Design, syntheses, and structure-activity relationships of novel NPY Y5 receptor antagonists: 2-{3-Oxospiro[isobenzofuran-1(3H),4′-piperidin]-1′-yl}benzimidazole derivatives

Article abstract of DOI:10.1016/j.bmcl.2008.08.018

Design, syntheses, and structure-activity relationships of a novel class of 2-{3-oxospiro[isobenzofuran-1(3H),4′-piperidin]-1′-yl}benzimidazole NPY Y5 receptor antagonists are described. The benzimidazole structures were newly designed based on the urea linkage of our prototype Y5 receptor antagonists (2 and 3). By optimizing substituents on the benzimidazole core part of the lead compound 5a, we were able to develop a potent, orally available, and brain-penetrable Y5 selective antagonist (5k). Crown Copyright

Full text of DOI:10.1016/j.bmcl.2008.08.018

Bioorganic & Medicinal Chemistry Letters 18 (2008) 5010–5014
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, syntheses, and structure–activity relationships of novel
NPY Y5 receptor antagonists: 2-{3-Oxospiro[isobenzofuran-
1(3H),40-piperidin]-10-yl}benzimidazole derivatives
*
Yoshio Ogino, Norikazu Ohtake , Yoshikazu Nagae, Kenji Matsuda, Minoru Moriya, Takuya Suga,
Makoto Ishikawa, Maki Kanesaka, Yuko Mitobe, Junko Ito, Tetsuya Kanno,
Akane Ishihara, Hisashi Iwaasa, Tomoyuki Ohe, Akio Kanatani, Takehiro Fukami
Banyu Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd, Okubo-3, Tsukuba 300-2611, Ibaraki, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 February 2008
Revised 15 July 2008
Accepted 6 August 2008
Available online 12 August 2008
Design, syntheses, and structure–activity relationships of a novel class of 2-{3-oxospiro[isobenzofuran-
1(3H),40-piperidin]-10-yl}benzimidazole NPY Y5 receptor antagonists are described. The benzimidazole
structures were newly designed based on the urea linkage of our prototype Y5 receptor antagonists (2
and 3). By optimizing substituents on the benzimidazole core part of the lead compound 5a, we were able
to develop a potent, orally available, and brain-penetrable Y5 selective antagonist (5k).
Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
Keywords:
Neuropeptide Y
Y5 receptor
Antagonist
Anti-obesity
Benzimidazole
Obesity is a serious and growing public health problem in the
world, and is associated with significant morbidity. Obesity-related
comorbidities include type 2 diabetes, hypertension, and cardio-
vascular diseases. Although several drugs are clinically used, ideal
treatments for obesity are strenuously pursued, especially in terms
of safety.
Neuropeptide Y (NPY) is a highly conserved 36-amino acid pep-
tide with potent, centrally mediated orexigenic effects.1 NPY is a
member of the peptide family that also includes peptide YY
(PYY) and pancreatic polypeptide (PP). Chronic administration of
NPY into the brain in female rats results in hyperphagia and body
weight gain.2 Concentrations of NPY and its messenger RNA
(mRNA) in the hypothalamus are markedly increased during food
deprivation and in some rodent genetic models of obesity.3 These
data suggest that NPY is one of the major regulators of physiolog-
ical feeding behaviors.
together, the data suggest that antagonism of the Y5 receptor
would be a beneficial treatment of obesity. Indeed, a recent 52
week clinical trial, a significant weight loss was observed with
the administration of the selective Y5 antagonist.7 To date, a num-
ber of potent Y5 receptor antagonists,8 each with distinct structure
classes that include sulfonamide,8a,8b pyrrolo[3,2-d]pyrimidine,8c
carbazole,8e imidazolylpyridine,8g and imidazolone8i classes have
been reported.
