1-(4-Amino-phenyl)-pyrrolidin-3-yl-amine and 6-(3-amino-pyrrolidin-1-yl)- pyridin-3-yl-amine derivatives as melanin-concentrating hormone receptor-1 antagonists

Article abstract of DOI:10.1016/j.bmcl.2005.05.130

Derivatives of 1-(4-amino-phenyl)-pyrrolidin-3-yl-amine and 6-(3-amino-pyrrolidin-1-yl)-pyridin-3-yl-amine were identified as potent and functionally active MCH-R1 antagonists. One compound with K_i = 2.3 nM demonstrated good oral bioavailabilit

Full text of DOI:10.1016/j.bmcl.2005.05.130

Bioorganic & Medicinal Chemistry Letters 15 (2005) 3701–3706
1-(4-Amino-phenyl)-pyrrolidin-3-yl-amine and
6-(3-amino-pyrrolidin-1-yl)-pyridin-3-yl-amine derivatives
as melanin-concentrating hormone receptor-1 antagonists
Charles Q. Huang,a Tracy Baker,a David Schwarz,b Jun Fan,b Christopher E. Heise,c
Mingzhu Zhang,a Val S. Goodfellow,a Stacy Markison,d Kathleen R. Gogas,d
Takung Chen,e Xiao-Chuan Wanga and Yun-Fei Zhua,*
aDepartment of Medicinal Chemistry, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
bDepartment of Molecular Biology, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
cDepartment of Pharmacology, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
dDepartment of Neurosciences, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
eDepartment of Pre-clinic Development, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
Received 28 March 2005; revised 9 May 2005; accepted 26 May 2005
Available online 6 July 2005
Abstract—Derivatives of 1-(4-amino-phenyl)-pyrrolidin-3-yl-amine and 6-(3-amino-pyrrolidin-1-yl)-pyridin-3-yl-amine were identi-
fied as potent and functionally active MCH-R1 antagonists. One compound with Ki = 2.3 nM demonstrated good oral bioavailabil-
ity (32%) and in vivo efficacy in rats.
Ó 2005 Elsevier Ltd. All rights reserved.
Melanin-concentrating hormone (MCH) is a cyclic
neuropeptide produced in the lateral hypothalamus
and zona incerta of the mammalian brain. These re-
gions have been implicated in the control of a variety
of biological functions, including the control of food
intake and body weight. Alterations of MCH expres-
sion suggest that this peptide plays a pivotal role in
modulating this feeding behavior. For instance, admin-
istration of exogenous MCH to rodents stimulates
feeding1 and body weight gain2,3 in a dose-dependent
manner, while elimination of the gene encoding the
peptide precursor results in animals that are hypopha-
gic and lean.4
peptide. First and foremost, rodents appear to express
only a single receptor for MCH, and that receptor
shares greatest homology with human MCH-R1. Fur-
thermore, elimination of the MCH-R1 locus in mice re-
sults in animals that are lean and resistant to diet-
induced obesity.10 Finally, these data have stimulated
the development of several small-molecule antagonists
for MCH-R1 that have been shown to reduce both food
intake and body weight gain when administered to ro-
dents.11–15
In humans, two independent receptors have been identi-
fied that bind MCH with high-affinity: MCH-R15,6 and
MCH-R2.7 While both receptors share a broad—and
often overlapping—pattern of expression within the
brain,7–9 it is MCH-R1 that appears to be primarily
responsible for mediating the orexigenic effects of the
Herein, we report the development of a series of small-
molecule MCH-R1 antagonists (I) using aminoaryl-
substituted 3-aminopyrrolidine as the central core. The
structure–activity relationship (SAR) studies resulted
in a series of potent and orally bioavailable MCH-R1
antagonists. One of the molecules was also proved to
be efficacious in animal feed models.
*
Corresponding author. Tel.: +1 858 617 7745; fax: +1 858 617
7619; e-mail: fzhu@neurocrine.com
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.05.130

