3-Arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides as novel and selective CXCR2 antagonists

Article abstract of DOI:10.1016/j.bmcl.2007.05.011

A series of 3-arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides were prepared and shown to be novel and selective antagonists of the CXCR2 receptor. Synthesis, structure and activity relationships, selectivity, and some developability properties are described.

Full text of DOI:10.1016/j.bmcl.2007.05.011

Bioorganic & Medicinal Chemistry Letters 17 (2007) 3864–3867
3-Arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides
as novel and selective CXCR2 antagonists
Yonghui Wang,a,* Jakob Busch-Petersen,b Feng Wang,a Lanping Ma,c Wei Fu,b
Jeffrey K. Kerns,b Jian Jin,a Michael R. Palovich,b Jing-Kang Shen,c Miriam Burman,d
James J. Foley,d Dulcie B. Schmidt,d Gerald E. Hunsberger,d
Henry M. Saraud and Katherine L. Widdowsonb
aDiscovery Medicinal Chemistry, Molecular Discovery Research, GlaxoSmithKline, 1250 South Collegeville Road,
Collegeville, PA 19426, USA
bMedicinal Chemistry, Respiratory and Inflammation CEDD, GlaxoSmithKline, 709 Swedeland Road,
King of Prussia, PA 19406, USA
cState Key Laboratory of Drug Research, Shanghai Institute of Material Medica, Chinese Academy of Sciences,
555 Zhuchongzhi Road, Shanghai 201203, China
dBiology, Respiratory and Inflammation CEDD, GlaxoSmithKline, 709 Swedeland Road, King of Prussia, PA 19406, USA
Received 16 April 2007; accepted 3 May 2007
Available online 10 May 2007
Abstract—A series of 3-arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides were prepared and shown to be novel and selective
antagonists of the CXCR2 receptor. Synthesis, structure and activity relationships, selectivity, and some developability properties
are described.
Ó 2007 Elsevier Ltd. All rights reserved.
Interleukin-8 (IL-8, CXCL8) and related ELR+ (Glu4-
Leu5-Arg6) containing CXC chemokines (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 inflamma-
tion which is consistent with their potential involvement
in pathophysiological processes such as arthritis, athero-
sclerosis, reperfusion injury, psoriasis, and asthma.
Indeed, elevated plasma levels of IL-8 and GROa have
been associated with these conditions in humans.1 Two
seven-transmembrane (7TM) G-protein coupled recep-
tors (CXCR1 and CXCR2) have been identified, which
are activated by IL-8. CXCR1 binds IL-8 and GCP-2
with high affinity while CXCR2 binds all of the
above-mentioned ELR+ chemokines with high affinity.2
The potential therapeutic value 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 with-
out apparent pathogenic consequences indicating that
these receptors are not required for normal physiology.3
As previously disclosed,4–6 a series of N,N0-diarylureas
has been identified as potent and selective CXCR2
antagonists. This series was later expanded to include
N,N0-diarylguanidines,
N,N0-diarylcyanoguanidines,7
and squaramides (3,4-diamino-1,2-dioxocyclobutenes)8,9
(Fig. 1). In N,N0-diarylureas and their bioisosteres,10 both
left-hand side (LHS) and right-hand side (RHS) aryl moi-
eties could freely rotate to adopt their optimal conforma-
tions when bound to the receptor. To examine if this free
rotation was required for potent CXCR2 binding affinity,
conformational restriction in the form of a six-membered
ring (e.g., 4 in Fig. 1) was introduced. Herein, we describe
the synthesis, initial structure and activity relationships
(SAR), selectivity, and some developability properties
of a novel series of 3-arylamino-2H-1,2,4-benzothiadia-
zin-5-ol-1,1-dioxides.
Keywords: CXCR2 antagonists; Interleukin-8; Chemokines; Cyclic
sulfonamides; Inflammation.
As shown in Scheme 1, the synthesis started with 2-
methoxy-anilines 5 which were easily obtained from
commercial sources or prepared from the corresponding
*
Corresponding author. Tel.: +1 610 917 6678; fax: +1 610 917
7391; e-mail: yonghui.2.wang@gsk.com
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.05.011

