Facile synthesis, ex-vivo and in vitro screening of 3-sulfonamide derivative of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxy lic acid piperidin-1-ylamide (SR141716) a potent CB1 receptor antagonist

Article abstract of DOI:10.1016/j.bmcl.2008.06.045

Facile synthesis of biaryl pyrazole sulfonamide derivative of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxy lic acid piperidin-1-ylamide (SR141716, 1) and an investigation of the effect of replacement of the -CO group in the com

Full text of DOI:10.1016/j.bmcl.2008.06.045

Bioorganic & Medicinal Chemistry Letters 18 (2008) 3882–3886
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Facile synthesis, ex-vivo and in vitro screening of 3-sulfonamide derivative of
5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxylic
acid piperidin-1-ylamide (SR141716) a potent CB1 receptor antagonist
Brijesh Kumar Srivastava a, , , Rina Soni a, Jayendra Z. Patel a, Satadru Jha a,à, Sandeep A. Shedage a,
*
Neha Gandhi b,§, Kalapatapu V. V. M. Sairam b, Vishwanath Pawar c, Nisha Sadhwani d, Prasenjit Mitra d,
Mukul R. Jain c, Pankaj R. Patel a
a Department of Medicinal Chemistry, Zydus Research Centre, Cadila Healthcare Ltd., Sarkhej-Bavla N. H.8A, Moraiya, Ahmedabad 382210, India
b Department of Bio-informatics, Zydus Research Centre, Cadila Healthcare Ltd., Sarkhej-Bavla N. H.8A, Moraiya, Ahmedabad 382210, India
c Department of Pharmacology, Zydus Research Centre, Cadila Healthcare Ltd., Sarkhej-Bavla N. H.8A, Moraiya, Ahmedabad 382210, India
d Department of Cell-Biology, Zydus Research Centre, Cadila Healthcare Ltd., Sarkhej-Bavla N. H.8A, Moraiya, Ahmedabad 382210, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Facile synthesis of biaryl pyrazole sulfonamide derivative of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-
4-methyl-1H-pyrazole-3-carboxylic acid piperidin-1-ylamide (SR141716, 1) and an investigation of the
effect of replacement of the –CO group in the compound 1 by the –SO2 group in the aminopiperidine
region is reported. Primary ex-vivo pharmacological testing and in vitro screening of sulfonamide deriv-
ative 2 showed the loss of CB1 receptor antagonism.
Received 5 February 2008
Revised 12 June 2008
Accepted 13 June 2008
Available online 18 June 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Mouse vas defense assay
Sulfonamide derivative
CB1 receptor antagonist
PLP (piece-wise linear potential) scores
hCB1(cAMP)assay
Pyrazole class of compounds are of great significance and have
been extensively used for different therapeutics.1 The biaryl pyra-
zole 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyr-
azole-3-carboxylic acid piperidin-1-ylamide 1 (SR141716, Fig. 1)
is an interesting ligand in the drug development program to treat
obesity and associated metabolic disorders.2
shown in the molecular modeling studies using the homology
model.5
However, no work has been published for the replacement of
the –CO group of the pyrazole ring of the compound 1 by the
–SO2 group. Most of the literature cites the sulfonation on the
5th position of the pyrazole nucleus,12 however, there is scarcity
The compound 1 acts as CB1 receptor antagonist and was re-
cently approved in Europe as AccompliaÒ.3 A number of reports
have been published with a pace to establish the structure–activity
relationship (SAR) for every position of pyrazole ring of rimona-
bant.1b,4–11 In compound 1 the carboxamide functionality on the
3rd position of the pyrazole is crucial for its therapeutic role as well
as for its interactions with key amino acid residue K3.28 (192), as
O
N
NH
4
3
5
N
1
2
N
Cl
Cl
* Corresponding author. Tel.: +91 2717 250801; fax: +91 2717 250606.
E-mail addresses: brijeshsrivastava@zyduscadila.com, bksri2000@yahoo.com
(B. Kumar Srivastava).
Cl
ZRC communication # 245.