3702
C. Q. Huang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3701–3706
Scheme 1. Reagents and conditions: (a) DMSO, rt, 1 h, 95–100% and (b) Na2S2O4, THF–H2O, 0.5 h, 97% for 4a; H2, Pd–C, THF, 5 h, 100% for 4b.
Scheme 1 outlines the synthesis of compounds 4a, b,
which served as common intermediates for further deriv-
atization. 4-Fluoronitrobenzene (1) was reacted with
N,N-disubstituted-aminopyrrolidines (2a, b) to give the
intermediates 3a, b. The nitro group was reduced either
by hydrogenation or sodium hydrosulfite to afford the
anilines 4a, b. A number of selected acids , acyl chlo-
rides, and isocyanates were coupled to 4a to form the
compounds 5b–j, 5q–s, and 5k, l (Scheme 2, Table 1).
Additionally, 4a was reacted with 2-(6-chloro)-nicotinyl
chloride to yield 5a, which was subjected to Suzuki cou-
pling conditions to give the desired compounds 5m, n. 5a
could also be reacted with a variety of amines to gener-
ate analogs exemplified by 5o, p. Variation of substitu-
ents on the basic amine was carried out according to
Scheme 3. Thus, 4b was coupled with biphenyl carbonyl
chloride to give compound 6. After TFA treatment, the
resulting secondary amine (7a) was subjected to reduc-
tive amination to yield 7b–f (Table 2). It was also acyl-
ated to form 7g.
The SAR studies initially focused on the left side of mol-
ecule I by scanning a variety of amides. The biphenyl
carboxamide 5b proved to be a potent MCH-R1 antag-
onist possessing a receptor affinity (Ki) of 5.2 nM (Table
1).16 Modifications targeting the biphenyl group were
then explored. Both insertion of an oxygen between
the two phenyl groups (5c) and cyclization of the biphe-
nyl group (5d) resulted in complete loss of activity. One
methylene extension between the biphenyl and carbonyl
groups also caused a substantial loss of potency (5e,
4.3 lM). However, modification of the ÔinternalÕ phenyl
group to a non-aromatic moiety, exemplified by 5f–l, led
to a moderate success. Among these analogs, 4-(4-
chloro-phenyl)-cyclohexylcarboxamide (5h) and 4-(4-
chlorophenyl)-4-oxo-butyramide (5j), were only about
2-fold less potent than 5b. Urea analogs (5k, 5l) were
a few folds less potent than the similar amides. Surpris-
ingly, replacement of the internal phenyl group with a
pyridyl group (5m) led to a 20-fold loss of affinity
(Ki = 110 nM). Interestingly, after incorporation of a
4-methoxyl group on the outside phenyl group, the
activity was almost restored (5n, 16 nM). Enhancement
of the binding affinity by 4-substitution of the phenyl
group was observed also in the case of 5j versus 5i. On
the other hand, attempts to replace the ÔoutsideÕ phenyl
group with piperidine and substituted piperazine result-
ed in very low to total loss of receptor affinity (5o, p).
Thus a less radical modification strategy was employed
by replacing the outside phenyl group with a hetero-
aromatic group, which is represented by the three
compounds 5q–s. The results showed that only the
thiophene 5q, the non-polar aromatic still maintained
a reasonable binding affinity (34 nM), where the com-
pounds with polar aromatic substituents (imidazole 5r
and oxazole 5s) showed a substantial loss of activity.
These results suggested that the outside phenyl group
The pyridyl equivalent of compound 7a, compound 10
(Scheme 4), was prepared in several steps from the com-
mercially available 2-chloro-5-nitro-pyridine (8) by
reacting with 3-(N-Boc-N-methyl)-aminopyrrolidine
(2b). The resulting intermediate 9 was reduced by hydro-
genation to the corresponding aniline, which was imme-
diately coupled with 4-biphenylcarbonyl choride due to
its unstable nature. The resulting product was deprotec-
ted, yielding the desired compound 10. To avoid han-
dling the unstable intermediate mentioned above, an
alternative approach employing 2-amino-5-chloropyri-
dine (11) as the starting material was used. Compound
11 was first acylated to form amide 12, which yielded
the same product 10 upon heating with Boc protected
(2) 3-amino-pyrrolidine and followed by deprotection.
Scheme 2. Reagents and conditions: (a) 6-Chloronicotinyl chloride, DCM, Et3N, 1 h, 30%; (b) ArB(OH)2, Pd(PPh3)4, Na2CO3, toluene, water,
100 °C, 24 h, 60–70%; (c) (R4)2NH, DMSO, 100 °C, 24 h, 61–99%; (d) R2COCl, Et3N or R2CO2H, EDC.HCl, HOBt, THF, 1–5 h, 30–70%; and (e)
R3NCO, THF, 2 h, 50%.

