Synthesis and biological evaluation of 2,3-diarylpyrazines and quinoxalines as selective COX-2 inhibitors

Article abstract of DOI:10.1016/j.bmc.2004.01.033

Several 2,3-diaryl pyrazines and quinoxalines with 4-sulfamoyl (SO ₂NH₂)/methylsulfonyl (SO₂Me)-phenyl pharmacophores have been synthesized and evaluated for the cyclooxygenase (COX-1/COX-2) inhibitory activity. Smaller groups such as methoxy, methyl and fluoro when substituted at/around position-4 of the adjacent phenyl ring, have great impact on the selective COX-2 inhibitory activity of the series. Many potential compounds were obtained from a brief structure-activity relationship (SAR) study. Two of these, compounds 11 and 25 exhibited excellent in vivo activity in the established animal model of inflammation. Since compound 25 possessed an amenable sulfonamide group, two of its prodrugs 48 and 49 were also synthesized. Both of them have excellent in vivo potential, and represent a new class of COX-2 inhibitor.

Full text of DOI:10.1016/j.bmc.2004.01.033

Bioorganic & Medicinal Chemistry 12 (2004) 1881–1893
Synthesis and biological evaluation of 2,3-diarylpyrazines and
quinoxalines as selective COX-2 inhibitors§,
?
Sunil K. Singh,a,* V. Saibaba,a V. Ravikumar,a Santosh V. Rudrawar,a Pankaj Daga,a
C. Seshagiri Rao,b V. Akhila,b P. Hegdeb and Y. Koteswar Raoa,*
aDiscovery Chemistry, Discovery Research-Dr. Reddy’s Laboratories Ltd., Bollaram Road, Miyapur, Hyderabad 500 049, India
bDiscovery Biology, Discovery Research-Dr. Reddy’s Laboratories Ltd., Bollaram Road, Miyapur, Hyderabad 500 049, India
Received 1 January 2004; revised 24 January 2004; accepted 26 January 2004
Abstract—Several 2,3-diaryl pyrazines and quinoxalines with 4-sulfamoyl (SO2NH2)/methylsulfonyl (SO2Me)-phenyl pharmaco-
phores have been synthesized and evaluated for the cyclooxygenase (COX-1/COX-2) inhibitory activity. Smaller groups such as
methoxy, methyl and fluoro when substituted at/around position-4 of the adjacent phenyl ring, have great impact on the selective
COX-2 inhibitory activity of the series. Many potential compounds were obtained from a brief structure–activity relationship
(SAR) study. Two of these, compounds 11 and 25 exhibited excellent in vivo activity in the established animal model of inflam-
mation. Since compound 25 possessed an amenable sulfonamide group, two of its prodrugs 48 and 49 were also synthesized. Both
of them have excellent in vivo potential, and represent a new class of COX-2 inhibitor.
# 2004 Elsevier Ltd. All rights reserved.
1. Introduction
inflammatory) in most of the cells and tissues, and
accounts for the anti-inflammatory activity along with
side effects.6 Thus, the selective inhibition of the induci-
ble COX-2, sparing constitutive COX-1, formed the
basis of designing COXIBs to have anti-inflammatory
agents with minimal degree of ulcerogenic risk. This
new concept of treating inflammation related disease
came into effect with the consecutive launch of celecoxib7
and rofecoxib.8 The latter efforts in this direction intro-
duced second generation drugs viz. valdecoxib,9 par-
ecoxib sodium10 and etoricoxib11 (Fig. 1). While these
COX-2 inhibitors have been successful in treating
inflammatory diseases like acute pain, rheumatoid
arthritis and osteoarthritis, a few of them are also being
studied for treating different types of cancer,12 and Alz-
heimer’s disease.13 Despite a few latest cautionary
reports,14 the COXIB treatment has a high degree of
benefit over risk.
The discovery of two isoforms of prostaglandin syn-
thase and their entirely different roles created a new
window for the pharmaceutical research.1 These iso-
zymes, COX-1 and COX-2, are reported to exhibit a
tissue dependent expression and regulation.2 The con-
stitutive COX-1, mainly expressed in gastrointestinal
tract, is responsible for the biosynthesis of PGs required
for the cytoprotection and platelet aggregation.3 So, any
interference with its normal activity for long time leads
to severe gastrointestinal toxicity such as ulceration,
bleeding and perforation.4 The COX-2, induced during
injury by the pro-inflammatory cytokines such as tumor
necrosis factor-a (TNF-a) and interleukines, plays a
major role in the biosynthesis of PGs required for
inflammatory cells such as monocytes and macrophages
causing swelling, pain and fever.5 The conventional
NSAIDs causing nonselective inhibition of these differ-
ently acting COX-1 and COX-2 enzymes, down regulate
the biosynthesis of PGs (cytoprotective as well as
Unlike traditional NSAIDs which have diverse class of
chemical structures, the COX-2 inhibitors can structu-
rally be restricted to only two classes, (1) the acidic
methane sulphonamide containing diphenyl ethers,
represented by nimesulide15 and NS-398,16 and (2) the
vicinal diaryl heterocycles having essentially either sul-
famoyl (SO2NH2) or methylsulfonyl (SO2Me) substition
at position-4 of one of the phenyl ring, represented by
celecoxib, rofecoxib, valdecoxib, parecoxib sodium and
Keywords: 2,3-Diarylpyrazines; 2,3-Diarylquinoxalines; COX-2 inhibitors.
§Supplementary data associated with this article can be found, in the
online version at, doi:10.1016/j.bmc.2004.01.033
?
DRL Publication No. 271A
* Corresponding authors. Tel.: +91-40-2304-5439; fax: +91-40-2304-
5438/2304-5007; e-mail addresses: sunilkumarsingh@drreddys.com;
koteswarraoy@drreddys.com
0968-0896/$ - see front matter # 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.01.033

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S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
rings of etoricoxib in one. During investigation, we
came across a similar compound which was reported to
be inactive in COX-2 assay.23 But, the scanty report on
these heterocycles provided us an opportunity to
explore them further. Therefore, a few suitably sub-
stituted 2,3-diarylpyrazines and quinoxalines, their
dihydro and tetrahydro analogues were synthesized and
studied for their COX-1/COX-2 inhibitory activity.
Herein, we wish to report the synthesis and a brief SAR
on these two diarylheterocycles, their in vivo activity
and a model of prodrug approach improving their
potency and water solubility.
Figure 1.
2. Results and discussion
2.1. Chemistry
etoricoxib (Fig. 1). The two adjacent phenyl rings of
these COX-2 inhibitors orient in rigid cis-stilbene geo-
metry and the phenyl ring having SO2NH2/SO2Me
group extends towards hydrophilic region of COX-2
secondary pocket. This feature has thus been proposed
to be the primary determinant for the COX-2 selectiv-
ity.17 During the rational design, many diaryl carbo-
cycles and heterocycles were identified which could
adopt this favorable geometry to explicit the desired
activity.18 In other words, lack of this rigid geometry
can also be reasoned for conventional NSAIDs to be
nonselective. Though many COXIBs have been laun-
ched in the market during a short span of time, there
still remains a need to develop more efficacious drugs
with high degree of patient acceptability as an alter-
native to the steroidal and narcotic drugs used in severe
surgical as well as postoperative pain which can check
the initial process of inflammation. To the best of our
knowledge, parecoxib sodium is only such COX-2 inhi-
bitor, derived from valdecoxib, available in its water
soluble form (injectable) which acts fast against the pain
induced after surgical incisions.10 The active ingradient
of this prodrug is released immediately after injection to
cause the desired action. This approach is very common
way to get water soluble prodrug which releases the
active ingradient in systemic circulation to cause
the desired effect. Though we have also reported a water
soluble form of celecoxib acting similarly in animal
model,19 it is still high time requirement for such type of
drug in this segment which can be used in the above
situations including ocular inflammation.20
Synthesis of important intermediates required for
methylsulfonylphenyl containing pyrazines and quinox-
alines is depicted in Scheme 1. The methylsulfanylphe-
nyl ethanones 1, were synthesized by Friedel–Crafts
acylation of thioanisole with substituted phenyl acetyl
chlorides. Methylsulfanylphenyl-1,2-diarylethanediones
(benzils) 2, were synthesized from 1 by simple SeO2
oxidation carried out in dioxane–water under reflux
condition whereas the corresponding methylsulfonyl-
phenyl-1,2-diarylethanediones 3 were either obtained
from 2 by H2O2 oxidation or from 1 by reversing the
order of two oxidations mentioned above via 4 in
almost equal yields (50–60% starting from 1). The
methylsulfanylphenyl and methylsulfonylphenyl a-bro-
moethanones 5 and 6 were prepared from the corres-
ponding ethanones 1 and 4 by electrophilic bromination
using liquid Br2, catalysed by HBr in dichloromethane.
The conversion of methylsulfanyl (SMe) to methylsul-
fonyl (SO2Me) was detected by the d shift from 2.03 to
3.08 for CH3 protons, that of ethanone to ethanedione
by the complete disappearance of CH2 protons from
4.20 and that of ethanone to a-bromoethanones by the
Out of many six-membered heterocycles studied as cen-
tral ring so far,21 etoricoxib has recently entered the
market as second generation therapy addressing many
long standing problems associated with the first genera-
tion COX-2 inhibitors.11 The possible reason for its
excellent performance in clinic is the presence of two
pyridyl rings improving its pharmacokinetic profile to
the maximum extent leading to high degree of bio-
availability and efficacy. Therefore, despite being
involved in the design of five-membered vicinal diaryl
structural motif,22 we decided to ventured into six
membered nitrogen containing heterocycles such as
pyrazine and quinoxalines which could be envisioned
as bringing the two nitrogen atoms of the two pyridyl
Scheme 1. Reagents and conditions: (a) AlCl3, CH2Cl2, 0–35 ꢀC, 2–4 h
(b) SeO2, 1,4-Dioxane–H2O, reflux, 1–2 h. (c) Br2/HBr, CH2Cl2,
AcOH, 0–35 ꢀC, 4–5 h. (d) H2O2/AcOH, 50–60 ꢀC, 3–4 h.

