Design and optimization of potent, selective antagonists of Oxytocin

Article abstract of DOI:10.1016/j.bmcl.2008.06.098

A novel series of Oxytocin antagonists are described. This series was identified through pharmacophoric overlap of in-house and literature antagonists. Subsequent optimization led to a series of potent, selective antagonists. Several analogues displayed o

Full text of DOI:10.1016/j.bmcl.2008.06.098

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4278–4281
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and optimization of potent, selective antagonists of Oxytocin
à
*
Alan Brown , Lindsay Brown , Dave Ellis, Nicholas Puhalo, Chris R. Smith ,
Olga Wallace z, Lesa Watson
Discovery Chemistry, Pfizer Global Research and Development, Ramsgate Road, Sandwich, Kent CT13 9NJ, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel series of Oxytocin antagonists are described. This series was identified through pharmacophoric
overlap of in-house and literature antagonists. Subsequent optimization led to a series of potent, selective
antagonists. Several analogues displayed oral bioavailability in vivo in the rat.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 9 June 2008
Revised 25 June 2008
Accepted 28 June 2008
Available online 3 July 2008
This paper is dedicated to the memory of
Olga Wallace.
Keywords:
Oxytocin
Antagonist
Triazole
Oxytocin (OT) is a nonapeptide hormone that acts on the OT
receptor, a seven-transmembrane (7TM) (Gq-coupled) receptor.
The OT receptor has no subtypes but is related to the vasopressin
receptors V1A, V1B and V2. OT antagonists have therapeutic poten-
tial in a number of areas including pre-term labour:1 Benign Pros-
tatic Hyperplasia2 and sexual dysfunction.3 As a result there is
significant interest in the identification of potent, selective, orally
bioavailable OT antagonists.
N
N
N
Me
O
N
O
5
OT Ki 304nM; V1A Ki 28nM; MWt 440,
cLogP 5.1; L.E. 0.28
Several templates have been investigated in the search for
potential OT antagonists, as represented by such compounds
as sulphonamide 1,4 piperidine amide 2,5 diketopiperazine 36
and oxime 47 (Scheme 1). The latter compound is particularly
noteworthy as it represents one of the most (heavy atom) li-
gand efficient OT antagonists reported to date.8 In addition,
high throughput screening (HTS) of the Pfizer file identified tri-
azole 5 as a possible starting point in our quest for a potent,
selective OT antagonist.9 In fact, 5 has been previously disclosed
as a selective antagonist for the V1A receptor.10 We were una-
ware of its OT activity until it was fully profiled in HTS fol-
low-up.
The fact that 5 is inversely selective for OT over V1A makes it
considerably less attractive as a starting point for the design of
OT selective antagonists. This and several other key issues had
to be addressed if this hit were to yield an attractive lead series.
Specifically, to increase our chances of achieving an acceptable
oral pharmacokinetic profile, potency and ligand efficiency
(L.E.) had to be improved and it was likely that inherent lipo-
philicity had to be reduced.11 Comparison of antagonists 4 and
5, as well as other HTS actives suggested a simple OT pharmaco-
phore, as depicted in Scheme 2. Direct comparison of oxime 4
and triazole 5 using this analysis suggested simplification of
hit 5 to compounds such as 6. This compound was prepared
and shown to have slightly improved OT antagonist potency
but with significantly reduced molecular weight, and hence
greatly superior ligand efficiency.
* Corresponding author. Tel./fax: +44 1304648240.
E-mail address: Alan.D.Brown@pfizer.com (A. Brown).
Present address: Organon Laboratories Ltd,A Part of Schering-Plough Corporation,
Newhouse, Motherwell, UK.
à
Present address: Medicinal Chemistry, SGX Pharmaceuticals, Inc., 10505 Roselle
Street, San Diego, CA 92122, USA.
z
Deceased author.
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.06.098

