Synthesis and antitubercular activity of novel 4-substituted imidazolyl-2,6-dimethyl-N3,N5-bisaryl-1,4-dihydropyridine-3,5-dicarboxamides

Article abstract of DOI:10.1016/j.ejmech.2009.03.027

A series of 4-substituted imidazolyl-2,6-dimethyl-N³,N⁵-bisaryl-1,4-dihydropyridine-3,5-dicarboxamides were prepared. They were screened as antitubercular agents against Mycobacterium tuberculosis H₃₇Rv. Minimum inhibitory

Full text of DOI:10.1016/j.ejmech.2009.03.027

European Journal of Medicinal Chemistry 44 (2009) 3253–3258
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antitubercular activity of novel 4-substituted imidazolyl-2,6-
dimethyl-N3,N5-bisaryl-1,4-dihydropyridine-3,5-dicarboxamides
,
b
,
a
a
a
c
Afshin Fassihi a , Zahra Azadpour , Neda Delbari , Lotfollah Saghaie , Hamid R. Memarian ,
*
Razieh Sabet a d, Abdolvahab Alborzi e, Ramin Miri d, Bahman Pourabbas e, Jalal Mardaneh e,
,
Pegah Mousavi d, Behzad Moeinifard f, Hojjat Sadeghi-aliabadi a
a Department of Medicinal Chemistry, Faculty of Pharmacy, Isfahan University of Medical Sciences, 81746-73461 Isfahan, Iran
b Isfahan Pharmaceutical Sciences Research Center, 81746-73461 Isfahan, Iran
c Department of Chemistry, Faculty of Sciences, University of Isfahan, 81746-73441 Isfahan, Iran
d Medicinal & Natural Products Chemistry Research Center, Shiraz University of Medical Sciences, Shiraz, Iran
e Prof. Alborzi Clinical Microbiology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran
f Department of Chemistry, Islamic Azad University, Shahreza Branch, Shahreza, Iran
a r t i c l e i n f o
a b s t r a c t
A series of 4-substituted imidazolyl-2,6-dimethyl-N3,N5-bisaryl-1,4-dihydropyridine-3,5-dicarboxamides
were prepared. They were screened as antitubercular agents against Mycobacterium tuberculosis H37Rv.
Minimum inhibitory concentrations (MICs) were determined using agar proportion method. Compound
3i with 1-benzyl-2-methylthio-1H-imidazole-5-yl substituent at C-4 position and 40-chloromophenyl
group at C-3 and C-5 positions of the 1,4-dihydropyridine ring was the most potent one among the tested
compounds. It was as potent as rifampicin against M. tuberculosis H37RV. Compound 3l also was an active
antitubercular agent with the same substituent as compound 3i at the C-4 position and 30-pyridyl group
at C-3 and C-5 positions of the 1,4-dihydropyridine ring.
Article history:
Received 1 December 2008
Received in revised form
3 March 2009
Accepted 19 March 2009
Available online 27 March 2009
Keywords:
Antitubercular activity
1,4-Dihydropyridine-3,5-dicarbamoxamide
derivatives
Ó 2009 Elsevier Masson SAS. All rights reserved.
Mycobacterium tuberculosis
1. Introduction
hydrophobic properties of mycobacterium envelope protect the
bacterium from its environment and provide a barrier to the
The unique structure of Mycobacterium tuberculosis cell wall is
responsible for the resistance of mycobacters. The acid-fast
bacillus M. tuberculosis, the causative agent of tuberculosis (TB),
possesses a cell wall that differs significantly in structure from
both Gram-negative and Gram-positive bacteria [1]. This cell wall
consists of mycolyl arabinogalactan units which are bonded to
peptidoglycan nucleus through covalent bonds. Mycolated
1,3-branched arabinofuranoside-based hexasaccharide motif forms
the mycolyl–arabinan domain in this structure. Mycolation occurs
via ester linkages at each of the four of the primary arabinose
hydroxyls [2,3]. The mycolyl moieties are high molecular weight
diffusion of commonly used hydrophilic antimicrobial agents [4,5].
According to Global Health Initiative one-third of the world’s
population has latent tuberculosis, an inactive form of the disease
that develops to active form in one-tenth people [6]. Other
statistics tell us that every year, approximately 8 million of these
people develop active tuberculosis (TB), and almost 2 million of
them will die from the disease [7]. Antitubercular drugs available
for the treatment were discovered in the period of 1945–1965. No
new drugs were synthesized during the last few decades [8].
