Identification of substituted 4-aminopiperidines and 3-aminopyrrolidines as potent MCH-R1 antagonists for the treatment of obesity

Article abstract of DOI:10.1016/j.bmcl.2006.07.053

A substituted 4-aminopiperidine was identified as showing activity in an MCH assay from an HTS effort. Subsequent structural modification of the scaffold led to the identification of a number of active MCH antagonists. 3,5-Dimethoxy-N-(1-(naphthalen-2-ylmethyl)piperidin-4-yl)benzamide (5c) was among those with the highest binding affinity to the MCH receptor (K_i = 27 nM), when variations were made at benzoyl and naphthylmethyl substitution sites from the initial HTS hit. Further optimization via piperidine ring contraction resulted in enhanced MCH activity in a 3-aminopyrrolidine series, where (R)-3,5-dimethoxy-N-(1-(naphthalen-2-ylmethyl)-pyrrolidin-3-yl)benzamide (10i) was found to be an excellent MCH antagonist (K_i = 7 nM).

Full text of DOI:10.1016/j.bmcl.2006.07.053

Bioorganic & Medicinal Chemistry Letters 16 (2006) 5445–5450
Identification of substituted 4-aminopiperidines and
3-aminopyrrolidines as potent MCH-R1 antagonists
for the treatment of obesity
Nick Kim, Kenneth M. Meyers, Jose L. Mendez-Andino, Namal C. Warshakoon,
Wei Ji, John A. Wos, Annyodile Colson, M. Chrissy Mitchell, Jan R. Davis,
Beth B. Pinney, Ofer Reizes and X. Eric Hu*
Procter and Gamble Pharmaceuticals, 8700 Mason-Montgomery Road, Mason, OH 45040, USA
Received 15 June 2006; revised 14 July 2006; accepted 17 July 2006
Available online 1 August 2006
Abstract—A substituted 4-aminopiperidine was identified as showing activity in an MCH assay from an HTS effort. Subsequent
structural modification of the scaffold led to the identification of a number of active MCH antagonists. 3,5-Dimethoxy-N-(1-(naph-
thalen-2-ylmethyl)piperidin-4-yl)benzamide (5c) was among those with the highest binding affinity to the MCH receptor
(Ki = 27 nM), when variations were made at benzoyl and naphthylmethyl substitution sites from the initial HTS hit. Further opti-
mization via piperidine ring contraction resulted in enhanced MCH activity in a 3-aminopyrrolidine series, where (R)-3,5-dime-
thoxy-N-(1-(naphthalen-2-ylmethyl)-pyrrolidin-3-yl)benzamide (10i) was found to be an excellent MCH antagonist (Ki = 7 nM).
Ó 2006 Elsevier Ltd. All rights reserved.
Obesity and overweight account for greater than 50% of
the US population and western countries.1 The epidemic
is also increasing in children and adolescents. The com-
plications of obesity and overweight include diabetes,
cardiac diseases, and certain forms of cancer.2 While
there is a significant effort at identifying effective phar-
macotherapies for obesity, there is currently no good
obesity drug on the market and the currently available
therapies are limited due to variable efficacies and unde-
sirable side effects.3 Over the past decade, multiple phar-
maceutical companies have focused on central nervous
system (CNS) targets, including the melanocortin,4
endocannabinoid,5 and melanin concentrating hormone
receptors.6
CNS are located in the lateral hypothalamus and zona
incerta with neuronal connections to widespread regions
in the brain.9 When injected intracerebroventricularly in
rats, MCH stimulates food intake.10 MCH levels are
found to increase during fasting and in leptin-deficient
obese mice.11 Transgenic MCH over-expression in the
brain leads to overweight mice with hyperphagia. In
contrast, MCH-deficient mice have reduced body weight
and leanness due to reduced feeding and an increased
metabolic rate.12 Finally, MCH-R1 deficient mice are
lean and hyperactive. Based on this evidence in mice,
there is a wide interest in modulating this ligand receptor
system as a mechanism to induce weight loss or as a
long-term weight maintenance therapy in treating the
obesity epidemic.
Melanin concentrating hormone (MCH) is a cyclic 19
amino acid CNS neuropeptide that is highly conserved
in vertebrates.7 MCH is implicated in diverse physiolog-
ical processes and, importantly, in feeding behavior and
energy balance.8 The MCH producing neurons in the
Structure 1 was identified as one of the hits from our
in-house high-throughput screening effort13 and showed
good MCH binding activity (Ki 125 nM).14 This scaffold
possessed a variety of attractive attributes like a potent
in vitro activity, low molecular weight, a number of
H-bonding acceptors/donors, and various sites for struc-
tural modifications for the optimization. Our strategy
included a three-component approach as delineated in
Figure 1: benzoyl (Section A), 4-aminopiperidine (Sec-
tion B), and naphthalene (Section C) moieties. In this
Keywords: MCH-R1; Antagonist; Obesity; Aminopiperidine;
Aminopyrrolidine.
*
Corresponding author. Tel.: +1 513 807 1162; e-mail:
huxe0415@yahoo.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.07.053

