New pyrrolopyrimidin-6-yl benzenesulfonamides: Potent A2B adenosine receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2006.04.074

A new series of 4-(1,3-dialkyl-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrrolo[3,2-d]pyrimidin-6 -yl)benzenesulfonamides has been identified as potent A_2B adenosine receptor antagonists. The products have been evaluated for their binding affinities for the human A_2B, A₁ and A₃ adenosine receptors. 6-(4-{[4-(4-Bromobenzyl)piperazin-1-yl]sulfonyl}phenyl)-1,3-dimethyl-1H- pyrrolo[3,2-d]pyrimidine-2,4(3H,5H)-dione (16) showed a high affinity for the A_2B adenosine receptor (IC₅₀ = 1 nM) and selectivity (A₁: 183x; A₃: 12660x). Synthesis and SAR of this novel class of compounds showing improved absorption properties is presented herein.

Full text of DOI:10.1016/j.bmcl.2006.04.074

Bioorganic & Medicinal Chemistry Letters 16 (2006) 3642–3645
New pyrrolopyrimidin-6-yl benzenesulfonamides:
Potent A2B adenosine receptor antagonists
a
b
b
b
b
´
´
´
Cristina Esteve, Arsenio Nueda, Jose Luis Dıaz, Jorge Beleta, Alvaro Cardenas,
Estrella Lozoya,c Maria Isabel Cadavid,d Maria Isabel Loza,d
Hamish Rydere and Bernat Vidala,*
aMedicinal Chemistry Department, Almirall, Treball 2-4, E-08960 St. Just Desvern, Barcelona, Spain
b
`
´
Biology Department, Almirall, Ctra. Laurea Miro 408, E-08980-St. Feliu de Llobregat, Barcelona, Spain
´
c
`
Structural Biology Department, Almirall, Ctra. Laurea Miro 408, E-08980-St. Feliu de Llobregat, Barcelona, Spain
dDepartamento de Farmacologı´a, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
e
`
´
Head of Drug Discovery, Almirall, Ctra. Laurea Miro 408, E-08980-St. Feliu de Llobregat, Barcelona, Spain
Received 30 March 2006; revised 24 April 2006; accepted 24 April 2006
Available online 11 May 2006
Abstract—A new series of 4-(1,3-dialkyl-2,4-dioxo-2,3,4,5-tetrahydro-1H-pyrrolo[3,2-d]pyrimidin-6-yl)benzenesulfonamides has
been identified as potent A2B adenosine receptor antagonists. The products have been evaluated for their binding affinities for the
human A2B, A1 and A3 adenosine receptors. 6-(4-{[4-(4-Bromobenzyl)piperazin-1-yl]sulfonyl}phenyl)-1,3-dimethyl-1H-pyrrolo[3,2-
d]pyrimidine-2,4(3H,5H)-dione (16) showed a high affinity for the A2B adenosine receptor (IC50 = 1 nM) and selectivity (A1: 183x;
A3: 12660x). Synthesis and SAR of this novel class of compounds showing improved absorption properties is presented herein.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Adenosine is an endogenous nucleoside that is normally
increased under conditions of hypoxia or high metabo-
lism typically occurring in pathological or stressful situ-
ations. Adenosine interacts with four G-protein-coupled
membrane receptors, A1, A2A, A2B and A3, with differ-
ent affinities. A1 and A2A are high affinity receptors
for adenosine with affinities in the range of 0.01 lM,
while A2B and A3 are low affinity receptors, with affini-
ties in the range of 5–10 lM.1
There is a large body of evidence linking the A2B recep-
tor to the pathophysiology of asthma:3
• Adenosine is present in the bronchoalveolar lavage
(BAL) of asthmatic subjects at concentrations up to
4-fold higher than in normal subjects (193 vs 60 lM)4
• It is well documented that the A2B receptor has likely
roles in mast cell degranulation and in the stimulation
of IL6, IL8, IL4/IL13, IL19 and MCP-1 secretion
pathways both in mast cells and in other cell types
like lung fibroblasts and bronchial smooth muscle
cells.5
Concentration of extracellular adenosine in normal tis-
sues is estimated to be below 1 lM, with levels increas-
ing to as much as 100 lM during inflammatory or
ischaemic conditions.2 Thus, while tissue expression of
all four adenosine receptors is ubiquitous, different affin-
ities for adenosine indicate that A2B and A3 receptors
would not be constitutively activated in normal
conditions.
The hypothesis that A2B receptor antagonism mediates
the antiasthmatic properties of theophylline, a clinically
proven antiasthmatic with severe safety limitations due
to poor selectivity,6 together with the recent description
of A2B receptors on human airway smooth muscle cells
mediating cytokine and chemokine release provides firm
basis to recognize A2B antagonists as potential novel
anti-asthma drugs.7
Keywords: A2B adenosine receptor antagonists; Asthma; Pyrrolopyr-
imidine; Sulfonamides.
As a first approach to design novel A2B adenosine recep-
tor antagonists, we developed a series of pyrrolopyrim-
idines8 that led to the discovery of compound (1)
*
Corresponding author. Tel.: +34 932 913 996; fax: +34 933 128
635; e-mail: bvidal@almirall.es
0960-894X/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.04.074

