Aminomethylpiperazines as selective urotensin antagonists

Article abstract of DOI:10.1016/j.bmcl.2008.07.067

Aminomethylpiperazines, reported previously as being κ-opioid receptor agonists, were identified as lead compounds in the development of selective urotensin receptor antagonists. Optimized substitution of the piperazine moiety has provided high affinity u

Full text of DOI:10.1016/j.bmcl.2008.07.067

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4470–4473
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Aminomethylpiperazines as selective urotensin antagonists
a
a
a
a
Mark A. Hilfiker a, , Daohua Zhang , Sarah E. Dowdell , Krista B. Goodman , John J. McAtee ,
Jason W. Dodson a, Andrew Q. Viet a, Gren Z. Wang a, Clark A. Sehon a, David J. Behm b, Zining Wu c,
Luz H. Carballo c, Stephen A. Douglas b, Michael J. Neeb a
*
a Department of Medicinal Chemistry, Cardiovascular and Urogenital Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, 709 Swedeland Road,
PO Box 1539, King of Prussia, PA 19406, USA
b Department of Biology, Cardiovascular and Urogenital Center of Excellence for Drug Discovery, GlaxoSmithKline Pharmaceuticals, 709 Swedeland Road,
PO Box 1539, King of Prussia, PA 19406, USA
c Screening and Compound Profiling, Research Triangle Park, 4117 Emperor Boulevard, Morrisville, NC 27703, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Aminomethylpiperazines, reported previously as being j-opioid receptor agonists, were identified as lead
compounds in the development of selective urotensin receptor antagonists. Optimized substitution of the
piperazine moiety has provided high affinity urotensin receptor antagonists with greater than 100-fold
selectivity over the j-opioid receptor. Select compounds were found to inhibit urotensin-induced vaso-
Received 5 June 2008
Revised 15 July 2008
Accepted 16 July 2008
Available online 20 July 2008
constriction in isolated rat aortic rings consistent with the hypothesis that an urotensin antagonist may
be useful for the treatment of hypertension.
Keywords:
Urotensin
Piperazine
Kappa
Ó 2008 Elsevier Ltd. All rights reserved.
Opioid
Hypertension
7-TM
Urotensin-II (U-II) is a cyclic undecapeptide originally isolated
from the goby urophysis.1 It was hypothesized to be involved pri-
marily in osmoregulation in fish.2 Human urotensin-II (hU-II)
was subsequently identified and cloned.3 In 1999, hU-II was iden-
tified as a ligand of human GPR-14 (hUT), an ‘‘orphan” G-protein-
coupled receptor predominantly expressed in cardiovascular tis-
sue.4 In non-human primates, urotensin-II acts effectively to con-
strict isolated blood vessels with vasoconstrictor activity 10
times greater than that of endothelin-1, making hU-II the most po-
tent mammalian vasoconstrictor identified to date.4 More recently,
vasoconstrictor activity was realized with administration of hU-II
in both cat5 and man.6,7 In addition to regulating cardiac contrac-
tility,7 hU-II is a natriuretic factor8 and is implicated in the
(dys)regulation of cardiorenal function.9 As a result, an hUT antag-
onist has been identified as a therapeutic target for the treatment
of numerous cardiorenal and metabolic diseases including hyper-
tension10, heart failure7,11, atherosclerosis12, renal failure13, and
diabetes.14 To this end, several non-peptidic UT ligands have re-
cently been reported.15
O
OMe
O
N
N
N
N
Cl
Cl
N
Cl
Cl
N
O
1
GR 89696
Cl
Cl
N
N
O
BRL 52537
Figure 1. HTS hit 1 and literature j-opioid agonists.
binding affinity (Ki) of 500 nM.16 Selectivity screening of 1 identi-
fied potent agonist activity at the -opioid receptor (EC50
3 nM).17 Due to the pharmacological effects attributed to
-opioid
j
j
High-throughput screening for compounds with hUT antagonist
activity identified compound 1 (Fig. 1) as a chemical lead with a
agonism (analgesia, sedation, diuresis, and dysphoria) it was desir-
able to design hUT antagonists devoid of this activity.18 Indeed,
subsequent analysis of the literature revealed that aminomethylpi-
peridines have been identified as
compounds in which the piperidine was modified to a N-substi-
j
-opioid agonists.19 In addition,
* Corresponding author. Tel.: +1 610 270 4472; fax: +1 610 270 4490.
E-mail address: mark.a.hilfiker@gsk.com (M.A. Hilfiker).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.07.067