Y. Wang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3864–3867
3865
Table 1. CXCR2 receptor antagonist binding affinities of 3-arylamino-
2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides (9)
NC
Cl
O2N
6
N
O
O
S
Compound
R1
R2
R3
Bindinga
N
H
N
N
N
2
OH
Me2N
H
H
H
IC50 (lM)
O
Ph
OH
O
Br
2
9a
9b
9c
9d
9e
9f
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-Cl
7-H
H
H
2.4
0.74
0.092
0.064
6.1
1
F
Cl
H
O
O
O
S
O2N
H
N
R1
Br
H
H
30-Br
40-Br
30-F
40-F
50-F
60-F
H
N
H
N
N
N
R2
H
H
H
H
Cl
5.1
OR
Br
OH
9g
9h
9i
0.064
0.12
3.9
4
3
Br
Br
Figure 1. Examples of urea (1)-, cyanoquanidine (2)-, squaramide (3)-
type CXCR2 antagonists and a new cyclic sulfonamide template (4).
9j
Br
Me
1.6
9k
9l
0.39
0.23
0.25
0.054
0.83
0.93
>30
4.5
Ph
OMe
H
9m
9n
9o
9p
9q
9r
H
nitro compounds through reduction.11 Reaction
of 5 with chlorosulfonylisocyanate led to substituted 5-
methoxy-2H-1,2,4-benzothiadiazin-3(4H)-one 1,1-diox-
ides 6.12 The 3-oxo compounds (6) were converted into
the corresponding amidoyl triflates 7, which upon
nucleophilic substitution by a variety of anilines
gave the N-aryl-5-methoxy-2H-1,2,4-benzothiadiazin-3-
amine 1,1-dioxides 8.13 Treatment of 8 with LiCl under
conventional heating or microwave conditions produced
the target compounds 9.14
OPh
CF3
H
H
OCF3
(40-Morpholinyl)
H
H
COMe
CO2H
Cl
H
9s
H
>30
5.2
9t
H
9u
9v
9w
9x
9y
9z
9aa
9ab
7-F
Br
Br
H
0.36
0.070
0.026
0.28
3.0
7-Br
7-NO2
7-Me
8-F
H
Br
Br
H
H
Br
Br
H
We first explored the SAR of the RHS moiety by pre-
paring analogs containing anilines with different substit-
uents (R2 and R3 in 9). As shown in Table 1, the nature
and location of these substituents were found to be
important for CXCR2 binding affinities. For analogs
with no or a halo substituent on 20-position of aniline
(9a–9d, 9w, and 9ab), CXCR2 binding affinity increased
with the size of the substituents (H < F < Cl < Br).
When shifting a halogen from the 20-position (9d) to
the 30- or 40-position (9e and 9f, respectively), CXCR2
binding affinity of the corresponding analogs decreased
dramatically. When introducing a second halogen on
the 30-position in addition to the one on the 20-position,
the CXCR2 binding affinity slightly increased (compar-
ing 9g with 9c). However, a second halogen on the 40-,
50- or 60-position decreased the CXCR2 binding affinity
(comparing 9h–j with 9d). Among other substituents
introduced at the 20-position of the aniline, the phenoxy
8-Cl
7-NO2
7-NO2
H
0.48
0.054
0.081
OPh
Cl
H
H
a CXCR2 binding assays were performed as described in Ref. 16.
group stands out and binding IC50s of the correspond-
ing analogs, 9n and 9aa, are both 0.054 lM. While the
binding IC50s of analogs with methyl, phenyl, methoxy,
trifluoromethyl, and trifluoromethoxy on the 20-position
of the aniline (9k–p, respectively) fell in the 0.2–1.0 lM
range, nitrogen- and carbonyl-containing compounds
were found to be much less active (9r) or completely
inactive (9q and 9s). Overall, the RHS SAR closely mir-
rors that of the diarylurea series.9
Subsequently, the SAR of the LHS moiety was explored
by changing substituents (R1 in 9) on the phenyl ring. As
O
O
O
O
S
S
N
NH
R1
R1
R1
b
a
N
H
OTf
NH2
N
H
O
OMe
OMe
OMe
6
7
5
1
O
O
O
O
8
5'
S
S
7
6
N2
6'
4'
N
d
R1
c
R3
R3
R1
3
3'
N
N
1'
N
H
N
2'
H4
H
5
H
OMe
R2
R2
OH
9
8
Scheme 1. Reagents and conditions: (a) nPrNO2, ClSO2NCO, AlCl3 (R1 = 7-Cl, 52%); (b) Tf2O, Pyr, CH2Cl2 (R1 = 7-Cl, 56%); (c) anilines, CH2Cl2
(R1 = 7-Cl, R2 = Cl, R3 = H, 63%); (d) LiCl, DMSO, heating (R1 = 7-Cl, R2 = Cl, R3 = H, 80%).

