Identification of a series of PPARγ/δ dual agonists via solid-Phase parallel synthesis

Article abstract of DOI:10.1016/S0960-894X(01)00596-0

We have developed a general solid-phase synthesis for identification of PPAR ligands. Synthesis of a 480-member library led to the identification of a potent PPARγ/δ dual agonist 23. Compound 23 showed good plasma exposure in rats and demonstrated antihyp

Full text of DOI:10.1016/S0960-894X(01)00596-0

Bioorganic & Medicinal Chemistry Letters 11 (2001) 2959–2962
Identification of a Series of PPARꢀ/ꢁ Dual Agonists Via
Solid-Phase Parallel Synthesis
Kevin G. Liu,a,* Millard H. Lambert,a Lisa M. Leesnitzer,a William Oliver, Jr.,b
a
Ronda J. Ott,b Kelli D. Plunket,a LudwigW. Stuart, Peter J. Brown,a
Timothy M. Willsona and Daniel D. Sternbachb,*
aNuclear Receptor Discovery Research, GlaxoSmithKline, Research Triangle Park, NC, 27709, USA
bMetabolic Diseases Drug Discovery, GlaxoSmithKline, Research Triangle Park, NC, 27709, USA
Received 25 July 2001; accepted 30 August 2001
Abstract—We have developed a general solid-phase synthesis for identification of PPAR ligands. Synthesis of a 480-member library
led to the identification of a potent PPARg/d dual agonist 23. Compound 23 showed good plasma exposure in rats and demon-
strated antihyperglycemic and antihyperlipidemic efficacy in diabetic fatty Zucker rats. # 2001 Elsevier Science Ltd. All rights
reserved.
The metabolic syndrome X, which consists of a cluster-
ingof several metabolic risk factors in a single patient,
contributes significantly to increased mortality.1,2 The
major components of the metabolic syndrome X include
dyslipidemia (characterized by the lipid triad of low
levels of HDL-c and high levels of triglycerides and
LDL-c), insulin resistance, obesity, and hypertension.
Although established therapies are available to treat
these risk factors individually (e.g., statins and fibrates
for dyslipidemia and metformin and glitazones for
insulin resistance), no single drug is yet available to treat
the multiple risk factors of the metabolic syndrome X.
known class of drugmolecules. However, we recently
reported a potent and subtype-selective PPARd agonist,
GW501516, which has therapeutic potential for treat-
ment of dyslipidemia.11 In insulin-resistant obese rhesus
monkeys, GW501516 increased HDL-c, decreased fast-
ingtriglycerides, and decreased VLDL in a dose-depen-
dent manner over the treatment period, relative to
vehicle-treated animals. These data suggest that PPARd
is a new molecular target for treatment of dyslipidemia.
Hence, PPARg/d dual agonists may provide an efficient
treatment for metabolic syndrome X by providingdual
control of glucose and lipid metabolism. As part of our
ongoing research in the identification of structurally
novel nuclear receptor ligands, we report the identifica-
tion of a PPARg/d dual agonist through solid-phase
parallel synthesis of a 480-member library of lipophilic
carboxylic acids.
Compelling evidence suggests that the hyperlipidemic
effects of the fibrate drugs and the antidiabetic effects of
the glitazones are due to activation of the a and g sub-
types, respectively, of the peroxisome proliferator-acti-
vated receptor (PPAR).3ꢀ7 The PPARs are orphan
receptors that belongto the nuclear receptor super-
family of ligand-activated transcription factors. Identi-
fication and development of PPARa/g dual agonists for
treatment of the metabolic syndrome X has therefore
become one of the major efforts in the pharmaceutical
industry.8ꢀ10 PPARd—the third subtype in the PPAR
family—has not been identified as a receptor for any
The general solid-phase synthesis of target molecules 1
and 2 is depicted in Scheme 1. The molecules have three
points of diversity: R1, R2, and the headgroup. The
headgroups have a carboxylic acid group, central
phenyl ring, and a linker to the urea or amide tail. This
general solid-phase synthesis is a modified version of
our previously published synthesis.12 In our previous
strategy, the R1 was introduced by borane reduction of
the amides. In this new approach, R1 is introduced
under milder and more convenient solid-phase Mitsu-
nobu reaction conditions usingFukuyama’s 2,4-dini-
*Correspondingauthors. Fax: +1-858-558-4859; e-mail: kevin_liu@
stromix.com (K. G. Liu); dds3687@gsk.com (D. D. Sternbach).
0960-894X/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00596-0

