Discovery of novel orally active ureido NPY Y5 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2007.11.132

We have derived a novel series of neuropeptide Y (NPY) Y5 receptor antagonists from the biphenylurea 3. Cyclohexylurea 21c, a member of the series, is a potent NPY Y5 receptor antagonist that exhibits excellent pharmacokinetic parameters in rats and dogs. On chronic oral administration to diet-induced obese rats, 21c displayed an anti-obesity profile, causing a modest reduction in food intake, a significant decrease in body weight gain, a decrease in adipose mass, and an increase in lean tissue mass.

Full text of DOI:10.1016/j.bmcl.2007.11.132

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 1146–1150
Discovery of novel orally active ureido NPY Y5
receptor antagonists
a,
a
c
b
Guoqing Li,a,* Andrew W. Stamford, Ying Huang, Kuo-Chi Cheng, John Cook,
*
Constance Farley,b Jun Gao,b Lorraine Ghibaudi,b William J. Greenlee,a Mario Guzzi,d
Margaret van Heek,b Joyce J. Hwa,b Joe Kelly,a Deborra Mullins,d Eric M. Parker,d
Sam Wainhausc and Xiaoping Zhangd
aDepartment of Chemical Research, Schering-Plough Research Institute, 2015 Galloping Hill Road MS 2545,
Kenilworth, NJ 07033-0359, USA
bDepartment of Cardiovascular and Metabolic Diseases, Schering-Plough Research Institute,
2015 Galloping Hill Road MS 2545, Kenilworth, NJ 07033-0359, USA
cDepartment of Exploratory Drug Metabolism and Pharmacokinetics, Schering-Plough Research Institute,
2015 Galloping Hill Road MS 2545, Kenilworth, NJ 07033-0359, USA
dDepartment of Neurobiology, Schering-Plough Research Institute, 2015 Galloping Hill Road MS 2545,
Kenilworth, NJ 07033-0359, USA
Received 27 September 2007; revised 29 November 2007; accepted 30 November 2007
Available online 5 December 2007
Abstract—We have derived a novel series of neuropeptide Y (NPY) Y5 receptor antagonists from the biphenylurea 3. Cyclohexylu-
rea 21c, a member of the series, is a potent NPY Y5 receptor antagonist that exhibits excellent pharmacokinetic parameters in rats
and dogs. On chronic oral administration to diet-induced obese rats, 21c displayed an anti-obesity profile, causing a modest reduc-
tion in food intake, a significant decrease in body weight gain, a decrease in adipose mass, and an increase in lean tissue mass.
Ó 2007 Elsevier Ltd. All rights reserved.
Neuropeptide Y (NPY) is a 36-amino acid neuropeptide
that is widely distributed in the mammalian central and
peripheral nervous systems.1 Over the last two decades,
a large body of knowledge related to the NPY system
has accumulated. NPY mediates a number of physiolog-
ical functions through several G protein-coupled recep-
tor subtypes designated Y1, Y2, Y4, Y5, and y6.2
Pharmacological studies have implicated the hypotha-
lamic Y5 subtype as a mediator of the effects of NPY
on food intake and energy homeostasis.3 Consequently,
over the past decade there have been numerous reports
of small molecule NPY Y5 receptor antagonists as po-
tential anti-obesity therapies.4 Until recently, evaluation
of these in various rodent studies has yielded inconclu-
sive and often conflicting results as to the role of the
Y5 receptor in food intake and body weight mainte-
nance. The recent report that the Y5 antagonist 1 had
significant anti-obesity effects in mice under conditions
of diet-induced obesity has provided clarity to this is-
sue.5 Thus, chronic administration of 1 to diet-induced
obese (DIO) mice resulted in suppression of body weight
gain, while there was no effect on body weight of lean
mice or of Y5À/À mice. Amelioration of the obese state
by chronic administration of 1 was shown to result from
reduced food intake and increased energy expenditure.6
Moreover, modest but significant anti-obesity effects of
the Y5 antagonist, MK-0557 (2), have recently been
demonstrated in obese human subjects.7 Herein we de-
scribe the design and SAR of a novel, structurally dis-
tinct ureido series of Y5 antagonists, and report the
profile of the optimized Y5 antagonist 21c in DIO rats.
Our first generation lead NPY Y5 antagonist biphenylurea
3 is a high affinity antagonist of human and rat Y5 recep-
tors (human Y5 Ki = 0.4 nM, rat Y5 Kb = 0.4 nM).8,9 In
rats, oral administration of compound 3 (ED50 0.4 mg/
kg) potently blocked food intake induced by centrally
Keywords: Neuropeptide Y; NPY Y5 antagonist; Obesity.
*
Corresponding authors. Tel.: +1 908 740 2511; fax: +1 908 740 7164
(G.L.); tel.: +1 908 740 3481 (A.W.S); e-mail addresses: guoqing.li@
spcorp.com; andrew.stamford@spcorp.com
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.11.132

