Synthesis and biological evaluation of some novel 1,4-dihydropyridines as potential antitubercular agents

Article abstract of DOI:10.1111/j.1747-0285.2011.01233.x

Recent studies showed that 1,4-dihydropyridine-3,5-dicarbamoyl derivatives with lipophilic groups have significant antitubercular activity. In this study, we have synthesized new derivatives of 1,4-dihydropyridines bearing carbmethoxy and carbethoxy group

Full text of DOI:10.1111/j.1747-0285.2011.01233.x

ª 2011 John Wiley & Sons A/S
doi: 10.1111/j.1747-0285.2011.01233.x
Chem Biol Drug Des 2011; 78: 881–886
Research Article
Synthesis and Biological Evaluation of Some
Novel 1,4-Dihydropyridines as Potential
AntiTubercular Agents
ades ago, effective anti-TB drugs have been launched, and one
could hardly find a TB case to be demonstrated at the medicinal
universities. But TB stroke back! (1) The return of tuberculosis was
declared by World Health Organization (WHO) as a global emer-
gency compared with a hypothetical third world war with 9 million
new TB cases and two million deaths reported each year (2,3);
about one-third of the world's population is already infected with
M. tuberculosis (a). The current frontline therapy for treatment of
tuberculosis requires a cocktail of three or more drugs such as iso-
niazide, rifampin, ethambutol and pyrazinamide over an extended
period of time (4). Furthermore, in recent times, the occurrence of
multidrug-resistant TB (MDR–TB), a form of TB that does not
respond to the standard treatments, is more common. It is a shock-
ing revelation that MDR–TB is present in almost all countries as
per the recent survey, made by the World Health Organization
(WHO) and its partners.
Amit Trivedi*, Dipti Dodiya, Bipin
Dholariya, Vipul Kataria, Vimal Bhuva
and Viresh Shah
Department of Chemistry, Saurashtra University, Rajkot-360005,
Gujarat, India
*Corresponding author: Amit Trivedi, drartrivedi@gmail.com
Recent studies showed that 1,4-dihydropyridine-
3,5-dicarbamoyl derivatives with lipophilic groups
have significant antitubercular activity. In this
study, we have synthesized new derivatives of
1,4-dihydropyridines bearing carbmethoxy and
carbethoxy group at C-3 and C-5 of the 1,4-dihy-
dropyridine ring. In addition, 1H-pyrazole ring
is substituted at C-4 position. These analogues
were synthesized by multi-component Hantzsch
reaction. The in vitro antitubercular activity
of compounds against Mycobacterium tuber-
culosis H37Rv was evaluated. The lowest minimum
Despite the efforts of agencies such as WHO, the Global Fund for
HIV, TB, and Malaria, and the Gates Foundation who have galva-
nized multilateral support and initiated public–private partnerships
to increase resources to combat this disease of poverty, only
seven candidate TB drugs from five different clinical classes were
undergoing clinical trials till very recently, i.e. fluoroquinolones
(gatifloxacin and moxifloxacin), diarylquinoline (TMC207), nitroimi-
dazoles (OPC67683 and PA824), pyrrole (LL3858) and ethylenadi-
amine (SQ109) (5). All aforementioned facts underscore the
importance of the development of new drugs with unique and
divergent structure and with a novel mechanism of action for effi-
cacious clinical control of patients with TB using ordinary antimy-
cobacterial drugs.
inhibitory
concentration
value,
0.02 lg/mL
and SI > 500, was found for dimethyl 1,4-dihydro-
4-(3-(4-nitrophenyl)-1-phenyl-1H-pyrazol-4-yl)-2,6-di-
methylpyridine-3,5-dicarboxylate
3f,
diethyl
1,4-dihydro-4-(3-(4-fluorophenyl)-1-phenyl-1H-pyra-
zol-4-yl)-2,6-dimethylpyridine-3,5-dicarbo-xylate 4c
and diethyl 1,4-dihydro-4-(3-(4-bromophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethyl pyridine-3,5-di-
carboxylate 4e, making them more potent than
first-line antitubercular drug isoniazid. In addition,
these compounds exhibited relatively low cytotox-
icity.
