2-Aminomethyl piperidines as novel urotensin-II receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2008.03.078

A series of 2-aminomethyl piperidines has been discovered as novel urotensin-II receptor antagonists. The synthesis, initial structure-activity relationships, and optimization of the initial hit that resulted in the identification of potent, cross-species active, and functional urotensin-II receptor antagonists such as 1a and 11a are described.

Full text of DOI:10.1016/j.bmcl.2008.03.078

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 2860–2864
2-Aminomethyl piperidines as novel urotensin-II
receptor antagonists
Jian Jin,a,* Yonghui Wang,b Feng Wang,c Dongchuan Shi,a Karl F. Erhard,b
Zining Wu,c Brian F. Guida,c Sarah K. Lawrence,c David J. Behm,a Jyoti Disa,a
Kalindi S. Vaidya,c Christopher Evans,a Lynette J. McMillan,c
Ralph A. Rivero,b Michael J. Neeba and Stephen A. Douglasa
aCardiovascular and Urogenital Center of Excellence for Drug Discovery, GlaxoSmithKline,
709 Swedeland Road, King of Prussia, PA 19406, USA
bOncology Center of Excellence for Drug Discovery, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, PA 19426, USA
cMolecular Discovery Research, GlaxoSmithKline, 1250 South Collegeville Road, Collegeville, PA 19426, USA
Received 12 February 2008; revised 24 March 2008; accepted 31 March 2008
Available online 8 April 2008
Abstract—A series of 2-aminomethyl piperidines has been discovered as novel urotensin-II receptor antagonists. The synthesis, ini-
tial structure-activity relationships, and optimization of the initial hit that resulted in the identification of potent, cross-species
active, and functional urotensin-II receptor antagonists such as 1a and 11a are described.
ꢀ 2008 Elsevier Ltd. All rights reserved.
Human urotensin-II (hU-II), the most potent mamma-
lian vasoconstrictor identified to date,1 and its cognate
receptor hUT (formerly known as the GPR-14 receptor)
are proposed to be involved in the (dys)regulation of
cardiorenal function,2 and have been implicated in the
etiology of numerous cardiorenal and metabolic diseases
including hypertension,3 heart failure,4,5 atherosclero-
sis,6 renal failure,7 and diabetes.8 The impressive phar-
macological activity of U-II has stimulated a great
deal of interest in developing small molecule UT modu-
lators. A number of non-peptidic UT ligands have re-
cently been reported.9 Herein we describe the
identification, synthesis, and initial structure-activity
relationships (SAR) of a novel 2-aminomethyl piperi-
dine series. Optimization of the series led to the identifi-
cation of potent, competitive, and reversible UT
antagonists such as 1a and 11a with excellent and broad
cross-species functional activity.
High throughput screening (HTS) of the corporate com-
pound collection using a fluorometric imaging plate
reader (FLIPR) assay (measuring inhibition of
hU-II-mediated [Ca2+]i-mobilization in HEK293 cells
expressing human recombinant UT receptor)10 led to
the identification of 211 as an antagonist with a pIC50
of 6.2 (Fig. 1). The compound also showed moderate
hUT binding affinity with a pKi of 6.4 in a [125I]hU-II
radioligand binding assay using HEK293 cell mem-
branes stably expressing human recombinant UT recep-
tors.10 Subsequent early exploration of the left-hand side
(LHS) of this hit quickly resulted in the identification of
an a-aryl acetamide sub-series exemplified by 3a (pK i
6.3).12 Despite the modest binding affinity, compounds
N
N
S
N
N
N
Cl
Cl
O
O
3a, hUT binding pKi = 6.3
Keywords: Urotensin-II receptor antagonist; UT antagonist; 2-amino-
methyl piperidine; Broad cross-species activity; Competitive, revers-
ible, and functional antagonist.
2, hUT binding pKi = 6.4
hUT FLIPR pIC50 = 6.2
Cl
*
Figure 1. Structures of HTS hit 2 and a-aryl acetamide sub-series hit
3a.