In the course of our program, which was aimed at developing
orally bioavailable Y5 receptor antagonists for the treatment of
obesity, we have been pursuing potent and selective Y5 antagonist
leads.8f,8j In particular, identification of 2-methanesulfonamid-
ephenylpiperazine derivative (1) was important because it gave
us a structural insight into further design of other novel Y5 antag-
onist lead structures.9,10 Based on the structure of 1, prototype Y5
antagonist leads (2 and 3) were identified by connecting a 2-meth-
ylsulfonyl-3-spiro(indolin-3,40-piperidine) 119 or 3-oxospiro[iso-
Presently, 5 distinct types of G protein-coupled NPY receptors
subtypes, Y1, Y2, Y4, Y5, and Y6, have been cloned thus far.4 Of
these, the Y5 receptor subtype is thought to be responsible for cen-
trally mediated NPY-induced feeding responses.5 Moreover, we
have found that the Y5 receptor subtype is involved in the regula-
tion and development of diet-induced obesity in rodents.6 Taken
benzofuran-1(3H),40-piperidine] 1710 part with
a substituted
aniline moiety through a urea bond. In the light of the phenylurea
sub-structure in 2 and 3, we further designed fused ring systems
such as benzimidazole and benzothiazole, which were directly at-
tached to the above-mentioned spiropiperidines or the corre-
sponding cyclohexane moiety (Fig. 1). The syntheses and in vitro
evaluation led to the identification of novel Y5 lead structures, 2-
[3-oxospiro[isobenzofuran-1(3H),40-piperidin]-10-yl]benzimidazole
* Corresponding author. Tel.: +81 29 877 2000; fax: +81 29 877 2029.
E-mail address: norikazu_ohtake@merck.com (N. Ohtake).
0960-894X/$ - see front matter Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.08.018

Y. Ogino et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5010–5014
5011
N
O
HN
O2
S
Cl
NH
N
N
H
N
1
N
N
N
H
N
O
R
S
HN
O
4
N
O
N
X
Y
X
Y
2; X = NSO2Me, Y = CH2, R = CONMe2
IC50 (Y5): 34 nM
O
O
5a, X = N, Y = NH
3; X = CO, Y = O, R = Cl
IC50 (Y5): 29 nM
6, X = N, Y =S
H
7, X = C
Y = NH
Y = NH
H
8, X =
C
Figure 1. Design of benzimidazole and related templates.
(5a) and the corresponding cyclohexan-4-ylbenzimidazole (7).
Although their affinity for the Y5 receptor subtype was moderate,
their structural uniqueness prompted us to further derivatize these
leads.
In this letter, we describe the syntheses and structure–activity
relationships (SARs) of 2-[3-oxospiro[isobenzofuran-1(3H),40-
piperidin]-10-yl]benzimidazole derivatives.11 In addition, the SARs
of 2-[3-oxospiro[isobenzofuran-1(3H),10-cyclohexan]-40-yl]benz-
imidazole derivatives (7) will be described.
General synthetic methods of the benzimidazole derivatives
(5a–5z, 5aa–5gg) are summarized in Scheme 1. Basically, these
benzimidazoles can be prepared through the coupling of spiropi-
peridine 11 and 2-chlorobenzimidazoles 15.12 The spiropiperidine,
3-oxospiro[isobenzofuran-1(3H),40-piperidine] 11,10b was pre-
pared from 2-bromobenzoic acid 9 as follows. Nucleophilic addi-
tion reaction of the dianion, generated from 9 and n-BuLi, to
N-benzyl-4-piperidone and a subsequent acidic treatment of the
reaction mixture afforded 10 in a 45% yield. Catalytic hydrogena-
tion of 10 in the presence of 20% palladium hydroxide on carbon
under an acidic condition (4 N HCl in EtOAc) gave 11 as a hydro-
chloride salt in 85% yield.
5a. As for the synthesis of 7 and 8, condensation of the carboxylic
acid 2010 and phenylenediamine (WSC, Py, rt) along with the sub-
sequent intramolecular cyclization of the resulting amide
(TsOHꢀH2O, xylene, reflux, 6 h) afforded a mixture of 7 and 8 (ra-
tio = 6.5:1) with a 65% yield.13 Separation of the mixture was easily
achieved through the use of silica gel column chromatography (1–
5% MeOH–CHCl3).
