Heterocyclic modification of a novel bicyclo[3.1.0]hexane NPY1 receptor antagonist

Article abstract of DOI:10.1016/j.bmcl.2013.04.095

A convergent synthesis route for the heterocyclic modification of a novel bicyclo[3.1.0]hexane NPY1 antagonist 2 was developed and the structure activity relationship of these modifications on NPY1 binding is reported. Two heterocyclic analogs 9 and 10 showed comparable Y1 binding potency to 2, but with improved aqueous solubility. Compound 9 demonstrated reduced spontaneous nocturnal food intake in a rat model when dosed ip. Compound 9 was also shown to be orally bioavailable and brain penetrable.

Full text of DOI:10.1016/j.bmcl.2013.04.095

Bioorganic & Medicinal Chemistry Letters 23 (2013) 3814–3817
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Heterocyclic modification of a novel bicyclo[3.1.0]hexane NPY1
receptor antagonist
a
a
a
b
b
Guanglin Luo a, , Ling Chen , Shuanghua Hu , Yazhong Huang , Gail Mattson , Lawrence G. Iben ,
⇑
John W. Russell a, Wendy J. Clarke a, John B. Hogan a, Ildiko Antal-Zimanyi b, Graham S. Poindexter a
a Molecular Sciences and Candidate Optimization, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, Connecticut 06492, USA
b Disease Sciences and Biologics, Bristol-Myers Squibb Research and Development, 5 Research Parkway, Wallingford, Connecticut 06492, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A convergent synthesis route for the heterocyclic modification of a novel bicyclo[3.1.0]hexane NPY1
antagonist 2 was developed and the structure activity relationship of these modifications on NPY1 bind-
ing is reported. Two heterocyclic analogs 9 and 10 showed comparable Y1 binding potency to 2, but with
improved aqueous solubility. Compound 9 demonstrated reduced spontaneous nocturnal food intake in a
rat model when dosed ip. Compound 9 was also shown to be orally bioavailable and brain penetrable.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 1 April 2013
Revised 26 April 2013
Accepted 29 April 2013
Available online 15 May 2013
Keywords:
Obesity
NPY1 receptor antagonist
Bicyclo[3.1.0]hexanes
Neuropeptide Y (NPY), a 36 amino acid, single-chain polypep-
tide, is widely distributed in both the peripheral and central nervous
systems and is highly homologous across different animal species. It
has long been suspected, and subsequently verified to be involved in
a variety of physiological processes and behaviors, including feed-
ing, energy homeostasis, cardiovascular regulations, anxiety, sei-
zures, memory, circadian rhythms, and sexual functions.1 NPY is
by far the most potent orexigenic substance known and central
administration of NPY greatly increases the food intake in a variety
of animal species with concomitant reduction of heat production in
brown adipose tissue. To date there are six known NPY receptors
and five of them are cloned. Among them both NPY1 and NPY5
receptors are believed to be involved in regulating the feeding
behaviors from various experimental results.1 Both NPY1 and
NPY5 receptor antagonists would reduce food intake and therefore
have potential use in the anti-obesity area. Many small molecule Y1
aqueous solubility and possibly other pharmacokinetic properties,
we intend to replace the N-phenyl group with other heterocycles.
The synthesis of 2 was achieved by a reaction between a phe-
nylpiperazinyl chloroenamine intermediate and 3-ethoxyl phenyl-
magnesium bromide.4 Similarly, as shown in Scheme 1, a common
intermediate 4 was designed and prepared, through benzyl pro-
tected intermediate 3.