Corresponding author. Tel.: +1 610 270 4881; fax: +1 610 270
4490; e-mail: jian.jin@gsk.com
0960-894X/$ - see front matter ꢀ 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.03.078

J. Jin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2860–2864
Table 1. SAR of the diamine region
2861
X
X
n
n
a, b, c
d
R1
N
X
3a-h
R1
N
OH
n
N
N
H
R2
N
R2
Boc
O
S
5
4
R
O
R
Ph
h, i, c
OH
e, f, g
N
N
Cl
H
N
N
NR1R2
hUT binding
(pKi)a
6a, R = Ph
Compound
n
X
5a, R = Ph
5b, R = Me
5c, R = OPr
O
6b, R = Me
6c, R = OPr
6d, R = c-hexyl
3a
3b
3c
3d
3e
3f
1
1
1
1
1
1
0
2
CH2 Pyrrolidin-1-yl
CH2 Piperidin-1-yl
CH2 Morpholin-4-yl
6.3
5.1
5.9
d
7a-d
Scheme 1. Reagents and conditions: (a) amine, EDC, HOAt, CH2Cl2,
rt; (b) 4 M HCl in dioxane, MeOH, rt; (c) LiAlH4, THF, 0 ꢁC–rt; (d) 2-
(5-chlorobenzothiophen-3-yl)acetic acid, EDC, HOAt, CH2Cl2, rt; (e)
m-CPBA, CH2Cl2, 0 ꢁC–rt; (f) (CH3)2NCOCl, TMSCN, CH2Cl2, rt;
(g) concd HCl and H2SO4, reflux; (h) pyrrolidine, EDC, HOAt,
CH2Cl2, rt; (i) H2, PtO2, HOAc, rt.
CH2 N-Methylpiperazin-1-yl <5.1
CH2 N,N-Diethylamino
Pyrrolidin-1-yl
<5.1
6.1
O
3g
3h
CH2 Pyrrolidin-1-yl
CH2 Pyrrolidin-1-yl
<5.1
5.7
a Mean of at least 3 determinations with standard deviation of < 0.3.
Table 2. Substitution on the central piperidine ring
2 and 3a were considered as reasonable starting points
for our hit-to-lead chemistry optimization aimed at
improving potency via SAR exploration.
R
O
4
5
3
N
S
N
We first investigated the 2-aminomethyl piperidine re-
gion, also referred to as the diamine region. Custom dia-
mines 5 were prepared from Boc-protected amino acids
4 via amide formation, deprotection, and LiAlH4 reduc-
tion (Scheme 1). Subsequent coupling of diamines 5 with
commercially available 2-(5-chlorobenzothiophen-3-
yl)acetic acid produced the desired compounds 3a–h.13
To explore the effect of 3-substituents on the central
piperidine ring, 3-phenylpyridine was first converted to
the corresponding 2-carboxylic acid 5a via N-oxide for-
mation, installation of the 2-CN group,14 and hydroly-
sis. Acid 5a and commercially available 5b–c were then
converted to racemic cis-3-substituted-2-pyrrolidinylm-
ethyl piperidines 6a–d via amide formation, reduction
of the pyridine ring, and subsequent amide reduction.15
Standard amide coupling of 6a–d with commercially
available acids produced the desired compounds 7a–d
and 8a–j.
Cl
Compound
R
Relative
stereochemistry
hUT binding
(pKi)a
3a
7a
7b
7c
7d
7e
7f
H
—
cis
6.3
8.1
6.7
7.5
7.6
6.7
7.5
3-Phenyl
3-Methyl
3-Propoxy
cis
cis
3-Cyclohexyl
4-Phenyl
5-Phenyl
cis
cis
trans
a Mean of at least 3 determinations with standard deviation of < 0.3.
After identifying 6a as the optimal diamine, we next
turned our attention to optimizing the left-hand side
(LHS) moiety of the a-aryl acetamide sub-series.
Compared to unsubstituted 3-benzothiophene (8c),
5-substituted-3-benzothiophenes (7a, 8a–b) were 15- to
30-fold more potent, with 5-Cl (7a) and 5-Br (8a) being
optimal (Table 3). Indole is less preferred (8d vs 8a)
and 1-naphthyl (8e) was 100-fold more potent than
2-naphthyl (8f). Monocyclic aromatic groups such as
3-thiophene (8g) and 3,4-dichlorophenyl (8h), the pre-
ferred LHS group in the a-amino acetamide sub-series
(vide infra), had much lower binding affinity. As for
the length of the carbon linker, one carbon was pre-
ferred over no or two carbons (8e vs 8i, 8b vs 8j).