Present address: Department of Organic Chemistry, Indian Institute of Science,
à
1
Bangalore, India.
Rimonabant (SR141716)
§
Present address: Western Australian Biomedical Research Institute, Curtin
University of Technology, Perth, Australia.
Figure 1. Potent CB1 receptor antagonist.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.06.045

B. Kumar Srivastava et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3882–3886
3883
compound 1 and opted to replace the –CO group of the carboxam-
ide by the –SO2 group. In this letter, we describe the synthesis,
molecular modeling, and ex-vivo screening of the sulfonamide
derivatives 2 and 3 (Fig. 2) in a mouse vas deferens assay, and in
vitro cAMP hCB1 functional assay for assessing cAMP activity (Ta-
ble 3).22,23 The synthesis of sulfonamide derivative 2, isolation and
identification of bipyrazole sulfonamide derivative 3 have been de-
picted in the Scheme 1.24
In order to validate the rationale for the modification on the 3rd
position of pyrazole nucleus in compound 1, the structures 1 and 2
were docked using CFF and random Monte-Carlo simulations in the
binding site as reported in our previous communication.16 Docking
analysis was observed on the basis of PLP (piece-wise linear poten-
tial) scores and hydrogen bonds of the ligands in the homology
model of CB1 (Table 1). The poses were ranked with PLP-1, PLP-
2, Dock score, and the conformations with the best scores were
checked visually.
Cl
Cl
Cl
N
N
O
O
N
NH
HN
N
O
N
S
S
O
N
N
Cl
Cl
Cl
Cl
Cl
Cl
2
3
From modeling studies, energy-minimized structures and the
PLP values (Table 1) of compound 1 and sulfonamide derivative
2, it is clear that both orientate similarly (Fig. 3) and the oxygen
of the carboxamide of 1 and sulfonamide of 2 form hydrogen bonds
with the Lys192. At the same time the PLP scores suggest favorable
binding of sulfonamide derivative 2 (PLP scores are in the arbitrary
units of energy and lower PLP scores indicate better ligand binding,
thus higher pKi values).
Figure 2. Novel Sulfonamide derivatives of rimonabant.
in the data for the sulfonation on the 3rd position of the pyrazole
nucleus.
In the continuation of our cannabinoid research13–21 herein, we
explored the 3rd position of 1,5-diaryl pyrazole system of the
O
NCO
O
N3
OH
N
(i, ii)
N
N
N
N
Cl
N
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
6
5
4
(iii)
H
O
N2+Cl¯
NH2.HCl
(iv, v)
Cl
N
O
(vi)
N
N
N
N
N
N
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
8
9
7
Cl
Cl
Cl
(vii)
O
O
N
S
SO2Cl
N
N
N
H
N
.HCl
(viii, ix)
N
N
N
+
O
HN
N
Cl
Cl
Cl
Cl
S
O
N
Cl
Cl
Cl
Cl
2
10
Cl
3
Scheme 1. Reagents and conditions : (i) (COCl)2, CH2Cl2, À20 to 25 °C, 2 h; (ii) TBAB, CH2Cl2, aq NaN3, 0–5 °C, 2–3 h; (iii) EtOH, 78–80 °C, 5 h; (iv) 10% aq NaOH, EtOH, 80–
82 °C, 5 h; (v) MeOH, etherealÁHCl, 0–5 °C, 1 h; (vi) aq NaNO2, concd HCl, AcOH, HCOOH, À8 to À6 °C, 20 min; (vii) AcOH, concd HCl, CuCl2Á2H2O, SO2, 25–27 °C, 30 min; (viii)
N-aminopiperidine, CH2Cl2, NEt3, 0–25 °C, 30 min; (ix) MeOH, etherealÁHCl, 0–5 °C, 1 h.

