Discovery and optimisation of a potent and selective tertiary sulfonamide oxytocin antagonist

Article abstract of DOI:10.1016/j.bmcl.2008.11.018

The optimisation of a tertiary sulfonamide high-throughput screening hit is described. A combination of high-throughput chemistry, pharmacophore analysis and in silico PK profiling resulted in the discovery of potent sulfonamide oxytocin receptor antagoni

Full text of DOI:10.1016/j.bmcl.2008.11.018

Bioorganic & Medicinal Chemistry Letters 19 (2009) 528–532
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery and optimisation of a potent and selective tertiary sulfonamide
oxytocin antagonist
Nicholas P. Barton a, Benjamin R. Bellenie a, Andrew T. Doran a, Amanda J. Emmons a, Jag P. Heer a,
,
*
Cristian M. Salvagno b
a GlaxoSmithKline Pharmaceuticals, New Frontiers Science Park (North), Coldharbour Road, Harlow, Essex CM19 5AD, England, UK
b GlaxoSmithKline S.p.A., Medicines Research Centre, Via Fleming 2, Verona, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
The optimisation of a tertiary sulfonamide high-throughput screening hit is described. A combination of
high-throughput chemistry, pharmacophore analysis and in silico PK profiling resulted in the discovery of
potent sulfonamide oxytocin receptor antagonists with oral exposure and good selectivity over vasopres-
sin receptors.
Received 13 October 2008
Revised 5 November 2008
Accepted 7 November 2008
Available online 12 November 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Oxytocin
Pharmacophore
HTS
Oxytocin, 1 is
a
peptide hormone acting on the
G
pro-
chemistry with templates derived from these aldehydes failed to
improve potency.
tein-coupled oxytocin receptor which modulates numerous
physiological roles including the control of uterine contrac-
tions.1–3 Antagonism of the oxytocin receptor is a potential treat-
ment for threatened pre-term birth and has been clinically
validated by the peptidic antagonist atosiban, 2, administered
by iv infusion.4 A small molecule, orally administered oxytocin
receptor antagonist is an attractive next generation therapeutic
agent (Fig. 1).
High-throughput screening of the GSK compound collection
identified the tricyclic quinolinone, 3 as a moderately potent oxy-
tocin receptor antagonist with good selectivity against the related
V1a vasopressin receptor but poor solubility and bioavailability.5 A
related, high molecular weight, oxytocin receptor antagonist 4
with in vivo activity has been reported by Serono Pharmaceutical
Research Institute.6 Our aim was to optimise the potency, solubil-
ity and oral bioavailability of 3 without significantly increasing
molecular weight (<500) (Fig. 2).
OH
O
H
N
H2N
N
H
O
O
O
O
NH
S
S
NH
O
N
N
H
O
H
N
NH2 NH2
O
N
O
H2N
H
O
O
oxytocin, 1
O
O
Chemistry (Scheme 1) was carried out to find novel isosteres for
the tricyclic quinolinone group of 3.
H
N
N
H
The moderately potent compounds 5–8 (Table 1) were identi-
fied in a fluorescence polarisation binding assay.5 All the tricyclic
quinolinone replacements (R1, Table 1) contained a distal phenyl
ring and were derived from commercially available heterocyclic
biaryl aldehydes (Scheme 1). Further rounds of high-throughput
O
NH
S
S
O
O
H2N
O
O
N
NH OH
NH2
H
N
N
H2N
H
O
O
N
H
O
O
atosiban, 2
* Corresponding author.
E-mail address: Jag_P_Heer@gsk.com (J.P. Heer).
Figure 1. Structures of oxytocin and atosiban.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.11.018

