Synthesis of new 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines: A search for novel nitric oxide donor anti-inflammatory agents

Article abstract of DOI:10.1016/j.bmc.2008.08.059

A group of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines (11-14) possessing a variety of substituents (Me, CO₂Et, H, N = O) attached to the 1,2,3,6-tetrahydropyridyl N¹-nitrogen atom were synthesized and evaluated as anti-inflammatory agents. Structure-activity relationship data showed that the N-methyl-1,2,3,6-tetrahydropyridyl moiety is a suitable bioisosteric replacement for the tolyl moiety in celecoxib. The most potent compound 4-[5-(1-methyl-1,2,3,6-tetrahydropyridin-4-yl)-3-trifluoromethylpyrazol-1-yl]benzenesulfonamide (11b; ED₅₀ = 61.2 mg/kg po) exhibited an anti-inflammatory activity between that of the reference drugs celecoxib (ED₅₀ = 10.8 mg/kg po) and aspirin (ED₅₀ = 128.7 mg/kg po). The synthesis of model hybrid nitric oxide donor N-diazen-1-ium-1,2-diolate derivatives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines (5) requires further investigation since the reaction of 1,2,3,6-tetrahydropyridines with nitric oxide furnished the undesired N-nitroso-1,2,3,6-tetrahydrohydropyridyl product rather than the desired N-diazen-1-ium-1,2-diolate-1,2,3,6-tetrahydropyridyl product.

Full text of DOI:10.1016/j.bmc.2008.08.059

Bioorganic & Medicinal Chemistry 16 (2008) 8882–8888
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of new 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-
2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines: A search for novel nitric oxide
donor anti-inflammatory agents
*
Morshed Alam Chowdhury, Khaled R. A. Abdellatif, Ying Dong, Edward E. Knaus
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alta., Canada T6G 2N8
a r t i c l e i n f o
a b s t r a c t
Article history:
A group of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahy-
dropyridines (11–14) possessing a variety of substituents (Me, CO2Et, H, N = O) attached to the 1,2,3,6-
tetrahydropyridyl N1-nitrogen atom were synthesized and evaluated as anti-inflammatory agents.
Structure–activity relationship data showed that the N-methyl-1,2,3,6-tetrahydropyridyl moiety is a suit-
able bioisosteric replacement for the tolyl moiety in celecoxib. The most potent compound 4-[5-(1-
Received 25 July 2008
Revised 22 August 2008
Accepted 26 August 2008
Available online 29 August 2008
methyl-1,2,3,6-tetrahydropyridin-4-yl)-3-trifluoromethylpyrazol-1-yl]benzenesulfonamide (11b; ED50
=
Keywords:
Pyrazoles
1,2,3,6-Tetrahydropyridines
Diazen-1-ium-1,2-diolate nitric oxide
donors
61.2 mg/kg po) exhibited an anti-inflammatory activity between that of the reference drugs celecoxib
(ED50 = 10.8 mg/kg po) and aspirin (ED50 = 128.7 mg/kg po). The synthesis of model hybrid nitric oxide
donor N-diazen-1-ium-1,2-diolate derivatives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoro-
methyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines (5) requires further investigation since the reaction
of 1,2,3,6-tetrahydropyridines with nitric oxide furnished the undesired N-nitroso-1,2,3,6-tetrahydrohy-
dropyridyl product rather than the desired N-diazen-1-ium-1,2-diolate-1,2,3,6-tetrahydropyridyl product.
Ó 2008 Elsevier Ltd. All rights reserved.
Anti-inflammatory activity
1. Introduction
anti-inflammatory activity.8 We previously reported NONO-coxib
ester prodrugs having a NO-donor diazen-1-ium-1,2-diolate moi-
Drugs that are highly selective inhibitors of the inducible cyclo-
oxygenase-2 (COX-2) isozyme in the periphery are effective anti-
inflammatory agents. However, some drugs within this group
(see structures in Fig. 1) such as rofecoxib (1) and valdecoxib
(3a) alter the natural balance in the COX pathway wherein the
amount of the desirable vasodilatory and anti-aggregatory prosta-
cyclin (PGI2) produced is decreased in conjunction with a concom-
itant increase in the level of the undesirable prothrombotic
thromboxane A2 (TxA2).1–3 This combination of adverse biochemi-
cal changes in the COX pathway are responsible for increased prev-
alence of high blood pressure and myocardial infarction that
subsequently necessitated the withdrawal of rofecoxib (VioxxÒ)
and valdecoxib (BextraÒ).4,5 Nitric oxide (NO) is an effective vaso-
dilation agent that also inhibits platelet aggregation and adhesion.6
Hybrid COX-2 inhibitors possessing a NO-donor moiety (NO-cox-
ibs) have been investigated as a method to increase the clinical
safety of COX-2 inhibitors. In this regard, NO-coxibs having a ni-
trate ester NO-donor moiety such as the oxazole (3b) exhibit
anti-inflammatory activity similar to valdecoxib with antithrom-
botic action at higher doses,7 and the pyrazole 4 that exhibits
ety that are effectively cleaved by esterases to release the parent
anti-inflammatory drug and NO.9–13 Accordingly, attachment of a
NO-donor diazen-1-ium-1,2-diolate moiety to highly selective
COX-2 inhibitors offers a potential drug design concept to circum-
vent the adverse cardiovascular events associated with their
chronic clinical use. We now describe an investigation directed to-
ward the design and synthesis of model hybrid nitric oxide donor
N-diazen-1-ium-1,2-diolate derivatives of 4-[2-(4-methyl(amino)
sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1,2,3,6-tetra-
hydropyridines (5) that are devoid of adverse cardiovascular ef-
fects (see structure 5 in Fig. 1).
2. Chemistry
A group of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoro-
methyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines (11–14) pos-
sessing a variety of substituents (Me, CO2Et, H, N = O) attached to
the 1,2,3,6-tetrahydropyridyl N1-nitrogen atom were synthesized
using the reaction sequence illustrated in Scheme 1. Accordingly,
reaction of a 4-(methylsulfonylphenyl)hydrazine-HCl (6a), or 4-
(sulfamoylphenyl)hydrazine-HCl (6b), with isonicotinoyltrifluoro-
acetone14 (7) in 95% ethanol at reflux afforded a mixture of the
* Corresponding author. Tel.: +1 780 492 5993; fax: +1 780 492 1217.