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K. G. Liu et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2959–2962
Scheme 1. Reagents and conditions: (a) 1,3-dimethyl-2-fluoropyridinium 4-toluenesulfonate (3 equiv relative to the resin), 2,6-lutidine (9 equiv
relative to the resin), SASRIN resin (0.89 mmol/g), CH2Cl2, rt, overnight; (b) R1OH (10 equiv), PPh3 (10 equiv), diisopropyl azodicarboxylate
(DIAD, 10 equiv), THF, rt, overnight; (c) mercaptoacetic acid (10 equiv), NEt3 (10 equiv), CH2Cl2, rt, 1.5 h; (d) R2NCO (10 equiv), DMF, rt,
overnight; (e) R2COOH (10 equiv), O-(7-azabenzotriazol-1-yl)-N,N,N0,N0-tetramethyluronium hexafluorophosphate (HATU, 10 equiv), iPr2NEt (10
equiv), rt, overnight; (f) 10% TFA/CH2Cl2 (v/v), rt, 30 min.
trobenzenesulfonamide chemistry.13 The synthesis starts
with loadingof the 2,4-dinitrobenenesulfonyl-deriva-
tized headgroup (vide infra) onto SASRIN resin
(0.89 mmol/g) with Mukaiyama’s reagent (1,3-dimethyl-
2-fluoropyridinium 4-toluenesulfonate)14 to provide 4.
Quantitative loadingwas achieved when more than
three equivalents of the 2,4-dinitrobenzenesulfonyl-
derivatized headgroup was used. Several other reaction
conditions (e.g., carbodiimides) for loading the starting
material to the support were also explored, but all these
conditions failed to provide high yields.
3a–c (Schemes 2–4) chosen for the library production
have been shown or hypothesized to provide good
potency on PPARd based on previous SAR, crystal
structures, and molecular modeling.16 Synthesis of the
2,4-dinitrobenzenesulfonyl-derivatized headgroups is
depicted in Schemes 2–4. The alcohol, isocyanate, and
carboxylic acid monomers17 selected for the library were
all commercially available except the alcohol monomer
2-cyclopropyl-4-hydroxymethylphenyl-1,2-4-oxadiazole
(monomers: R1OH, f). These monomers were selected
based on previous SAR, molecular modeling, and syn-
thetic compatibility.
The efficient loadingis critical in order to ensure high
purity of the final products 1 and 2 because it was found
that the free hydroxyl groups left on the solid support
could react 15 with the sulfonamide moiety at other sites
on the resin duringthe subsequent Mitsunobu reaction,
which ultimately leads to inseparable impurities after
cleavage from the resin. Mitsunobu reaction between 4
and the desired alcohols provided 5 with different R1
functionality. After removal of the 2,4-dini-
trobenzenesulfonyl group with mecaptoacetic acid, the
secondary amines 6 were then reacted with either iso-
cyanates or carboxylic acids to provide support-bound
compounds 7 and support-bound compounds 8, respec-
tively, which upon cleavage with TFA/CH2Cl2 furnished
the targeted compounds 1 and 2.
The library was produced in a spatially-separated for-
mat usingRobins plates with 50 mgof resin in each
well. For each headgroup, 10 alcohols and eight iso-
cyanates or eight carboxylic acids were used. Totally,
480 compounds (240 compounds 1 and 240 compounds
2) were synthesized via this methodology. All the final
compounds were analyzed by LC–MS and the average
purity was greater than 70%.
The library was screened against all three human PPAR
subtypes in a SPA bindingassay. 18 Based on the binding
assay results, 23 compounds were identified with >50%
displacement of radioligand [3H]-GW2433 at 1 mM in
the PPARd bindingassay. Followingscreeningof these
compounds in a cell-based assay,19 a subset of six com-
pounds was remade in solution phase for confirmation
of activity and the functional data is depicted in Table 1.
From this effort we identified a potent and selective dual
PPARg/d dual agonist 23 (Fig. 1). Compound 23 has
The previous SAR of PPAR ligands has shown that the
structure of the headgroup is critical in order to achieve
good affinity to all three PPAR subtypes, with PPARd
beingthe most difficult one to achieve. The headgroups
Scheme 2. Reagents and conditions: (a) CH3COCl, MeOH, reflux, overnight; (b) dimethylthiocarbamoyl chloride, 4-dimethylamino pyridine
(DMAP), NEt3, 1,4-dioxane, reflux, 4 h; (c) tetradecane, 250 ꢁC, 5 h, 83% (3 steps); (d) NaOMe, MeOH; (e) tert-butyl N-(2-(p-tosyloxy)ethyl)-car-
bamate (prepared from tert-butyl N-(2-hydroxyethyl)-carbamate and tosyl chloride), MeOH, rt, overnight, 77% (2 steps); (f) 4 M HCl/1,4-dioxane,
rt, 2 h; (g) Na2CO3; (h) 2,4-dinitrobenzenesulfonyl chloride, NEt3, CH2Cl2, 0 ꢁC, 1 h, 52% (3 steps); (i) LiOH, THF/H2O/MeOH (4:1:0.4), 95%.