Key words: 1,4-dihydropyridines, antimycobacterial activity, Myco-
bacterium tuberculosis, tuberculosis
Recently, studies showed that 3,5-dicarbamoyl derivatives of
1,4-dihydropyridine (DHP) with lipophilic groups have considerable
antitubercular activity against M. tuberculosis H37Rv (6). It was also
observed that esters or substituted isosters of pyridine and pyrazine
carboxylic acids (such as tetrazoles) have been more active than
the parent acids, especially against resistant strains. These esters
are presumably activated by an esterase to parent acid (7–10).
Indeed, esters of pyrazinoic acids have been shown to possess
activity against pyrazinamide-resistant isolates, which has been
attributed to a deficiency of nicotinamidase (7–10). In addition, pyr-
azoles exhibited significant antitubercular activity (11). Recognizing
these facts and in continuation of our work on antitubercular
agents (12–16), it appeared of interest to design and synthesize
new derivatives of 1,4-dihydropyridines bearing carbmethoxy and
Received 21 December 2010, revised 26 August 2011 and accepted for
publication 28 August 2011.
Tuberculosis (TB) is a global epidemic caused by various strains of
mycobacterium, usually Mycobacterium tuberculosis. Tuberculosis
has been considered to be a disease of poverty for many years
with quite rare occurrence in the developed countries. Unfortu-
nately, recently, more people in the developed world are contracting
tuberculosis, because their immune systems are compromised by
immunosuppressive drugs, substance abuse or AIDS. Several dec-
881

Trivedi et al.
carbethoxy group at C-3 and C-5 of the DHP ring, respectively. It
seems that such replacements could effectively overcome the resis-
tant isolates, which have been attributed to a deficiency of ami-
dase or esterase. In addition, pyrazole moiety is substituted at C-4
position of dihydropyridine ring. The antimycobacterial activity of
synthesized compounds was evaluated against M. tuberculosis
H37Rv (MTB).
Dimethyl 1,4-dihydro-4-(3-(4-hydroxyphenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3b)
Yield: 69%, mp = 163–165 ꢀC; IR (KBr): 3319, 3015, 2924, 1690,
1590 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 6.93–7.79 (m, 10H, Ar-H),
5.27 (s, 1H, CH), 5.67 (s, 1H, NH), 4.73 (s, 1H, OH), 3.84 (s, 6H, 2-
OCH3), 2.03 (s, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.4,
156.7, 150.2, 149.8, 132.5, 133.3, 129.5, 128.4, 127.8, 121.4, 123.0,
117.7, 116.8, 104.4, 52.5, 35.6, 16.3. Anal. Calcd. for C26H25N3O5: C,
67.96; H, 5.48; N, 9.14%. Found: C, 67.88; H, 5.39; N, 9.17.
Methods and Materials
All of the synthesized compounds were chemically characterized by
thin-layer chromatography (TLC), infrared (IR), proton nuclear mag-
netic resonance (1H NMR) and elemental microanalyses (CHN).
Melting points were determined in open capillary tubes and are
uncorrected. Formation of the compounds was routinely checked by
TLC on silica gel-G plates of 0.5 mm thickness and spots were
Dimethyl 1,4-dihydro-4-(3-(4-fluorophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3c)
Yield: 54%, mp = 167–169 ꢀC; IR (KBr): 3314, 3015, 2925, 1693,
1595 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.03–7.92 (m, 10H, Ar-H),
5.25 (s, 1H, CH), 5.68 (s, 1H, NH), 3.82 (s, 6H, 2-OCH3), 2.02 (s, 6H,
2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.7, 161.3, 150.3, 149.5,
136.2, 133.5, 129.3, 128.4, 127.5, 122.8, 121.2, 117.8, 116.6, 104.3,
52.3, 35.7, 16.4. Anal. Calcd. for C26H24FN3O4: C, 67.67; H, 5.24; N,
9.11%. Found: C, 67.59; H, 5.15; N, 9.02.