3884
B. Kumar Srivastava et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3882–3886
Table 1
Table 3
Results of modeling of the homology model of CB1 with compound 1 and sulfonamide
derivative 2
In vitro hCB1 functional assay for assessing cAMP activity for compounds 2, 3, and 1
Compound
Concentration (
l
M)
hCB1 (cAMP)a pmol/
lg protein
Compound
PLP-1
PLP-2
DMSO
Forskolin
WIN-55212-2
2
3
1
0.04 0.00
10.01 0.54
3.10 0.05
0.12 0.04
0.09 0.02
13.15 0.42
2
1
À71.62
À70.58
À67.84
À65.75
10
100
10
10
10
a
Values indicate mean SD performed in duplicate and the results being rep-
resentative of at least three independent experiments.
Control
100
75
50
25
0
2 (10 µM)
3 (10 µM)
1 (1 µM)
10-9
10-8
10-7
10-6
10-5
Molar concentration of WIN-55212-2
Figure 3. Superimposition of energy-minimized structure of molecule 2 (Ball and
stick model) with 1 (Stick model).
Figure 4. Effect of WIN-55212-2 on electrically evoked contractions of the mouse
vas deferens in the presence of 1, 2, and 3. Each point corresponds to the
mean SEM obtained using three different tissue preparations of mouse vas
deferens.
The 1,5-diarylpyrazole-3-carboxylic acid 4 was synthesized as
per literature procedure.5 The sulfonamide derivative 2 was syn-
thesized as depicted in Scheme 1. The method comprised the reac-
tion of 1,5-diarylpyrazole-3-carboxylic acid 4 with oxalyl chloride
to afford acid chloride derivative which was taken in dichloro-
methane with sodium azide under phase transfer conditions
using tetrabutyl ammonium bromide to furnish the 1,5-diarylpy-
razole-3-carboxazide derivative 5.25 The 1,5-diarylpyrazole-
We also propose the condition under which bipyrazole sulfon-
amide derivative 3 might be formed. In fact, there is no quantifica-
tion for the conversion of amino derivative 8 to its corresponding
diazonium derivative 9, since its unstable nature and at the same
time the amino derivative 8 remaining as such in the reaction mix-
ture competes with aminopiperidine and virtually attacks on the
sulfonyl chloride derivative 10, thereby forming the bipyrazole sul-
fonamide derivative 3.
The CB1 receptor antagonists in the dose-dependent manner
produce inhibition of electrically evoked contractions of the mouse
vas deferens.23 The WIN-55212-2 produced concentration-related
inhibition of electrically evoked contractions of the mouse vas def-
erens in presence of vehicle (Fig. 4 and Table 2). The IC50 value of
3-carboxazide derivative
5 thus obtained was converted to
1,5-diarylpyrazole-3-carbamate derivative 7 via formation of iso-
cyanate 6. The carbamate derivative 7 rearranged to 3-amino-
1,5-diarylpyrazole derivative 8 under basic condition.26 Finally,
the 3-amino-1,5-diarylpyrazole derivative 8 was diazotized to
afford diazonium salt 9, which was subsequently reacted with
gaseous sulfur dioxide to afford sulfonyl chloride derivative 10.27
The sulfonyl chloride derivative 10 was coupled with N-aminopi-
peridine to afford 1,5-diaryl-3-sulfonamide derivative 2. The
column-chromatography of the final reaction mixture afforded an
impurity 3, which was also subjected to ex-vivo and in vitro
screening (Tables 2, 3 and Fig. 4).
WIN-55212-2 in the presence of vehicle was 0.02 0.01
lM. At a
concentration of 1 M, the compound 1 behaved as a competitive
l
surmountable antagonist of WIN-55212-2 producing parallel
rightward shift.