M. A. Hilfiker et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4470–4473
4471
Bn
N
Bn
N
a
NHBn
NHBn
d
O
O
b, c
N
N
H
N
Bn
CO2Et
O
2
3
R 1
N
H
N
Bn
N
e, f
g, h, i, or j
N
N
N
N
N
R 2
N
H
R 2
O
O
5
4
Scheme 1. Reagents and conditions: (a) BrCH(CO2Et)2, MeCN, reflux, 18 h, 81%; (b) H2, Pd/C, EtOH, 25 °C, 24 h, 88%; (c) pyrrolidine, NMP, 200 °C, 0.5 h, 66%; (d) LiAlH4, THF,
25 °C, 4 h, 62%; (e) acid chloride, Et3N, DCM, 25 °C; (f) H2 (1 atm), Pd/C, THF, H2O, HCl, 25 °C, 80%; (g) R1 = aryl; ArB(OH)2, Cu(OAc)2, Et3N, DCM, 25 °C, 20–50%; (h) R1 = amide;
acid chloride, Et3N, DCM, 25 °C, 43–50%; (i) R1 = sulfonamide; aryl or alkyl sulfonylchloride, Et3N, DCM, 25 °C, 39–60%; (j) R1 = phenylurea; PhNCO, DIEA, DCM, 25 °C, 61%.
Table 1
tuted piperazine (GR 89696 for example) are also reported to have
j
-agonist activity.20 In general, the arylacetamide group and the
SAR analysis of piperazine substitution
basic amine are conserved in these known
j
-agonists. While the
R
N
basic amine is required for attaining hUT affinity in this series,
we hypothesized that modification of the arylacetamide group
may provide an opportunity to design selective hUT antagonists.
In addition, the piperazine core scaffold contains an added ring
nitrogen which serves as an alternative point of diversity and could
provide an additional opportunity for achieving high hUT affinity
N
Me
N
N
Cl
Cl
O
and selectivity over the j-receptor.
Compound
R
hUT
Kappa
EC50 (nM)
b
Kia (nM)
Synthesis of the racemic pyrrolidinylmethylpiperazine core was
accomplished as shown in Scheme 1 starting with the previously
described synthesis of oxopiperazine 2 prepared by the condensa-
tion of N,N0-dibenzylethylenediamine with diethylbromomalo-
nate.20f Selective debenzylation of the more basic nitrogen by
catalytic hydrogenolysis followed by amidation with pyrrolidine
provided pyrrolidine amide 3. Double amide reduction using
LiAlH4 provided 1-benzyl-3-(pyrrolidinylmethyl)piperazine 4.
Selective functionalization of the piperazine nitrogens was accom-
plished by acylation of the unprotected amine followed by deben-
zylation and subsequent functionalization of piperazine 5. N-
Arylpiperazines were prepared by copper-catalyzed coupling of
arylboronic acids and piperazine 5.21 Piperazine sulfonamides,
amides, and ureas were synthesized via standard reaction of 5 with
sulfonylchlorides, acid chlorides, and isocyanates.
Initial SAR efforts focused on piperazine substitution conserving
the N-arylsarcosine moiety (Table 1). Arylpiperazines (6–9) are
substantially more active at kappa than hUT displaying low nano-
molar potency at kappa. Incorporation of amides, ureas, and sul-
fonamides on the piperazine effectively reversed this selectivity
in favor of hUT antagonism. Arylamides and sulfonamides in par-
ticular showed significant improvement in binding affinity relative
to HTS hit 1 and achieved greater than 10-fold selectivity over kap-
pa. Interestingly, the methanesulfonyl analog 21 was very potent
6
7
8
Ph
250
100
50
1.3
6.3
3.2
4.0
4000
7900
>10,000
3200
630
>10,000
250
200
3,4-Di-F-Ph
3-MeO-Ph
3-Cl-Ph
Ph-NH(CO)
PhCO
(3,4-Di-MeO-Ph)CO
(4-CN-Ph)CO
(Pyridine-4-yl)CO
(3-Cl-Ph)CO
Ph-SO2
3-Cl-Ph-SO2
4-Cl-Ph-SO2
3-MeO-Ph-SO2
3,4-Di-F-Ph-SO2
MeSO2
9
63
10
11
12
13
14
15
16
17
18
19
20
21
790
200
400
1300
100
130
20
160
100
79
790
79
400
3.0
130
100
a
Mean of at least two determinations with a standard deviation of < 0.3 log
units.
b
Single determination or a mean of two determinations with a standard devia-
tion of < 0.3 log units.
selectivity favoring kappa agonism. Translation of this group to
piperazinesulfonamide 26 resulted in decreased hUT affinity and
similar levels of selectivity, but the incorporation of chlorine sub-
stitution in compound 27 restored the hUT affinity and selectivity.
Having identified the 5-chlorobenzoxazolone acetamide as the
optimal piperazine amide group, a survey of arylsulfonamide sub-
stitution based on 27 was explored (Table 3). In general, a variety
of substitution patterns were well tolerated with para-substitution
providing greater than 100-fold selectivity over kappa agonism in
many cases. hUT affinity was significantly improved with ortho-
bromine substitution as seen in 30 and 35. In addition to simple
ether substitution, polar functional groups such as the acetamide
and carboxylic acid (37–39) were well tolerated giving high hUT
affinity and good levels of selectivity. Compounds in this series
were also found to have similar binding affinities at the rat UT
receptor (Table 4) allowing for them to be studied in a functional
rat tissue assay.
and selective for the
j-receptor much like the arylpiperazines
(6–9). This result would indicate that the larger arylsulfonamide
substituents (16–20) engage in negative steric or conformational
interactions at the
j-receptor which are more easily accommo-
dated in the UT binding pocket.
After surveying piperazine substitution the nature of the amide
group was explored (Table 2). The insertion of an amino group
within the standard arylacetamide moiety, as exemplified by HTS
hit 1, provided an attachment point for incorporating additional
polar groups within this region of the molecule. Within the N-phe-
nylpiperazine series (22–25) benzoxazolone 25 demonstrated the
most potential for achieving improved hUT affinity and
ity while other heterocyclic acetamides retained high levels of
j-selectiv-

