Discovery of substituted 2,4,4-triarylimidazoline derivatives as potent and selective neuropeptide Y Y5 receptor antagonists

Article abstract of DOI:10.1016/j.bmcl.2009.01.101

Novel imidazoline derivatives were discovered to be potent neuropeptide Y Y5 receptor antagonists. High-throughput screening of Merck sample collections against the human Y5 receptor resulted in the identification of 2,4,4-triphenylimidazoline (1), which had an IC₅₀ of 54 nM. Subsequent optimization led to the identification of several potent derivatives.

Full text of DOI:10.1016/j.bmcl.2009.01.101

Bioorganic & Medicinal Chemistry Letters 19 (2009) 1670–1674
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of substituted 2,4,4-triarylimidazoline derivatives as potent
and selective neuropeptide Y Y5 receptor antagonists
*
Nagaaki Sato , Makoto Jitsuoka, Shiho Ishikawa, Keita Nagai, Hiroyasu Tsuge, Makoto Ando,
Osamu Okamoto, Hisashi Iwaasa, Akira Gomori, Akane Ishihara, Akio Kanatani, Takehiro Fukami
Tsukuba Research Institute, Merck Research Laboratories, Banyu Pharmaceutical Company, Ltd, 3 Okubo, Tsukuba 300-2611, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel imidazoline derivatives were discovered to be potent neuropeptide Y Y5 receptor antagonists.
High-throughput screening of Merck sample collections against the human Y5 receptor resulted in the
identification of 2,4,4-triphenylimidazoline (1), which had an IC50 of 54 nM. Subsequent optimization
led to the identification of several potent derivatives.
Received 17 November 2008
Revised 28 January 2009
Accepted 30 January 2009
Available online 4 February 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Neuropeptide Y Y5 recepter antagonist
Brain and CSF permeable
Inhibition of food intake in mice
Imidazoline derivatives
NPY is a 36 amino acid peptide neurotransmitter which was
discovered in 1982 as a member of the pancreatic polypeptide
family, like peptide YY, and a pancreatic polypeptide.1 NPY is a
widely distributed peptide in both the central and the peripheral
nervous systems and has various physiological functions. Concen-
trations of NPY and mRNA levels in the hypothalamus respond to
feeding status, including food deprivation and refeeding.2,3 Chronic
central infusion of NPY in rodents results in a syndrome similar to
that in some genetic obesity models, characterized by hyperphagia,
insulin resistance, hyperinsulinemia, and reduced thermogenic
activity in brown adipose tissue.4 Furthermore, NPY-deficient ob/
ob mice are less obese and have reduced food intake compared
with ob/ob mice.5 Therefore, NPY is thought to have a major role
in the physiological control of energy homeostasis.
been targeted by many pharmaceutical companies as potential
anti-obesity drugs.11
Our in-house chemical collection was screened against the hu-
man Y5 receptor, resulting in the identification of 2,4,4-tripheny-
limidazoline (1). Subsequently, the 2-phenyl portion was
extensively optimized to identify several potent derivatives. In this
Letter, the synthesis and structure–activity relationships of the po-
tent and selective imidazoline class of Y5 antagonists are
described.
The synthetic route for the derivatives reported herein is de-
scribed in Schemes 1 and 2. The synthesis of diamine intermediates
38a and 38b is outlined in Scheme 1. The diamine 38a was pre-
pared from 4,40-difluorobenzophenone 35 by formation of corre-
sponding imine 36a, followed by the addition of cyanide and
subsequent reduction of the nitrile. Benzophenone 35 was con-
verted to the imine 36a,12 which was treated with trimethylsilyl
cyanide in the presence of catalytic amounts of zinc iodide fol-
lowed by reduction with DIBAL to give the diamine 38a.13 Com-
mercially available imine 36b was converted to the
corresponding diamine 38b in the same manner. Imidazoline rings
of 1–12, 14–16, 18, 20–32, and 34 were prepared either by direct
condensation of the diamines with aryl imidates (1, 2, 10–12, 15,
26, 27, and 29),14 thermal condensation of the diamines with aryl
esters (3–9, 16, 18, 20–22, 24, 31, and 32),15,16 or coupling of dia-
mines with aryl carboxylic acid followed by thermal cyclization
of the resultant amides (14, 23, 25, 28, 30, and 34)15 as shown in
Scheme 2. Ester 15 was converted to alcohol 17 by reduction with
DIBAL followed by oxidation using MnO2 to afford aldehyde 13.
Five distinct NPY receptor subtypes (Y1, Y2, Y4, Y5, and mouse
Y6) have been cloned to date,6 and pharmacological data suggest
that the NPY Y5 receptor is involved in feeding regulation. Admin-
istration of Y5 antagonists suppresses Y5 agonist-induced food in-
take and diet-induced body weight gain,7,8 and mice lacking the Y5
show a reduced response to exogenously administered Y5 ago-
nists.9 In addition, chronic intracerebroventricular administration
of a Y5-specific agonist, D
-Trp34NPY, produces obesity in rodents.10
These results suggest that Y5 is a key regulator involved in the
development of obesity in rodents; hence, Y5 antagonists have
* Corresponding author. Tel.: +81 29 877 2004; fax: +81 29 877 2029.
E-mail address: nagaaki_sato@merck.com (N. Sato).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.01.101

