Structure-activity relationships of a novel series of melanin-concentrating hormone (MCH) receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2004.05.051

A new series of 2-aminoquinolines has been identified as antagonists of the melanin concentrating hormone receptor (MCH-1R). Syntheses and structure-activity relationships are described leading to a compound having low nanomolar activity against the receptor and demonstrating functional antagonism. Studies also showed that some of the compounds were selective against a range of other G protein-coupled receptors.

Full text of DOI:10.1016/j.bmcl.2004.05.051

Bioorganic& Medicinal Chemistry Letters 14 (2004) 4099–4102
Structure–activity relationships of a novel series of
melanin-concentrating hormone (MCH) receptor antagonists
Rosa Arienzo, David E. Clark, Sue Cramp, Stephen Daly, Hazel J. Dyke,* Peter Lockey,
Dennis Norman, Alan G. Roach, Keith Stuttle, Maxine Tomlinson, Melanie Wong
and Stephen P. Wren
Argenta Discovery Limited, 8/9 Spire Green Centre, Flex Meadow, Harlow, Essex CM19 5TR, UK
Received 2 January 2004; revised 7 May 2004; accepted 10 May 2004
Available online
Abstract—A new series of 2-aminoquinolines has been identified as antagonists of the melanin concentrating hormone receptor
(MCH-1R). Syntheses and structure–activity relationships are described leading to a compound having low nanomolar activity
against the receptor and demonstrating functional antagonism. Studies also showed that some of the compounds were selective
against a range of other G protein-coupled receptors.
Ó 2004 Elsevier Ltd. All rights reserved.
Obesity has reached epidemic proportions in the US and
Western Europe, and it is currently estimated that over
30% of Americans are obese.1 The incidence of obesity
in children and adolescents is also increasing. Obesity
has been linked to a number of co-morbidities such as
stroke, heart disease, diabetes, hypertension, osteo-
arthritis and certain cancers. There exists a clear need
for novel, safe and effective treatments for obesity, and
the rapid expansion in incidence of this disease provides
a clear incentive for the development of a suitable
therapeuticagent. Although it is known that obesity is
due to an imbalance between energy expenditure and
food intake, the reasons for this imbalance in any given
individual are not fully understood.
rates.3 Conversely, mice over-expressing MCH are sus-
ceptible to obesity and insulin resistance.4
The effects of MCH are mediated through two distinct
receptors, MCH-1R and MCH-2R, both of which are
members of the G protein-coupled receptor (GPCR)
superfamily. MCH-1R has been identified in mammals
and rodents, whereas functional MCH-2R receptors
have not been found in rodents. The sequence identity
between the two receptor types is only about 36%. The
localisation of MCH-1R in the brain is in good agree-
ment with the distribution of MCH itself.5 The effects of
small molecule MCH-1R antagonists in rodent feeding
models have been described by two groups,6;7 and the
results support the hypothesis that MCH-1R antago-
nists should provide a novel treatment for obesity.
Melanin-concentrating hormone (MCH) is a cyclic
19-amino acid peptide, which is produced predomi-
nantly by neurons in the lateral hypothalamus and zona
incerta, which project throughout the brain. The
important role played by MCH in the regulation of
energy balance and body weight has been demonstrated
in several ways. Central administration of MCH in rats
stimulates food consumption,2 whilst fasting results in
an increase in MCH expression. Mice lacking MCH are
lean, hypophagicand maintain elevated metabolic
The identification of a potent hit compound (1) by vir-
tual screening has been reported by us separately.8 This
communication describes the synthesis and structure–
activity relationships of a series of novel, potent and
selective MCH-1R antagonists based on (1) (Fig. 1).
The syntheticroutes used to prepare analogues of the hit
compound (1) were devised in order to maximise the
possible variations at each end of the molecule. Scheme
1 depicts the synthetic route used to vary the amide at
the final stage. Reaction of 2-chloro-4-methylquinoline
with 1-methyl-piperazine followed by nitration gave the
* Corresponding author. Tel.: +44-(0)1279-645650; fax: +44-(0)1279-
645646; e-mail: hazel.hunt@argentadiscovery.com
0960-894X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2004.05.051

