From partial to full agonism: Identification of a novel 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole as a full agonist of the human GPR119 receptor

Article abstract of DOI:10.1016/j.bmcl.2012.10.119

A novel GPR119 agonist based on the 2,4,5,6-tetrahydropyrrolo[3,4-c] pyrazole scaffold was designed through lead optimization starting from pyrazole-based GPR119 agonist 1. The design is centered on the conformational restriction of the core scaffold, while minimizing the change in spatial relationships of two key pharmacophoric elements (piperidine-carbamate and aryl sulfone).

Full text of DOI:10.1016/j.bmcl.2012.10.119

Bioorganic & Medicinal Chemistry Letters 23 (2013) 194–197
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
From partial to full agonism: Identification of a novel 2,4,5,6-tetrahydropyr-
rolo[3,4-c]pyrazole as a full agonist of the human GPR119 receptor
⇑
Kentaro Futatsugi , Vincent Mascitti, Cristiano R. W. Guimarães, Nao Morishita, Cuiman Cai,
Michael P. DeNinno, Hua Gao, Michael D. Hamilton, Richard Hank, Anthony R. Harris, Daniel W. Kung,
Sophie Y. Lavergne, Bruce A. Lefker, Michael G. Lopaze, Kim F. McClure, Michael J. Munchhof,
Cathy Preville, Ralph P. Robinson, Stephen W. Wright, Paul D. Bonin, Peter Cornelius,
Yue Chen, Amit S. Kalgutkar
Pfizer Worldwide Research & Development, Groton Laboratories, Eastern Point Rd, Groton, CT 06340, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel GPR119 agonist based on the 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole scaffold was designed
through lead optimization starting from pyrazole-based GPR119 agonist 1. The design is centered on
the conformational restriction of the core scaffold, while minimizing the change in spatial relationships
of two key pharmacophoric elements (piperidine-carbamate and aryl sulfone).
Ó 2012 Elsevier Ltd. All rights reserved.
Received 30 August 2012
Revised 19 October 2012
Accepted 29 October 2012
Available online 5 November 2012
Keywords:
GPR119
Intrinsic activity
Conformational restriction
GPR119 is a target of significant interest to the pharmaceutical
industry for the treatment of diabetes based on a recent patent
analysis of the therapeutic area.1,2 Indeed, there has been a large
increase in the number of composition of matter applications for
GPR119 agonists over the past 5 years. Interest in targeting this
class A G-protein coupled receptor (GPCR) stems from the potential
for agonists to provide improved glucose control with a low risk of
hypoglycemia.3,4 In addition, recent data suggest that the preserva-
tion of beta cell function may also be possible through the activa-
tion of this receptor.5,6 Oleoylethanolamide (OEA) has been
reported to be the endogenous agonist for this receptor,7 although
a recent report shows that other endogenous lipids may act as ago-
nists, including monoacylglycerols (MAG).8 While OEA has helped
define some of the potential benefits of GPR119 activation, studies
in transgenic mice suggest that not all of these effects are GPR119
mediated.9 Nevertheless, there are a number of small molecule
agonists described that show antihyperglycemic effects in ro-
dents.10–21 Most of these compounds, like most small molecule
GPR119 agonists reported show two key structural elements: (i)
a piperidine-carbamate group or its isostere, and (ii) an aryl sul-
fone group or its isostere (Fig. 1).
As part of our systematic approach to this target we also evaluated
conformational restriction of the core region of the molecule. The
proving ground for this effort was in a series of pyrazole analogs
exemplified by compound 1 (Fig. 2). Herein we describe the SAR
of these pyrazole-based compounds and the identification of a no-
vel GPR119 agonist centered on a rigid 2,4,5,6-tetrahydropyrrol-
o[3,4-c]pyrazole scaffold.
The pyrazole structure in 1 derives from our emphasis on iden-
tifying a polar core to provide flexibility in the balancing of phar-
macology and ADME properties. While compound
1 shows
modest potency with partial agonism in our cAMP assay,23 by vir-
tue of its relative polarity (LogD = 2.3)24 it shows reasonable hu-
man microsomal stability. In addition to addressing the
deficiency in both EC50 and intrinsic activity, our optimization ef-
fort focused on the embedment of the aniline structural motif to
mitigate potential reactive metabolite formation and idiosyncratic
toxicity risks.25 Based on these objectives, the medicinal chemistry
effort commenced with the structural modification of the piperi-
dine-carbamate group and 2-fluoro-4-methylsulfonyl aniline
group.
Analogs based on 1 were synthesized through the general se-
quence described in Scheme 1. Starting from the known intermedi-
ate 4,26 reductive amination with aromatic primary amines 2 and 3
afforded the corresponding secondary amine derivatives in good
yields. Oxidation of the thioether group with m-CPBA, cleavage of
the Boc group and subsequent reactions with the various chloro-
formates and heteroaromatic halides furnished analogs 5–8.
Recently we disclosed the importance of the conformational
disposition of the piperidine-carbamate for GPR119 activation.22
⇑
Corresponding author. Tel.: +1 6175513268; fax: +1 6175513084.
E-mail address: Kentaro.futatsugi@pfizer.com (K. Futatsugi).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.10.119