N. Sato et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1670–1674
1671
F
R
R
R
a
c
b
CN
NH2
NH2
O
NH
NH2
F
R
R
R
35
36a (R = F): 100%
36b (R = H)b
37a: 100%
37b: 46%
38a: 41%
38b: 94%
Scheme 1. Synthesis of diamine intermediates. Reagents and conditions: (a) TiCl4, NH3, toluene, ꢀ30 °C; (b) TMSCN, cat. ZnI2, toluene, rt; (c) DIBAL, toluene, ꢀ78 °C ? rt.
bCommercially available reagent.
R
R
a, b, c, d, e or f
NH2
NH
Ar
NH2
N
R
R
38a (R = F) or 38b (R = H)
1−12, 14−16, 18,
20−32, 34
g
COOMe
)
OH
17 (R = F, Ar =
)
15 (R = F, Ar =
88%
h
CHO
13 (R = F, Ar =
)
80%
NO2
)
i
NH2
10 (R = F, Ar =
19 (R = F, Ar =
)
quant.
j
CN
25 (R = F, Ar =
)
33 (R = F, Ar =
)
N
N
21% over 2 steps
Scheme 2. Synthesis of derivatives 1–34. Reagents and conditions: (a) Ar(C@NH)OMeꢁHCl, MeOH, rt; (b) ArCOOMe, AlMe3, toluene, 80–110 °C; (c) (i) ArCOOH, CDI, Et3 N, THF,
rt, then 38a, rt, (ii) neat, 180 °C; (d) (i) ArCOOH, EDCI, Et3 N, CHCl3, rt, (ii) PCl5, toluene, reflux; (e) (i) ArCOOH, CDI, Et3 N, THF, rt, then 38a, rt, (ii) POCl3, reflux; (f) ArCOOMe,
neat or xylene, 180ꢀ200 °C; (g) DIBAL, CH2Cl2, 0 °C; (h) MnO2, CHCl3, rt; (i) NH2NH2ꢁH2O, Raney-Ni, EtOH, THF, rt; (j) (i) mCPBA, CHCl3, rt, (ii) TMSCN, Et3 N, CH3CN, reflux.
The nitro group of 10 was reduced to give the desired amine 19.
Oxidation of pyridine 25 with mCPBA and successive treatment
of the resulting pyridine N-oxide with trimethylsilyl cyanide affor-
ded 33.17
Imidate hydrochlorides employed in the present study were
prepared from corresponding aryl cyanides by treatment with
0.1 equiv of sodium methoxide followed by addition of hydrogen
chloride solution as shown in Scheme 3,18 except for commercially
available methyl benzenecarboximidoate hydrochloride. Synthesis
of carboxylic acid 40 used for preparing compound 30 is shown in
Scheme 4. Oxidation of the hydroxymethyl group of 39 followed by
hydrolysis of the nitrile group with 2 N hydrochloric acid afforded
the desired carboxylic acid 40.
The series of imidazoline compounds was tested in a [125I]PYY
binding assay using LMtkꢀ cell membranes expressing human re-
combinant Y5 receptors.19 High-throughput screening of Merck
sample collections against the human Y5 receptor resulted in the
identification of 2,4,4-triphenylimidazoline (1), which has an IC50
of 54 nM. In vitro metabolism of compound 1 was studied in rat
and human microsomes, and oxidation of the 4,4-diphenyl moie-