Compounds were tested in an initial screen for the binding
affinity against human NPY Y5 receptor subtype (Y5) in transfected
LMtk- cells.5b Subsequently, selected compounds were examined
for their subtype selectivity over the other NPY receptors (Y1, Y2,
and Y4) and their Y5 antagonist activity (Ca2+ flux).5b
As described above, derivatives bearing the 2-(substituted piper-
idin-1-yl)benzimidazoles (4, 5a), benzothiazole (6), imidazo[4,5-
b]pyridine (18), 2-(substituted piperidin-1-ylmethyl)benzimid-
azole (19), trans-2-(substituted cyclohexyl)benzimidazole (7) and
the corresponding cis-isomer (8) were evaluated in the Y5 receptor
binding assay (Table 1). Among these, 5a and 7 had moderate Y5
binding affinity (IC50: 100–200 nM), while the others exhibited
IC50 values of more than 1000 nM. Based on these results, we firstly
focused on developing SARs of 5a as a novel Y5 lead.
Syntheses of the 2-chlorobenzimidazoles 15 were carried out
from commercially available substituted phenylenediamines 12
or substituted anthranilic acids 13. Phenylenediamines 12 were
treated with 1,10-carbonyldiimidazole to give benzimidazol-2-ones
14. Chlorination of 14 through treatment with POCl3 at 110 °C re-
sulted in 40–70% yields of 2-chlorobenzimidazoles 15. On the other
hand, anthranilic acids 13 were treated with diphenylphosphoryl
azide to produce good yields of 14, which were converted to 15
by treatment with POCl3. Under basic conditions (K2CO3, Na2CO3,
or Cs2CO3) at 100–150 °C coupling of 11 with 15 produced the de-
sired benzimidazole derivatives (5a–5z, 5aa–5gg) with 30–70%
yields. When N-Boc-protected 2-chlorobenzimidazoles 16 were
used in place of 15, the coupling reaction proceeded at a lower
temperature (80–90 °C) with 30–50% yields.
We hypothesized that incorporation of substituents into the
phenyl ring of the benzimidazole core part would be an effective
way to enhance the Y5 affinity based on the superimposition of
the entire structures of 1 and 5a. Therefore, as a first step we fo-
cused on the optimization of the incorporation of substituents into
the benzimidazole core part. To examine the effects of mono-sub-
stitution at the 4- or 5-position of the benzimidazole ring on the Y5
binding affinity (Table 2), various substituents, such as a fluorine
atom, methyl, trifluoromethyl, and phenyl groups, were intro-
duced. Generally, incorporation of a substituent into the 4- or
5-position was tolerated in the Y5 binding affinity, with the 5-sub-
stitution resulting in a greater improvement as compared to the
corresponding 4-substitution. In particular, the 5-chloro- (5i),
5-trifluoromethyl- (5k), and 5-phenyl- (5m) benzimidazoles had
Syntheses of the other derivatives (4, 6–8, 18, 19) are summa-
rized in Scheme 2. Basically, the derivatives (4, 6, 18, and 19) were
prepared in a similar manner as described for the preparation of
single digit nanomolar binding affinities (IC50: 5i = 6.6 nM,
5k = 3.5 nM, 5m = 2.4 nM) for the Y5 receptor and achieved
approximately a 20- to 60-fold improvement, as compared with

5012
Y. Ogino et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5010–5014
CO2H
(a)
(b)
Br
Bn
N
NH
HCl
O
O
O
O
9
10
11
R1
HO2C
H2N
13
R2
(d)
R1
R1
R1
H
H2N
H2N
N
(e)
N
(c)
Cl
O
N
R
N
H
R2
R2
R2
12
15: R = H
14
(f)
16: R = Boc
R1
(g)
(h)
N
15
16
N
R2
N
H
O
O
5a-5z, 5aa-5gg
Scheme 1. Syntheses of benzimidazole derivatives (5a–5z, 5aa–5gg). Reagents and conditions: (a) 1—n-BuLi, N-benzyl-4-piperidone, THF, ꢁ70 °C; 2—concd HCl, H2O, reflux;
(b) 20% Pd(OH)2, H2, 4 N HCl in EtOAc–MeOH, rt; (c) CDI, DMF, 80 °C; (d) (PhO)2P(O)N3, NEt3, THF, 80 °C; (e) POCl3, N,N-dimethylaniline, 110 °C; (f) DIBOC, DMAP, CHCl3, rt; (g)
11, Cs2CO3, DMF,150 °C; (h) 11, Cs2CO3, DMF, 80 °C, then TFA, rt.