1
located by iodine. H NMR was determined in DMSO-d6 solution on
a Bruker DPX 300 MHz spectrometer (Bruker India, Mumbai, India).
13C NMR (75 and 125 MHz) spectra were registered on a Bruker
AC 200, DPX 300 and ARX 500, at 25 ꢀC, in DMSO-d6. Infrared
spectra were recorded on SHIMADZU-FT-IR-8400 using KBr pellets.
Elemental analyses of the newly synthesized compounds were car-
ried out on Carlo Erba 1108 analyzer (Carlo Erba, Milan, Italy), and
the data were within range of the theoretical values.
Dimethyl 1,4-dihydro-4-(3-(4-chlorophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3d)
Yield: 65%, mp = 151–153 ꢀC; IR (KBr): 3320, 3013, 2927, 1693,
1596 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.15–7.84 (m, 10H, Ar-H),
5.28 (s, 1H, CH), 5.65 (s, 1H, NH), 3.84 (s, 6H, 2-OCH3), 2.01 (s, 6H,
2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.4, 150.4, 149.6, 137.5,
134.1, 131.6, 129.7, 129.4, 128.7, 127.5, 122.9, 121.4, 117.8, 104.3,
52.2, 35.8, 16.5. Anal. Calcd. for C26H24ClN3O4: C, 65.34; H, 5.06; N,
8.79%. Found: C, 65.27; H, 4.95; N, 8.69.
Synthesis of 3-(aryl)-1-phenyl-1H-pyrazole-4-
carbaldehydes (1)
Synthesis of 3-(aryl)-1-phenyl-1H-pyrazole-4-carbaldehydes was
achieved by reported method (17).
General procedure for the synthesis of 1,4-
dihydropyridines (3a–h to 4a–h)
To a stirred solution of the methyl acetoacetate ⁄ ethyl acetoacetate
(0.02 mole, 2 eq) and an appropriate 3-(aryl)-1-phenyl-1H-pyrazole-
4-carbaldehyde (0.01 mole, 1 eq) in methanol (20 mL), ammonia
(1 mL) was added dropwise. The reaction mixture was allowed to
reflux for 18–20 h. After completion of the reaction, as indicated
by TLC (ethyl acetate:hexane 2:3), the reaction mixture was
allowed to stand overnight, and the solid product that separated
was isolated. The product was washed with 15 mL of cold diethyl
ether. Finally, it was purified by silica gel (60–100 mesh) column
chromatography using ethyl acetate and hexane (2:3) as the elu-
ents.
Dimethyl 1,4-dihydro-4-(3-(4-bromophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3e)
Yield: 70%, mp = 126–128 ꢀC; IR (KBr): 3319, 3020, 2932, 1695,
1596 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.08–7.89 (m, 10H, Ar-H),
5.23 (s, 1H, CH), 5.68 (s, 1H, NH), 3.82 (s, 6H, 2-OCH3), 2.02 (s, 6H,
2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.6, 150.5, 149.6, 138.8,
133.8, 132.5, 129.5, 128.7, 127.4, 123.1, 122.5, 121.1, 117.8, 104.3,
52.3, 35.7, 16.4. Anal. Calcd. for C26H24BrN3O4: C, 59.78; H, 4.63;
N, 8.04%. Found: C, 59.67; H, 4.54; N, 7.92.
Dimethyl 1,4-dihydro-2,6-dimethyl-4-(1,3-
diphenyl-1H-pyrazol-4-yl)pyridine-3,5-
dicarboxylate (3a)
Dimethyl 1,4-dihydro-4-(3-(4-nitrophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3f)
Yield: 59%, mp = 88–90 ꢀC; IR (KBr): 3325, 3018, 2928, 1695,
1590 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.36–8.14 (m, 10H, Ar-H),
5.26 (s, 1H, CH), 5.61 (s, 1H, NH), 3.81 (s, 6H, 2-OCH3), 2.04 (s, 6H,
2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.6, 150.5, 149.6, 146.1,
145.6, 133.6, 129.5, 128.7, 127.4, 123.1, 121.6, 121.1, 117.7, 104.5,
52.3, 35.6, 16.2. Anal. Calcd. for C26H24N4O6: C, 63.93; H, 4.95; N,
11.47%. Found: C, 63.84; H, 4.83; N, 11.40.