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N. Kim et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5445–5450
C
B
A
Confirmed HTS hit:
F
Structural
H
modification
N
H
F
N
N
O
N
O
1 Ki = 125 nM
Figure 1.
context, we wish to report our SAR results from the
structural modification of the 4-aminopiperidine series,
as well as the identification of the more potent 3-amino-
pyrrolidine series.
no analogs (5m–n), in which an H-bond donor or accep-
tor group negatively impacted the MCH activity.
The 3,5-dimethoxybenzoyl moiety in the 4-aminopiperi-
dine was found to be among the most promising substit-
uents based on the SAR profile for the modification in
Section A. Therefore, this moiety was chosen during
the course of our SAR investigation in Section C of
the 4-aminopiperidine scaffold. The chemistry for pre-
paring these analogs in Scheme 2 includes a 3-step se-
quence starting from commercially available 1-benzyl-
4-aminopiperidine 6. Coupling with substituted 3,5-
dimethoxybenzoyl acid followed by hydrogenation
afforded a key intermediate 8. The alkylation with
naphthylmethylbromide finished the synthesis of
compound 9.
Our initial interest was to modify the benzoyl moiety to
examine the substitution impact on MCH in vitro activ-
ity by introducing various groups to the aryl ring (Sec-
tion A in Fig. 1). The chemistry for the preparation of
5a–n is outlined in Scheme 1. Starting from tert-butyl
piperidin-4-ylcarbamate, alkylation with 2-(bromometh-
yl)naphthalene and deprotection of the Boc group fol-
lowed by coupling gave the final products. The robust
chemistry procedure allowed us to quickly generate a
pool of analogs for the in vitro MCH screening, and
the results are tabulated in Table 1.
Structural modification at the benzoyl moiety in the 4-
aminopiperidine scaffold had shown significant substitu-
ent effects impacting the MCH-R1-binding affinity. It
was found that an electron-rich alkoxy group at meta
positions resulted in an increase of binding activity in
5b–d, compared to the non-substituted parent 5a. Inter-
estingly, para substitution of methoxy in 5e–f was detri-
mental to the activity. In addition, incorporation of
fluorine atom(s) to the phenyl proved to be beneficial
as seen in 5g–j. In this case, the substitution position
does not seem to influence binding results. Since both
methoxy and fluoro groups were contributing to in vitro
activity, the combination of 3-methoxy and 4-fluoro in
5k exhibited more pronounced binding activity relative
to its mono-substituted counterparts (5b and 5g) as
expected. The great potency of the fluorinated analogs
coupled with potential metabolic stability warrants fur-
ther investigation of these compounds in in vivo testing.
In contrast, other halogen substitution such as 4-chloro
in 5l showed a decrease in the binding affinity. Similar
results were observed in 3-hydroxy and 3-dimethylami-
A part of our interest in developing SAR was to explore
an alternative group for the naphthalyl moiety to im-
prove the solubility property of analogs in the series.
Substitution of the naphthalene with fluoro (9b) showed
basically no effect in binding affinity compared to the
parent 5c, whereas methoxy analog (9c) was about
3-fold less active. Interestingly, a-substitution of the
naphthalenylmethyl in 9d (a racemate) retained the in vi-
tro activity. This implies that a space tolerance at this
particular site is present in the MCH-R1-binding
pocket. Although heteroaryl substitution was, in gener-
al, less favored, an indole analog (9f) was found to be
about 4-fold more active than a quinoline counterpart
(9e). Partial saturation of the naphthalene in analog 9g
(a racemate) resulted in a slight loss of the in vitro
activity.
These compelling data suggest the outer benzene ring is
likely more important for the MCH binding activity.
This was further illustrated in cinnamyl analogs 9h
exhibiting excellent binding affinity.15 In contrast, 9i
NH2
H
N
H
N
Boc
Boc
a
b
N
HN
N
4
2
3
OMe
H
c
N
OMe
N
O
5
Scheme 1. Reagents: (a) 2-(bromomethyl)naphthalene, TEA, CH2Cl2; (b) TFA, CH2Cl2; (c) HOBT, EDCI, NMM, THF.

