Discovery of 2-hydroxy-N,N-dimethyl-3-{2-[[(R)-1-(5-methylfuran-2-yl) propyl]amino]-3,4-dioxocyclobut-1-enylamino}benzamide (SCH 527123): A potent, orally bioavailable CXCR2/CXCR1 receptor antagonist

Article abstract of DOI:10.1021/jm0609622

Structure-activity studies on lead cyclobutenedione 3 led to the discovery of 4 (SCH 527123), a potent, orally bioavailable CXCR2/CXCR1 receptor antagonist with excellent cell-based activity. Compound 4 displayed good oral bioavailability in rat and may be a potential therapeutic agent for the treatment of various inflammatory diseases.

Full text of DOI:10.1021/jm0609622

J. Med. Chem. 2006, 49, 7603-7606
7603
Discovery of
2-Hydroxy-N,N-dimethyl-3-{2-[[(R)-1-(5-
methylfuran-2-yl)propyl]amino]-3,4-dioxo-
cyclobut-1-enylamino}benzamide (SCH 527123):
A Potent, Orally Bioavailable CXCR2/CXCR1
Receptor Antagonist
Michael P. Dwyer,*,† Younong Yu,† Jianping Chao,†
Cynthia Aki,† Jianhua Chao,† Purakkattle Biju,†
Figure 1. CXCR2-selective and CXCR2/CXCR1 receptor antagonists.
Viyyoor Girijavallabhan,† Diane Rindgen,† Richard Bond,†
Rosemary Mayer-Ezel,† James Jakway,† R. William Hipkin,†
James Fossetta,† Waldemar Gonsiorek,† Hong Bian,†
Xuedong Fan,† Carol Terminelli,† Jay Fine,† Daniel Lundell,†
J. Robert Merritt,§ Laura L. Rokosz,§ Bernd Kaiser,§ Ge Li,§
Wei Wang,§ Tara Stauffer,§ Lynne Ozgur,§
in a number of neutrophil animal models.7 Researchers at Pfizer
reported a series of quinoxalines represented by 2, which showed
inhibition of CXCL8 receptor binding and CXCL8-mediated
neutrophil chemotaxis.8 Since these initial disclosures, several
other classes of small-molecule CXCR2 antagonists have been
disclosed, and this area has been recently reviewed in depth.9
John Baldwin,§ and Arthur G. Taveras†,‡
Schering-Plough Research Institute, 2015 Galloping Hill Road,
Kenilworth, New Jersey 07033, and Pharmacopeia Drug DiscoVery,
Inc., 3000 Eastpark BouleVard, Cranbury, New Jersey 08512
Herein, we report the culmination of our ongoing efforts in
the synthesis and SAR development of a series of novel of 3,4-
diamino-3-cyclobutene-1,2-dione CXCR2 receptor antagonists.10
Preliminary studies11 identified the 3,4-diamino-3-cyclobutene-
1,2-dione motif to be central to the development of potent
CXCR2 receptor antagonists as represented by 3. In this Letter,
we disclose the design, synthesis, and SAR development of the
3,4-diamino-3-cyclobutene-1,2-dione derivatives from our early
lead compound 3, which led to the discovery of 4, a potent
CXCR2/CXCR1 receptor antagonist (Figure 1).12 A report13 has
appeared recently on the ability of 4 to inhibit smoke-induced
pulmonary neutrophilia in mice, using the designation SCH-N.
The preparation of the 3,4-diamino-3-cyclobutene-1,2-dione
derivatives began with the preparation of the requisite optically
pure amine fragments utilizing a diastereoselective chiral
addition route14 (Scheme 1). Condensation of substituted aryl
or heteroaryl aldehydes 5a-f with R-valinol in the presence of
MgSO4 followed by TMS protection afforded the protected
imines 6a-f. Treatment of imines 6a-f with commercially
available organolithium (i-PrLi and t-BuLi) or in situ generated
species (EtLi and cyclopropylLi) afforded the diastereoselective
addition products,15 which were directly subjected to oxidative
cleavage conditions to provide amines 7a-j. Nitrosalicyclic acid
8 was converted to the dimethylamide adduct, which upon
hydroreduction afforded aniline 9 (Scheme 2). Coupling of 9
with diethyl squarate in EtOH afforded 10, which upon treatment
