Design and synthesis of the potent, orally available, brain-penetrable arylpyrazole class of neuropeptide Y5 receptor antagonists

Article abstract of DOI:10.1021/jm025513q

Novel arylpyrazole derivatives were synthesized and evaluated as neuropeptide Y (NPY) Y5 receptor antagonists. Compound (-)-7, which features a novel chiral 2,3-dihydro-1H-cyclopenta [a] naphthalene moiety, showed good binding affinity and antagonistic ac

Full text of DOI:10.1021/jm025513q

666
J . Med. Chem. 2003, 46, 666-669
Letters
Ch a r t 1
Design a n d Syn th esis of th e P oten t,
Or a lly Ava ila ble, Br a in -P en etr a ble
Ar ylp yr a zole Cla ss of Neu r op ep tid e Y5
Recep tor An ta gon ists
Nagaaki Sato,* Toshiyuki Takahashi,
Takunobu Shibata, Yuji Haga, Aya Sakuraba,
Masaaki Hirose, Miki Sato, Katsumasa Nonoshita,
Yuko Koike, Hidefumi Kitazawa, Naoko Fujino,
Yasuyuki Ishii, Akane Ishihara, Akio Kanatani, and
Takehiro Fukami
Tsukuba Research Institute,
Banyu Pharmaceutical Co., Ltd.,
Okubo 3, Tsukuba 300-2611, J apan
Sch em e 1
Received February 19, 2002
Abstr a ct: Novel arylpyrazole derivatives were synthesized
and evaluated as neuropeptide Y (NPY) Y5 receptor antago-
nists. Compound (-)-7, which features a novel chiral 2,3-
dihydro-1H-cyclopenta[a]naphthalene moiety, showed good
binding affinity and antagonistic activity for the Y5 receptor.
After intracerebroventricular administration in SD rats, (-)-7
significantly inhibited food intake that was induced by the
centrally administered Y5-preferring agonist, bovine pancre-
atic polypeptide, but had only a negligible effect on NPY-
induced feeding.
In tr od u ction . Neuropeptide Y (NPY) is a highly
conserved 36 amino acid peptide with potent, centrally
mediated orexigenic effects.1-4 Chronic administration
of NPY into the brain induces hyperphagia and body
weight gain.5,6 Concentrations of NPY and its mRNA
in the hypothalamus were markedly increased during
food deprivation and in some genetic models of obesity
in rodents.7-11 In addition, NPY-deficient ob/ob mice are
less obese and have reduced food intake when compared
with ob/ob mice.12 These data suggest that NPY may
be one of the major regulators of physiological feeding
behavior.
Five distinct types of G-protein coupled NPY receptors
(Y1, Y2, Y4, Y5, and y6) have been cloned.13 On the basis
of the correlation between the in vitro functional and
binding activity of different peptide agonists and their
potent stimulation of food intake in rodent models, the
Y5 receptor has been found to be a major feeding
receptor.14 In addition, a reduction in food intake
induced by NPY and related peptides in Y5 receptor
deficient (Y5 -/-) mice were observed,15,16 thereby
supporting the role of the Y5 receptor in food intake.
On the basis of these findings, the antagonism of the
Y5 receptor may have considerable therapeutic benefits
in treating obesity. CGP 71683 was the first Y5 antago-
nist reported in the literature, along with a description
of its pharmacological data,17,18 and many structural
classes of compounds that target the Y5 receptor have
only recently begun to appear in the literature.19-23
Since in vivo specificity of those compounds is unclear,
additional structurally diverse Y5 antagonists are im-
portant in order to probe the role of the Y5 receptor.