Synthesis of 3 followed the synthesis of 2 as described previ-
ously.4 Thus, commercially available 4-methylcyclohexanone and
N-benzylpiperazine were refluxed in toluene in the presence of
catalytical amount of TsOH overnight to afford the enamine inter-
mediate, which after concentration, was chlorinated at À50 °C in
ether to afford the intermediate chloroenamine. The side product
succinamide was removed by filtration. Reaction of the crude chlo-
roenamine in ether with freshly prepared Grignard reagent in THF
afforded, after purification, 3 in over 80% yield.5 The debenzylation
was effected by Pd/C catalyzed hydrogenolysis to afford 4 in
quantitative yield.5 With the intermediate 4 in hand, modifications
of the phenyl ring of 2 were achieved by means of nucleophilic aro-
matic substitutions with various halogenated heterocycles.
As shown in Scheme 2, various electronically deficient substi-
tuted phenyl and heterocyclic analogs (5–10) were synthesized
via direct nucleophilic aromatic substitution conditions. The
nucleophilic aromatic substitutions were typically run with
aromatic halide in the presence of a base at room temperature
(6) or at the elevated temperatures (5, 7–10).6 Further modifica-
tions by hydrogenolysis afforded aniline 11 and dehalogenated
compounds 12 and 13.6 Compounds 9 and 10 had also been
synthesized in large quantities from the commercially available
and Y5 receptor antagonists have been reported.1,2
In previous patents,3 Peterson et al. disclosed a novel, small
molecule NPY1 receptor antagonist 1 with good oral bioavailability
(Fig. 1). Subsequently, we reported a similar but structurally very
different novel bicyclic compound 2 (Fig. 1), the structure of which
was unequivocally determined by X-ray crystallagraphy.4 Com-
pound 2, was found to be a non-competitive antagonist, and was
shown to be equally potent as 1 towards NPY1 receptor.4 However,
2 had very low aqueous solubility, which potentially complicated
further pharmacologic characterization. In order to improve its
⇑
Corresponding author. Tel.: +1 2036776640; fax: +1 2036777702.
E-mail address: guanglin.luo@bms.com (G. Luo).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.04.095

G. Luo et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3814–3817
3815
a
OEt
OEt
OEt
OEt
N
N
N
N
N
N
N
H
N
R3
4
R3
1
2
14:
16:
Figure 1. Novel lead NPY1 receptor antagonists.
N
N
N
N
15:
17:
N
OMe
H
Me
O
N
N
Scheme 3. Reagents and conditions: (a) 14: 3-bromopyridine, Pd2(dba)3, BINAP,
NaOtBu, toluene, 70 °C, 3 h, 90%; 15: 5-bromopyrimidine, similar to 14, 8.5 h, 87%;
16: 4-bromopyridineÁHCl, Pd(OAc)2, dppp, NaOtBu, toluene, 70 °C, 2 h, 70%; 17:
2-chloro-6-methoxypyridine, Pd(OAc)2, BINAP, NaOtBu, toluene, 70 °C, 9 h, 52%.
Cl
a, b
N
N
+
published procedures afforded the desired heterocycles 14–17 as
shown in Scheme 3.6
All the compounds prepared were subject to a NPY1 receptor
binding assay as previously described.4 The IC50’s for the series as
well as that of the lead compound 2 are listed in Table 1.
From Table 1, it is clear that structural modification of the phe-
nyl group had a very profound effect on NPY1 activity. Binding
affinity is completely lost in the absence of the phenyl group (4).
Additionally one carbon extension 3 completely abolished the Y1
activity as well. Any substitution on the phenyl or heterocycle ring
(7, 11 and 17) also abolished the Y1 activity.
With regard to the 6-membered ring, heterocyclic replacements
of the phenyl ring, the number and position of the nitrogen atoms
were crucial to the Y1 activity. Triazine derivative 12 gave almost
70-fold diminished affinity. While pyrazine, pyridazine, 5-substi-
tuted pyrimidine, 3- and 4-substituted pyridine derivatives all
gave diminished or abolished Y1 binding, we found that both the
2-pyridine and 2-pyrimidine analogs, 9 and 10, gave slightly im-
proved Y1 binding affinity compared to 2. More importantly, both
9 and 10 showed enhanced aqueous solubility in comparison to 2.