N
(a)
N
NH
N
H
N
O
N
O
S
S
O
O
17
4
N
X
(b)
N
(CH2)n
6
Y
O
(c)
(d)
O
11
18
19
6: n = 0, X = S, Y = CH
18: n = 0, X = NH, Y = N
19: n = 1, X = NH, Y = N
O
N
CO2H
(e)
N
(f)
N
H
H
O
O
H2N
O
O
O
O
20
21
7: trans-isomer
8: cis-isomer
Scheme 2. Synthesis of the other derivatives (4, 6–8, 18, 19). Reagents and conditions: (a) Na2CO3, 2-chlorobenzimidazole, DMF, 100 °C; (b) Cs2CO3, 2-chlorobenzothiazole,
dioxane, 80 °C; (c) K2CO3, 2-chloromethylbenzimidazole, DMF, 100 °C; (c) Na2CO3, N-Boc-2-chloroimidazo(4,5-b)pyridine, dioxane, 90 °C; (e) WSC, phenylenediamine, Py, rt;
(f) TsOHꢀmonohydrate (0.2 equiv), xylene, reflux.
the original lead 5a. These results suggested that a hydrophobic
substituent at the 5-position significantly contributed to the
enhancement noted in the Y5 binding affinity. Therefore, further
derivatization was focused on the substitutions at the 5-position.
Introduction of an ester group such as methyl ester (5q) or ethyl
ester (5r) in place of the hydrophobic substituents retained the Y5
binding affinity, while introduction of more hydrophilic substitu-
ent such as a carbamoyl (5t), dimethylcarbamoyl (5v), methanesul-
fonamide (5y), or methanelsulfonyl (5z) resulted in significant
decreases in the Y5 binding. These SARs suggested that the Y5 po-
tency would be influenced by steric factors rather than electronic
nature of the substituents on the benzimidazole core ring.

Y. Ogino et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5010–5014
5013
Table 1
Binding affinity of benzimidazole and related compounds to the Y5 receptor
N
R
X
N
N
H
N
O
O
O
S
5a, 6-8, 18, 19
4
O
Compound
X
R
Y5 (IC50, nM)a
>1000
Compound
X
R
Y5 (IC50, nM)a
4
N
N
5a
6
N
N
N
140
19
7
N
4900
91
N
H
N
H
N
H
N
>10,000
1600
C
N
H
S
N
(
(
trans-isomer)
N
H
C
18
8
1400
N
H
N
H
N
cis-isomer)
a
Values are the mean of two or more independent assays (Ref. 14).
