (q, 2H, J = 7.2 Hz,
CH2), 1.40 (s, 9H, 3 × CH3), 1.36 (t, 3H, J = 7.2 Hz, CH3);
ESIMS: m/z 197 (M + 1); Anal. C10H16N2O2 (C, H, N).
To a solution of 1H-imidazole-4-carboxylic acid (1 mmol)
in abs. ethanol (200 ml) was passed anhydrous HCl gas for
2 h. The reaction mixture evaporated under reduced pressure,
and residue is dissolved in water and neutralized with solid
sodium bicarbonate. The separated solid filtered, washed
with cold water, and air-dried. The aqueous filtrate extracted
with ethyl acetate (4 × 50 ml), dried over Na2SO4, and
evaporated under reduced pressure to yield additional quan-
tities of product.
8.4. 2,5-Di-tert-butyl-1H-4-imidazole carboxylic acid ethyl
ester (2d)
Yield: 13%; m.p. 144–146 °C; IR (KBr): 1710 cm–1; 1H
NMR (CDCl3): d 4.33 (q, 2H, J = 7.2 Hz, CH2), 1.44 (s, 9H,
3 × CH3), 1.40 (s, 9H, 3 × CH3), 1.36 (t, 3H, J = 7.2 Hz, CH3);
ESIMS: m/z 253 (M + 1); Anal. C14H24N2O2 (C, H, N).
Yield: 72%; m.p. 156–158 °C; IR (KBr): 1714 cm–1; 1H
NMR (CDCl3): d 8.03 (s, 1H, H-2), 7.77 (s, 1H, H-5), 4.40
(q, 2H, J = 7.1 Hz, CH2), 1.37 (t, 3H, J = 7.1 Hz, CH3); EIMS:
m/z 140 (M+); Anal. C6H8N2O2 (C, H, N).
8.5. 2-Cyclopentyl-1H-4-imidazole carboxylic acid ethyl
ester (2e)
8. General method for the synthesis of 2-alkyl
and 2,5-dialkyl-1H-4-imidazole carboxylic acid ethyl
esters (2a–j)
Yield: 17%; m.p. 131–132 °C; IR (KBr): 1722 cm–1; 1H
NMR (CDCl3): d 7.61 (s, 1H, 5-H), 4.33 (q, 2H, J = 7.1 Hz,
CH2), 3.18 (m, 1H, CH), 1.84 (m, 8H, 4 × CH2), 1.37 (t, 3H,
J = 7.1 Hz, CH3); APCIMS: m/z 209 (M + 1); Anal.
C11H16N2O2 (C, H, N).
1H-Imidazole-4-carboxylic acid ethyl ester (1, 1 mmol),
was added to a mixture of silver nitrate (0.6 mmol) and
alkyl/cycloalkylcarboxylic acid (3 mmol) in 10% H2SO4
(10 ml). Reaction mixture was stirred vigorously and heated
to 70–80 °C. A freshly prepared solution of ammonium
persulfate (3 mmol) in water (10 ml) was added drop wise
over 15 min. The heating source was then removed and the
reaction proceeded with evolution of carbon dioxide. After
15 min, the reaction was terminated by pouring it onto ice.
The resulting mixture was made alkaline with 30% NH4OH
8.6. 2,5-Dicyclopentyl-1H-4-imidazole carboxylic acid
ethyl ester (2f)
Yield: 11%; m.p. 154–155 °C; IR (KBr): 1710 cm–1; 1H
NMR (CDCl3): d 4.33 (q, 2H, J = 7.1 Hz, CH2), 2.77 (m, 1H,
CH), 1.91 (m, 1H, CH), 1.81 (m, 16H, 8 × CH2), 1.36 (t, 3H,
J = 7.1 Hz, CH3); APCIMS: m/z 277 (M + 1); Anal.
C16H24N2O2 (C, H, N).

810
P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
8.7. 2-Cyclohexyl-1H-4-imidazole carboxylic acid ethyl
ester (2g)
9.3. 2-tert-Butyl-1H-4-imidazole carbohydrazide (3c)
Yield: 91%; m.p. 159–160 °C; 1H NMR (CDCl3): d 8.80
(bs, 1H, NH), 7.56 (s, 1H, 5-H), 3.49 (bs, 2H, NH2), 1.25 (s,
9H, 3 × CH3); APCIMS: m/z 183 (M + 1); Anal. C8H14N4O
(C, H, N).
Yield: 13%; m.p. 151–152 °C; IR (KBr): 1722 cm–1; 1H
NMR (CDCl3): d 7.60 (s, 1H, 5-H), 4.34 (q, 2H, J = 7.2 Hz,
CH2), 2.78 (m, 1H, CH), 1.61 (m, 10H, 5 × CH2), 1.37 (t, 3H,
J = 7.2 Hz, CH3); ESIMS: m/z 223 (M + 1); Anal.
C12H18N2O2 (C, H, N).
