4-[5-Methyl-3-phenylisoxazol-4-yl]-benzenesulfonamide, Valdecoxib: A potent and selective inhibitor of COX-2 [4]

Full text of DOI:10.1021/jm990577v

J . Med. Chem. 2000, 43, 775-777
775
protein in inflamed tissues was appreciably higher than
in normal tissues.6 The amount of COX could be
increased by stimulating cells with selected cytokines
such as interleukin-1, TNF-R, or bacterial endotoxin.
The increase in COX protein synthesis was found to be
blocked by glucocorticoids, whereas the level of free
arachidonic acid did not appreciably change.7,8 These
observations led to the hypothesis that a second form
of COX existed. In 1991, the inducible form of the
enzyme, COX-2, was cloned.9-11 The cloned COX-2 was
the same as a unique form of the enzyme that had
previously been reported.12,13 It is now known that the
constitutive enzyme (COX-1) is expressed in essentially
all tissues, whereas COX-2 expression is largely absent
unless induced by inflammatory stimuli. The discovery
of a second enzyme, intimately associated with inflam-
matory states, led to the hypothesis that selective
inhibitors of COX-2 would be antiinflammatory with
diminished side effects.
Since the mid-1990s, a number of reports have ap-
peared on the preparation and biological activity of
selective COX-2 inhibitors.14 Recently we detailed the
synthesis and biological profile of celecoxib (1).15 As part
of our continuing efforts to identify inhibitors with
greater potency and high specificity for COX-2, we
prepared a series of diarylisoxazole derivatives that
possess exceptional antiinflammatory properties. Herein
we detail our study on two of the diarylisoxazole COX-2
inhibitors. This research effort culminated in the iden-
tification of SC-65872 (valdecoxib, 2) which is currently
in clinical evaluation for the management of pain and
inflammation.
4-[5-Meth yl-3-p h en ylisoxa zol-4-yl]-
ben zen esu lfon a m id e, Va ld ecoxib: A
P oten t a n d Selective In h ibitor of COX-2
J ohn J . Talley,* David L. Brown, J effery S. Carter,
Matthew J . Graneto, Carol M. Koboldt,
J aime L. Masferrer, William E. Perkins,†
Roland S. Rogers,‡ Alexander F. Shaffer,
Yan Y. Zhang, Ben S. Zweifel, and Karen Seibert
Searle Research and Development,
700 Chesterfield Parkway, St. Louis, Missouri 63198, and
4901 Searle Parkway, Skokie, Illinois 60077
Received November 17, 1999
In tr od u ction . Nonsteroidal antiinflammatory drugs
(NSAIDs) are among the most widely used prescription
and over the counter medications, used primarily for
the treatment of pain and inflammation, particularly
arthritis. In the 1970s, it was demonstrated that aspirin
and other NSAIDs block the formation of prostaglandins
(PGs) produced from arachidonic acid by the enzyme
cyclooxygenase (COX), sometimes called prostaglandin
synthase.1 PGs are produced by most cells, and their
presence in tissues elicits a broad array of biological
responses. Most notably, PGs in the gastrointestinal
tract are cytoprotective, in the kidney they are respon-
sible for normal renal function, and they allow platelets
to aggregate. PGs mediate a number of characteristic
features of the body’s response to tissue injury or
inflammation. Dilation of small blood vessels leading
to development of redness and heat is mediated by PGs.
They contribute to an increase in vascular permeability
leading to the characteristic swelling of tissues. In
addition, PGs sensitize peripheral nerve endings to
transmit pain signals to the brain and spinal cord. Thus,
it is now known that PGs play an important role in
pathologic as well as physiologic processes.
Consumption of NSAIDs for inflammatory diseases
unavoidably leads to blockade of PGs required for
normal physiology. It is now evident that the therapeu-
tic effects and side effects of this class of drug are related
to their mechanism of action. The first-line mode of
therapeutic intervention of chronic inflammatory dis-
eases such as osteoarthritis and rheumatoid arthritis
is NSAIDs. As a consequence, NSAID users suffer from
a high incidence of gastrointestinal irritation, including
the development of life-threatening gastrointestinal
ulcers.2 Additionally, consumption of NSAIDs can lead
to abnormal renal physiology.3,4 More advanced means
of treatment of chronic inflammatory diseases are
glucocorticoids and immunosuppressives that possess
an even greater array of side effects.5
Ch em istr y. The synthesis of 2 was very concise and
is outlined in Scheme 1. Deoxybenzoin was converted
to the corresponding oxime by treatment with hydroxy-
lamine hydrochloride in the presence of sodium ac-
etate.16 Deprotonation of the oxime with 2 equiv of
butyllithium followed by condensation with ethyl ac-
etate afforded isoxazoline 4.17 Treatment of 4 with
chlorosulfonic acid followed by reaction of the incipient
sulfonyl chloride with aqueous ammonia afforded 2 in
good yield.
Until the latter part of the 1980s, most researchers
in the prostaglandin field felt that the formation of PGs
was limited only by the available pool of arachidonic
acid. Several observations suggested this view was not
entirely accurate. It was found that the amount of COX
* To whom correspondence should be addressed. Tel: 636-737-7373.
Fax: 636-737-7425. E-mail: john.j.talley@monsanto.com.
† Searle Research and Development, IL.
After some experimentation, a workable method for
the preparation of 3 was identified, Scheme 2. The route
involved condensation of the dianion of deoxybenzoin
‡ Deceased.
10.1021/jm990577v CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/23/2000