Moreover the recent emergence of outbreaks of multidrug resis-
tant tuberculosis, MDR-TB, to the first-line drugs: isoniazid (INH),
rifampicin (RIF), ethambutol (ETH), streptomycin (STR), and pyr-
azinamide (PYR) have made the disease hard to be cured [9]. This
obstacle in the treatment of tuberculosis and the statistical facts
about its prevalence tell us about the necessity of searching and
synthesizing new more potent and less prone to resistance
compounds with less side-effects. The number of publications
providing a better insight about M. tuberculosis, the process of the
disease and numerous novel molecules as potential leads for TB
a
-alkyl, b-hydroxy fatty acids that are responsible for producing
the hydrophobic character of the cell envelope. The unique
* Corresponding author. Department of Medicinal Chemistry, Faculty of Phar-
macy, Isfahan University of Medical Sciences, Hezar Jerib, 81746-73461 Isfahan,
Iran. Tel.: þ98 311 7922562; fax: þ98 0311 6680011.
E-mail address: fassihi@pharm.mui.ac.ir (A. Fassihi).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.03.027

3254
A. Fassihi et al. / European Journal of Medicinal Chemistry 44 (2009) 3253–3258
drug discovery have increased since the mid-1990s [10–18].
Among them are reviews on drugs currently used in antituber-
culosis treatment, compounds undergoing clinical trials and new
synthetic molecules with antimycobacterial activity [10,18]. The
search for new anti tubercular drugs may be done using the
biochemical and chemical methods. Anti tubercular agents or
antimycobacterials fall into at least eleven categories according to
their mechanisms of action. These categories and prominent
examples are: fatty acid biosynthesis inhibitors such as isoniazid,
arabinogalactan and peptidoglycan biosynthesis inhibitors with
ethambutol as an example, inhibitors of protein synthesis like
streptomycin, inhibitors of DNA-based processes such as rifam-
picin, inhibitors of dihydrofolate reductase or siderophore
biosynthesis with p-aminosalicylic acid as an example, inhibitors
of the proton pump F0F1 Hþ ATPase, for example. TMC 207,
inhibitors of mycobacterial cytochrome P450 mono-oxygenase,
FtsZ protein targeting compounds like carbamoyl-bearing pteri-
dines and related pyridines, inhibitors of branched-chain amino
acid biosynthesis, nucleoside monophosphate kinase inhibitors
with pyrimidine or purine structure, and signaling kinase inhibi-
tors [18]. It has been shown that substitution of carboxylate ester
with aryl carboxamide group in the usual cardiovascular 1,4-
dihydropyridines dramatically reduces calcium channel blocking
activity but provides them significant antitubercular properties
[19]. Preparation and antimycobacterial evaluation of some new
1,4-dihydropyridine-3,5-dicarboxamide derivatives with lipophilic
groups were reported by Desai et al. [8] in 2001. They believed that
these compounds may act as precursors, and after penetration into
the cell wall may lead to the 3,5-carboxylate anions by enzymatic
hydrolysis. Previous studies have shown moderate to good activity
for phenyl or substituted phenyl at the C-4 position of 1,4-dihy-
dropyridine-3,5-dicarboxamide compounds comparable to rifam-
picin [8,19–21]. There are a few reports about evaluation of
1,4-dihydropyridine-3,5-dicarboxamide derivatives containing
heteroaromatic rings at the C-4 position. Recently Amini et al.
reported the synthesis of new 1,4-dihydropyridine-3,5-dicarbox-
amide derivatives with a 4-(4,5-dichloroimidazole-2-yl) moiety
[22]. The reported compounds were weak to moderate inhibitors
of M. tuberculosis (H37Rv) compared with rifampicin.
the appropriate arylamine [24]. Structural properties of the final
compounds are summarized in Table 1.
The structures of the title compounds were confirmed by IR, 1H
NMR, ESI-MS mass spectrometry, and elemental analysis. Some of
the characterization data of the prepared compounds are summa-
rized in Table 2.
All compounds showed in the IR spectra a shouldered absorp-
tion band at 1645–1680 cmꢀ1, typical of the stretch vibrations of
the two carboxamide C]O groups. The reason of shouldered
absorption bond is that the two carboxamide groups are not the
same due to different geometrical isomerism of the two carbonyl
groups at C-3 and C-5 positions of the 1,4-dihydropyridine ring
(Fig. 1).
The 1H NMR spectra of the final compounds contained a singlet
in the
d 1.95–2.22 ppm region due to CH3 protons at C-2 and C-6
positions and another singlet at 5.05–5.20 ppm, due to the C-4
proton of the 1,4-dihydropyridine ring. These two singlets are
indicatives for the presence of the 1,4-dihydropyridine ring. Other
1H NMR spectral signals were in accordance with the proposed
structures.