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N. Sato et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1670–1674
1) 0.1 equiv of NaOMe, MeOH, rt
2) 10% HCl-MeOH or 4 N HCl-EtOAc
NH
OMe
HCl
ArCN
Ar =
Ar
N
N
R
N
N
N
N
R = NO2, CN, Ms, COOMe
Scheme 3. Synthesis of the imidates.
2.6% aq. KMnO4 , 50 °C,
4 h, then 2 N HCl
HO
HO
N
CONH2
N
CN
O
80%
39
40
Scheme 4. Synthesis of carboxylic acid intermediate 40.
Table 1
ties was found to be a major metabolic pathway (data not shown).
Therefore, the fluorine substituted derivative 2 was synthesized
and evaluated. The 4,4-difluoro derivative 2 was found to have
an improved activity and utilized as a template for the present
SAR study (Fig. 1).
SAR of derivatives 2ꢀ20a
F
Substituent effects on the 2-phenyl ring of 2 were studied ini-
tially (Table 1). Positional scanning with chlorine as in the deriva-
tives 3–5 showed a clear result. The 3-chloro derivative 4 was
sixfold more potent than the parent 2, while the 2-chloro deriva-
tive 3 displayed a 20-fold decrease in potency. The 4-chloro deriv-
NH
N
2
4
R
3
F
ative
5
exhibited
a
fourfold decrease in activity. With
trifluoromethyl substitution, the same positional effect was ob-
served where the 3-substituted derivative 6 was fivefold more po-
tent, and the 4-subsituted derivative 7 was fivefold less potent
than 2. Based on these observations, additional 3-susbstitued
derivatives were prepared and evaluated. The bromo derivative 8
was equipotent to the chloro derivative 4, and the fluoro derivative
9 showed a slightly decreased potency. The 3-nitro and cyano
derivatives 10 and 11 were more potent than the chloro derivative
2, and the methanesulfonyl derivative 12 was slightly less potent
than the chloro derivative 4.
Compound
R
hY5R bindingb
IC50 (nM)
Cyclization condition
and yieldc
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
H
32
8
a , 75%
b, 31%
b, 4%
b, 13%
b, 28%
b, 55%
b, 20%
b, 24%
a, 85%
a, 51%
a, 88%
—
c, 34%
a, 91%
b, 42%
—
b, 15%
—
2-Cl
3-Cl
4-Cl
630 29
5.4 0.5
130 25
6.2 0.6
160 24
4.8 0.5
3-CF3
4-CF3
3-Br
A set of carbonyl derivatives showed variable activities. The for-
myl derivative 13 showed good activity, and the acetyl derivative
14 was equipotent to the parent 2. The methoxycarbonyl deriva-
3-F
10
2
3-NO2
3-CN
3-SO2CH3
3-CHO
3-COCH3
3-CO2CH3
3-CH3
3-CH2OH
3-OCH3
3-NH2
4.3 0.6
2.7 0.1
9.2 0.9
8.7 2.3
F
44
270 26
30
59 15
51
8
6
8
300 91
>1000
NH
NH
3-N(CH3)2
b, 20%
N
N
a
The values represent the mean SEM (n = 3).
b
F
[
125I]PYY binding assay in LMtk– cells expressing human recombinant Y5
receptors.
c
See Scheme 2 for the cyclization conditions.
1
2
hY5 IC50 = 54 nM
hY5 IC50 = 32 nM
tive 15 displayed a significant loss of potency. With the exception
of the methoxycarbonyl group as in 15, a range of electron-with-
Figure 1. Structure and hY5 activity of compounds 1 and 2.