As MsOH salts, compound 9 had greater than 50 mg/mL while
compound 10 had 10 mg/mL solubility in 40% aqueous trappsol.
OEt
N
N
c
d
OEt
N
N
H
3
4
Scheme 1. Reagents and conditions: (a) TsOH (cat.), toluene, 130 °C, 18 h. (b) NCS
(1.0 equiv), CH2Cl2, À50 °C – rt, 3 h. (c) 3-Ethoxyphenylmagnesium bromide (2.5
equiv), ether, rt, 18 h, 82% (three steps). (d) Pd/C (10%), MeOH, H2 (55 psi), 18 h,
100%.
1-(2-pyridinyl)piperazine or 1-(2-pyrimidinyl)piperazine follow-
ing the procedure as described for the synthesis of 3.6
With less electron-deficient halogenated heterocycles, direct
nucleophilic aromatic substitutions were unsuccessful, even at
elevated temperature. Palladium catalyzed aromatic amination
has been widely studied and amination of halogenated pyridines
or pyrimidines has been documented.7 Direct application of the
Table 1
NPY1 binding data for compounds 2–17
a
b
OEt
OEt
4
N
N
OEt
N
N
R1
N
R2
N
R
R1
R2
NO2
NH2
b
Compd
2
3
4
7
Ra
Ph
Bn
H
NPY1 IC50 (nM)
62
>10,000
>10,000
>10,000
265
42
54
>10,000
4270
4380
N
N
5:
6:
7:
8:
11:
12:
N
N
N
N
N
N
6-(3-Cl-pyradazine)
2-Pyrazine
2-Pyridine
2-Pyrimidine
2-Aniline
2-(1,3,5-Triazine)
3-Pyrazine
3-Pyridine
5-Pyrimidine
4-Pyridine
6-(2-MeO-pyridine)
9:
Cl
N
Cl
N
8
9
10
11
12
13
14
15
16
17
N
N
N
N
N
10:
13:
Cl
892
5032
>10,000
>10,000
Scheme 2. Reagents and conditions: (a) 5: 2-nitrofluorobenzene, Hunig’s base,
toluene, 120 °C, 8 h; 6: cyanuric chloride (1.0 equiv), acetone, rt, 40 min; 7: 3,6-
dichloropyridazine (1.1 equiv), Et3N, toluene, 120 °C, 12 h, 68%; 8: 2-chloropyra-
zine, KOtBu, DMSO, 80 °C, 5 h, 9%; 9: 2-chloropyridine, Hunig’s base, toluene,
120 °C; 10: similar to 9. (b) 11: Pd/C (10%), MeOH–EtOAc (1:1), H2 (50 psi), 4 h, 90%
(two steps); 12: Pd/C (10%), MeOH–EtOAc (1:1), NaHCO3, H2 (55 psi), 5 h, 50% (two
steps); 13: Pd/C (10%), MeOH–EtOAc (1:1), K2CO3, H2 (55 psi), 4 h, 90%.
All compounds are fully characterized by 1H NMR, 13C NMR, LCMS and ele-
a
mental analysis.
b
Average of at least two duplicated experiments.

3816
G. Luo et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3814–3817
4
IP, F = 40%
PO, F = 53%
3
1000
100
10
IC
50 = 19 ng/mL (~50nM)
p=0.007
**
p=0.002
**
2
1
0
0
10
30
9 (IP mg/kg)
9
8
7
6
5
4
3
2
1
0
p=0.03
**
p=0.01
**
1
0
5
10
15
20
25
Time (hours)
Figure 2. Plasma concentration of 9 after oral (20 mg/kg) and intraperitoneal
(10 mg/kg) administration to the male rat.
0
10
30
9 (IP mg/kg)
1000
Figure 4. Intraperitoneal administration of 9 (as MsOH salt) at 10 and 30 mg/kg
dose to male Sprague–Dawley rats (220–280 g) 1 h before the onset of darkness
reduced food intake in rats. The vehicle used was 45% trappsol and 55% water.