Two different modes, ESIþ and ESIꢀ, were used in obtaining
mass spectra, so molecular ions are M þ H or M ꢀ H. In the case of
compound 3l there is a peak for M ꢀ H: 550.15 and a base peak at
586.15 which is an adduct ion (M þ Clꢀ) that was presumably an
impurity of the solvent.
2.2. Antitubercular activity
Ten compounds (3a–i, 3l) were tested in vitro against
M. tuberculosis H37RV strain ATCC 27294 which is susceptible to
rifampicin and isoniazid. Minimum inhibitory concentration (MIC)
was determined using agar proportion method in Middlebrook
7H10 medium. Rifampicin and isoniazid (Sigma Chemical Co.) were
used as reference drugs. The antitubercular activity of the tested
compounds is provided in Table 2.
2.3. MTT-based cytotoxicity assay
In order to understand the structure–antitubercular activity
relationship, we decided to prepare some novel 1,4-dihydropyr-
idine-3,5-dicarboxamide derivatives and determined their inhibi-
tory activity against M. tuberculosis H37Rv. The prepared
compounds had 1-benzyl-2-methylthio-1H-imidazole-5-yl or 1-
phenylamino-2-methylthio-1H-imidazole-5-yl at the C-4 position
and various aryl carboxamide derivatives at C-3 and C-5 positions
of the 1,4-dihydropyridine ring.
The cytotoxic effect of six compounds (3a, 3e, 3i, 3h, 3k, 3l)
against four different cell lines was determined by MTT assay
method. Doxorubicin was used as a reference drug. Assay proce-
dure and cell survival calculations were performed according to
previous studies [25]. The cytotoxicity of compounds is listed in
Table 3 as IC30 (mg/mL).
Here, we report the synthesis of 12 novel 4-substituted imida-
zolyl-2,6-dimethyl-N3,N5-bisaryl-1,4-dihydropyridine-3,5-dicar-
boxamides. Ten of these derivatives were screened for their
antitubercular activity against M. tuberculosis (H37Rv) (ATCC 27294;
American type culture collection, Rockville, MD).
3. Conclusions
Comparison of the activities of tested compounds (3a–i, 3l)
indicates that compound 3i with 1-benzyl-2-methylthio-1H-imid-
azole-5-yl substituent at the C-4 position and 40-chlorophenyl
group at C-3 and C-5 positions of the 1,4-dihydropyridine ring was
the most potent one among the tested compounds. It was as potent
as rifampicin against M. tuberculosis H37RV. Compound 3l also was
2. Results and discussion
2.1. Chemistry
1,4-Dihydropyridine-3,5-dicarboxamide derivatives 3a–l were
prepared in 55–86% from condensation of substituted imidazole-5-
carboxaldehydes 1, appropriate N-aryl-acetoacetamide derivatives
2a–f and ammonium acetate in absolute ethanol (Scheme 1).
an active antitubercular agent with MIC ¼ 2
mg/mL with the same
substituent as compound 3i at the C-4 position and 30-pyridyl
group at C-3 and C-5 positions of the 1,4-dihydropyridine ring. The
other substituents did not show good antitubercular activity. The
results demonstrate that a substituted imidazole group is a suitable
equivalent for nitro phenyl group which was previously reported in
the structure of anti tubercular 1,4-dihydropyridinedicarboxamides
[19].
Preparation of substituted imidazole-5-carbaldehydes
1
(X ¼ NH or CH2) is described [23]. N-Arylacetoacetamide deriva-
tives 2a–f were prepared according to modified method of Clemens
by simple condensation of 2,2,6-trimethyl-1,3-dioxine-4-one with

A. Fassihi et al. / European Journal of Medicinal Chemistry 44 (2009) 3253–3258
3255
SCH3
N
N
X
1: X=NH, CH2
CHO
O
O
Ar
Ar
N
H
N
H
2a-f
O
NH4CH3COO
CH3
H3C
O
SCH3
N
N
X
O
O
Ar
Ar
N
H
N
H
CH3
N
H
H3C
3a-l
3g: Ar=2-Chlorophenyl, X=CH2
3h: Ar=3-Chlorophenyl, X=CH2
3i: Ar=4-Chlorophenyl, X=CH2
3j: Ar=4-Bromophenyl, X=CH2
3k: Ar=2-Pyridyl, X=CH2
3a: Ar=2-Chlorophenyl, X=NH
3b: Ar=3-Chlorophenyl, X=NH
3c: Ar=4-Chlorophenyl, X=NH
3d: Ar=4-Bromophenyl, X=NH
3e: Ar=2-Pyridyl, X=NH
3l: Ar=3-Pyridyl, X=CH2
3f: Ar=3-Pyridyl, X=NH
Scheme 1. Synthesis of 1,4-dihydropyridine3,5-dicarboxamide derivatives.