Yield: 64%, mp = 177–179 ꢀC; IR (KBr): 3315, 3010, 2929,
1695, 1596 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.35–7.82 (m,
11H, Ar-H), 5.24 (s, 1H, CH), 5.62 (s, 1H, NH), 3.80 (s, 6H, 2-
OCH3), 2.00 (s, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.4,
149.6, 150.3, 140.2, 133.5, 129.6, 129.8, 128.4, 127.8, 126.6,
122.9, 120.4, 117.5, 104.5, 52.7, 35.7, 16.5. Anal. Calcd. for
C26H25N3O4: C, 70.41; H, 5.68; N, 9.47%. Found: C, 70.32; H,
5.56; N, 9.38.
882
Chem Biol Drug Des 2011; 78: 881–886

Synthesis and Biological Evaluation of Some Novel 1,4-Dihydropyridines
Dimethyl 1,4-dihydro-4-(3-(4-methylphenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3g)
1.11 (t, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.3, 163.2,
150.9, 150.4, 139.9, 129.9, 129.5, 128.3, 126.4, 120.6, 123.3,
117.4, 116.8, 102.3, 61.9, 35.4, 16.4, 14.3. Anal. Calcd. for
C28H28FN3O4: C, 68.70; H, 5.77; N, 8.58%. Found: C, 68.62; H,
5.68; N, 8.49.
Yield: 64%, mp = 145–147 ꢀC; IR (KBr): 3322, 3015, 2928, 2920,
1
1694, 1595 ⁄ cm. H NMR (DMSO-d6): d (ppm) 7.23–7.82 (m, 10H, Ar-
H), 5.22 (s, 1H, CH), 5.64 (s, 1H, NH), 3.81 (s, 6H, 2-OCH3), 2.35 (s, 3H,
CH3), 2.01 (s, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.5, 150.5,
149.6, 137.1, 136.2, 133.4, 129.5, 129.1, 128.7, 127.5, 122.9, 120.8,
117.7, 104.4, 52.3, 35.6, 24.7, 16.1. Anal. Calcd. for C27H27N3O4: C,
70.88; H, 5.95; N, 9.18%. Found: C, 70.77; H, 5.88; N, 9.10.
Diethyl 1,4-dihydro-4-(3-(4-chlorophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (4d)
Yield: 54%, mp = 128–130 ꢀC; IR (KBr): 3325, 3013, 2932, 2854,
1
1698, 1595 ⁄ cm. H NMR (DMSO-d6): d (ppm) 7.27-7.96 (m, 11H, Ar-
Dimethyl 1,4-dihydro-4-(3-(4-methoxyphenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (3h)
H), 5.87 (s, 1H, NH), 5.64 (s, 1H, CH), 3.96–4.06 (q, 2H, CH2CH3),
3.83-3.91 (q, 2H, CH2CH3), 2.34 (s, 6H, 2-CH3), 1.11-1.19 (t, 6H, 2-
CH3). 13C NMR (DMSO-d6): d (ppm) 167.3, 150.8, 150.1, 139.7,
135.1, 131.4, 129.4, 129.6, 128.7, 126.5, 123.3, 120.1, 117.4, 102.7,
62.1, 35.6, 16.5, 14.3. Anal. Calcd. for C28H28ClN3O4: C, 66.46; H,
5.58; N, 8.30%. Found: C, 66.37; H, 5.50; N, 8.18.