A. Brown et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4278–4281
4279
O
O
O
N S
O
N
O
NH2
N
O
N
N
O
HN
S
O
O
O
O
1
2
OT Ki 8nM
MWt 555
L.E. 0.31
OT Ki 20nM
MWt 507
L.E. 0.29
N
Me
O
O
O
N
N
O
O
N
Me
N
N
N
N
O
O
Me
O
4
3
OT Ki 50nM
MWt 376
OT Ki 3nM
MWt 495
L.E.0.33
L.E. 0.36
Scheme 1. Representation of published OT antagonists with calculated heavy atom ligand efficiencies (L.E.).
Exploration of SAR around the C5 (methyl) triazole substitu-
ent of 7 identified methoxymethyl as a substituent which typi-
cally gave ca. 3Â improvement in OT potency. However,
incorporation of this substituent also (typically) resulted in a
slight reduction in selectivity over V2, as demonstrated by com-
pounds such as 8.
N
N
N
N
O
Me
Scheme 2. OT pharmacophore overlay based on compounds 4 and 5.
OMe
N
N
N
N
N
N
Me
N
OMe
OMe
OMe
6
8
OT Ki 16nM; MWt 402; clogP3.4; L.E. 0.36
1A Ki 270nM; V1B >10uM; V2 Ki 160nM
OT Ki 143nM; MWt 341, clogP 5; LE 0.36
V
Closer inspection of our pharmacophoric overlap model suggested
incorporation of a pyridyl N in 6 (overlapping with the oxime N of
4), as well as incorporation of an ortho substituent in the biaryl sub-
stituent. These changes gave compound 7, where OT antagonism had
increased further, whilst lipophilicity had been reduced by 1.8 log
units. Selectivity profilingof this compound revealeda somewhat im-
proved profile with respect to V1A antagonism. However, significant
(antagonist) activityagainstV2 receptorswas also observed. No activ-
Replacement of the central aryl of the C3 biaryl triazole substi-
tuent with a pyrazine, as in compound 9, gave a significant reduc-
tion in V2 antagonism. In addition, this modification routinely gave
a >1 log unit reduction in clogP, which we believe would be poten-
tially beneficial in terms of optimising metabolic stability and
aqueous solubility.13
ity was observed against V1B.
12 Nonetheless, the potency, (low) lipo-
OMe
N
N
N
philicityandexcellentligandefficiencyofcompound 7 encouragedus
to focus on this lead series. We thus set about optimising potency,
selectivity and pharmacokinetic properties.
N
N
N
OMe
9
N
N
N
Me
OT Ki 43nM; MWt 374; clogP2.1; L.E. 0.37
V1A Ki 44nM; V1B >10uM; V2 Ki > 10uM
N
OMe
OMe
We next switched our attention to the optimisation of the left-
hand side aryl substituent in 9. The compounds described in Table
1 illustrate three key SAR points for this region of our OT
antagonists:
7
OT Ki 56nM; MWt 372; clogP 3.2; L.E. 0.36
V
1A Ki 525nM; V1B >10uM; V2 Ki 500nM