S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
1883
shift of CH2 protons at 4.2 to 6.3 ppm for CH protons
in 1H NMR.
tion by preparative HPLC and identification for decid-
ing the correct isomer responsible for COX-2 inhibition.
Synthesis of intermediates required for sulfamoylphenyl
containing pyrazines and quinoxalines is outlined in
Scheme 2. The 4-sulfamoylphenyl ethanediones (benzils)
9, were obtained from diphenylethanones 7 (prepared
by the Friedel–Crafts acylation of suitably substituted
benzene using phenylacetyl chloride). The step wise
chlorosulfonation and amination of 7 afforded 4-sulfa-
moylphenyl ethanones 8 which were converted to
corresponding ethanediones 9 by SeO2 oxidation. The
sulfamoylphenyl a-bromoethanones 10 were prepared
by the method described above for corresponding
methylsulfanyl/sulfonyl derivatives 5 or 6 (Scheme 1).
Synthesis of tetrahydropyrazines 40–43 and dihy-
droquinoxalines 44–47 is depicted in Scheme 4. The
coupling of a-bromoethanones 5, 6 and 10 (Schemes 1
and 2) with 1,2-diaminoethane and 1,2-diaminopropane
in methanol yielded tetrahydropyrazines 40 and 43
whereas with phenylenediamine afforded dihy-
droquinoxalines 44 and 47. A few N-acylated deriva-
tives of these compounds were also prepared for
comparison sake using acetic anhydride and trifluoro
acetic anhydride in presence of triethyl amine. In case of
coupling using 5, the oxidation of methylsulfanyl (SMe)
to methylsulfonyl (SO2Me) after acylation was observed
to be higher yielding when compared to the oxidation
followed by acylation process. These tetrahydropyrazines
and dihydroquinoxalines were screened as racemic mixture.
Synthesis of diarylpyrazines and quinoxalines, having
sulfamoyl and methylsulfonyl groups 11–39 is depicted
in Scheme 3. The 2,3-dihydropyrazines, obtained from
coupling of diones (benzils) 2, 3 and 9 (Schemes 1 and 2)
with 1,2-diaminoethane and 1,2-diaminopropane in
methanol, was further dehydrogenated to afford the
fully aromatized pyrazines using Pd-C in ethanol under
heating condition whereas coupling with phenylenedia-
mine directly afforded aromatic quinoxalines. Coupling
product of 3 and 9 in few cases directly afforded pyr-
azines due to the formation of energetically favored
aromatic nucleus. The coupling product of 2 required
further oxidation with H2O2 and suffered a comparative
yield loss. The compounds obtained as a result of 1,2-
diaminopropane coupling, were approximately a 60:40
mixture of regioisomers which could not be separated
by column chromatography, and were screened as such
in the COX-1/COX-2 in vitro assay. However, the two
regioisomers of active compound 24, are under separa-
Synthesis of the prodrugs of compound 25 is depicted in
Scheme 5. The N-propionylation of sulfamoyl group of
25 with propionic anhydride in presence of triethyl
amine afforded its N-propionyl derivative 48 which on
treatment with 0.95 equivalent of NaHCO3 in methanol
at room temperature afforded the desired water soluble
sodium salt 49.10,19 The conversion of acyl derivative 48
to sodium salt 49 was characterized by the dis-
1
appearance of NH signal in H NMR spectra and dra-
matic increase in melting point. All the compounds
reported herein were well characterized using spectro-
1
scopic methods such as IR, H NMR and Mass and
they were found to be highly pure (above 97%) by
HPLC/C, H, N analysis.
2.2. Biology
Initially, all the compounds were screened for their
ability to inhibit the recombinant human COX-2
enzyme, expressed in sf-9 cells infected with baculovirus,
and COX-1 enzyme, obtained from microsomal fraction
Scheme 4. Reagents and conditions: (a) 1,2-Diaminoethane, MeOH,
0–30 ꢀC, 4–6 h. (b) (R1CO)2O, TEA, CH2Cl2, reflux, 6–7 h. (c) o-
Phenylenediamine, MeOH, 0–35 ꢀC, 4–6 h. (d) H2O2/AcOH, 50–60 ꢀC,
3–4 h, in case of coupling with 5.
Scheme 2. Reagents and conditions: (a) ClSO3H, CH2Cl2, 0–35 ꢀC, 2–
3 h, (b) aq. NH3, 0–10 ꢀC, 5–10 min. (c) SeO2, 1,4-Dioxane–H2O,
reflux, 1–2 h. (d) Br2/HBr, CH2Cl2, AcOH, 0–35 ꢀC, 4–5 h.
Scheme 3. Reagents and conditions: (a) o-Phenylenediamine, MeOH,
0–30 ꢀC, 4–6 h. (b) 1,2-Diaminoethane or, 1,2-Diaminopropane,
MeOH, 0–30 ꢀC, 4–6 h. (c) Pd/C, EtOH, reflux, 12–14 h. (d) H2O2/
AcOH, 50–60 ꢀC, 3–4 h, in case of coupling with 2.
Scheme 5. Reagents and conditions: (a) (C2H5CO)2O, TEA, CH2Cl2,
reflux, 8–9 h. (b) NaHCO3, MeOH, 0–35 ꢀC, 4–5 h.

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S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
of Ram Seminal Vesicles at 100 mM concentration.
Based on their initial in vitro efficacy, the promising
compounds were tested further at lower concentrations.
The enzyme activity was measurement by TMPD
method and IC50s for COX-1 and COX-2 were calcu-
lated using non-linear regression analysis of percent
inhibitions.24 Celecoxib and indomethacine were used as
reference standard for COX-2 selective and nonselective
inhibitors. Compounds were selected for in vivo screen-
ing25 based on the higher ratio of IC50s (COX-1/COX-2),
known as selectivity index (SI).
Table 2. In vitro activity of sulfonamide containing 2,3-diaryl pyr-
azines
Compd
Ar
R
H
% Inhibitiona,b (IC50, mM)c
COX-1 COX-2
21
22
23
24
25
26
27
28
29
4-Me-phenyl
4-Me-phenyl
4-OMe-phenyl
4-OMe-phenyl
4-F-phenyl
0 (>1000) 43 (8.11ꢁ0.10)
Me 13 (>100)
0 (131.4)
Me 41 (97)
63 (1.22ꢁ0.04)
75 (1.93ꢁ0.06)
100 (0.46ꢁ0.01)
83 (1.07ꢁ0.03)
67 (4.45ꢁ0.09)
75 (7.26ꢁ0.08)
75 (3.91ꢁ0.04)
88 (1.62ꢁ0.03)
H
The results of COX-1/COX-2 inhibition are summar-
ized in Tables 1–3. The 4-methylsulfonylphenyl con-
taining 2,3-diarylpyrazines with small groups on the
adjacent phenyl ring with electron donating/electron
withdrawing nature were preferred for the study. In few
cases, a methyl group on the pyrazine nucleus was also
tried. The electron withdrawing groups at position-4
were generally unfavorable, for example, nitro group
was found totally inactive. But the activity started
increasing with the introduction of electron donating
groups, and 4-methoxy, 3-fluoro and 4-fluoro sub-
stituted phenyls and unsubstituted phenyl were found
reasonably COX-2 selective. Particularly, these groups
along with a methyl group at pyrazine nucleus showed
highly improved activity, for example, 4-methoxy and 4-
fluorophenyl analogues 13 and 15, though screened as
60:40 mixture of regioisomers, respectively exhibited
IC50s of 1.62 and 5.43 mM when compared to their
corresponding non-methylated poorly active analogues
(Table 1).23a Out of four compounds 11, 13, 15 and 20
(in vitro active) studied in vivo in the carrageenan
induced rat paw edema model of inflammation at 30
mg/kg (po), 11 and 13 showed 56% and 32% reduction
in paw volume (Table 4). Recalling the lower potency
exhibited by methylsulfonyl (SO2Me) group when
H
H
H
H
0 (>300)
0 (401)
31 (>300)
0 (>300)
4-Cl-phenyl
4-Br-phenyl
4-OMe-3-Me-phenyl
4-OMe-3-Me-phenyl Me 0 (285)
30
31
32
H
H
0 (251)
100 (1.01ꢁ0.02)
100 (4.42ꢁ0.08)
100 (1.65ꢁ0.06)
19 (190)
Me 38 (16)
48
49
—
—
—
—
0
0
67
25
Parecoxib
Sodium
—
—
0
17
> Represents precipitation beyond this concentration and the IC50 for
COX-1 can be much higher than the values mentioned here.
a At 10 mM concentration.
b Average of three determinations with experimental error of
< ꢁ12%.
c Mean of two determinations with standard deviation of < ꢁ10%.
Table 1. In vitro activity of methylsulfonyl containing 2,3-diaryl pyrazines
Compd
Ar
R
% Inhibitiona,b (IC50, mM)c
COX-1
COX-2
11
12
13
14
15
16
17
18
Phenyl
4-OMe-phenyl
4-OMe-phenyl
4-F-phenyl
4-F-phenyl
4-NO2-phenyl
4-Me-phenyl
4-Me-phenyl
3-F-phenyl
3-F-phenyl
—
H
H
Me
H
Me
H
H
Me
H
Me
—
—
49
29 (>100)
29 (>30)
15
0 (>100)
0
66
44 (11.81ꢁ0.12)
75 (1.62ꢁ0.06)
34
71 (5.43ꢁ0.11)
0
37
27
22
67
43
19
20
19
22 (>300)
11 (15.33ꢁ0.03)
100 (0.067ꢁ0.001)
88 (4.4ꢁ0.10)
100 (0.07ꢁ0.005)
97 (7.80ꢁ0.11)
Celecoxib
Indomethacin
—
>Represents precipitation beyond this concentration and the IC50 for COX-1 can be much higher than the values mentioned here.
a At 10 mM concentration.
b Average of three determinations with experimental error of < ꢁ12%.
c Mean of two determinations with standard deviation of < ꢁ10%.