Yield: 58%, mp = 132–134 ꢀC; IR (KBr): 3315, 3015, 2928, 1690,
1595 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.05–7.93 (m, 10H, Ar-H),
5.26 (s, 1H, CH), 5.68 (s, 1H, NH), 3.91 (s, 3H, OCH3), 3.84 (s, 6H, 2-
OCH3), 2.34 (s, 3H, CH3), 2.04 (s, 6H, 2-CH3). 13C NMR (DMSO-d6): d
(ppm) 167.7, 159.1, 150.4, 149.6, 133.3, 132.5, 129.6, 128.7, 127.4,
123.0, 121.5, 117.7, 115.1, 104.3, 55.5, 52.4, 35.5, 16.3. Anal. Calcd.
for C27H27N3O5: C, 68.48; H, 5.75; N, 8.87%. Found: C, 68.39; H,
5.77; N, 8.76.
Diethyl 1,4-dihydro-4-(3-(4-bromophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (4e)
Yield: 59%, mp = 153–155 ꢀC; IR (KBr): 3325, 3015, 2928, 2860,
1
1698, 1596 ⁄ cm. H NMR (DMSO-d6) d ppm: 7.32–8.14 (m, 11H, Ar-
Diethyl 1,4-dihydro-2,6-dimethyl-4-(1,3-
diphenyl-1H-pyrazol-4-yl)pyridine-3,5-
dicarboxylate (4a)
H), 5.89 (s, 1H, NH), 5.66 (s, 1H, CH), 4.05-4.11 (q, 2H, CH2CH3),
3.88–3.95 (q, 2H, CH2CH3), 2.30 (s, 6H, 2-CH3), 1.12-1.21 (t, 6H, 2-
CH3). 13C NMR (DMSO-d6): d (ppm) 167.3, 150.9, 150.5, 140.7,
140.1, 132.3, 130.1, 129.6, 126.2, 123.7, 123.2, 120.4, 117.2, 102.5,
62.0, 35.8, 16.5, 14.4. Anal. Calcd. for C28H28BrN3O4: C, 61.10; H,
5.13; N, 7.63%. Found: C, 60.97; H, 5.04; N, 7.56.
Yield: 37%, mp = 195–197 ꢀC; IR (KBr): 3324, 3013, 2928, 2855,
1696, 1595 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.25–8.10 (m, 11H,
Ar-H), 5.88 (s, 1H, NH), 5.62 (s, 1H, CH), 3.96–4.05 (q, 2H, CH2CH3),
3.77–3.84 (q, 2H, CH2CH3), 2.23 (s, 6H, 2-CH3), 1.05–1.14 (t, 6H, 2-
CH3). 13C NMR (DMSO-d6): d (ppm) 167.5, 150.6, 150.1, 139.9,
133.1, 130.1, 129.8, 128.5, 127.6, 126.5, 123.3, 120.5, 117.4, 102.7,
62.1, 35.6, 16.5, 14.3. Anal. Calcd. for C28H29N3O4: C, 71.32; H,
6.20; N, 8.91%. Found: C, 71.23; H, 6.08; N, 8.82.
Diethyl 1,4-dihydro-4-(3-(4-nitrophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (4f)
Yield: 64%, mp = 101–103 ꢀC; IR (KBr): 3316, 3015, 2930, 1690,
1590 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.35–8.19 (m, 11H, Ar-H),
5.90 (s, 1H, NH), 5.64 (s, 1H, CH), 4.03–4.14 (q, 2H, CH2CH3), 3.84–
3.98 (q, 2H, CH2CH3), 2.26 (s, 6H, 2-CH3), 1.08–1.19 (t, 6H, 2-CH3).
13C NMR (DMSO-d6): d (ppm) 167.2, 151.3, 150.6, 148.7, 140.5,
139.3, 129.3, 128.6, 126.4, 123.4, 121.8, 120.4, 117.4, 102.5, 61.9,
35.7, 16.8, 14.3. Anal. Calcd. for C28H28N4O6: C, 65.11; H, 5.46; N,
10.85%. Found: C, 65.01; H, 5.35; N, 10.78.