E-mail address: eknaus@pharmacy.ualberta.ca (E.E. Knaus).
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.08.059

M. A. Chowdhury et al. / Bioorg. Med. Chem. 16 (2008) 8882–8888
8883
Me
O
O
Me
NH2
S
S
O
O
N
O
N
O
F3C
1 (Rofecoxib)
2 (Celecoxib)
O
O
S
NH2
NH2
S
N
N
O
O
N
O
R
O2NOCH2
4
3a, R = Me (Valdecoxib)
3b, R = CH2ONO2 (NMI-1093)
+
O
N
N
+
O
Na
O
N
R
S
O
N
N
F3C
5, R = Me, NH2
Figure 1. Chemical structures of the selective cyclooxygenase-2 (COX-2) inhibitors rofecoxib (1), celecoxib (2) and valdecoxib (3a), the nitric oxide donor nitrate esters NMI-
1093 (3b) and 4, and the putative hybrid nitric oxide donor N-diazen-1-ium-1,2-diolate derivatives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-
3-yl]-1,2,3,6-tetrahydropyridines (5).
respective acyclic aryl hydrazone15 (8a, 21% or 8b, 30%) and the
1,5-diaryl-3-trifluoromethylpyrazole regioisomer (9a, 37% or 9b,
41%).16 Products 8 and 9 were separated by silica gel column chro-
matography. It is well documented that the cyclization-dehydra-
tion reaction proceeds in a regiospecific manner to yield the 1,5-
diaryl-3-trifluoromethylpyrazole product (9) when a phenylhydr-
azine hydrochloride is employed and the reaction is carried out
in ethanol at reflux temperature.16 The structural assignment of
the 1,5-diaryl-3-trifluoromethyl regioisomer 9a was confirmed
by a nuclear Overhauser enhancement (NOE) experiment. In this
regard, irradiation of the resonance at d 7.69 (phenyl H-2, H-6)
showed a very strong NOE enhancement for the resonance at d
7.35 (25%, pyridyl H-3, H-5) indicating that the pyridyl and phenyl
rings must be attached to adjacent positions on the pyrazole ring.
This NOE experiment provides unambiguous evidence that com-
pound 9a is the 1,5-diaryl-3-trifluoromethylpyrazole, rather than
the 1,3-diaryl-5-trifluoromethylpyrazole, regioisomer. Reaction of
the pyridyl compounds (9a and 9b) with methyl iodide in ace-
tone17 at 25 °C afforded the corresponding N-methylpyridinium
salt 10a (90%) or 10b (93%). Reduction of the N-methylpyridinium
salts 10a and 10b using sodium borohydride in methanol18
furnished the respective 4-[2-(4-methanesulfonylphenyl)-5-tri-
fluoromethyl-2H-pyrazol-3-yl]-1-methyl-1,2,3,6-tetrahydropyr-
idine (11a, 99%) or 4-[5-(1-methyl-1,2,3,6-tetrahydropyridin-4-
yl)-3-trifluoromethylpyrazol-1-yl]-benzenesulfonamide
(11b,
90%). Subsequent treatment of the N-methyl-1,2,3,6-tetrahydro-
pyridine 11a or 11b with ethyl chloroformate at reflux in 1,2-
dichloroethane19 afforded the respective N-ethoxycarbonyl-
1,2,3,6-tetrahydropyridine 12a (94%) or 12b (60%). Removal of
the N-ethoxycarbonyl substituent present in 12a and 12b by reac-
tion with 10 N hydrochloric acid at reflux temperature19 yielded
4-[2-(4-methanesulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-
3-yl]-1,2,3,6-tetrahydropyridine (13a, 55%) and 4-[5-(1,2,3,6-tetra-
hydropyridin-4-yl)-3-trifluoromethylpyrazol-1-yl]-benzenesulfon-
amide (13b, 33%), respectively. Reaction of the 1,2,3,6-tetra-
hydropyridine compound 13a with nitric oxide gas (40 psi) at
25 °C in the presence of NaOMe20 furnished a product which exhi-
bited a molecular ion in the positive ion electrospray mass
spectrum (m/z 423.02, M+Na) and microanalytical data that was
consistent with the N-nitroso product 4-[2-(4-methanesulfonyl-
phenyl)-5-trifluoromethyl-2H-pyrazol-3-yl]-1-nitroso-1,2,3,6-
tetrahydropyridine (14, 53%).
The decomposition pathway of the N-amino-N-diazen-1-ium-
1,2-diolate moiety (see structure 5 in Fig. 1) is dependent upon
the site of protonation. In this regard, protonation at the 1,2,3,6-
tetrahydropyridine nitrogen and then decomposition would pro-
duce the 1,2,3,6-tetrahydropyridine compound 13 and 2 molecules
of NO as illustrated below.

8884
M. A. Chowdhury et al. / Bioorg. Med. Chem. 16 (2008) 8882–8888
+
H
O
N
O
O
N
R2NH + 2NO
O
O
N
O
+
+
R2N
N
R2N
N
N
R2N
H
Alternatively, protonation of the diazen-1-ium-1,2-diolate N2-
(such as product 14 in Scheme 1) and a nitroxyl species (HNO) as
nitrogen and then decomposition would furnish a nitrosamine
indicated below.
