Identification and characterization of amino-piperidinequinolones and quinazolinones as MCHr1 antagonists

Article abstract of DOI:10.1016/j.bmcl.2006.02.044

Several potent, functionally active MCHr1 antagonists derived from quinolin-2(1H)-ones and quinazoline-2(1H)-ones have been synthesized and evaluated. Pyridylmethyl substitution at the quinolone 1-position results in derivatives with low-nM binding potency and good selectivity with respect to hERG binding.

Full text of DOI:10.1016/j.bmcl.2006.02.044

Bioorganic & Medicinal Chemistry Letters 16 (2006) 2621–2627
Identification and characterization of
amino-piperidinequinolones and quinazolinones
as MCHr1 antagonists
Christopher Blackburn,a,* Matthew J. LaMarche,a James Brown,a Jennifer Lee Che,a
Courtney A. Cullis,a Sujen Lai,a Martin Maguire,a Thomas Marsilje,a Bradley Geddes,a
Elizabeth Govek,a Vivek Kadambi,a Colleen Doherty,a Brian Dayton,b Sevan Brodjian,b
Kennan C. Marsh,b Christine A. Collinsb and Philip R. Kymb
aMillennium Pharmaceuticals, Inc., 40 Landsdowne St. Cambridge, MA 02139, USA
bMetabolic Diseases Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064, USA
Received 2 December 2005; revised 14 February 2006; accepted 15 February 2006
Available online 9 March 2006
Abstract—Several potent, functionally active MCHr1 antagonists derived from quinolin-2(1H)-ones and quinazoline-2(1H)-ones
have been synthesized and evaluated. Pyridylmethyl substitution at the quinolone 1-position results in derivatives with low-nM
binding potency and good selectivity with respect to hERG binding.
Ó 2006 Elsevier Ltd. All rights reserved.
Melanin concentrating hormone (MCH) is a cyclic
19-membered orexigenic neuropeptide found in the lat-
eral hypothalamus and zone incerta that regulates feed-
ing behavior and energy expenditure in mammals.1,2
ICV injection of MCH stimulates food intake in ro-
dents3 causing an increase in body weight,4 whereas
mice lacking the gene encoding MCH are hypophagic,
lean and have increased metabolic rates.5 Furthermore,
MCH receptor knockout mice have been shown to be
hyperphagic on regular chow yet less susceptible to diet
induced obesity and to have reduced fat mass.6,7
Infusion (ICV) of MCH did not induce food intake or
obesity in the receptor knockout mice.7 These pharma-
cological data suggest that oral administration of
brain-permeable MCHr1 antagonists may provide a
novel therapy for obesity. Indeed, recently reported
MCHr1 antagonists from several structural types have
been reported to show in vivo efficacy in animal
models.8–14 As discussed in earlier communications,
aminopiperidine benzamides11–13 and coumarins14 have
been optimized from screening hits based on an
125I-MCH binding assay. For example, coumarin-based
4-aminopiperidine 1 was identified as a potent MCHr1
antagonist (IC50 = 2 nM in the binding assay and
28 nM in a functional assay measuring inhibition of
MCH-mediated Ca2+ release) and proved to be effica-
cious in rodent weight loss models.14 However, even
the most attractive compounds from these series in
terms of both potency and pharmacokinetics required
surprisingly high brain and plasma concentrations in or-
der to provide prolonged receptor antagonism in vivo.
Thus, for compound 1, plasma concentrations of the
order of 2 lg/mL (5 lM) were necessary in order to
provide comparable brain levels leading to sustained
weight loss. These high circulating plasma concentra-
tions present a safety challenge in terms of off-target ef-
fects. In consequence, improved MCHr1 potency,
selectivity, and brain penetration characteristics will be
required in order to develop a safe, orally bioavailable
anti-obesity therapeutic. In particular, several com-
pounds based on analogs 1 and 2 showed severe cardio-
toxicity in anesthetized dogs.12–14 While the mechanism
of these effects has yet to be established, we reasoned
that more potent MCHr1 antagonists would provide a
better opportunity to achieve an acceptable therapeutic
index for efficacy relative to cardiovascular effects. In
addition, it was also of interest to screen the compounds
in an assay measuring binding to the hERG potassium
channel as one predictor of cardiovascular liabilities.15
Keywords: Obesity; MCH antagonist; Quinolone; hERG.
*
Corresponding author. Tel.: +1 617 761 6811; fax: +1 617 444
1483; e-mail: chris.blackburn@mpi.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.02.044

