Design, synthesis and antimycobacterial evaluation of novel 3-substituted-N-aryl-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c] pyrazole-2-carboxamide analogues

Article abstract of DOI:10.1016/j.bmcl.2011.06.018

In the present investigation, a series of 3-substituted-N-aryl-6,7- dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide analogues were synthesized and were evaluated for antitubercular activity by two fold serial dilution technique. All the newly synthesized compounds showed moderate to high inhibitory activities against Mycobacterium tuberculosis H₃₇Rv and INH resistant M. tuberculosis. The compound N,3-bis(4-fluorophenyl)-6,7- dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide (4c) was found to be the most promising compound active against M. tuberculosis H₃₇Rv and isoniazid resistant M. tuberculosis with minimum inhibitory concentration 0.78 μM.

Full text of DOI:10.1016/j.bmcl.2011.06.018

Bioorganic & Medicinal Chemistry Letters 21 (2011) 4451–4453
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis and antimycobacterial evaluation of novel
3-substituted-N-aryl-6,7-dimethoxy-3a,4-dihydro-3H-indeno
[1,2-c]pyrazole-2-carboxamide analogues
Mohamed Jawed Ahsan a,b, , Jeyabalan Govinda Samy a, Kunduri Rajeswar Dutt b, Uttam K. Agrawal a,
⇑
Bhawani Shankar Yadav a, Swati Vyas a, Ravinder Kaur a, Garima Yadav a
a New Drug Discovery Research, Department of Medicinal Chemistry, Alwar Pharmacy College, Alwar, Rajasthan 301 030, India
b Department of Pharmaceutical Sciences, National Institute of Medical Sciences University, Jaipur 303 121, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present investigation,
a series of 3-substituted-N-aryl-6,7-dimethoxy-3a,4-dihydro-3H-
Received 17 January 2011
Revised 26 May 2011
Accepted 6 June 2011
Available online 17 June 2011
indeno[1,2-c]pyrazole-2-carboxamide analogues were synthesized and were evaluated for antitubercular
activity by two fold serial dilution technique. All the newly synthesized compounds showed moderate to
high inhibitory activities against Mycobacterium tuberculosis H37Rv and INH resistant M. tuberculosis. The
compound N,3-bis(4-fluorophenyl)-6,7-dimethoxy-3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxam-
ide (4c) was found to be the most promising compound active against M. tuberculosis H37Rv and isoniazid
Keywords:
Pyrazolines
Antitubercular agents
resistant M. tuberculosis with minimum inhibitory concentration 0.78 lM.
Ó 2011 Elsevier Ltd. All rights reserved.
Now a day’s tuberculosis, TB is a major public health problem
and over one third of the world population is infected with this
dreadful disease caused by Mycobacterium tuberculosis.1 The effec-
tive treatment of TB becomes more complicated due to the resis-
tance developed by bacteria, M. tuberculosis. More than 1.7
million people died and 9.4 million new cases worldwide in 2009
are reported as per WHO survey. It has been estimated that up to
50 million people are infected with drug-resistant forms of TB.
There are estimated 1.3 million multi/extensively drug resistant
TB (M/XDR-TB) cases will need to be treated between 2010 and
2015.2 The treatment of TB with frontline drugs is associated with
severe side effects including hepatotoxicity, thrombocytopenia,
itching, rashes, fever, drug induced hepatitis, etc.3,4 A recent threat
to TB is the development of drug resistant strains. The drug resis-
tant TB is classified into two categories such as multi drug resistant
tuberculosis (MDR-TB) that is resistant to isoniazid and rifampicin
and extensively drug resistant tuberculosis (XDR-TB) that is resis-
tant either to quinolones or to any one of kanamycin, capreomycin,
or amikacin.