S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
1885
prising result because compound 24, despite exhibiting
excellent in vitro activity, could not perform well in
animal model study. But, this observation was similar to
that of 4-methoxyphenyl analogue 13 in animal model.
Though the exact reason behind this abnormality is not
known, the metabolic conversion of 4-methoxyphenyl
group to 4-hydroxyphenyl can not be ignored. This
possible explanation is based on the fact that COX-2
enzyme accepts only a hydrophobic group at this posi-
tion.26 In contrast, the 4-fluorophenyl analogue 25
which showed lesser COX-2 in vitro potency than 24
was found to be the best among all in the animal study.
The possible reason for this fact could be a better
metabolic stability of the 4-fluorophenyl group under
physiological condition.27 The in vitro study of quinox-
alines, substituted with sulfamoyl (SO2NH2) and
methylsulfonyl (SO2Me) groups at position-4 of phenyl
ring is summarized in Table 3. Like 4-methoxyphenyl
substituted analogue of methylsulfonyl containing pyr-
azine 13 (Table 1), the corresponding quinoxaline 36
was also found to be potent. This similarity continued
further and sulfamoyl containing quinoxalines such as
4-methoxy-3-methylphenyl analogue 38 and bicyclic
indanyl analogue 39 showed very good in vitro COX-2
potency. But, the in vivo profile of these quinoxalines
was quite discouraging as the two potent COX-2 inhi-
bitors of the series 36 and 39 showed only ꢂ22%
reduction in paw volume even after repeated study at 30
mg/kg, po (Table 4). A number of dihydropyrazines,
obtained during coupling reaction which are not repor-
ted here (Scheme 3), tetrahydropyrazines 40 and 43,
dihydroquinoxalines 44 and 47, and a few of their acyl
derivatives 41-42 and 45-46 (Scheme 4) were also
screened for their COX-1/COX-2 activity but none of
them showed significant COX-2 inhibition (less than
50% at 100 mM, not tabulated here). This showed the
essentiality of an aromatic heterocyclic nucleus as cen-
tral core providing suitable hydrophobic interaction
with the similar pocket of COX-2 enzyme for its effec-
tive inhibition. Presumably, this is the reason why above
hydrogenated central rings and their acyl derivatives
failed to inhibit the COX-2 enzyme. Similarly, the rela-
tively lesser potency of quinoxalines can be attributed
to its larger size lacking effective accommodation in to
COX-2 pocket.
Table 3. In vitro activity of methylsulfonyl and sulfonamide con-
taining 2,3-diaryl quinoxalines
Compd
R
Ar
% Inhibitiona,b (IC50, mM)c
COX-1 COX-2
33
34
35
36
37
38
Me
Me
NH2
Me
Me
Phenyl
0
12
0
10
0
40
4-Me-phenyl
4-Me-phenyl
4-OMe-phenyl
3-F-phenyl
0 (>30)
0
0 (30)
81 (0.40ꢁ0.05)
19
100 (2.10ꢁ0.07)
NH2 4-OMe-3-Me-phenyl
39
NH2
47 (30)
100 (0.32ꢁ0.04)
>Represents precipitation beyond this concentration and the IC50 for
COX-1 can be much higher than the values mentioned here.
a At 10 mM concentration.
b Average of three determinations with experimental error of
< ꢁ12%.
c Mean of two determinations with standard deviation of < ꢁ10%.
Table 4. In vivo data for selected compounds
Compd
% Reduction in Paw Vol.a (30 mg / kg)b,c
11
13
24
25
30
39
48
49
56
32
20
63
37
22
73
48
53
Celecoxib
Parecoxib
Sodium
45
a Carrageenan induced rat paw edema model, using six animal group
of male Wistar rats on per oral dosing.
b Mean of two experiments.
c Experimental error < ꢁ20%.
compared to sulfonamide (SO2NH2) in general,7 we
synthesized a few sulfamoylphenyl containing pyrazines
(Table 2). As expected, several potential COX-2 inhibi-
tors with varying degree of potency were obtained from
the series. The 4-methoxyphenyl analogue 24, though
screened as 65:35 mixture of regioisomers, was found to
have excellent COX-2 selectivity (0.46 mM) in conjuga-
tion with a methyl group on the pyrazine ring. The 4-
fluorophenyl analogue 25 topped in COX-2 potency
(1.07 mM) and selectivity among halogens. The 4-meth-
oxy-3-methylphenyl analogues 28 and 29, the bicyclic
indanyl analogue 30 and 2,3-dihydrobenzofuranyl ana-
logue 31 showed very good in vitro potency. In almost
every observation, a methyl group on the pyrazine
nucleus was found to play a crucial role in increasing
the selectivity and potency. But, the repeated in vivo
study of these compounds indicated only 25 and 30 as
potential candidates (Table 4). This was a quite sur-
We focused our attention to 4-fluorophenyl analogue
25, a potent compound from benzenesulfonamide con-
taining pyrazine class (Table 2) which showed excellent
in vivo activity (63% at 30 mg/kg, po) in repeated study.
As it was found to be fairly better than both celecoxib
(53%) and parecoxib (45%), studied at same dose, we
studied its prodrugs with a view to have a better drug
candidate for animal study. While its N-propionyl deri-
vative 48 showed reasonably good in vitro activity (67%
at 10 mM), its sodium salt 49 was found to be poorly
active (25%) at this concentration. But it was not sur-
prising because salts generally fail to release the active
ingredients in cell based assay, as parecoxib sodium was
also found to be poorly active in this assay (17% at 10
mM). The compounds 48 and 49 showed excellent in
vivo activity of 73% and 48% respectively at 30 mg/kg,
po in repeated study and were found to be better than

1886
S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
Figure 2. (a) Docking of 25 (orange). (b) Docking of 24a (green) and 24b (orange) in COX-2 pocket. Both the figures show that the sulfonamide
group lies always in the close proximity of the hydrophilic pocket. All ligands are shown in ball and stick while amino acids residues in capped stick
rendering. All hydrogens are removed for clarity.
the two reference compounds, celecoxib and parecoxib
sodium (Table 4). But compound 49, despite being less
potent than 48 in this initial study, was preferred for
further animal study due to its great water solubility
(200 mg/mL) at ambient temperature and with the hope
that it could be developed as an injectable like parecoxib
sodium which can be used in postoperative and other
similar conditions of inflammation. The results of fur-
ther pharmacokinetic and pharmacodynamic studies
will be reported elsewhere.
2.3. Molecular modeling
Docking the potent COX-2 inhibitors 24a, 24b, 25 and
SC-558 into COX-2 active site (6COX)17 generated var-
ious structures with different orientations. The orient-
ations and the hydrogen bonding interactions of the
most energetically favored conformations in the COX-2
complex is depicted in Figure 2. The binding site of
COX-2 enzyme is roughly divided into three small
pockets. One of these pockets which is constituted by
the hydrophilic amino acid residues His-90, Gln-192,
Ser-353, Leu-352 and backbone of Phe-518, accom-
modates the benzenesulfonamide group of these repre-
sentative ligands 24a (regioisomer in which the methyl
group is nearer to benzenesulfonamide), 24b (regioi-
somer in which the methyl group is farther) and 25. The
various hydrogen bond interactions responsible for this
binding are through different atoms of sulfonamide
group and resemble the binding pattern of SC-558.
Similarly, the second pocket of COX-2, constituted by
several hydrophobic amino acid residues Phe-381, Leu-
384, Tyr-385, Trp-387, Leu-517, Phe-518, Met-522 and
Gly-526, accommodates the adjacent phenyl ring. Size
of this pocket being large, can accommodate both the 4-
methoxyphenyl as well as a 4-fluorophenyl groups. Due
to the larger differential volume (calculated using
SYBYL 6.9), the 4-methoxy group (ꢂ80 A3) of 24a and
24b fits better than the 4-fluoro (ꢂ15 A3) of 25 into this
pocket. The third pocket, formed by the amino acid
residues Arg-120, Val-349, Leu-359 and Leu-531, can
Figure 3. Superimposition of four ligands in the COX-2 binding
pocket. SC-558 is shown by grey colored carbon, 25 (orange), 24a
(magenta) and 24b (green). All the ligands are shown in ball and stick
while amino acid residues in capped stick rendering. All hydrogens are
removed for clarity. Results indicate that CH3 group of 24a binds to
the same pocket as CF3 group of SC-558.
accommodate the groups like CH3, CF3, Cl, F and even
smaller ones. But, the steric interactions observed due to
groups like CH3 and CF3 in 24 and SC-558 are rela-
tively favorable. Thus, the molecular modeling studies
of the representative analogues of the series demon-
strated that the novel COX-2 inhibitors 24a, 24b
(though not studied separately in vitro) and 25 have
very good binding affinity with the COX-2 enzyme
which confirms their in vitro potency.
Superimposition of these potent ligands 24a, 24b and 25
on SC-558 in the COX-2 pocket, also showed a high

S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
1887
degree of similarity in the binding mode and further
supported the rational design of the new class of COX-2
inhibitors (Fig. 3).
4.2. Procedure A. General preparation of methylsulfonyl
containing diaryl pyrazines 11–20 and quinoxalines 33–
34, 36 and 37
Step 1. Representative preparation of 1-(4-methylsulfa-
nylphenyl)-2-phenyl-1-ethanone 1 (Ar, Ph)
3. Conclusion
In this report, we have described the synthesis and
(COX-1/COX-2) inhibitory activity of a few newly dis-
covered 2,3-diarylpyrazines and quinoxalines having 4-
methylsulfonyl (SO2Me)/sulfonamide (SO2NH2)-phenyl
pharmacophores. A few of them, substituted at adjacent
phenyl ring with smaller hydrophobic groups at/around
position-4, such as 13, 24, 25, 30 and 39 were found to
be potent COX-2 inhibitors. Of these, compound 25 and
two of its prodrugs 48 and 49 have shown excellent in
vivo activity and have the potential for further devel-
opment. The prodrug 49, which is exceptionally water
soluble, has an additional advantage of being developed
as an injectable for the postoperative and similar
inflammatory pains. In summary, we have identified
novel series of diarylpyrazines and quinoxalines which
represent a potential class of COX-2 inhibitors and have
the ability to deliver an effective anti-inflammatory drug
with minimal side effects.
Phenylacetyl chloride (2.0 mL, 15.13 mmol) was intro-
duced to a suspension of anhydrous aluminium chloride
(2.1 g, 15.84 mmol) in dichloromethane (25 mL) under
argon atmosphere at 0–5 ꢀC. After stirring the reaction
mixture for 0.5 h at this temperature, thioanisole (1.7
mL, 13.57 mmol) was slowly added for a period of 15
min. After maintaining the reaction mixture at this
temperature for 2 h, it was allowed to stir at room
temperature for 10–12 h and poured over crushed ice. It
was extracted with dichloromethane (3ꢃ50 mL), and
the combined organic layer after washing with water,
was dried (anhydrous Na2SO4) and evaporated to get
an oil which was purified by column chromatography
using ethyl acetate–petroleum ether (5%) to afford a
viscous liquid of the title compound (2.5 g, 75% ) which
was used in the next step without further purification.
IR (KBr) 3443, 1681, 1587, 1333 cmꢄ1 1H NMR
.
(CDCl3) d 7.92 (d, J=8.4 Hz, 2H), 7.31–7.22 (m, 7H),
4.23 (s, 2H), 2.50 (s, 3H). MS (CI method) 242 (M+),
185, 165, 151.
4. Experimental
4.1. Chemistry protocols
Step 2. Representative preparation of 1-(4-methylsulfa-
nylphenyl)-2-phenyl-1,2-ethanedione 2 (Ar, Ph)
Research chemicals and reagents such as thioanisole,
phenylacetic acids, phenylacetyl chlorides, ethylenedia-
mine, propylenediamine and o-phenylenediamine, were
purchased from Lancaster Co. and used as such for the
reactions. Solvents except LR grade, were distilled
before use. Reactions were monitored by thin layer
Selenium dioxide (2.0 g, 18.02 mmol) was dissolved in a
mixture of 1,4-dioxane-water (50 mL, 48:2) under heat-
ing, and cooled to room temperature. The 1,4-dioxane
solution of 1-(4-methylsulfanylphenyl)-2-phenyl-1-etha-
none (2.0 g, 8.26 mmol), prepared in step 1, was added
to the reaction mixture and refluxed overnight. The
precipitated selenium was filtered off and the filtrate was
poured over ice water. After repeated extraction with
ethyl acetate, the combined organic layer was washed
with water, dried and evaporated to get yellow solid of
the title compound (1.95 g, 92%) which was used in the
next step without further purification. IR (KBr) 2957,
chromatography (TLC) on silica gel plates (60 F254
;
Merck), visualizing with ultraviolet light or iodine
spray. Usually the flash column chromatographic pur-
ification was performed over 100–200 or 230–400 mesh
silica gel using mixture of ethyl acetate and petroleum
ether. The reference samples such as celecoxib,7 and
parecoxib sodium10 were prepared according to litera-
ture procedure whereas indomethacin was extracted
from the capsules bought from medical store. The yields
reported here are un-optimized. Melting points were
determined on Buchi melting point B-540 apparatus and
are uncorrected. IR spectra were recorded on Perkin–
1
1677, 1582 cmꢄ1. H NMR (CDCl3) d 8.10 (d, J=8.2
Hz, 2H), 7.41–7.12 (m, 7H), 2.63 (s, 3H). MS (CI
method) 256 (M+, 100%), 151, 104.
1
Elmer FT-IR 1650 spectrometer. H NMR experiments
Step 3. Representative preparation of 1-(4-methylsulfo-
nylphenyl)-2-phenyl-1,2-ethanedione 3 (Ar, Ph)
were performed at 200 MHz Varian Gemini 200 spec-
trometer and their chemical shifts are reported in d units
with respect to TMS as internal standard. Mass spectra
were recorded on HP-5989A spectrometer. Elemental
analysis were carried out for C, H, N using Perkin–
Elmer 2400 series II CHN-O analyzer. All the analyses
were performed by the Analytical Research Group of
Discovery-Research, Dr. Reddy’s Laboratories Ltd.
The purity of the final compounds were determined by
HPLC using ‘System 1’ which consisted column
Hichrom RPB (250 mm), mobile phase 0.01 M
KH2PO4/CH3CN (50:50) and ‘System 2’ which com-
prised column Intersil ODS 3V (250 mm), mobile phase
H2O/CH3CN (50:50), both running at 1.0 mL/min with
UV detection at respective l max.
30% Hydrogen peroxide solution (3.5 mL, 29.41 mmol)
was slowly added to a mixture of 1-(4-methylsulfanyl-
phenyl)-2-phenyl-1,2-ethanedione (1.9 g, 7.85 mmol,
prepared in step 2) in glacial acetic acid (10 mL). The
reaction mixture was heated at 50 ꢀC for 5 h. The cooled
mass was poured over ice-water and extracted with di-
chloromethane. The combined organic layer was
washed with water, dried and evaporated. The crude
solid was triturated with dichloromethane–petroleum
ether mixture to get a light brown solid of the title
compound (1.87 g, 87%) which was used in the next
step without further purification. IR (KBr) 3442, 1666,
1
1595, 1398 cmꢄ1. H NMR (CDCl3) d 8.18–8.00 (m,