4280
A. Brown et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4278–4281
Table 1
LHS aryl SAR
N
N
CO2Me
B(OH)2
+
N
N
CO2Me
Me
a
F
Me
Cl
N
N
N
F
21
20
N
N
X
R1
22
N
6
3
5
4
R2
2
b
OMe
Compound
R1
R2
X
Ki (nM)
V1A
N
N
N
CONHNH2
N
N
c
Me
OT
43
4
17
84
6
V2
Me
N
N
9
10
11
12
13
14
15
16
17
18
19
H
H
–OCH3
–OCH3
–OCH3
–OCH3
H
44
132
1220
3230
388
>10,000
103
>10,000
>10,000
>10,000
n.t.a
>10,000
>10,000
>10,000
>10,000
n.t.a
2-CH3
3-CH3
3-CN
2-CH3
2-Cl
2-CH3
3-CH3
2-CH3
3-CH3
2-Cl
3-CH3
4-F
H
4-F
H
4-CH3CH2S–
4-CH3O–
4-CN
N
F
F
OMe
23
13
H
H
2
202
Scheme 3. Reagents and conditions: (a) Pd(0) catalyst,17 Cs2CO3, Dioxan, reflux, 2 h,
quant; (b) NH2NH2, ethanol, reflux, 15 h, 80%; (c) i—dimethoxyacetamidedimethy-
lacetal, AcOH, 60 °C, 3 h; ii—5-amino-2-methoxypyridine, AcOH, 100 °C, 6 h; iii—
recrystallisation, 30% overall for step c.
232
537
14
201
1
n.t.a
2410
4300
432
–OCH3
–OCH3
–OCH3
H
4-CH3
3-F
732
a
n.t., not tested.
In summary, we have utilised pharmacophoric overlap of a high
throughput screening hit and published OT antagonists followed
by subsequent optimisation to yield several potent, selective Oxyto-
cin antagonists. Two of these compounds displayed promising phar-
macokinetic profiles in the rat and represent potential tools for
further preclinical investigation of the therapeutic potential of OT
antagonism. Further development of this series will be reported in
due course.
(1) Highly potent compounds typically carry two substituents
such as methyl and chloro (e.g., compounds 10, 13, 14 and
19).
(2) Electron-withdrawing substituents in the 3 or 4 position
typically result in a drop in V1A activity (e.g., compounds 9
vs 12 and compounds 14 vs 19).
(3) Larger four substituents (beyond Fluoro and Cyano) result in
a drop in OT potency (e.g., compounds 13 vs 15 and com-
pounds 16 and 18).
Acknowledgments
Compounds 13 and 17 emerged from this analysis as our most
promising OT antagonist from this series.
We acknowledge the contributions of the following co-workers:
Mark Lewis, Simon Pegg and Nicola Robinson.
N
N
N
References and notes
Me
N
1. Gullam, J. E.; Chatterjee, J.; Thornton, S. Drug Discovery Today: Ther. Strateg.
2005, 2, 47–52.
2. Tiwari, A.; Nanda, K.; Chugh, A. Expert Opin. Investig. Drugs 2005, 14, 1359–
1372.
N
N
F
Me
OMe
13
3. See, for example, WO 2005028452 and the references therein.
4. Williams, Peter D.; Anderson, Paul S.; Ball, Richard G.; Bock, Mark G.; Carroll,
LeighAnne; Lee Chiu, Shuet-Hing; Clineschmidt, Bradley V.; Chris Culberson, J.;
Erb, Jill M., et al J. Med. Chem. 1994, 37, 565–571.
5. Williams, Peter D.; Clineschmidt, Bradley V.; Erb, Jill M.; Freidinger, Roger M.;
Guidotti, Maribeth T.; Lis, Edward V.; Pawluczyk, Joseph M.; Pettibone, Douglas
J.; Reiss, Duane R., et al J. Med. Chem. 1995, 38, 4634–4636.
6. Borthwick, A. D.; Davies, D. E.; Exall, A. M.; Hatley, R. J. D.; Hughes, J. A.; Irving,
W. R.; Livermore, D. G.; Sollis, S. L.; Nerozzi, F.; Valko, K. L.; Allen, M. J.; Perren,
M.; Shabbir, S. S.; Woollard, P. M.; Price, M. A. J. Med. Chem. 2006, 49, 4159–
4170; Borthwick, A. D.; Davies, D. E.; Exall, A. M.; Livermore, D. G.; Sollis, S. L.;
Nerozzi, F.; Allen, M. J.; Perren, M.; Shabbir, S. S.; Woollard, P. M.; Wyatt, P. G. J.
Med. Chem. 2005, 48, 6956–6969.
OT Ki 6nM; MWt 376; clogP2.9; L.E. 0.41
V1A Ki 388nM; V1B >10uM; V2 Ki > 10uM
OMe
N
N
N
N
N
N
NC
Me
OMe
17
7. See WO2002102799.
8. Hopkins, A. L.; Groom, C. R.; Alex, A. Drug Discovery Today 2004, 9, 430–431.
9. All data reported herein represents functional antagonism, as measured against
the corresponding cloned human receptor in a cell based b lactamase reporter
assay, using technology licensed from Rhoto Pharmaceuticals.
10. Kakefuda, A.; Suzuki, T.; Tobe, T.; Tahara, A.; Sakamoto, S.; Tsukamoto, S.-i.
Bioorg. Med. Chem. 2002, 10, 1905.
11. See for example Leeson, P. D.; Springthorpe, B.Nat. Rev. Drug Disc. 2007, 6, 881–
890. and the references therein.
12. In fact, no significant V1B activity was detected (at 10
compounds screened in the series disclosed in this letter.
OT Ki 14nM; MWt 413; clogP1.7; L.E. 0.35
V1A Ki 4.3uM; V1B >10uM; V2 Ki > 10uM
Compounds 13 and 17 were then subjected to wider profiling.
Although they displayed relatively low solubilities14 both displayed
promising pharmacokinetic profiles in the rat.15 In addition, wide li-
gand profiling of 13 and 17 showed no significant activity (<50%
lM) for any of the
13. Subsequent analysis across this series suggested that there was indeed a greater
binding at <3 l
M) across a range (>70) of receptors and enzymes.16
probability of achieving improved in vitro metabolic stability at lower clogP.
14. Aqueous solubilities measured for compounds 13 and 17 were 6
7.4 and 24 g/ml at pH 7.2, respectively; solubilities measured on fully
crystalline material.
lg/ml at pH
The preparation of compound 13 is described in Scheme 3.
Commercially available boronic acid 20 underwent smooth Suzuki
coupling17 with commercial chloropyrazine 21. Hydrazinolysis
was then followed by a two-step/one-pot conversion to 13.18
l
15. Rat PK parameters were as follows. (a) Compound 13: oral pharmacokinetics
(dose: 0.5 mg/kg of a crystalline suspension)—Cl 50 ml/min/kg; T1/2 1 h; F

A. Brown et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4278–4281
4281
24%. Iv pharmacokinetics (1 mg/kg bolus dose)—Cl 48 ml/min/kg. (b)
Compound 17: oral pharmacokinetics (dose 2 mg/kg of crystalline
suspension) Cl 28 ml/min/kg; T1/2 0.7 h; F 30%. Iv pharmacokinetics (2 mg/
kg, bolus dose)—Cl 28 ml/min/kg.
17. See Bedford, R. B.; Cazin, C. S. J. Chem. Commun. 2001, 1540–1541. Suzuki
catalyst 3 from this paper was utilised in this coupling. More generally, this
catalyst was successfully utilised in a wide range of related Suzuki couplings in
this series.
a
16. Representative examples of (off target) pharmacology targets against which 13
and 17 were profiled: Angiotensin Converting Enzyme; human Cyclooxygenase
2 enzyme; human 5-HT1A receptor; human Endothelin A and B receptors;
human Cannabinoid 1 and 2 receptors; hERG Potassium channel.
18. Spectroscopic data for compound 13 are as follows: 1H NMR (CDCl3, 400 MHz)
d: 2.39 (s, 3H), 2.41 (s, 3H), 4.01 (s, 3H), 6.89 (d, 1H), 6.95–7.03 (m, 2H), 7.33
(dd, 1H), 7.54 (dd, 1H), 8.09 (d, 1H), 8.38 (d, 1H), 9.49 (d, 1H). Mass
Spectroscopy (APCI+): m/z 377 [MH+].