The discovery of novel 8-azabicyclo[3.2.1]octan-3-yl)-3-(4-chlorophenyl) propanamides as vasopressin V1A receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2011.02.096

The discovery of a novel series of 8-azabicyclo[3.2.1]octan-3-yl)-3-(4- chlorophenyl) propanamide antagonists of the vasopressin V_1A receptor is disclosed. Compounds 47 and 48 were found to be high affinity, selective vasopressin V_1A antagonists.

Full text of DOI:10.1016/j.bmcl.2011.02.096

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3163–3167
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
The discovery of novel 8-azabicyclo[3.2.1]octan-3-yl)-3-(4-chlorophenyl)
propanamides as vasopressin V1A receptor antagonists
Susan Napier a, , Grant Wishart a, , William Arbuckle a, James Baker c, David Barn a, Matilda Bingham a,
Angus Brown a, Alan Byford c, Chris Claxton c, Mark Craighead b, Kirsteen Buchanan a, Lee Fielding a,
Lindsay Gibson a, Richard Goodwin a, Susan Goutcher b, Nicholas Irving b, Cliona MacSweeney c,
Rachel Milne b, Chris Mort a, Jeremy Presland b, Hazel Sloan c, Fiona Thomson b,
Zara Turnbull c, Trevor Young a
⇑
⇑
a Department of Chemistry, MSD, Newhouse, Lanarkshire ML1 5SH, UK
b Department of Molecular Pharmacology, MSD, Newhouse, Lanarkshire ML1 5SH, UK
c Department of Pharmacology, MSD, Newhouse, Lanarkshire ML1 5SH, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
The discovery of a novel series of 8-azabicyclo[3.2.1]octan-3-yl)-3-(4-chlorophenyl) propanamide antag-
onists of the vasopressin V1A receptor is disclosed. Compounds 47 and 48 were found to be high affinity,
selective vasopressin V1A antagonists.
Received 21 December 2010
Revised 21 February 2011
Accepted 23 February 2011
Available online 4 March 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Vasopressin
V1A
Antagonist
Arginine vasopressin (AVP) is a 9 amino acid cyclic peptide pro-
duced in the hypothalamus. It is released from the posterior pitu-
itary gland into the bloodstream or directly into the brain. AVP
exerts its effects through four different G-protein coupled recep-
tors, V1A, V1B, V2 and oxytocin (OT). V1A receptors are localised in
the liver (glycogenolysis), vascular smooth muscle cells (vasocon-
striction, uterine blood flow, contraction) and the brain (stress
adaptation, memory formation, temperature, circadian rhythm).
Johnson have developed a brain penetrant V1A antagonist,
JNJ-17308616 (2) which was found to be active in a number of
rat models of anxiety. Although JNJ-17308616 is a potent antago-
nist at human V1A and selective against human V1B, V2 and OT,
the compound’s affinity for rat V1A is lower and has equipotent
affinity for rat V2.6 Azevan have developed selective V1A antago-
nists SRX-251 (3) and SRX-246 (4), claimed to be orally bioavail-
able and brain penetrant.7 SRX-251 was shown to inhibit
aggression in hamsters. Both compounds have completed Phase 1
studies with Phase 2 studies planned for SRX-251 for the treatment
of dysmenorrhoea.