At a concentration of 10 lM the compounds 2 and 3 produced
slight dextral shift of WIN-55212-2 indicative of weak antagonistic
activity. The IC50 values of WIN-55212-2 in the presence of ligands
2 and 3 were 0.12 0.04 and 0.32 0.11 lM, respectively. We fur-
Table 2
ther tested the compounds 2 and 3 in hCB1 (cAMP)assay.15 The
compounds 2 and 3 did not respond significantly in the for-
skolin-stimulated cAMP assay as compared to positive control 1
Ex-vivo screening of compounds 2, 3, and 1 against mouse vas deferens assay
Compound
Concentration (
l
M)
IC50 value of WIN-55212-2a
(lM)
Controlb
2
3
1
—
10
10
1
0.02 0.01
0.12 0.04
0. 32 0.11
3.27 0.87
(Table 3) and unlike 1 none of the compounds rescued 100 lM
WIN-55212-2 mediated decrease of forskolin-induced cyclic AMP
generation. Supporting the fact that replacement of the –CO group
of the carboxamide region in the rimonabant by the –SO2 group
influences the antagonism activity and results in inferior antago-
nistic activity.
In summary, the introduction of –SO2 group at 3rd position of1,5-
diarylpyrazole core structure of rimonabant was successfully ob-
tained by employing the conventional Curtius reaction and is re-
a
Values indicate the mean SEM obtained using three different tissue prepara-
tions of mouse vas deferens for the three tissues and IC50 (concentration of WIN-
55212-2 required to produce 50% inhibition of contractile response) values were
calculated from nonlinear regression (sigmoidal dose–response) curve fit analysis
using Graph pad Prizm 4 software.
b
1% v/v DMSO and 5% v/v Tween 80 in water.

B. Kumar Srivastava et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3882–3886
3885
and Central Pathways Regulating Energy Homeostasis, Obesity (J2)
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20. Lohray, B. B.; Lohray, V. B.; Srivastava, B. K. WO patent 2006/025069, 2006.;
Lohray, B. B.; Lohray, V. B.; Srivastava, B. K. Chem. Abstr. 2006, 144, 292751.
21. Lohray, B. B.; Lohray, V. B.; Jain, M. R.; Srivastava, B. K. US patent 2006/
0025448, 2006.; Lohray, B. B.; Lohray, V. B.; Jain, M. R.; Srivastava, B. K. Chem.
Abstr. 2006, 144, 164295.
22. Ex-vivo mouse vas deferens assay: Vas deferens of Swiss Albino Mice weighing
30–45 g was isolated. Tissues were mounted in bath containing Kreb’s
Hanseleit (Mg free) solution at 32 1 °C and aerated with carbogen. The
composition of the Krebs solution was (mM): NaCl 118.2, KCl 4.75, KH2PO4
1.19, NaHCO3 25.0, glucose 11.0, and CaCl2.6H2O 2.54. Isometric contractions
were evoked by stimulation with 0.9 s trains of three pulses of 110% maximal
voltage (train frequency 0.1 Hz; pulse duration 0.9 ms) through a platinum
electrode attached to the upper end and a stainless steel electrode attached to
the lower end of each bath. Contractile response was recorded using Spel
Isosys computer aided data acquisition system (Experimetria, Hungary).
Concentration response curve of WIN-55212-2 was taken in presence of
control, 1, 2, and 3 using three different tissue preparations of mouse vas
deferens. WIN-55212-2 was dissolved in 5% v/v Tween 80 in water, and test
compounds were dissolved in 1% v/v DMSO and 5% v/v Tween 80 in water.
Further dilutions were achieved by adding water both to the stock solution of
WIN-55212-2 and test compounds.
ported for the first time. The isolation and characterization of the
bipyrazole sulfonamide derivative 3 justified the loss in the yield
of reaction during the formation of targeted sulfonamide derivative
2.
Preliminary ex-vivo experiments and the results of in vitro
cAMP hCB1 functional assay showed a loss of CB1 receptor antag-
onism for 2 compared to rimonabant, suggesting a misfitting of the
bulky –SO2 group in place of the –CO group and this in spite of the
favorable PLP values and docking scores. However, at this stage the
other factors contributing for the loss of CB1 receptor antagonism
cannot be ruled out.
Acknowledgments
We thank all the reviewers for number of excellent suggestions,
management of Zydus group including Dr. B.B. Lohray and Dr. V.B.
Lohray for encouragement, and analytical department of Zydus Re-
search Centre for support.