with commercially available or prepared amines (7a-j) afforded
the final products 3, 4, and 11-24 as depicted in Tables 1 and
2.
The in vitro affinities of these compounds for the CXCR2
and CXCR1 receptors were determined by a membrane binding
assay,16,17 while the functional activity was assessed in a human
neutrophil (hPMN) chemotaxis assay in the presence of various
chemoattractants (CXCL8 or CXCL1).18 The blood levels in
rats after oral administration were determined according to a
rapid rat pharmacokinetic screen.19
With our initial early lead compound 3 in hand, we focused
our discovery program upon improving the in vitro potencies
for the chemokine receptors, functional activity, and oral
bioavailability in rat of this class of compounds. Initial SAR
studies11 in this structural series established the importance of
the three key H-bonding elements (two -NH and one -OH)
and the dimethylamide phenol aniline in 3 as essential for
CXCR2 receptor affinity. While 3 displayed reasonable affinity
ReceiVed August 9, 2006
Abstract: Structure-activity studies on lead cyclobutenedione 3 led
to the discovery of 4 (SCH 527123), a potent, orally bioavailable
CXCR2/CXCR1 receptor antagonist with excellent cell-based activity.
Compound 4 displayed good oral bioavailability in rat and may be a
potential therapeutic agent for the treatment of various inflammatory
diseases.
IL-8a (CXCL8) is a member of the CXC chemokine family
that plays a role in the trafficking of neutrophils to the site of
inflammation.1 In 1990, two chemokine G-protein-coupled,
seven-transmembrane receptors (CXCR1 and CXCR2) were
cloned and identified and are activated by CXCL8.2,3 While
CXCR2 binds with high affinity to CXCL8 and other ELR+
chemokines such as GCP-2 (CXCL6), ENA-78 (CXCL5), and
Gro-R (CXCL1), CXCR1 is less promiscuous and binds only
CXCL8 and CXCL6 with high affinity.4 When CXCL8 interacts
with CXCR2 and CXCR1 on neutrophils, an intracellular
response occurs, including calcium flux, degranulation, and
subsequent chemotaxis.5 In addition, elevated levels of CXCL8
and CXCL1 have been observed in humans with arthritis,
asthma, and COPD, suggestive of the critical role that these
CXC chemokines may play in such processes.6
Owing to the relevance of CXCL8 and related chemokines
in a wide range of inflammatory diseases, CXCR2 and CXCR1
antagonists have attracted attention as targets for small-molecule
drug discovery. In 1998, Widdowson and co-workers reported
the first small-molecule CXCR2 selective antagonists repre-
sented by urea 1 (Figure 1).7 Analogues in this structural class
have been reported to be potent, selective CXCR2 receptor
antagonists that possess good bioavailability and in vivo activity
* To whom correspondence should be addressed. Phone: 908-740-4478.
Fax: 908-740-7152. E-mail: michael.dwyer@spcorp.com.
† Schering-Plough Research Institute.
§ Pharmacopeia Drug Discovery, Inc.
‡ Current address: Alantos Pharmaceuticals, 840 Memorial Drive,
Cambridge, Massachusetts 02139.
a Abbreviations: IL-8, interleukin-8; COPD, chronic obstructive pul-
monary disease; CXC, cysteine (C)-X-C motif; ELR+, glutamic acid-
leucine-arginine; GCP-2, human granulocyte chemotactic protein-2; ENA-
78, epithelial-derived neutrophil attractant-78; Gro-R, growth-related protein-
R; hPMN, human polymorphonuclear leukocyte; AUC, area under curve;
HPBCD, hydroxypropyl-â-cyclodextrin.
10.1021/jm0609622 CCC: $33.50 © 2006 American Chemical Society
Published on Web 12/07/2006