V1A receptors are also localised in blood platelets and are involved
in platelet aggregation. A selective V1A antagonist may have clinical
utility in dysmenorrhoea, preterm labour, hypertension, Raynaud’s
disease, depression, anxiety, hyponatremia and congestive heart
failure.1,2
Compound 5 (Table 1) was originally identified from an internal
V1B optimisation program. Routine cross screening at the human
Relatively few small molecule V1A antagonists have progressed
into clinical development, reflecting the challenges associated with
the development of non-peptidic ligands for the vasopressin family
of peptide GPCRs. Relcovaptan (SR 49059, 1), Sanofi-Aventis, is a
highly potent and selective peripherally acting V1A antagonist
which has shown clinical efficacy for the treatment of Raynaud’s
disease, dysmenorrhoea and preterm labour (Fig. 1).3–5 No further
development has been reported for this compound. Johnson and
V1A receptor revealed greater than two orders of magnitude higher
affinity for the V1A receptor over the human V1B receptor
(hV1A pKi = 8.53, hV1B pKi = 5.90). However, 5 suffers from high
molecular weight (MWt = 641.3), high lipophilicity (c log P = 6.208)
and high flexibility. This was accompanied by poor in vitro meta-
bolic stability in human liver microsomes (CLint = 262 lL/min/
mg). In this publication the SAR exploration around compound 5
leading to a novel series of V1A antagonists is disclosed. The initial
optimisation strategy focussed upon improving the physico-chem-
ical properties while maintaining high V1A receptor affinity. Bind-
ing affinities for compounds at the human and rat V1A receptors
were measured in [3H]AVP binding assays in CHO cells expressing
⇑
Corresponding authors. Tel.: +44 7729 182555 (S.N.); +44 7929 191161 (G.W.).
E-mail addresses: susannapier67@googlemail.com (S. Napier), grantwishart@
btinternet.com (G. Wishart).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.02.096

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S. Napier et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3163–3167
N
O
NH
Cl
OH
Cl
N
O
NH2
O
N
O
N
N
O
N
N
N
O
N
N
O
O
O
S
N
N
O
O
O
O
F
O
N
O
HN
O
O
F3C
N
H
O
O
SRX-246, 4
SRX-251, 3
Relcovaptan (SR49059), 1
JNJ-17308616, 2
Figure 1. Structures of compounds 1–4.
Table 1
Table 2
O
H
O
1
N
O
R
N
N
H
O
S
2
N
R
N
N
N
O
N
R
Cl
R1
Compd
R2
hV1A pKi
Compd
R
hV1A pKi
14
15
16
17
18
H
SO2Ph
SO2CH2Ph
COPh
COCH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
CH2Ph
<6
6.63
6.63
6.03
6.77
*
5
9
8.53
7.29
Cl
Cl
*
O
O
O
O
O
S
19
20
21
22
H
7.02
7.25
7.62
7.82
*
*
*
*
O
*
10
11
7.51
7.78
O
S
Et
*
O
*
O
S
nPr
iPr
12
13
6.83
6.62
O
H
O
S
the human V1A receptor or rat V1A receptor, respectively. Binding
affinities at human V1B, V2 and OT receptors were measured in
[3H]AVP or [3H]OT binding assays in CHO cells expressing the hu-
man V1B, V2 or OT receptors, respectively. In all assays pKi values
O
were determined from
experiments.
a
minimum of two independent
sequence of modifications and deletions. All compounds were ini-
tially measured for human V1A affinity (Tables 1–4), subsequent
compounds (Table 5) were measured for both human and rat V1A
affinity. Modifications around the ‘amino-acid’ moiety are shown
in Table 1. Stereochemistry inversion to give the R enantiomer 9 re-
sulted in a 17-fold decrease in V1A affinity, suggesting that both
enantiomers may afford high affinity V1A ligands. Phenyl analogue
10 gave a 10-fold loss in affinity. The unsubstituted benzyl com-
pound 11 showed a modest sixfold decrease in V1A affinity com-
pared to the 4-chloro benzyl starting point 5. However, the
saturated cyclohexyl methyl analogue 12 showed a 50-fold de-
crease in affinity. Deletion analogue 13 lost almost two orders of
magnitude in V1A affinity versus 5. Table 2 shows changes to
the aryl sulfonamide and the N-benzyl moieties. Deletion of the
4-methoxy-2,3,6-trimethylphenylsulfonyl group to afford primary
The compounds appearing in Tables 1–5 were synthesised via
the general route outlined in Scheme 1. All starting materials and
reagents were purchased from commercial sources unless other-
wise stated. Boc-protected amino acids 6 were reacted with
amines under standard amide coupling conditions to afford inter-
mediates 7. Amines were either commercially available or pre-
pared by reductive alkylation according to Scheme 2. Boc-
deprotection of intermediate 7 with TFA in DCM afforded amines
8 which were subsequently reacted with either a sulfonyl chloride
or carboxylic acid to afford the desired sulfonamides or amides,
respectively.