23. Pertwee, R. G.; Griffin, G.; Lainton, J. A. H.; Huffman, J. W. Eur. J. Pharmacol.
1995, 284, 241.
24. Procedures for synthesis of compounds 5, 7, 8, 2, and 3: Synthesis of 5-(4-
chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carbonyl azide
5: The 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-
carboxylic acid 4 (1.2 g, 3.14 mmol) was taken in dichloromethane (12 mL) to
which oxalyl chloride (0.35 mL, 4.08 mmol) was added drop wise at À20 °C. The
solution was stirred at 0–5 °C for 30 min and stirred at 25–27 °C for a period of
1 h. The progress of the reaction was monitored by TLC using 5% methanol in
chloroform as a mobile phase. The solvents were evaporated on a rotatory
evaporator under reduced pressure to afford an oil (1.25 g, 100%), which was
dissolved in dichloromethane (14.5 mL) and to this tetrabutylammonium
bromide (3.0 mg, 9.0 mmol) was added followed by addition of 35% aqueous
sodium azide (1 mL) at 0 °C. The resulting mixture was stirred at 0–5 °C for 2 h.
The progress of the reaction was monitored by TLC using 40% EtOAc in petroleum
ether as a mobile phase. The organic layer was separated and washed with water
(15 mL), and the dichloromethane layer was dried over anhydrous Na2SO4. The
solvents were evaporated on a rotatory evaporator under reduced pressure and
residue obtained was triturated in diisopropyl ether to get a solid. The solid was
filtered on a Buchner funnel under suction and dried to afford the title compound
5 as brown solid (1.18 g, 92%); 99.01% purity by HPLC; mp 106–107 °C; 1H NMR
(300 MHz, DMSO-d6): d 7.80 (d, J = 1.89 Hz, 1 H), 7.73 (d, J = 8.52 Hz, 1H), 7.60–
7.57 (dd, J = 8.43 and 1.98 Hz, 1H), 7.47 (d, J = 8.34 Hz, 2H), 7.24 (d, J = 8.34 Hz,
2H), 2.25 (s, 3H); IR (KBr) 3425, 2129, 1693, 1492 cmÀ1; ESI-MS: 407 [M+H]+;
Anal. calcd for C17H10Cl3N5O: C 50.21%, H 2.48%, N 17.22%; found: C 50.07%, H
2.46%, N 17.04%.
References and notes
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Synthesis of [5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazol-
3-yl]-carbamic acid ethyl ester 7: The 5-(4-chlorophenyl)-1-(2,4-
dichlorophenyl)-4-methyl-1H-pyrazole-3-carbonyl azide 5 (3.39 g, 8.34 mmol)
in ethanol (16.9 mL) was refluxed at 78–80 °C for a period of 5 h. The progress of
the reaction mixture was monitored by TLC using 30% EtOAc in petroleum ether
as a mobile phase. To the reaction mixture was added H2O (17 mL) at 0–5 °C and
stirred at 0–5 °C for over a period of 16–18 h. The solvents were evaporated on a
rotatory evaporator under reduced pressure to afford an oily residue. The residue
was dissolved in EtOAc (20 mL). The organic layer was washed with water
(2 Â 20 mL) followed by brine (20 mL), and the dichloromethane layer was dried
over anhydrous Na2SO4. The solvents were evaporated on a rotatory evaporator
under reduced pressure and the residue obtained was triturated in petroleum
ether (10 mL) to afford solid. The solid was filtered on a Buchner funnel under
suction and dried to afford the title compound 7 as yellow solid (3.1 g, 87%);
99.66%purity by HPLC; mp 150–152 °C; 1H NMR (300 MHz, CDCl3): d7.39 (s, 1H),
7.30–7.24 (m, 5H), 7.07 (d, J = 8.46 Hz, 2H), 4.27–4.20 (q, 2H), 2.06 (s, 3H), 1.31 (t,
3H); IR (KBr) 3400, 3276, 1701, 1485 cmÀ1; ESI-MS: 425 [M+H]+; Anal. calcd for
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Synthesis of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazol-
3-ylamine hydrochloride 8: The [5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-
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taken in ethanol (26 mL) to which 10% aqueous solution of NaOH (25.6 mL) was
added and refluxed at 100 °C for a period of 5 h. The progress of the reaction was
monitored by TLC using 5% methanol in chloroform as a mobile phase. The
reaction mixture was neutralized by 10% dilute HCl at 0–5 °C. The solvents were
removed on a rotatory evaporator under reduced pressure to afford oily residue.