4. Experimental protocols
thin layer chromatography (TLC) on silica gel plate using chloro-
form and methanol.
4.1. Chemistry
4.1.1. General procedure for the preparation of 1,4-dihydropyridine-
3,5-dicarbamoyl derivatives (3a–l)
Chemicals from Merck and Sigma–Aldrich Chemical Co. were
used without further purification. Analytical thin-layer chroma-
tography (TLC) was performed on Merck silica gel (60F254) plates.
Column chromatography was performed on silica gel 60 (Merck,
70–235 mesh). Melting points were determined on a Mettler
capillary melting point apparatus and were uncorrected. The IR
spectra were recorded with a Perkin Elmer 1420 Ratio Recording IR
A mixture of 1-phenylamine (benzyl)-2-methylthio-1H-imid-
azole-5-carbaldehyde 1 (1 mmol), appropriate N-arylacetoaceta-
nilide 2a–f (2 mmol) and ammonium acetate (1 mmol) was
refluxed in 6 mL of absolute ethanol for 24 h. The solvent was
removed under reduced pressure. The residue was purified by
column chromatography using chloroform/methanol as eluent.
Crystallization from acetone and petroleum ether gave pure
compounds 3a–l.
spectrometer as a KBr disc (
d6) were recorded on a Bruker 300 MHz spectrometer. Chemical
shifts ( ) are reported in ppm downfield from the internal standard
g
, cmꢀ1). The 1H NMR spectra (DMSO-
d
tetramethylsilane (TMS). Electrospray mass spectra (ESI-MS) were
obtained in negative and positive ion mode on a SHIMADZU LCMS-
2010 EV spectrometer using methanol and dimethylsulfoxide as
solvent, a capillary voltage of 4500 V and a cone voltage of 10 V.
Elemental microanalyses were within ꢁ0.4% of the theoretical
values for C, H and N. The purity of the compounds was checked by
4.1.1.1. 4-(2-(Methylthio)-1-(phenylamino)-1H-imidazol-5-yl)-2,6-
dimethyl-N3,N5-di(20-chlorophenyl)-1,4-dihydropyridine-3,5-dicar-
boxamide (3a). IR: (KBr) cmꢀ1: 3260 (NH), 1660 (C]O); 1H NMR
(DMSO-d6):
d 2.22 (s, 6H, dihydropyridine C2, C6, CH3), 2.49 (s, 3H,
SCH3), 5.11 [s, 1H, dihydropyridine C4–H], 7.11 (t, J ¼ 7.50 Hz, 2H,

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A. Fassihi et al. / European Journal of Medicinal Chemistry 44 (2009) 3253–3258
Table 1
4.1.1.3. 4-(2-(Methylthio)-1-(phenylamino)-1H-imidazol-5-yl)-2,6-di
methyl-N3,N5-di (40-chlorophenyl)-1,4-dihydropyridine-3,5-dicar-
boxamide (3c). IR: (KBr) cmꢀ1: 3290 (NH), 1675 (C]O); 1H NMR
(DMSO-d6): 2.12 (s, 6H, dihydropyridine C2, C6, CH3), 2.55 (s, 3H,
SCH3), 5.14 [s, 1H, dihydropyridine C4–H], 7.31 (d, J ¼ 9.00 Hz, 4H,
Structural properties of compounds 3a–l.
SCH3
N
d
N
0
0
2 ꢂ C2 –H, C6 –H), 7.44–7.55 (m, 5H, –NHC6H5), 7.65 (d, J ¼ 9.00 Hz,
X
O
0
0
4H, 2 ꢂ C3 –H, C5 –H), 8.45 (s, 1H, imidazole C4–H), 9.77 (s, 2H,
2 ꢂ amide –NH). ESI-MS (þ): m/z 620.2 (M þ Hþ) (5), 478.10 (100).
O
Ar
Ar
4.1.1.4. 4-(2-(Methylthio)-1-(phenylamino)-1H-imidazol-5-yl)-2,6-di
N
H
N
H
methyl-N3,N5-di
(40-bromophenyl)-1,4-dihydropyridine-3,5-dicar-
boxamide (3d). IR: (KBr) cmꢀ1: 3300 (NH), 1660 (C]O); 1H NMR
(DMSO-d6): 2.07 (s, 6H, dihydropyridine C2, C6, CH3), 2.49 (s, 3H,
d
H3C
N
H
CH3
SCH3), 5.14 [s, 1H, dihydropyridine C4–H], 7.43–7.62 (m, 15H,
dihydropyridine NH, –NHC6H5, –NHC6H5, 2 ꢂ –C6H4Br), 8.45 (s, 1H,
imidazole C4–H), 9.76 (s, 2H, 2 ꢂ amide –NH). ESI-MS (þ) m/z (%):
709 (M þ Hþ) (5), 393.20 (100).