+
H
R2N
N
O
O
N
O
O
N
+
O
N
O
O
+
HNO
+
R2N
N
R2N
N
N
R2N
H
N
CF3
O
OH
CF3
NHNH2.HCl
F3C
HN
N
a
N
O
N
N
N
7
SO2R
6a, R = Me
6b, R = NH2
SO2R
SO2R
9a, R = Me
9b, R = NH2
8a, R = Me
8b, R = NH2
b
CF3
CF3
CF3
d
c
N
N
N
N
N
N
N
N
N
EtO 2C
Me
Me
I
SO2R
SO2R
SO2R
12a, R = Me
12b, R = NH2
11a, R = Me
11b, R = NH2
10a, R = Me
10b, R = NH2
e
CF3
CF3
N
f
N
N
N
N
HN
N
O
SO2Me
14
SO2R
13a, R = Me
13b, R = NH2
Scheme 1. Reagents and conditions: (a) ethanol (95%), reflux, 20 h; (b) MeI, acetone, 25 °C, 12 h; (c) NaBH4, MeOH, 5 °C ? 25 °C, 0.5 h; (d) ClCO2Et, 1,2-dichloroethane, reflux,
12 h; (e) i—10 N HCl, reflux, 3 h; ii—Na2CO3; (f) compound 13a, nitric oxide gas, 40 psi, MeCN/diethyl ether (1:1, v/v), NaOMe, 25 °C, 48 h.

M. A. Chowdhury et al. / Bioorg. Med. Chem. 16 (2008) 8882–8888
8885
NaOMe in MeOH
NaOMe
16 (46%)
Et2O, NO, 25 °C, 1 h
MeCN-Et2O
NO, 25 °C, 1 h
N
N
N
H
O
15
16 (27%)
MeCN-Et2O
NO, -78 °C, 1 h
16 (40%)
Scheme 2. Synthesis of N-nitroso-1,2,3,6-tetrahydropyridine (16).
The formation of the N-nitroso product 14 upon reaction of 13a
with nitric oxide indicates that the intermediate N-amino-N-dia-
zen-1-ium-1,2-diolate product [see structure 5 (R = Me) in Fig. 1]
must undergo protonation of the more basic diazen-1-ium-1,2-
diolate N2-nitrogen that is unstable undergoing subsequent elimi-
nation of a HNO species.21
The reaction of 1,2,3,6-tetrahydropyridine (15) with nitric oxide
under a variety of experimental conditions (aprotic and protic sol-
vent systems, various temperatures) afforded N-nitroso-1,2,3,6-
tetrahydropyridine (16) as the sole isolable product (see Scheme
2). For example, reaction in the aprotic MeCN/Et2O solvent system
in the presence of NaOMe at 25 °C afforded 16 in 27% yield. A 40%
yield of 16 was isolated when the same reaction was performed at
ꢀ78 °C. Alternatively, reaction of 15 in a protic solvent system con-
sisting of NaOMe in MeOH (25% w/v) and Et2O at 25 °C furnished
16 (46%). These data indicate that 1,2,3,6-tetrahydropyridine
(15), or a substrate such as the 1,2,3,6-tetrahydropyridyl com-
pound 13a, are not suitable precursors for the synthesis of isolable
nitric oxide donor N-diazen-1-ium-1,2-diolate derivatives.
Table 1
Anti-inflammatory activities for the 4-[2-(4-methane(amino)sulfonylphenyl)-5-tri-
fluoromethyl-2H-pyrazol-3-yl]-1-substituted-1,2,3,6-tetrahydropyridines (11–14)
CF3
N
N
N
R1
SO2R2
Compound
R1
R2
AI activitya: ED50 (mg/kg)
11a
11b
12a
12b
13a
13b
14
Celecoxib
Aspirin
Me
Me
EtO2C
EtO2C
H
SO2Me
SO2NH2
SO2Me
SO2NH2
SO2Me
SO2NH2
SO2Me
—
95.3
61.2
Moderate activityb
Inactivec
128.7
H
Weak activityd
115.1
O@N
—
3. Results and discussion
10.8
—
—
128.7
Hybrid nitric oxide donor N-diazen-1-ium-1,2-diolate deriva-
tives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoromethyl-
2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines (see structure 5 in
Fig. 1) constitute a potential class of selective COX-2 inhibitor com-
pounds that are devoid of adverse cardiovascular properties. The
model structure 5 was designed based on structure–activity data
showing that (i) a COX-2 pharmacophore such as MeSO2 or
H2NSO2 at the para-position of a N1-phenyl ring on a pyrazole ring
template confers potent and selective COX-2 inhibitory activity,16
(ii) attachment of a 1,2,3,6-tetrahydropyridine ring substituent
via its C-4 sp2 hyridized carbon atom is consistent with the obser-
vation that two aryl rings on adjacent positions of a 5-membered
heterocyclic ring template (scaffold) generally provide optimum
COX-2 inhibitory activity,22 and (iii) the 1,2,3,6-tetrahydropyridyl
secondary amino group, such as that present in compounds 13,
provides a logical synthon for elaboration to the corresponding ni-
tric oxide donor N-diazen-1-ium-1,2-diolates.9–13 Unfortunately,
reaction of the 1,2,3,6-tetrahydropyridyl compound 13a with nitric
oxide (see Scheme 1) afforded the N-nitroso product 14 rather than
the desired unisolable intermediate N-diazen-1-ium-1,2-diolate
product 5 (R = Me).
a
Inhibitory activity in a carrageenan-induced rat paw edema assay. The results
are expressed as the ED50 value (mg/kg) at 3 h after oral administration of the test
compound.
b
A 24.1% inhibition of inflammation was observed at a 100 mg/kg oral dose.
Inactive at a 100 mg/kg oral dose.
A 7.1% inhibition of inflammation was observed at a 100 mg/kg oral dose.
c
d
moiety was SO2Me > SO2NH2 when R1 is CO2Et or H, but SO2NH2 > -
SO2Me when R1 is Me, (ii) within the SO2Me group of compounds
Me > N = O > H > CO2Et with respect to the R1 substituent, (iii)
within the SO2NH2 group of compounds Me > H > CO2Et (inactive)
with respect to the R1 substituent, and iv) the two most potent
compounds 11a (SO2Me; ED50 = 95.3 mg/kg po) and 11b (SO2NH2;
ED50 = 61.2 mg/kg po) having a N-methyl-1,2,3,6-tetrahydropyr-
idyl moiety exhibited anti-inflammatory activities between that
of the reference drugs celecoxib (ED50 = 10.8 mg/kg po) and aspirin
(ED50 = 128.7 mg/kg po).