4100
R. Arienzo et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4099–4102
orous conditions were required for reaction with pri-
mary amines (225 °C for 60 min).
Cl
H
N
O
Compounds were screened in a scintillation proximity
assay in competition with 125I-[Phe13,Tyr19]-MCH
binding to MCH-1R membranes.
O
N
N
N
(1)
Figure 1. Hit compound identified by virtual screening.
Our first objective was the exploration of the SAR of the
substitution on the phenyl ring. We initially investigated
a range of substituents in the 4-position, and the results
are provided in Table 1. Electron-withdrawing substit-
uents such as chloro, trifluoromethyl and trifluoro-
methoxy provided the most potent compounds
(compounds A, C and E). The lack of potency of the 4-
fluoro compound (G) and the 4-cyano compound (F)
suggested that there was also a stericrequirement at the
4-position. A comparison between 4-, 3- and 2-chloro
compounds suggested that substitution in the 4-position
was favoured over substitution in either the 2- or 3-
position. This conclusion was confirmed by the lack of
potency of the 2-methyl, 2-methoxy and 3-methoxy
analogues (compounds J, K and M). The absence of a
substituent in any position (compound H) was clearly
detrimental. The potency of the 2,4-dichloro compound
suggested that incorporation of a suitable substituent at
desired 6-nitro derivative.9 Subsequent reduction of the
nitro group and coupling of the resultant amine with a
range of carboxylic acids gave the target compounds.
Scheme 2 shows the synthetic route used to prepare
compounds in which the amine was varied. In this case
nitration of 2-hydroxy-4-methylquinoline gave the de-
sired 6-nitro isomer.10 Conversion of the hydroxyl sub-
stituent to
a chloro substituent provided a key
functionality for later variation. Reduction of the nitro
group gave the corresponding amine, which was coupled
with the appropriate carboxylic acid to give the inter-
mediate chloro derivative ready for derivatisation at the
2-position. Reaction of the 2-chloro compound with a
range of secondary amines could be achieved in the
microwave11 at 180 °C for 20 min, although more vig-
NO2
a
b
N
N
N
N
Cl
N
N
N
c
H
R
NH2
N
d
O
O
N
N
N
N
N
N
Scheme 1. Synthesis of compounds with variation of the amide. Reagents and conditions: (a) 1-methylpiperazine, toluene, reflux; (b) HNO3, H2SO4,
<0 °C; (c) H2, 10% Pd/C, EtOH; (d) ArOCH2CO2H, EDCI, HOBt, DMF.
NO2
NO2
NH2
a
b
c
HO
N
HO
N
Cl
N
Cl
N
d
CF3
CF3
H
N
H
N
e
O
O
R1
O
O
N
N
Cl
N
R2
Scheme 2. Synthesis of compounds with variations of the amine. Reagents and conditions: (a) fuming HNO3, H2SO4, <10 °C; (b) POCl3, reflux; (c)
Fe, HCl, EtOH, reflux; (d) ArOCH2CO2H, HATU, (iso-Pr)2EtN, DMF; (e) R1R2NH, NMP, microwave, 180 °C for 20 min or 225 °C for 60 min.