G. Li et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1146–1150
Table 1. Human Y5 binding affinity of compounds 11a–z
1147
administered D-Trp[34]-NPY, a selective Y5 agonist.10
However, given the known potent mutagenicity of biphe-
nylamines, the possibility of liberation in vivo of the
biphenylamine fragment 4, a substructure of 3, posed an
unacceptable safety risk. We therefore sought to eliminate
this liability by replacing the phenylene linker with a pipe-
ridinyl or cyclohexyl ring, represented by structure 5.
Compound
R
Ar
Kia (nM)
11a
11b
11c
11d
11e
11f
11g
11h
11i
CH3SO2–
EtSO2–
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
Ph
3.2
2.8
3.4
3.2
7.4
6.3
5.9
2.6
303
405
52
n-PrSO2–
i-PrSO2–
CH3CO–
EtCO–
H
N
O
n-PrCO–
i-PrCO–
H
N
N
HO
O
N
O
N
F
O
N O
O
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
CH3SO2–
S
F
N
O
11j
3-Pyridyl
2-Me-Ph
2-F-Ph
F
O
11k
11l
O
88
35
1
3
2 (MK-0557)
11m
11n
11o
11p
11q
11r
11s
11t
11u
11v
11w
11x
11y
11z
3-F-Ph
3-Cl-Ph
H
N
13
20
N
NH2
3-Me-Ph
3-Br-Ph
F
X
O
N O
S
F
8.8
27
O
3-CN-Ph
3-MeO-Ph
3-Acetyl-Ph
4-F-Ph
F
F
4
5
X= N, C
311
164
799
130
819
48
The synthesis of piperidine analogs 11a–h (Scheme 1)
commenced from 1,4-dioxa-azaspiro(4,5)decane 6,
which was first N-arylated using Buchwald–Hartwig
conditions and then subjected to acid hydrolysis of the
ketal to give piperidin-4-one 7. Reductive amination of
7 with benzylamine, followed by reductive cleavage of
the benzyl group, gave amine 8, which was coupled with
1-Boc-4-methylaminopiperidine in the presence of
disuccinimidyl carbonate (DSC) in THF to afford the
urea 9. Following removal of the Boc protecting group
the resulting amine 10 was derivatized with anhydrides,
acyl chlorides or sulfonyl chlorides to provide 11a–h
(Table 1). In order to further explore the SAR within
this series, we fixed the (4-methylamino)piperidinesulf-
onamide group and varied the N-aryl substituent (com-
pounds 11i–z, Table 1). Thus, Cu(II)-mediated arylation
of intermediate 13 with aryl boronic acids afforded tar-
gets 11i–z (Scheme 1).11
4-Cl-Ph
4-Br-Ph
3,4-di-Cl-Ph
3,4-di-F-Ph
3-Cl, 4-F-Ph
3,5-di-Cl-Ph
312
160
1.1
a Average of two determinations.
stituted derivative 11i. The most favorable monosubsti-
tution was 3-bromo, followed by chloro, methyl, cyano,
and fluoro. Less well tolerated were 3-methoxy and 3-
acetyl, as well as all para-substitution. 3,5-Disubstituted
analogs afforded the best potency in the series; 3,5-
difluorophenyl 11a and 3,5-dichlorophenyl 11z were
substantially more potent than 11i. Compounds 11a–h
and 11z were subjected to a rat oral pharmacokinetic
screen at a dose of 10 mg/kg and while substantial plas-
ma levels were typically observed, these analogs suffered
from poor brain penetration. For example, acetamide
11e exhibited a plasma AUC0–6 h of 104 lM.h and a
6 h plasma concentration of 10 lM, however 11e was
not detected in brain extracts from rats 6 h post-dose.
We were encouraged to find that 3,5-difluorophenyl-
substituted derivatives 11a–h retained single digit nano-
molar Y5 receptor binding affinity (Table 1). While
monosubstitution at the 3-position afforded compounds
that were generally less potent (11m–s), these analogs
were generally 10–30-fold more potent than the unsub-
H
NH2
O
N
N
Br
O
F
O
N
F
N
F
N
F
O
N
a, b
f
e
c, d
Boc
+
N
H
6
F
F
F
F
F
9
7
8
H
N
H
NH2
H
N
N
N N
g
N
h, i
j
O
N
O
N
O
N
HN
N
O
N
H
S
O
Ar
R
N
Boc
F
10
11
12
13
Scheme 1. Reagents and conditions: (a) Pd(OAc)2, dppp, NaOBut, anhydrous toluene, N2, 90 °C, 16 h, 86%; (b) 5 N HCl, THF, rt, 16 h, 79%; (c)
benzylamine, NaBH(OAc)3, DME, 80%; (d) 10% Pd/C, HCO2H/MeOH, 83%; (e) DSC, Py, THF, 0 °C, then 1-Boc-4-methylaminopiperidine, 80%;
(f) 10% TFA/CH2Cl2, 86%; (g) RCOCl, Et3N, 86–96% or RSO2Cl, Et3N, 70–84%; (h)DSC, Py, THF, 0 °C, then 1-methanesulfonyl-4-
methylaminopiperidine, 58%; (i) 4 N HCl/dioxane in CH2Cl2, 88%; (j) ArB(OH)2, Et3N, Cu(OAc)2, CH2Cl2, yields range from 7% to 26%.