The residue was dissolved in EtOAc (25 mL) and organic layer was washed with
water (2 Â 25 mL) followed by brine (25 mL) and dried over anhydrous Na2SO4.
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pressure to afford oil. The residue was taken in methanol (10 mL) to which
ethereal HCl (2 mL) was added at 0–5 °C and stirred for 1 h. The solid precipitated
was filtered on a Buchner funnel under suction and dried to afford the title
compound 8 as off-white solid (2.2 g, 70%); 98.90% purity by HPLC; mp 234–
236 °C; 1H NMR (300 MHz, DMSO-d6): d 7.76 (s, 1H), 7.61–7.51 (m, 2H), 7.45 (d,
J = 7.26 Hz, 2H), 7.20 (d, J = 7.20 Hz, 2H), 4.02–4.00 (br s, 2H), 2.03 (s, 3H); IR (KBr)
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0062424, 2008.
14. Lohray, B. B.; Lohray, V. B.; Srivastava, B. K. US patent 2008/0051386, 2008.
15. Srivastava, B. K.; Soni, R.; Joharapurkar, A.; Kalapatapu, S.; Patel, J. Z.; Goswami,
A.; Shedage, S. A.; Kar, S. S.; Salunke, R. P.; Gugale, S. B.; Dhawas, A.; Kadam, P.;
Mishra, B.; Sadhwani, N.; Unadkat, V. B.; Mitra, P.; Jain, M. R.; Patel, P. R. Bioorg.
Med. Chem. Lett. 2008, 18, 963.
16. Srivastava, B. K.; Joharapurkar, A.; Raval, S.; Patel, J. Z.; Soni, R.; Raval, P.; Gite,
A.; Goswami, A.; Sadhwani, N.; Patel, H.; Mishra, B.; Solanki, M.; Pandey, B.;
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R.; Sadhwani, N.; Patel, P. R. Med. Chem. Res. 2007, 15, 75.
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208, Keystone Symposia on Molecular and Cellular Biology, Obesity: Peripheral
3423, 2894, 2563, 1492 cmÀ1
;
ESI-MS: 352 [M+HÀHCl]+; Anal. calcd for
C16H13Cl4N3: C 49.39%, H 3.37%, N 10.80%; found: C 48.84%, H 3.67%, N 10.65%.

3886
B. Kumar Srivastava et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3882–3886
Hydrochloride salt of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-
pyrazole-3-sulfonic acid piperidin-1-ylamide 2: To solution of 5-(4-
white solid (0.15 g, 19%); 98.59% purity by HPLC; mp 146–147 °C; 1H NMR
a
(300 MHz, DMSO-d6): d 7.44 (d, J = 1.92 Hz, 1H), 7.31 (d, J = 8.48 Hz, 2H), 7.25 (d,
J = 3.33 Hz, 2H), 7.07 (d, J = 8.45 Hz, 2H), 3.34–3.30 (br s, 4H), 2.28 (s, 3H), 1.68–
1.65 (br s, 4H), 1.54–1.52 (br s, 2H); 13CNMR (100 MHz, DMSO-d6): d 22.5, 23.2,
26.6, 56.26, 120.6, 128.3, 129.2, 130.2, 130.6, 131.4, 131.8, 133.7, 135.6, 136.7,
137.0, 138.6, 141.8; IR (KBr) 3440, 1496, 1338, 1163 cmÀ1; ESI-MS: 538 [M]+;
Anal. calcd for C21H21Cl3N4O2S: C 50.46%, H 4.23%, N 11.21%; found: C 49.75%, H
4.16%, N 11.06%.
