5-(Pyridinon-1-yl)indazoles and 5-(furopyridinon-5-yl)indazoles as MCH-1 antagonists

Article abstract of DOI:10.1016/j.bmcl.2010.09.039

A new series of 5-(pyridinon-1-yl)indazoles with MCH-1 antagonist activity were synthesized. Potential cardiovascular risk for these compounds was assessed based upon their interaction with the hERG potassium channel in a mini-patch clamp assay. Selected compounds were studied in a 5-day diet-induced obese mouse model to evaluate their potential use as weight loss agents. Structural modification of the 5-(pyridinon-1-yl)indazoles to give 5-(furopyridinon-5-yl) indazoles provided compounds with enhanced pharmacokinetic properties and improved efficacy.

Full text of DOI:10.1016/j.bmcl.2010.09.039

Bioorganic & Medicinal Chemistry Letters 20 (2010) 7015–7019
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
5-(Pyridinon-1-yl)indazoles and 5-(furopyridinon-5-yl)indazoles
as MCH-1 antagonists
Matthew D. Surman a, , Emily E. Freeman a, James F. Grabowski a, Mark Hadden a, Alan J. Henderson a,
⇑
Guowei Jiang a, Xiaowu (May) Jiang a, Michele Luche a, Yuri Khmelnitsky a, Steven Vickers b,
Jean Viggers b, Sharon Cheetham b, Peter R. Guzzo a
a AMRI, 26 Corporate Circle, PO Box 15098, Albany, NY 12212-5098, USA
b RenaSci Consultancy Ltd, Biocity, Nottingham, NG1 1GF, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of 5-(pyridinon-1-yl)indazoles with MCH-1 antagonist activity were synthesized. Potential
cardiovascular risk for these compounds was assessed based upon their interaction with the hERG potas-
sium channel in a mini-patch clamp assay. Selected compounds were studied in a 5-day diet-induced
obese mouse model to evaluate their potential use as weight loss agents. Structural modification of
the 5-(pyridinon-1-yl)indazoles to give 5-(furopyridinon-5-yl)indazoles provided compounds with
enhanced pharmacokinetic properties and improved efficacy.
Received 6 August 2010
Revised 3 September 2010
Accepted 8 September 2010
Available online 16 September 2010
Keywords:
Ó 2010 Elsevier Ltd. All rights reserved.
Melanin concentrating hormone
MCH-1 antagonists
Obesity
Indazoles
Obesity is a growing concern for public health in industrialized
nations across the globe. The World Health Organization (WHO)
estimates that nearly 1 billion people worldwide are overweight
as defined as having a body mass index (BMI) of 25 kg/m2 or
greater.1 Additionally, approximately one third of the overweight
population is obese as defined as having a body mass index of
30 kg/m2 or greater. In the United States, over 60% of the popula-
tion is overweight and over 30% of these people are obese.2
Obesity is associated with a variety of comorbidities such as dia-
betes,3 dyslipidemia,4 coronary heart disease,5 stroke6 and certain
cancers.7 Indeed, even modest weight loss (5–10%) can provide
significant improvements in risk factors such as blood pressure,
glucose tolerance and lipid profile.8 However, weight loss through
life style management (dieting and exercise) generally has proven
to have limited effectiveness for long term weight maintenance.
Additionally, current pharmaceutical treatments suffer from weak
efficacy and significant side effects that limit their use. Thus, a
major need exists for new pharmaceutical agents that can provide
a safe and effective mechanism for inducing weight loss.
Many of the MCH-1 antagonists described in the literature suf-
fer from cardiovascular risks. In fact, such risks have been proposed
as a major reason for the scarcity of MCH-1 antagonists reaching
the clinic.10 Therefore, we sought to discover high affinity MCH-1
antagonists with minimized cardiovascular risk, namely by reduc-
ing interaction with the hERG potassium channel. Herein, we
describe a series of 5-(pyridinon-1-yl)indazoles with such proper-
ties. We found that adjustments to a pendant amine group could
be used to attenuate hERG binding. Further modification of the
5-(pyridinon-1-yl)indazole core to a 5-(furopyridinon-5-yl)inda-
zole scaffold provided compounds with enhanced pharmacokinetic
properties and improved in vivo efficacy.