Diethyl 1,4-dihydro-4-(3-(4-hydroxyphenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (4b)
Yield: 61%, mp = 161–163 ꢀC; IR (KBr): 3325, 3013, 2922, 2852,
1696, 1595 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.03–7.94 (m, 11H,
Ar-H), 5.89 (s, 1H, NH), 5.65 (s, 1H, CH), 4.72 (s, 1H, OH), 4.02–4.12
(q, 2H, CH2CH3), 3.83-3.91 (q, 2H, CH2CH3), 2.32 (s, 6H, 2-CH3),
1.11-1.16 (t, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.3, 158.8,
150.8, 150.4, 140.1, 129.7, 128.8, 126.5, 125.4, 123.3, 117.4, 116.9,
102.3, 61.9, 35.3, 16.6, 14.2. Anal. Calcd. for C28H29N3O5: C, 68.98;
H, 6.00; N, 8.62%. Found: C, 68.86; H, 5.89; N, 8.53.
Diethyl 1,4-dihydro-2,6-dimethyl-4-(1-phenyl-3-
p-tolyl-1H-pyrazol-4-yl)pyridine-3,5-
dicarboxylate (4g)
Yield: 70%, mp = 145–147 ꢀC; IR (KBr): 3316, 3015, 2930, 1690,
1590 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.16–7.95 (m, 11H, Ar-H),
5.86 (s, 1H, NH), 5.67 (s, 1H, CH), 3.98–4.07 (q, 2H, CH2CH3), 3.86–
3.94 (q, 2H, CH2CH3), 2.26 (s, 6H, 2-CH3), 2.35 (s, 3H, CH3), 1.11–
1.20 (t, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.2, 151.3,
150.6, 140.5, 138.3, 130.5, 129.6, 129.3, 127.6, 126.2, 123.4, 120.1,
117.4, 102.5, 62.1, 35.6, 16.8, 24.9, 14.3. Anal. Calcd. for
C29H31N3O4: C, 71.73; H, 6.43; N, 8.65%. Found: C, 71.65; H, 6.45;
N, 8.53.
Diethyl 1,4-dihydro-4-(3-(4-fluorophenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (4c)
Yield: 65%, mp = 109–111 ꢀC; IR (KBr): 3325, 3013, 2928, 2856,
1695, 1595 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.05–7.89 (m, 11H,
Ar-H), 5.86 (s, 1H, NH), 5.68 (s, 1H, CH), 3.95–4.06 (q, 2H,
CH2CH3), 3.79–3.86 (q, 2H, CH2CH3), 2.26 (s, 6H, 2-CH3), 1.03-
Chem Biol Drug Des 2011; 78: 881–886
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Trivedi et al.
Diethyl 1,4-dihydro-4-(3-(4-methoxyphenyl)-1-
phenyl-1H-pyrazol-4-yl)-2,6-dimethylpyridine-
3,5-dicarboxylate (4h)
8.19 ppm. The 13C NMR signal of methine group can be observed
at 35.3–35.8 ppm. IR spectra of DHP derivatives were also in
agreement with the structures (Figures S1–S3).
Yield: 52%, mp = 97–99 ꢀC; IR (KBr): 3320, 3012, 2926, 1695,
1597 ⁄ cm. 1H NMR (DMSO-d6): d (ppm) 7.16–7.95 (m, 11H, Ar-H),
5.88 (s, 1H, NH), 5.67 (s, 1H, CH), 3.98–4.07 (q, 2H, CH2CH3), 3.86-
3.94 (q, 2H, CH2CH3), 3.80 (s, 3H, OCH3), 2.29 (s, 6H, 2-CH3), 1.05-
1.13 (t, 6H, 2-CH3). 13C NMR (DMSO-d6): d (ppm) 167.2, 159.9, 151.1,
150.6, 140.2, 129.7, 129.1, 126.5, 125.5, 123.1, 120.1, 117.4, 114.8,
102.3, 57.1, 62.1, 35.7, 16.8, 14.3. Anal. Calcd. for C29H31N3O5:
C, 69.44; H, 6.23; N, 8.38%. Found: C, 69.37; H, 6.14; N, 8.27.
