GPR109a agonists. Part 2: Pyrazole-acids as agonists of the human orphan G-protein coupled receptor GPR109a

Article abstract of DOI:10.1016/j.bmcl.2010.06.041

5-Alkyl and aryl-pyrazole-acids have been identified as a new class of selective, small-molecule, agonists of the human orphan G-protein-coupled receptor GPR109a, a high affinity receptor for the HDL-raising drug nicotinic acid.

Full text of DOI:10.1016/j.bmcl.2010.06.041

Bioorganic & Medicinal Chemistry Letters 20 (2010) 4472–4474
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
GPR109a agonists. Part 2: Pyrazole-acids as agonists of the human orphan
G-protein coupled receptor GPR109a
a
a
a
a
Jason E. Imbriglio a, , Sookhee Chang , Rui Liang , Subharekha Raghavan , Darby Schmidt ,
Abby Smenton a, Scott Tria a, Thomas O. Schrader d, Jae-Kyu Jung d, Craig Esser a, Tom G. Holt b,
Michael S. Wolff b, Andrew K. P. Taggart c, Kang Cheng c, Ester Carballo-Jane c, M. Gerard Waters c,
James R. Tata a, Steven L. Colletti a
*
a Department of Medicinal Chemistry, Merck Research Laboratories, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065-0900, United States
b Department of Drug Metabolism, Merck Research Laboratories, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065-0900, United States
c Department of Cardiovascular Diseases, Merck Research Laboratories, Merck & Co., Inc., PO Box 2000, Rahway, NJ 07065-0900, United States
d Department of Medicinal Chemistry, Arena Pharmaceuticals, 6166 Nancy Ridge Drive, San Diego, CA 92121, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
5-Alkyl and aryl-pyrazole-acids have been identified as a new class of selective, small-molecule, agonists
of the human orphan G-protein-coupled receptor GPR109a, a high affinity receptor for the HDL-raising
drug nicotinic acid.
Received 7 May 2010
Accepted 7 June 2010
Available online 10 June 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Niacin
GPR109a
Agonists
Nicotinic acid (niacin) 1 has been a leading treatment for dysl-
ipidemia and for the prevention of atherosclerosis for over
40 years.1 Long term clinical studies have demonstrated niacin’s
ability to reduce mortality from coronary heart disease.2 In spite
of niacin’s clinical significance, patients treated with niacin show
low compliance of use due to an intense flushing side effect.3,4 As
a result, a number of drug discovery programs have focused on
the development of a ‘flush-free’ niacin-like therapy. Despite con-
siderable effort in the field, the absence of a niacin-related target
and/or mechanism of action, has limited such investigations.
Recently, a G-protein-coupled receptor, GPR109a, was identi-
fied as a molecular target for niacin.5 Following this breakthrough,
our group initiated a drug discovery program focused on the devel-
opment of a high affinity ‘flush-free’ niacin-like agonist. Previously,
we reported on the identification of a pyrazole-tetrazole agonist
2a, a compound that showed potential as a ‘flush-free’ agonist of
GPR109a.6 The intriguing pharmacology of compound 2a inspired
continued interests within this structure class. Subsequent work
in the group showed that C5-alkyl- and aryl-substituted pyra-
zole-tetrazole derivatives had improved in vitro affinities and sim-
ilar pharmacology to 2a.7
With a continued interest in this structure class, we proceeded to
explore further structure based improvements. In this effort, we dis-
covered that the tetrazole moiety of compound 2a could be suitably
replaced with a carboxylic acid group. Curious as to the effect of this
functional group exchange on the pharmacological profile for the
class, we proceeded to develop this class of pyrazole-carboxylic acid
derivatives.
Initially, we focused our effort on synthesis of the C5-alkyl and
aryl derived pyrazole–acids. In this regard, generation of the series
of C5-alkyl pyrazole-acids 5a–c and the N-methyl pyrazole deriva-
tive 8f was accomplished in a linear fashion from the commercially
available ethoxy-cyclopentenone 3 (Scheme 1). Addition of the
O
CO2Et
R1
i-iii
N
N
EtO
H
4
3
CO2H
R1
iv-v
N
N
H
5a-c, 8f
* Corresponding author.
Scheme 1. Reactions and conditions: (i) R1Li; (ii) tBuOK, diethyl oxalate; (iii)
E-mail address: jason_imbriglio@merck.com (J.E. Imbriglio).