2622
C. Blackburn et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2621–2627
O
N
O
O
N
H
O
N
N
H
N
Cl
O
H
Cl
O
O
S
N
2
1
R1
R1
N
N
H
H
N
N
R2
R2
6
R
4
3
N
1
O
N
R3
O
N
3
4
R3
The first compounds described herein are based on the
generic structure 316 which has clear similarities to our
earlier series in that the quinolone (systematically, 1-
alkylquinolin-2(1H)-one) core serves as a replacement
for the coumarin ring system and also provides a config-
urationally restrained version of the ortho-amino benz-
amide13 series. We have developed synthetic routes
placing emphasis on derivatives substituted at the
1- and 3-positions thereby exploring space not readily
accessed in series 1 and 2. In addition, we have also pre-
pared related compounds based on the quinazoline-
2(1H)-one ring system (4).
derivatives 3k–3o (Table 2) were synthesized according
to Scheme 2. Thus, 6-chloroisatoic anhydride was treat-
ed with malonic ester in the presence of base to give 4-
hydroxyquinolin-2(1H)-one 8a. Conversion to the corre-
sponding tosylate followed by reaction with 1-piperonyl-
4-aminopiperidine and subsequent N-methylation gave
3n. A similar malonate condensation was conducted
with an N-methylated isatoic anhydride and the product
treated with pyrrolidine to give 8b, which was then con-
verted to 3o. The 3-cyano analogues were obtained via
coupling methyl 2-amino-5-chlorobenzoates with cyano-
acetic acid followed by cyclization to give 9. Conversion
of 9b to the corresponding chloride followed by reaction
with the appropriate 1-benzyl-4-aminopiperidine affor-
ded 3l and 3m. Treatment of 9a with POCl3 afforded
2,4-dichloroquinoline derivative 1018 which underwent
nucleophilic displacement with 1-piperonyl-4-aminopi-
peridine; subsequent acid hydrolysis afforded quinolone
3k.
We began by developing synthetic routes to quinolin-
2(1H)-one derivatives 3 that permit ready variation
at the 1-, 3-, and 6-positions. In one such route
(Scheme 1), several N-substituted anilines were pre-
pared, coupled to mono-t-butylmalonate in the presence
of EDCI, and the products, 5, cyclized to 6 by treatment
with P2O5.17 In some instances (R3 = Me) condensation
of the aniline with malonic acid afforded 6 directly. 4-
Hydroxyquinolin-2(1H)-ones (6) were activated toward
nucleophilic substitution by conversion to the corre-
sponding triflate and then allowed to react with a pro-
tected 4-aminopiperidine to give 7. Deprotection
followed by reaction with the appropriate benzyl or
cinnamyl halide afforded 3a–3j (Table 1). 3-Substituted
Formal replacement of the 3-methine of the 1-alkylquin-
olin-2(1H)-one series with the N-atom affords the qui-
nazoline-2(1H)-one series of compounds 4. The
synthesis of these analogs began with the ortho-lithiation
of N-Boc-4-chloroaniline19 followed by amidation with
t-butylisocyanate. Upon heating, intramolecular dis-
placement of the adjacent t-BuO group took place
Scheme 1. Reagents and conditions: (a) For R3 = –CH2Ar: ArCHO, CH2Cl2, AcOH, NaBH(OAc)3, 25 °C, 3 h, 60–94%; (b) For R3 = Me:
i—EtOCOCl, DIEA, DMAP, THF, 25 °C, 70–85%; ii—LiAlH4, THF, 60 °C, 60–70%; (c) HOOCCH2COOtBu, EDCI, CH2Cl2 25 °C, 3 h, 60–85%;
(d) P2O5, MeSO3H, 100 °C, 15 min, 50–71%; (e) CH2(COOH)2, POCl3, 25 °C, 16 h, 20–25%; (f) i—NaH, Tf2NPh, MeCN, 50 °C, 1 h; ii—1-
carbethoxy-4-aminopiperidine, MeCN, 100 °C, 7 h, sealed tube, 50–84%; (g) i—HBr, HOAc, sealed tube, 110 °C, 1 h; ii—ArCH2Br, NaCO3, DMF,
25 °C, 16 h, 40–80%.