N. Kim et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5445–5450
5447
Table 1. MCH-R1-binding for 4-aminopiperidines with various ben-
zoyl moietiesa
showed little activity in the MCH binding assay due to
lack of conformational rigidity. However, adding a
hydroxyl group a to the benzene in 9l regained consider-
able in vitro activity, which may be rationalized by
re-positioning of the phenyl group through a directing
effect from the hydroxyl group in the binding pocket.
Moreover, substitution with only the inner benzene ring
also produced some in vitro activity as shown in analog
9k–l, however these compounds were still 7-fold less
active compared to the parent 5c and ꢀ20-fold less to
the cinnamyl analog 9h.
H
N
R
N
O
5a-r
Compound
Moiety (R)
Ki (nM)
5a
347
With the encouraging SAR results from the modification
in the Sections A and C, we turned our attention to
expand SAR to the aminopiperidine core portion (Sec-
tion B) to further improve the in vitro activity. Initially,
we substituted the 4-aminopiperidine with alkyl
functionality at different positions to see how these
changes might impact the MCH in vitro activity.
N-Methyl-4-aminopiperidine 10a showed about a 7-fold
decrease in binding activity compared to the unsubstitut-
ed 5c, whereas 4-methyl-4-aminopiperidine 10b showed a
3-fold loss in the activity. Interestingly, stereochemical
bias did not seem to be a factor governing thein vitro
activity as shown in cis and trans 3-methyl isomers 10c
and 10d. It was also found that a heavily substituted
piperidine near the ring nitrogen in 10e resulted in a sig-
nificant loss of the in vitro activity, which suggests the
basic nitrogen may play an important role for the bind-
ing affinity. In addition, 3-amido benzoyl piperidine ana-
log 10f exhibited essentially no MCH activity,
presumably due largely to the positional distortion of
the benzoyl moiety in the MCH-R1-binding pocket.
We then focused our attention on the modification of
the ring size and opened ring system to evaluate SAR
outcomes. Intriguingly, fused bicyclic analogs showed a
great stereochemical preference, excellent MCH activity
in trans isomer 10g over its counterpart 10h. We hypoth-
esized the trans isomer adapts the requisite structural
conformation accommodated in the receptor for tight
binding. The most promising finding in the structural
modification in Section B was the identification of pyr-
rolidine 10i showing single digit nano-molar activity.16
We suspect this compelling result reveals a key confor-
mational requirement needed to allow MCH antagonists
to fit into the receptor pocket tightly. The fine tuning of
the conformational orientation of the benzamide group
defined the activity in the following order of activity: 3-
aminopyrrolidine (10i, Ki 7 nM) > 4-aminopiperidine
(5c, Ki 27 nM) > 3-aminopiperidine (10f, Ki > 10,000 nM).
Finally, an open ring form in 10j was found to be com-
pletely inactive because of missing ring rigidity.
5b
5c
29
27
OMe
OMe
OEt
OMe
5d
5e
5f
56
1000
286
OEt
OMe
OMe
OMe
OMe
OMe
F
5g
5h
5i
36
18
9
F
F
F
F
F
F
5j
65
13
F
F
5k
OMe
Cl
5l
232
570
As a follow-up to the modification of the 4-aminopiperi-
dine series, the 3-aminopyrrolidine was identified to be
the most active MCH antagonist series. Therefore, we
focused on additional iteration of analogs for the
3-aminopyrrolidine to further optimize MCH activity.
Using the SAR information from Tables 1 and 2, a num-
ber of aminopyrrolidine analogs were assembled and
screened for in vitro data (Tables 3 and 4). The
3-aminopyrrolidine analogs clearly demonstrated a
conformational preference, in which the (R)-isomer 10i
5m
OH
N
5n
125
a The data represent means of at least two experiments, unless other-
wise indicated.