For the 2-aminomethyl moiety, pyrrolidine (3a) was
greater than 10-fold more potent compared to piperi-
dine (3b) and acyclic analog (3e) (Table 1). Interestingly,
unlike piperidine (3b), morpholine (3c) showed moder-
ate binding affinity while N-methyl piperazine (3e) had
no appreciable affinity. The SAR indicated that the size
and the basicity of the 2-aminomethyl moiety were crit-
ical to UT binding. As for the central piperidine ring
moiety, 6-membered ring (3a) was preferred compared
to 5- and 7-membered rings (3g and h ) while morpho-
line (3f) was tolerated. Additional substituents on the
central piperidine ring were then explored. We were
pleased to find that 3-substituents (7a–d) improved affin-
ity with 3-phenyl (7a) being optimal—resulting in close
to 100-fold affinity improvement compared to 3a (Table
2). The 4- and 5-phenyl analogs (7e and f )16 also had
higher binding affinity compared to 3a, but were less po-
tent compared to 3-phenyl compound 7a.
To efficiently explore the a-amino acetamide sub-series,
a solid-phase synthetic route outlined in Scheme 2 was
developed. Resin-bound a-amino acetic acid 9 was
prepared via loading of 3,4-dichloroaniline onto com-
mercially available 2,6-dimethoxy-4-polystyrene-benzyl-

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J. Jin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2860–2864
Table 3. SAR of the LHS moiety of the a-aryl acetamide sub-series
Table 4. SAR of the LHS moiety of the a-amino acetamide sub-series
N
N
N
R
N
N
R
O
n
Ar
O
Compound
R
n
hUT binding
(pKi)a
Compound Ar
R
hUT
binding
(pKi)a
7a
8a
8b
8c
8d
8e
8f
5-Chlorobenzothiophen-3-yl
5-Bromobenzothiophen-3-yl
5-Methylbenzothiophen-3-yl
Benzothiophen-3-yl
5-Bromoindol-3-yl
1-Naphthyl
1
1
1
1
1
1
1
1
1
0
2
8.1
8.1
7.8
6.6
6.2
7.1
5.1
<5.1
5.6
<5.1
5.5
10a
10b
10c
10d
10e
10f
10g
10h
10i
3,4-Dichlorophenyl
3,4-Dichlorophenyl
3,4-Dichlorophenyl
3,4-Dichlorophenyl
3,4-Dichlorophenyl
3,4-Dichlorophenyl
3,4-Dimethylphenyl
2-Naphthyl
Hydrogen
Methyl
Ethyl
7.2
7.8
7.5
Cyclopropyl-methyl 7.3
Acetyl
5.8
7.1
6.7
6.8
7.1
6.3
6.1
7.0
6.4
6.1
5.5
5.4
2-Naphthyl
Thiophen-3-yl
Methylsulfonyl
Methyl
Methyl
8g
8h
8i
3,4-Dichlorophenyl
1-Naphthyl
5-Methylbenzothiophen-3-yl
3-Chlorophenyl
4-Chlorophenyl
Methyl
Methyl
8j
10j
a Mean of at least 3 determinations with standard deviation of < 0.3.
10k
10m
10n
10p
10q
10r
2-Chlorophenyl
3-Trifluoromethyl-phenyl Methyl
Methyl
3-Methylphenyl
3-Methoxyphenyl
Phenyl
Methyl
Methyl
Methyl
Methyl
DMHB
O
NH2
a, b, c
Cl
Cl
3,4-Dichlorobenzyl
N
Cl
Cl
d, e
a Mean of at least 3 determinations with standard deviation of < 0.3.
OH
9
and the unsubstituted phenyl (10q) was least preferred.