The initial optimisation strategy was to explore the potential
importance of the substructural motifs of starting point 5 via a

S. Napier et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3163–3167
3165
Table 3
Table 4
O
O
H
N
O
N
H
1
O
S
N
N
2
R
H
R
O
R
O
Compd
R1
H
R2
hV1A pKi
HLMa CLint
RLMb CLint
*
Cl
Compd
R
hV1A pKi
31
7.05
23
<12
23
24
NHCH3
NHCH2Ph
6.47
8.25
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
*
*
*
*
*
*
*
*
N
32
33
34
35
36
37
38
39
2-Cl
6.54
7.25
7.65
7.47
8.31
7.40
7.32
<5
25
N
7.90
*
N
H
N
N
*
26
27
6.96
6.74
N
3-Cl
H
*
N
N
4-Cl
28
29
6.95
7.31
*
N
H
2,3 Di-Cl
3,4 Di-Cl
2,4 Di-Cl
H
N
*
*
N
H
191
167
N
30
6.89
N
H
amine 14 resulted in a profound loss of V1A binding affinity. Unsub-
stituted phenyl and benzyl sulfonamides 15 and 16 showed almost
two orders of magnitude decreases in affinity upon comparison
with 5. Phenyl amide 17 afforded a further decrease in V1A affinity,
although the benzyl amide analogue 18 showed similar affinity to
that of the unsubstituted sulfonamides 15 and 16. Deletion of the
N-benzyl moiety to afford 19 gave a 32-fold decrease in affinity
compared to the initial hit compound 5. N-Ethyl analogue 20
showed a slight increase in affinity compared to the secondary
amide 19. Increasing the size of the alkyl substituent to n-propyl
(21) and isopropyl (22) afforded further increases in affinity com-
pared to 19.
27
70
H
a
In vitro human liver microsome intrinsic clearance (
In vitro rat liver microsome intrinsic clearance (
l
L/min/mg).
b
lL/min/mg).
The initial deletion SAR indicated that removal of the N-benzyl
moiety was slightly better tolerated than removal of the 4-chloro
benzyl group. A decision was therefore taken to remove the N-ben-
zyl substituent and focus on SAR exploration around 19. Keeping
Table 5
2
3
4
O
R
N
R
R
H
N
1
N
R
H
O
Cl
Compd
R1
R2
R3
R4
hV1A pKi
rV1A pKi
HLMa CLint
RLMb CLint
40
41
42
43
44
45
3,4 Di-Cl
4-Cl
4-F
4-CH3
4-OCH3
4-Cl
H
H
H
H
H
CH3
H
H
H
H
H
CH3
H
6.89
8.68
7.57
8.15
7.76
8.50
6.71
6.69
<6
6.42
<6
29
50
30
42
84
54
CH3
CH3
CH3
CH3
CH3
6.88
84
119
46
47
4-Cl
4-Cl
CH3
H
8.78
9.63
7.26
7.66
274
<12
259
42
H
H
48
4-Cl
H
9.25
8.38
58
55
a
In vitro human liver microsome intrinsic clearance (
l
L/min/mg).
b
In vitro rat liver microsome intrinsic clearance (
lL/min/mg).