1888
S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
3H), 7.98 (d, J=7.4 Hz, 2H), 7.70–7.00 (m, 4H), 3.08 (s,
3H). MS (CI method) 289 (M+H)+, 183, 151, 121.
Hz, 2H), 7.45–7.39 (m, 2H), 7.08 (t, J=8.2 Hz, 2H),
3.07 (s, 3H). MS 329 (M+H)+. HPLC (Method 1)
99.6%. Anal. calcd (C17H13FN2O2S) C, H, N.
Step 4. Representative preparation of 5-(4-methylsulfo-
nylphenyl)-6-phenyl-2,3-dihydropyrazine
4.6. Compound 15
Mixture of 1-(4-methylsulfonylphenyl)-2-phenyl-1,2-
ethanedione, prepared in step 3 (280 mg, 0.97 mmol)
and ethylenediamine (97 mL, 1.45 mmol) dissolved in
methanol (2 mL) was stirred overnight at room temp-
erature. The reaction mixture was poured over ice-water
and extracted with ethyl acetate. The crude product
isolated after evaporation was purified by column chro-
matography using ethyl acetate–petroleum ether (10%)
to get a white solid of the title compound (115 mg, 38%)
which was used in the next step without further pur-
Yield 64%. Mp 148–150 ꢀC. IR (KBr) 3025, 2915, 1588,
1
1510, 1385, 1311 cmꢄ1. H NMR (CDCl3) d 8.54–8.51
(d, J=5.37 Hz, 1H), 7.92–7.86 (m, 2H), 7.67–7.60 (m,
2H), 7.44–7.34 (m, 2H), 7.06–6.97 (m, 2H), 3.05 (s, 3H),
2.68 (s, 3H). MS (CI Method) 343 (M+H)+, 342 (M+),
262, 194, 121, 102, 90. HPLC (System 1) 99.5% (Mixt.
of regioisomers, 62:37.5). Anal. calcd (C18H15FN2O2S)
C, H, N.
4.7. Compound 16
ification. IR (KBr) 3431, 1560, 1310, 1150 cmꢄ1 1H
.
NMR (CDCl3) d 7.83 (d, J=8.2 Hz, 2H), 7.59 (d,
J=7.8 Hz, 2H), 7.33–7.27 (m, 5H), 3.74 (s, 4H), 3.01 (s,
3H). MS (CI method) 313 (M+H)+.
Yield 59%. Mp 250–252 ꢀC. IR (KBr) 3426, 2926, 2360,
1597, 1513, 1388, 1346, 1312 cmꢄ1. 1H NMR (CDCl3) d
8.74 (s, 2H), 8.21 (d, J=8.8 Hz, 2H), 7.93 (d, J=8.4 Hz,
2H), 7.68–7.61 (m, 4H), 3.08 (s, 3H). MS (CI Method)
356 (M+H)+, 340, 326, 325. HPLC (Method 1) 97.9%.
Anal. calcd (C17H13N3O4S) C, H, N.
Step 5. Representative preparation of 2-(4-methylsulfo-
nylphenyl)-3-phenylpyrazine 11
10% Pd-C (5 mg) was added to a 2 mL ethanolic solu-
tion of 5-(4-methylsulfonylphenyl)-6-phenyl-2,3-dihy-
dropyrazine (100 mg, 0.32 mmol), prepared in step 4
and refluxed the mixture for 5 h. The reaction mixture
was filtered on celite bed and the filtrate after concen-
tration was purified by column chromatography using
ethyl acetate–petroleum ether (20%) to get a white solid
of the title product (55 mg, 55%). Mp 142–144 ꢀC. IR
4.8. Compound 17
Yield 63%. Mp 148–150 ꢀC. IR (KBr) 3441, 3023, 2920,
1390, 1300 cmꢄ1. H NMR (CDCl3) d 8.67–8.61 (m,
2H), 7.89 (d, J=8.3 Hz, 2H), 7.68 (d, J=8.3 Hz, 2H),
7.32–7.11 (m, 4H), 3.06 (s, 3H), 2.37 (s, 3H). MS (CI
Method) 325 (M+H)+, 309 (100%), 245, 230, 117.
HPLC (Method 2) 97.5%. Anal. calcd (C18H16N2O2S)
C, H, N.
1
(KBr) 3437, 2919, 1599, 1390, 1309 cmꢄ1 1H NMR
.
(CDCl3) d 8.66 (d, J=6.2 Hz, 2H), 7.90 (d, J=8.4 Hz,
2H), 7.67 (d, J=8.2 Hz, 2H), 7.44–7.20 (m, 5H), 3.05 (s,
3H). MS (CI Method) 311 (M+H)+, 231 (100%), 204,
176, 150, 119, 103. HPLC (Method 1) 98.8%. Anal.
calcd (C17H14N2O2S) C, H, N.
4.9. Compound 18
Yield 68%. Mp 178–180 ꢀC. IR (KBr) 3433, 2921, 1437,
.
1309, 1151 cmꢄ1 1H NMR (CDCl3) d 8.53–8.48 (d,
J=10.2 Hz, 1H), 7.90–7.84 (m, 2H), 7.68–7.61 (m, 2H),
7.31–7.10 (m, 4H), 3.04 (s, 3H), 2.68 (s, 3H), 2.35 (s,
3H). MS (CI Method) 338 (M+, 100%), 337, 259, 244,
189, 117, 102, 90. HPLC (Method 2) 98.7% (Mixt. of
regioisomers, 65:33.7). Anal. calcd (C19H18N2O2S) C,
H, N.
4.3. Compound 12
Yield 65%. Mp 183–185 ꢀC. IR (KBr) 3427, 2915, 1592,
1385, 1302 cmꢄ1. H NMR (CDCl3) d 8.42 (d, J=6.8
Hz, 2H), 7.78 (d, J=8.0 Hz, 2H), 7.56–7.35 (m, 4H), 7.00
(d, J=6.8 Hz, 2H), 3.85 (s, 3H), 3.07 (s, 3H). MS (CI
Method) 341 (M+H)+, 325, 231, 203, 151. HPLC
(Method 1) 97.9%. Anal. calcd (C18H16N2O3S) C, H, N.
1
4.10. Compound 19
Yield 64%. Mp 200–202 ꢀC. IR (KBr) 3425, 2917, 1730,
1
1575, 1442, 1362, 1310 cmꢄ1. H NMR (CDCl3) d 8.56
4.4. Compound 13
(d, J=8.0 Hz, 2H), 7.92–7.75 (m, 4H), 7.55–7.35 (m,
2H), 7.10–6.95 (m, 2H), 3.01 (s, 3H). MS (CI Method)
329 (M+H, 100%)+, 248, 192. HPLC (Method 1)
97.7%. Anal. calcd (C17H13FN2O2S) C, H, N.
Yield 72%. Mp 208–210 ꢀC. IR (KBr) 3422, 2921, 1609,
1512, 1437, 1311 cmꢄ1. H NMR (CDCl3) d 8.50 (d,
J=11.2 Hz, 1H), 7.91–7.87 (m, 2H), 7.69–7.63 (m, 2H),
7.37–7.26 (m, 2H), 6.86–6.82 (m, 2H), 3.81 (s, 3H), 3.04
(s, 3H), 2.66 (s, 3H). MS (CI Method) 355 (M+H)+,
275, 133. HPLC (Method 1) 98.2% (Mixt. of regio-
isomers, 60:38.2). Anal. calcd (C19H18N2O3S) C, H, N.
1
4.11. Compound 20
Yield 53%. Mp 210–212 ꢀC. IR (KBr) 3429, 2919, 1733,
1585, 1446, 1422, 1365, 1312 cmꢄ1. 1H NMR (CDCl3) d
8.56–8.54 (m, 1H), 7.92–7.87 (m, 2H), 7.68–7.61 (m, 2H),
7.26–7.18 (m, 2H), 7.10–7.02 (m, 2H), 3.01 (s, 3H), 2.70
(s, 3H). MS (CI Method) 343 (M+H)+, 262, 261, 194,
121, 102, 97. HPLC (Method 2) 99.0% (Mixt of regio-
isomers, 65:34). Anal. calcd (C18H15FN2O2S) C, H, N.
4.5. Compound 14
Yield 57%. Mp 142–144 ꢀC. IR (KBr) 3050, 2923, 1598,
1506, 1390, 1319 cmꢄ1. H NMR (CDCl3) d 8.67 (t,
J=8.1 Hz, 2H), 7.90 (d, J=8.3 Hz, 2H), 7.67 (d, J=8.3
1