We screened our in-house chemical collections for
structurally diverse novel Y5 leads that have molecular
weights in the neighborhood of 350 and found the
arylpyrazole class compound, N-[5-(4-chlorophenyl)-1H-
pyrazol-3-yl]-2-indanecarboxamide (1) (Chart 1). Con-
sequent structural modification resulted in the potent,
orally bioavailable, brain-penetrable, selective Y5 an-
tagonist (-)-7 (Chart 1). In the present study, we report
the discovery of the novel arylpyrazole class of Y5
antagonist (-)-7, together with its pharmacokinetic
profile and preliminary pharmacological effects on ago-
nist-induced feeding in Sprague-Dawley (SD) rats.
Ch em istr y. Our target compounds were prepared by
condensation of the corresponding 3-amino-5-arylpyr-
azoles and carboxylic acids, which is represented by the
synthesis of (-)-7 (Scheme 1). The 3-amino-5-arylpyr-
azoles represented by 9 were prepared following the
literature procedure.24 Herein, we describe the synthesis
of the novel optically active benzindanecarboxylic acid
(-)-10. Optically active acid (-)-10 was synthesized
from the dibromide 11 (Scheme 2). 11 was reacted with
diethyl malonate in the presence of sodium hydride
(NaH) in tetrahydrofurane (THF) to provide the corre-
sponding diethyl cyclopentyldicarboxylate. The mal-
onate cycloalkylation step required a dilute condition
* To whom correspondence should be addressed. Phone: 81-298-77-
2000. Fax: 81-298-77-2029. E-mail: satoung@banyu.co.jp.
10.1021/jm025513q CCC: $25.00 © 2003 American Chemical Society
Published on Web 01/24/2003

Letters
J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5 667
Sch em e 2a
Ta ble 2. Y5 Binding Affinities of the Parallel Synthesis
Library Samplesa
a
Reagents: (a) (i) CH2(CO2Et)2, NaH, THF, room temp, (ii) 2
N aqueous KOH-EtOH, 80 °C, (iii) 200 °C, neat, (77%); (b) (i)
crystallization with (+)-1-(naphthyl)ethylamine from 1,4-dioxane,
(ii) decomposition of the salt with a 1 N HCl solution.
Ta ble 1. Y5 Binding Affinities of Compounds 1 and 2a -g
(Variation of the 5-Aryl Moiety)a
binding affinityb
compd
Ar
(Ki, nM)
1
2a
2b
2c
2d
2e
2f
2g
hNPY
4-chlorophenyl
phenyl
59 ( 1
260 ( 60
120 ( 25
450 ( 22
80 ( 16
62 ( 6
3-chlorophenyl
2-chlorophenyl
4-methylphenyl
4-methoxyphenyl
4-isopropoxyphenyl
3,4-dimethoxyphenyl
92 ( 14
33( 3
1.2( 0.3
a
b
The values represent the mean ( SE for n ) 3. Human
recombinant Y5 receptors in LMtk- cells, [125I]PYY; see ref 27.
(<0.01 M substrate concentration) for good yield. Sub-
sequent saponification and decarboxylation yielded (()-
10 in 77% overall yield. The resulting racemate was
resolved by crystallization with (+)-1-(naphthyl)ethyl-
amine to give (-)-10. The diastereomeric excess of the
amine salt was determined by HPLC analysis of the
corresponding amide that was generated by treating a
portion of the amine salt with 1-(3-dimethylamino-
propyl)-3-ethylcarbodiimide hydrochloride (EDCI). The
optical purity of (-)-10 was tentatively determined to
be >98% ee, which was confirmed by the analysis of (-)-
7. Determination of the absolute stereochemistry of (-)-
10 is currently underway. A mixture of amine 9 and
carboxylic acid (-)-10 in pyridine was treated with
EDCI to give (-)-7 in good yield (Scheme 1). Subse-
quently (-)-7 was converted to its hydrochloride and
used for pharmacological experiments. The optical
purity of (-)-7 was determined to be 98.6% ee by HPLC.