3866
Y. Wang et al. / Bioorg. Med. Chem. Lett. 17 (2007) 3864–3867
Table 2. CXCR2 FLIPR calcium mobilization activity, CXCR1
binding affinity, and aqueous solubility for exemplar compounds 9
shown in Table 1, introduction of a substituent on the
7-position of LHS phenyl ring enhanced the CXCR2
binding affinity (comparing 9t with 9c). With regard to
the 7-substituents (9d, 9u–9x), the CXCR2 binding
affinity increased in the following order: F, Me < Cl,
Br < NO2. This suggests that both electron withdrawing
ability and size are important factors for substituents at
this position. Analogs with substituent on the 8-position
were found to be less potent than those with substituent
on the 7-position (comparing 9y with 9u and 9z with
9d).15
Compound R1
R2
R3 CXCR2
FLIPRa
CXCR1
bindingb
Aqueous
solubilityc
IC50, (lM) IC50, (lM) (lM)
9aa
9w
9ab
9n
NO2 OPh
NO2 Br
NO2 Cl
H
H
H
H
H
H
F
0.49
0.60
1.1
7.6
3.2
12
20
13
24
13
2
233
188
<1
Cl
Cl
Cl
Cl
OPh
Br
0.32
0.40
0.52
0.46
9d
9c
31
68
Cl
Cl
9g
160
a CXCR2 FLIPR assays were performed as described in Ref. 18.
b CXCR1 binding assays were performed as described in Ref. 16.
c Aqueous solubility was measured in 0.05 M, pH 7.4, phosphate buffer
containing 2% DMSO using standard HPLC based high throughput
techniques.
Three of the 5-methoxy substituted intermediates 8g, 8t,
and 8w were also tested in order to examine the influence
of the 5-hydroxy group on CXCR2 binding affinity. The
IC50s were >30, >30, and 12 lM, respectively, and there-
fore it seems quite clear that having the free phenol is of
great importance to the receptor binding of this series
which is entirely consistent with the findings obtained
from the diarylurea series.5,10 However, one aspect of
the LHS SAR which appears to differ from the
diarylurea series is the fact that the cyclic sulfonamide
is attached to the aryl moiety in what is referred to as
the 6-position in the diarylurea series (see Fig. 1). It
has previously been shown that this position is highly
intolerant of substitution,5,9c however, this may be due
to the 6-substituent interfering with the co-planarity of
the aryl ring with the urea moiety. In contrast, the sul-
fonamide ring in the present series enforces this co-
planarity.
For example, 9aa showed CXCR2 selectivity over the
following receptors (IC50, lM): P2Y1, >25; PAI-1, 7.9;
P38 Alpha, 25; Histamine H3, >3.2; 5HT1A, >3.2;
5HT1B, >3.2; 5HT1D, >3.2; 5HT6, >7.9; 5HT7, 25;
Adrenergic Alpha 1A, 1.0; Histamine H1, >10; Adrener-
gic Beta 1, >25; Dopamine D2, >3.2; Dopamine D3,
>3.2; 5HT4A, >25; 5HT2C, >10; Beta 2, >25; Adeno-
sine A2a, 25; Adrenergic A1, >25.
The compounds in the series exhibited a range of aque-
ous solubilities (Table 2). While compounds with a RHS
20-phenoxyaniline had poor solubility, other compounds
with a 20-chloro- or 20-bromoaniline showed moderate
to good aqueous solubility. In a CYP450 screen, com-
pound 9ab showed no inhibition for 4 major P450 iso-
zymes (>25 lM for 1A2, 2C9, 2D6, 3A4) but some
activity at 2C9 with IC50 of 0.6 lM. Compound 9ab
was also evaluated in in vivo rat PK studies (1.6 mg/kg
iv and 3.2 mg/kg po). The compound demonstrated
moderate clearance (Clb = 23 mL/min/kg) with t1/2 of