S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
1889
4.12. Compound 33
the combined organic layer and evaporated. 25% aq
ammonia solution (5 mL) was slowly added to the vis-
cous mass maintained at 0–5 ꢀC and reaction mixture
stirred at room temperature for 10 min. The reaction
mixture was poured over ice-water and extracted with
ethyl acetate. The combined organic layer was washed
with water, dried and evaporated to get a solid mass
which upon trituration with ethyl acetate–petroleum
ether afforded a white solid (1.1 g, 40%). This product
was used in the next step without further purification.
Yield 65%. Mp 254–256 ꢀC. IR (KBr) 3442, 2359, 1347,
.
1301 cmꢄ1 1H NMR (CDCl3) d 8.25–8.17 (m, 2H),
7.95–7.73 (m, 3H), 7.70–7.51 (m, 3H), 7.52–7.40 (m,
2H), 7.37–7.27 (m, 3H), 3.07 (s, 3H). MS (CI Method)
361 (M+H, 100%)+, 281, 179, 151, 140. HPLC
(Method 1) 99.7%. Anal. calcd (C21H16N2O2S) C, H, N.
4.13. Compound 34
IR (KBr) 3315, 1669, 1597, 1343 cmꢄ1 1H NMR
.
Yield 72%. Mp 218–220 ꢀC. IR (KBr) 3440, 1614, 1154
cmꢄ1. 1H NMR (CDCl3) d 8.22–8.14 (m, 2H), 7.95–7.73
(m, 6H), 7.40–7.14 (m, 4H), 3.06 (s, 3H), 2.38 (s, 3H).
MS (CI Method) 375 (M+H)+, 359, 295, 280, 192, 178,
165, 116, 91. HPLC (Method 2) 99.2%. Anal. calcd
(C22H18N2O2S) C, H, N.
(DMSO-d6) d 8.18–8.11 (m, 2H), 7.77 (d, J=8.2 Hz,
2H), 7.46–7.39 (m, 4H), 4.53 (s, 2H). MS (EI Method)
294 (M+H)+, 277, 255, 229.
Step 3. Representative procedure for 4-[2-(4-fluoro-
phenyl)-2-oxoacetyl]-1-benzenesulfonamide 9 (R, F)
The title compound was obtained by the selenium dioxide
oxidation of the above prepared 4-[2-(4-fluorophenyl)-2-
oxoethyl]-1-benzenesulfonamide 8, following procedure
A, step 2, in 79% yield, and used in the next step with-
out further purification. IR (KBr) 3370, 3253, 1674,
4.14. Compound 36
Yield 66%. Mp 188–192 ꢀC. IR (KBr) 3438, 2923, 1604,
1514, 1475, 1419, 1302 cmꢄ1. 1H NMR (CDCl3) d 8.21–
8.13 (m, 2H), 7.94 (d, J=8.2 Hz, 2H), 7.82–7.74 (m,
4H), 7.66 (d, J=8.4 Hz, 2H), 6.88 (d, J=8.8 Hz, 2H),
3.84 (s, 3H), 3.06 (s, 3H), MS (CI Method) 391
(M+H)+, 376. HPLC (Method 1) 97.4%. Anal. calcd
(C22H18N2O3S) C, H, N.
1
1598 cmꢄ1. H NMR (DMSO-d6) d 8.17–8.01 (m, 6H),
7.48 (t, J=8.4 Hz, 2H). MS (CI Method) 308 (M+H)+,
291, 243, 215, 184.
Step 4. Representative procedure for 4-[6-(4-fluoro-
phenyl)-2,3-dihydro-5-pyrazinyl]-1-benzenesulfonamide
4.15. Compound 37
Yield 68%. Mp 158–160 ꢀC. IR (KBr) 3435, 2915, 1735,
The title compound was obtained by the condensation
of above prepared 4-[2-(4-fluorophenyl)-2-oxoacetyl]-1-
benzenesulfonamide 9 and ethylenediamine, using the
procedure A, step 4, in 68% yield, and used in the next
step without further purification. IR (KBr) 3322, 3044,
1
1577, 1445, 1365 cmꢄ1. H NMR (CDCl3) d 8.55 (d,
J=7.8 Hz, 2H), 7.88–7.76 (m, 6H), 7.45–7.38 (m, 2H),
7.05–6.90 (m, 2H), 3.02 (s, 3H). MS (CI Method) 379
(M+H, 100%)+, 364. HPLC (Method 2) 98.4%. Anal.
calcd (C21H15FN2O2S) C, H, N.
1598, 1506 cmꢄ1 1H NMR (DMSO-d6) d 7.74 (d,
.
J=8.4 Hz, 2H), 7.52 (d, J=8.4 Hz, 2H), 7.43–7.32 (m,
2H), 7.16 (t, J=8.8 Hz, 2H), 3.64 (s, 4H). MS (CI
Method) 332, (M+H)+, 315, 250, 183.
4.16. Procedure B. General preparation of sulfonamide
containing pyrazines 21–32 and quinoxalines 35, 38 and
39
Step 5. Representative procedure for 4-[3-(4-fluoro-
phenyl)-2-pyrazinyl]-1-benzenesulfonamide 25
Step 1. Representative procedure for 1-(4-fluorophenyl)-
2-phenyl-1-ethanone 7 (R, F)
The title compound was synthesized by the dehy-
drogenation of above prepared 4-[6-(4-fluorophenyl)-
2,3-dihydro-5-pyrazinyl]-1-benzenesulfonamide (Proce-
dure B, step 4) using general method described in pro-
cedure A, step 5. Yield 65%. Mp 178–180 ꢀC. IR (KBr)
The title compound was prepared in 71% yield using
fluorobenzene and phenylacetyl chloride following the
general method described above (Procedure A, step 1),
and was used in the next step without further purifica-
1
tion. IR (KBr) 3361, 1689, 1598, 1452 cmꢄ1. H NMR
3381, 2926, 2361, 1726, 1601, 1511, 1389 cmꢄ1 1H
.
(CDCl3) d 8.07–8.00 (m, 2H), 7.44–7.26 (m, 5H), 7.12 (t,
J=8.8 Hz, 2H), 4.26 (s, 2H), 3.06 (s, 3H). MS (EI
Method) 215 (M+H)+, 183, 165, 136.
NMR (CDCl3) d 8.66 (d, J=2.4 Hz, 2H), 7.88 (d,
J=8.2 Hz, 2H), 7.60 (d, J=6.6 Hz, 2H), 7.45–7.39 (m,
2H), 7.08 (t, J=3.9 Hz, 2H), 4.98 (bs, 2H). MS (CI
Method) 330 (M+H)+. HPLC (Method 1) 98.9%.
Anal. calcd (C16H12FN3O2S) C, H, N.
Step 2. Representative procedure for 4-[2-(4-fluoro-
phenyl)-2-oxoethyl]-1-benzenesulfonamide 8 (R, F)
4.17. Compound 21
1-(4-Fluorophenyl)-2-phenyl-1-ethanone 7 (2.0 g, 9.34
mmol), prepared above (Procedure B, step 1), was dis-
solved in dichloromethane (20 mL) and cooled to 0–
5 ꢀC. Chlorosulfonic acid (3.8 g, 32.7 mmol) was slowly
added and the reaction mixture was allowed to stir at
room temperature for 15 h. Poured the reaction mixture
over ice-water, extracted with dichloromethane, dried
Yield 61%. Mp 222–224 ꢀC. IR (KBr) 3365, 2924, 1609,
1
1389, 1325 cmꢄ1. H NMR (CDCl3) d 8.61 (d, J=4.8
Hz, 2H), 7.86 (d, J=8.2 Hz, 2H), 7.58 (d, J=8.4 Hz,
2H), 7.34 (d, J=2.6 Hz, 2H), 7.12 (d, J=7.8 Hz, 2H),
6.2 (bs, 2H), 2.36 (s, 3H). MS (CI Method) 326
(M+H)+, 310 (100%), 245, 230, 218, 189, 176, 117, 91.