Two general strategies were employed to construct the
5-(pyridinon-1-yl)indazole core. One method involved the use of
an initial SNAr reaction between benzyloxypyridinone 1 and fluo-
ronitrotoluene 2 (Scheme 1). Reduction of the nitro group with iron
powder and ammonium chloride followed by treatment of the
resulting aniline with sodium nitrite provided 5-(benzyloxypyrid-
inon-1-yl)indazole 4. Pendant amines could be attached to the
indazole ring using several methods. Selectivity for N1 versus N2
alkylation varied based upon the alkylating agent.11 Indazole 4
was reacted with bromo-alkylchloride 5 under basic conditions
to give substituted indazoles 6. Treatment of 6 with a variety of
amines afforded indazole derivatives 7. A hydroxyl group was
incorporated into the linker between the indazole and the amine
by alkylating the indazole with epoxide 8. The epoxide was opened
with lithium perchlorate and dimethyl amine to give indazole
Antagonists of the melanin concentrating hormone receptor-1
(MCH-1) have generated considerable interest as potential new
weight loss agents. Indeed, a variety of small molecule MCH-1
antagonists have been shown to effectively reduce body weight
in rodent models of obesity.9
⇑
Corresponding author.
E-mail address: matthew.surman@amriglobal.com (M.D. Surman).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.09.039

7016
M. D. Surman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7015–7019
NO2
CH3
NO2
CH3
H
O
O
1. Fe Powder, NH4Cl,
EtOH, H2O
85%
N
O
F
N
NH
2
N
N
O
Cs2CO3, DMF, 90 ºC
66%
2. NaNO2, AcOH, H2O
63%
O
N
O
1
3
4
n
n
R2
N
R1
Cl
N
O
N
O
5
N
Cl
n
"amine", K2CO3, KI
Br
N
N
4
4
DMF
17-95%
Cs2CO3, DMSO
48-56%
O
O
6
7
OH
CH3
O
N
N
CH3
O
N
O
N
Br
N
8
(CH3)2NH
O
N
N
LiClO4, THF
93%
O
Cs2CO3, DMSO
31%
O
10
9
N
OCH3
O
N
N
H
O
NH2
N
N
O
H2N
OCH3
N
Br
N
13
11
N
O
O
Al(CH3)3, Toluene, reflux
32%
4
Cs2CO3, DMSO
63%
O
12
14a
Scheme 1. Synthesis of 5-(pyridinon-1-yl)indazole MCH-1 antagonists.
derivative 10.12 Imidazoline derivatives were made by alkyling
indazole 4 with methyl bromoacetate to give substituted indazole
12. Treatment of indazole 12 with ethylenediamine and trimethyl-
aluminum gave imidazoline derivative 14a.
The 5-(pyridinon-1-yl)indazole core also was made through the
assembly of the indazole portion of the molecule, followed by cou-
pling to the benzyloxypyridinone segment. As shown in Scheme 2,
5-bromoindazole (16) was made from commercially available
5-bromo-2-fluorobenzaldehyde (15) by treatment with anhydrous
hydrazine at 100 °C. Attachment of the desired aminoethyl group
using the corresponding alkyl chloride and potassium carbonate
provided indazoles 18 (generally as a 2:1 mixture of N1 and N2
regioisomers, separable by column chromatography). Coupling of
indazoles 18 with benzyloxypyridinone 1 with copper(I) iodide
and 8-hydroxyquinoline at 130 °C afforded 5-(benzyloxypyridon-
1-yl)indazoles 7.
Early MCH-1 SAR around the 5-(pyridinon-1-yl)indazole scaf-
fold highlighted the importance of including a basic amine off of
the indazole ring. For example, 1-butyl indazole 19 showed little,
if any MCH-1 binding (Table 1). However, the addition of a dimeth-
ylaminoethyl group on the indazole ring created a compound (7a)
with single digit nanomolar MCH-1 affinity.