biosynthesis of lipids.6,7 Most of the antitubercular drugs (isonia-
zid, pyrazinamid, etc) are inhibitors of mycobacterial cell wall syn-
thesis by inhibiting fatty acid synthetase. Pyrazoline is an
important class of heterocyclic compounds, and were found to
have various biological activities including antiamoebic, anticon-
vulsant, antimicrobial, anti-inflammatory, antiviral, antiarrhyth-
mic, antidepressant, anticancerous, antidiabetic, antitubercular,
etc.8–17 Hence it is worth to synthesize such compounds. In the
current work eighteen novel 3-substituted-N-aryl-6,7-dimethoxy-
3a,4-dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide analogues
were designed and synthesized based on the structure of the
known antitubercular agent, thiacetazone (Fig. 1). All the synthe-
sized compounds were evaluated for their anti-tubercular
activities.
The 3-substituted-N-aryl-6,7-dimethoxy-3a,4-dihydro-3H-in-
deno[1,2-c]pyrazole-2-carboxamide analogues (4a–r) described
in this study are shown in Table 1 and the reaction sequence
for the synthesis is summarised in Scheme 1. In the initial step
5,6-dimethoxy-2,3-dihydro-1H-inden-1-one (0.1 mol) and appro-
priate aromatic aldehydes (0.1 mol) in diluted methanolic so-
dium hydroxide solution stirred at room temperature giving
the (2E)-2-substituted-5,6-dimethoxy-2,3-dihydro-1H-indene-1-
one derivatives (3a–f). In the subsequent step 2-substituted-
5,6-dimethoxy-2,3-dihydro-1H-indene-1-one derivatives treated
with appropriate semicarbazides furnished the titled compounds
(4a–r). The substituted phenyl semicarbazides were synthesized
as per the reported method.18,19 The yields of the titled com-
pounds were ranging from 62% to 88% after recrystallization
In an effort to discover new and effective therapeutic agents, we
recently reported the in vitro antimycobacterial activity of novel
diketones.5 The azole group of heterocyclic compounds possess
significant pharmacokinetic property, lipophilicity that influence
the ability of drug to reach the target by transmembrane diffusion
and show promising activity against resistant TB by inhibiting the
⇑
Corresponding author. Tel.: +91 9694087786; fax: +91 144 5121120.
E-mail address: jawedpharma@gmail.com (M.J. Ahsan).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.06.018

4452
M. J. Ahsan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4451–4453
CH
CH
O
Isosteric replacement of 'S' with 'O'
O
3
O
3
O
CH OH/NaOH
3
O
1
+
Ar CHO
H C
H C
1
3
3
O
Ar
O
2a-f
Ar2
3a-f
1
N
N
N
H
O
O
2
AcOH
N
Ar
NHCONHNH
2
Ar1
O
2
Ar
CH
O
3
N
Title compounds (4a-r)
N
H
S
1
Ar
H C
3
O
4a-r
N
NH2
N
Scheme 1. Protocol for the synthesis.
H
O
3112–3481 cmÀ1 and C@O stretching at 1315–1357 cmÀ1 bands.
In the Nuclear Magnetic Resonance spectra (1H NMR) the sig-
nals of the respective protons of the synthesized titled
compounds were verified on the basis of their chemical shift,
multiplicities and coupling constants in DMSO-d6. The spectra
showed triplet at d 3.20–3.57 ppm corresponding to CH; a
doublet at d 3.43–3.48 ppm corresponding to CH2 group; a
H3C
N
H
Thiacetazone
Figure 1. Design of the title compounds based on known antitubercular drug.
singlet at
d
3.79–3.83 ppm corresponding to OCH3 group;
with absolute ethanol. The purity of the compounds was
checked by TLC using eluant benzene: acetone (9:1) and ele-
mental analyses. Both the analytical and spectral data (IR, 1H
NMR) of all the synthesized compounds were in full accordance
with the proposed structures. In general, the IR spectra of the
compounds afforded pyrazoline C@N stretching at 1501–
1576 cmÀ1, C–H deformation at 1362–1464 cmÀ1, C2–N1 stretch-
ing at 1069–1189 cmÀ1, and carbamoyl group N–H stretching at
a doublet at 4.9–5.4 ppm corresponding to CH; multiplet at d
6.51–8.38 ppm corresponding to aromatic protons; broad singlet
at d 8.88–11.52 ppm corresponding to CONH. The elemental
analysis results were within 0.4% of the theoretical values.