9.4. 2,5-Di-tert-butyl-1H-4-imidazole carbohydrazide (3d)
8.8. 2,5-Dicyclohexyl-1H-4-imidazole carboxylic acid ethyl
ester (2h)
Yield: 78%; m.p. 76–78 °C; 1H NMR (CDCl3): d 8.55 (bs,
1H, NH), 3.48 (bs, 2H, NH2), 1.48 (s, 9H, 3 × CH3), 1.25 (s,
9H, 3 × CH3); APCIMS: m/z 239 (M + 1); Anal. C12H24N4O
(C, H, N).
Yield: 10%; m.p. 147–159 °C; IR (KBr): 1703 cm–1; 1H
NMR (CDCl3): d 4.32 (q, 2H, J = 7.2 Hz, CH2), 3.17 (m, 1H,
CH), 2.77 (m, 1H, CH), 1.84 (m, 20H, 10 × CH2), 1.36 (t, 3H,
J = 7.2 Hz, CH3); ESIMS: m/z 305 (M + 1);Anal. C8H28N2O2
(C, H, N).
9.5. 2-Cyclopentyl-1H-4-imidazole carbohydrazide (3e)
Yield: 92%; m.p. 228–230 °C; 1H NMR (CDCl3): d 8.21
(bs, 1H, NH), 7.43 (s, 1H, 5-H), 3.75 (bs, 2H, NH2), 2.75 (m,
1H, CH), 1.81 (m, 8H, 4 × CH2); APCIMS: m/z 195 (M + 1);
Anal. C9H14N4O (C, H, N).
8.9. 2-Adamantan-1-yl-1H-4-imidazole carboxylic acid
ethyl ester (2i)
Yield: 33%; m.p. 218–220 °C; IR (KBr): 1717 cm–1; 1H
NMR (CD3OD): d 7.56 (s, 1H, 5-H), 4.32 (q, 2H, J = 7.2 Hz,
CH2), 1.81 (m, 15H, adamantyl protons), 1.35 (t, 3H,
J = 7.2 Hz, CH3); APCIMS: m/z 275 (M + 1); Anal.
C16H22N2O2 (C, H, N).
9.6. 2,5-Dicyclopentyl-1H-4-imidazole carbohydrazide (3f)
Yield: 93%; m.p. 118–120 °C; 1H NMR (CDCl3): d 8.35
(bs, 1H, NH), 3.95 (bs, 2H, NH2), 2.77 (m, 1H, CH), 2.33 (m,
1H, CH), 1.80 (m, 16H, 8 × CH2);APCIMS: m/z 263 (M + 1);
Anal. C14H22N4O (C, H, N).
8.10. 2,5-Diadamantan-1-yl-1H-4-imidazole carboxylic
acid ethyl ester (2j)
9.7. 2-Cyclohexyl-1H-4-imidazole carbohydrazide (3g)
Yield: 22%; m.p. 164–165 °C: IR (KBr): 1694 cm–1; 1H
NMR (CDCl3): d 4.32 (q, 2H, J = 7.2 Hz, CH2), 1.88 (m,
30H, adamantyl protons), 1.32 (t, 3H, J = 7.2 Hz, CH3);
APCIMS: m/z 409 (M + 1); Anal. C26H36N2O2 (C, H, N).
Yield: 93%; m.p. 82–84 °C; 1H NMR (CDCl3): d 8.25 (bs,
1H, NH), 7.51 (s, 1H, 5-H), 4.01 (bs, 2H, NH2), 2.71 (m, 1H,
CH), 1.61 (m, 10H, 5 × CH2); APCIMS: m/z 209 (M + 1);
Anal. C10H16N4O (C, H, N).
9. General procedure for synthesis of 2-alkyl
and 2,5-dialkyl-1H-4-imidazole carbohydrazides 3(a–j)
9.8. 2,5-Dicyclohexyl-1H-4-imidazole carbohydrazide (3h)
Yield: 93%; m.p. 218–219 °C; 1H NMR (CDCl3): d 8.60
(bs, 1H, NH), 3.92 (bs, 2H, NH2), 3.54 (m, 1H, CH), 2.63 (m,
1H, CH), 1.65 (m, 20H, 10 × CH2); ESIMS: m/z 291 (M + 1);
Anal. C16H26N4O (C, H, N).
To a solution of 2-alkyl or 2,5-dialkyl-1H-4-imidazole
carboxylic acid ethyl ester (2a–j, 1 mmol) in ethanol (2 ml),
hydrazine hydrate (2 ml) was added, and reaction mixture
was heated under reflux for 8 h. The carbohydrazides (3a–j)
were obtained in quantitative yields directly after evapora-
tion of the reaction solution.
9.9. 2-Adamantan-1-yl-1H-4-imidazole carbohydrazide
(3i)
9.1. 2-Isopropyl-1H-4-imidazole carbohydrazide (3a)
Yield: 96%; m.p. 116–117 °C; 1H NMR (CDCl3): d 8.08
(bs, 1H, NH), 7.51 (s, 1H, 5-H), 3.82 (bs, 2H, NH2), 1.94 (m,
15H, adamantyl protons); APCIMS: m/z 261 (M + 1); Anal.