When the dimethylamine was replaced with a pyrrolidine ring,
the resulting compound (7b) maintained high MCH-1 affinity.
Compound 7b also showed a 1000-fold separation between the
MCH-1 Ki value and the hERG IC50 (as measured in a mini-patch
clamp assay).
Interaction with the hERG channel could be reduced through
the incorporation of a hydroxyl group in a position b to the basic
amine. For example, addition of a hydroxyl group on the propyl
linker in compound 10 decreased hERG binding nearly ninefold
compared to compound 7c. Similarly, adding a hydroxyl group
on the pyrrolidine ring in compounds 7d and 20b provided re-
duced hERG interaction compared with the parent compounds
7b and 20a, respectively. Interestingly, conversion of the hydroxyl
moiety to a methoxy group decreased or eliminated the beneficial
effect on hERG (compare compounds 7d to 7e and 7f to 7g).
Incorporation of the pendant amine into a variety of heterocy-
cles provided positive effects on hERG. Imidazoline derivative
14a showed a nearly fivefold decrease in hERG binding compared
to dimethylamine derivative 7a. This benefit was lost by methylat-
ing the imidazoline to give compound 14b. Morpholine derivative
H
N
F
H2NNH2
N
100 ºC
50%
Br
CHO
Br
15
16
R2
R2
N
R1
N
Cl
N
17
R1
N
K2CO3, DMSO
Br
50%*
O
18
NH
R2
N
O
7h showed very little hERG interaction (IC50 >30 lM); however,
N
O
1
R1
N
the MCH-1 affinity dropped approximately ninefold compared
to dimethylamine analogue 7a. The MCH-1 affinity could be
improved 2.5-fold by converting the morpholine to bicyclic
structure 7i. Compound 7i maintained a nearly 1000-fold separa-
tion between MCH-1 and hERG binding. Similar to morpholine,
piperazine derivative 7j showed reduced hERG interaction (nine-
fold) compared to dimethylamine analogue 7a.
8-hydroxyquinoline, CuI
N
DMSO, 130 ºC
58%*
O
7
*Yields given for the synthesis of 7b.
Scheme 2. Alternative synthesis of 5-(pyridinon-1-yl)indazole MCH-1 antagonists.

M. D. Surman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7015–7019
7017
Table 1
Indazole amine SAR
R
N
O
N
N
O
Compound
R
MCH-1 bindinga,b Ki (nM)
hERGc IC50
(lM)
19
>5000
Not determined
1.8
7a
7b
4.7
2.6
N
N
2.5
7c
10
12.6
37.7
1.4
N
N
OH
12.1
OH
O
7d
7e
4.7
9.4
9.0
1.8
N
N
20a
20b
12.0
33.0
2.0
HN
HN
OH
>30
HO
7f
3.1
2.3
0.8
N
O
7g
11.2
N
N
14a
14b
22.6
30.4
8.5
3.3
HN
N
N
O
7h
7i
43.4
17.3
24.3
>30
N
N
16.0
16.4
O
NH
7j
N
a
Displacement of [3H]compound 7b from MCH-1 expressed in CHO-K1 cells (Kd = 1.42 0.08 nM and Bmax = 13.3 0.7 pmol/mg protein; mean SEM, n = 4).
Values are means of at least two determinations where each determination is within 40% of the mean value shown.
Mini-patch clamp assay using HEK cells stably expressing the hERG potassium channel.
b
c
A selected set of analogues was chosen for further in vitro and
Table 2
in vivo analysis (Table 2). Compounds 7b, 7d and 14a showed good
aqueous solubility and greater than 1000-fold separation between
MCH-1 affinity and cytochrome P450 inhibition (six isoforms
tested). Compounds 7b, 7d and 14a also were examined in a 5-day
diet-induced obese (DIO) mouse model of weight loss (Figure 1).
All three compounds showed statistically significant reductions in
body weight when given at a screening dose of 30 mg/kg twice daily.