Table 2
The binding affinity of benzimidazole derivatives (5a–5z) to the Y5 receptor
R
N
N
N
H
O
O
Compound
R
Y5 (IC50, nM)a
Compound
R
Y5 (IC50, nM)a
5a
5b
5c
5d
5e
5f
5g
5h
5i
H
140
500
28
74
36
250
37
51
6.6
83
3.5
17
5n
5o
5p
5q
5r
5-Bromo
5-Nitro
10
10
19
1.8
2.7
2.0
110
20
4-Fluoro
5-Fluoro
5-Cyano
5-iso-Butyl
5-Methoxycarbonyl
5-Ethoxycarbonyl
5-Carbamoyl
5-N-Methylcarbamoyl
5-N,N-Dimethylcarbamoyl
5-Carboxy
4-Methyl
5-Methyl
4-Methoxy
5-Methoxy
4-Chloro
5s
5t
5u
5v
5w
5x
5y
5z
5-Chloro
58
5j
5k
5l
4-Trifluoromethyl
5-Trifluoromethyl
4-Phenyl
>1000
130
56
5-Acetylamino
5-Methanesulfonylamino
5-Methanesulfonyl
5m
5-Phenyl
2.4
85
a
Values are the mean of two or more independent assays (Ref. 14).
Di-substituted benzimidazole derivatives were prepared and
assessed in the Y5 binding assay (Table 3). Generally, these di-
substituted benzimidazoles (5aa–5ee) were more potent than the
corresponding mono-substituted compounds. For example, the
5,6-dichlorobenzimidazole 5bb (IC50: 1.6 nM) was approximately
other NPY receptors (Y1, Y2, Y4) in addition to having potent
antagonist activity, as demonstrated via the inhibition of the
NPY-induced [Ca2+] increases in LMtk- cells that expressed the
Y5 receptor. To examine the oral absorption in rats, these com-
pounds were orally administered at 10 mg/kg, and then the plasma
levels were measured at 2 and 4 h after the administration. Of the
compounds administered, two derivatives (5i and 5k) showed high
4-fold more potent than the 5-chlorobenzimidazole 5i (IC50
:
6.6 nM). Furthermore, comparison of the Y5 affinity of 4,6-dichlo-
robenzimidazole 5aa with that of the 5,6-dichlorobenzimidazole
5bb suggested that the 5,6-disubstitution was more likely to have
higher affinity than the 4,6-disubstitution. Among the di-substi-
tuted benzimidazoles, 5bb showed the best binding affinity for
the Y5 receptor.
Further characterization of the representative benzimidazole
derivatives (5i, 5k, 5m, 5r, 5bb) was conducted (Table 4). These
compounds had more than 1000-fold subtype selectivity over the
plasma exposures (>10 lM) even at 4 h after the administration,
suggesting that these derivatives were long lasting Y5 antagonists
with excellent oral absorption in rats. The plasma levels of 5i and
5k at 4 h were higher than those at 2 h, which was more than likely
due to low hepatic clearance and slow intestinal absorption.15 In
contrast, the derivative 2r showed the lower plasma level
(0.1
lM) at 4 h after the oral administration. This was probably
due to the high hepatic clearance that is often observed in rats.15

5014
Y. Ogino et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5010–5014
2. (a) Stanley, B. G.; Kyrkouli, S. E.; Lampert, S.; Leibowitz, S. F. Peptides 1986, 7,
Table 3
1189; (b) Zarjevski, N.; Cusin, I.; Vettor, R.; Rohner-Jeanrenaud, F.; Jeanrenaud,
B. Endocrinology 1993, 133, 1753.
The binding affinity of benzimidazole derivatives (5aa–5gg) to the Y5 receptor
3. (a) Clark, J. T.; Kalra, P. S.; Crowley, W. R.; Kalra, S. P. Endocrinology 1984, 115,
427; (b) Stanley, B. G.; Magdalin, W.; Seirafi, A.; Nguyen, M. M.; Leibowitz, S. F.
Peptides 1992, 13, 1189; (c) Parrott, R. F.; Heavens, R. P.; Baldwin, B. A. Physiol.
Behav. 1986, 36, 523; (d) Sakatani, N.; Inui, A.; Inoue, T.; Oya, M.; Morioka, H.;
Baba, S. Peptides 1987, 8, 651; (e) Miner, J. L.; Della-Fera, M. A.; Paterson, J. A.;
Baile, C. A. Am . J . Physiol. 1989, 257, R383.