4. Conclusions
The anti-inflammatory (AI) activities for this group of 4-[2-(4-
methyl(amino)sulfonylphenyl)-5-trifluoromethyl-2H-pyrazol-3-
yl]-1,2,3,6-tetrahydropyridines (11–14) possessing a variety of R1-
substituents (Me, CO2Et, H, N = O) attached to the 1,2,3,6-tetrahy-
dropyridyl N1-nitrogen atom were determined using a carra-
geenan-induced rat foot paw edema model (see data in Table 1).
Structure–activity relationships acquired showed that the relative
AI potency profile (i) with respect to the COX-2 pharmacophore
A group of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoro-
methyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines
(11–14)
were synthesized in which the tolyl (para-methylphenyl) moiety
present in celecoxib (2) was replaced by 4-(N-substituted (Me,
CO2Et, H, N = O)-1,2,3,6-tetrahydropyridyl moiety that were evalu-
ated as anti-inflammatory agents. Anti-inflammatory structure–
activity relationships showed that the N-methyl-1,2,3,6-tetrahy-
dropyridyl ring (11b) is the best bioisosteric replacement for the

8886
M. A. Chowdhury et al. / Bioorg. Med. Chem. 16 (2008) 8882–8888
tolyl group in celecoxib. The 1,2,3,6-tetrahydropyridyl ring moiety
present in compounds 13 is not a suitable precursor to prepare
putative hybrid nitric oxide donor N-diazen-1-ium-1,2-diolate
derivatives of 4-[2-(4-methyl(amino)sulfonylphenyl)-5-trifluoro-
methyl-2H-pyrazol-3-yl]-1,2,3,6-tetrahydropyridines (5) since the
unstable N-diazen-1-ium-1,2-diolate intermediate product under-
goes protonation and elimination of a HNO species to furnish a
N-nitroso-1,2,3,6-tetrahydropyridyl product (14).
5.1.3. 4-[2-(4-Methanesulfonylphenyl)-5-trifluoromethyl-2H-
pyrazol-3-yl]pyridine (9a)
Yield, 37%; pale yellow solid; mp 158–160 °C; IR (film) 1325,
1160 (SO2) cmꢀ1 1H NMR (DMSO-d6) d 3.29 (s, 3H, SO2Me), 7.35
;
(d, 2H, J = 6.1 Hz, pyridyl H-3, H-5), 7.50 (s, 1H, pyrazole H-4),
7.69 (d, J = 8.5 Hz, 2H, phenyl H-2, H-6), 8.06 (d, J = 8.5 Hz, 2H, phe-
nyl H-3, H-5), 8.65 (d, 2H, J = 6.1 Hz, pyridyl H-2, H-6); MS (M+H)+
368.05.
5.1.4. 4-(5-Pyridin-4-yl-3-trifluoromethylpyrazol-1-yl)-
benzenesulfonamide (9b)
5. Experimental
Yield, 41%; pale yellow solid; mp 237–239 °C (lit.16 mp 236–
Melting points were determined on a Thomas–Hoover capillary
apparatus and are uncorrected. Unless otherwise noted, infrared
(IR) spectra were recorded as films on NaCl plates using a Nicolet
550 Series II Magna FT-IR spectrometer. 1H NMR spectra were
measured on a Bruker AM-300 spectrometer in CDCl3, DMSO-d6,
or CDCl3 + DMSO-d6 with TMS as the internal standard. Microanal-
yses were performed for C, H, N (MicroAnalytical Service Labora-
tory, Department of Chemistry, University of Alberta) and were
within 0.4% of theoretical values. Nominal mass, positive polarity,
electrospray, spectra were acquired using a Water’s Micromass ZQ
4000 mass spectrometer. Silica gel column chromatography was
performed using Merck silica gel 60 ASTM (70–230 mesh). 4-
(Methylsulfonylphenyl)hydrazine-HCl (6a) was synthesized in
53% yield starting from 1-chloro-4-methanesulfonylbenzene23
which was prepared by the Friedel–Crafts reaction of methanesul-
fonyl chloride with chlorobenzene.24 4-(Sulfamoylphenyl)hydra-
zine-HCl (6b) was synthesized in 84% yield starting from
sulfanilamide.25 All other reagents, purchased from the Aldrich
Chemical Company (Milwaukee, WI), were used without further
purification.
238 °C); IR (film) 3374, 3281 (NH2), 1325, 1165 (SO2) cmꢀ1 1H
;
NMR (DMSO-d6) d 7.34 (d, 2H, J = 6.1 Hz, pyridyl H-3, H-5), 7.48
(s, 1H, pyrazole H-4), 7.56 (s, 2H, SO2NH2 that exchanges with
D2O), 7.61 (d, J = 8.5 Hz, 2H, phenyl H-3, H-5), 7.91 (d, J = 8.5 Hz,
2H, phenyl H-2, H-6), 8.64 (d, 2H, J = 6.1 Hz, pyridyl H-2, H-6);
MS (M+H)+ 369.01.
5.2. General procedure for the synthesis of N-methylpyridinium
iodides (10a–b)
Methyl iodide (0.66 mL, 10.40 mmol) was added to a stirred
solution of either 9a or 9b (10 mmol) in acetone (25 mL) and the
reaction mixture was stirred at 25 °C for 12 h according to a re-
ported procedure.17 The solid that precipitated from solution was
filtered out to furnish the respective methyl iodide salt 10. Some
physical and spectroscopic data for 10a and 10b are listed below.
5.2.1. 1-Methyl-4-[2-(4-methanesulfonylphenyl)-5-
trifluoromethyl-2H-pyrazol-3-yl]pyridinium iodide (10a)
Yield, 90%; yellow solid; mp 255–258 °C; IR (film) 1340, 1125
(SO2) cmꢀ1 1H NMR (CDCl3 + DMSO-d6) d 3.16 (s, 3H, SO2Me),
;
5.1. General method for the synthesis of hydrazones (8a–b) and
celecoxib analogs (9a–b)
4.36 (s, 3H, NMe), 7.58 (s, 1H, pyrazole H-4), 7.67 (d, 2H,
J = 8.5 Hz, phenyl H-2, H-6), 7.95 (d, 2H, J = 6.7 Hz, pyridinium H-
3, H-5), 7.69 (d, J = 8.5 Hz, 2H, phenyl H-2, H-6), 8.04 (d,
J = 8.5 Hz, 2H, phenyl H-3, H-5), 9.02 (d, 2H, J = 6.7 Hz, pyridinium
H-2, H-6).