1890
S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
HPLC (Method 1) 97.8%. Anal. calcd (C17H15N3O2S)
C, H, N.
245, 231, 147, 132, 102. HPLC (Method 2) 97.9%. Anal.
calcd (C18H17N3O3S) C, H, N.
4.18. Compound 22
4.24. Compound 29
Yield 67%. Mp 180–182 ꢀC. IR (KBr) 3349, 1728, 1612,
Yield 66%. Mp 216–218 ꢀC. IR (KBr) 3316, 2924, 1607,
1
1
1554, 1437, 1337 cmꢄ1. H NMR (CDCl3) d 8.50 (d,
1505, 1438, 1345 cmꢄ1. H NMR (DMSO-d6) d 8.57 (d,
J=8.7 Hz, 1H), 7.85–7.80 (m, 2H), 7.61–7.55 (m, 2H),
7.30–7.24 (m, 2H), 7.13–7.09 (m, 2H), 4.94 (bs, 2H),
2.67 (s, 3H), 2.34 (s, 3H). MS (CI Method) 340
(M+H)+, 324, 259, 244, 189, 117, 91. HPLC (Method
1) 97.9% (Mixture of regioisomers, 60.1:37.8). Anal.
calcd (C18H17N3O2S) C, H, N.
J=5.8 Hz, 1H), 7.77 (d, J=7.8 Hz, 2H), 7.57 (d, J=7.8
Hz, 2H), 7.41 (bs, 2H), 7.32 (s, 1H), 7.06 (d, J=8.3 Hz,
1H), 6.84 (d, J=8.1 Hz, 1H), 3.77 (s, 3H), 2.59 (s, 3H),
2.11 (s, 3H). MS (CI Method) 370 (M+H)+, 369, 354,
289, 274, 245, 132, 104, 91. HPLC (Method 1) 99.8%
(Mixt. of regioisomers, 63.5:36.3). Anal. calcd
(C19H19N3O3S) C, H, N.
4.19. Compound 23
4.25. Compound 30
Yield 51%. Mp 174–176 ꢀC. IR (KBr) 3430, 1607, 1514,
1344 cmꢄ1. H NMR (DMSO-d6) d 8.73–8.68 (m, 2H),
Yield 49%. Mp 140–142 ꢀC. IR (KBr) 3386, 3270, 1382,
1
1
7.78 (d, J=8.3 Hz, 2H), 7.59 (d, J=8.3 Hz, 2H), 7.43 (s,
2H), 7.36 (d, J=8.3 Hz, 2H), 6.91 (d, J=8.7 Hz, 2H),
3.76 (s, 3H). MS (CI Method) 342 (M+H)+, 325, 315,
261, 207, 133. HPLC (Method 2) 99.3%. Anal. calcd
(C17H15N3O3S) C, H, N.
1336 cmꢄ1. H NMR (CDCl3) d 8.72 (s, 2H), 7.77 (d,
J=7.8 Hz, 2H), 7.59 (d, J=7.8 Hz, 2H), 7.40 (s, 1H),
7.14 (d, J=7.8 Hz, 1H), 7.02 (d, J=7.2 Hz, 1H), 2.84
(m, 4H), 2.05 (m, 2H). MS (CI Method) 352 (M+H)+,
335, 323, 270. HPLC (Method 1) 97.5%. Anal. calcd
(C19H17N3O2S) C, H, N.
4.20. Compound 24
4.26. Compound 31
Yield 58%. Mp 142–144 ꢀC. IR (KBr) 3366, 3064, 1655,
1609, 1513, 1342 cmꢄ1. H NMR (CDCl3) d 8.49 (d,
Yield 65%. Mp 160–162 ꢀC. IR (KBr) 3286, 1703, 1612,
1
1
J=10.7 Hz, 1H), 7.82 (d, J=6.8 Hz, 2H), 7.61–7.55 (m,
2H), 7.36–7.26 (m, 2H), 6.83 (d, J=7.8 Hz, 2H), 5.05 (s,
2H), 3.80 (s, 3H), 2.67 (s, 3H). MS (CI Method) 356
(M+H)+, 339, 173. HPLC (Method 2) 98.9% (Mixture
of regioisomers, 65.1:33.8). Anal. calcd (C18H17N3O3S)
C, H, N.
1496 cmꢄ1. H NMR (CDCl3) d 8.68 (d, J=3.0 Hz,
2H), 7.79 (d, J=8.4 Hz, 2H), 7.60 (d, J=8.4 Hz,
2H), 7.41 (s, 1H), 7.02 (d, J=8.4 Hz, 1H), 6.67 (d,
J=8.4 Hz, 1H), 4.56 (t, J=8.4 Hz, 2H), 3.19 (t, J=8.8
Hz, 2H). MS (CI Method) 353 (M+), 272, 243, 145.
HPLC (Method 1) 97.4%. Anal. calcd (C18H15N3O3S)
C, H, N.
4.21. Compound 26
4.27. Compound 32
Yield 62%. Mp 92–94 ꢀC. IR (KBr) 3428, 1621, 1336
cmꢄ1. H NMR (CDCl3) d 8.66 (s, 2H), 7.88 (d, J=8.4
Yield 42%. Mp 85–87 ꢀC. IR (KBr) 3293, 1608, 1495,
1
1
Hz, 2H), 7.57 (d, J=7.2 Hz, 2H), 7.40 (d, J=8.4 Hz,
2H), 7.31 (d, J=8.8 Hz, 2H), 3.85 (bs, 2H). MS (CI
Method) 346 (M+H)+, 313, 252, 217, 190, 180, 153.
1446 cmꢄ1. H NMR (CDCl3) d 8.56 (d, J=5.0 Hz,
1H), 7.77 (d, J=8.2 Hz, 2H), 7.57 (d, J=8.4 Hz, 2H),
7.4 (s, 1H), 7.98 (d, J=8.2 Hz, 1H), 6.65 (d, J=8.4 Hz,
1H), 4.55 (t, J=8.8 Hz, 2H), 3.14 (t, J=8.8 Hz, 2H),
2.58 (s, 3H). MS (CI Method) 368 (M+H)+, 353.
HPLC (Method 1) 99.3% (Mixt. of regioisomers,
65.1:34.2). Anal. calcd (C19H17N3O3S) C, H, N.
HPLC
(Method
(C16H12ClN3O2S) C, H, N.
2)
99.6%.
Anal.
calcd
4.22. Compound 27
Yield 59%. Mp 210–212 ꢀC. IR (KBr) 3440, 2360, 1631,
4.28. Compound 35
1
1325 cmꢄ1. H NMR (CDCl3) d 8.66 (s, 2H), 7.88 (d,
J=8.4 Hz, 2H), 7.57 (d, J=7.2 Hz, 2H), 7.40 (d, J=8.4
Hz, 2H), 7.31 (d, J=8.8 Hz, 2H), 3.85 (bs, 2H). MS (CI
Method) 392 (M+2, 100%)+, 390, 312, 180, 153, 91.
Yield 52%. Mp 220–222 ꢀC. IR (KBr) 3356, 3034, 1612,
1
1345, 1162 cmꢄ1. H NMR (DMSO-d6) d 8.20–8.15 (m,
2H), 7.91–7.88 (m, 3H), 7.81 (d, J=8.3 Hz, 2H), 7.69 (d,
J=8.3 Hz, 2H), 7.40–7.38 (m, 3H), 7.20 (d, J=7.8 Hz,
2H), 2.34 (s, 3H). MS (CI Method) 376 (M+H)+, 360,
339, 295, 259, 192, 165, 112. HPLC (Method 1) 97.7%.
Anal. calcd (C21H17N3O2S) C, H, N.
HPLC
(Method
(C16H12BrN3O2S) C, H, N.
2)
98.9%.
Anal.
calcd
4.23. Compound 28
Yield 68%. Mp 238–240 ꢀC. IR (KBr) 3374, 1605, 1505,
4.29. Compound 38
1
1422, 1376, 1344 cmꢄ1. H NMR (DMSO-d6) d 8.69 (d,
J=4.3 Hz, 2H), 7.79 (d, J=8.3 Hz, 2H), 7.59 (d, J=8.3
Hz, 2H), 7.44 (bs, 2H), 7.33 (s, 1H), 7.10 (d, J=6.8 Hz,
1H), 6.87 (d, J=6.8 Hz, 1H), 3.78 (s, 3H), 2.11 (s, 3H).
MS (CI Method) 356 (M+H)+, 355, 340, 308, 275, 260,
Yield 70%. Mp 202–204 ꢀC. IR (KBr) 3341, 3256, 2927,
.
1731, 1602, 1504, 1440, 1341, 1315 cmꢄ1 1H NMR
(DMSO-d6) d 8.17–8.13 (m, 2H), 7.90–7.86 (m, 2H),
7.82 (d, J=8.7 Hz, 2H), 7.69 (d, J=8.3 Hz, 2H), 7.45 (s,

S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
1891
2H), 7.19 (d, J=8.7 Hz, 2H), 6.89 (d, J=8.7 Hz, 1H),
3.80 (s, 3H), 2.14 (s, 3H). MS (EI Method) 406
(M+H)+, 391, 376. HPLC (Method 1) 97.9%. Anal.
calcd (C22H19N3O3S) C, H, N.
231, 183, 103. HPLC (Method 1) 97.6%. Anal. calcd
(C17H18N2O2S) C, H, N.
4.32. Compound 43
Yield 52%. Mp 143–145 ꢀC. IR (KBr) 3440, 1695, 1560,
4.30. Compound 39
1
1345 cmꢄ1. H NMR (CDCl3) d 7.95 (d, J=8.0 Hz,
Yield 68%. Mp 134–136 ꢀC. IR (KBr) 3221, 1557, 1324,
2H), 7.77 (d, J=7.8 Hz, 2H), 7.50 (bs, 3H), 7.26–7.14
(m, 3H), 6.82 (d, J=7.6 Hz, 2H), 3.85 (s, 3H), 3.75 (s,
4H). MS (CI Method) 345 (M+), 223, 181, 103. HPLC
(Method 1) 98.8%. Anal. calcd (C17H19N3O3S) C, H, N.
1
1163 cmꢄ1. H NMR (CDCl3) d 8.16 (m, 2H), 7.90 (d,
J=8.4 Hz, 2H), 7.78 (m, 2H), 7.69 (d, J=8.4 Hz, 2H),
7.51 (s, 1H), 7.11 (m, 2H), 2.92 (t, J=7.4 Hz, 4H), 2.10
(t, J=7.4 Hz, 2H). MS (EI Method) 401(M+), 321, 254,
218. HPLC (Method 2) 98.9%. Anal. calcd
(C23H19N3O2S) C, H, N.
4.33. Compound 44
Yield 61%. Mp 248–250 ꢀC. IR (KBr) 3399, 1605, 1484,
1
1454, 1319 cmꢄ1. H NMR (CDCl3) d 8.12 (d, J=8.8
4.31. Procedure C. General preparation of methylsulfo-
nyl and sulfonamide containing tetrahydropyrazines 40
and 43, and dihydroquinoxalines 44 and 47
Hz, 2H), 7.93 (d, J=8.4 Hz, 2H), 7.47 (d, J=7.8 Hz,
1H), 7.27–7.20 (m, 5H), 7.03 (t, J=6.8 Hz, 1H), 6.80 (t,
J=6.6 Hz, 1H), 6.50 (d, J=7.8 Hz, 1H), 4.45 (bs, 1H),
3.02 (s, 3H). MS (CI Method) 362 (M+), 285, 281, 207,
179, 152, 140, 127, 102. HPLC (Method 1) 99.2%. Anal.
calcd (C21H18N2O2S) C, H, N.
Step 1. Representative preparation of (2RS)-2-bromo-1-
(4-methylsulfonylphenyl)-2-phenyl-1-ethanone 6 (Ar, Ph)
The corresponding 1-(4-methylsulfonylphenyl)-2-phenyl-
1-ethanone 4 (3.0 g, 10.95 mmol), obtained in two steps
by the Friedel–Crafts acylation of thioanisole using
phenyl acetyl chloride followed by the H2O2 oxidation
(Procedure A, step 1 and 3), was dissolved in dichloro-
methane (50 mL). Glacial acetic acid (3 mL) and HBr
(0.5 mL) was added to this stirred solution at room
temperature and cooled to 0–5 ꢀC. Liquid bromine (0.51
mL, 9.85 mmol) was slowly introduced and the reaction
mixture was allowed to stir at room temperature for 4–5
h. After pouring the reaction mixture to ice-water mix-
ture, it was extracted with dichloromethane and the
combined organic layer was washed with water. The
dried layer on evaporation afforded a gummy mass
which on purification by column chromatography using
ethyl acetate–petroleum ether (3%) afforded viscous
liquid of the title compound (1.5 g, 39%) which was
used in the next step without further purification. IR
4.34. Compound 47
Yield 68%. Mp 233–235 ꢀC. IR (KBr) 3430, 1610, 1510,
1
1422, 1325 cmꢄ1. H NMR (CDCl3) d 8.10 (d, J=8.0
Hz, 2H), 7.90 (d, J=8.0 Hz, 2H), 7.40–7.20 (m, 6H),
7.10 (bs, 2H), 6.95 (t, J=6.6 Hz, 1H), 6.80 (d, J=7.6
Hz, 2H), 3.82 (s, 3H). MS (CI Method) 394 (M+H)+,
378, 215, 205, 159. HPLC (Method 1) 98.6%. Anal.
calcd (C21H19N3O3S) C, H, N.
4.35. Representative procedure for (2RS)-1-[3-(4-methyl-
sulfonylphenyl)-2-phenyl-1,2-dihydro-1-quinoxalinyl]-1-
ethanone 45
Triethyl amine (231 mL, 1.65 mmol) was added to the
solution of 3-(4-methylsulfonylphenyl)-2-phenyl-1,2-
dihydroquinoxaline 44 (400 mg, 1.10 mmol), prepared
above (Procedure C, Step 2), in dichloromethane (20
mL). Acetic anhydride (167 mL, 1.64 mmol) was slowly
added at room temperature and the reaction mixture
was refluxed overnight. After pouring the reaction mix-
ture to ice-water, it was extracted with dichloromethane.
The combined organic layer was washed with water,
dried and evaporated to get a gummy mass which on
column purification using ethyl acetate–petroleum ether
(25%) afforded a white solid of the titled compound
(250 mg, 56%). Mp 238–240 ꢀC. IR (KBr) 3431, 2920,
(KBr) 3434, 1713, 1395, 1300 cmꢄ1
.
1H NMR
(CDCl3) d 8.17 (d, J=7.8 Hz, 2H), 8.04 (d, J=8.4 Hz,
2H), 7.49–7.40 (m, 2H), 7.39–7.20 (m, 3H), 6.32 (s,
1H), 3.06 (s, 3H). MS (CI Method) 353 (M+), 275,
183, 121.
Step 2. Representative procedure for (6RS)-5-(4-methyl-
sulfonylphenyl)-6-phenyl-1,2,3,6-tetrahydropyrazine 40
Ethylenediamine (0.21 mL, 3.23 mmol) was drop-wise
introduced to the solution of above prepared 2-bromo-
1-(4-methylsulfonylphenyl)-2-phenyl-1-ethanone 6 (1.2
g, 3.4 mmol) in methanol (10 mL) and allowed to stir
for 24 h at room temperature. After pouring to ice-
water, the content was extracted with ethyl acetate, and
the combined organic layer after washing with water
was dried and evaporated to get a gummy mass which
after trituration with dichloromethane–petroleum ether
afforded a white solid of the title compound (410 mg,
38%). Mp 164–166 ꢀC. IR (KBr) 3415, 1688, 1575,
1662, 1611, 1478, 1320 cmꢄ1. H NMR (CDCl3) d 8.27
1
(d, J=8.2 Hz, 2H), 8.02 (d, J=8.8 Hz, 2H), 7.64 (d,
J=7.4 Hz, 1H), 7.31–7.10 (m, 5H), 7.05–7.00 (m, 4H),
3.06 (s, 3H), 2.40 (s, 3H). MS (CI Method) 404 (M+),
361, 285, 282, 207, 180, 152, 104. HPLC (Method 1)
97.6%. Anal. calcd (C23H20N2O3S) C, H, N.
4.36. Compound 46
Yield 63%. Mp 152–154 ꢀC. IR (KBr) 3432, 2923, 1689,
1
1
1360, 1312 cmꢄ1. H NMR (CDCl3) d 7.85 (d, J=8.2
1485, 1322 cmꢄ1. H NMR (CDCl3) d 8.26 (d, J=8.2
Hz, 2H), 8.05 (d, J=8.2 Hz, 2H), 7.66 (d, J=7.2 Hz,
1H), 7.42–7.10 (m, 5H), 7.05–7.00 (m, 4H), 3.07 (s, 3H).
Hz, 2H), 7.61 (d, J=8.2 Hz, 2H), 7.33–7.26 (m, 6H),
3.71 (s, 4H), 3.02 (s, 3H). MS (CI Method) 314 (M+),