Compd. no.
Ar
X
Mol. formula
31H28Cl2N6O2S
C31H28Cl2N6O2S
C31H28Cl2N6O2S
C31H28Br2N6O2S
Mol. weight
3a
3b
3c
3d
3e
3f
3g
3h
3i
2-Chlorophenyl
3-Chlorophenyl
4-Chlorophenyl
4-Bromophenyl
2-Pyridyl
NH
NH
NH
NH
NH
NH
CH2
CH2
CH2
CH2
CH2
CH2
C
619.56
619.56
619.56
708.47
552.65
552.65
617.58
617.58
617.58
707.48
551.66
551.66
4.1.1.5. 4-(2-(Methylthio)-1-(phenylamino)-1H-imidazol-5-yl)-2,6-di
methyl-N3,N5-di(pyridin-2-yl)-1,4-dihydropyridine-3,5-dicarboxamide
(3e). IR: (KBr) cmꢀ1: 3300 (NH), 1660 (C]O); 1H NMR (DMSO-d6):
C29H28N8O2S
C29H28N8O2S
3-Pyridyl
2-Chlorophenyl
3-Chlorophenyl
4-Chlorophenyl
4-Bromophenyl
2-Pyridyl
C32H29Cl2N5O2S
C32H29Cl2N5O2S
C32H29Cl2N5O2S
C32H29Br2N5O2S
C30H29N7O2S
d
2.16 (s, 6H, dihydropyridine C2, C6, CH3), 2.71 (s, 3H, SCH3), 5.20 [s,
1H, dihydropyridine C4–H], 7.02 (t, J ¼ 6.00 Hz, 2H, 2 ꢂ pyridine C5–
H), 7.40–7.56 (m, 6H, –NHC6H5, dihydropyridine NH), 7.72 (t,
J ¼ 7.80 Hz, 2H, 2 ꢂ pyridine C4–H), 8.06 (d, J ¼ 8.40 Hz, 2H,
2 ꢂ pyridine C6–H), 8.26–8.30 (m, 2H, 2 ꢂ pyridine C3–H), 8.68 (s,1H,
imidazole C4–H), 10.40 (s, 2H, 2 ꢂ amide –NH). ESI-MS (þ) m/z (%):
553.20 (M þ Hþ) (10), 539.20 (100).
3j
3k
3l
3-Pyridyl
C30H29N7O2S
4.1.1.6. 4-(2-(Methylthio)-1-(phenylamino)-1H-imidazol-5-yl)-2,6-di
methyl-N3,N5-di(pyridin-3-yl)-1,4-dihydropyridine-3,5-dicarboxamide
(3f). IR: (KBr) cmꢀ1: 3280 (NH), 1650 (C]O); 1H NMR (DMSO-d6):
0
0
2 ꢂ C5 –H), 7.29 (t, J ¼ 7.50 Hz, 2H, 2 ꢂ C4 –H), 7.43–7.58 (m, 8H,
0
–NHC6H5, dihydropyridine NH, 2 ꢂ C6 –H), 7.92 (d, J ¼ 8.10, Hz, 2H,
0
2 ꢂ C3 –H), 8.73 (s, 1H, imidazole C4–H), 9.17 (s, 2H, 2 ꢂ amide –NH).
d
2.14 (s, 6H, dihydropyridine C2, C6, CH3), 2.49 (s, 3H, SCH3), 5.20 [s,
ESI-MS (þ) m/z (%): 620.2 (M þ Hþ) (5), 478.10 (100).
1H, dihydropyridine C4–H], 7.30 (dd, J ¼ 8.16 Hz, J ¼ 4.66 Hz, 2H,
2 ꢂ pyridine C5–H), 7.40–7.55 (m, 6H, –NHC6H5, dihydropyridine
NH), 8.04 (d, J ¼ 8.40 Hz, 2H, 2 ꢂ pyridine C4–H), 8.20 (d, J ¼ 4.50 Hz,
2H, 2 ꢂ pyridine C6–H), 8.50 (s, 1H, imidazole C4–H), 8.76 (s, 2H,
2 ꢂ pyridine C2–H), 9.82 (s, 2H, 2 ꢂ amide –NH). ESI-MS (þ) m/z (%):
553.20 (M þ Hþ) (7), 437.20 (100).