Resu lts a n d Discu ssion . Screening of our in-house
chemical collections against the human Y5 receptor
resulted in the identification of the arylpyrazole class
lead 1. This lead has a Ki value of 59 nM, and its low
molecular weight (MW ) 337.80) is expected to be
advantageous for oral bioavailability and brain pen-
etrability. Modification of the 5-aryl moiety was made
initially (Table 1). Although significant potency en-
hancement was not achieved, our preliminary modifica-
tion of this site provided insights into structure-activity
relationships (SAR). Removing the 4-Cl group as in 2a
reduced activity. Ortho- and meta-substituted phenyl
derivatives 2b and 2c showed a decrease in potency.
Para-substituted derivatives 2d -f were generally equi-
active to 1. Since the methoxy and isopropoxy deriva-
a
b
The values represent the mean ( SE for n ) 3. Human
recombinant Y5 receptors in LMtk- cells, [125I]PYY; see ref 27.
tives (2e and 2f) are equipotent, more sterically de-
manding substituents might be tolerated at this position.
The 3,4-dimethoxyphenyl derivative 2g displayed slightly
improved activity. At this point, we turned our attention
to modification of the left-hand indane carbonyl moiety,
aiming at significant potency improvement. For this
purpose, an exploratory library was prepared using a
parallel synthesis method, which allowed for rapid
access to potent compounds by not employing purifica-
tion methods (Table 2).25 A 5-(4-chlorophenyl)-1H-pyr-
azole-3-amino group was chosen as the template be-
cause of its chemical accessibility and potency, and
selection of the carboxylic acids was based on finding
an optimum orientation of the left-hand aromatic groups.
The 2-naphthylmethyl derivative (entry 8) appeared to
be the most potent compound in this library. Thus, an
analytically pure sample (compound 3) was prepared,
and its IC50 and Ki values were confirmed (Table 3). The
corresponding 5-(3,4-dimethoxyphenyl) derivative 4 was
also potent (Ki ) 8.3 nM) (Table 3). We accomplished
significant potency enhancement by the design of a
benzindane structure (2,3-dihydro-1H-cyclopenta[a]-
naphthalene group) as in (()-5 (Table 3). It was not a
difficult task to realize the novel benzindane structure
based on the given information. Since (()-5 showed very
low oral bioavailability, we needed to examined the
5-aryl portion again and identified the orally available
structure (()-6 (Table 3) (screening pharmacokinetic
data not shown). Replacing the 4-pyridinyl group of

668 J ournal of Medicinal Chemistry, 2003, Vol. 46, No. 5
Letters
Ta ble 3. Y5 Binding Affinities and Antagonistic Activities of
Compounds 3-7a
binding affinityb
[Ca2+]i responsec
(IC50, nM)
compd
(Ki, nM)
3
16.0 ( 3.0
(16.3 ( 3.1)d
8.3 ( 1.5
2.8 ( 0.7
10 ( 2
7.3 ( 0.3
25 ( 0.3
3.5 ( 0.3
e
F igu r e 1. Effects of ICV-injected (-)-7 on NPY and bPP-
induced food intake in SD rats. Significant differences with
respect to controls are indicated by an asterisk (/, P < 0.05).
The data shown are expressed as the mean ( SE. The graph
shows the cumulative food intake in SD rats up to 2 h after
ICV injection of drugs. n ) 8 rats/group. See ref 27 for details.
4
e
e
e
e
(()-5
(()-6
(()-7
(+)-7
(-)-7
28 ( 4
14 ( 3
a
b
Ch a r t 2
The values represent the mean ( SE for n ) 3. Human
recombinant Y5 receptors in LMtk- cells, [125I]PYY; see ref 27.
c Antagonistic activities (human recombinant Y5 receptors/Gqi5
d
in CHO cells) at 100 nM NPY stimulation. The value in paren-
theses is IC50 (mean ( SE for n ) 3). e Not determined.
