N,N′-Diarylcyanoguanidines as antagonists of the CXCR2 and CXCR1 chemokine receptors

Article abstract of DOI:10.1016/j.bmcl.2006.08.042

A series of N-(2-hydroxy-3-sulfonamidobenzene)-N′-arylcyanoguanidines was prepared. In general, these compounds proved to be potent antagonists of CXCR2 while the selectivity versus CXCR1 ranged from non-selective to >200-fold.

Full text of DOI:10.1016/j.bmcl.2006.08.042

Bioorganic & Medicinal Chemistry Letters 16 (2006) 5513–5516
N,N0-Diarylcyanoguanidines as antagonists of the CXCR2
and CXCR1 chemokine receptors
Hong Nie,* Katherine L. Widdowson, Michael R. Palovich, Wei Fu,
John D. Elliott, Deborah L. Bryan, Miriam Burman, Dulcie B. Schmidt,
James J. Foley, Henry M. Sarau and Jakob Busch-Petersen*
GlaxoSmithKline, 709 Swedeland Road, King of Prussia, PA 19406, USA
Received 17 July 2006; revised 7 August 2006; accepted 8 August 2006
Available online 24 August 2006
Abstract—A series of N-(2-hydroxy-3-sulfonamidobenzene)-N0-arylcyanoguanidines was prepared. In general, these compounds
proved to be potent antagonists of CXCR2 while the selectivity versus CXCR1 ranged from non-selective to >200-fold.
Ó 2006 Elsevier Ltd. All rights reserved.
Interleukin-8 (IL-8, CXCL8) and related CXC chemo-
kines (ENA-78 (CXCL5), GCP-2 (CXCL6), GROa
(CXCL1), GROb (CXCL2), and GROc (CXCL3)) play
an important role in the trafficking of immune cells to
sites of inflammation which is consistent with their po-
tential involvement in pathophysiological processes such
as arthritis, reperfusion injury, and asthma. Indeed, ele-
vated plasma levels of IL-8 and GROa have been asso-
ciated with these conditions in humans.1 Thus far, two
seven-transmembrane G-protein coupled receptors have
been identified, which are activated by IL-8 (CXCR1
and CXCR2). CXCR1 binds IL-8 and GCP-2 with high
affinity, while CXCR2 binds several ELR+ chemokines
including IL-8, GCP-2, ENA-78, GROa, GROb, and
GROc with high affinity.2 The potential therapeutic val-
ue for small-molecule antagonists of the IL-8 receptors
is further supported by studies done with CXCR2
mouse gene knockouts which show elevated leukocytes
and lymphocytes without apparent pathogenic conse-
quences indicating that these receptors are not required
for normal physiology.3
O2N
O
O
N
H
N
H
Br
Br
OH
OH
Cl
O
S
N
H
N
H
Me2N
O
OH
NC
N
N
H
N
H
Br
OH
Figure 1. Examples of urea- and guanidine-type CXCR2 antagonists.
As a natural extension of the work with N,N0-diarylgua-
nidines, it was decided to examine guanidine-like urea
isosters. A series of N,N0-diarylcyanoguanidines was
prepared as part of this study. The syntheses started
from the sulfonyl chlorides 1 which were prepared in
high yields according to a previously published proce-
dure.4,8 These were reacted with a variety of amines
yielding the sulfonamides 2 which upon hydrolysis of
the oxazole moiety gave the aminophenols 3. Treatment
with thioisocyanates resulted in the formation of the thi-
oureas 4. Protection of the phenolic function as the TBS
ether followed by exposure to methanesulfonyl chloride
in the presence of triethylamine yielded the carbodii-
mides 5.9 Addition of cyanamide followed by TBS ether
cleavage produced the target compounds 6 (Scheme 1).
As previously disclosed,4–6 a series of N,N0-diarylureas
has been identified as potent, selective CXCR2 antago-
nists. This series was later expanded to include N,N0-
diarylguanidines7 (Fig. 1).
Keywords: CXCR2; CXCR1; Cyanoguanidine.
*
Corresponding authors. Tel.: +1 601 270 7831; fax: +1 610 270
4451; e-mail: jakob.2.busch-petersen@gsk.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.08.042