4.1.1.2. 4-(2-(Methylthio)-1-(phenylamino)-1H-imidazol-5-yl)-2,6-di
methyl-N3,N5-di(30-chlorophenyl)-1,4-dihydropyridine-3,5-dicarbox-
amide (3b). IR: (KBr) cmꢀ1: 3260 (NH), 1680 (C]O); 1H NMR
(DMSO-d6):
d 2.12 (s, 6H, dihydropyridine C2, C6, CH3), 2.56 (s, 3H,
SCH3), 5.15 [s, 1H, dihydropyridine C4–H], 7.04 (d, J ¼ 7.80 Hz, 2H,
0
0
4.1.1.7. 4-(1-Benzyl-2-(methylthio)-1H-imidazol-5-yl)-2,6-dimethyl-
N3,N5-bis (20-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxamide
(3g). IR: (KBr) cmꢀ1: 3350 (NH), 1660 (C]O); 1H NMR (DMSO-d6):
2 ꢂ C6 –H), 7.29 (t, J ¼ 8.10 Hz, 2H, 2 ꢂ C5 –H), 7.44–7.55 (m, 8H,
0
0
–NHC6H5, dihydropyridine NH, 2 ꢂ C4 –H), 7.84 (s, 2H, 2 ꢂ C2 –H),
8.48 (s, 1H, imidazole C4–H), 9.81 (s, 2H, 2 ꢂ amide –NH). ESI-MS
(þ) m/z (%): 620.2 (M þ Hþ) (7), 393.15 (100).
d
1.95 (s, 6H, dihydropyridine C2, C6, CH3), 2.35 (s, 3H, SCH3), 5.20 (s,
Table 2
Characterization data and antitubercular screening results of the compounds 3a–l.
Compd. no.
M.P. (ꢃC)
Yield (%)
Analysis (%)
MIC (mg/mL)
Found (calculated)
C
H
N
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
230–231
231–232
221–223
239–240
221–223
198–199
235–236
238–239
218–220
240–242
211–212
200–201
–
86
81
73
76
86
60
88
80
73
73
85
55
–
60.22 (60.10)
59.95 (60.10)
59.89 (60.10)
52.21 (52.55)
63.37 (63.03)
63.26 (63.03)
59.95 (62.13)
62.45 (62.13)
59.03 (62.13)
54.71 (54.33)
64.93 (65.32)
65.12 (65.32)
–
4.44 (4.56)
4.36 (4.56)
4.55 (4.56)
4.02 (3.98)
4.98 (5.11)
4.86 (5.11)
4.65 (4.73)
4.45 (4.73)
4.82 (4.73)
3.96 (4.13)
5.58 (5.30)
5.06 (5.30)
–
13.78 (13.56)
13.65 (13.56)
13.45 (13.56)
12.12 (11.86)
20.54 (20.28)
20.12 (20.28)
11.45 (11.32)
11.64 (11.32)
11.21 (11.32)
10.12 (9.90)
18.01 (17.77)
17.72 (17.77)
–
>16
>16
>16
>16
>16
>16
>16
>16
1
NDa
ND
2
Rifampicin
Isoniazide
1
0.2
–
–
–
–
–
a
ND: Not determined.

A. Fassihi et al. / European Journal of Medicinal Chemistry 44 (2009) 3253–3258
3257
O
Ar
O
O
Ar
NHAr'
NHAr'
Ar
NHAr'
NHAr'
O
O
O
Ar'HN
Ar'HN
s-trans
s-trans
s-trans
s-cis
s-cis
s-cis
N
H
CH3
N
H
N
H
CH3
CH3
H3C
H3C
H3C
Fig. 1. Different geometrical isomerisms of the two carbonyl groups of 1,4-dihydropyridinedicarboxamides.