N. P. Barton et al. / Bioorg. Med. Chem. Lett. 19 (2009) 528–532
529
O
OT fpKi = 6.7
O
S
V1a fpKi < 5
Molecular weight = 460
N
O
Solubility < 1 ug/mL
Fpo = 4%
N
O
3
O
Cl
NH
OT Ki = 0.65 nM
O
V1a Ki = 42 nM
Molecular weight = 624
S
N
O
O
N
N
NH
Inhibition of rat uterine contractions:
O
72% @10 mg/kg(iv) (non-pregnant)
35% @30 mg/kg(po)(non-pregnant)
30% @30 mg/kg(po) (late-term pregnant)
N
H
4
Figure 2. Tertiary sulfonamide oxytocin receptor antagonists.
O
X
O
X
O
X
O
R2
NH2
S
(a)
(b)
S
N
NH
O
+
O
R2
R1
R1
O
Cl
O
R1
Scheme 1. Reagents and conditions: (a) i—Na2SO4, DCM, 100 °C, 10 min (sealed microwave vial); ii—NaBH4, DCM/MeOH, rt, 1 h (yield 60–95%); (b) pyridine, rt, 1 day then
150 °C, 10 min (yield 40–90%).
A pharmacophore based on known active oxytocin receptor
antagonists 9 and 10 (Figs. 3 and 4) was generated in an attempt
to overcome the potency plateau without increasing molecular
weight.7,8
Sulfonamide 11 (Fig. 6), containing a biaryl motif similar to that
found in 9, showed better pharmacophore alignment but binding
affinity did not improve (Table 2). Presumably this was due to lack
of conformational rigidity compared to 9.
Mapping compounds 5–8 to the pharmacophore in Figure 4
(Fig. 5) suggested poor alignment of the biaryl unit to the plane
of the indane aromatic element.
The pharmacophore maps the biaryl fragment as a plane
aromatic (distal phenyl) and hydrogen bond acceptor (pyridine)
(Fig. 7). The model requires the vectors of the pyridine and distal
phenyl ring to adopt a non-co-planar arrangement (45 deg from
co-planar). Compounds 12–15 were prepared (Scheme 2) to
increase conformational rigidity, preventing the rings adopting a
co-planar arrangement.
Table 1
SAR from optimisation of 3.
This strategy resulted in the discovery of potent compounds
(Table 2). Compounds were profiled in binding and functional
assays to confirm functional antagonism and selectivity.5
Selectivity against V1a was poor but the functional potencies of
13 and 14 were encouraging and PK (pharmacokinetic) profiling
was carried out (Table 3). Both compounds had relatively poor
CYP (cytochrome P450 enzyme) profiles and poor solubility, result-
ing in low oral exposure.
O
X
O
R2
S
N
O
R1
Compound
R1
R2
X
OT pKi
The serious PK shortcomings were tackled by in silico profil-
ing. Our efforts targeted the aryl sulfonamide because pharmaco-
phore analysis (Fig. 7) suggested only the sulfonamide oxygen
atoms are required as hydrogen bond acceptors. The phenyl ring
can be replaced to optimise the PK properties and retain potency.
A number of highly potent oxytocin receptor antagonists were
prepared with both electron rich and electron deficient aryl sul-
fonamides (Table 4).
Only the compounds with low clogD7.4 (calculate log
distribution coefficient at pH 7.4), the imidazole sulfonamides 21
and 22, were predicted to have good solubility and improved CYP
profiles. Measured solubility and CYP inhibition of 21 and 22 were
*
N
N
5
N
7.4
S
N
*
O
*
6
7
N
N
7.4
7.2
N
O
O
N
*
*
*
N
N
N
N
*
8
CH
7.2
S
*

530
N. P. Barton et al. / Bioorg. Med. Chem. Lett. 19 (2009) 528–532
O
N
N
N
N
O
O
O
N
O
N
N
N
HN
O
H
O
9
10
Figure 3. Antagonists used in pharmacophore generation.
Table 2
Selectivity SAR for tertiary sulfonamides.
O
O
N
N
O
S
N
O
X
Compound
X
OT
OT fpKi
V1a fpKi
V1b fpKi
V2 fpKi
pKi
(FLIPR)
(FLIPR)
(FLIPR)
(Yeast)
11
12
13
14
15
H
6.9
—
—
—
—
CN 8.0
Cl 7.9
Me 8.1
8.2
8.2
8.5
8.7
8.1
7.3
7.6
7.8
7.3
Inactive
Inactive
Inactive
Inactive
6.3
5.9
6.6
7.2
Figure 4. Consensus pharmacophore derived for compounds 9 (grey) and 10 (gold).
Key elements of note include two hydrogen bonding acceptors (green arrows)
mapped on pyridines of 9 and diketopiperazine amide carbonyl groups of 10, a
plane aromatic (bronze spheres) mapped on the phenyl group of 9 and indane
group of 10, a small hydrophobe (cyan spheres) based on pyridine methoxy group
of 9 and the sec-butyl group of 10 and a hydrogen bonding acceptor (green arrow)
mapped to the triazole of 9 and the morpholine amide carbonyl group of 10.
F
Figure 7. Pharmacophoric alignment of 11.
Figure 5. Pharmacophoric alignment of 5–8 (in gold) and 9.
better than 13 and 14 in agreement with in silico profiling (Table
5). The oral bioavailability was determined for 21 and found to
be superior to 13 and 14.
Selectivity profiles for 21 were determined in functional assays
and in lower throughput filtration binding assays.9 A significant
improvement in selectivity was achieved (Fig. 8).
In summary, the moderately potent tricyclic quinolinone 3 has
been optimised to give a highly potent tertiary sulfonamide antag-
onist 21 with encouraging PK properties using a combination of
high-throughput chemistry, pharmacophore analysis and in silico
profiling. Data generated for 21 met requirements for hit to lead
transition.
O
O
N
N
O
S
N
O
Figure 6. Structure of sulfonamide 11.