K. Futatsugi et al. / Bioorg. Med. Chem. Lett. 23 (2013) 194–197
195
Table 1
SAR around 1
Figure 1. General structural features of GPR119 agonists.
Compd R1
A
R2
EC50 SDa
(nM)
IA SDa
(%)
LogD24
1
5
6
7
8
F
Me
F
F
F
CH CO2iPr
CO2iPr
CH CO2iBu
CH CO2cBu
CH 5-Et-2-
Pyrimidyl
181 76
>10000
240 82
462 135
47 27
41
6
2.3
1.6
2.8
2.5
3.0
N
N.D.b
24
42
43
3
9
3
a
Values are arithmetic means of at least three experiments. See Ref. 22 for
details.
b
N.D. = not determined.
Figure 2. In vitro profile of 1.
Scheme 1. Synthesis of pyrazole-based GPR119 agonists. Reagents and conditions:
(a) 2 or 3 (1 equiv), NaBH(OAc)3 (2 equiv), AcOH (2.2 equiv), DCE, rt, 92% (from 2),
71% (from 3); (b) m-CPBA (2.5 equiv), DCM, rt, 85% (from 2), 48% (from 3); (c) HCl/
MeOH or AcOEt, rt, followed by RCOCl (1 equiv), NMM/DCM or 2-chloro-5-
ethylpyrimidine (1 equiv), DIPEA (4 equiv), DMSO, 120 °C, 31–62%.
Figure 3. Superposition of 9 and 10.
As shown in Table 1, changes made to the carbamate or aro-
matic sulfone had little impact on the intrinsic activity of these
compounds. The attempt to replace the aniline motif in 1 with
an aminopyridine derivative 5 led to a significant decrease in po-
tency. Modifications to the carbamate group varied the potency
with minimal impact on the intrinsic activity. The lowest EC50 in
this compound set was achieved when the iPr carbamate group
was replaced by 5-Et-2-pyrimidyl group (8), however, again no in-
crease in intrinsic activity was achieved.
Based on the above results, we next turned our attention to the
modification of the central core/spacer region. It was hypothesized
that restriction of free rotation around the –CH2NH– bond might
lead to potency gains and/or increases in intrinsic activity.
To this end, compound 9 possessing the 2,4,5,6-tetrahydropyr-
rolo[3,4-c]pyrazole scaffold was designed in order to highly con-
strain the positions available for the key pharmacophoric
elements, as shown in Figure 3. Parallel to this effort, a ‘flipped’
version based on this bicyclic core was designed to embed the ani-
line structural motif from 9 (Fig. 3). This design was driven by the
hypothesis that the core/spacer functions to position the two key
pharmacophoric elements (piperidine-carbamate and aryl sul-
fone). Unsurprisingly, the superposition of 9 and 10 after global
minimization27 supported that the 2,4,5,6-tetrahydropyrrolo[3,4-
c]pyrazole scaffold positions the two key pharmacophoric ele-
ments of 9 and 10 in similar space.
Analogs based on this hypothesis were prepared as outlined in
Scheme 2. The synthesis of 10, 13 and 14 started from the SNAr reac-
tion of N-Boc 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole, prepared
from the commercially available dihydrochloride salt 11, and 1,2-
difluoro-4-(methylsulfonyl)benzene, to afford a ꢀ1:1 mixture of
N-1 and N-2 adducts. After silica gel column chromatography, the
desired N-1 adduct 12 was obtained.28 Boc cleavage, followed by
reductive amination with various piperidone derivatives furnished
analogs 10 and 13. The corresponding N-oxide 14 was also synthe-
sized by treating 13 with m-CPBA. Compound 9 was synthesized
analogously through SNAr reaction of 11 with 1,2-difluoro-4-(meth-
ylsulfonyl)benzene and subsequent SN2 reaction with isopropyl 4-
(methylsulfonyloxy)piperidine-1-carboxylate.
The results obtained from these core modifications are summa-
rized in Table 2. Conformationally restricted analog 9 showed com-
parable potency to the lead pyrazole 1 with similar intrinsic
activity, suggesting that this mode of conformational restriction
is sub-optimal to elicit a full agonist response. In contrast, a
significant increase in intrinsic activity was achieved when the
‘flipped’ core C was examined, albeit with a decrease in potency