K. G. Liu et al. / Bioorg. Med. Chem. Lett. 11 (2001) 2959–2962
2961
Scheme 3. Reagents and conditions: (a) 4-iodophenol, Pd2(dba)3, tri-O-tolylphospine, NEt3, pyridine, 55%; (b) benzyl N-(2-(p-tosyloxy)ethyl)-car-
bamate (prepared from benzyl N-(2-hydroxyethyl)-carbamate and tosyl chloride), Cs2CO3, DMF, rt, overnight, 50%; (c) H2, 10% Pd/C, 98%; (d)
2,4-dinitrobenzenesulfonyl chloride, NEt3, CH2Cl2, 0 ꢁC, 1 h, 60%; (e) TFA/CH2Cl2, rt, 2 h, 100%.
Scheme 4. Reagents and conditions: (a) 1-methyl-1-trichloromethylethanol, NaOH, acetone, 99%; (b) isobutylene, H2SO4, CH2Cl2, 70%; (c) N-
allylphthalimide, Pd(OAc)2, tri-O-tolylphospine, iPr2NEt, CH3CN, 60%; (d) H2, 10% Pd/C, 95%; (e) EtOH, NH2NH2, reflux, 88%; (f) 2,4-dini-
trobenzenesulfonyl chloride, NEt3, CH2Cl2, 0 ꢁC, 1 h, 62%; (g) TFA/CH2Cl2, rt, 2 h, 100%.
Table 1. Transient transfectiona data of the library remakes
Compd
Headgroup
R1OH
R2NCO
R2COOH
EC50 (nM)
hPPARg
EC50 (nM)
hPPARd
EC50 (nM)
hPPARa
18
19
20
21
22
23
3c
3c
3c
3c
3c
3c
i
i
f
f
f
i
c
0.5
30
81
170
320
4
160
93
430
1000
1000
19
230
710
620
230
59
d
e
d
a
e
620
aCompounds were assayed for agonist activity on PPAR-GAL4 chimeric receptors in transiently transfected CV-1 cells as described;19 EC50=the
concentration of test compound that gave 50% of the maximal reporter activity. All data ꢂ15% (n=3).
sub-nanomolar potency against PPARg and PPARd
and has greater than 30-fold selectivity versus PPARa in
both bindingand functional assays. Compound 23 was
also tested against the three murine PPAR subtypes in
the functional assay and showed EC50 of 28 nM, 19 nM,
and >1000 nM on murine PPARg, PPARd, and
PPARa, respectively. The in vivo exposure of 23 was
evaluated in rats (n=3) with an oral dose of 3 mg/kg. At
0.5, 1.0, and 2.0 h, the mean plasma concentrations of
23 were found to be 373, 722, and 524 ng/mL, respec-
tively. The in vivo antihyperglycemic and antihyperlipi-
demic efficacy of 23 were then evaluated in male ZDF
rats (n=6). When dosed orally at 30 mg/kg bid, the
compound reduced plasma glucose by 47% and serum
triglyerides by 51% of the vehicle animals after 7 days
of administration. Duringthe same period of adminis-
tration, compound 23 increased the HDL-c by 24%
compared to the vehicle animals.
In summary, we have developed a general solid-phase
synthesis of lipophilic carboxylic acids that led to the
identification of a potent PPARg/d dual agonist. Com-
pounds with this dual receptor activity may provide a
new approach to the development of drugs for the
metabolic syndrome X.
Acknowledgements
The authors would like to thank Rodolfo Cadilla for
providingstartingmaterials for resynthesis of active
compounds and Brad Henke for valuable suggestions
and discussions duringthe manuscript preparation.
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Figure 1. A PPARg/d dual agonist.

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