1148
G. Li et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1146–1150
H
N
H
N
H
N
N
NH2
N
Ph
Ph
O
b
a
c
d, e
O
N
O
N
Boc
Ar
R
Ar
Ar
Ar
Ar
17 (trans
)
19 (trans
)
21 (trans
)
15 (trans
)
14a Ar = Ph
18 (cis
)
20 (cis
)
22 (cis
)
16 (cis
)
14b Ar = 3,5-diF-Ph
i
F
F
F
h
g
f
O
O
O
24
O
O
O
TfO
O
O
O
F
26
25
23
Scheme 2. Reagents and conditions commencing with 14a: (a) NaBH(OAc)3, Ph2CHNH2, DME, 82%; (b) 10% Pd/C, HCO2H/MeOH, 84%; (c)
DSC, Py, THF, 0 °C, then 1-Boc-4-methylamino-piperidine in THF, 88%; (d) 4 N HCl in dioxane, rt, 96%; (e) (RCO)2O, Et3N, 77–84% or RSO2Cl,
Et3N, CH2Cl2, 0 °C, 45–66%; (f) LDA, followed by PhNTf2 in THF, À78 °C, 92%; (g) 3,5-difluorophenylboronic acid, Pd(PPh3)4, LiCl, Na2CO3,
DME/H2O, 55%; (h) 10% Pd/C, H2; (i) TFA/CH2Cl2/H2O, 64%.
To examine the cyclohexylene linker as a replacement
for the phenylene of biphenylurea 3, 4-phenylcyclohexa-
none 14a (Scheme 2) was subjected to reductive
amination with benzhydrylamine and sodium triacet-
oxyborohydride which gave a 1:3 mixture of trans and
cis isomers 15 and 16 (Ar = Ph), which were readily sep-
arable. Each of the isomers was transformed into the
trans and cis targets 21a,b and 22a,b (Table 2), respec-
tively. The trans isomers were at least 10-fold more po-
tent than the cis isomers, presumably because the
topology of trans diequatorial 1,4-cyclohexyl substitu-
ents more closely resembles that of the biphenyl urea 3.
pling of 3,5-difluorophenylboronic acid with enol triflate
24 derived from cyclohexanone 23. Hydrogenation of the
styrene 25 to give 26, followed by ketal hydrolysis, affor-
ded 14b which were converted to the trans 3,5-dif-
luorophenylcyclohexyl targets (21c–h, Table 2).
Trans-cyclohexyl analogs with 3,5-difluorophenyl sub-
stitution were uniformly more potent at the Y5 receptor
compared to the non-fluorinated analogs (Table 2). Of
the analogs prepared, Y5 antagonist 21c offered an
attractive overall profile with respect to Y5 receptor
binding affinity, functional activity, and pharmacoki-
netic properties, and was selected for additional profil-
ing. In order to provide gram quantities of 21c for
further in vivo studies, we developed an efficient stereo-
selective synthesis (Scheme 3). Reduction of 14b with
L-Selectride at À78 °C produced the cis-alcohol 27 in
78% yield. Mesylation of 27 followed by SN2 displace-
ment with NaN3 gave trans azide 28 in 71% yield.
Reduction of 28 with tin(II) chloride quantitatively
To identify cyclohexyl analogs with improved Y5
receptor affinity, 3,5-difluorophenyl substitution was
incorporated. The requisite 4-(3,5-difluorophenyl)-cyclo-
hexanone 14b was synthesized (Scheme 2) via Suzuki cou-
Table 2. Structure–activity relationship of 21a–h and 22a–b
Compound
Ar
R
Y5 Kia (nM)
afforded
trans-4-(3,5-difluorophenyl)cyclohexylamine
22a
22b
21a
21b
21c
21d
21e
21f
Ph
Ph
CH3CO–
CH3SO2–
CH3CO–
CH3SO2–
CH3CO
EtCO–
>1000
500
59
29 which was then coupled with 1-acetyl-4-methylamin-
opiperidine in the presence of DSC to provide 21c in
70% yield.
Ph
Ph
52
1.8
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
3,5-di-F-Ph
1.5
2.0
Compound 21c has high affinity for the Y5 receptor (hu-
man Y5 Ki = 1.8 nM), negligible affinity for human Y1,
Y2, and Y4 receptors (Ki > 10,000 nM), and is a func-
tional antagonist of the rat Y5 receptor (Kb = 2.7 nM).
In counterscreening assays, 21c did not significantly
cross-react with a panel of 60 receptors, enzymes, and
n-PrCO
CH3SO2–
EtSO2–
n-PrCO–
1.2
21g
21h
0.75
2.4
a Average of two determinations.
F
F
F
F
F
d
a
b, c
N3
H2N
14b
HO
F
28
27
29
H
N
N
e
O
N
F
COCH3
21c
F
Scheme 3. Reagents and conditions: (a) L-Selectride, THF, À78 °C, 78%; (b) MsCl, Et3N, CH2Cl2, 0 °C–rt; (c) NaN3, DMSO, 40 °C, 71% for two
steps; (d) SnCl2 2H2O, THF/H2O; (e) DSC, Py, THF, 0 °C, then 1-acetyl-4-methylaminopiperidine in THF, 70% for two steps.