7604 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26
Scheme 1. Preparation of Chiral Amines 7a-ja
Letters
Table 1. Aryl and Heteroaryl Derivatives 3, 4, and 11-20
a Reagents and conditions: (a) R-valinol, MgSO4, CH2Cl2; (b) TMSCl,
Et3N (90% two steps); (c) R1Li, Et2O, -40 °C; (d) H5IO6, MeNH2 (40%
in H2O) or Pd(OAc)4.
Scheme 2. Preparation of 3,4-Diamino-3-cyclobutene-1,2-dione
Derivatives 3, 4, 11-24a
a Reagents and conditions: (a) (COCl)2, DMF, then HNMe2, 93%; (b)
Pd/C (10%), H2 (40 psi), 97%; (c) diethyl squarate, EtOH, room temp, 70%;
(d) 7a-j, EtOH, room temp or reflux, 41-96%.
for the CXCR2 receptor, functional activity,11 and modest oral
bioavailability in rat (Table 1), additional SAR work focused
upon optimization of the diethylamino fragment of 3 to improve
the biological profile of this series of compounds. Toward this
end, initial incorporation of a benzylic functionality was not
impressive (11-13); however, a trend in terms of preferred
stereochemistry was observed (Table 1). While benzylic deriva-
tive (11) and the enantiomeric R-methyl derivatives (12 and
13) showed reduced binding affinity to the CXCR2 receptor
versus the branched alkyl derivative 3, the ethyl-substituted
derivatives (14 and 15) revealed a significant difference in the
overall biological profile between the (R)- and (S)-enantiomers
with respect to both chemokine receptor affinity (CXCR2 and
CXCR1) and rat pharmacokinetics (Table 1). Compound 15
demonstrated an improvement in affinity for the CXCR2 and
CXCR1 receptor and improved oral exposure in rat versus lead
compound 3. In addition, the corresponding (S)-enantiomer (14)
showed a reduced affinity for the CXCR2 receptor and very
poor rat pharmacokinetics. Having established the critical
importance of the (R)-ethyl derivative side chain for improved
CXCR2 and CXCR1 receptor affinity and rat pharmacokinetics,
a brief survey of substitution around the phenyl motif of 15
was conducted. Incorporation of electron-withdrawing (16) and
electron-donating substituents (17) on the phenyl ring displayed
affinities comparable to those of the CXCR2 receptor and
CXCR1 receptor while maintaining reasonable oral drug
exposure in rat (Table 1). Bioisosteric replacement of the phenyl
ring of 15 with a 2-thienyl (18) or 2-furyl (19) motif yielded
derivatives with improved CXCR2 and CXCR1 receptor af-
finities compared to 15. While these heteroaryl derivatives
a Values reported are the mean ( range (n ) 2) except 4 (mean ( SEM,
n ) 4). b na ) not active at >10000 nM.
Table 2. 5-Methylfuryl Derivatives 4 and 21-24
IC50 for
IC50 for
rat AUC
compd
R
CXCR2 (nM)a
CXCR1 (nM)a
(po) (µM‚h)20
21
4
22
23
24
Me
Et
Cp
i-Pr
t-Bu
5.4 ( 1.0
2.6 ( 0.3
3.6 ( 0.5
6.2 ( 1.4
3.8 ( 0.4
775 ( 27
36 ( 5
55 ( 3
34 ( 2
11 ( 1
34.0
49.0
1.4
3.2
2.6
a Values reported are the mean ( range (n ) 2) except 4 (mean ( SEM,
n ) 4).
displayed excellent affinity for the CXCR2 and CXCR1
receptors, poor oral bioavailability in rat limited their utility
(Table 1). Because of concerns about the metabolic liability of
the 5-H substitution in 18 and 19, a 5-methyl substituent was
introduced to provide thiophene 20 and furyl derivative 4. These
derivatives displayed comparable affinity for the CXCR2