Twice daily dosing was found to be necessary for robust weight
loss. In the case of compound 7b, providing the same overall daily
dose in a single dose (60 mg/kg po, qd) reduced the efficacy in the
5-day DIO mouse model (2.8% weight loss versus 6.0% at 30 mg/kg
b.i.d.).
Additional in vitro and in vivo data for selected 5-(pyridinon-1-yl)indazoles
Compound CYP 3A4a
Half-life (min) Aqueous
Weight
IC50
(lM)
solubilityd
(lM)
losse (%)
MLMb HLMc
7b
7d
14a
10
7.7
38
695
433
580
303
289
260
492
>500
410
6.0
3.3
3.5
a
1A2, 2B6, 2C9, 2C19, 2D6 and 3A4 isoforms tested. Isoforms not reported have
IC50s greater than 10 M.
l
b
Mouse liver microsomes.
Human liver microsomes.
c
d
e
PBS at pH 7.4.
5-day DIO mouse study at 30 mg/kg po, b.i.d.; see Figure 1.

7018
M. D. Surman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7015–7019
41.0
40.0
39.0
38.0
37.0
36.0
35.0
in 46% yield. Selective bromination of 25 at the 2-position of the
furopyridinone was accomplished with pyridinium tribromide in
9:1 CH2Cl2/AcOH at 35 °C to afford compound 26 in 31% yield.
Suzuki or Stille coupling of 26 with the appropriate aryl boronic
acid or heteroaryl stannane afforded a small library of compounds
27a–j in 10–36% yield.
Exploration of the MCH-1 SAR surrounding the phenyl ring in
compound 27a revealed that substituents in the para-position
were well tolerated (see compounds 27a–27c in Table 3). Substitu-
tion in the ortho- or meta-position resulted in losses in MCH-1
affinity. For example, ortho- or meta-chloro derivatives 27d and
27e showed 5–7-fold increases in Ki values compared with
p-chloro derivative 27c. Ortho and para disubstitution was toler-
ated when the ortho group was small, as in 4-chloro-2-fluoro deriv-
ative 27g. However, when larger ortho groups were introduced
(such as methoxy in analogue 27h), losses in binding affinity were
observed. Replacement of the phenyl ring with aromatic heterocy-
cles such as pyridine and pyrimidine (27i and 27j, respectively) led
to 6–160-fold decreases in MCH-1 affinity.
*
*
*
Vehicle bid
**
***
7b (30 mg/kg po) bid -6.0%
7d (30 mg/kg po) bid -3.3%
14a (30 mg/kg po) bid -3.5%
***
***
Day -2 Day -1 Day 0 Day 1 Day 2 Day 3 Day 4 Day 5 Day 6
Time
Figure 1. Effect of compounds 7b, 7d and 14a (dosed at 30 mg/kg, po, b.i.d. in 1%
methylcellulose in water) on the body weight of male C57BL/6 J DIO mice. Data are
adjusted means (n = 10). SEMs are calculated from the residuals of the statistical
model. Data analysed by ANCOVA with body weight on day 1 as covariate followed
by Dunnett’s test for adjusted data; *p <0.05, **p <0.01, ***p <0.001. Figures in
legend refer to % difference from control on day 6 (i.e., after 5 days dosing).
Compound 27c was selected for additional in vitro and in vivo
evaluation. Compound 27c gave comparable results to 7b in the
MCH-1 radioligand binding assay and a functional Ca2+ mobiliza-
The requirement for twice daily dosing was attributed, at least
in part, to suboptimal PK and CNS penetration. Therefore, a strat-
egy was employed to remove potential metabolically labile
positions to improve PK and to reduce the number of rotatable
bonds to improve CNS exposure. The furopyridinone scaffold was
explored as a structural derivative of the benzyloxypyridinone
system that would achieve these structural changes. The furopy-
ridinone removes a benzylic site of potential metabolism and elim-
inates two rotatable bonds. The increased rigidity of the
furopyridinone was anticipated to improve brain penetration13
and hence improve in vivo efficacy.