C14H20N4O (C, H, N).
Yield: 92%; m.p. 208–209 °C; 1H NMR (CDCl3): d 8.43
(bs, 1H, NH), 7.49 (s, 1H, 5-H); 3.62 (bs, 2H, NH2), 1.48 (m,
1H, CH), 1.35 (m, 6H, 2 × CH3); APCIMS: m/z 169 (M + 1);
Anal. C7H12N4O (C, H, N).
9.10. 2,5-Diadamantan-1-yl-1H-4-imidazole
carbohydrazide (3j)
9.2. 2,5-Diisopropyl-1H-4-imidazole carbohydrazide (3b)
Yield: 98%; m.p. 144–145 °C; 1H NMR (CDCl3): d 8.59
(bs, 1H, NH), 3.82 (bs, 2H, NH2), 1.93 (m, 30H, adamantyl
protons); ESIMS: m/z 395 (M + 1); Anal. C24H34N4O (C, H,
N).
Yield: 91%; m.p. 108–110 °C; 1H NMR (CDCl3): d 8.95
(bs, 1H, NH), 3.91 (m, 1H, CH), 3.49 (bs, 2H, NH2), 2.96 (m,
1H, CH), 1.32 (m, 6H, 2 × CH3), 1.27 (m, 6H, 2 × CH3);
APCIMS: m/z 211 (M + 1); Anal. C10H18N4O (C, H, N).

P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
811
10. General procedure for the synthesis
of 2-adamantan-1-yl and 2,5-diadamantan-1-yl-1H-
imidazole-4-carboxylic acid alkylidene/
benzylidene-hydrazides (4a–f)
10.6. 2,5-Diadamantan-1-yl-1H-imidazole-4-carboxylic
acid (4-methoxy-benzylidene)hydrazide (4f)
Yield: 68%; m.p. 158–159 °C; 1H NMR (CDCl3): d 8.20
(s, 1H, CH), 7.67 (m, 2H, Ar–H), 6.92 (m, 2H, Ar–H), 5.19
(bs, 1H, NH), 3.83 (s, 3H, OCH3), 1.40 (m, 30H, adamantyl
protons); APCIMS: m/z 513 (M + 1); Anal. C32H40N4O2 (C,
H, N).
A mixture of 2-adamantan-1-yl-1H-imidazole carbohy-
drazide (3i, 1 mmol) or 2,5-diadamantan-1-yl-1H-imidazole
carbohydrazide (3j, 1 mmol) and the appropriate commer-
cially available aldehyde (1 mmol) in ethanol (2 ml) was
heated at reflux for 2 h. Solvent was removed under reduced
pressure and crude product purified on silica using
EtOAc/hexanes (40:60) to afford 2-adamantan-1-yl-1H-
11. General procedure for synthesis of 2-alkyl
and 2,5-dialkyl-1H-4-imidazole carboxylic acids (5a–j)
A solution of 2-alkyl or 2,5-dialkyl-1H-4-imidazole car-
boxylic acid ethyl ester (2a–j, 1 mmol) in 6 N HCl (5 ml) was
heated under reflux for 8 h. 2-Alkyl and 2,5-dialkyl-1H-4-
imidazole carboxylic acids (5a–j) were obtained directly
after evaporation of the acids hydrolysis solutions as hydro-
chloride salts.
imidazole-4-carboxylic
acid
alkylidene/benzylidene-
hydrazides (4a–d) and 2,5-diadamantan-1-yl-1H-imidazole-
4-carboxylic acid alkylidene/benzylidene-hydrazides (4e–f)
in good yields.
10.1. 2-Adamantan-1-yl-1H-imidazole-4-carboxylic acid
isobutylidene-hydrazide (4a)
11.1. 2-Isopropyl-1H-4-imidazole carboxylic acid
hydrochloride (5a)
Yield: 55%; m.p. 111–112 °C; 1H NMR (CDCl3): d 7.65
(s, 1H, CH), 7.50 (s, 1H, 5-H), 5.10 (bs, 1H, NH), 2.70 (m,
1H, CH), 1.80 (m, 15H, adamantyl protons), 0.90 (m, 6H, 2 ×
CH3); ESIMS: m/z 315 (M + 1);Anal. C18H26N4O (C, H, N).
1
Yield: 85%; m.p. 171–173 °C (dec.); H NMR (DMSO-
d6): d 7.75 (s, 1H, 5-H), 3.50 (m, 1H, CH), 1.75 (m, 6H, 2 ×
CH3);APCIMS: m/z 155 (M + 1);Anal. C7H11ClN2O2 (C, H,
N).