2H, –CH2–C6H5), 5.23 (s, 1H, dihydropyridine C4–H), 6.92 (m, 3H,
C2–H, C4–H, C6–H of –CH2–C6H5), 7.10–7.16 (m, 5H, C3–H and C5–H
4.1.1.11. 4-(1-Benzyl-2-(methylthio)-1H-imidazol-5-yl)-2,6-dimethyl-
N3,N5-bis(pyridin-2-yl)-1,4-dihydropyridine-3,5-dicarboxamide
(3k). IR: (KBr) cmꢀ1: 3420 (NH), 1675 (C]O); 1H NMR (DMSO-d6):
0
of –CH2–C6H5, dihydropyridine NH, 2 ꢂ C5 –H), 7.29 (t, J ¼ 8.10 Hz,
0
0
2H, 2 ꢂ C4 –H), 7.44 (d, J ¼ 7.80 Hz, 2H, 2 ꢂ C6 –H), 7.62 (d, J ¼ 8.10,
d 1.94 (s, 6H, dihydropyridine C2, C6, CH3), 2.30 (s, 3H, SCH3), 5.05 (s,
0
Hz, 2H, 2 ꢂ C3 –H), 8.44 (s, 1H, imidazole C4–H), 8.80 (s, 2H,
2H, –CH2–C6H5), 5.29 (s, 1H, dihydropyridine C4–H), 6.68 (m, 3H,
C2–H, C4–H, C6–H of –CH2–C6H5), 6.91–6.97 (m, 3H, C3–H and C5–H
of –CH2–C6H5, dihydropyridine NH), 7.06 (t, J ¼ 6.00 Hz, 2H,
2 ꢂ pyridine C5–H), 7.73 (t, J ¼ 7.50 Hz, 2H, 2 ꢂ pyridine C4–H), 8.00
(d, J ¼ 8.40 Hz, 2H, 2 ꢂ pyridine C6–H), 8.27–8.30 (m, 2H,
2 ꢂ pyridine C3–H), 8.43 (s, 1H, imidazole C4–H), 10.17 (s, 2H,
2 ꢂ amide –NH). ESI-MS (ꢀ) m/z (%): 550.00 (M ꢀ Hþ) (100).
2 ꢂ amide –NH). ESI-MS (þ) m/z (%): 618.15 (M þ Hþ) (100).
4.1.1.8. 4-(1-Benzyl-2-(methylthio)-1H-imidazol-5-yl)-2,6-dimethyl-
N3,N5-bis (30-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxamide
(3h). IR: (KBr) cmꢀ1: 3335 (NH), 1645 (C]O); 1H NMR (DMSO-d6):
d
1.98 (s, 6H, dihydropyridine C2,C6, CH3), 2.27 (s, 3H, SCH3), 5.04 [s,
1H, dihydropyridine C4–H], 5.17 (s, 2H, –CH2–C6H5), 6.8–6.84 (m,
3H, C2–H, C4–H, C6–H of –CH2–C6H5), 6.99–7.06 (m, 5H, dihy-
4.1.1.12. 4-(1-Benzyl-2-(methylthio)-1H-imidazol-5-yl)-2,6-dimethyl-
N3,N5-bis(pyridin-3-yl)-1,4-dihydropyridine-3,5-dicarboxamide
(3l). IR: (KBr) cmꢀ1: 3200 (NH), 1660 (C]O); 1H NMR (DMSO-d6):
0
dropyridine NH, C3–H, C5–H of –CH2–C6H5, 2 ꢂ C6 –H), 7.27 (t,
J ¼ 8.10 Hz, 2H, 2 ꢂ C5
´
–H), 7.42 (d, J ¼ 8.40 Hz, 2 ꢂ C4
´
–H), 7.70 (s, 2H,
–H), 8.38 (s, 1H, imidazole C4–H), 9.57 (s, 2H, 2 ꢂ amide –NH).
2 ꢂ C2
´
d 2.00 (s, 6H, dihydropyridine C2, C6, CH3), 2.27 (s, 3H, SCH3), 5.11 (s,
ESI-MS (þ) m/z (%): 617.95 (M þ Hþ) (100).
1H, dihydropyridine C4–H), 5.18 (s, 2H, –CH2–C6H5), 6.81–6.84 (m,
3H, C2–H, C4–H, C6–H of –CH2–C6H5), 6.97–6.98 (m, 3H, C3–H and
C5–H of –CH2–C6H5, dihydropyridine NH), 7.28 (dd, J ¼ 8.16 Hz,
J ¼ 4.66 Hz, 2H, 2 ꢂ pyridine C5–H), 7.95 (d, J ¼ 8.40 Hz, 2H,
2 ꢂ pyridine C4–H), 8.20 (d, J ¼ 4.00 Hz, 2H, 2 ꢂ pyridine C6–H), 8.40
(s, 1H, imidazole C4–H), 8.67 (s, 1H, 2 ꢂ pyridine C2–H), 9.63 (s, 2H,
2 ꢂ amide –NH). ESI-MS (ꢀ) m/z (%): 550.15 (M ꢀ Hþ) (22), 586.15
(100).