Table 3
5-(Furo[3,2-c]pyridin-4(5H)on-5-yl)indazole aryl ring SAR
N
N
O
N
N
R
O
Compound
R
MCH-1 binding Kia,b (nM)
The strategy utilized to synthesize the furopyridinone deriva-
tives is shown in Scheme 3. Reaction of aniline 21 with NaNO2
in 40:1 AcOH/H2O and subsequent alkylation of the indazole
intermediate with alkyl chloride 22 and Cs2CO3 afforded indazole
23 in 52% yield over the two steps. A small amount of the unde-
sired alkylation regiosiomer (2-position of the indazole) was also
obtained. The regioisomers were separable by column chromatog-
raphy. Treatment of 23 with furopyridinone 24,14 CuI, 8-hydroxy-
quinoline and Cs2CO3 in DMSO at 130 °C gave furopyridinone 25
27a
27b
27c
27d
27e
27f
27g
27h
27i
Phenyl
9.7
6.1
5.2
28
38
14
4.2
48
59
4-Fluorophenyl
4-Chlorophenyl
2-Chlorophenyl
3-Chlorophenyl
2,4-Dichlorophenyl
4-Chloro-2-fluorophenyl
4-Chloro-2-methoxyphenyl
Pyridin-2-yl
27j
Pyrimidin-2-yl
1679
a
Displacement of [3H]compound 7b from MCH-1 expressed in CHO-K1 cells
(Kd = 1.42 0.08 nM and Bmax = 13.3 0.7 pmol/mg protein; mean SEM, n = 4).
1. NaNO2, 40: 1 AcOH/H2O
(99%)
b
Values are means of at least two determinations.
N
NH2
N
N
N
N
2. Cs2CO3, DMSO,
I
I
Cl
N
Table 4
21
23
22
Comparison of selected in vitro and in vivo properties of compounds 7b and 27c
(52%)
O
In vitro
7b
27c
N
MCH-1 binding Kia,b (nM)
2.6
14
5.2
23
NH
O
Ca2+ release IC50 (nM)
c
O
24
N
Mouse PK
Dose (mg/kg)
CuI, 8-hydroxyquinoline,
DMSO, Cs2CO3,130 ºC
O
30
10
25
d
[Plasma]6h (ng/mL)
2224
1485
0.7
141
2253
16
e
(46%)
[Brain]6h (ng/g)
N
B/P ratiof
N
O
N
Pyridinium tribromide,
5-Day DIO mouse efficacy
Dose (mg/kg)
Body weight loss
N
30 (b.i.d.), 60 (qd)
6.0%***, 2.8%*
30 (qd)
4.5%***
Br
9:1 CH2Cl2/AcOH, 35 ºC
(31%)
O
26
Displacement of [3H]Compound 7b from MCH-1 expressed in CHO-K1 cells
a
N
(Kd = 1.42 0.08 nM and Bmax = 13.3 0.7 pmol/mg protein; mean SEM n = 4).
R–B(OH)2
Pd(PPh3)2Cl2,
N
b
O
Values are means of at least four determinations.
N
c
Inhibition of MCH-mediated Ca2+ release in AequoScreenTM MCH-1 cells.
N
d
Plasma concentration 6 h post dose.
Brain concentration 6 h post dose.
Ratio of brain concentration to plasma concentration at 6 h.
R
K2CO3, DMSO
(10–36%)
e
O
27
f
*
p <0.05.
p <0.001.
Scheme 3. Synthesis of 5-(furo[3,2-c]pyridin-4(5H)on-5-yl)indazole MCH-1
***
antagonists.

M. D. Surman et al. / Bioorg. Med. Chem. Lett. 20 (2010) 7015–7019
7019
5. Okosun, I. S.; Chandra, K. M. D.; Choi, S.; Christman, J.; Dever, G. E. A.; Prewitt, T.
E. Obes. Res. 2001, 9, 1.
6. Yatsuka, H.; Folsom, A. R.; Yamagishi, K.; North, K. E.; Brancati, F. L.; Stevens, J.
Stroke 2010, 4, 417.