C. Q. Huang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3701–3706
Table 1. Binding affinities of compounds 5b–s on human MCH-R1
3703
is one of the key interaction sites with MCH-R1, while
the internal phenyl group might have dual roles. It could
serve as a spacer to control the orientation of the outside
phenyl group and also as a lipophilic site to interact with
the receptor. The phenyl group might prove to be one of
the best spacers, it was replaceable by both rigid and
flexible, but relatively liophilic groups. On the other
hand, the potency was less dependent on the substitu-
tion of the basic nitrogen, as evidenced by compounds
7a–7c, 7f, where substitution even as large as a phenyl-
propyl exhibited similar binding profiles. The basic
nitrogen might be one of the key features for the recep-
tor binding since the non-basic intermediate 6 was not
active and the acetamide 7g was only a weak binder.
Compounds
R
Ki (nM SEM)
5b
5.2 1.0
5c
5d
>10,000
>10,000
Although the calculated log P for compound 7a indicat-
ed that it was not a highly lipophilic molecule (clog
P = 3.2),17 its solubility as a hydrogen chloride salt in
water was poor (approx. 0.25 mg/ml) based on a simple
measurement.18 Because of the potential experimental
difficulty for in vivo efficacy studies due to the poor
water solubility for this series, the SAR was expanded
by using the more hydrophilic template, 6-(3-amino-
pyrrolidin-1-yl)-pyridin-3-yl-amine template (molecule
I where X = N). The binding affinities of this series of
compounds were found to be comparable to the corre-
sponding 1-(4-amino-phenyl)-pyrrolidin-3-yl-amine ser-
ies. For example, compound 10 has a binding affinity
of 2.3 nM (Ki), which is similar to compound 7a
(3.1 nM). As expected, its solubility in water was indeed
much improved. The solubility of pyridine 10 as a
hydrogen chloride salt19 was measured at 25 versus
0.25 mg/ml of phenyl analog 7a in water.
5e
4300 780
5f
5g
5h
5i
>10,000
14 3.8
12 3.6
250 2.8
5j
13 0.4
43 2.5
The functional antagonism of such compounds was ini-
tially confirmed based on their ability to inhibit the
MCH-stimulated Ca2+ influx in a dose-dependent man-
ner. For example, compounds 7a and 10 had a IC50 of
166 and 122 nM in this assay. Functional activity of
compound 10 was further established by the GTPcS as-
say (IC50 = 61 nM).20 Compound 10 as a HCl salt also
showed promising pharmacokinetic properties. In rats,
after the dosing at 10 mg/kg for both iv and po admin-
istrations, it exhibited 32% oral bioavailability with a
terminal half-life of 2.7 h.21
5k
5l
52 12
110 4.1
16 3.3
5m
5n
5o
In vivo efficacy of compound 10 (as a HCl salt) was
investigated in two feeding models. In the first study,
food-deprived male Wistar rats (221 10 g; n = 7–8/
group) were given compound 10 (3–30 mg/kg, po), and
45 min later were allowed to eat. Orally administered
compound 10 significantly suppressed food intakes at
all doses out to 6 h post-dose (p < 0.01; Fig. 1). We also
examined compound 10 in a chronic feeding model. In
this study, Wistar rats (217 9 g; n = 6–8/group) were
implanted with a 7-day osmotic pump that contained
compound 10 (10 mg/kg/day) in 50% DMSO or vehicle
alone. In addition to ad libitum fed vehicle-treated ani-
mals, we included a vehicle-treated pair-fed group to
examine the potential effects of MCH antagonism on
metabolism. Rats in the pair-fed group were fed the
same amount of food that the drug-treated animals
ate. Results indicated that food intake was significantly
2400 320
5p
5q
5r
5s
>10,000
34 1.5
>10,000
>10,000

3704
C. Q. Huang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3701–3706
Scheme 3. Reagents and conditions: (a) 4-biphenylcarbonyl choride, Et3N, DCM, 2 h, 74%; (b) TFA, DCM, 4 h, 100%; (c) aldehyde, NaBH(OAc)3,
MeOH, DCM, 14 h; and (d) acetic anhydride, DIPEA, DCM, 5 h, 85%.
Table 2. Binding affinities of compounds 6, 7a–g, and 10 on human
MCH-R1
Compounds
R1
Ki (nM SEM)
6
—
—
>10,000
3.1 0.7
5.9 0.3
7a
7b
Ethyl
7c
7d
5.5 0.6
31 4.7
7e
7f
130 16
8.6 0.3
7g
10
—
—
3000a
2.3 0.3
Figure 1. Effect of orally administered compound 10 (3–30 mg/kg, po,
dosed in 0.25% methylcellulose) on deprivation-induced feeding in
rats. Cumulative food intake was significantly suppressed out to 6 h at
all doses tested (*p < 0.01). Values are means SEM.
a Only assayed once.
decreased in drug-treated animals (and in the pair-fed
group) relative to vehicle-controls (p < 0.001; Fig. 2A).
Body weight was also significantly suppressed in both
groups (p < 0.001). Interestingly, although the pair-fed
and drug-treated groups ate the same amount of food,
rats given compound 10 lost significantly more weight
than their pair-fed counterparts (p < 0.001; Fig. 2B).
This finding suggests that in addition to anorectic
effects, antagonism of the MCH1-R can result in meta-
bolic changes.
In summary, SAR around 1-(4-amino-phenyl)-pyrroli-
din-3-yl-amine and its closely related analog 6-(3-ami-
no-pyrrolidin-1-yl)-pyridin-3-yl-amine yielded potent
Scheme 4. Reagents and conditions: (a) CH3CN, rt, 4 h, 80%; (b) H2, Pd/C, THF, 1 h, 81%; (c) 4-biphenylcarbonyl chloride, Et3N, DCM, 3 h, 42–
97%; (d) HCl, ether, 5 h, 89%; and (e) 2b in DMSO, 100 °C, 72 h, 12%.