3166
S. Napier et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3163–3167
O
O
O
O
H
N
H
N
H
a
b
c
R2
O
H2N
R2
R4
R2
O
N
OH
S
N
N
R1 R3
8,14
N
R1 R3
O
O
R1
R1 R3
O
O
6
7
5,9-13,15,16,19-22
O
H
R5
N
R2
d
N
R1
O
R3
17,18,23-48
Scheme 1. Reagents and conditions: (a) R2R3NH, HBTU, DIPEA, DCM, rt; (b) 20% TFA in DCM, rt; (c) R4SO2Cl, Et3N, DMF, rt; (d) R5COOH, HBTU, DIPEA, DCM, rt.
pre-clinical in vivo models. The potential for species differences
N
N
a
N
NH2
between human and rodent V1A receptors for particular V1A recep-
tor antagonists has been described in the literature. Site directed
mutagenesis experiments have revealed several key amino acids
that contribute to the species difference, in particular a GLY337
(human) to ALA342 (rat) difference in transmembrane helix 7.9,10
A final optimisation cycle was undertaken in an effort to in-
crease rat V1A affinity while maintaining reasonable microsomal
stabilities (Table 5). The secondary amine 40 showed decreased
human V1A affinity. This was accompanied by a greater than
10-fold increase in rat V1A affinity compared to 38 resulting in sim-
ilar affinities at the human and rat receptors whilst maintaining
microsomal stability. Modifying the N-benzyl amide 4-position
failed to make any major impact upon rat V1A receptor affinity with
compounds 41–44 all showing relatively low rat affinity upon
comparison to the human receptor data. Maintaining a 4-chloro
N-benzyl amide, substitution of the benzylic carbon was explored.
Dimethyl analogue 45 maintained a similar profile to 41 whereas
the cyclopropyl compound 46 demonstrated increased rat V1A
affinity. Combination of the 4-chloro benzyl amide and secondary
amine to give compound 47 showed high human V1A receptor
affinity, good rat V1A receptor affinity and reasonable microsomal
intrinsic clearances. Compound 48 incorporating the cyclopropyl
motif also showed high human and rat V1A receptor affinity and
moderate microsomal intrinsic clearance.
Compounds 47 and 48 were selected for further profiling. In
selectivity screening versus human V1B, V2 and OT receptors both
compounds showed low affinities across all three receptors
(pKi 6 5.0). Functional antagonism in CHO cells expressing the hu-
man V1A receptor was determined in a calcium flux assay. Both 47
(pIC50 = 7.26) and 48 (pIC50 = 7.43) acted as potent V1A antagonists
inhibiting the release of intracellular calcium induced by the vaso-
pressin receptor agonist AVP. Furthermore 47 (pKi = 5.38) and 48
(pKi = 5.80) show relatively low affinity for the hERG channel in a
[3H]dofetilide binding assay.11
In vivo activity was assessed by the reversal of V1A mediated
AVP induced diastolic blood pressure increases in conscious rats
as described in the literature.3,12 Compound 47 (4 mg/kg, iv) de-
creased the AVP pressor response by 77.4 12% and 58 3% at
15 and 30 min post-drug, respectively (n = 2). Whereas 48 (4 mg/
kg, iv) decreased the AVP pressor response for at least 60 min
post-drug, with a maximal decrease of 50 14% at 60 min (n = 3).13
Pharmacokinetic studies were performed in male Wistar rats at
doses of 1 mg/kg iv and 10 mg/kg orally (Table 6). Plasma clear-
ances were low to moderate for both compounds, reflecting
improvements made in microsomal stability. Extensive distribu-
tion was also observed, resulting in promising half-lives (8–12 h).
However, the oral Cmax was very low for 47 and 48 and both
showed disappointingly low oral bioavailability, suggesting poor
absorption and/or extensive extra-hepatic first pass metabolism.
Improving oral bioavailability would be a significant aspect of sub-
sequent optimisation for the series.