4.1.1.9. 4-(1-Benzyl-2-(methylthio)-1H-imidazol-5-yl)-2,6-dimethyl-
N3,N5-bis (40-chlorophenyl)-1,4-dihydropyridine-3,5-dicarboxamide
(3i). IR: (KBr) cmꢀ1: 3180 (NH), 1650 (C]O); 1H NMR (DMSO-d6):
d
1.97 (s, 6H, dihydropyridine C2, C6, CH3), 2.27 (s, 3H, SCH3), 5.04 [s,
1H, dihydropyridine C4–H], 5.15 (s, 2H, –CH2–C6H5), 6.82–6.85 (m,
2H, C3–H and C5–H of –CH2–C6H5), 7.00–7.02 (m, 3H, C2–H, C4–H,
C6–H of –CH2–C6H5), 7.30 (d, J ¼ 8.70 Hz, 4H, 2 ꢂ C2
´ ´
–H,C6–H), 7.55
´ –H,C5–H) 8.32 (s, 1H, imidazole C4–H),
´
(d, J ¼ 8.70 Hz, 4H, 2 ꢂ C3
9.51 (s, 2H, 2 ꢂ amide –NH). ESI-MS (þ) m/z (%): 618.05 (M þ Hþ)
4.2. Antitubercular activity
(100).
Ten compounds (3a–i, 3l) were tested in vitro against M.
tuberculosis H37RV strain ATCC 27294 which is susceptible to
rifampicin and isoniazid. Minimum inhibitory concentration (MIC)
was determined using agar proportion method in Middlebrook
7H10 medium. Rifampicin and isoniazid (Sigma Chemical Co.) were
4.1.1.10. 4-(1-Benzyl-2-(methylthio)-1H-imidazol-5-yl)-2,6-dimethyl-
N3,N5-bis (40-bromophenyl)-1,4-dihydropyridine-3,5-dicarboxamide
(3j). IR: (KBr) cmꢀ1: 3200 (NH), 1660 (C]O); 1H NMR (DMSO-d6):
d
1.96 (s, 6H, dihydropyridine C2, C6, CH3), 2.26 (s, 3H, SCH3), 5.03 [s,
1H, dihydropyridine C4–H], 5.15 (s, 2H, –CH2–C6H5), 6.79 (s, 1H,
dihydropyridine NH), 6.85 (m, 2H, C3–H and C5–H of –CH2–C6H5),
7.02 (m, 3H, C2–H, C4–H, C6–H of –CH2–C6H5), 7.42 (d, J ¼ 9.00 Hz,
used as a reference drugs at 1 mg/mL and 0.2 mg/mL, respectively.
Solutions of compounds in dimethylsulfoxide were added to the
Middlebrook 7H10 Agar (Quelab Co., UK) medium with glycerol and
enriched with OADC (Oleic acid, Albumin, Dextrose Catalase). The
following concentrations were used: 0.05, 0.1, 0.2, 0.5, 1, 2, 4, 8 and
0
0
0
0
4H, 2 ꢂ C3 –H,C5 –H), 7.50 (d, J ¼ 9.00 Hz, 4H, 2 ꢂ C2 –H,C6 –H), 8.33
(s, 1H, imidazole C4–H), 9.51 (s, 2H, 2 ꢂ amide –NH). ESI-MS (þ) m/z
(%): 707.95 (M þ Hþ) (100).
16 mg/mL. A culture of M. tuberculosis H37Rv cultivated in 7H9 broth
(Quelab Co., UK) at 37 ꢃC for a period of 4–7 days, was adjusted,
using the same medium, to the optical density of McFarland stan-
dard no. 1. Two dilutions of this suspension, 10ꢀ2 and 10ꢀ4, were
used as an inoculum, 0.1 mL per each tubes. MIC values were
determined after incubation at 37 ꢃC in the presence of 5–7% CO2
for a period of 21 days. The colonies on each tube were counted, and
the numbers of colonies on drug-containing tubes were compared
with that on the drug-free control [26,27]. The present results were
obtained from two independent measurements.
Table 3
Cytotoxicity assay results of six of the prepared compounds.
Compound
Cell line
Jurkat
Raji
Hela
Kga-1
3a
3e
3i
3h
3k
3l
7.76a
13.48
12.30
47.86
43.65
37.15
2.13
43.65
>100
85.11
69.18
60.25
75.85
1.51
>100
67.6
>100
>100
58.88
26.3
19.051
27.54
ND
>100
>100
>100
91.2
Acknowledgments
Doxorubicin
NDb
a
This work was supported by Isfahan Pharmaceutical Sciences
Research Center.
IC30
(
m
g/mL).
b
Not determined.

3258
A. Fassihi et al. / European Journal of Medicinal Chemistry 44 (2009) 3253–3258
[13] A.K. Sanki, J. Boucau, P. Srivastava, S.S. Adams, D.R. Ronning, S.J. Sucheck,
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