R. Arienzo et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4099–4102
Table 1. Optimisation of the aryl substituent Table 3. Investigation of the linker
4101
H
N
H
N
X
L
O
O
O
N
N
Cl
N
N
N
N
Compound
Linker L
IC50 (nM) or % @
1 lM
Compound
X
IC50 (nM) or % @
1 lM
A
W
X
Y
CH2O
55
300
A
B
C
D
E
F
4-Cl
55
80
CH2CH2
CH2SCH2
CH2OCH2
4-CH3
4-CF3
4-OCH3
4-OCF3
4-CN
4-F
38%
19%
14
152
36
370
1682
2%
470
1050
0%
19%
9%
24
G
H
I
of potency of the N-methyl-N-benzyl compound (com-
pound V) suggests a stericlimitation.
H
2-Cl
J
2-CH3
2-OCH3
3-Cl
Removal of the methyl substituent in the 4-position of
the quinoline was also detrimental. The 4-desmethyl
analogue of compound A showed only 38% inhibition at
1 lM in the MCH-1 binding assay.
K
L
M
N
3-OCH3
2,4-Di-Cl
Finally, we investigated the linker between the quinoline
and phenyl rings, and the results are summarised in
Table 3. The originally discovered oxyacetamide linker
was found to be optimal, but a propionamide linker also
provided a compound with some activity (compound
W). Either increasing or reducing the length of the linker
was detrimental, and N-methylation of the amide
abolished activity (data not shown).
the 2-position in addition to substitution at the 4-posi-
tion was beneficial (compare compound N with com-
pound A).
Our next objective was the investigation of the amino
substituent at the 2-position of the quinoline, and the
results are summarised in Table 2. Replacement of the
N-methylpiperazine by morpholine resulted in only a
small reduction in potency, indicating that the remote
basic nitrogen was not essential for activity. The incor-
poration of piperidine resulted in a reduction in potency,
but the smaller pyrrolidine provided a very potent
compound (compare compounds P and Q). Small sec-
ondary amines were also well tolerated, with isoprop-
ylamine providing the most potent compound in this
series (compound S). Incorporation of a remote basic
nitrogen is also well tolerated (compound U). The lack
MCH-1 induced Ca2þ release from CHO cells trans-
fected with human MCH-1R was used to evaluate the
functional antagonist potency of selected compounds.
The compounds were pre-incubated with the cells for
5 min prior to addition of 0.1 lM MCH (a concentration
producing 80% of maximal Ca2þ release). None of the
compounds caused a release of Ca2þ from the cells and
thus no MCH-1R agonist activity was noted. All the
compounds tested showed functional antagonism in this
assay, and selected results are included in Table 4.
In addition, the specificity of selected compounds for
MCH-1R over several other GPCRs was determined,
and these results are also provided in Table 4. Although
the original hit compound (compound A) exhibited
significant binding affinity for other receptors, in par-
ticular 5-HT2B and 5-HT2C, it was possible to identify
compounds, such as compound Q, with a significantly
improved profile. Thus, whereas compound A only
exhibited sixfold selectivity for MCH-1R over 5-HT2B
receptors, compound Q was greater than 200-fold
selective.
Table 2. Optimisation of the 2-amino substituent
CF3
H
N
O
R1
O
N
N
R2
Compound
NR1R2
IC50 (nM) or % @
1 lM
C
O
P
Q
R
S
N-Methylpiperazino
Morpholino
Piperidino
55
91
In conclusion, we have described the optimisation of a
series of 2-aminoquinoline MCH-1R antagonists first
identified using a virtual screening approach. Com-
pounds in this series provided functional antagonism in
a calcium flux assay, and no agonism was observed with
any compound tested. In addition to improving binding
affinity and functional activity, a significant improve-
ment in specificity for MCH-1R over other GPCRs has
226
15
Pyrrolidino
Cyclopentylamino
Isopropylamino
Dimethylamino
(CH3)2NCH2CH2N(CH3)
PhCH2N(CH3)
38
11
T
U
V
174
22
40%

4102
R. Arienzo et al. / Bioorg. Med. Chem. Lett. 14 (2004) 4099–4102
Table 4. Activity of selected compounds at MCH-1R and other human amine GPCRs. The selectivity ratios of compounds for MCH-1R versus
5-HT2B receptors are shown
Compd
MCH-1R
IC50 (nM)
Ca2þ release
IC50 (nM)
5-HT2A IC50
5-HT2B IC50
5-HT2C IC50
(nM) or % @ (nM) or % @ (nM) or % @
D2 % @ 1 lM a1A % @
1 lM
Ratio
5-HT2B:MCH-1
1 lM
1 lM
1 lM
A
C
N
O
Q
S
55
14
24
91
15
11
71
63
2180
27%
10%
27%
11%
18%
349
442
970
35%a
41%a
35%a
43%
7%
84%a
85%a
55%a
5%
6
32
39%
33%
27%
7%
NT
124
10
201
8
19%
>3000
400
>11
>200
36
10%
24%
NT
18%
2%
NT ¼ not tested.
a % inhibition @ 10 lM.
6. Takekawa, S.; Asami, A.; Ishihara, Y.; Terauchi, J.; Kato,
K.; Shimomura, Y.; Mori, M.; Murakoshi, H.; Kato, K.;
Suzuki, N.; Nishimura, O.; Fujino, M. Eur. J. Pharmacol.
2002, 438, 129.
been achieved. Our efforts are continuing in this area,
and will be reported in due course.
7. Borowsky, B.; Durkin, M. M.; Ogozalek, K.; Marzabadi,
M. R.; DeLeon, J.; Heurich, R.; Lichtblau, H.; Shaposh-
nik, Z.; Daniewska, I.; Blackburn, T. P.; Branchek, T. A.;
Gerald, C.; Vaysse, P. J.; Forray, C. Nature Med. 2002, 8,
825.
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