5448
N. Kim et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5445–5450
OMe
OMe
NH2
H
H
b
a
N
N
N
OMe
OMe
N
O
HN
O
6
8
7
OMe
H
c
N
OMe
N
O
9
Scheme 2. Reagents: (a) HOBT, EDCI, NMM, THF; (b) Pd/C, H2, MeOH; (c) 2-(bromomethyl)naphthylene, TEA, CH2Cl2.
Table 3. MCH-R1-binding for aminopiperidine, aminopyrrolidine
and aminoazitidine analogsa,b
Table 2. MCH-R1-binding for 4-(3,5-dimethoxybenzamido)peridines
containing N-alkyl moietiesa
Compound
Moiety (R0 = 2-naphthyl)
Ki (nM)
OMe
OMe
OMe
OMe
H
10a
169
N
N
OMe
OMe
OMe
OMe
R'
R'
R'
N
N
N
O
N
O
R'
H
9a-9r
10b
10c
10d
86
170
133
N
Compound
Moiety (R0)
Ki (nM)
O
H
N
5c
27
F
OMe
OMe
O
9b
9c
32
99
H
N
MeO
OMe
OMe
R'
N
O
O
H
N
10e
>105
9d
9e
25
R'
R'
N
N
625
O
N
OMe
N
10f
10g
10h
>105
40
H
Me
N
9f
142
O
OMe
F
N
9g
9h
9i
136
12
H
R'
R'
N
N
O
F
F
>105
N
H
F
OMe
>105
O
10i
10j
7
NH
N
R'
OMe
OMe
9j
505
302
OH
H
N
>105
9k
OMe
R'
NH
O
Cl
Cl
9l
205
a The data represent means of at least two experiments, unless other-
wise indicated.
b The procedures described in Scheme 1 were used to prepare analogs
10a–j.
a The data represent means of at least two experiments, unless other-
wise indicated.