5514
H. Nie et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5513–5516
R"
O
R'
O
R"
O
R"
O
R'
O
R'
O
N
S
Cl
S
N
S
N
S
O
O
OH
R
R
R
R
OH
O
N
O
N
a
b
c
S
t-Bu
t-Bu
N
N
H
NH2
R'''
2
H
3
1
4
d,e
R"
R'
R"
O
R'
N
S
N
S
O
O
O
OH
OTBS
CN
R
R
f,g
N
.
N
N
H
N
N
R'''
R'''
H
6
5
Scheme 1. Preparation of N,N0-diarylcyanoguanidines. Reagents and conditions: (a) R0R00NH, Et3N, CH2Cl2, rt; (b) 10% H2SO4, reflux; (c)
ArN@C@S, DMF, rt; (d) TBSCl, imidazole, CH2Cl2, rt; (e) MsCl, Et3N, rt; (f) NH2CN, (i-Pr)2NEt, rt; (g) CsF, MeOH, 0 °C.
Figure 2. X-ray crystal structure of 6c (CCDC 616833).
Single crystal X-ray crystallographic analysis of 6c
showed that the cyano group was situated trans to the
phenol-bearing aniline moiety (Fig. 2).10
observed with previous compound series. This allowed
us to gather important pharmacophore information on
this receptor as well and determine similarities and dif-
ferences between the binding sites of two receptors.
Our findings indicate that a range of small substituents
are tolerated at the 4-position: Neither receptor shows
a great deal of discrimination between chloro, fluoro,
methyl, trifluoromethyl or hydrogen. It appears that
the electronic nature of the substituent has little effect
on the binding affinity for either receptor. In the urea
series, the degree of phenol-ionization at neutral pH
has been found to significantly influence the affinity
for the CXCR2 receptor.11 That may be the case in this
series as well since it appears that in the presence of the
sulfonamide, the substituent at the 4-position has sur-
prisingly little influence on the pKa of the phenol. Thus,
the 4-chloro compound 6l has a pKa of 6.41, while the
similar 4-hydro compound 6r has a pKa of 6.48. As
for the substitution on the sulfonamide, a clear differ-
ence between the receptors was observed: While the
introduction of a carboxylic acid moiety had little influ-
ence on the CXCR2 affinity, the CXCR1 affinity was in-
creased considerably, thus yielding a potent dual
The compounds 6 were prepared under the assumption
that the structure activity relationships (SAR) which
had been observed in the urea series relative to CXCR2
would translate into the cyanoguanidine series. There-
fore, the acidic phenol function at the 2-position was re-
tained because it had been found to be essential for high
receptor affinity and the 5-, 6-, 40-, 50-, and 60-positions
as well as the cyanoguanidine nitrogens were left unsub-
stituted since substitution at these positions had been
found to reduce receptor affinity.5,11 Also, the 3-sulfon-
amido group was incorporated as it has been demon-
strated to enhance bioavailability by reducing the rate
of glucuronidation of the adjacent phenol.6 This
assumption largely held true and allowed us to focus
on examining the SAR related to the 4-, 1-0, 20-, and
30-positions as well as the substitution on the sulfon-
amide. One surprising finding was that a number of
these compounds displayed substantially lower selectiv-
ity versus the CXCR1 receptor relative to what had been