A solution of the hydrazine hydrochloride 6a or 6b (36 mmol)
and the dione 7 (7.10 g, 32.73 mmol) in 95% ethanol (400 mL)
was heated at reflux with stirring for 20 h. After cooling to
25 °C, the reaction mixture was concentrated in vacuo to yield
a gummy residue. The two products were separated by silica
gel column chromatography using acetone/hexanes (1:1, v/v) as
eluent to furnish the respective products 8a or 8b and 9a or
9b. Some physical and spectroscopic data for 8a–b and 9a–b
are listed below.
5.2.2. 1-Methyl-4-[2-(4-sulfamoylphenyl)-5-trifluoromethyl-
2H-pyrazol-3-yl]pyridinium iodide (10b)
Yield, 93%; greenish yellow solid; mp 175–177 °C; IR (film)
3325 (broad, NH2), 1339, 1165 (SO2) cmꢀ1 1H NMR (DMSO-d6) d
;
3.97 (s, 3H, NMe), 6.87 (s, 2H, SO2NH2 that exchanges with D2O),
7.03 (s, 1H, pyrazole H-4), 7.10 (d, J = 8.6 Hz, 2H, phenyl H-2, H-
6), 7.46 (d, 2H, J = 6.8 Hz, pyridinium H-3, H-5), 7.58 (d,
J = 8.6 Hz, 2H, phenyl H-3, H-5), 8.62 (d, 2H, J = 6.8 Hz, pyridinium
H-2, H-6).
5.1.1. 4,4,4-Trifluoro-3-[(4-methanesulfonylphenyl)-
hydrazono]-1-pyridin-4-ylbutan-1-one (8a)
Yield, 21%; yellow solid; mp 201–204 °C; IR (film) 3510 broad
(NH), 1290, 1150 (SO2) cmꢀ1 1H NMR (DMSO-d6) d 3.18 (s, 3H,
;
5.3. General procedure for the synthesis of N-methyl-1,2,3,6-
SO2Me), 3.70 (d, 1H, J = 19.5 Hz, @C(CF3)CHH0CO–), 4.07 (d, 1H,
J = 19.5 Hz, @C(CF3)CHH0CO–), 7.70–7.80 (m, 4H, pyridyl H-3, H-5,
phenyl H-2, H-6), 7.85 (d, J = 9.1 Hz, 2H, phenyl H-3, H-5), 8.70
(d, 2H, J = 6.1 Hz, pyridyl H-2, H-6), 8.84 (s, 1H, NH that exchanges
with D2O); MS (M+H)+ 386.05.
tetrahydropyridines (11a–b)
A solution of the N-methylpyridinium iodide 10a or 10b
(8.84 mmol) in methanol (250 mL) was cooled to 5 °C18 and so-
dium borohydride (1.50 g, 39.65 mmol) was added in small ali-
quots with stirring during
a period of a few minutes. The
5.1.2. 4-[N-(3-Oxo-3-pyridin-4-yl-1-trifluoromethyl-
propylidene)hydrazino]benzenesulfonamide (8b)
Yield, 30%; yellow solid; mp 170–172 °C; IR (film) 3500–3150
reaction mixture was allowed to warm to 25 °C and the reaction
mixture was stirred for an additional 30 min at 25 °C. The contents
of the reaction mixture were concentrated in vacuo to dryness and
a solution of saturated Na2CO3 (150 mL) was added. This mixture
was extracted with EtOAc (3ꢁ 100 mL), the organic phase was
washed successively with water and brine, and the EtOAc fraction
was dried (MgSO4). Filtration and then removal of the solvent in
vacuo from the organic fraction gave the respective N-methyl-
1,2,3,6-tetrahydropyridine 11a or 11b. Some physical and spectro-
scopic data for 11a and 11b are listed below.
broad (NH2), 1300, 1120 (SO2) cmꢀ1 1H NMR (CDCl3 + DMSO-d6)
;
d
3.65 (d, 1H, J = 18.9 Hz, @C(CF3)CHH0CO–), 3.85 (d, 1H,
J = 18.9 Hz, @C(CF3)CHH0CO–), 7.06 (s, 2H, SO2NH2), 7.65 (d, 2H,
J = 5.5 Hz, pyridyl H-3, H-5), 7.71 (d, J = 9.1 Hz, 2H, phenyl H-3,
H-5), 7.82 (d, J = 9.1 Hz, 2H, phenyl H-2, H-6), 8.44 (s, 1H, NH that
exchanges with D2O), 8.68 (d, 2H, J = 5.5 Hz, pyridyl H-2, H-6); MS
(M+H)+ 386.99.

M. A. Chowdhury et al. / Bioorg. Med. Chem. 16 (2008) 8882–8888
8887
5.3.1. 4-[2-(4-Methanesulfonylphenyl)-5-trifluoromethyl-2H-
pyrazol-3-yl]-1-methyl-1,2,3,6-tetrahydropyridine (11a)
Yield, 99%; white solid; mp 153–155 °C; IR (film) 1317, 1165
fluxed for 3 h using a modified literature method.19 The reaction
mixture was cooled to 25 °C prior to evaporated to dryness in
vacuo. A solution of saturated NaCO3 (20 mL) was added and
the mixture was extracted with EtOAc (3 ꢁ 25 mL). The com-
bined organic extracts were washed successively with water
and then brine, and the EtOAc fraction was dried (MgSO4). Filtra-
tion and removal of the solvent from the organic fraction in va-
cuo afforded the impure product which was purified by silica gel
column chromatography. Elution with EtOAc/methanol (1:1, v/v)
furnished the respective 1,2,3,6-tetrahydropyridine product 13a
or 13b. Some physical and spectroscopic data for 13a and 13b
are listed below.