4
3
2
1
0
100
Brain, IP
Plasma, IP
10X - IC50 = 190 ng/mL (~500 nM)
10
0
35.6
9 (mg/kg)
60
100
0
1
2
3
4
5
6
Time (hours)
Figure 5. Oral administration of 9 (as MsOH salt) at 35.6, 60 and 100 mg/kg dose to
male Sprague–Dawley rats (220–280 g) 2.5 h before the onset of darkness reduced
food intake in rats. The vehicle used was 50% PEG400 and 50% water.
Figure 3. Concentration of 9 in brain and plasma after intraperitoneal (10 mg/kg)
administration to the male rat.
Further PK studies with compound 9 were carried out. Com-
pound 9 showed 53% oral bioavailability in male rats when dosed
orally at 20 mg/kg (Fig. 2). When dosed intraperitoneally at 10 mg/
kg, brain uptake appeared to be very rapid (Fig. 3). The concentra-
tion of 9 in the brain was higher than 100 nM after 15 min and con-
sistently 10 times higher than its IC50 after 1 h.
orally available, small molecule NPY1 antagonists will be useful
in further evaluating the role of NPY in animal food intake as well
as other clinical indications.
References and notes
Compound 9 was tested in vivo in a spontaneous nocturnal
feeding model with male Sprague–Dawley rats4,8 at 10 and
30 mg/kg, ip (Fig. 4). Food intake was significantly suppressed dur-
ing the first hour and first 3 h of darkness. This result is comparable
to the reduction of spontaneous nocturnal food intake seen with
BMS-193885 (data not shown).8
There were also further feeding studies with PO dosing of 9
which showed a strong trend at 35.6 and 60 mg/kg for reducing
food intake, but it was not significant (Fig. 5), possibly due to lower
exposure than that predicted by the PK studies. The exposure in
the PO dosing studies was not analyzed. In the PK studies we did
not administer doses as high as those used in the feeding study
so there could have been non-linear PK or the physicochemical
properties that could have caused a lower exposure.
1. For recent reviews, see: (a) Yulyaningsih, E.; Lei Zhang, L.; Herzog, H.; Sainsbury,
A. Br. J. Pharmacol. 2011, 163, 1170; (b) Walther, C.; Morl, K.; Beck-Sickinger, A.
G. J. Pept. Sci. 2011, 17, 233; (c) Nguyen, A. D.; Herzog, H.; Sainsbury, A. Curr.
Opin. Endocrinol. Diabetes Obes. 2011, 18, 56; (d) Antal-Zimanyi, I.; Poindexter, G.
S. Drug Dev. Res. 2000, 51, 94.
2. For a recent review, see: (a) Stamford, A. W.; Parker, E. M. In Annual Reports in
Medicinal Chemistry; Academic Press, 1999; Vol. 34,; pp 31–40; NPY1
antagonists: (b) Aiglstorfer, I A.; Hendrich, I.; Moser, C.; Bernhardt, G.; Dove,
S.; Buschauer, A. Bioorg. Med. Chem. Lett. 2000, 10, 1597; (c) Kanatani, A.;
Kanno, T.; Ishihara, A.; Hata, M.; Sakuraba, A.; Tanaka, T.; Tsuchiya, Y.; Mase,
T.; Fukuroda, T.; Fukami, T.; Ihara, M. Biochem. Biophys. Res. Commun. 1999,
266, 88; (d) Britton, T. C.; Spinazze, P. G.; Hipskind, P. A.; Zimmernan, D. M.;
Zarrinmayeh, H.; Schober, D. A.; Gehlert, D. R.; Bruns, R. F. Bioorg. Med. Chem.