R1
N
N
R2
N
4. Blomqvist, A. G.; Herzog, H. Trends Neurosci. 1997, 20, 294.
H
O
5. (a) Gerald, C.; Walker, M. W.; Criscione, L.; Gustafson, E. L.; Batzl-Hartmann, C.;
Smith, K. E.; Vaysse, P.; Durkin, M. M.; Laz, T. M.; Linemeyer, D. L.; Schaffhauser, A.
O.; Whitebread, S.; Hofbauer, K. G.; Taber, R. I.; Branchek, T. A.; Weinshank, R. L.
Nature 1996, 382, 168; (b) Kanatani, A.; Ishihara, A.; Iwaasa, H.; Nakamura, K.;
Okamoto, O.; Hidaka, M.; Ito, J.; Fukuroda, T.; MacNeil, D. J.; Van der Ploeg, L. H. T.;
Ishii, Y.; Okabe, T.; Fukami, T.; Ihara, M. Biochem. Biophys. Res. Commun. 2000, 272,
169.
6. Ishihara, A.; Kanatani, A.; Mashiko, S.; Tanaka, T.; Hidaka, M.; Gomori, A.;
Iwaasa, H.; Murai, N.; Egashira, S.; Murai, T.; Mitobe, Y.; Matsushita, H.;
Okamoto, O.; Sato, N.; Jitsuoka, M.; Fukuroda, T.; Ohe, T.; Guan, X.; MacNeil, D.
J.; Van der Ploeg, L. H. T.; Nishikibe, M.; Ishii, Y.; Ihara, M.; Fukami, T. Proc. Natl.
Acad. Sci. U.S.A. 2006, 103, 7154.
7. Erondu, N.; Gantz, I.; Musser, B.; Suryawanshi, S.; Mallick, M.; Addy, C.; Cote, J.;
Bray, G.; Fujioka, K.; Bays, H.; Hollander, P.; Sanabria-Bohórquez, S. M.; Eng, W.;
Långström, B.; Hargreaves, R. J.; Burns, H. D.; Kanatani, A.; Fukami, T.; MacNeil,
D. J.; Gottesdiener, K. M.; Amatruda, J. M.; Kaufman, K. D.; Heymsfield, S. B. Cell
Metabolism 2006, 4, 275.
O
Compound
R1, R2
Y5 (IC50, nM)a
5i
5-Chloro
4,6-Dichloro
5,6-Dichloro
5,6-Dimethyl
6.6
5.7
1.6
9.2
4.8
6.7
9.3
2.2
5aa
5bb
5cc
5dd
5ee
5ff
5,6-Difluoro
5-Chloro-6-fluoro
5,6-Methylenedioxy
5,6-Difluoromethylenedioxy
5gg
a
Values were the mean of two or more independent assays (Ref. 14).
8. (a) Rueeger, H.; Rigollier, P.; Yamaguchi, Y.; Schmidlin, T.; Shilling, W. M.;
Criscione, L.; Whitebread, S.; Chiesi, M.; Walker, M. W.; Dhanoa, D.; Islam, I.;
Zhang, J.; Gluchowski, C. Bioorg. Med. Chem. Lett. 2000, 10, 1175; (b) Youngman,
M. A.; McNally, J. J.; Lovenberg, T. W.; Reitz, A. B.; Willard, N. M.; Nepomuceno, D.
H.; Wilson, S. J.; Crooke, J. J.; Rosenthal, D.; Vaidya, A. H.; Dax, S. L. J. Med. Chem.