H
N
N
49
50
Scheme 2. Reagents and conditions: (a) benzaldehyde, NaBH4, MeOH, rt.
the 4-chloro benzyl and 4-methoxy-2,3,6-trimethylphenylsulfonyl
groups in place, variation of the amide substituent was investi-
gated in detail. Selected key analogues are shown in Table 3. Re-
moval of the amine sidechain of 19 to give N-methyl amide 23
gave a 3.5-fold decrease in V1A affinity whereas N-benzyl amide
24 showed a 17-fold increase in affinity. It was clear from the
SAR that a basic moiety is not a requirement for high V1A receptor
affinity however it does positively contribute to physico-chemical
properties such as solubility. The chain shortened piperazine ana-
logue of 19, compound 25 showed increased V1A affinity although
the dimethylamine equivalent 26 was of similar affinity to 19.
N-Methyl piperazine amide 27 and compound 28 also exhibited
similar affinity to 19. Amino tropane stereoisomers 29 and 30 both
showed good V1A affinity with the highest affinity residing with the
endo isomer.
In order to further improve physico-chemical properties it was
desirable to replace the sulfonamide moiety completely. Combina-
tion of 4-methoxy-2,3,6-trimethylphenyl sulfonamide replace-
ments with different amide substituents (data not shown) led to
the identification of compound 31 (Table 4), where the endo amino
tropane amide substituent is combined with an N-benzyl amide
sulfonamide replacement. Compound 31 shows good V1A receptor
affinity and importantly low intrinsic clearance in human and rat
in vitro microsomal stability assays. This is perhaps consistent with
the significantly lower lipophilicity of 31 (c log P = 2.87) upon com-
parison to the starting compound 5 (c log P = 6.20). In an effort to
increase V1A affinity yet maintain reasonable microsomal stability
simple substitution around the N-benzyl amide was pursued
(Table 4). 3-Chloro racemate 33 showed similar affinity to 31,
whereas the 2-chloro analogue 32 afforded a threefold decrease.
The 4-chloro compound 34 resulted in a fourfold increase in V1A
affinity. Dichloro compounds 35 and 37 showed no further advan-
tage over the 4-chloro derivative 34. The 3,4-dichloro analogue 36
gave a 4.5-fold increase in affinity over 34. However this was
accompanied by high intrinsic clearances. Synthesis of the enanti-
omers of 31 yielded a surprising outcome. REnantiomer 38 showed
high V1A affinity whereas the S enantiomer 39 was effectively inac-
tive. It is speculated that the introduction of the amino tropane and
benzyl amide moieties may lead to a slightly different binding
mode to the sulfonamides. Human microsomal intrinsic clearance
for compound 38 was similar to that of its racemate 31 but rat
microsomal clearance was higher. In vivo pharmacokinetic studies
in male Wistar rats for compound 38 (2 mg/kg iv and 10 mg/kg or-
ally, 10% dimethylacetamide in water) showed 12% oral bioavail-
ability. However, 38 (pKi 6 5.5) showed significantly lower rat
V1A receptor affinity which would compromise its use in
In summary compounds 47 and 48 have been identified as
novel selective vasopressin V1A receptor antagonists. Both

S. Napier et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3163–3167
3167
Table 6
4. Serradeil-Le Gal, C.; Herbert, J. M.; Delisee, C.; Schaeffer, P.; Raufaste, D.; Garcia,
C.; Dol, F.; Marty, E.; Maffrand, J. P.; Le Fur, G. Am. J. Physiol. 1995, 268,
Pharmacokinetic parameters for compounds 47 and 48
H404.
0
47a
48a
5. Brouard, R.; Bossmar, T.; Fournié-Lloret, D.; Chassard, D.; ÅAkerlund, M. Br. J.
Obstet. Gynaecol. 2000, 107, 614.
6. Bleickardt, C. J.; Mullins, D. E.; MacSweeney, C. P.; Werner, B. J.; Pond, A. J.;
Guzzi, M. F.; Martin, F. D. C.; Varty, G. B.; Hodgson, R. A. Psychopharmacology
2009, 202, 711.