C. Esteve et al. / Bioorg. Med. Chem. Lett. 16 (2006) 3642–3645
3643
(Fig. 1) showing good potency and selectivity (against
A2A and A3 receptors) but modest selectivity versus A1
adenosine receptor. Additionally, amide metabolic lia-
bility together with a low solubility (thermodynamic sol-
ubility <10 lg/mL at any pH) that we recognized as a
limiting factor for absorption, led us to direct our efforts
to expand this series toward more selective, stable and
soluble derivatives.
by conventional nitration gave the 6-methyl-5-nitroura-
cil derivatives. Condensation with benzaldehyde and
subsequent reductive cyclization provided the 6-phenyl-
pyrrolopyrimidine nucleus.
Regioselective chlorosulfonylation occurs para to the
phenyl group in the presence of chlorosulfonic acid
and thionyl chloride, to provide the sulfonyl chloride
derivatives. The final step of sulfonamide formation
was achieved using either triethylamine or polymer sup-
ported morpholine as a base. The latter reagent allowed
the use of solution phase parallelization techniques to
systematically explore SAR around the sulfonamide
moiety.
Recently, in a series of similar A2B antagonists, amide
bond was replaced by heterocyclic 5-membered rings
leading to compounds such as (2) (Fig. 1) in order to
achieve metabolic stability and oral bioavailability.9
From our lead compound 1 bearing a phenoxyaceta-
mide moiety, we synthesized a number of pyrrolopyrim-
All compounds described herein were tested for their
ability to bind the A2B adenosine receptor. Binding affin-
ities for A1 and A3 receptors were determined for the
interesting compounds.11 As shown in Table 1, we first
explored the variation of the sulfonamide group keeping
a methyl group in R1 and R2. Our initial idea was testing
the presence of moieties of ranging basicity such as pyr-
idine, piperidine or piperazine. Pyridine ring either
idine derivatives with
a
metabolically stable
benzenesulfonamide group.10 Additionally, in order to
increase solubility and achieve oral bioavailability we in-
stalled a basic ionizable function at the sulfonamide
moiety.
Synthesis of compounds of general formula 3 (Scheme
1) was initiated by reaction of a monosubstituted urea
derivative with diketene. Further alkylation followed
Table 1. Structure and binding affinities of selected sulfonamides
bearing 1,3-dimethyl groups at the pyrrolopyrimidine core
O
O
H
O
H
N
N
Br
R3
O
O
N
H
N
N
O
N
S
N
R4
1
O
O
N
O
N
H
N
N
N
N
N
Compound NR3R4
a
hA2B IC50 hA1 IC50 hA3 IC50
a
a
O
N
N
O
(nM)
(nM)
(nM)
2
HN
HN
N
4
5
12
68
1354
Figure 1. Structure of compounds 1 and 2.
N
18
20
14
17
43
90
16
6
54
101
150
396
—
1525
38,050
2085
6438
—
O
O
O
O
N
R1
R1
NO2
a
b
HN
c
R2 NHCONH2
N
N
N
HN
HN
6
O
N
N
R2
O
O
N
R2
R2
O
N
O
O
7
R1
R1
H
N
NO2
d
N
e
f
N
CHO
O
N
O
N
R2
O
R2
HN
8
O
O
R1
N
O
R1
9
H
H
R3
N
N
HN
N
N
g
N
SO2Cl
S
N
R4
O
N
O
N
O
R2
R2
10
11
12
—
—
N
3
Scheme 1. General synthesis of 6-phenylpyrrolopyrimidines. Reagents
and conditions: (a) diketene, AcOH, reflux (60–75%); (b) Me2SO4 or
R1I, 4 N NaOH, EtOH, 25 ꢁC (88–99%); (c) HNO3, H2SO4, 0 ꢁC (81–
415
—
3169
—
N
N
˚
94%); (d) PhCHO, piperidine, 3A molecular sieves, EtOH, reflux (43–
73%); (e) Na2S2O4, formic acid, reflux (35–94%); (f) ClSO3H, SOCl2,
0 ꢁC (51–92%); (g) HNR3R4, TEA or polymer supported morpholine,
DCM, 25 ꢁC (35–75%).
N
N
a Values are means of two experiments.