H. Nie et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5513–5516
5515
receptor antagonist (6j). The presence of other types of
hydrogen bond donors or acceptors as well as steric bulk
did not seem to affect either receptor greatly. The other
clear difference between the receptors was observed at
the 20-position. Here, CXCR1 displayed different steric
and perhaps electronic requirements than CXCR2.
The CXCR2 receptor tolerated quite large aromatic
substituents (such as 6d and 6e), while the bulkier iso-
propyl substituent (6g) substantially reduced the activi-
ty. The electronic nature of the 20-substituent seemed
to be inconsequential to CXCR2, while the requirements
for CXCR1 were less obvious. Bromine appeared to be
optimal for CXCR1, while larger substituents as well as
fluorine resulted in sharply reduced affinities. Substitu-
tion at the 30- and especially the 40-position negatively
affected the affinity for both receptors. These findings
suggest that the yet to be identified small molecule bind-
ing regions13 of the CXCR2 and CXCR1 receptors are
relatively similar in structure, but that the CXCR1
receptor is relatively restrictive, whereas the CXCR2
receptor can accommodate a wider range of pharmaco-
phors (Table 1). This is further illustrated by the fact
that no CXCR1 selective and IL-8 competitive antago-
nist has been described to date, while a substantial num-
ber of structurally distinct, selective CXCR2 antagonists
have been reported.14
In conclusion, a series of N,N0-diarylcyanoguanidines
were prepared and evaluated as antagonists of CXCR1
and CXCR2. The majority of the prepared compounds
were potent CXCR2 antagonists while the selectivity rel-
ative to CXCR1 ranged from non-selective (6j) to >200-
fold (6i). The discovery of potent dual antagonists is a
promising development which may lead to novel
Table 1. Affinities of N,N0-diarylcyanoguanidines for CXCR1 and CXCR2a
R2
O
4
S
O
3
R1
CN
4'
OH
N
2
3'
R4
1'
N
2'
R3
N
1
H
H
6
Compound 6
R1
R2
R3
R4
CXCR2b (IC50, nM)
CXCR1b (IC50, nM)
a
b
c
d
e
f
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
NMe2
Me
F
H
H
H
H
H
H
H
H
Cl
17
9
378
1548
55
Br
5
Obn
Ph
Et
9
293
752
13
15
112
12
29
512
g
h
i
i-Pr
CF3
F
7289
411
6204
j
Cl
Cl
Cl
CO2H
Br
Br
Br
H
H
H
16
22
9
22
188
215
N
k
l
H2N
N
O
O
N
N
m
Cl
Me
H
17
1082
n
o
Me
Me
NMe2
Br
Br
H
H
7
6
187
104
O
N
N
p
q
F
CF3
NMe2
NMe2
Br
Br
H
H
4
7
192
100
r
H
Br
H
12
582
O
a Binding assays were performed on Chinese hamster ovary (CHO) cell lines expressing either CXCR1 or CXCR2. The CHO-CXCR1 and CHO-
CXCR2 membranes were prepared according to Kraft and Anderson.12 All assays were performed in 96-well microtiter plates using radiolabeled
[
125I]IL-8 (human recombinant, concn: 0.23 nM). The binding results are expressed as a mean of three individual experiments.
b The functional activities of compounds 6c, 6d, and 6l were tested in a calcium mobilization assay performed with human neutrophils using GROa as
the ligand. The resulting IC50s were within 5-fold of the binding IC50s reported in this table.

5516
H. Nie et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5513–5516
(N „ C–NH–C(@NR)NR0) may play a substantial role.
For lead references on cyanoguanidine structure, see: (a)
Alia, J. M.; Edwards, H. G. M.; Garcia Navarro, F. J.
J. Mol. Struct. 2001, 597, 49; Enriz, R. D.; Jaurgui, E.
A. J. Mol. Struct. 1990, 207, 269; (b) Molecular
mechanics studies of 6c using MOE (Molecular Oper-
ating Environment, Chemical Computing Group Inc.,
Montreal, Canada) suggest that there is little difference
therapeutic agents that effectively block all aspects of
ELR+ chemokine induced inflammatory responses. In
addition, these compounds may be useful for the further
elucidation of CXCR1 pharmacology.15
Acknowledgment
in energy between
cyanoguanidine.
11. Widdowson, K.; Nie, H.; Jurewicz, A. J.; Hertzberg, R. P.;
Sarau, H. M.; Foley, J. J.; Lee, J.; White, J. R.; Veber, D.
F. Lett. Peptide Sci. 1998, 5, 235.
E and Z conformers of the
Dr. R. Curtis Haltiwanger is acknowledged for X-ray
crystallographic analysis of compound 6c.
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