Antitubercular activity
All compounds were initially screened for their in vitro antimycobac-
terial activity at 6.25 lg ⁄ mL against MTB H37Rv strain by the
Tuberculosis Antimicrobial Acquisition and Coordinating Facility (TA-
ACF) in BACTEC 12B medium using the Microplate Alamar Blue
Assay (18). Compounds exhibiting ‡90% inhibition in the initial
screen were retested at and below 6.25 lg ⁄ mL using twofold dilu-
tion to determine the actual MIC (Table 1).
Determination of 50% inhibitory concentrations
(IC50) in VERO cells
In the preliminary screening, six compounds (3f, 4a–c, 4e and 4f)
inhibited MTB with 90–100%. In the secondary level, three com-
pounds (3f, 4c and 4e) inhibited MTB with MIC of <1 lg ⁄ mL and
two compounds (4a and 4b) with MIC of <2 lg ⁄ mL. When com-
pared to isoniazid (MIC: 0.03 lg ⁄ mL), three compounds, dimethyl
1,4-dihydro-2,6-dimethyl-4-(3-(4-nitrophenyl)-1-phenyl-1H-pyrazol-4-yl)
pyridine-3,5-dicarboxylate 3f, diethyl 4-(3-(4-fluorophenyl)-1-phenyl-
1H-pyrazol-4-yl)-1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylate 4c
and diethyl 4-(3-(4-bromophenyl)-1-phenyl-1H-pyrazol-4-yl)-1,4-dihy-
dro-2,6-dimethylpyridine-3,5-dicarboxylate 4e, were found to be the
most active compounds in vitro with MIC of 0.02 lg ⁄ mL against
MTB and were more potent than isoniazid. The preliminary antimy-
cobacterial evaluation results showed that DHP derivatives bearing
alkyl ester group at C-3 and C-5 position along with electron-with-
drawing groups at the 4th position of 3-aryl substituents on pyraz-
ole nucleus have exhibited comparatively higher antimycobacterial
activity probably due to their higher lipophilicity. Extensive struc-
ture–activity relation could be derived in future with various other
modifications.
Concurrent with the determination of minimum inhibitory concentra-
tions (MIC's), compounds were tested for cytotoxicity (IC50) in VERO
cells at concentrations less than or equal to 62.5 lg ⁄ mL or 10
times the MIC for M. tuberculosis H37Rv. After 72 h of exposure,
viability was assessed on the basis of cellular conversion of MTT
into a formazan product using the Promega CellTiter 96 Non-radio-
active Cell Proliferation Assay (Promega, Madison, WI, USA). The
selectivity index (SI = IC50 ⁄ MIC) was also determined; it was con-
sidered significant when SI > 10.
Results and Discussion
Chemistry
Various 3-(aryl)-1-phenyl-1H-pyrazole-4-carbaldehydes (1a–h) bear-
ing a range of electron-withdrawing and electron-releasing substit-
uents, viz., 4-OH, 4-F; 4-Cl; 4-Br; 4-NO2; 4-CH3; 4-OCH3, were
prepared according to the previously reported procedure (17). All
the symmetrical 1,4-DHPs (3a–h to 4a–h) were synthesized by
the multi-component Hantzsch reaction involving 3-(aryl)-1-phenyl-
1H-pyrazole-4-carbaldehydes 1, ethyl ⁄ methyl acetoacetate 2 and
ammonia (Scheme 1). Designed series of molecules (3a–h to
Having identified good number of active antimycobacterial dihydro-
pyridines, the next step was to examine the toxicity of the drug
candidates. Compounds exhibiting reasonably low MICs (from 0.02
to 3.13 lg ⁄ mL) were tested for cytotoxicity (IC50) in VERO cells,
and a selectivity index (SI), defined as IC50: MIC, was calculated.
The IC50 and SI values are shown in Table 1. The compounds 4b
and 4f were somewhat more toxic than the 3f, 4a, 4c and 4e.