10.2. 2-Adamantan-1-yl-1H-imidazole-4-carboxylic acid
benzylidene-hydrazide (4b)
11.2. 2,5-Diisopropyl-1H-4-imidazole carboxylic acid
hydrochloride (5b)
Yield: 75%; m.p. 171–173 °C; 1H NMR (CDCl3): d 8.20
(s, 1H, CH), 8.10 (s, 1H, 5-H), 7.76 (m, 2H, Ar–H), 7.39 (m,
3H, Ar–H), 4.93 (bs, 1H, NH), 1.81 (m, 15H, adamantyl
protons); APCIMS: m/z 349 (M + 1); Anal. C21H24N4O (C,
H, N).
1
Yield: 86%; m.p. 206–207 °C (dec.); H NMR (D2O): d
3.55 (m, 1H, CH), 2.81 (m, 1H, CH), 0.85 (m, 6H, 2 × CH3),
0.76 (m, 6H, 2 × CH3); APCIMS: m/z 197 (M + 1); Anal.
C10H17ClN2O2 (C, H, N).
11.3. 2-tert-Butyl-1H-4-imidazole carboxylic acid
hydrochloride (5c)
10.3. 2-Adamantan-1-yl-1H-imidazole-4-carboxylic acid
(4-methoxy-benzylidene)hydrazide (4c)
1
Yield: 80%; m.p. 119–121 °C (dec.); H NMR (D2O): d
Yield: 57%; m.p. 218–219 °C; 1H NMR (CDCl3): d 8.11
(s, 1H, CH), 7.75 (s, 1H, 5-H), 7.71 (m, 2H, Ar–H), 6.92 (m,
2H, Ar–H), 5.20 (bs, 1H, NH), 3.84 (s, 3H, OCH3), 1.81 (m,
15H, adamantyl protons); ESIMS: m/z 379 (M + 1); Anal.
C22H26N4O2 (C, H, N).
7.78 (s, 1H, 5-H), 1.30 (s, 9H, 3 × CH3); APCIMS: m/z 169
(M + 1); Anal. C8H13ClN2O2 (C, H, N).
11.4. 2,5-Di-tert-butyl-1H-4-imidazole carboxylic acid
hydrochloride (5d)
1
Yield: 85%; m.p. 177–179 °C (dec.); H NMR (D2O): d
10.4. 2-Adamantan-1-yl-1H-imidazole-4-carboxylic acid
pentafluorophenylmethylene-hydrazide (4d)
1.55 (s, 9H, 3 × CH3), 1.30 (s, 9H, 3 × CH3); APCIMS: m/z
225 (M + 1); Anal. C12H21ClN2O2 (C, H, N).
Yield: 60%; m.p. 97–99 °C; 1H NMR (CDCl3): d 8.15 (s,
1H, CH), 8.10 (s, 1H, 5-H), 4.46 (bs, 1H, NH), 1.80 (m, 15H,
adamantyl protons); APCIMS: m/z 439 (M + 1); Anal.
C21H19F5N4O (C, H, N).
11.5. 2-Cyclopentyl-1H-4-imidazole carboxylic acid
hydrochloride (5e)
Yield: 76%; m.p. 127–129 C (dec.); 1H NMR (CD3OD): d
7.50 (s, 1H, 5-H), 3.30 (m, 1H, CH), 1.91 (m, 8H, 4 × CH2);
APCIMS: m/z 181 (M + 1); Anal. C9H13ClN2O2 (C, H, N).
10.5. 2,5-Diadamantan-1-yl-1H-imidazole-4-carboxylic
acid isobutylidene-hydrazide (4e)
11.6. 2,5-Dicyclopentyl-1H-imidazole-4-carboxylic acid
hydrochloride (5f)
Yield: 59%; m.p. 112–114 °C; 1H NMR (CDCl3): d 8.10
(s, 1H, CH), 5.31 (bs, 1H, NH), 3.10 (m, 1H, CH), 1.71 (m,
30H, adamantyl protons), 0.87 (m, 6H, 2 × CH3); APCIMS:
m/z 449 (M+); Anal. C28H40N4O (C, H, N).
1
Yield: 71%; m.p. 227–229 °C (dec.); H NMR (D2O): d
4.21 (m, 1H, CH), 2.61 (m, 1H, CH), 1.80 (m, 16H, 8 × CH2);
APCIMS: m/z 249 (M + 1); Anal. C14H21ClN2O2 (C, H, N).

812
P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
11.7. 2-Cyclohexyl-1H-4-imidazole carboxylic acid
hydrochloride (5g)
12.2. [(2,5-Di-tert-butyl-1H-imidazole-4-carbonyl)amino]
acetic acid methyl ester (6b)
Yield: 42%; m.p. 184–185 °C, 1H NMR (CDCl3): d 8.58
(bs, 1H, NH), 3.76 (s, 2H, CH2), 3.49 (s, 3H, OCH3), 1.67 (s,
9H, 3 × CH3), 1.36 (s, 9H, 3 × CH3); APCIMS: m/z 296 (M +
1); Anal. C15H25N3O3 (C, H, N).
Yield: 73%; m.p. 169–170 °C (dec.); 1H NMR (CD3OD):
d 7.72 (s, 1H, 5-H), 2.99 (m, 1H, CH), 1.60 (m, 10H, 5 ×
CH2); ESIMS: m/z 195 (M + 1); Anal. C10H15ClN2O2 (C, H,
N).