C. Q. Huang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3701–3706
3705
Figure 2. Effect of compound 10 delivered via osmotic pump (10 mg/kg/day) over 7 days on food intake (A) and body weight (B) in rats. Both food
intake and body weight were significantly suppressed in compound 10-treated and pair-fed animals relative to controls (pÕs < 0.001). Furthermore,
body weight was significantly lower in rats given compound 10 compared to pair-fed animals (p < 0.001). Values are means SEM.
MCH-R1 antagonists.22 Variation of the substitutions
8. An, S.; Cutler, G.; Zhao, J. J.; Huang, S. G.; Tian, H.; Li,
W.; Liang, L.; Rich, M.; Bakleh, A.; Du, J.; Chen, J. L.;
Dai, K. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 7576.
9. Sailer, A. W.; Sano, H.; Zeng, Z.; McDonald, T. P.; Pan,
on the carboxamide showed that a bi-aryl group was
preferred with the outside phenyl group as the critical
receptor-binding component. At the other end of the
J.; Pong, S. S.; Feighner, S. D.; Tan, C. P.; Fukami, T.;
molecule, a basic amine was required to give high poten-
cy, although substitution on the basic amine was not
Iwaasa, H.; Hreniuk, D. L.; Morin, N. R.; Sadowski, S. J.;
Ito, M.; Bansal, A.; Ky, B.; Figueroa, D. J.; Jiang, Q.;
crucial for the binding. One of the potent compounds
Austin, C. P.; MacNeil, D. J.; Ishihara, A.; Ihara, M.;
demonstrated good oral bioavailability and in vivo effi-
cacy in rats. The SAR knowledge from this work pro-
vided the starting point for design and optimization of
the next generation MCH-R1 antagonists.
Kanatani, A.; Van der Ploeg, L. H.; Howard, A. D.; Liu,
Q. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 7564.
10. Marsh, D. J.; Weingarth, D. T.; Novi, D. E.; Chen, H. Y.;
Trumbauer, M. E.; Chen, A. S.; Guan, X. M.; Jiang, M.
M.; Feng, Y.; Camacho, R. E.; Shen, Z.; Frazier, E. G.;
Yu, H.; Metzger, J. M.; Kuca, S. J.; Shearman, L. P.;
Gopal-Truter, S.; MacNeil, D. J.; Strack, A. M.; MacIn-
tyre, D. E.; Van der Ploeg, L. H.; Qian, S. Proc. Natl.
Acad. Sci. U.S.A. 2002, 99, 3240.
11. Takekawa, S.; Asami, A.; Ishihara, Y.; Terauchi, J.; Kato,
K.; Shimomura, Y.; Mori, M.; Murakoshi, H.; Suzuki, N.;
Nishimura,O.;Fujino,M.Eur.J.Pharmacol.2002,438,129.
12. Borowsky, B.; Durkin, M. M.; Ogozalek, K.; Marzabadi,
M. R.; DeLeon, J.; Lagu, B.; Heurich, R.; Lichtblau, H.;
Shaposhnik, Z.; Daniewska, I.; Blackburn, T. P.; Bran-
chek, T. A.; Gerald, C.; Vaysse, P. J.; Forray, C. Nat.
Med. 2002, 8, 825.
Acknowledgments
Authors are grateful to Ms. Monica Mistry for support-
ing in vitro experiments; Ms. Dacie R. Lewis and Ms.
Helena Choe for technical assistance in in vivo
experiments.
References and notes
1. Rossi, M.; Choi, S. J.; OÕShea, D.; Miyoshi, T.; Ghatei, M.
A.; Bloom, S. R. Endocrinology 1997, 138, 351.
2. Della-Zuana, O.; Presse, F.; Ortola, C.; Duhault, J.;
Nahon, J. L.; Levens, N. Int. J. Obes. Relat. Metab.
Disord. 2002, 26, 1289.