NH2NH2–HCl; (iv) HCO2NH4, Pd–C; (v) LiOH.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.06.041

J. E. Imbriglio et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4472–4474
4473
desired alkyl lithium or the lithiated N-methyl pyrazole to 3 in-
O
O
i
stalled the desired C5-alkyl and N-methyl pyrazole moiety. Further
elaboration of the core to the pyrazole derivative 4 was achieved
via acylation with diethyl oxalate followed by condensation with
hydrazine–HCl. Transfer hydrogenation reduced the olefin and
saponification successfully converted the ester to the desired car-
boxylic acid to afford the C5-pyrazole derivatives 5a–c and 8f.
Synthesesof the C5-aryl-pyrazole-acids 8a–e were accomplished
via the readily available iodocyclopentenone 6 (Scheme 2). Suzuki
coupling of the corresponding aryl boronic acid to enone 6 afforded
the desired aryl-substituted cyclopentenone 7. Conversion of enone
7 to the desired pyrazole-acids was achieved, following previously
outlined conditions, via acylation of the enone with diethyl oxalate,
condensation with hydrazine–HCl, transfer hydrogenation, and a
final saponification.
The preparation of N-linked pyrazole and triazole derivatives
11a and 11b is outlined in Scheme 3. Treatment of commercially
available cyclopentenone 9 with either commercially available
pyrazole or triazole afforded the desired adduct 10. Following pre-
viously described conditions, ketone 10 was further elaborated to
the desired class of C5-substituted pyrazole-acids.
N
N
9
10
X
X= N, C
O
OH
ii-iv
N
X
N
N
N
H
11a,b
X= N, C
Scheme 3. Reactions and conditions: (i) pyrazole or triazole, 70 °C; (ii) tBuOK,
diethyl oxalate; (iii) NH2NH2–HCl; (iv) LiOH.
Table 1
Affinity of C5 substituted pyrazole-acids for GPR109a
As illustrated in Table 1, the in vitro affinities for this pyrazole-
acid series compared favorably with the similar class of pyrazole-
H
N
H
N
H
N
CO2H
N
N
N
tetrazoles. In this regard, n-propyl derivative 5a (0.25
0.38 M) showed good affinity on both the human receptor
(GPR109a, hNBA) and murine receptor (PUMA-G, mNBA), while
the branched alkyl derivatives 5b (0.99 M and 1.7 M) and 5c
(1.1 M and 1.3 M) showed only modest affinity for the niacin
receptor.
lM and
H
N
H
N
l
N
CO2H
N
N
R1
R1
N
N
N
N
1
2a
2b
5a-c, 8a-f, 11a,b
l
l
l
l
Further studies into the C5 phenyl series of molecules showed
parallel trends to the pyrazole-tetrazole class. As demonstrated
b
Compds
R1
IC50
(lM)
in Table 1, the phenyl substituted pyrazole-acid 8a (0.15
0.20 M) showed improved affinity for both mouse and human
receptors.
The 2,3,5-trifluoro analog 8b (0.03 M and 0.02 lM), showed
l
M and
mNBA
hNBA
0.14(0.14)c
1.5
l
1
—
—
0.14
1.2
0.07
0.25
0.99
1.1
2a
2b
5a
5b
5c
ent-2,3,5-F-Ph
n-Propyl
i-Propyl
0.08(4.0)c
0.38(0.75)c
l
excellent intrinsic affinity for GPR109a, and a marked improve-
ment over the pyrazole-tetrazole derivative 2b. However, despite
the promising intrinsic activity of compound 8b, when screened
in our competition binding assay in the presence of 4% human ser-
um, compound 8b showed an eightfold reduction in affinity for the
receptor. The intrinsic affinity of pyrazole-tetrazole derivative 2b
was similarly affected by the presence of serum. Concerned with
the role this serum shift effect may have on the in vivo efficacy,
our focus turned towards identifying a low-serum shifted agonist.