N. Kim et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5445–5450
Table 4. MCH-R1-binding for 3-aminopyrrolidine analogsa
5449
activity. In contrast to 5k in the 4-aminopiperidine ser-
ies, mixed substitution of 4-fluoro-3-methoxybenzamide
in 11c was not preferred in the 3-aminopyrrolidine ser-
ies. In this case, the SAR trend did not correlate well
when we duplicated the substitution patterns from the
4-aminopiperidine series to the 3-aminopyrrolidine
series. Moreover, replacement of a cinnamyl group for
the naphthalene in 11e resulted in improved MCH activ-
ity consistent with that in the 4-aminopiperidine series.
a-Methyl substitution in analogs 11d and 11f also
retained the MCH in vitro activity. Again, a smaller aryl
group in 11g for the naphthalene showed a significant
decrease of the binding affinity.
O
R
NH
N
OMe
R'
(R)- or (S)-
10j and 11a-d
Compound
Moiety (R0 = 2-naphthyl)
Config.
Ki (nM)
10i
5-MeO
5-MeO
H
(R)-
(S)-
(R)-
(R)-
7
484
67
11a
11b
11c
4-F
62
We used MCH-R1-induced Ca2+ release from CHO
cells transfected with human MCH-R1 to measure the
functional antagonism.17 To confirm our binding affini-
ty relative to functional antagonism at MCH-R1, a
group of selected compounds are tabulated in Table 5.
Most of compounds tested in our in vitro assays showed
good correlation between binding activity and function
potency. The discrepancy within a 3-fold range between
the assays indicates the compounds bind to the MCH
receptor as well as display functional antagonism.
11d
11e
(R)-
(R)-
12
17
11f
(R)-
(R)-
23
11g
8070
a The data represent means of at least two experiments, unless other-
wise indicated.
In summary, our HTS finding led us to explore SAR in a
4-aminopiperidine scaffold, which resulted in the identi-
fication of a number of highly potent MCH antagonists.
The combination of a 3,5-dimethoxybenzamide or a 3,4-
difluorobenzamide with a 2-naphthylmethyl moiety
proved to be the optimal substituents for MCH binding
was significantly more active (ꢀ70-fold) than the (S)-iso-
mer 11a. Therefore, SAR was focused in the (R)-series in
this subclass. The mono-substituted 3-methoxybenza-
mide (11b) showed about 10-fold diminution in binding
Table 5. MCH-R1-binding and function data for 4-aminopiperidine and (3R)-aminopyrrolidine analogsa
Compound
Structure
MCH binding Ki (nM)
MCH function IC50 (nM)
H
N
F
1
125
109
N
O
H
N
5a
5c
347
27
948
62
N
O
OMe
H
N
OMe
N
O
F
H
N
5h
18
52
F
N
N
O
O
OMe
OMe
N
10i
7
18
42
H
OMe
O
N
N
11e
17
H
OMe
a The data represent means of at least two experiments, unless otherwise indicated.

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N. Kim et al. / Bioorg. Med. Chem. Lett. 16 (2006) 5445–5450
Tempest, P. A.; Hulme, C.; Bannon, T. Abstracts of
Papers. In 224th ACS National Meeting, Boston, MA,
United States, August 18–22, MEDI-343, 2002.
activity. In addition, modification on the piperidine ring
enabled us to discover the 3-aminopyrrolidine series,
leading to further enhancement in the MCH in vitro
activity (to nano-molar values). Further optimization
and in vivo activity of these compounds will be reported
in due course.
14. Compounds were assayed for binding using an HEK-
293 cell line that overexpresses the MCH-R1 (SLC-1).
Competitive binding assays were performed using euro-
pium labeled MCH at
a concentration of 25 nM.
Varying concentrations of compounds were incubated
with the MCH-R1 cells in the presence of 25 nM
europium labeled MCH. Subsequently, cells were
washed free of excess europium labeled MCH and
residual bound MCH was quantified. Non-specific
binding was determined by incubating cells with 10 lM
unlabeled MCH.
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17. Functional MCH activity was assayed in the same HEK-
293 cell line that overexpresses the MCH-R1 (SLC-1). The
cells stably expressed a reporter construct containing the
serum response element regulating the expression of the
firefly luciferase gene. Functional MCH activity was
detected by assaying luciferase activity. Prior to initiating
the assay, cells were washed free of serum-containing
media and incubated overnight in serum-free media. For
functional antagonist assays, cells were incubated with
varying concentrations of the test compound and 25 nM
MCH for 4 h. Cells were then processed for luciferase
activity as a measure of receptor activation.
13. A similar work was reported by an Amgen group during
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