13. Souers, A. J.; Gao, J.; Brune, M.; Bush, E.; Wodka, D.;
Vasudevan, A.; Judd, A. S.; Mulhern, M.; Brodjian, S.;
Dayton, B.; Shapiro, R.; Hernandez, L. E.; Marsh, K. C.;
Sham, H. L.; Collins, C. A.; Kym, P. R. J. Med. Chem.
2005, 48, 1318.
3. Ito, M.; Gomori, A.; Ishihara, A.; Oda, Z.; Mashiko, S.;
Matsushita, H.; Yumoto, M.; Sano, H.; Tokita, S.;
Moriya, M.; Iwaasa, H.; Kanatani, A. Am. J. Physiol.
Endocrinol. Metab. 2003, 284, E940.
14. McBriar, M. D.; Guzik, H.; Xu, R.; Paruchova, J.; Li, S.;
Palani, A.; Clader, J. W.; Greenlee, W. J.; Hawes, B. E.;
Kowalski, T. J.; OÕNeill, K.; Spar, B.; Weig, B. J. Med.
Chem. 2005, 48, 2274.
4. Shimada, M.; Tritos, N. A.; Lowell, B. B.; Flier, J. S.;
Maratos-Flier, E. Nature 1998, 396, 670.
15. Chaki, S.; Funakoshi, T.; Hirota-Okuno, S.; Nishiguchi,
M.; Shimazaki, T.; Iijima, M.; Grottick, A. J.; Kanuma,
K.; Omodera, K.; Sekiguchi, Y.; Okuyama, S.; Tran, T.
A.; Semple, G.; Thomsen, W. J. Pharmacol. Exp. Ther.
2005, 313, 831.
16. All compounds described here were assayed for their
ability to competitively displace radiolabeled [125I-Tyr13]-
MCH from HEK 293 cells expressing human MCH1-R1
that has been modified for optimal expression. Ki values
are averages of at least three determinations.
5. Chambers, J.; Ames, R. S.; Bergsma, D.; Muir, A.;
Fitzgerald, L. R.; Hervieu, G.; Dytko, G. M.; Foley, J. J.;
Martin, J.; Liu, W. S.; Park, J.; Ellis, C.; Ganguly, S.;
Konchar, S.; Cluderay, J.; Leslie, R.; Wilson, S.; Sarau, H.
M. Nature 1999, 400, 261.
6. Saito, Y.; Nothacker, H. P.; Wang, Z.; Lin, S. H.; Leslie,
F.; Civelli, O. Nature 1999, 400, 265.
7. Hill, J.; Duckworth, M.; Murdock, P.; Rennie, G.;
Sabido-David, C.; Ames, R. S.; Szekeres, P.; Wilson,
S.; Bergsma, D. J.; Gloger, I. S.; Levy, D. S.;
Chambers, J. K.; Muir, A. I. J. Biol. Chem. 2001,
276, 20125.
17. ACDLabs8.0 was used for the calculation.
18. The measurement of water solubility was performed
empirically as follows: 25 mg of a compound as its salt
form was initially stirred with a minimum volume of DI

3706
C. Q. Huang et al. / Bioorg. Med. Chem. Lett. 15 (2005) 3701–3706
water (such as 0.5 ml) for at least 10 min, then additional
Schwarz, D.; Saunders, J.; Goodfellow, V.S. Bioorg.
Med. Chem. Lett. 2005, 15, 999.
21. po dose (10 mg/kg): Cmax = 82.6 ng/ml, AUC (0–24 h) =
393 ng h/ml; iv dose(10 mg/kg): Cl = 139.3 ml/min kg;
Vd = 32 L/kg, AUC (0–24 h) = 1236 ng h/ml; brain AUC
(0–24 h) = 8905 ng h/ml (from iv dose).
22. Sometime after this work was completed, a patent
application (WO2004072025) claiming molecules related
to this two series has appeared.
water may be added with stirring until the solid completely
dissolved. Solubility was then calculated by 25 mg/volume
of water. The pH was not controlled during the
measurement.
19. Elemental analysis indicated that the salt contained two
molecules of hydrogen chloride.
20. Grey, J.; Dyck, B.; Rowbottom, M. R.; Tamiya, J.;
Vickers, T.D.; Zhang, M.; Zhao, L.; Heise, C. E.;