Generally, compounds with MIC £6.25 lg ⁄ mL and SI ‡10 are
1
4a–h) were characterized by H NMR, 13C NMR, and Mass spec-
1
trometry techniques and their purity by elemental analysis. The H
NMR spectra of DHPs 3a–h to 4a–h have the typical singlet of
methine group lying in the region 5.22–5.68 ppm and multiplet of
aromatic part of molecules occurring in region between 6.93 and
N
N
R1
O
O
H
O
O
N
N
R2
H3C
R2
CH3
3a-h to 4a-h
a
R1
+
R2
CH3
N
H
CHO
2
1
3a-h R1 = H, 4-OH, 4-F, 4-Cl, 4-Br, 4-NO2, 4-CH3, 4-OCH3; R2 = OCH3
4a-h R1 = H, 4-OH, 4-F, 4-Cl, 4-Br, 4-NO2, 4-CH3, 4-OCH3; R2 = OC2H5
Scheme 1: Synthesis of 1,4-dihydropyridines 3a–h to 4a–h.
884
Chem Biol Drug Des 2011; 78: 881–886

Synthesis and Biological Evaluation of Some Novel 1,4-Dihydropyridines
Table 1: In vitro antitubercular screening data of dihydropyridines 3a–h to 4a–h
MICa
IC50
SIc
b
Sr. no.
Molecule no.
R1
R2
% Inhibi-tion
lg ⁄ mL
VERO cells
(SI = IC50 ⁄ MIC)
mi Log P d
3a
3b
3c
3d
3e
3f
3g
3h
4a
4b
4c
4d
4e
4f
298021
298022
298023
298024
298025
298026
298027
298028
298003
298004
298005
298006
298007
298008
298009
298010
–
H
4-OH
4-F
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OCH3
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
–
12
38
71
62
40
100
71
05
95
97
100
70
100
93
84
52
–
n.d.
n.d.
n.d.
n.d.
n.d.
0.02
n.d.
n.d.
1.56
1.56
0.02
n.d.
0.02
3.13
n.d.
n.d.
0.03
n.d.
n.d.
n.d
n.d.
n.d.
n.d.
n.d.
n.d.
500
n.d.
n.d.
6.42
2.73
500
n.d.
500
2.82
n.d.
n.d.
–
4.485
4.006
4.649
5.163
5.294
4.444
4.934
4.542
5.237
4.758
5.401
5.915
6.046
5.196
5.686
5.294
4-Cl
n.d.
n.d.
>10
n.d.
n.d.
>10
4.27
>10
n.d.
>10
8.83
n.d.
n.d.
–
4-Br
4-NO2
4- CH3
4-OCH3
H
4-OH
4-F
4-Cl
4-Br
4-NO2
4- CH3
4-OCH3
–
4g
4h
INH
n.d., not determined.
aMinimum inhibitory concentration against H37Rv strain of M. tuberculosis (lg ⁄ mL).
bMeasurement of cytotoxicity in VERO cells: 50% inhibitory concentrations (lg ⁄ mL).
cSelectivity index (in vitro): IC50 in VERO cells ⁄ MIC against M tuberculosis.
dmi Log P: Molinspiration Cheminformatics (http://www.molinspiration.com) calculated Log P using online Molinspiration Property Engine v2009.01.
interesting compounds, and a MIC £1 lg ⁄ mL in a novel compound
class is considered an excellent lead (19), which makes 1,4-dihydro-
pyridines 3f, 4c and 4e very promising antimycobacterial com-
pounds. Further in vitro studies of compounds 3f, 4c and 4e as
well as synthesis of analogues of these lead compounds are cur-
rently in progress.
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This work was funded by CSIR through grant no. 01(02348) ⁄
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Additional Supporting Information may be found in the online ver-
sion of this article:
Figure S1. Mass spectrum of compound 4e.
1
Figure S2. H NMR (300MHz) spectrum of compound 4e.
Figure S3. 13C NMR (300MHz) spectrum of compound 4e.
Please note: Wiley-Blackwell is not responsible for the content or
functionality of any supporting materials supplied by the authors.
Any queries (other than missing material) should be directed to the
corresponding author for the article.
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Synthesis of oxime derivatives of 1,3-diphenylpyrazole-4-carbox-
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886
Chem Biol Drug Des 2011; 78: 881–886