2 h, volume of distribution (Vdss) of 0.53 L/kg, and bio-
availability (F) of 5%. These preliminary developability
data suggest that this series constitutes a reasonable
starting point for further lead optimization.
As an extension of exploration for RHS moiety, a few
non-aniline analogs such as those with RHS benzylam-
ines (10a and 10b) and alkylamines (11a and 11b) were
prepared.17 The CXCR2 binding IC50s of 10a, 10b,
11a, and 11b were found to be 8.0, >30, 15, and
20 lM, respectively, which are much less potent than
the aniline analogs.
O
O
O
O
Cl
S
Cl
S
N
N
X
R
N
H
N
N
H
N
In summary, we have designed and synthesized a series
of cyclic sulfonamides as novel and selective CXCR2
antagonists. The initial SAR was explored, demonstrat-
ing that the nature and location of substituents on both
RHS aniline ring and LHS phenol ring are important to
CXCR2 binding affinity. Although the functional activ-
ity of the series appears to be somewhat lower, and a few
developability issues were identified (e.g., 2C9 inhibi-
tion, %F), the series does appear to be an acceptable
starting point for further lead optimization.
H
H
OH
OH
11a (R=
11b (R=
)
)
10a (X=H)
10b (X=Cl)
In addition to the SAR explorations, a few exemplar
compounds were further evaluated in a CXCR2 func-
tional assay, selectivity and initial developability assays.
As shown in Table 2, the compounds in the series exhib-
ited good CXCR2 antagonist activity in a FLIPR
assay18 although the IC50s dropped 5-fold or more,
relative to the affinity obtained in the binding assay.
References and notes
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The compounds in Table 2 were tested in a CXCR1
binding assay and found to be at least 100-fold selective
for CXCR2. A few exemplar compounds (e.g., 9aa, 9ab,
and 9w) were also evaluated against a panel of 19 other
7TM in vitro assays and found to be CXCR2 selective.

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O
Cl
S
N
N
H
Cl
OMe
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or CXCR1. For preparation of CHO-CXCR2 and CHO-
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formed on a CHO-K1 (Chinese hamster ovary) cell line
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and grown for 24 h in 96-well, black wall, clear bottom
plates (Packard View). On day of assay, cells were loaded
with fluoro-4-acetoxymethyl ester fluorescent indicator
dye (Fluoro-4 AM, from Molecular Probes) and treated
for 10 min at 37 °C with a concentration range of
compound (0.01–33 lM). Plates were placed onto FLIPR
(Fluorometric Imaging Plate Reader, Molecular Devices,
Sunnyvale, CA) for analysis as described previously.19 The
percent of maximal human IL-8 induced Ca2+ mobiliza-
tion induced by 1.0 nM IL-8, an EC80 concentration
against CXCR2, was determined after treatment of cells
with each concentration of compound and the IC50
calculated as the concentration of test compound that
inhibits 50% of the maximal response induced by IL-8.
The FLIPR results are expressed as a mean of two or more
individual experiments.
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4-Cl) was prepared from 4-chloro-2-(methyloxy)-1-nitro-
benzene by reduction using 10% Pt/C and ammonium
formate in MeOH (yield: 97%).