4472
M. A. Hilfiker et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4470–4473
Table 2
Table 4
Evaluation of acetamide group substitution
Inhibition of UT-induced contraction of isolated rat aortic rings
R1
N
Compound
Rat UT
Rat aorta
Kb (nM)
Kb/rat Ki
Ratio
b
Kia (nM)
30
35
37
38
39
ND
10.0
4.0
32.0
8.0
52.8 13.0
14.2 13.7
13.1 3.6
81.8 38.2
10.0 2.2
N
1.4
3.3
2.6
1.3
N
R2
O
a
Compound
R1
Ph
R2
hUT
Kappa
EC50 (nM)
ND, not determined; mean of at least two determinations with a standard
deviation of < 0.3 log units.
b
Kia (nM)
b
A mean of two determinations SEM.
CH2
22
320
63
1.6
In an effort to assess functional inhibition of UT on isolated rat
blood vessels, a number of optimized inhibitors were evaluated
in vitro for their ability to inhibit UT-mediated aortic ring contrac-
tion (Table 4).22 All of the compounds studied demonstrated po-
tent and competitive inhibition of UT-induced vasoconstriction
with similar potencies (Kb) to their binding affinities (rat UT Ki).
In conclusion, a number of racemic pyrrolidinylmethyl pipera-
zines have been synthesized. The dichlorophenylacetamide func-
tionality common to many kappa agonists was modified to the 5-
chlorobenzoxazolone resulting in compounds with high hUT affin-
ity. Complementary arylsulfonamide substitution provided a di-
verse set of high affinity hUT inhibitors with greater than 100-
fold selectivity over kappa. In vitro, results from the rat isolated
aortic contraction bioassay show that this series demonstrates po-
tent, competitive inhibition of the aortic contractile response to
exogenous hU-II consistent with the hypothesis that UT antago-
nists have the potential to mediate the effects of hU-II on vascular
tone.
S
23
24
25
26
Ph
2.0
Cl
CH2
CF3
N
N
Ph
79
4.0
CH2
CH2
N
Ph
130
500
20
400
1000
790
O
O
O
CH2
N
PhSO2
PhSO2
O
CH2
N
Cl
27
O
References and notes
O
a
Mean of at least two determinations with a standard deviation of < 0.3 log
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b
Single determination or a mean of two determinations with a standard devia-
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Table 3
Survey of arylsulfonamide substitution
O
S
O
R
N
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N
Cl
O
N
O
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Compound
R
hUT
Kappa
EC50 (nM)
Kia (nM)
b
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28
29
30
31
32
33
34
35
36
37
38
39
3-CN
3-CF3
2-Br
2-Cl-5-CF3
3-MeO
10
50
630
2000
2000
1000
320
2000
320
1300
790
8.0
13
25
25
13
1.6
130
2.5
25
13
4-MeO
3,4-Di-MeO
2-Br-3,4-di-MeO
3-Br-6-MeO
4-NHAc
4-CO2H
3-OH-4-CO2H
1300
2000
7900
a
Mean of at least two determinations with a standard deviation of < 0.3 log
units.
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b
Single determination or a mean of two determinations with a standard devia-
tion of < 0.3 log units.

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