Extending the phenyl to benzyl such as 10r resulted in
significant affinity loss.
f, g, or h
10b-f
10a
Scheme 2. Reagents and conditions: (a) 2,6-dimethoxy-4-polystyre-
nebenzyloxy-benzaldehyde, Na(OAc)3BH, DIEA, 1% of HOAc in
NMP, rt; (b) methyl bromoacetate, DIEA, NMP, 80 ꢁC; (c) potassium
trimethylsilanolate, THF, rt; (d) 6a, PyBOP, DIEA, NMP, rt; (e) 50%
of TFA in DCE, rt; (f) aldehyde, Na(OAc)3BH, HOAc, DIEA, DCE,
rt; (g) acyl chloride, TEA, CH2Cl2, rt; (h) MeSO2Cl, pyridine, CH2Cl2,
rt.
We then investigated the preferred stereochemistry and
found that (2R, 3R) was preferred as illustrated in Table
5. The (2R, 3R) enantiomers 1a and 11a were greater
than 100-fold more potent than the (2S, 3S) enantiomers
1b and 11b.17
In addition to the high affinity to the hUT receptor, the
preferred enantiomers 1a and 11a showed excellent
oxybenzaldehyde resin (DMHB resin), followed by
alkylation and hydrolysis. Amide coupling of resin-
bound acid 9 with diamine 6a and subsequent resin
cleavage provided compound 10a, which was further
elaborated into 10b–f via reduction amination, acyla-
tion, or sulfonylation. Compounds 10g–r were prepared
in a similar manner as 10b by replacing 3,4-dichloroan-
iline with various commercially available amines.
Table 5. Preferred stereochemistry
3
3
N
N
S
N
2
N
2
As shown in Table 4, the optimal R group is methyl
(10b). While hydrogen (10a) and alkyl groups (10b–d)
showed good binding affinity, acetyl (10e) had very poor
affinity. Interestingly, methylsulfonyl (10f) was quite
potent—indicating that the weakly basic center in this
region was unnecessary for UT binding. 3,4-Dichloro-
phenyl (10b) was the optimal aryl (Ar) group. Bioisos-
teres such as 3,4-dimethylphenyl (10g) and 2-naphthyl
(10h) were 10-fold less potent. Meta-substituted phenyl
(10i) was preferred over para- (10j) and ortho- (10k)
substituted ones. Comparing substituents on the phenyl
ring, 3-chloro (10i) and 3-trifluoromethyl (10m) were
preferred over 3-methyl (10n) and 3-methoxy (10p),
N
Cl
Cl
O
O
11a and 11b
1a and 1b
Cl
Compound
Stereochemistry and ee
hUT binding (pKi)a
1a
1b
2R, 3R (98% ee)
2S, 3S (>99% ee)
2R, 3R (98% ee)
2S, 3S (>99% ee)
8.4
6.0
8.2
5.8
11a
11b
a Mean of at least 3 determinations with standard deviation of < 0.3.

J. Jin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2860–2864
2863
Table 6. Binding affinity versus ortholog receptors and functional
activity in rat and cat isolated arteries
4. Russell, F. D.; Meyers, D.; Galbraith, A. J.; Bett, N.;
Toth, I.; Kearns, P.; Molenaar, P. Am. J. Physiol. 2003,
285, H1576.
Compound UT binding (pKi)a
Functional activity (pKB)a
5. (a) Douglas, S. A.; Tayara, L.; Ohlstein, E. H.; Halawa,
N.; Giaid, A. Lancet 2002, 359, 1990; (b) Ng, L. L.; Loke,
I.; O’Brien, R. J.; Squire, I. B.; Davies, J. E. Circulation
2002, 106, 2877; (c) Richards, A. M.; Nicholls, M. G.;
Lainchbury, J. G.; Fisher, S.; Yandle, T. G. Lancet 2002,
360, 545; (d) Lapp, H.; Boerrigter, G.; Costello-Boerrigter,
L. C.; Jaekel, K.; Scheffold, T.; Krakau, I.; Schramm, M.;
Guelker, H.; Stasch, J. P. Int. J. Cardiol. 2004, 94, 93.