2000, 43, 346; (c) Norman, M. H.; Chen, N.; Chen, Z.; Fotsch, C.; Hale, C.; Han, N.;
Hurt, R.; Jenkins, T.; Kincaid, J.; Liu, L.; Liu, Y.; Moreno, O.; Santora, V. J.;
Sonnenberg, J. D.; Karbon, W. J. Med. Chem. 2000, 43, 4288; (d) Itani, H.; Ito, H.;
Sakata, Y.;Hatakeyama, Y.; Oohashi, H.;Satoh, Y. Bioorg. Med. Chem. Lett. 2002, 12,
799; (e) Block, M. H.; Boyer, S.; Brailsford, W.; Brittain, D. R.; Carroll, D.; Chapman,
S.; Clarke, D. S.; Donald, C. S.; Foote, K. M.; Godfrey, L.; Lander, A.; Marsham, P. R.;
Masters, D. J.; Mee, C. D.; O’donovan, M. R.; Pease, J. E.; Pickup, A. G.; Rayner, J. W.;
Roberts, A.; Schofield, P.; Suleman, A.; Turnbull, A. V. J. Med. Chem. 2002, 45, 3509;
(f) Sato, N.; Takahashi, T.; Shibata, T.; Haga, Y.; Sakuraba, A.; Hirose, M.; Sato, M.;
Nonoshita, K.; Koike, Y.; Kitazawa, H.; Fujino, N.; Ishii, Y.; Ishihara, A.; Kanatani,
A.; Fukami, T. J. Med. Chem. 2003, 46, 666; (g) Elliot, R. L.; Oliver, R. M.; LaFlamme,
J. A.; Gillaspy, M. L.; Hammond, M.; Hank, R. F.; Maurer, T.; Baker, D. L.; DaSilva-
Jardine, P. A.; Stevenson, R. W.; Mack, C. M.; Casella, J. V. Bioorg. Med. Chem. Lett.
2003, 13, 3593; (h) Guba, W.; Neidhart, W.; Nettekoven, M. Bioorg. Med. Chem.
Lett. 2005, 15, 1599; (i) Gillman, K. W.; Higgins, M. A.; Poindexter, G. S.; Browning,
M.; Clarke, W. J.; Flowers, S.; Grace, J. E., Jr.; Hogan, J. B.; McGovern, R. T.; Iben, L.
G.; Mattson, G. L.; Ortiz, A.; Rassnick, S.; Russell, J. W.; Antal-Zimanyi, I. Bioorg.
Med. Chem. 2006, 14, 5517; (j) Takahashi, T.; Sakuraba, A.; Hirohashi, T.; Shibata,
T.; Hirose, M.; Haga, Y.; Nonoshita, K.; Kanno, T.; Ito, J.; Iwaasa, H.; Kanatani, A.;
Fukami, T.; Sato, N. Bioorg. Med. Chem. 2006, 14, 7501.
Table 4
Biological properties of the representative compounds
Compound
Y5
Y1
Y2
Y4
Y5a
Rat plasma
levelsc
B/Pd
(
lM)
b
b
IC50 (nM)
IC50
(nM)
2 h
4 h
Ratio
5i
6.6
3.5
2.4
2.7
1.6
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
>10,000
1.2
6.4
1.8
1.5
1.4
27.8
15.3
1.8
25.6
17.5
1.3
—
5k
5m
5r
0.31
0.35
0.08
—
3.2
0.1
5bb
2.9
4.6
a
Antagonist activity was determined by the amount of inhibition of NPY-induced
[Ca2+] increase in LMtk- cells expressing the human Y5 receptor.
b
Values are the mean of two or more independent assays.
Compounds (10 mg/kg) were orally administered to rats (n = 3), and the plasma
c
levels were measured at 2 and 4 h.
d
Compounds (10 mg/kg) were orally administered to rats (n = 3), and the plasma
and brain levels were measured at 2 h. B/P means the ratio of the brain level (nmol/
g) to plasma level (lM) of the compounds.
9. (a) Gao, Y.; MacNeil, D. J.; Yang, L.; Morin, N. R.; Fukami, T.; Kanatani, A.;
Fukuroda, T.; Ishii, Y.;Ihara, M. PCT Int. Appl. WO2000027845.; (b)Maligres, P. E.;
Houpis, I.; Rosen, K.; Molina, A.; Sager, J.; Upadhyay, V.; Wells, K. M.; Reamer, R.