N. P. Barton et al. / Bioorg. Med. Chem. Lett. 19 (2009) 528–532
531
O
N
O
O
N
N
O
O
N
O
O
N
N
NH2
O
O
S
N
(a)
(b)
(c)
S
O
NH
N
+
O
N
N
Br
Br
X
Br
Scheme 2. Reagents and conditions: (a) i—Na2SO4, DCM, 100 °C, 10 min; ii—NaBH4, DCM/MeOH, rt, 1 h (yield 84%); (b) 4-MeO-Benzenesulfonyl chloride, pyridine, rt, 1 day
then 150 °C, 10 min (yield 92%); (c) 2-X-Phenylboronic acid, Na2CO3, DME:H2O:EtOH (7:3:2), Pd(PPh3)4, 140 °C, 5 min (yield 62–93%).
Table 3
Table 5
PK profiles of potent tertiary sulfonamides.
Optimised PK profiles of potent tertiary sulfonamides.
Compound
13
14
Compound
Solubility (
21
22
Solubility (
l
M)
9
6
lM)
259
214
CYP (
1A2
2C9
2C19
2D6
3A4 (DEF)
3A4 (7BQ)
l
M)
CYP (
1A2
2C9
2C19
2D6
lM)
>33
0.52
0.45
>33
0.75
2.2
>33
0.81
0.69
>33
0.71
2.1
18
6.7
13
31
1.3
4.8
19
0.78
25
29
2.8
>33
3A4 (DEF)
3A4 (7BQ)
Fpo (%)
12
9
Fpo (%)
40
—
Table 4
Sulfonamide SAR.
O
N
N
O
R
S
N
O
Compound
R
OT pKi
logDa
Compound
R
OT pKi
logDa
O
O
N
N
16
8.8
3.7
3.6
21
7.9
1.0
*
*
O
N
N
17
8.6
22
7.9
0.9
*
*
*
O
N
N
S
18
19
8.4
8.2
8.0
2.3
2.5
3.3
23
24
25
7.9
7.9
7.9
2.7
2.9
2.6
*
*
*
O
O
S
S
*
*
20
S
O
O
a
clogD7.4 determined by ACD V8.0.

532
N. P. Barton et al. / Bioorg. Med. Chem. Lett. 19 (2009) 528–532
Functional Assays:
OT (FLIPR) fpKi
N
O
N
N
8.3
6.1
inactive
6.5
O
V1a (FLIPR) fpKi
V1b (FLIPR) fpKi
V2 (Yeast) fpKi
Filtration Binding Assays:
OT pKi
N
S
N
O
9.1
7.2
7.5
4.9
V1a pKi
V1b pKi
V2 pKi
21
Figure 8. Selectivity profile of orally bioavailable sulfonamide.
functional FLIPR assays using recombinant human vasopressin V2 receptors
stably transfected in yeast cells. Oxytocin receptor binding (pKi) was
determined by fluorescence polarisation (FP) using recombinant human
oxytocin receptors stably transfected in CHO cells and Bodipy TMR-oxytocin
obtained from Perkin Elmer.
Acknowledgment
The authors acknowledge the contribution of Blaise Bridier to
the preparation of example compounds.
6. Quattropani, A.; Dorbais, J.; Covini, D.; Pittet, P.; Colovray, V.; Thomas, R. J.;
Coxhead, R.; Halazy, S.; Scheer, A.; Missotten, M.; Ayala, G.; Bradshaw, C.; De
Raemy-Schenk, A.; Nichols, A.; Cirillo, R.; Tos, E. G.; Giachetti, C.; Golzio, L.;
Marinelli, P.; Church, D. J.; Barberis, C.; Chollet, A.; Schwarz, M. K. J. Med. Chem.
2005, 48, 7882.
7. Compound 9: Brown, A. D.; Ellis, D.; Smith, C. R. U.S. Patent 7,291,640.
8. Compound 10: Liddle, J.; Allen, M. J.; Borthwick, A. D.; Brooks, D. P.; Davies, D. E.;
Edwards, R. M.; Exall, A. M.; Hamlett, C.; Irving, W. R.; Mason, A. M.; McCafferty,
G. P.; Nerozzi, F.; Peace, S.; Philp, J.; Pollard, D.; Pullen, M. A.; Shabbir, S. S.; Sollis,
S. L.; Westfall, T. D.; Woollard, P. M.; Wu, C.; Hickey, D. M. B. Bioorg. Med. Chem.
Lett. 2008, 18, 90.
References and notes
1. Gimpl, G.; Fahrenholz, F. Physiol. Rev. 2001, 81, 629.
2. Borthwick, A. D. Annu. Rep. Med. Chem. 2006, 41, 409.
3. Stubbs, T. M. Clin. Obstet. Gynaecol. 2000, 43, 489.
4. Tsatsaris, V.; Carbonne, B.; Cabrol, D. Drugs 2004, 64, 375.
5. Functional vasopressin (V1a/V1b) and oxytocin receptor antagonism (fpKi)
was determined in functional FLIPR assays using recombinant human
oxytocin or vasopressin (V1a/V1b) receptors stably transfected in CHO cells.
Functional vasopressin V2 receptor antagonism (fpKi) was determined in
9. Filtration binding was determined by displacement of 3H-oxytocin from
recombinant human oxytocin receptors stably transfected in CHO cells.