(SO2) cmꢀ1 1H NMR (CDCl3 + DMSO-d6) d 2.25–2.29 (m, 2H, tetra-
;
hydropyridyl H-3), 2.37 (s, 3H, NMe)ß 2.56 (t, 2H, J = 5.5 Hz, tetra-
hydropyridyl H-2), 3.02–3.06 (m, 2H, tetrahydropyridyl H-6), 3.09
(s, 3H, SO2Me), 5.82–5.86 (m, 1H, tetrahydropyridyl H-5) 6.59 (s,
1H, pyrazole H-4), 7.76 (d, 2H, J = 8.5 Hz, phenyl H-2, H-6), 8.05
(d, J = 8.5 Hz, 2H, phenyl H-3, H-5); MS (M+H)+ 386.09. Anal. Calcd
for C17H18F3N3O2S: C, 52.98; H, 4.71; N, 10.90. Found: C, 52.94; H,
4.93; N, 11.09.
5.3.2. 4-[5-(1-Methyl-1,2,3,6-tetrahydropyridin-4-yl)-3-
trifluoromethylpyrazol-1-yl]benzenesulfonamide (11b)
Yield, 90%; white solid; mp 243–245 °C; IR (film) 3322 (broad
5.5.1. 4-[2-(4-Methanesulfonylphenyl)-5-trifluoromethyl-2H-
pyrazol-3-yl]-1,2,3,6-tetrahydropyridine (13a)
NH2), 1325, 1145 (SO2) cmꢀ1
;
1H NMR (CDCl3 + DMSO-d6) d
Yield, 55%; brown solid; mp 88–91 °C; IR (film) 3337 (NH),
1320, 1160 (SO2) cmꢀ1; 1H NMR (CDCl3) d 2.11–2.23 (m, 2H, tetra-
hydropyridyl H-3), 2.65 (br s, 1H, tetrahydropyridyl NH that ex-
changes with D2O), 2.98 (t, 2H, J = 5.5 Hz, tetrahydropyridyl H-2),
3.08 (s, 3H, SO2Me), 3.42–3.51 (m, 2H, tetrahydropyridyl H-6),
5.90–5.98 (m, 1H, tetrahydropyridyl H-5) 6.58 (s, 1H, pyrazole H-
4), 7.77 (d, 2H, J = 8.5 Hz, phenyl H-2, H-6), 8.04 (d, J = 8.5 Hz, 2H,
phenyl H-3, H-5); MS (M+H)+ 372.08. Anal. Calcd for
2.13–2.19 (m, 2H, tetrahydropyridyl H-3), 2.26 (s, 3H, NMe)ß 2.47
(t, 2H, J = 5.5 Hz, tetrahydropyridyl H-2), 2.93–2.96 (m, 2H, tetra-
hydropyridyl H-6), 5.78–5.79 (m, 1H, tetrahydropyridyl H-5),
6.58 (s, 1H, pyrazole H-4), 7.28 (s, 2H, SO2NH2 that exchanges with
D2O), 7.58 (d, 2H, J = 8.5 Hz, phenyl H-3, H-5), 7.95 (d, J = 8.5 Hz,
2H, phenyl H-2, H-6); MS (M+H)+ 387.12. Anal. Calcd for
C16H17F3N4O2S: C, 49.73; H, 4.43; N, 14.50. Found: C, 49.55; H,
4.75; N, 14.40.
C
16H16F3N3O2Sꢂ1/3H2O: C, 50.92; H, 4.45; N, 11.13. Found: C,
51.26; H, 4.72; N, 10.85.
5.4. General procedure for the synthesis of N-ethoxycarbonyl-
1,2,3,6-tetrahydropyridines (12a–b)
5.5.2. 4-[5-(1,2,3,6-Tetrahydropyridin-4-yl)-3-
trifluoromethylpyrazol-1-yl]benzenesulfonamide (13b)
Yield, 33%; brown solid; IR (film) 3320 (broad NH), 1350, 1150
(SO2) cmꢀ1; 1H NMR (CDCl3 + DMSO-d6) d 1.71–1.82 (m, 2H, tetra-
hydropyridyl H-3), 2.06 (t, 2H, J = 5.5 Hz, tetrahydropyridyl H-2),
2.50–2.61 (m, 2H, tetrahydropyridyl H-6), 5.35–5.45 (m, 1H, tetra-
hydropyridyl H-5), 6.15 (s, 1H, pyrazole H-4), 6.80 (s, 2H, SO2NH2
that exchanges with D2O), 7.18 (d, 2H, J = 8.5 Hz, phenyl H-3, H-
5), 7.56 ppm (d, J = 8.5 Hz, 2H, phenyl H-2, H-6); 13C NMR
(DMSO-d6) d 27.9 (tetrahydropyridyl C-3), 42.0 (tetrahydropyridyl
C-2 or C-6), 44.6 (tetrahydropyridyl C-6 or C-2), 104.9 (pyrazole C-
4), 123.0 (pyrazole C-5), 124.8 (CF3), 125.3 (phenyl C-3, C-5), 126.9
(phenyl C-2, C-6), 132.2 (tetrahydropyridyl C-5), 141.5 (phenyl C-
4), 142.1 (tetrahydropyridyl C-4), 143.9 (phenyl C-1), 146.5 (pyra-
zole C-3); MS (M+H)+ 373.08.
Ethyl chloroformate (2.23 mL, 23.37 mmol) was added drop
wise to a stirred solution of a N-methyl-1,2,3,6-tetrahydropyridine
11a or 11b (7.79 mmol) in 1,2-dichloroethane (30 mL) at 25 °C fol-
lowing a procedure analogous to a literature method.19 The reac-
tion was allowed to proceed at reflux with stirring for 12 h, and
the solvent was removed in vacuo to afford the crude product.
Purification by silica gel column chromatography using EtOAc/hex-
anes (2:1, v/v) as eluent furnished the respective N-ethoxycar-
bonyl-1,2,3,6-tetrahydropyridine 12a or 12b. Some physical and
spectroscopic data for 12a and 12b are listed below.