C. Blackburn et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2621–2627
2623
Table 1. MCHr1 binding affinity and functional activity of quinolin-2(1H)-one compounds
R1
N
H
N
R2
N
R3
O
3
Compound
R2
R3
R1
MCH binding
IC50 (nM)
MCH FLPR
IC50 (nM)
hERG binding
Ki (nM)
O
3a
3b
3c
3d
3e
3f
Cl
H
4
10
5
1
2
1
1
2
2
26
88
2
4
7
3
4
112
6
2
8
O
Cl
Me
Me
Me
Me
Me
Bn
30
Cl
100
20
215
O
MeO
CHF2O
CF3
Cl
3
778 15
O
O
5
34
>2000
O
O
34
104 21
1800 100
280 12
355 30
O
O
3g
3h
3i
0.8 0.1
1.1 0.1
0.9 0.1
1.2 0.2
42
29
5
5
O
O
Cl
N
O
N
N
Cl
55 10
88
7
O
O
3j
Cl
20
7
550 40
affording 11. Alkylation of the N-1 lactam, followed by
acid induced removal of the t-butyl group, gave the qui-
nazoline-2,4(1H,3H)-diones 12.20 Treatment of 12 with
POCl3 gave the corresponding 4-chloro-compounds
which were converted to the final products, 4, under
comparable conditions to those used in the quinolone
series. In order to probe conformational effects in the
diamine moiety, a bicyclic alternative to the 4-aminopi-
peridine linker was also investigated (Scheme 4). Hydro-
genation of N-carbethoxy-4-tropinone (13) afforded the
endo-alcohol, which was converted to the mesylate 14,
then subjected to SN2 displacement with sodium azide
followed by hydrogenation (H2, Pd/C) to provide the
exo-amine 15. The endo-stereoisomer 16 was accessed
via hydrogenation of oxime 17.21 Representative quinaz-
oline-2-(1H)-ones 4g-i (Table 3) were then synthesized
from the tropane-based amines 15 and 16 in a manner
analogous to Scheme 3.
IMR 32 cells22 and for functional antagonism of
MCH-mediated Ca2+ release.23 Binding potencies of
compounds at the hERG potassium channel24 were
also determined25 and data are compiled in Tables
1–3. In the 1-alkylquinolin-2(1H)-one series (3) substi-
tutions at the piperidine 1-position and the 6-position
of the quinolinone ring led to similar trends as in the
coumarin14 and benzamide series.12,13 Thus, with chlo-
rine at the 6-position potent MCHr1 binding was ob-
served when the piperidine N-1 substituents were
piperonyl (3a), cinnamyl (3b), and naphthyl (3c) with
potencies improved slightly compared to their couma-
rin counterparts14 (Table 1). In addition to chloro,
other small hydrophobic groups at the 6-position such
as alkyl (not shown), alkoxy (3d), and the fluorinated
derivatives 3e and 3f conferred high potency. The rel-
ative potencies in the functional assay were in good
agreement with the binding data. In general, high
potency (30–800 nM) in the hERG binding assay
was also observed but this was significantly reduced
for the latter two compounds.
Compounds were screened in a binding assay for
MCHr1 using receptor obtained from human neuronal