A.; Lynch, J. E.; Askin, D.; Volante, R. P.; Reider, P. J. Tetrahedron 1997, 53, 10983.
10. (a) Fukami, T.; Kanatani, A.; Ishihara, A.; Ishii, Y.; Takahashi, T.; Haga, Y.;
Sakamoto, T.; Itoh, T. PCT Int. Appl. WO 2001014376.; (b) Marxer, A.;
Rodriguez, H. R.; McKenna, J. M.; Tsai, H. M. J. Org. Chem. 1975, 40, 1427.
11. Y5 receptor antagonists with benzimidazole structures were disclosed from
Neurogen Co.; Bakthavatchalam, R.; Blum, C. A.; Brielmann, H. L.; Darrow, J. W.;
Delombaert, S.; Hutchinson, A.; Tran, J.; Zheng, X.; Elliott, R. L.; Hammond, M.
PCT Int. Appl. WO 2002048152.
The brain penetration (B/P) of the compounds (5k, 5m, and 5r)
was examined in rats. The results suggested that the lipophilic
compounds (5k and 5m) had moderate brain penetration (B/
P = ꢂ0.3), while the brain penetrability of the hydrophilic com-
pound 5r was poor (B/P = ꢂ0.08). Since we found that 5k showed
excellent brain exposure in rats, we evaluated the in vivo efficacy
of 5k on D-Trp34 NPY-induced food intake in rats. Oral administra-
tion of 5k (10 mg/kg) significantly suppressed intracerebroventric-
ular (ICV) injected D-Trp34NPY-induced food intake in rats.16,17
In conclusion, we designed and synthesized the novel
2-[3-oxospiro[isobenzofuran-1(3H),40-piperidin]-10-yl]benzimidazole
structure (5a) along with other related compounds (4, 6–8, 18, 19),
based on the urea linkage of the prototype Y5 antagonists (2 and 3),
resulting in the identification of 5a and 7 as novel Y5 antagonist leads.
The SAR studies on 5a along with the subsequent characterization of
the selectedcompounds revealed that 5kwas a potent, orally available,
and brain-penetrable Y5 selective antagonist.
12. Parrodi, C. A.; Quintero-Cortés, L.; Sadoval-Ramírez, J. Synth. Commun. 1996, 26,
3323.
13. Generation of 8 was probably due to epimerization of the intermediate amide
21 under this acidic cyclization condition. The compound 8 was exclusively
prepared from the cis-isomer of the carboxylic aid 20 (Ref. 10). The
stereochemistry of the cis-carboxylic acid was unambiguously assigned by
NOESY NMR experiment.
14. A selective Y5 antagonist in Ref. 10a was used as an internal control across all
assay plates for data validation. The IC50 of this compound is 1.8 0.2 nM.
15. The rank orders of predicted hepatic availability (FH: %) and hepatic clearance
(CLH, u int.: mL/min/kg) using rat hepatocytes (Shibata, Y.; Takahashi, H.; Ishii,
Y. Drug Metab. Dispos. 2000, 28, 1518) were A, B for 5i and 5k, and B, C for 5r.
16. Parker, E. M.; Balasubramaniam, A.; Guzzi, M.; Mullins, D. E.; Salisbury, B. G.;
Sheriff, S.; Wittten, M. B.; Hwa, J. J. Peptides 2000, 21, 393.
17. A selective Y5 agonist, D-Trp34 NPY (1
lg/0.4 lL/head, synthetic CSF containing
References and notes
0.05% bovine serum albumin) was injected into the third ventricule of SD rats
via guide cannula. The compound 5r (10 mg/kg) was administered orally 2 h
before the ICV injection of D-Trp34 NPY, and the food consumption was
measured 2 h after the administration of D-Trp34 NPY.
1. (a) Tatemoto, K.; Mutt, M. Nature 1980, 285, 417; (b) Tatemoto, K.; Carlquist,
M.; Mutt, V. Nature 1982, 296, 659.