1892
S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
MS (CI Method) 458 (M+), 389, 381, 361, 282, 205,
178, 152. HPLC (Method 1) 97.3%. Anal. calcd
(C23H17F3N2O3S) C, H, N.
4.41. In-vitro biochemical assay. Spectrophotometric
assay for COX-1 and COX-2 inhibition24
Microsomal fraction of ram seminal vesicles were used
as a source of COX-1 enzyme, and microsomes from
sf-9 cells infected with baculovirus containing human
COX-2 c-DNA were used as a source of COX-2 enzy-
me.24a Enzyme activity was measured using a chromo-
genic assay based on oxidation of N,N,N0,N0-
tetramethyl-p-phenylenediamine (TMPD) during the
reduction of PGG2 to PGH2. The assay mixture (1000
mL) contained 100 mM Tris pH 8.0, 3 mM EDTA, 15
mM hematin, 150 units of enzyme and 8% DMSO. The
mixture was preincubated at 25 ꢀC for 15 min before
initiation of enzymatic reaction in presence of com-
pound/vehicle. The reaction was initiated by the addi-
tion of 100 mM arachidonic acid and 120 mM TMPD.
The enzyme activity was measured by estimation of the
initial velocity of TMPD oxidation over the first 25 s of
the reaction followed by tracking the increase in absor-
bance at 603 nM. The IC50 values were calculated using
nonlinear regression analysis.24b
4.37. Compound 41
Yield 46%. Mp 180–182 ꢀC. IR (KBr) 3320, 2925, 1675,
1
1465, 1319 cmꢄ1. H NMR (CDCl3) d 8.24 (d, J=8.0
Hz, 2H), 8.01 (d, J=8.0 Hz, 2H), 7.66–7.32 (m, 6H),
3.90 (s, 4H), 3.08 (s, 3H), 2.42 (s, 3H). MS (CI Method)
356 (M+), 313, 280, 203, 175, 151. HPLC (Method 1)
99.3%. Anal. calcd (C19H20N2O3S) C, H, N.
4.38. Compound 42
Yield 55%. Mp 149–152 ꢀC. IR (KBr) 3345, 2935, 1685,
1
1475, 1325 cmꢄ1. H NMR (CDCl3) d 8.44 (d, J=8.4
Hz, 2H), 8.10 (d, J=8.4 Hz, 2H), 7.70–7.45 (m, 6H),
3.98 (s, 4H), 3.10 (s, 3H). MS (CI Method) 410 (M+),
313, 281, 151. HPLC (Method 2) 98.1%. Anal. calcd
(C19H17F3N2O3S) C, H, N.
4.39. N1-Propionyl-4-[3-(4-fluorophenyl)-2-pyrazinyl]-1-
benzenesulfonamide 48
4.42. In vivo screening method. Carrageenan-induced rat
paw edema25
A mixture of 4-[3-(4-fluoro phenyl)-2-pyrazinyl]-1-ben-
zene sulfonamide 25 (2.0 g, 6.07 mmol), triethylamine
(2.1 mL, 15.19 mmol) and propionic anhydride (1.18
mL, 9.10 mmol), dissolved in dichloromethane (30 mL),
was refluxed for 12 h. The cooled reaction mixture was
poured over ice-water, acidified with dil. HCl and
extracted with dichloromethane. The combined organic
layer was washed with water, dried and evaporated to
get a gummy mass which after column purification
using ethyl acetate–petroleum ether (15%) afforded a
white solid of the title compound (1.5 g, 65%). Mp 100–
102 ꢀC. IR (KBr) 3250, 1724, 1601, 1501, 1413, 1344,
Male Wistar rats (120–140 g) were fasted for 16 h before
the experiment. Compounds were suspended in 0.25%
carboxymethylcellulose (CMC) and administered orally
in a volume of 10 mL/kg, 2 h before carrageenan injec-
tion. Paw edema was induced in rats by intradermal
injection of 50 mL of 1% l-carrageenan in saline into
the plantar surface of the right hind paw. Paw volume
was measured 3 h before and after carrageenan injection
by plethysmometer (Ugo-Basile, Italy). Paw edema was
compared with the vehicle control group and percent
inhibition was calculated.
1
1159 cmꢄ1. H NMR (CDCl3) d 8.65 (d, J=4.0 Hz,
2H), 8.19 (bs, 1H), 8.02 (d, J=8.7 Hz, 2H), 7.63 (d,
J=8.7 Hz, 2H), 7.45–7.38 (m, 2H), 7.00 (t, J=8.7 Hz,
2H), 2.35–2.22 (m, 2H), 1.10 (t, J=7.3 Hz, 3H). MS 386
(M+H)+, 333 (100%). HPLC (Method 2) 99.5%.
Anal. calcd (C19H16FN3O3S) C, H, N.
4.43. Molecular modeling
Energies of the diarylpyrazines 24 (regioisomers, a and
b) and 25 were minimized using the MMFF94 force
field and charges in SYBYL 6.9.28 A co-crystal structure
of COX-2 with the selective ligand SC-55817 (PDB:
6COX)29 was used for docking. ‘Two-Stage Docking
Method for Protein-Ligand Docking’ as described by
Hoffmann et al.,30 was adopted. FlexX31 docked all the
ligands including SC-558 in the same binding pocket as
reported in the crystal structure. The best conforma-
tions, generated by FlexX based on CScore and Total
Score, were selected and merged into the 6COX crystal
structure to carry out the minimization. The energy-
minimized complexes were analyzed for ligand-receptor
interactions in the active site.
4.40. Sodium salt of N1-propionyl-4-[3-(4-fluorophenyl)-
2-pyrazinyl]-1-benzenesulfonamide 49
Powdered NaHCO3 (310 mg, 3.69 mmol) was added to
a stirred solution of N1 propionyl-4-[3-(4-fluorophenyl)-
2-pyrazinyl]-1-benzenesulfonamide 48 (1.5 g, 3.89
mmol) in methanol (10 mL) at 0–5 ꢀC. The reaction
mixture was stirred for 5 h at room temperature. Sol-
vent was evaporated completely to get a gummy mass
which on trituration with ethyl acetate–petroleum ether
afforded a white solid of the title compound (1.12 g,
75%). Mp 260–262 ꢀC. IR (KBr) 3460, 2935, 1720,
1
1625, 1522 cmꢄ1. H NMR (CDCl3) d 8.6 (s, 2H), 7.99
Acknowledgements
(d, J=8.3 Hz, 2H), 7.39–7.38 (m, 4H), 7.00 (t, J=8.3
Hz, 2H), 2.20 (q, J=7.3 Hz, 2H), 1.06 (t, J=7.3 Hz,
3H). MS 385 (M-22)+, 322, 277, 266, 183, 102. HPLC
(Method 2) 98.7%. Anal. calcd (C19H17FN3O4SNa) C,
H, N.
The authors are thankful to Drs. K. Anji Reddy, A.
Venkateswarlu, R. Rajagopalan and Prof. J. Iqbal for
their constant support and encouragement, and to
Analytical Research group, DRL, for spectral analysis.