Isolation and identification of 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-
methyl-1H-pyrazole-3-sulfonic acid [5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-
4-methyl-1H-pyrazol-3-yl]-amide 3: During the formation of 5-(4-
chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-sulfonic acid
piperidin-1-ylamide 2, one of the major impurities formed was isolated
through the column-chromatography using silica gel of 230-400 mesh and
petroleum ether: EtOAc (9:1) as an eluent. The fractions were pooled and
solvents were evaporated on a rotatory evaporator under reduced pressure to
afford oil. The oil was triturated in petroleum ether (15 mL) to afford the brown
solid (0.41 g, 37%); 96.12% purity by HPLC; mp 132–134 °C; 1H NMR (300 MHz,
DMSO-d6):d 10.44 (s, 1H), 7.77–7.73 (dd, J = 10.38 and 2.09 Hz, 2H), 7.64–7.57
(m, 2H), 7.55–7.50 (m, 2H), 7.46–7.41 (m, 4H), 7.16–7.12 (m, 4H), 2.05 (s, 3H),
1.93 (s, 3H); 13CNMR (100 MHz, DMSO-d6): d 21.6, 22.8, 102.6, 118.6, 128.3,
129.6, 130.5, 130.8, 131.6, 132.1, 133.2, 135.6, 136.6, 136.8, 138.8, 139.6, 142.8,
158.6; IR (KBr) 3433, 1488, 1340, 1164 cmÀ1; ESI-MS: 753 [M]+; Anal. calcd for
chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazol-3-ylamine hydro-
chloride 8 (0.55 g, 1.41 mmol), acetic acid (2 mL), con. HCl (6.7 mL), and formic
acid(6.7 mL)wasadded the75%aqueous solutionofsodiumnitrite(0.3 mL)drop
wise at À8 to À6 °C. The diazotized solution 9 was stirred for 10–15 min and then
poured portion wise at 15 °C into a freshly prepared mixture of cupric chloride
dihydrate (0.24 g, 1.41 mmol) and acetic acid (18.4 mL) saturated with sulfur
dioxide. The mixture was stirred at 25–27 °C for 30–40 min. to afford sulfonyl
chloride derivative 10. The solvents were evaporated on a rotatory evaporator
under reduced pressure to afford oily residue. The residue was dissolved in
dichloromethane (10 mL). The organic layer was separated and washed with
water (10 mL), and dried over anhydrous Na2SO4. The solvents were evaporated
on a rotatory evaporator under reduced pressure to afford oily residue. The
residue was dissolved in dichloromethane (10 mL) to which N-amino piperidine
(0.26 mL, 1.89 mmol) was added followed by TEA (0.20 mL, 1.89 mmol) at 0–
5 °C. The reaction mixture was stirred at 0–5 °C for over a period of 30 min. The
progress of the reaction was monitored by TLC using 5% methanol in chloroform
as a mobile phase. The organic layer was washed with water (10 mL) and
dichloromethane layer was dried over anhydrous Na2SO4. The solvents were
evaporated on a rotatory evaporator under reduced pressure to afford oily
residue. The oily residue was purified through flash column-chromatography
using petroleum ether: EtOAc (9:1) as an eluent. The fractions were pooled and
solvents were evaporated on a rotatory evaporator under reduced pressure to
afford oil. To a solution of oily residue in methanol (5 mL) was added ethereal HCl
(1 mL) at 0–5 °C and stirred for 1 h. The solid precipitated was filtered on a
Buchner funnel under suction and dried to afford the title compound 2 as off-
C
32H21Cl6N5O2S: C 51.09%, H 2.81%, N 9.31%; found: C 49.13%, H 2.71%, N 8.96%.
25. Pfister, J. R.; Wymann, W. E. Synthesis 1983, 1, 38.
26. Duffin, G. F.; Kendall, J. D. J. Chem. Soc. 1954, 408.
27. Bellemin, R.; Festal, D. J. Heterocycl. Chem. 1984, 21, 1017.