All the synthesized compounds (4a–r) were tested for their
in vitro antimycobacterial activity against MTB and INHR-MTB by
agar dilution method using double dilution technique similar to
Table 1
Physical constant and antimycobacterial activity of the synthesized compounds
O
Ar2
N
N
N
O
O
1H
Ar
4a-4r
Compound
Ar1
Ar2
Yield (%)
Mp (°C)
MIC (lM)
MTBa
MTBb
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4-Pyridinyl-
4-Fluorophenyl-
4-Fluorophenyl-
4-Fluorophenyl-
4-Fluorophenyl-
4-Fluorophenyl-
4-Fluorophenyl-
4-Bromophenyl-
4-Bromophenyl-
4-Bromophenyl-
4-Bromophenyl-
4-Bromophenyl-
4-Bromophenyl-
3-Chloro-4-fluorophenyl-
3-Chloro-4-fluorophenyl-
3-Chloro-4-fluorophenyl-
3-Chloro-4-fluorophenyl-
3-Chloro-4-fluorophenyl-
3-Chloro-4-fluorophenyl-
—
72
76
70
84
82
76
62
68
72
88
72
66
72
68
70
78
72
68
—
186
180
176
170
166
188
168
130
144
168
160
164
230
185
194
202
154
162
—
3.12
6.25
0.78
>10
>6.25
10
6.25
>6.25
3.12
>10
>6.25
>10
>6.25
6.25
0.78
>6.25
6.25
>6.25
0.78
0.006
6.25
12.5
0.78
NT
10
12.5
10
10
6.25
NT
>10
NT
10
12.5
3.12
12.5
12.5
12.5
12.5
3.12
2-Chlorophenyl-
4-Fluorophenyl-
3,4-Dimethoxyphenyl-
Phenyl-
4-Methoxyphenyl-
4-Pyridinyl-
2-Chlorophenyl-
4-Fluorophenyl-
3,4-Dimethoxyphenyl-
Phenyl-
4-Methoxyphenyl-
4-Pyridinyl-
2-Chlorophenyl-
4-Fluorophenyl-
3,4-Dimethoxyphenyl-
Phenyl-
4-Methoxyphenyl-
—
INH
Rifampin
—
—
—
—
a
M. tuberculosis H37Rv.
INHR-TB.
b
NT = not tested.

M. J. Ahsan et al. / Bioorg. Med. Chem. Lett. 21 (2011) 4451–4453
4453
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that recommended by the National Committee for Clinical Labora-
tory Standards.20 The MTB and INHR-MTB clinical isolate was ob-
tained from Tuberculosis Research Center, Alwar, India. The MIC
was defined as the minimum concentration of compound required
to inhibit 90% of bacterial growth and MIC of the compounds were
reported in Table 1 with standard drug INH and rifampin for
comparison.