3644
C. Esteve et al. / Bioorg. Med. Chem. Lett. 16 (2006) 3642–3645
Table 2. SAR around selected benzylpiperazinyl sulfonyl derivatives
adenosine receptor (IC50 < 20 nM) and variable selectiv-
ities versus A1 adenosine receptor. Concerning A3 aden-
osine receptor, all products show a very good selectivity.
Although, basic amines at the sulfonamide moiety such
as those in compounds 4–8 showed good affinities, N-(1-
benzylpiperidine-4-yl)sulfonamides 9–10 were less po-
tent. The (4-benzylpiperazin-1-yl)sulfonyl derivative 11
came out as one of the most promising groups both in
terms of potency and selectivity.
O
H
O
N
N
S
N
N
R5
O
O
N
Compound R5
a
hA2B IC50 hA1 IC50 hA3 IC50
a
a
(nM)
(nM)
(nM)
3169
8888
Even though compound 12 showed the highest potency,
we did not further characterize this product because of
the low basicity of the phenylpiperazino moiety, leading
to a very limited solubility. Actually, while compound
12 showed a thermodynamic solubility lower than
10 lg/mL at any pH, compounds 7 and 11 displayed in-
creased solubility in acidic media (pH: 1.2, 57 and 70 lg/
mL, respectively).
11
13
14
15
16
17
18
Ph
3-F–Ph
16
7
415
152
—
4-F–Ph
2,4-DiF–Ph
4-Br–Ph
10
7
—
—
126
183
102
—
1
12,260
5249
—
5-Chloro-2-thienyl
4-Pyridyl
4
27
a Values are means of two experiments.
directly attached to the sulfonamide moiety (compounds
4 and 5) or via a one, two or three atom linker
(compounds 6–8) showed similar affinities for the A2B
Taking benzylpiperazines as a promising starting point
we explored the SAR of diversely substituted N-arylm-
ethylpiperazines. As can be seen in Table 2, substitution
Table 3. Structure and binding affinities of selected sulfonamides bearing diverse alkyl groups at positions 1 and 3 of the pyrrolopyrimidine core
O
R1
O
H
R3
R4
O
N
N
S
N
O
N
R2
a
hA2B IC50 (nM)
a
hA1 IC50 (nM)
a
hA3 IC50 (nM)
Compound
R1
Et
R2
Et
NR3R4
F
19
15
350
205
140
59
21,880
4314
N
N
F
20
21
22
23
Et
Et
12
75
18
6
HN
N
HN
N
Et
Et
18,950
1467
nPr
nPr
nPr
Me
HN
N
N
370
950
N
N
HN
N
24
25
26
27
nPr
nPr
Me
Me
Me
Me
nPr
nPr
17
15
17
13
123
12
844
7600
—
N
HN
O
F
—
N
N
N
O
O
102
14,860
N
a Values are means of two experiments.

C. Esteve et al. / Bioorg. Med. Chem. Lett. 16 (2006) 3642–3645
3645
with halogens at the phenyl ring of benzylpiperazines in-
creased potency for the A2B adenosine receptor up to the
low nanomolar level (compounds 13–16) and particular-
ly compound 16 showed an outstanding potency (IC50
A2B: 1 nM) and good selectivity (A1: 183x; A3: 12260x)
relative to compound 11. Substituted thienyl rings (com-
pound 17) showed a very good potency inhibiting A2B
adenosine receptor. In the case of substitution with a
4-pyridyl (compound 18), a lower affinity was observed.
compounds constitute a promising starting point to
develop novel A2B antagonists for clinical progress.
References and notes
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we next studied the effect of variation of the R1 and R2
substituents at the pyrimidinedione central core by using
combinations with methyl, ethyl and n-propyl groups
with some of the best NR3R4 moieties identified (Table
3). Lower alkyl groups in R1 and R2 have proven to be
the preferred substituents in this type of structures.8–10
In compounds 19–27, although potency antagonizing
A2B adenosine receptor is acceptable (most of them
showing IC50 < 20 nM) we were not able to observe a
clear improvement in selectivity versus A1 adenosine
receptor. Only in the case of compound 23 (p-cyanoben-
2. Hasko, G.; Cronstein, B. N. Trends Immunol. 2004, 21, 33.
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zylpiperazine) we observed excellent potency (IC50 A2B
:
6 nM) and a good selectivity against A1 and A3 adeno-
sine receptors (A1: 62x; A3: 160x).
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11. Biological assay procedures. (i) A1 receptor assay: a
radioligand binding assay was used with [3H]DPCPX as a
ligand and membranes from CHO cells transfected with
human A1 receptor; (ii) A2B receptor assay: a radioligand
binding assay was used with [3H]DPCPX as a ligand and
membranes from HEK 293 cells transfected with human
Compounds 7 and 11 were chosen as representative for
pharmacokinetics. When dosed orally at 10 mg/kg in
rats moderate AUC of 985 and 252 ng h/mL, respective-
ly, with a tmax in both cases of 6 h. were observed. These
results can be considered as an improvement since after
oral administration of compound 1 (10 mg/kg) in rat, an
AUC < 20 ng h/mL was observed.
In conclusion, we have identified a series of pyrrolopyr-
imidin-6-yl benzenesulfonamides as potent A2B adeno-
sine receptor antagonists and selective versus A1 and
A3 adenosine receptors with improved physicochemical
properties, resulting
bioavailability.
in
an
increased
oral
Furthermore, compounds 16 and 23 showed an out-
standing profile of potency against A2B adenosine recep-
tor (IC50: 1 and 6 nM, respectively) as well as good
selectivity versus A1 and A3.
A
2B receptor; (iii) A3 receptor assay: a radioligand binding
assay was used with [3H]NECA as a ligand and membranes
from HeLa cells transfected with human A3 receptor.
The overall pharmacological activity of the pyrrolopyr-
imidine benzenesulfonamides suggests that these novel