196
K. Futatsugi et al. / Bioorg. Med. Chem. Lett. 23 (2013) 194–197
With a full agonist 10 in hand, we next focused on potency opti-
mization. Based on our earlier results, it was hypothesized that
replacement of the iPr carbamate group with a 5-Et-2-pyrimidyl
group might increase potency. This transformation indeed led to
the identification of 13 with increased potency relative to 10 while
maintaining high intrinsic activity. Thus, the compound 13 had
achieved our two initial objectives: (i) increase both potency and
intrinsic activity, and (ii) embed the aniline structural motif start-
ing from the lead compound 1. Further in vitro profiling revealed
that 13 demonstrated modest metabolic stability in human liver
microsome (HLM) despite the moderate increase in logD, possibly
as a result of its decreased flexibility. An attempt to further reduce
intrinsic clearance of 13 by preparing the corresponding amine N-
oxide 14, with significantly reduced logD, led to a decrease in po-
tency, while clearance was improved as anticipated.
In conclusion, a series of pyrazole-based GPR119 agonists were
designed and characterized. Starting from a partial agonist 1, a no-
vel and potent GPR119 full agonist 13 was identified through a
conformational restriction-core flipping strategy. The present work
highlights the importance of the core optimization as a way to eli-
cit the desired functional response. While compound 13 repre-
sented a novel lead that formed the basis of further work, 13 was
roughly 10-fold less potent than exemplars from other series
working in our laboratory. In order to deliver a viable clinical agent
from this series, further strategies to increase potency will be
required.
Scheme 2. Synthesis of 9, 10, 13 and 14. Reagents and conditions: (a) 1,2-difluoro-
4-(methylsulfonyl)benzene (1 equiv), DIPEA (4 equiv), DMSO, 100 °C, followed by
isopropyl
4-(methylsulfonyloxy)piperidine-1-carboxylate
(2 equiv),
Cs2CO3
(4 equiv), DMSO, 100 °C, 23%; (b) Boc2O (1 equiv), DIPEA (3 equiv), DCM/MeOH,
rt, followed by 1,2-difluoro-4-(methylsulfonyl)benzene (1.5 equiv), NaHMDS
(2 equiv), THF, microwave, 100 °C, 35%; (c) HCl in AcOEt, rt, 77%; (d) NaBH(OAc)3
(2 equiv), ketone (1 equiv), AcOH (1.2 equiv), DCE, rt, 16% (for 10), 41% (for 13); (e)
m-CPBA (2 equiv), DCM, rt, 56%.
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Compd Core
R
EC50 SDa
(nM)
IA SDa
(%)
LogD24 HLM CLint
(lL/
min/mg)
1
8
9
10
13b
14
A
A
B
C
C
D
I
II
I
I
II
181 76
47 27
260 161
864 478
83 14
41
43
48
105
118
6
3
7
7
9
2.3
3
3.2
2.2
2.9
1.1
9.7
148
36.1
10.5
23
II 498 255
107 10
9.8
a
Values are means of at least three experiments. See Ref. 22 for details.
Tested as hydrochloride salt.
b
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Morgan, M.; Chen, W. C.; Sebring, K.; Chu, Z. L.; Leonard, J. N.; Al-Shamma, H.;
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(compound 10, Table 2). The core flipping from 9 to 10 leads to the
creation of a sp3-hybridized weakly basic nitrogen atom29 directly
connected to the piperidine-carbamate group. The profound effect
on intrinsic activity of 10 could be a result of the subtle change in
spatial relationships of the two key pharmacophoric elements
(piperidine-carbamate and aromatic sulfone).30