N. Sato et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1670–1674
1673
Table 2 (continued)
Table 2
SAR of derivatives 21–34a
Compound Ar
hY5 bindingb IC50
(nM)
Cyclization condition and
yieldc
F
CN
O
33
4.8 0.5
—
N
NH
Ar
H
N
N
34
8.1 1.5
c, 42%
F
Compound Ar
hY5 bindingb IC50
Cyclization condition
and yieldc
(nM)
a
The values represent the mean SEM (n = 3).
[
b
125I]PYY binding assay in LMtkꢀ cells expressing human recombinant Y5
receptors.
2
32
8
a, 75%
b, 50%
b, 34%
c, 38%
b, 36%
c, 8%
c
See Scheme 2 for the reaction conditions.
21
93 20
S
drawing substituents introduced to the 3-position was effective to
enhance potency.
Next, electron-donating substituents were examined. The 3-methyl
derivative 16 was equipotent to the parent 2. The hydroxymethyl and
methoxy derivatives 17 and 18 were slightly less potent than the parent
2. Introduction of more electron-donating amino and dimethylamino
groups as in 19 and 20 were detrimental to potency. In this study, it be-
came apparent that substitution of the 3-position by electron-withdraw-
ing groups increases potency. Of them, the 3-cyano derivative 11 was
identified as the most potent compound.
S
N
22
23
24
25
54
6
160 39
7.2 0.6
160 23
N
Finally, heteroaromatics were investigated on the 2-position of
the imidazoline ring of compound 2 (Table 2). The thiophene deriv-
atives 21 and 22 were less potent than 2. As a result of positional
scanning with a pyridine, the significantly potent 3-pyridyl deriva-
tive 24 was identified. The 2- and 4-pyridyl substitutions as in 23
and 25 resulted in noticeable decreases in potency. Among the dia-
zine analogs 26–29, the potent pyrazine derivative 26 was identi-
fied. The 5-pyrimidine derivative 27 was equipotent to the parent
2, and the substitution with 2-pyrimidine and 3-pyridazine groups
as in 28 and 29 resulted in significant loss of potency. A nitrogen
atom was introduced to the potent cyano derivative 11 as in 30–
33. The 4-cyanopyridin-2-yl and 2-cyanopyridin-4-yl derivatives
31 and 33 displayed retained activities. It was interesting to find
that the 2-pyridon-6-yl derivative 34 exhibited potent activity.
Among the derivatives possessing potent Y5 activity, com-
pounds 11, 26, and 31 were evaluated for their brain and cerebro-
spinal fluid (CSF) penetrability in Sprague–Dawley (SD) rats (Table
3). All three compounds showed very good brain permeability
based on the brain-to-plasma ratios. Brain unbound concentration
is one of the critical factors that should be taken into consideration
for CNS targeting agents, and the brain unbound concentration is
estimated by CSF concentration for highly brain permeable com-
pounds.20 Compound 26 displayed the highest CSF concentration
N
N
26
27
28
29
30
31
32
4.3 0.2
47 11
a, 64%
a, 2%
N
N
N
N
N
350 85
560 130
d, 2%
N
N
N
a, 32%
e, 42%
f, 49%
f, 29%
CN
39
7
(0.064 lM) and brain free fraction (CSF-to-brain ratio: 0.01) among
the three tested compounds. Hence, compound 26 was selected for
further in vivo studies. In addition to its good brain and CSF perme-
ability profile, compound 26 showed a potent antagonistic activity
CN
CN
2.0 0.4
N
Table 3
Brain penetration of compounds 11, 26, and 31a
Plasma
M)
Brain (nmol/ CSF
Brain-to-plasma
ratio
CSF-to-brain
ratio
17
3
(
l
g)
(lM)
N
11 1.4
26 1.2
31 1.3
8.1
5.9
6.4
0.027
0.064
0.025
5.8
4.9
4.9
0.003
0.01
0.004
a
The brain, plasma, and CSF concentrations were measured 2 h following oral
administration of 10 mg/kg of the compounds in rats. The values represent the
mean for n = 3.

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N. Sato et al. / Bioorg. Med. Chem. Lett. 19 (2009) 1670–1674
References and notes
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
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*
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26 (mg/kg, PO)
34
D-Trp NPY 1 µg/head
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experimental details.
Figure 2. Effect of 26 on food intake induced by
D
-Trp34NPY. Compound 26 was
orally administered 2 h before third ventricle injection of
The values represent the mean SEM (n = 7–8). *P < 0.05 (compared with only the
-Trp34NPY treated group).
D lg/head).
-Trp34NPY (1
D
(IC50 = 2.4 0.5 nM)21 and selectivity over other NPY receptor sub-
types (hY1, hY2, and hY4 binding: >10
M).19
l
Compound 26 was tested in an agonist-induced food intake
model (Fig. 2).22 The compound was orally administered 2 h before
animals were treated with either a Y5 selective agonist D
-Trp34NPY
or artificial CSF, and cumulated food intake was measured for the
following 2 h. Compound 26 showed dose-dependent inhibition
of food intake in this feeding model.
In summary, modification of the 2-aryl portion of lead 1 re-
sulted in several potent derivatives. Of them, compound 26
showed potent antagonistic activity and a suitable brain penetra-
tion profile. Compound 26 showed dose-proportional inhibition
of food intake in the agonist-induced food intake model.
22. Sato, N.; Jitsuoka, M.; Shibata, T.; Hirohashi, T.; Nonoshita, K.; Moriya, M.; Haga,
Y.; Sakuraba, A.; Ando, M.; Ohe, T.; Iwaasa, H.; Gomori, A.; Ishihara, A.;
Kanatani, A.; Fukami, T. J. Med. Chem. 2008, 51, 4765.
Acknowledgments
We thank Naoko Fujino, Mikiko Hata, Masahiko Sato, and Dr.
Atsushi Shimizu for collecting DMPK data.