7. Bray, G. A.; Bellanger, T. Endocrine 2006, 29, 109.
8. (a) Sjostrom, C. D.; Lissner, L.; Sjostrom, L. Obes. Res. 1997, 5, 519; (b) Seidell, J.
C.; Verschuren, W. M.; Van-Leer, E. M.; Kromhout, D. Arch. Int. Med. 1996, 156,
958.
9. McBriar, M. D. Curr. Opin. Drug Discovery Dev. 2006, 9, 496.
10. (a) Mendez-Andino, J. L.; Wos, J. A. Drug Discovery Today 2007, 12, 972; (b)
Dyke, H. J.; Ray, N. C. Expert Opin. Ther. Patents 2002, 12, 1639; (c) Rokosz, L. L.;
Hobbs, D. W. Drug News Perspect. 2006, 19, 273.
tion assay (Table 4). However, 27c showed a 20-fold increase in
mouse brain to plasma concentration ratio (B/P = 16) compared
to 7b (B/P = 0.7), leading to increased brain exposure at one third
the dose.15 Compound 27c also provided improved efficacy in the
5-day DIO mouse model with once daily dosing (4.5% weight loss,
30 mg/kg po, qd) compared to 7b (2.8% weight loss, 60 mg/kg po,
qd) at half the dose.
In conclusion, a potent series of 5-(pyridinon-1-yl)indazole
MCH-1 antagonists was synthesized. Interaction with the hERG
channel could be attenuated by adjustments to a pendant amine
group. Further modification of the 5-(pyridinon-1-yl)indazole core
to a 5-(furopyridinon-5-yl)indazole scaffold provided compounds
with enhanced pharmacokinetic properties and improved in vivo
efficacy. Additional strategies for improving the efficacy of the lead
series will be described in subsequent reports.16
11. Hunt, K. W.; Moreno, D. A.; Suiter, N.; Clark, C. T.; Kim, G. Org. Lett. 2009, 11,
5054.
12. Chini, M.; Crotti, P.; Macchia, F. Tetrahedron Lett. 1990, 31, 4661.
13. Hitchcock, S. A.; Pennington, L. D. J. Med. Chem. 2006, 49, 7559.
ˇ
14. Korenova, A.; Krutosikova, A.; Kovac, J.; Celec, S. Collect. Czech. Chem. Commun.
1997, 52, 192.
15. McBriar et al. demonstrated the need for robust brain exposure (>70% ex vivo
MCH-1 receptor occupancy) at 6 h post dose to elicit in vivo efficacy. Using this
observation as a guide, brain levels were measured at 6 h post dose. McBriar,
M. D.; Guzik, H.; Xu, R.; Paruchova, J.; Li, S.; Palani, A.; Clader, J. W.; Greenlee,
W. J.; Hawes, B. E.; Kowalski, T. J.; O’Neill, K.; Spar, B.; Weig, B. J. Med. Chem.
2005, 48, 2274.
16. (a) Hadden, M.; Deering, D. M.; Henderson, A. J.; Guzzo, P. R.; Surman, M. D.;
Luche, M.; Khmelnitsky, Y.; Vickers, S.; Viggers, J.; Cheetham, S. Bioorg. Med.
Chem. Lett. 2010, 20, 7020; (b) Henderson, A. J.; Deering, D. M.; Grabowski, J. F.;
Guzzo, P. R.; Hadden, M.; Jiang, X.; Khmelnitsky, Y.; Luche, M.; Surman, M. D.;
Cheetham, S.; Vickers, S.; Viggers, J. Bioorg. Med. Chem. Lett. 2010, 20, 7024.
References and notes
1. Abelson, P.; Kennedy, D. Science 2004, 304, 1413.
2. Ogden, C. L.; Carroll, M. D.; Curtin, L. R.; McDowell, M. A.; Tabak, C. J.; Flegal, K.
M. J. Am. Med. Assoc. 2006, 295, 5249.
3. Colditz, G. A.; Willett, W. C.; Rotnitzky, A.; Manson, J. E. Ann. Int. Med. 1995, 122,
481.
4. Després, J. P. Balliere’s Clin. Endocrinol. Metab. 1994, 8, 629.