K. Futatsugi et al. / Bioorg. Med. Chem. Lett. 23 (2013) 194–197
197
20. Negoro, K.; Yonetoku, Y.; Misawa-Mukai, H.; Hamaguchi, W.; Maruyama, T.;
24. LogD (pH = 7.4) determined by shake flask method.
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J. A.; Laber, D.; Leach, A. G.; Macfaul, P. A.; McKerrecher, D.; Pickup, A.;
Schofield, P.; Svensson, P. H.; Sorme, P.; Teague, J. J. Med. Chem. 2012, 55, 5361.
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Samp, L.; Lefker, B. A.; Futatsugi, K.; Kung, D.; Bonin, P. D.; Cornelius, P.; Wang,
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23. The intrinsic activity is the percent of maximal activity of the test compound
25. Kalgutkar, A. S.; Soglia, J. R. Expert Opin. Drug. Metab. Toxicol. 2005, 1, 91.
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C.; Hierl, M.; Huang, L.; Janosky, B.; Knop, J.; Malmberg, A.; McDermott, J. S.;
Nguyen, H. Q.; Springer, S. K.; Waldon, D.; Woodin, K.; McDonough, S. I. Bioorg.
Med. Chem. Lett. 2008, 18, 5209.
27. A conformational analysis of 9 and 10 was performed using OPLS_2005 and the
GB/SA solvation model. Few low energy conformations were selected and
further refined using LMP2/6-311G⁄⁄ with solvent effect (water).
28. N-1 and N-2 Regio-isomers were assigned based on 1H–19F NOE and 1H–13C-
HMBC experiments.
relative to the activity of
a
standard GPR119 agonist, 4-[[6-[(2-fluoro-4
29. Measured basic pKa = 6.5.
methylsulfonylphenyl)amino]pyrimidin-4-yl]oxy]piperidine-1-carboxylic acid
isopropyl ester (WO2005121121), or (S)-1-methylcyclopropyl 4-(1-fluoro-2-
(2-(2,3,6 trifluorophenyl)acetamido)ethyl)piperidine-1-carboxylate (Bioorg.
30. MCMM conformational search using Batchmin in water indicates that there are
a few axial conformers of the piperidine ring within 5 kcal/mol from the lowest
energy equatrial conformer for compound 10, while no axial conformers were
found for compound 9. The presence of these axial conformers may contribute
to the increase in intrinsic activity of compound 10 and its related analogues.
For the importance of the axial conformation of the piperidine ring in GPR119
agonism, see Ref 22.
Med. Chem. Lett. 2011, 21, 1306) at a final concentration of 10 lM. Both
standards produced a level of cAMP accumulation that was comparable to the
maximum level of cAMP produced by the putative native GPR119 ligand
oleoylethanolamide.