Letters
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26 7605
Table 3. hPMN Chemotaxis Assay for 4, 21, and 15
chemotaxis inhibition IC50 (nM);a n ) 2
pharmacokinetics in rat. This compound should be appropriate
for exploring the role of these receptors in human disease.
CXCL8
CXCL1
Acknowledgment. We thank Dr. John Piwinski and Dr.
Robert Aslanian for insightful suggestions and comments and
Dr. Jesse Wong, Dr. Jianshe Kong, Dr. Mark Liang, and Tao
Meng for scale-up of intermediates.
compd
mean
range
mean
range
4
21
15
16
251
398
1.5
1.4
1.2
<1.0
2.4
48
1.2
1.6
a Derived by testing the effect of increasing concentrations of compound
on the chemotaxis AUC in response to CXCL8 (0.03-30 nM) or CXCL1
(0.1-100 nM). Therefore, IC50 is the compound concentration (nM) at which
the chemotaxis AUC was inhibited 50%.
Supporting Information Available: Experimental procedures
and characterization data for 3-24. This material is available free
of charge via the Internet at http://pubs.acs.org.
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1). The 5-methylfuryl derivative 4 emerged from these efforts
possessing excellent affinity for the CXCR2 and CXCR1
receptors and having excellent oral exposure in the rapid rat
pharmacokinetic screen.
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In a human neutrophil (hPMN) chemotaxis assay,18
4
displayed superior inhibition of chemotaxis in vitro induced by
CXCL1 or CXCL8 versus 15 or 21 (Table 3). Compound 4
demonstrated complete inhibition of CXCL1-mediated neutro-
phil chemotaxis at 2 nM, while inhibition of CXCL8-mediated
chemotaxis was less potent.18 In addition, 4 was equipotent in
blocking CXCL1 and CXCL8 binding (and receptor signaling)
in CXCR2 recombinants (data not shown). Experiments with
CXCR2-selective compounds such as 15, 21, and 1 indicate
that CXCL8 stimulates chemotaxis of isolated hPMN primarily
through activation of CXCR1.22 The effect of 4 was specific in
that chemotaxis of human neutrophils induced by other neu-
trophil activating agents such as C5a and fMLP was not affected
(data not shown). In an extensive counterscreen assay, concen-
trations of 2-20 µM of 4 showed less than 15% inhibition of
other closely related chemokine receptors (CXCR3, CCR5, etc.),
indicative of its overall selectivity for the CXCR2 and CXCR1
receptors.22
In summary, we have identified a series of potent, orally
bioavailable substituted 3,4-diamino-3-cyclobutene-1,2-dione
CXCR2/CXCR1 receptor antagonists with excellent functional
activity. Subsequent optimization of receptor affinities and
pharmacokinetics resulted in the discovery of furyl derivative
4, a potent inhibitor of human neutrophil chemotaxis with good

7606 Journal of Medicinal Chemistry, 2006, Vol. 49, No. 26
Letters
(12) Presented in part: Dwyer, M. P.; Yu, Y.; Chao, J.; Aki, C.; Chao,
J.; Purakkattle, B.; Rindgen, D.; Bond, R.; Jakway, J.; Hipkin, R.
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Rokosz, L. L.; Kaiser, B.; Li, G.; Wang, W.; Stauffer, T.; Ozgur, L.;
Taveras, A. Discovery of a potent CXCR2 receptor antagonist for
the treatment of inflammatory disorders. Presented at the 231st
National Meeting of the American Chemical Society, Atlanta, GA,
March, 2006; Abstract MEDI-19.
differences in the binding affinities. The complete assay conditions
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(18) Full experimental details for this assay and subsequent data analysis
can be found in Supporting Information.
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(20) Rats (n ) 2) were orally administered with 10 mg/kg of compound
in 20% HPBCD. Blood was drawn at intervals over a 6 h period.
Plasma from the two animals was pooled at each sampled time point.
AUC was calculated over a 0-6 h period. See ref 19 for a detailed
description of this protocol.
(15) The diastereoselectivities of the organometallic additions were
determined to be consistently >15:1 by 1H NMR analysis of the
corresponding â-amino alcohol in accordance with ref 14.
(16) The CXCR2 binding data for 3 depicted in Table 1 is 3-fold higher
than the reported value in ref 11. Different assay conditions were
employed for the compounds in Tables 1 and 2 leading to subtle
(21) Dwyer, M. P.; Yu, Y.; Chao, J.; Aki, C.; Chao, J.; Purakkattle, B.;
Taveras, A. G. Unpublished results.
(22) A detailed description of the pharmacology and in vivo properties
of 4 will be reported in due course.
JM0609622