7. Guillon, C. D.; Koppel, G. A.; Brownstein, M. J.; Chaney, M. O.; Ferris, C. F.; Lu, S.-
F.; Fabio, K. M.; Miller, M. J.; Heindel, N. D.; Hunden, D. C.; Cooper, R. D. G.;
Kaldor, S. W.; Skelton, J. J.; Dressman, B. A.; Clay, M. P.; Steinberg, M. I.; Bruns,
R. F.; Simon, N. G. Bioorg. Med. Chem. 2007, 15, 2054.
8. c log P 4.3, BioByte Corp. 201 W. 4th St. #204 Claremont, CA 91711-4707, USA.
9. Shinoura, H.; Take, H.; Hirasawa, A.; Inoue, K.; Ohno, Y.; Hashimoto, K.;
Tsujimoto, G. FEBS Lett. 2000, 466, 255.
CLb (mL/min/kg)
Vssb (L/kg)
16
44
10.8
11.5
6
1.2
<1
17.7
8.2
19
3.5
4
b
t1/2 (h)
c
Cmax (ng/mL)
c
tmax (h)
Fc (%)
a
b
c
5% (v/v) cremophor EL in saline.
1 mg/kg iv dosing.
10 mg/kg po dosing.
10. Thibonnier, M.; Coles, P.; Conarty, D. M.; Plesnicher, C. L.; Shoham, M. J.
Pharmacol. Exp. Ther. 2000, 294, 195.
compounds display reversal of V1A mediated increases in diastolic
blood pressure induced by the endogenous ligand AVP. However,
both compounds show disappointing oral pharmacokinetic param-
eters, optimisation of which will be the subject of a subsequent
publication.
11. The affinity of the test drugs for the hERG cardiac K+ channel was determined
by their ability to displace tritiated dofetilide in membrane homogenates from
HEK-293 cells expressing the hERG channel.
12. Tskuda, J.; Tahara, A.; Tomura, Y.; Kusayama, T.; Wada, K.; Ishii, N.; Taniguchi,
N.; Suzuki, T.; Yatsu, T.; Uchida, W.; Shibasaki, M. Vasc. Pharmacol. 2005, 42,
47.
13. Surgical procedures were carried out under isoflurane anaesthesia. Male
Wistar BRL rats were implanted with TL11M2-C50-PXT radiotelemetric
transmitters (Data Sciences International, St Paul MN, USA) for monitoring
blood pressure (BP) and heart rate (HR) via the descending aorta. After a
minimum of 14 days recovery a polyethylene catheter was placed in the
right external jugular vein and exteriorised on the dorsal side of the neck.
The catheter was filled with glycerol containing 100 I.U. heparin. Prior to
drug testing animals were allowed to recover for another 3 days. The jugular
Acknowledgements
We would like to thank our Analytical Chemistry colleagues for
structure and purity determination.
References and notes
vein was connected to
followed by minimum of 30 min habituation. Prior to test compound
administration, AVP ([Arg8]-Vasopressin, Sigma) was dosed iv (30 mU/kg,
0.1 mL/kg) two or three times at 15 min intervals to establish stable
a 3-way infusion line for drug administration
a
1. Thibonnier, M.; Coles, P.; Thibonnier, A.; Shoham, M. Annu. Rev. Pharmacol.
Toxicol. 2001, 41, 175.
a
2. Ring, R. H. Curr. Pharm. Des. 2005, 11, 205.
control pressor response (approximately a 30–50 mmHg rise in diastolic BP).
Test compounds (4 mg/kg) were administered iv in 20% dimethylacetamide
(DMA) in water and AVP pressor responses were measured at 15, 30 and
60 min.
3. Serradeil-Le Gal, C.; Wagnon, J.; Garcia, C.; Lacour, C.; Guiraudou, P.;
Christophe, B.; Villanova, G.; Nisato, D.; Maffrand, J. P.; Le Fur, G.; Guillon, G.;
Cantau, B.; Barberis, C.; Trueba, M.; Ala, Y.; Jard, S. J. Clin. Invest. 1993, 92, 224.