S. K. Singh et al. / Bioorg. Med. Chem. 12 (2004) 1881–1893
1893
References and notes
Higuchi, S.; Otomo, S. Prostaglandins 1994, 47, 55. (b)
Huff, R.; Collins, P.; Kramer, S.; Seibert, K.; Koboldt, C.;
Gregory, S.; Isakson, P. A. Inflammation. Res. 1995, 44,
S145.
1. (a) Xie, W.; Chipman, J. G.; Robertson, D. L.; Erikson,
R. L.; Simmons, D. L. Proc. Natl. Acad. Sci. U.S.A. 1991,
88, 2692. (b) Hla, T.; Neilson, K. Proc. Natl. Acad. Sci.
U.S.A. 1992, 89, 7384. (c) Kujubu, D. A.; Fletcher, B. S.;
Varnum, B. C.; Lim, R. W.; Herschman, H. R. J. Biol.
Chem. 1991, 266, 12866. (d) Vane, J. R.; Bakhle, Y. S.;
Botting, R. M. Annu. Rev. Pharmacol. Toxicol. 1998, 38,
97.
17. Kurumbail, R. G.; Stevens, A. M.; Gierse, J. K.;
McDonald, J. J.; Stegeman, R. A.; Pak, J. Y.; Gildehaus,
D.; Miyashiro, J. M.; Penning, T. D.; Seibert, K.; Isakson,
P. C.; Stallings, W. C. Nature 1996, 384, 644.
18. Dannhardt, G.; Laufer, S. Curr. Med. Chem. 2000, 7,
1101 and references cited therein.
2. Wallace, J. L. Am. J. Med. 1999, 107, 11 S.
19. Rao, N. V. S. M.; Ramesh, M.; Jagannath, K.; Ravi-
kanth, B.; Ansar, A. K.; Kasiram, K.; Srinivasaraju, D.;
Singh, S. K.; Rao, Y. K.; Rao, S. C.; Srinivas, N. R.;
Ramanujam, R. Biopharm. Drug Disp. 2002, 23, 273.
20. BenEzra, D. Ocular Inflammation: Basic and Clinical
Concepts; Martin Dunitz: London, 1999, 523.
21. (a) Almansa, C.; Alfon, J.; de Arriba, A. F.; Cavalcanti,
F. L.; Escamilla, I.; Gomez, L. A.; Miralles, A.; Soliva,
R.; Bartroli, J.; Carceller, E.; Merlos, M.; Rafanell, J. G.
J. Med. Chem. 2003, 46, 3463. (b) Joo, Y. H.; Kim, J. K.;
Kang, S. H.; Noh, M. S.; Ha, J. Y.; Chio, J. K.; Lim,
K. M.; Lee, C. H.; Chung, S. Bioorg. Med. Chem. Lett.
2003, 13, 413. (c) Li, C. S.; Brideau, C.; Chan, C. C.;
Savoie, C.; Claveau, D.; Charleson, S.; Gordon, R.;
Greig, G.; Gauthier, J. Y.; Lau, C. K.; Riendeau, D.;
Therien, M.; Wong, E.; Prasit, P. Bioorg. Med. Chem.
Lett. 2003, 13, 597. (d) Praveen, R. P. N.; Amini, M.; Li,
H.; Habeeb, G.; Knaus, E. E. Bioorg. Med. Chem. Lett.
2003, 13, 2205.
3. (a) Schafer, A. I. J. Clin. Pharmacol. 1995, 35, 209. (b)
Clive, D. M.; Stoff, J. S. N. Engl. J. Med. 1984, 310, 563.
4. (a) Allison, M. C.; Howatson, A. G.; Torrance, C. J.; Lee,
F. D.; Russel, R. I. G. N. Engl. J. Med. 1992, 327, 749. (b)
Meyer-irchrath, J.; Schror, K. Curr. Med. Chem. 2000, 7,
1121 and references cited therein.
5. (a) DeWitt, D. L. Mol. Pharmacol. 1999, 55, 625. (b)
Kalgutkar, A. S.; Zhao, Z. Curr. Drug. Targets 2001, 2,
79.
6. Griswold, D. E.; Adams, J. L. Med. Res. Rev. 1996, 16,
181.
7. Penning, T. D.; Talley, J. J.; Bertenshaw, S. R.; Carter,
J. S.; Collins, P. W.; Docter, S.; Granto, 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.; Cog-
burn, J. N.; Gregory, S. A.; Koboldt, C. M.; Perkins,
W. E.; Seibert, K.; Veenhuizen, A. M.; Zhang, Y. Y.;
Isakson, P. C. J. Med. Chem. 1997, 40, 1347.
8. Prasit, P.; Wang, Z.; Brideau, C.; Chan, C.-C.; Charleson, S.;
Cromlish, W.; Either, D.; Evans, J. F.; Ford-Hutchinson,
A. W.; Gauthier, J. Y.; Gordon, R.; Guay, J.; Gresser,
M.; Kargman, S.; Kennedy, B.; Leblanc, Y.; Leger, S.;
Mancini, J.; O’Neil, G. P.; Ouellet, M.; Percival, M. D.;
Perrier, H.; Riendeau, D.; Rodger, I.; Tagari, P.; Therien,
M.; Vickers, P.; Wong, E.; Xu, L.-J.; Young, R. N.;
Zamboni, R.; Boyce, S.; Rupniak, N.; Forrest, M.; Visco,
D.; Patrick, D. Bioorg. Med. Chem. Lett. 1999, 9, 1773.
9. Talley, J. J.; Brown, D. L.; Carter, J. S.; Graneto, M. J.;
Koboldt, C. M.; Masferrer, J. L.; Perkins, W. E.; Rogers,
R. S.; Shaffer, A. F.; Zhang, Y. Y.; Zweifel, B. S.; Seibert,
K. J. Med. Chem. 2000, 43, 775.
10. Talley, J. J.; Bertenshaw, S. R.; Brown, D. L.; Carter, J. S.;
Graneto, M. J.; Kellogg, M. S.; Koboltd, C. M.; Yuan, J.;
Zhang, Y. Y.; Seibert, K. J. Med. Chem. 2000, 43, 1661.
11. (a) Riendeau, D.; Percival, M. D.; Brideau, C.; Charleson,
S.; Dube, D.; Ethier, D.; Falgueyret, J.-P.; Friesen, R. W.;
Gordon, R.; Greig, G.; Guay, J.; Mancini, J.; Ouellet, M.;
Wong, E.; Xu, L.; Boyce, S.; Visco, D.; Girard, Y.; Prasit,
P.; Zamboni, R.; Rodger, I. W.; Gresser, M.; Ford-
Hutchinson, A. W.; Young, R. N.; Chan, C. C. J. Phar-
macol. Exp. Ther. 2001, 296, 558. (b) Sorbera, L. A.;
Castaner, R. M.; Silvestre, J.; Castaner, J. Drugs Fut.
2001, 26, 346.
22. Singh, S. K.; Reddy, P. G.; Rao, K. S.; Lohray, B. B.;
Misra, P.; Rajjak, S. A.; Rao, Y. K.; Venkateswarlu, A.
Bioorg. Med. Chem. Lett. 2004, 14, 499.
23. (a) Li, J. J.; Norton, M. B.; Reinhard, E. J.; Anderson,
G. D.; Gregory, S. A.; Isakson, P. C.; Koboldt, C. M.;
Masferrer, J. L.; Perkins, W. E.; Seibert, K.; Zhang, Y.;
Zweifel, B. S.; Reitz, D. B. J. Med. Chem. 1996, 39, 1846.
(b) Pinto, D. J. P.; Batt, D. G.; Pitts, W. J.; Petraitis, J. J.;
Orwat, M. J.; Wang, S.; Jetter, J. W.; Sherk, S. R.;
Houghton, G. C.; Copeland, R. A.; Covington, M. B.;
Trzaskos, J. M.; Magolda, R. L. Bioorg. Med. Chem. Lett.
1999, 9, 919.
24. (a) Cromlish, W. A.; Payette, P.; Culp, S. A.; Ouellet, M.;
Percival, M. D.; Kennedy, B. P. Archives of Biochemistry
and Biophysics 1994, 314, 193. (b) Chan, C. C.; Boyce, S.;
Brideau, C.; Charleson, S.; Cromlish, W.; Ethier, D.; Evans,
J.; Ford-Hutchinson, A. W.; Forrest, M. J.; Gauthier,
J. Y.; Gordon, R.; Gresser, M.; Guay, J.; Kargman, S.;
Kennedy, B.; Leblanc, Y.; Leger, S.; Mancini, J.; O’Neill,
G. P.; Ouellet, M.; Patrick, D.; Percival, M. D.; Perrier,
H.; Prasit, P.; Rodger, I.; Tagari, P.; Therien, M.; Vickers,
P.; Visco, D.; Wang, Z.; Webb, J.; Wong, E.; Xu, L. J.;
Young, R. N.; Zamboni, R.; Riendeau, D. J. Pharmacol.
Exp. Ther. 1999, 290, 551.
25. Winter, C. A.; Risley, E. A.; Nuss, G. W. Pro. Soc. Exp.
Biol. Med. 1962, 111, 544.
12. (a) Giercksky, K. E. Best Practice & Res. Clin. Gastro-
enterology 2001, 15, 821. (b) Vainio, H. (General Review).
Int. J. Cancer, 2001, 94, 613 (c) Subbaramaiah, K.;
Norton, L.; Gerald, W.; Dannenberg, A. J. J. Biol. Chem.
2002, 277, 18649. (d) Niki, T.; Kohno, T.; Iba, S.; Moriya,
Y.; Takahashi, Y.; Saito, M.; Maeshima, A.; Yamada, T.;
Matsuno, Y.; Fukayama, M.; Yokota, J.; Hirohashi, S.
Am. J. Pathology 2002, 160, 1129.
26. Iwasaki, K.; Shiraga, T.; Matsuda, H.; Nagase, K.;
Tokuma, Y.; Hata, T.; Fujii, Y.; Sakuma, S.; Fujitsu, T.;
Fujikawa, A. J. Pharmacol. Exp. Ther. 1995, 23, 28.
27. Park, B. K.; Kitteringham, N. R.; O’Neill, P. M. Ann.
Rev. Pharmacol. Toxicol. 2001, 41, 443.
28. SYBYL 6.9. Molecular Modelling Software, Tripos
Associates Inc; St. Louis, MO 63144.
13. Pasinetti, G. M. J. Neurosci. Res. 1998, 54, 1.
14. Mukherjee, D.; Nissen, S. E.; Topol, E. J. J. Am. Med.
Assoc. 2001, 286, 954.
29. Berman, H. M.; Westbrook, J.; Feng, Z.; Gilliland, G.;
Bhat, T. N.; Weissig, H.; Shindyalov, I. N.; Bourne, P. E.
Nucleic Acids Res. 2000, 28, 235.
15. (a) Xavier, R. Drugs Today 1996, 32, 365. (b) Cignarella,
G.; Vianello, P.; Berti, F.; Rossoni, G. Eur. J. Med. Chem.
1996, 31, 359.
30. Hoffmann, D.; Kramer, B.; Washio, T.; Steinmetzer, T.;
Rarey, M.; Lengauer, T. J. Med. Chem. 1999, 42, 4422.
31. Rarey, M.; Kramer, B.; Lengauer, T.; Klebe, G. J. Mol.
Biol. 1996, 261, 470.
16. (a) Futaki, N.; Takahashi, S.; Yokoyama, M.; Arai, I.;