12.3. [(2-Adamantan-1-yl-1H-imidazole-4-carbonyl)amino]
acetic acid methyl ester (6c)
11.8. 2,5-Dicyclohexyl-1H-4-imidazole carboxylic acid
hydrochloride (5h)
Yield: 50%; m.p. 211–213 °C; 1H NMR (CDCl3): d 9.18
(bs, 1H, NH), 7.55 (s, 1H, 5-H), 3.77 (s, 2H, CH2), 3.48 (s,
3H, OCH3), 1.64 (m, 15H, adamantyl protons); APCIMS:
m/z 318 (M + 1); Anal. C17H23N3O3 (C, H, N).
1
Yield: 75%; m.p. 171–173 °C; H NMR (DMSO-d6): d
3.97 (m, 1H, CH), 2.77 (m, 1H, CH), 1.61 (m, 20H, 10 ×
CH2); ESIMS: m/z 277 (M + 1); Anal. C16H25ClN2O2 (C, H,
N).
11.9. 2-Adamantan-1-yl-1H-4-imidazole carboxylic acid
hydrochloride (5i)
13. Synthesis of 3-(1H-imidazol-4-yl)acrylic acid methyl
ester (8)
Yield: 78%; m.p. 227–229 °C (dec.); 1H, NMR (D2O): d
7.84 (s, 1H, 5-H), 1.80 (m, 15H, adamantyl protons);
APCIMS: m/z 247 (M + 1); Anal. C14H19ClN2O2 (C, H, N).
To a chilled solution of 3-(1H-imidazol-4-yl)acrylic acid
(7, 3.6 mmol) in anhydrous methanol (200 ml), a slow con-
tinuous stream of dry HCl gas was passed for 1 h. Reaction
mixture was left overnight at ambient temperature. Solvent
was evaporated under reduced pressure to yield 8 as hydro-
chloride salt.
11.10. 2,5-Diadamantan-1-yl-1H-4-imidazole carboxylic
acid hydrochloride (5j)
Yield: 98%; m.p. 213–214 °C (dec.); IR (KBr):
1711 cm–1; 1H NMR (D2O): d 7.70 (s, 1H, 2-H), 7.61 (d, 1H,
J = 15.7 Hz, CH), 7.27 (s, 1H, 5-H), 6.49 (d, 1H, J = 15.7 Hz,
CH), 3.78 (s, 3H, OCH3); EIMS: m/z 152 (M+); Anal.
C7H8N2O2 (C, H, N).
1
Yield: 73%; m.p. 273–274 °C (dec.); H NMR (D2O): d
1.73 (m, 30H, adamantyl protons); APCIMS: m/z 381 (M +
1); Anal. C24H33ClN2O2 (C, H, N).
12. General procedure for the synthesis of [(2-alkyl/
2,5-dialkyl-1H-imidazole-4-carbonyl)amino]acetic acid
methyl esters (6a–c)
14. Synthesis of 3-(1H-imidazol-4-yl)propionic acid
methyl ester (9)
To a solution of 2-alkyl or 2,5-dialkyl-1H-imidazole-4-
carboxylic acid hydrochloride (5a,b,i, 1 mmol) in anhydrous
DMF (5 ml) was added glycine methyl ester dihydrochloride
(1.1 mmol) followed by triethylamine (1 ml), and reaction
To a solution of 3-(1H-imidazol-4-yl)acrylic acid methyl
ester (8, 3.3 mmol) in methanol (75 ml) was added 10%
Pd–C (250 mg) and triethylamine (1 ml). The reaction mix-
ture was hydrogenated at ambient temperature and atmo-
spheric pressure for 24 h. Catalyst filtered through a pad of
celite, and filtrate was evaporated under reduced pressure to
mixture stirred for 15 min at
5 °C. 1,3-Dicyclo-
hexylcarbodiimide (1.2 mmol) was added in one portion to
the reaction mixture, and stirring continued overnight at
ambient temperature. Solvent was removed under reduced
pressure, and residue was dissolved in ethyl acetate (25 ml).
Organic layer was washed with water (2 × 5 ml) followed
with brine (2 × 5 ml), and dried over Na2SO4. Evaporation of
the organic solvent provided crude product, which was puri-
fied by column chromatography using EtOAc/hexanes
(50:50) to afford pure compounds (6a–c).
1
afford 9 as oil. Yield: 93%; oil; IR (CHCl3) 1734 cm–1; H
NMR (CDCl3): d 7.55 (s, 1H, 2-H), 6.80 (s, 1H, 5-H), 3.80 (s,
3H, OCH3), 2.68 (t, 2H, J = 7.0 Hz, CH2), 2.93 (t, 2H,
J = 7.0 Hz, CH2); EIMS: m/z 154 (M+);Anal. C7H10N2O2 (C,
H, N).