2624
C. Blackburn et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2621–2627
Table 2. MCHr1 binding affinity and functional activity of 3-substituted quinolin-2-(1H)-ones and quinazoline-2-(1H)-ones
R1
R1
N
N
H
N
HN
Cl
R4
O
Cl
3
N
6
3
6
1
N
R3
1
N
R3
O
3
4
Compound
R3
R4
R1
MCH binding
IC50 (nM)
MCH FLPR
IC50 (nM)
hERG binding
Ki (nM)
O
3k
3l
H
CN
CN
CN
15
12
24
3
2
4
20
1
420 30
>2,000
O
Me
194 116
O
3m
3n
3o
4a
4b
4c
4d
4e
4f
Me
69
9
>2000
O
O
Me
COOMe
97 33
452 39
1440 150
>2000
O
O
O
N
Me
16
7
7
2
1
2
2
1
3
53
3
O
Me
72 11
160 15
360 15
1750 100
O
O
Me
9
47
66
62
29
5
3
9
4
Me
12
5
N
CH2CF3
CH2CF3
n-Pentyl
150
5
O
2
445 30
135 15
O
O
12
50 12
O
Compounds N-methylated at the 1-position (R3) were
found to have comparable potency to the unsubstituted
compounds (see for example 3a and 3c, Table 1 and 3k
and 3l of Table 2). Other alkyl groups (not shown) as
well as benzylic groups (compound 3g, for example)
were well tolerated. Particularly noteworthy were the
pyridyl–methyl moieties which imparted a boost in
potency suggesting that these compounds can access
an additional receptor binding pocket not available to
their coumarin counterparts. These analogs (3h–3j) all
exhibited approximately 1 nM binding affinities but, in
general, their functional activity was not improved to
the same degree possibly due to impaired cell permeabil-
ity. In addition, hERG ion channel binding remained
unacceptably high (Table 1). Substitution of the 3-posi-
tion (R4) with electron-withdrawing groups resulted in
approximately 2- to 5-fold losses in MCH1r binding
potency and significant lowering of the hERG binding
potency provided the quinolone nitrogen was alkylated
(Table 2 compounds 3l–3n).
Replacement of the quinolin-2(1H)-one ring system with
quinazoline-2(1H)-one did not adversely affect MCH
binding potency (compare, for example, 4a with 3c)
but the hERG binding profile was not improved. How-
ever, substitution of the piperidine N-1 position by a
quinolyl group (compound 4c) resulted in a considerably
improved (140-fold) MCH1r/hERG selectivity. At the 1-
position, alkyl and fluoroalkyl substituents were well
tolerated (for example, compounds 4d and 4e). Even
compounds bearing aliphatic groups with multiple de-
grees of freedom such as n-pentyl (4f) retained low nano-
molar MCH binding potency and further illustrate the
steric tolerance at this site. In addition, locking the

C. Blackburn et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2621–2627
2625
Scheme 2. Reagents and conditions: (a) MeI, Na2CO3, DMF, 25 °C, 16 h, 78%; (b) Dimethylmalonate, NaH, DMF, 120 °C, 3 h, 47–55%; (c)
Pyrrolidine, DMF, 130 °C, 1 h, 90%; (d) TsCl, DIEA, MeCN, 25 °C, 75–85%; (e) 1-piperonyl-4-aminopiperidine, DIEA, DMF, 50 °C, 8 h, 60–65%;
(f) NaH, MeI, DMF, 25 °C, 8 h, 40%; (g) HOOCCH2CN, EDC, THF, 16 h, 60%; (h) NaOMe, MeOH, 60 °C, 2 h, 70%; (i) POCl3, 90 °C, 1 h, 30–
70%; (j) 1-benzyl-4-aminopiperidine, DIEA, DMF, 75 °C, 2 h, 55–60%; (k) 1 N HCl, THF, 70 °C, 24 h, 50%.
one series were conducted (Table 4). While oral admin-
istration of compounds 3h and 3m from the former
series and 4b from the latter provided comparable
plasma levels to those achieved by related benzam-
ide12,13 and coumarin14 compounds, brain permeation
was considerably lower. Compound 3h exhibits the
highest brain levels but the Cmax value is 2-fold lower
than that of efficacious coumarin 1 and the AUC is
some 6-fold lower. The low brain/plasma AUC ratios
(0.29 or less) imply that any efficacious dose will result
in a considerable concentration of compound remain-
ing in the systemic circulation with consequent cardio-
vascular risk. Hence, despite their superior potencies
in vitro, it is unlikely that this compound class will
provide anti-obesity agents with an improved efficacy
and/or safety window compared to the benzamide
and coumarin derivatives that we have described
previously.26
Scheme 3. Reagents and conditions: (a) t-BuLi, THF, À78 to À20 °C,
2 h; then tBuNCO, À20 to 70 °C, 12 h, 98%; (b) i—RI, NaH, DMF,
25 °C, 3 h, 80–90% or CF3CH2OTf, CsCO3, MeCN, 50 °C, 48 h, 50–
65%; ii—HBr, HOAc, 25 °C, 3 h, 95%; (c) i—POCl3, DIEA, 100 °C,
4 h, 45–75%; ii—1-carbethoxy-4-aminopiperidine, Et3N, DMF, 50 °C,
12 h, 25–55%; iii—HBr, HOAc, 100 °C, sealed tube, 2 h; iv—
ArCH2Cl, Et3N, DMF, 50 °C, 24 h, 55–80%.
In conclusion, quinolone and quinazolinone MCHr1
antagonists have been designed, synthesized, and their
potency, selectivity, and PK properties determined. Sev-
eral compounds from these series are considerably more
potent than their coumarin14 and benzamide12,13 coun-
terparts and in some cases exhibit sub-nanomolar
MCHr1 binding potency and >500-fold selectivity with
respect to hERG binding. However, these properties
are compromised by relatively low MCH1r functional
activity and poor brain penetration in the DIO mouse,
following oral dosing.
conformation of the diamine linker in the case of
bridged diamines 4g–4i afforded potent compounds in
the binding and functional assays but again no signifi-
cant improvements in hERG selectivity could be
achieved. The exo-stereochemical configuration resulted
in the more potent compounds in the MCHr1 binding
assays (compare 4g and 4i, Table 3).
Pharmacokinetic analyses of representative members of
the 1-alkylquinolin-2(1H)-one and quinazoline-2(1H)-