776 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 5
Ta ble 1. In Vitro Activity of 1-3
Communications to the Editor
IC50, µM (n)
human ex vivo whole blood
human recombinant enzymes
serum TXB2 COX-1
LPS-induced PGE2 COX-2
assay
no.
COX-1
COX-2
assay
1
2
3
15 ( 3.4 (7)
140 ( 19 (10)
1120 ( 198 (6)
0.04 ( 0.01 (7)
0.005 ( 0.001 (10)
0.18 ( 0.04 (7)
6.67 ( 1.32 (3)
25.4 ( 1.2 (3)
>50 (4)
0.164 ( 0.065 (7)
0.89 ( 0.033 (6)
0.329 ( 0.101 (4)
Sch em e 1a
) 10.2 ( 1.4 mg/kg (n ) 2)]. Chronic antiinflammatory
activity was achieved with 2 in the rat adjuvant
arthritis model22 [ED50 ) 0.032 ( 0.002 mg/kg/day (n
) 2)], a potency exceeding that obtained with the most
potent NSAIDs. Blockade of prostaglandin production
at the inflammatory site was demonstrated in the rat
carrageenan air pouch model23 [ED50 ) 0.05 ( 0.02 mg/
kg (n ) 2)]. These data indicate that 2 is a highly potent
and selective inhibitor of COX-2 that possesses excellent
oral activity as an antiinflammatory in animal models
typically used to develop NSAIDs.
a
(a) NH2OH‚HCl, NaOAc, aq EtOH; (b) 1. 2 equiv nBuLi, 2.
EtOAc; (c) 1. ClSO3H, 2. NH4OH.
Sch em e 2a
Additionally, 2 is converted in vivo in rodents and
dogs, and in very low abundance in humans, to an active
metabolite 3. In vitro 3 showed an IC50 ) 1120 ( 198
µM (n ) 6) against COX-1 and an IC50 ) 0.18 ( 0.04
µM (n ) 7) against COX-2, Table 1. Pharmacological
evaluation of independently synthesized 3 showed it
possessed oral activity in the acute antiinflammatory
assay [carrageenan paw edema; ED50 ) 1.06 ( 0.01 mg/
kg (n ) 3)]. Chronic antiinflammatory activity was
achieved with 3 in the rat adjuvant arthritis model
[ED50 ) 1.49 ( 0.37 mg/kg/day (n ) 3)]. Compound 3,
while more potent in the carrageenan paw edema assay
than 2, was less potent against the isolated enzyme and
in the air pouch or adjuvant arthritis assays. These
seemingly incongruous data likely reflect the different
pharmacokinetics and tissue distribution of these two
compounds in the different animal models.
a
(a) 1. ClSO3H, 2. NH4OH; (b) 1. HCO2H, Et3N, 2. aq NaOH.
Ta ble 2. In Vivo Activity of 1-3
EC50, mg/kg (n)
rat adjuvant
arthritisa
rat carrageenan
edemab
no.
rat air pouch
1
2
3
0.33 ( 0.08 (2)
0.05 ( 0.02 (2)
0.81 ( 0.19 (2)
0.373 ( 0.163 (3)
0.032 ( 0.002 (2)
1.49 ( 0.37 (3)
7.13 ( 0.79 (2)
10.2 ( 1.4 (2)
1.06 ( 0.01 (3)
a
ED50 values were determined using a minimum of four dose
b
points, 8-10 animals/group. ED50 values were determined using
a minimum of four dose points, 5 animals/group.
Con clu sion . We have shown that 2 is a highly
selective and potent inhibitor of COX-2 in human whole
blood and against the recombinant human enzyme. In
animal models of acute and chronic inflammation, 2
showed exceptional potency after oral administration.
An active metabolite, 3, formed in rodents and dogs was
also found to be a COX-2-selective inhibitor. Valdecoxib
(2) is currently in clinical evaluation for the treatment
of arthritis and pain.
with methyl chloroacetate to provide isoxazoline 5.
Chlorosulfonation and treatment of the corresponding
sulfonyl chloride with aqueous ammonia afforded sul-
fonamide 6. Treatment of 6 with formic acid in the
presence of triethylamine provided the formate ester
which was hydrolyzed with aqueous sodium hydroxide
to afford 3 in excellent yield.18
Resu lts a n d Discu ssion . As an initial screen for
activity, 2 was evaluated against human recombinant
COX-1 and COX-2 enzymes.19 Against COX-1 2 showed
weak inhibitory activity with an IC50 ) 140 ( 19 µM (n
) 10), whereas the compound showed potent activity
against COX-2 with an IC50 ) 0.005 ( 0.001 µM (n )
10), Table 1. Cellular in vitro activity and selectivity
was evaluated in human whole blood.20 For assessment
of the extent of COX-2 inhibition, human heparinized
whole blood was cultured with lipopolysaccharide (LPS)
overnight in the presence of inhibitor, and plasma was
assayed for PGE2 production as a function of COX-2
inhibition. For COX-1 activity, inhibitors were added
to heparinized whole blood for 15 min prior to the
addition of calcium ionophore, A-23187. After 10 min,
plasma was collected for analysis of TxB2 as a function
of COX-1 activity, Table 1. As summarized in Table 2,
2 showed potent oral activity in an acute antiinflam-
matory assay [rat carrageenan foot pad edema;21 ED50
Su p p or tin g In for m a tion Ava ila ble: Biological proce-
dures, synthetic procedures, and spectral data for compounds
2 and 3. This material is available free of charge via the
Internet at http://pubs.acs.org.
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