Lett. 1999, 9, 475; NPY5 antagonists: (e) Rueeger, H.; Rigollier, P.; Yamaguchi,
Y.; Schmidlin, T.; Schilling, W.; Criscione, L.; Whitebread, S.; Chiesi, M.; Walker,
M. W.; Dhanoa, D.; Islam, I.; Zhang, J.; Gluchowski, C. Bioorg. Med. Chem. Lett.
2000, 10, 1175; (f) Kordik, C. P.; Luo, C.; Zanoni, B. C.; Dax, S. L.; McNally, J. J.;
Lovenberg, T. W.; Wilson, S. J.; Reitz, A. B. Bioorg. Med. Chem. Lett. 2001, 11,
2283.
In conclusion, we have developed a convergent route to explore
part of SAR on the novel bicyclo[3.1.0]hexane NPY1 antagonist.
Several derivatives have not only improved Y1 binding to the lead
but more importantly, increased aqueous solubility. These potent,
3. Peterson, J. M.; Blum, C. A.; Cai, G; Hutchison, A. U.S. Patent 5900415, 1999.; (b)
Allen, D. J.; Brostron, L. R.; Kord, A. S.; Whipple, L. A. WO 9823603, 1998.
4. Hu, S.; Huang, Y.; Deshpande, M.; Luo, G.; Bruce, M. A.; Chen, L.; Mattson, G.;
Iben, L. G.; Zhang, J.; Russell, J. W.; Clarke, W. J.; Hogan, J. B.; Ortiz, A.; Flint, O.;

G. Luo et al. / Bioorg. Med. Chem. Lett. 23 (2013) 3814–3817
3817
Henwood, A.; Gao, Q.; Antal-Zimanyi, I.; Poindexter, G. S. ACS Med. Chem. Lett.
2012, 3, 222.
J = 9.2 Hz, 1H,), 6.79–6.74 (m, 4H), 4.12 (d, J = 12.7 Hz, 2H), 4.01 (q, J = 7.0 Hz,
2H), 3.47 (s, CH3SO3H), 3.34 (t, J = 10.8 Hz, 2H), 3.00 (d, J = 11.8 Hz, 2H), 2.86 (s,
CH3SO3H), 2.58–2.48 (m, 1H), 2.31 (t, J = 10.8 Hz, 2H), 2.07 (dd, J = 13.4 and
8.1 Hz, 2H), 1.76 (d, J = 4.0 Hz, 2H), 1.62–1.55 (m, 2H), 1.41 (t, J = 7.0 Hz, 3H),
0.97 (d, J = 6.8 Hz, 3H); 13C (75.5 MHz, CDCl3) d 158.8 (C), 152.2 (C), 143.8 (CH),
139.4 (C), 139.0 (CH), 129.0 (CH), 123.2 (CH), 117.5 (CH), 113.1 (CH), 112.5 (CH),
111.4 (CH), 63.7 (CH2), 56.8 (C), 49.7 (CH2), 47.1 (CH2), 39.6 (CH3SO3H), 37.4
(CH), 35.4 (CH2), 32.7 (CH), 22.5 (CH3), 15.1 (CH3); elemental analysis calcd for:
C24H31N3OÁ0.45H2OÁ3.01CH3SO3H: C, 48.04; H, 6.56; N, 6.22. Found: C, 48.05; H,
6.44; N, 6.12. 10 (free base): 1H NMR (300 MHz, CDCl3) d 8.23 (d, J = 4.8 Hz, 2H),
7.15 (t, J = 8.0 Hz, 1H), 6.81–6.68 (m, 3H), 6.40 (t, J = 4.8 Hz, 1H), 4.59 (d,
J = 11.3 Hz, 2H), 4.00 (q, J = 7.0 Hz, 2H), 2.99 (dt, J = 12.3 and 2.9 Hz, 2H), 2.81 (d,
J = 11.4 Hz, 2H), 2.76–2.60 (m, 1H), 2.37–2.02 (m, 4H), 1.78–1.71 (m, 2H), 1.61–
1.51 (m, 2H), 1.40 (t, J = 7.0 Hz, 3H), 0.98 (d, J = 6.8 Hz, 3H); 13C NMR (75.5 MHz,
CDCl3) d 161.4, 158.5, 157.8, 140.3, 128.6, 123.3, 117.4, 112.6, 109.5, 63.5, 56.5,
50.3, 44.6, 37.1, 35.5, 32.6, 22.6, 15.1; MS: [M+H]+ = 379; hydrated MsOH salt:
elemental analysis calcd for: C23H30N4O1ÁCH3SO3HÁH2O: C, 58.51; H, 7.37; N,
11.37. Found: C, 58.76; H, 7.36; N, 11.40.
5. Analytical data for 3: 1H NMR (300 MHz, CDCl3) d 7.38–7.12 (m, 6H), 6.78–6.69
(m, 3H), 4.01 (q, J = 7.0 Hz, 2H), 3.45 (s, 2H), 2.76–2.54 (m, 5H), 2.28 (t,
J = 10.6 Hz, 2H), 2.13 (t, J = 10.2 Hz, 2H), 2.03 (dd, J = 13.1 and 8.1 Hz, 2H), 1.70–
1.66 (m, 2H), 1.56–1.45 (m, 2H), 1.41 (t, J = 7.0 Hz, 3H), 0.97 (d, J = 6.8 Hz, 3H);
13C NMR (75.5 MHz, CDCl3) d 158.5 (C), 140.5 (C), 129.5 (CH), 128.5 (CH), 128.4
(CH), 127.2 (CH), 123.3 (CH), 117.5 (CH), 112.5 (CH), 63.5 (CH2), 56.1 (C), 54.1
(CH2), 50.0 (CH2), 37.0 (CH), 35.4 (CH2), 32.4 (CH), 22.6 (CH3), 15.1 (CH3); MS:
[M+H]+ = 391; elemental analysis calcd for: C26H34N2O1: C, 79.96; H, 8.77; N,
7.17. Found: C, 79.86; H, 8.79; N, 7.07. Analytical data for 4: 1H NMR (300 MHz,
CDCl3) d 7.20–7.13 (m, 1H), 6.79–6.69 (m, 3H), 4.01 (q, J = 7.0 Hz, 2H), 2.88–2.54
(m, 7H), 2.38 (br, 1H), 2.14 (dt, J = 11.1 and 3.4 Hz, 2H), 2.03 (dd, J = 13.1 and
8.1 Hz, 2H), 1.70–1.66 (m, 2H), 1.56–1.45 (m, 2H), 1.41 (t, J = 7.0 Hz, 3H), 0.96 (d,
J = 6.8 Hz, 3H); 13C NMR (75.5 MHz, CDCl3) d 158.5 (C), 140.4 (C), 128.6 (CH),
123.3 (CH), 117.5 (CH), 112.5 (CH), 63.5 (CH2), 56.8 (C), 51.6 (CH2), 46.6 (CH2),
37.0 (CH), 35.5 (CH2), 32.4 (CH), 22.6 (CH3), 15.1 (CH3); MS: [M+H]+ = 301;
elemental analysis calcd for: C19H28N2O1: C, 75.96; H, 9.39; N, 9.32. Found: C,
75.71; H, 9.36; N, 9.10.
7. Wagaw, S.; Buchwald, S. L. J. Org. Chem. 1996, 61, 7240.
6. All compounds had been characterized by 1H NMR, 13C NMR, DEPT, LRMS and
8. Antal-Zimanyi, I.; Bruce, M.; LeBoulluec, K.; Iben, L.; Mattson, G.; McGovern, R.;
Hogan, J.; Leahy, C.; Flowers, S.; Stanley, J.; Ortiz, A.; Poindexter, G. Eur. J.
Pharmacol. 2008, 590, 224.
elementary analysis. Analytical data for representative compounds:
9
(methanesulfonic acid salt): 1H NMR (300 MHz, CDCl3) d 8.35 (dd, J = 6.3 and
1.5 Hz, 1H), 7.77 (dd, J = 8.1 and 1.8 Hz, 1H), 7.19 (t, J = 7.8 Hz, 1H), 6.88 (d,