5.4.1. 4-[2-(4-Methanesulfonylphenyl)-5-trifluoromethyl-2H-
pyrazol-3-yl]-1-ethoxycarbonyl-1,2,3,6-tetrahydropyridine (12a)
Yield, 95%; viscous oil; IR (film) 1693 (CO), 1325, 1153 (SO2)
cmꢀ1 1H NMR (CDCl3) d 1.27 (t, 3H, J = 7.1 Hz, CH2CH3), 2.11–
;
5.6. 4-[2-(4-Methanesulfonylphenyl)-5-trifluoromethyl-2H-
pyrazol-3-yl]-1-nitroso-1,2,3,6-tetrahydropyridine (14)
2.29 (m, 2H, tetrahydropyridyl H-3), 3.12 (s, 3H, SO2Me), 3.51–
3.65 (m, 2H, tetrahydropyridyl H-2), 4.02–4.12 (m, 2H, tetrahydro-
pyridyl H-6), 4.17 (q, 2H, J = 7.1 Hz, CH2CH3), 5.82–6.02 (m, 1H, tet-
rahydropyridyl H-5) 6.62 (s, 1H, pyrazole H-4), 7.74 (d, 2H,
J = 8.5 Hz, phenyl H-2, H-6), 8.07 (d, J = 8.5 Hz, 2H, phenyl H-3, H-
5); MS (M+Na)+ 466.09.
4-[2-(4-Methanesulfonylphenyl)-5-trifluoromethyl-2H-pyra-
zol-3-yl]-1,2,3,6-tetrahydropyridine (13a, 0.83 g, 2.24 mmol) was
added to a solution of NaOMe (2.24 mmol, 0.5 mL of a 25% w/v
solution in MeOH) and diethyl ether (10 mL) with stirring at
25 °C. Acetonitrile (10 mL) was then added to the reaction mixture
to increase the solubility of 13a. This mixture was purged with dry
nitrogen gas for 5 min, and then the reaction was allowed to pro-
ceed under an atmosphere of nitric oxide (40 psi internal pressure)
with stirring at 25 °C for 48 h. Removal of the solvents in vacuo
gave a the dark brown residue that was purified by silica gel col-
umn chromatography using a EtOAc/hexane (1:1, v/v) as eluent
to yield the N-nitroso product (14) in 53% yield, mp 190–192 °C;
5.4.2. 4-[2-(4-Sulfamoylphenyl)-5-trifluoromethyl-2H-pyrazol-
3-yl]-1-ethoxycarbonyl-1,2,3,6-tetrahydropyridine (12b)
Yield, 60%; viscous oil; IR (film) 3310 (broad NH2), 1708 (CO),
1377, 1160 (SO2) cmꢀ1 1H NMR (CDCl3) d 1.25 (t, 3H, J = 7.3 Hz,
;
CH2CH3), 2.13–2.21 (m, 2H, tetrahydropyridyl H-3), 3.54 (t, 2H,
J = 5.5 Hz, tetrahydropyridyl H-2), 4.04–4.10 (m, 2H, tetrahydropyr-
idylH-6), 4.13 (q, 2H, J = 7.3 Hz, CH2CH3), 5.49 (s, 2H, SO2NH2 thatex-
changes with D2O), 5.85–5.94 (m, 1H, tetrahydropyridyl H-5), 6.59
(s, 1H, pyrazole H-4), 7.63 (d, 2H, J = 8.5 Hz, phenyl H-2, H-6), 8.01
(d, J = 8.5 Hz, 2H, phenyl H-3, H-5); MS (M+Na)+ 467.05.
IR (film) 1320, 1160 (SO2) cmꢀ1 1H NMR (CDCl3) d 2.45–2.55 (m,
;
2H, tetrahydropyridyl H-3), 3.12 (s, 3H, SO2Me), 4.30–4.38 (m,
2H, tetrahydropyridyl H-6), 4.43 (t, 2H, J = 5.5 Hz, tetrahydropyr-
idyl H-2), 5.95–6.0 (m, 1H, tetrahydropyridyl H-5) 6.66 (s, 1H, pyr-
azole H-4), 7.73 (d, 2H, J = 8.5 Hz, phenyl H-2, H-6), 8.09 (d,
J = 8.5 Hz, 2H, phenyl H-3, H-5); MS (M+Na)+ 423.02. Anal. Calcd
for C16H15F3N4O3S: C, 48.00; H, 3.78; N, 13.99. Found: C, 48.07;
H, 4.03; N, 13.81.
5.5. General Procedure for the synthesis of 1,2,3,6-
tetrahydropyridines (13a–b)
A solution of a N-ethoxycarbonyl-1,2,3,6-tetrahydropyridine
12a or 12b (6 mmol) in hydrochloric acid (10 N, 10 mL) was re-

8888
M. A. Chowdhury et al. / Bioorg. Med. Chem. 16 (2008) 8882–8888
3. Mukherjee, D. Biochem. Pharmacol. 2002, 63, 817.
4. Scheen, A. J. Rev. Med. Liege 2004, 59, 565.
5.7. N-Nitroso-1,2,3,6-tetrahydropyridne (16)
5. Dogné, J.-M.; Supuran, C. T.; Pratico, D. J. Med. Chem. 2005, 48, 2251.
6. Butler, A. R.; Williams, D. L. H. Chem. Soc. Rev. 1993, 22, 233.
7. Dhawan, V.; Schwalb, D. J.; Shumway, M. J.; Warren, M. C.; Wexler, R. S.;
Zemtseva, I. S.; Zifcak, B. M.; Janero, D. R. Free Radical Biol. Med. 2005, 39,
1191.
8. Ranatunge, R. R.; Augustyniak, M.; Bandarage, U. K.; Earl, R. A.; Ellis, J. L.;
Garvey, D. S.; Janero, D. R.; Letts, L. G.; Martino, A. M.; Murty, M. G.; Richardson,
S. K.; Schroeder, J. D.; Shumway, M. J.; Tam, S. W.; Trocha, M.; Young, D. V. J.
Med. Chem. 2004, 47, 2180.