With this goal in mind, we proceeded to explore the C5-hetero-
aryl class of pyrazole-acids. Initial efforts, focused on a thiophene
replacement, demonstrated little improvement. The 2-thiophene
1.7(>1
1.3(>1
l
l
M)c
M)c
sec-Butyl
8a
8b
8c
8d
8e
8f
Ph
0.15
0.03
0.25
0.08
1.6
0.45
3.4
5.2
0.20(2.7)c
0.02(0.15)c
0.24(1.0)c
0.09(1.0)c
2.1(2.3)c
2,3,5-F-Ph
2-Thiophene
3-Thiophene
4-N-Methyl pyrazole
ent-5-N-Methyl pyrazole
N-Pyrazole
0.39(0.45)c
1.9(2.0)c
11a
11b
N-Triazole
4.0(5.3)c
a
b
c
Values are an average of two or greater. Individual assays.
[3H]-Nicotinic acid binding competition assay.
[3H]-Nicotinic acid binding competition assay with 4% human serum.
derivative 8c (0.25 lM and 0.24 lM), a surrogate to the phenyl
moiety, demonstrated only a modest boost in activity, when com-
pared to 2a. In addition, compound 8c demonstrated a further
reduction in affinity when assayed in the presence of human ser-
um. Similarly, while thiophene analog 8d (0.08 lM and 0.09 lM)
showed improved intrinsic affinity for GPR109a, when compared
with 2a, compound 8d also demonstrated reduced in vitro activity
when assayed in the presence of human serum.
We proceeded to explore the C5 N-methyl pyrazole derivatives.
While the 4-N-methyl pyrazole derivative, 8e (1.6 lM and 2.1 lM),
O
O
i
showed only modest intrinsic affinity for the niacin receptor, more
intriguing was the limited effect serum had on the compound’s
intrinsic affinity. Even more promising was the 5-N-methyl pyra-
I
R1
6
7
zole-acid 8f (0.45
affinity and nearly comparable activity in the presence of serum. Fi-
nally, theC-5-N-pyrazoleandN-triazolederivatives11a(3.4 Mand
1.9 M) and 11b (5.2 M and 4.0 M) demonstrated only modest
affinity for the receptor, despite a minimal serum shift effect.
In light of the promising in vitro activity for the series, we pro-
ceeded to investigate the ADME properties of select members of
the class. In this regard, the mouse pharmacokinetic (mPK) profiles
lM and 0.39 lM) which showed good intrinsic
CO2H
R1
ii-v
l
N
l
l
l
N
H
8a-e
Scheme 2. Reactions and conditions: (i) RB(OH)2, Pd(dppf)Cl2; (ii) tBuOK, diethyl
oxalate; (iii) NH2NH2–HCl; (iv) HCO2NH4, Pd–C; (v) LiOH.

4474
J. E. Imbriglio et al. / Bioorg. Med. Chem. Lett. 20 (2010) 4472–4474
Table 2
Vehicle, n=7
NA 30 mg/kg, n=13
8f 30 mg/kg, n=8
2b 30 mg/kg, n=8
Mousea pharmacokinetics of pyrazole-acids
c
Compds
Fb (%)
Clp (mL/kg/min)
Vdss (L/kg)
t1/2 (h)
80
60
40
20
0
Niacin
2b
8b
100
10
53
145
27
24
1.0
1.1
9.3
4.2
0.02
2.4
—
8f
27
86
2.3
a
b
c
C57BL/6-mice.
Dose: 1 mg/kg iv; 2 mg/kg po.
t1/2 = plasma half-life(0–8 h)
.
0
-10
-20
-30
-40
-50
-5
0
5
10
15
Time (min)
Figure 2. Mouse vasodilation (mVD).
(IP) for 15 min, three times the dose for FFA reduction. As illus-
trated in Figure 2, niacin administered in 13 mice at 30 mpk (IP)
showed an 80% change in perfusion,8 characteristic of a flushing re-
sponse in the mouse. In contrast, compound 8f showed no change
in perfusion under similar experimental conditions.
In summary, we have identified a new class of pyrazole-acids
that act as selective agonists of GPR109a. In particular, optimiza-
tion of the pyrazole-acid series resulted in the identification of
compound 8f, a potent, low-serum shift, and flush-free agonists
of GPR109a that demonstrated superior in vivo efficacy when com-
pared to previous members of the class. Further investigations are
currently underway.
Figure 1. Mouse pFFA reduction studies.
of lead candidates 8b, a compound with excellent intrinsic affinity
but an eightfold serum shift effect and compound 8f, a compound
with good intrinsic affinity and minimal serum-effect, were studied.