2626
C. Blackburn et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2621–2627
Scheme 4. Reagents and conditions: (a) H2, RaNi, EtOH, 70 °C, 12 h, 95%; (b) MsCl, Et3N, CH2Cl2, 25 °C, 2 h, 88%; (c) NaN3, DMF, 100 °C, 5 h,
100%; (d) H2, Pd/C, MeOH, 1 atm, 12 h, 25 °C, 73%; (e) NH2OHÆHCl, Na2CO3, EtOH, H2O, 80 °C, 1 h; 80%; (f) H2, PtO2, MeOH, HOAc, 25 °C,
50 psi, 48 h, 75%.
Table 3. MCHr1 binding affinity and functional activity of quinazoline-2(1H)-ones with bicyclic amine linkers
O
L
Cl
O
N
6
1
N
O
R3
Compound
R3
Diamine
MCH binding IC50 (nM)
MCH FLPR IC50 (nM)
hERG binding Ki (nM)
N
4g
Me
9
4
4
1
53
31
6
7
6
540 50
NH
NH
H
N
4h
CH2CF3
120 20
H
N
4i
Me
68 24
136
310 20
H
HN
Acknowledgments
Table 4. Pharmacokinetic parameters of some quinolin-2(1H)-one and
quinazoline-2(1H)-ones dosed at 10 mg/kg in DIO mice
We thank Michael Patane for helpful comments and
Nelson Troupe and Ashok Patil for Analytical support.
3h
3m
4b
Plasma AUC (lg h/ml)
Brain AUC (lg h/ml)
Plasma T1/2 (h)
2.1
5.9
5.1
0.73
2.3
0.62
1.9
0.65
1.6
References and notes
Brain T1/2 (h)
2.5
2.0
1.6
1.9
2.2
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Plasma Cmax (lg/ml)
Brain Cmax (lg/ml)
Brain/plasma AUC
0.68
0.2
0.16
0.11
0.23
0.13
0.29

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26. It is unclear why these compounds exhibit less
desirable brain permeation properties than earlier
series. For the compounds listed in Table 4, the
respective calculated SlogP and polar surface areas are
3h (5.1, 67.8), 3m (3.8, 77.8), and 4b (3.9, 66.4). These
properties are not atypical for compounds that pass
the blood–brain barrier. Moreover, compounds 3h, 3m,
and 4b were found to have moderate to high perme-
abilities in PAMPA and Caco assays (with no evidence
that the compounds are efflux substrates). It did not
prove possible to conduct receptor occupancy experi-
ments in vivo. Thus, it is unclear why such high total
brain concentrations of MCH1r antagonists, relative to
in vitro potency, are required in order to observe
efficacy12–14 though high binding to brain lipids is one
possibility.