6. (a) Bousette, N.; Patel, L.; Douglas, S. A.; Ohlstein, E. H.;
Giaid, A. Atherosclerosis 2004, 176, 117; (b) Maguire, J. J.;
Kuc, R. E.; Wiley, K. E.; Kleinz, M. J.; Davenport, A. P.
Peptides 2004, 25, 1767.
7. (a) Totsune, K.; Takahashi, K.; Arihara, Z.; Sone, M.;
Satoh, F.; Ito, S.; Kimura, Y.; Sasano, H.; Murakami, O.
Lancet 2001, 358, 810; (b) Shenouda, A.; Douglas, S. A.;
Ohlstein, E. H.; Giaid, A. J. Histochem. Cytochem. 2002,
50, 885; (c) Langham, R. G.; Gow, R.; Thomson, N. M.;
Dowling, J. K.; Gilbert, R. E. Am. J. Kidney Dis. 2004, 44,
826.
Human Cat Rat Rat aorta Cat femoral artery
1a
11a
8.4
8.2
8.0 8.5 7.7
8.1 8.2 7.9
7.2
7.2
a Mean of at least 3 determinations with standard deviation of < 0.3.
affinity to cat and rat UT receptors,18 demonstrating
broad cross-species activity (Table 6). In the rat isolated
aorta,18 compounds 1a and 11a blocked hU-II induced
contraction with respective pKBs of 7.7 and 7.9, and
1a was found to be a competitive and reversible antago-
nist with a pA2 of 8.0, which was comparable to the rat
receptor binding affinity. In the cat isolated femoral ar-
tery,19 1a and 11a also blocked hU-II induced contrac-
tion with pKBs of 7.2 and 7.2, respectively. The
competitiveness and broad cross-species activity of 1a
distinguish it from early UT antagonists such as palosu-
ran.9c However, several early compounds in the series
had poor cytochrome P450 (CYP450) and in vivo phar-
macokinetic (PK) parameters. For example, compound
10b had 2D6 (IC50 0.8 lM) and 3A4 (IC50 1.4 lM) lia-
bility, and high clearance and low oral bioavailability
in rat PK studies (CL 97 mL/min/kg, F 0–3%, T1/2
3.8 h, Vdss 23 L/kg, 1.2 mg/kg iv and 2.2 mg/kg po).
8. (a) Totsune, K.; Takahashi, K.; Arihara, Z.; Sone, M.;
Satoh, F.; Ito, S.; Murakami, O. Clin. Sci. 2003, 104, 1; (b)
Wenyi, Z.; Suzuki, S.; Hirai, M.; Hinokio, Y.; Tanizawa, Y.;
Matsutani, A.; Satoh, J.; Oka, Y. Diabetologi 2003, 46, 972.
9. (a) Flohr, S.; Kurz, M.; Kostenis, E.; Brkovich, A.;
Fournier, A.; Klabunde, T. J. Med. Chem. 2002, 45, 1799;
(b) Croston, G. E.; Olsson, R.; Currier, E. A.; Burstein, E.
S.; Weiner, D.; Nash, N.; Severance, D.; Allenmark, S. G.;
Thunberg, L.; Ma, J.; Mohell, N.; O’Dowd, B.; Brann, M.
R.; Hacksell, U. J. Med. Chem. 2002, 45, 4950; (c) Clozel,
M.; Binkert, C.; Birker-Robaczewska, M.; Boukhadra, C.;
Ding, S.; Fischli, W.; Hess, P.; Mathys, B.; Morrison, K.;
Muller, C.; Muller, C.; Nayler, O.; Qiu, C.; Rey, M.;
Scherz, M. W.; Velker, J.; Weller, T.; Xi, J.; Ziltener, P. J.
Pharma. Exp. Ther. 2004, 311, 204; (d) Jin, J.; Dhanak, D.;
Knight, S. D.; Widdowson, K.; Aiyar, N.; Naselsky, D.;
Sarau, H. M.; Foley, J. J.; Schmidt, D. B.; Bennett, C. D.;
Wang, B.; Warren, G. L.; Moore, M. L.; Keenan, R. M.;
Rivero, R. A.; Douglas, S. A. Bioorg. Med. Chem. Lett.
2005, 15, 3229; (e) Douglas, S. A.; Behm, D. J.; Aiyar, N.