G. Li et al. / Bioorg. Med. Chem. Lett. 18 (2008) 1146–1150
1149
ion channels (<50% inhibition of binding at 10 lM).12
In rats, 21c has excellent oral bioavailability
(%F = 100), a brain/plasma ratio of 0.3, and a relatively
short IV t1/2 of 1.4 h. The half-life of 21c is considerably
longer in beagle dogs (IV t1/2 = 24 h) and bioavailability
remained high in this species (%F = 94).
kg, and did not antagonize food intake induced by cen-
trally administered galanin, consistent with a Y5-specific
mechanism for inhibition of feeding. Compound 21c
administered orally to DIO rats for 28 days caused a
dose-dependent reduction in food intake that reached
statistical significance at the 10 mg/kg/day dose
(Fig. 1a).13 Administration of 21c also caused a dose-
dependent reduction in body weight gain at the 3 and
10 mg/kg doses that was significantly different from the
control group (Fig. 1b). Analysis of body composition
by DEXA scanning demonstrated a dose-dependent de-
crease in adipose mass, while lean body mass increased
(Fig. 1c). In contrast, control animals gained adiposity
and exhibited no change in lean mass over the course
of the study. The significant increase in lean mass that
accompanied the decrease in body mass at the 10 mg/
kg/day dose is presumably a consequence of enhanced
fat utilization as energy source, and partitioning of
nutrients to lean tissue. This highly interesting observa-
tion indicates that measurement of body weight alone
does not adequately reflect underlying changes in body
composition over the course of treatment.
In vivo, oral administration of 21c blocked D-
Trp[34]NPY-induced feeding with an ED50 of 2.3 mg/
a
In summary, a series of novel and potent cyclohexylure-
ido NPY Y5 receptor antagonists have been discovered
by modifying a biaryl urea lead. The cyclohexylurea 21c
displayed excellent pharmacokinetic properties and pro-
duced significant inhibition of food intake and body
weight gain in a 28 day DIO rat model at an oral dose
of 10 mg/kg/day. This corresponded to a significant de-
crease in adipose mass and increase in lean mass over
the course of the study. The present study contributes
to a growing body of evidence demonstrating that signif-
icant Y5 mechanism-specific anti-obesity effects can be
obtained with chronic administration of Y5 antagonists
to obese mammals, and that in DIO rats, through either
neuronal or hormonal mechanisms that result from Y5
receptor blockade, these effects are not limited to adi-
pose tissue alone.5–7
b
c
10
5
*
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Figure 1. (a) Food intake of DIO rats dosed with 21c for 28 days. (b)
Body weight change of DIO rats dosed with 21c for 28 days. (c) %
Change in fat and lean mass of DIO rats dosed with 21c for 28 days.

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12. Counterscreening performed by CEREP, France. Com-
pound 21c (10 lM) displayed <10% inhibition of binding to
serotonin receptor subtypes (5-HT2A, 5-HT2B, 5-HT2C, 5-
HT3, 5-HT5A, 5-HT6, 5-HT7) and monoamine transporters
(norepinephrine, dopamine, serotonin, GABA), and <25%
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13. Ghibaudi, L.; Cook, J.; Farley, C.; van Heek, M.; Hwa, J.
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prior to commencing the 28-day study. At the start of the
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were offered food and water ad libitum throughout the
study. Compound 21c was admixed into low fat diet
(Research Diets); doses delivered (1, 3, or 10 mg/kg/day)
were calculated based on food consumption during the
treatment period. Average plasma levels of 21c were
approximately 13 lM at the 10 mg/kg/day dose. Body
composition was determined by DEXA scanning; data are
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the ability of compounds to displace [125I]PYY binding to
a chimeric rat/human NPY Y5 receptor expressed in