Ta ble 4. Pharmacokinetic Parameters of (-)-7 in SD Ratsa
iv (1 mg/kg)
t1/2 ) 0.88 ( 0.03 h
Vdss ) 0.62 ( 0.03 L kg-1
CLtot ) 9.52 ( 0.03 mL min-1 kg-1
t1/2 ) 1.9 ( 0.6 h
relative importance of the Y5 receptor in feeding regula-
tion is still controversial; therefore, it is an extremely
important finding that two structurally distinct Y5
antagonists, (-)-7 and 8, displayed similar profiles in
feeding behaviors elicited by ICV-administered bPP and
NPY. To address the role of the Y5 receptor, the
evaluation of structurally diverse new classes of com-
pounds could be critical. Our investigation into the role
of the Y5 receptor using the arylpyrazole derivatives
described herein, the xanthene derivatives, and related
analogues is currently underway in physiological and
pathophysiological feeding models.
In summary, a preliminary SAR of the novel arylpyr-
azole class of Y5 antagonists and the discovery of (-)-7
are described. The novel benzindanecarbonyl portion of
(-)-7 has a significant effect on potency enhancement.
This novel Y5 antagonist has good oral bioavailability
and brain permeability. After ICV administration in SD
rats, (-)-7 significantly inhibited food intake induced
by centrally administered bPP in SD rats but had only
a negligible effect on NPY-induced feeding. The struc-
turally distinct selective ligand (-)-7 is a powerful tool
that may be used to probe the pharmacologic properties
of the Y5 receptor. The investigation into the role of the
Y5 receptor and the search for improved analogues are
ongoing. The updated results will be reported in due
course.
po (10 mg/kg)
Tmax ) 2.0 h
Cmax ) 5.0 ( 1.3 mM
F ) 70 ( 9%
a
The values represent the means ( SE for n ) 3.
(()-6 with a 4-(2-ethylpyridinyl) group aided us in
identifying the more potent compound (()-7 (Table 3).
Hence, optically active (-)-7 and (+)-7 were synthesized.
(-)-7 proved to be a highly potent (Ki ) 3.5 nM) and
selective Y5 antagonist (IC50 > 10 µM at human Y1, Y2,
and Y4). A good pharmacokinetic profile of (-)-7 was
observed after oral (10 mg/kg) and intravenous (1 mg/
kg) administration in SD rats (Table 4). The antago-
nistic activity of (-)-7 was measured by its ability to
inhibit NPY-induced [Ca2+]i increases in LMtk- cells,
which expressed the recombinant human Y5 receptor.
In this [Ca2+]i functional assay, (-)-7 dose-dependently
inhibited the [Ca2+]i increase (Table 3).
We evaluated the effects of (-)-7 on NPY and bovine
pancreatic polypeptide (bPP) induced food intake in SD
rats.26 After intracerebroventricular (ICV) administra-
tion, (-)-7 significantly inhibited bPP-induced food
intake (Figure 1). After oral administration, (-)-7 (10
and 30 mg/kg) showed only moderate dose-dependent
efficacy in suppressing feeding induced by bPP (data not
shown). The brain concentration of (-)-7 (10 mg/kg) in
SD rats 2 h after oral administration was 0.45 µM. We
surmised that the distribution of (-)-7 in the brain after
oral administration is not efficient. Therefore, the
availability of the molecule to the target Y5 receptor
may not be sufficient to show significant efficacy. We
are currently searching for more potent oral compounds
in this class. Interestingly, ICV-administered (-)-7 did
not affect NPY-induced food intake to a significant
degree in SD rats (Figure 1), contrary to the previously
reported observation by Synaptic and Novartis groups.17
In addition, our xanthene class Y5 antagonist 8 (Chart
2) showed exactly the same behavior as did (-)-7.27 The
Ack n ow led gm en t. We thank Dr. Yoshimi Tsuchiya
and his group for analytical and spectral studies. We
are grateful to Merck CLIC service for editing the
manuscript.
Su p p or tin g In for m a tion Ava ila ble: Synthetic proce-
dures including the exploratory library. This material is
available free of charge via the Internet at http://pubs.acs.org.
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J M025513Q