V.; Naselsky, D.; Disa, J.; Brooks, D. P.; Ohlstein, E. H.;
Gleason, J. G.; Sarau, H. M.; Foley, J. J.; Buckley, P. T.;
Schmidt, D. B.; Wixted, W. E.; Widdowson, K.; Riley, G.;
Jin, J.; Gallagher, T. F.; Schmidt, S. J.; Ridgers, L.;
Christmann, L. T.; Keenan, R. M.; Knight, S. D.;
Dhanak, D. Br. J. Pharmacol. 2005, 145, 620; (f)
Lehmann, F.; Pettersen, A.; Currier, E. A.; Sherbukhin,
V.; Olsson, R.; Hacksell, U.; Luthman, K. J. Med. Chem.
2006, 49, 2232; (g) Luci, D. K.; Ghosh, S.; Smith, C. E.;
Qi, J.; Wang, Y.; Haertlein, B.; Parry, T. J.; Li, J.;
Almond, H. R.; Minor, L. K.; Damiano, B. P.; Kinney,
W. A.; Maryanoff, B. E.; Lawson, E. C. Bioorg. Med.
Chem. Lett. 2007, 17, 6489; For a recent review, see: (h)
Jin, J.; Douglas, S. A. Expert Opin. Ther. Patents 2006, 16,
467.
In summary, SAR exploration of a novel 2-aminomethyl
piperidine series identified via HTS led to the discovery
of competitive and reversible UT receptor antagonists
such as 1a and 11a with excellent affinity and functional
activity, and broad cross-species activity. The further
optimization of this series to improve PK and CYP450
properties will be the subject of future publications.
Acknowledgments
We thank Doug Minick for VCD, Bing Wang for
NMR, Qian Jin for LC/MS, Carl Bennett for purifica-
tion, and Christina Schulz-Pritchard, Parvathi Rao,
Jim Fornwald, Jeffrey Guss and Lorena Kallal for assay
support.
References and notes
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N.; Aiyar, N. V.; Romanic, A. M.; Louden, C. S.; Foley, J.
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Holmes, S. D.; Stadel, J. M.; Martin, J. D.; Liu, W. S.;
Glover, G. I.; Wilson, S.; McNulty, D. E.; Ellis, C. E.;
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3. (a) Matsushita, M.; Shichiri, M.; Imai, T.; Iwashina, M.;
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10. For radioligand binding and [Ca2+]i-mobilization assay
details, see Ref. 9e.
11. The chiral centers in the structures shown in the paper are
racemic except the ones in 1a, 1b, 11a and 11b.
12. The radioligand binding assay was used as the primary
assay to generate SAR.
13. All new compounds in this paper were characterized via
1
LC/MS and H NMR.
14. Sakamoto, T.; Kaneda, S.; Nishimura, S.; Yamanaka, H.
Chem. Pharm. Bull. 1985, 3, 565.
15. Diamine 6d was produced as an over reduction by-product
in the hydrogenation step from conversion of 5a to 6a.

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J. Jin et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2860–2864
16. Compounds 7e and 7f were prepared from the
corresponding commercially available amino acids in
the same way as the preparation of 3a from 4 in
Scheme 1.
17. (a) Intermediate 6a was separated via chiral HPLC into
two enantiomers, which were converted to 1a, 1b, 11a, and
11b. Chiral separation conditions: Chiralpak AD
(77 · 240 mm, 20 lM) eluting at 300 mL/min with 0.1%
isopropylamine in MeOH gave two components at RT 3.3
and 5.1 min; (b) Stereochemistry was assigned by Vibra-
tional Circular Dichroism (VCD) analysis of both
enantiomers.
18. For cat and rat UT receptor radioligand binding and rat
isolated aorta contractile assay details, see Ref. 9e.
19. For cat isolated femoral artery assay details, see: Behm, D.
J.; Stankus, G.; Doe, C. P.; Willette, R. N.; Sarau, H. M.;
Foley, J. J.; Schmidt, D. B.; Nuthulaganti, P.; Fornwald,
J. A.; Ames, R. S.; Lambert, D. G.; Calo’, G.; Camarda,
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