15. General method for the synthesis of 3-(2-alkyl-1
H-imidazol-4-yl)propionic acid methyl esters (10a–c)
12.1. [(2-tert-Butyl-1H-imidazole-4-carbonyl)amino]acetic
acid methyl ester (6a)
3-(1H-Imidazol-4-yl)propionic acid methyl ester (9,
1 mmol), was added to a mixture of silver nitrate (0.6 mmol)
and alkylcarboxylic acid (3 mmol) in 10% H2SO4 (10 ml)
while reaction mixture was heated to 70–80 °C. A freshly
prepared solution of ammonium persulfate (3 mmol) in water
(5 ml) was added drop wise over 10 min. The heating source
Yield: 33%; m.p. 178–180 °C; 1H NMR (CDCl3): d 9.19
(bs, 1H, NH), 7.51 (s, 1H, 5-H), 3.77 (s, 2H, CH2), 3.48 (s,
3H, OCH3), 1.30 (s, 9H, 3 × CH3); APCIMS: m/z 240 (M +
1); Anal. C11H17N3O3 (C, H, N).

P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
813
was removed and reaction proceeded with evolution of car-
bon dioxide. After the effervescence ceases, the reaction was
terminated by pouring it onto ice. The resulting mixture was
made alkaline with 30% ammonia solution, and extracted
with ethyl acetate (3 × 50 ml). The combined extracts were
washed with brine (2 × 20 ml) and dried over Na2SO4.The
solvent was removed under reduced pressure to afford oil,
which upon flash column chromatography over silica gel
using ethyl acetate/hexane (70:30) gave compounds 10a–c in
9–36% yield.
2.95 (t, 2H, J = 6.9 Hz, CH2), 2.70 (t, 2H, J = 6.9 Hz, CH2),
1.86 (m, 10H, 5 × CH2); ESIMS: m/z 223 (M + 1); Anal.
C12H19ClN2O2 (C, H, N).
16.3. 3-(2-Adamantan-1-yl-1H-imidazol-4-yl)propionic
acid hydrochloride (11c)
Yield: 87%; m.p. 73–74 °C (dec.); IR (KBr): 1695 cm–1;
1H NMR (DMSO-d6): d 6.59 (s, 1H, 5-H), 2.49 (m, 2H,
CH2), 2.66 (m, 2H, CH2), 1.87 (m, 15H, adamantyl protons);
ESIMS: m/z 275 (M + 1); Anal. C16H23ClN2O2 (C, H, N).
15.1. 3-(2-Cyclopentyl-1H-imidazol-4-yl)propionic acid
methyl ester (10a)
17. General method for the synthesis
of 3-(2-adamantan-1-yl-1H-imidazol-4-yl)-
N-alkyl-propionamides (12a–c)
Yield: 9%; oil; IR (CHCl3): 1731 cm–1; 1H NMR
(CDCl3): d 6.64 (s, 1H, 5-H), 3.68 (s, 3H, OCH3), 3.30 (m,
1H, CH), 2.87 (t, 2H, J = 6.9 Hz, CH2), 2.64 (t, 2H,
J = 6.9 Hz, CH2), 1.88 (m, 8H, 4 × CH2); EIMS: m/z 222
(M+); Anal. C12H18N2O2 (C, H, N).
To an ice cooled stirred solution of 3-(2-adamantan-1-yl-
1H-imidazol-4-yl)propionic acid (11c, 1.8 mmol) and alkyl
amine (2.7 mmol) in dichloromethane (5 ml), 1,3-
dicyclohexylcarbodiimide (2.7 mmol) was added in one por-
tion. The reaction mixture was allowed to attain room tem-
perature and stirring continued for another 4 h. The reaction
mixture was kept in refrigerator overnight, and separated
1,3-dicyclohexylurea (DCU) was filtered. The filtrate was
concentrated under reduced pressure, and ethyl acetate
(50 ml) was added to the residue. The additional separated
DCU was filtered, and the filtrate was washed with saturated
NaHCO3 solution (3 × 10 ml), water (2 × 10 ml) and dried
over Na2SO4. Solvent removed in vacuo to yield crude prod-
uct that was purified by flash column chromatography over
silica gel (230–400 mesh) using CH3OH/CHCl3 (2:98) to
afford 12a–c in good yield.
15.2. 3-(2-Cyclohexyl-1H-imidazol-4-yl)propionic acid
methyl ester (10b)
Yield: 10%; oil; IR (CHCl3): 1730 cm–1; 1H NMR
(CDCl3): d 6.64 (s, 1H, 5-H), 3.68 (s, 3H, OCH3), 3.30 (m,
1H, CH), 2.87 (t, 2H, J = 7.1 Hz, CH2), 2.65 (t, 2H,
J = 7.1 Hz, CH2), 1.90 (m, 10H, 5 × CH2); ESIMS: m/z 237
(M + 1); Anal. C13H20N2O2 (C, H, N).