Among the eighteen synthesized compounds, eight compounds
were found to be active with minimum inhibitory concentration of
0.78–6.25
against MTB at a MIC of 0.78
compounds 4c and 4o were found to be active against INHR-MTB
at a MIC of 0.78 M and 3.12 M respectively. When compared
lM. The compounds 4c and 4o were found to be active
lM comparable to that of INH. The
l
l
with INH the compound, 4c was 16 folds more active while com-
pound, 4o was 4 folds more active against INHR-MTB. In the title
compounds (4a–r), both the C3 aryl group and the N-aryl group
influenced the antitubercular activity. The 3- substituted com-
pounds with electron withdrawing groups such as 4-flourophenyl,
4-pyridyl produced more inhibitory and 2-chlorophenyl produced
moderate inhibitory activity while the electron releasing groups
such as 4-methoxyphenyl, 3,4-dimethoxyphenyl showed less
inhibitory activity. The 4-flouro substitution on N-aryl group
showed maximum inhibitory activity as compared to 4-bromo
and 3-chloro-4-flouro substitution. The compounds 4b, 4g, 4n,
4q, 4a and 4i showed moderate to good inhibitory activity against
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Compound (4c): 5,6-dimethoxy-2,3-dihydro-1H-inden-1-one (1.92 g, 0.001
mole) with 4-fluorobenzaldehyde (1.24 g, 0.001 mole) in diluted methanolic
sodium hydroxide solution was stirred under room temperature for 4 h giving
MTB at MIC 6.25
All the active compounds were tested for cytotoxicity (IC50) in
VERO cells at concentrations of 62.5 g/mL or 10 times the MIC.
lM and 3.12 lM.
l
the
(2E)-2-(4-fluorobenzylidene)-5,6-dimethoxy-2,3-dihydro-1H-indene-1-
After 72 h exposure, viability was assessed on the basis of cellular
conversion of MTT into a formazan product using the Promega Cell
Titer 96 Non-radioactive Cell proliferation method. Most of the ac-
one which was then refluxed with 4-fluorophenyl semicarbazides in glacial
acetic acid for 12 h furnished N,3-bis(4-fluorophenyl)-6,7-dimethoxy-3a,4-
dihydro-3H-indeno[1,2-c]pyrazole-2-carboxamide (4c). The entire chemicals
were supplied by E. Merck (Germany) and S.D. Fine Chemicals (India). Melting
points were determined by open tube capillary method and are uncorrected.
Purity of the compounds was checked on TLC plates (Silica gel G) using eluants
benzene–acetone (9:1), the spots were located under iodine vapours or UV
light. IR spectra were obtained on a Schimadzu 8201 PC, FT-IR spectrometer
tive compounds were found to be non-toxic up to 62.5 l
g/mL.21 All
these derivatives can be further modified to exhibit more potency.
Further studies to acquire more information about Quantitative
Structure–Activity Relationships (QSAR) and MDR are in progress
in our laboratory. The pyrazoline derivatives discovered in this
study may provide valuable therapeutic intervention for the treat-
ment of tubercular disease.
(KBr pellets). 1H NMR spectra were recorded on
a Bruker AC 300 MHz
spectrometer using TMS as internal standard in DMSO. Mass spectra were
recorded on a Bruker Esquire LCMS using ESI and elemental analyses were
performed on Perkin-Elmer 2400 Elemental Analyzer. IR (KBr) cmÀ1: 3334
(NH), 1642 (C@O), 1571(C@N), 1387 (CH), 1181 (C–N), 786 (C–F); 1H NMR
(DMSO-d6) ppm: 3.20–3.35 (1H, t, CH), 3.41–3.43 (2H, d, J = 6.2 Hz, CH2), 3.83
(6H, s, OCH3), 5.1 (1H, d, J = 6.4 Hz, CH), 6.68–8.31 (10H, m, Ar), 8.89 (1H, s,
CONH); 13C NMR (DMSO-d6) ppm: 191.94 (C@O), 156.22, 151.8, 150.73,
149.93, 145.97, 142.63, 140.85, 130.08, 128.59, 124.60, 108.48, 105.10 (12C,
Ar) 68.0 (CH), 56.16 (OCH3), 56.55 (OCH3). 39.94 (CH) 31.87 (CH2) Mass (m/z)
450 (M+H)+; Cacld/Anal. [C (66.81) 66.82, H (4.71) 4.72, O (10.68) 10.69, N
(9.35) 9.37].
Acknowledgments
Authors are thankful to the management people of Alwar Phar-
macy College, Alwar, Rajasthan, India for providing research
facilities.
References and notes
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