As illustrated in Table 2, both 8b and 8f showed mPK profiles
that compared favorably with niacin and pyrazole-tetrazole 2b.
The high affinity agonist 8b demonstrated good bioavailability
and low clearance when compared to niacin. Similarly, agonist 8f
with a promising in vitro profile and low-serum shift effect,
showed modest results across all parameters.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.06.041.
References and notes
1. Carlson, L. A. J. Int. Med. 2005, 258, 94.
2. Tavintharan, S.; Kashyap, M. L. Curr. Atheroscler. Rep. 2001, 3, 74.
3. Knopp, R. H. Am. J. Cardiol. 2000, 86, 51L.
Inan effort to understand theeffect thisserum shiftmightbe hav-
ing on the in vivo efficacy, we performed a head-to-head comparison
of compounds 2b and 8f in our mouse PD assay. In this regard, we
dosed compound 8f in our mouse plasma free fatty acid assay (pFFA)
and our mouse vasodilation assay (mVD). As illustrated in Figure 1,
six male C57 B1/6 mice were each dosed at 10 mpk (IP) for 15 min
with 8f and compared to mice dosed, 10 mpk (IP) of 2b, and
100 mpk (IP) with niacin and the characteristic reduction in plasma
free fatty acids was measured. In the case of compound 8f, the mice
that were treated showed a 41% reduction in plasma free fatty acids
at 10 mpk, compared to a 21% reduction in plasma free fatty acid
upon administration of 2b and a 38% reduction with niacin.
Having demonstrated the ability of agonist 8f to effectively low-
er plasma free fatty acids in our mouse PD model, further investi-
gations hinged on whether or not this class of agonists would elicit
a flushing response in our mouse vasodilation assay. With this goal
in mind, compound 8f was administered to eight mice at 30 mpk
4. For a discussion on the clinical use of the D2 receptor antagonist laropripant as a
means of suppressing the nicotinic acid-induced vasodilation in humans, refer
to: Paolini, J. F.; Mitchel, Y. B.; Reyes, R.; Kher, U.; Lai, E.; Watson, D. J.; Norquist,
J. M.; Meehan, A. G.; Bays, H. E.; Davidson, M.; Ballantyne, C. M. Am. J. Cardiol.
2008, 101, 625.
5. (a) Lorenzen, A.; Stannek, C.; Lang, H.; Andrianov, V.; Kalvinsh, I.; Schwabe, U.
Mol. Pharmacol. 2001, 59, 349; (b) Wise, A.; Foord, S. M.; Fraser, N. J.; Barnes, A.
A.; Elshourbagy, N.; Eilert, M.; Ignar, D. M.; Murdock, P. R.; Steplewski, K.; Green,
A.; Brown, A. J.; Dowell, S. J.; Szekeres, P. G.; Hassall, D. G.; Marshall, F. H.;
Wilson, S.; Pike, N. B. J. Biol. Chem. 2003, 278, 9869; (c) Soga, T.; Kamohara, M.;
Takasaki, J. M.; Shun-Ichiro, S.; Tetsu, O.; Takahide, H.; Hideki, M. A.;
Matsushime, H.; Furuichi, K. Biochem. Biophys. Res. Commun. 2003, 303, 364.
6. Semple, G.; Skinner, P. J.; Gharbaoui, T.; Shin, Y. J.; Jung, J. K.; Cherrier, M. C.;
Webb, P. J.; Tamura, S. Y.; Boatman, P. D.; Sage, C. R.; Schrader, T. O.; Chen, R.;
Colletti, S. L.; Tata, J. R.; Waters, G.; Cheng, K.; Taggart, A. K.; Cai, T. Q.; Jane, E. C.;
Behan, D. P.; Connolly, D. T.; Richman, J. G. J. Med. Chem. 2008, 51, 5105.
7. Imbriglio, J. E.; Chang, S.; Liang, R.; Raghavan, S.; Schmidt, D.; Smenton, A.; Tria,
S.; Schrader, T. O.; Jung, J. K.; Esser, C.; Taggart, A. K. P.; Cheng, K.; Carballo-Jane,
E.; Waters, M. G.; Tata, J. R.; Colletti, S. L. Bioorg. Med. Chem. Lett. 2009, 2121.
8. Measured using a Periscan PIMII Laser Doppler Perfusion Imager system.