15.3. 3-(2-Adamantan-1-yl-1H-imidazol-4-yl)propionic
acid methyl ester (10c)
Yield: 36%; m.p. 76–78 °C; IR (KBr): 1742 cm–1; H
1
NMR (CDCl3): d 6.67 (s, 1H, 5-H), 3.69 (s, 3H, OCH3), 2.88
(t, 2H, J = 6.8 Hz, CH2), 2.64 (t, 2H, J = 6.8 Hz, CH2), 1.93
(m, 15H, adamantyl protons); CIMS (CH4): m/z 289 (M + 1);
Anal. C17H24N2O2 (C, H, N).
17.1. 3-(2-Adamantan-1-yl-1H-imidazol-4-yl)-N-pentylpro-
pionamide (12a)
Yield: 75%; oil; IR (CHCl3): 1680 cm–1; 1H NMR
(CDCl3): d 6.66 (s, 1H, 5-H), 3.30 (t, 2H, J = 7.8 Hz, CH2),
2.91 (t, 2H, J = 6.2 Hz, CH2), 2.73 (t, 2H, J = 6.2 Hz, CH2),
1.79 (m, 6H, 3 × CH2), 1.18 (m, 15H, adamantyl protons),
0.89 (t, 3H, J = 7.8 Hz, CH3); EIMS: m/z 343 (M+); Anal.
C21H33N3O (C, H, N).
16. General method for the synthesis of 3-(2-alkyl-1
H-imidazol-4-yl)propionic acids (11a–c)
A solution 3-(2-alkyl-1H-imidazol-4-yl)propionic acid
methyl ester (10a–c, 1 mmol) in 6 N HCl (5 ml) was heated
under reflux for 8 h. The solvent was evaporated under
reduced pressure to afford 11a–c as the hydrochloride salt.
17.2. 3-(2-Adamantan-1-yl-1H-imidazol-4-yl)-N-hexylpro-
pionamide (12b)
16.1. 3-(2-Cyclopentyl-1H-imidazol-4-yl)propionic acid
hydrochloride (11a)
Yield: 80%; oil; IR (CHCl3): 1677 cm–1; 1H NMR
(CDCl3): d 6.63 (s, 1H, 5-H), 3.27 (t, 2H, J = 7.5 Hz, CH2),
2.95 (t, 2H, J = 6.3 Hz, CH2), 2.71 (t, 2H, J = 6.3 Hz, CH2),
1.72 (m, 8H, 4 × CH2), 1.14 (m, 15H, adamantyl protons),
0.88 (t, 3H, J = 7.8 Hz, CH3); EIMS: m/z 357 (M+); Anal.
C22H35N3O (C, H, N).
Yield: 90%; m.p. 82–84 °C (dec.); IR (KBr): 1666 cm–1;
1H NMR (CD3OD): d 7.20 (s, 1H, 5-H), 3.21 (m, 1H, CH),
2.91 (t, 2H, J = 6.9 Hz, CH2), 2.68 (t, 2H, J = 6.9 Hz, CH2),
1.85 (m, 8H, 4 × CH2); ESIMS: m/z 209 (M + 1); Anal.
C11H17ClN2O2 (C, H, N).
17.3. 3-(2-Adamantan-1-yl-1H-imidazol-4-yl)-N-heptylpro-
pionamide (12c)
16.2. 3-(2-Cyclohexyl-1H-imidazol-4-yl)propionic acid
hydrochloride (11b)
Yield: 85%; m.p. 76–78 °C (dec.); IR (KBr): 1666 cm–1;
Yield: 83%; oil; IR (CHCl3): 1673 cm–1; 1H NMR
(CDCl3): d 6.67 (s, 1H, 5-H), 3.29 (t, 2H, J = 7.6 Hz, CH2),
1H NMR (CD3OD): d 7.15 (s, 1H, 5-H), 3.10 (m, 1H, CH),

814
P. Gupta et al. / European Journal of Medicinal Chemistry 39 (2004) 805–814
2.90 (t, 2H, J = 6.2 Hz, CH2), 2.76 (t, 2H, J = 6.2 Hz, CH2),
1.75 (m, 10H, 5 × CH2), 1.15 (m, 15H, adamantyl protons),
0.85 (t, 3H, J = 8.0 Hz, CH3); EIMS: m/z 371 (M+); Anal.
C23H37N=O (C, H, N).
Lowenstein–Jensen slants was inoculated into 100 ml of 7H9
broth medium (7H9 medium supplemented with 10% ADC
and 0.001% Tween 80), and incubated at 37 °C for two
weeks. Two days before the susceptibility testing, the culture
was diluted 1:10 in fresh 7H9 broth medium. After two days,
the culture was ultrasonicated to make a single cell suspen-
sion, and further diluted 1:10 in 7H9 broth just prior to the
inoculation of microdilution tubes. This procedure yielded
an actively growing culture, which reproducibly contained
5 × 106 CFU/ml as determined by plating. The stock solu-
tions of the compounds were prepared in DMSO diluted 1:3
times in 7H9 broth. Further, serial twofold dilutions of the
compounds were prepared from the stock solutions in 7H9
broth medium to provide the final concentrations of 4.0, 2.0,
1.0, 0.5, and 0.25 µg/ml. The same concentrations were
tested for isoniazid (INH), which was taken as the positive
control. The autoclaved microdilution tubes contained
1600 µl 7H9 broth medium, 200 µl of drug dilution, and
200 µl of 1:10 times diluted and ultrasonicated M. tubercu-
losis inocula. All the test tubes were tightly screw-capped
and incubated at 37 °C for 14 days. The tubes were checked
for the surface growth layer. The MIC was defined as the
lowest concentration of test compounds at which the surface
growth layer could not be observed. The negative controls
included 7H9 broth with no drug and with equivalent
amounts of DMSO as the experimental tubes. DMSO did not
inhibit the growth of M. tuberculosis in the concentrations
used for dissolving the compounds.