9. Abdellatif, K. R. A.; Dong, Y.; Chen, Q.-H.; Chowdhury, M. A.; Knaus, E. E. Bioorg.
Med. Chem. 2007, 15, 6796.
10. Abdellatif, K. R. A.; Chowdhury, M. A.; Dong, Y.; Chen, Q.-H.; Knaus E, E. Bioorg.
Med. Chem. 2008, 16, 3302.
11. Velázquez, C. A.; Praveen Rao, P. N.; Citro, M. L.; Keefer, L. K.; Knaus, E. E. Bioorg.
Med. Chem. 2007, 15, 4767.
12. Velázquez, C. A.; Chen, Q.-H.; Citro, M. L.; Keefer, L. K.; Knaus, E. E. J. Med. Chem.
2008, 51, 1954.
13. Abdellatif, K. R. A.; Chowdhury, M. A.; Dong, Y.; Knaus, E. E. Bioorg. Med. Chem.
2008, 16, 6528.
14. Levine, R.; Sneed, J. K. J. Am. Chem. Soc. 1951, 73, 4478.
15. Thomas, J.; Berkoff, C. E.; Flagg, W. B.; Gallo, J. J.; Haff, R. F.; Pinto, C. A. J. Med.
Chem. 1975, 18, 245.
1,2,3,6-Tetrahydropyridine (15, 100 mg, 1.2 mmol) was added
to a solution of NaOMe (65 mg of 95% purity, 1.2 mmol) in Et2O
(5 mL) and acetonitrile (2 mL) with stirring at 25 °C. This mixture
was purged with argon for 5 min, and the reaction was allowed
to proceed under an atmosphere of nitric oxide gas (40 psi internal
pressure) with stirring at 25 °C for 1 h. The reaction mixture was
filtered to remove some solid material which 1H NMR indicated
did not contain any of the sodium diazeniumdiolate product. The
solvent was removed from the filtrate to furnish N-nitroso-
1,2,3,6-tetrahydropyridine (16) in 27% yield. A similar reaction per-
formed using NaOMe (25% in MeOH) in Et2O afforded 16 in 46%
yield. In a third reaction, nitric oxide gas was bubbled into a solu-
tion of 15 using an aprotic solvent system26 comprised of acetoni-
trile and diethyl ether (1:0.5, v/v) at -78 °C to also give N-nitroso-
1,2,3,6-tetrahydropyridine (16) as a dark brown liquid in 40% yield.
1H NMR (CDCl3) d 2.22 (m, 0.4H, H-3), 2.48 (m, 1.6H, H-3), 3.96 (t,
J = 6.0 Hz, 0.4H, H-2), 4.37 (t, J = 6.0 Hz, 1.6H, H-2), 4.20 (m, 1.6H,
H-6), 4.77 (m, 0.4H, H-6), 5.65–6.00 (m, 2H, H-4, H-5); MS
(M+H)+ 113.02. This 1H NMR spectral data is in agreement with
previously reported data for N-nitroso-1,2,3,6-tetrahydropyridine
(16).27
16. Penning, T. D.; Talley, J. J.; Bertenshaw, S. R.; Carter, J. S.; Collins, P. W.; Docter,
S.; Graneto, M. J.; Lee, L. F.; Malecha, J. W.; Miyashiro, J. M.; Rogers, R. S.; Rogier,
D. J.; Yu, S. S.; Anderson, G. D.; Burton, E. G.; Cogburn, J. N.; Gregory, S. A.;
Koboldt, C. M.; Perkins, W. E.; Seibert, K.; Veenhuizen, A. W.; Zhang, Y. Y.;
Isakson, P. C. J. Med. Chem. 1997, 40, 1347.
17. Nielsen, A. T.; Moore, D. W.; Mazur, J. H.; Berry, K. H. J. Org. Chem. 1964, 29,
2898.
18. Waters, J. A.; Spivak, C. E.; Hermsmeier, M.; Yadav, J. S.; Liang, R. F.; Gund, T. M.
J. Med. Chem. 1988, 31, 545.
5.8. In vivo anti-inflammatory assay
19. Labouta, I. M.; Falch, E.; Hjeds, H.; Krogsaard-Larsen, P. Eur. J. Med. Chem. 1982,
17, 531.
20. Tang, X.; Xian, M.; Trikha, M.; Honn, K. V.; Wang, P. G. Tetrahedron Lett. 2001,
42, 2625.
21. Toscano, J. P.; Pavlos, C. M.; Boppana, K. International PCT Patent, WO 2005/
074598 A2, Issued August 18, 2005.
The test compounds 11–14, and the reference drugs celecoxib
and aspirin, were evaluated using the in vivo carrageenan-induced
foot paw edema model reported previously.28
22. Rao, P. N. P.; Amini, M.; Li, H.; Habeeb, A. G.; Knaus, E. E. J. Med. Chem. 2003, 46,
4872. and references cited therein.
Acknowledgment
23. Pommery, N.; Taverne, T.; Telliez, A.; Goossens, L.; Charlier, C.; Pommery, J.;
Goossens, J.-F.; Houssin, R.; Durant, F.; Henichart, J.-P. J. Med. Chem. 2004, 47,
6195.
24. Truce, W. E.; Vriesen, C. W. J. Am. Chem. Soc. 1953, 75, 5032.
25. Soliman, R. J. Med. Chem. 1979, 22, 321.
The authors are grateful to the Canadian Institutes of Health Re-
search (CIHR) (MOP-14712) for financial support of this research.
26. Cai, T. B.; Tang, X.; Nagorski, J.; Brauschweigerb, P. G.; Wanga, P. G. Bioorg. Med.
Chem. 2003, 11, 4971.
References and notes
27. Saavedra, J. E. J. Org. Chem. 1979, 44, 4511.
28. Winter, C. A.; Risley, E. A.; Nuss, G. W. Proc. Soc. Exp. Biol. Med. 1962, 111, 544.
1. Hinz, B.; Brune, K. Pharmacol. Exp. Ther. 2002, 300, 367.
2. Patel, H. H.; Gross, G. J. J. Mol. Cell. Cardiol. 2002, 34, 1.