18. General method for the synthesis of 3-(2-alkyl-1
H-imidazol-4-yl)propionic acid hydrazides (13a–c)
To a solution of 3-(2-alkyl-1H-imidazol-4-yl)propionic
acid methyl ester (10a–c, 1 mmol) in ethanol (2 ml), hydra-
zine hydrate (2 ml) was added, and reaction mixture was
heated under reflux for 8 h. The hydrazides (13a–c) were
obtained in quantitative yields directly after evaporation of
the reaction solution.
18.1. 3-(2-Cyclopentyl-1H-imidazol-4-yl)propionic acid
hydrazide (13a)
Yield: 91%; m.p. 122–124 °C; 1H NMR (CD3OD): d 8.07
(bs, 1H, NH), 6.67 (s, 1H, 5-H), 3.10 (m, 1H, CH), 2.87 (t,
2H, J = 7.5 Hz, CH2), 2.49 (t, 2H, J = 7.5 Hz, CH2), 2.10 (bs,
2H, NH2), 1.82 (m, 8H, 4 × CH2); ESIMS: m/z 223 (M + 1);
Anal. C11H18N4O (C, H, N).
18.2. 3-(2-Cyclohexyl-1H-imidazol-4-yl)propionic acid
hydrazide (13b)
Yield: 97%; m.p. 117–118 °C; 1H NMR (CD3OD): d 8.13
(bs, 1H, NH), 6.65 (s, 1H, 5-H), 3.15 (m, 1H, CH), 2.80 (t,
2H, J = 7.5 Hz, CH2), 2.47 (t, 2H, J = 7.5 Hz, CH2), 2.03 (bs,
2H, NH2), 1.85 (m, 10H, 5 × CH2); ESIMS: m/z 237 (M + 1);
Anal. C12H20N4O (C, H, N).
References
[1] D.B. Young, Nature 393 (1998) 515–516.
[2] L.A. Mitscher, W. Baker, Med. Res. Rev. 98 (1998) 363–374.
[3] E. Manoharam, K.R. John, A. Joseph, K.S. Jacob, Ind. J. Tub. 48
(2001) 77–80.
[4] S.H.E. Kaufmann, Nature Rev. Immun. 1 (2001) 20–30.
[5] D.E. Schraufnagel, Int. J. Tuber. Lung. Dis. 3 (1999) 651–662.
[6] R. Jain, B. Vaitilingam, A. Nayyar, P.B. Palde, Bioorg. Med. Chem.
Lett. 13 (2003) 1051–1054.
[7] S. Vangapandu, M. Jain, R. Jain, S. Kaur, P.P. Singh, Bioorg. Med.
Chem. 12 (2004) 2501–2508.
[8] T.Y. Shen, A. Matzuk, C.P. Dorn, Chem. Abstr. 71 (1969) 61386t US
Patent 3,438,992, 1969.
18.3. 3-(2-Adamantan-1-yl-1H-imidazol-4-yl)-propionic
acid hydrazide (13c)
Yield: 95%; m.p. 111–112 °C; 1H NMR (CD3OD): d 8.20
(bs, 1H, NH), 6.62 (s, 1H, 5-H), 2.83 (t, 2H, J = 7.5 Hz, CH2),
2.43 (t, 2H, J = 7.5 Hz, CH2), 2.11 (bs, 2H, NH2), 1.89 (m,
15H, adamantyl protons); ESIMS: m/z 289 (M + 1); Anal.
C16H24N4O (C, H, N).
[9] F. Minisci, R. Bernardi, F. Bertini, R. Galli, M. Perchinummo, Tetra-
hedron 27 (1971) 3575–3579.
[10] R. Jain, L.A. Cohen, Tetrahedron 53 (1997) 2365–2370.
[11] R. Jain, L.A. Cohen, Tetrahedron 53 (1997) 4539–4548.
[12] S. Narayanan, S. Vangapandu, R. Jain, Bioorg. Med. Chem. Lett. 11
(2001) 1133–1136.
19. Microbiological assays
19.1. Broth microdilution assay
A loop full of M. tuberculosis H37Rv strain (ATCC
27294, susceptible both to rifampin and isoniazid) from
[13] L. Collins, S.G. Franzblau, Antimicrob. Agents Chemother. 41 (1997)
1004–1009.