1520
M. L. Sznaidman et al. / Bioorg. Med. Chem. Lett. 13 (2003) 1517–1521
EC50=8.8, >10, 0.03, PPARa, PPARg, and PPARd,
respectively).
When dosed to insulin-resistant middle-aged rhesus mon-
keys, 7k causes a dramatic dose-dependent rise in serum
HDLc while lowering the levels of LDLc, fasting trigly-
cerides, and fasting insulin.16 At the cellular level, com-
pound 7k increased expression of the reverse cholesterol
transporter ATP-binding cassette A1 (ABCA1) and
induced apolipoprotein A1-specific cholesterol efflux.
Conclusions
We were able to identify the first truly selective PPARd
agonists, GW501516 (7k) and GW0742 (7l), starting
with high-throughput screening, then using combina-
torial chemistry to develop small focused libraries, and
finally using structure guided lead optimization. These
compounds will be valuable tools for determining the
biological activity of the PPARd receptor and as poten-
tial therapeutic agents for the treatment of diseases
associated with raised serum triglycerides and low levels
of HDLc.
Figure 1. X-ray data showing the binding interactions of cinnamic
acid 7c to the hPPARd receptor.
were potent PPARd agonists in vitro, they were unsui-
table for use as chemical tools in vivo.
The phenyl acetic acid derivative 7a is unable to
undergo b-oxidation but its weak PPARd activity
(EC50=1.77 mM) and the fact that crystallographic
studies13 indicated that a two-atom spacer between the
carboxylic acid and the aryl ring would be preferred led
us to explore other alternatives. Replacement of the
propionic side chain of 7e with an isosteric oxyacetic
acid side chain in 7g would also serve to block b-oxida-
tion. Unfortunately, 7g was significantly less potent on
PPARd (0.47 mM) and showed no selectivity over
PPARg.
Acknowledgements
We gratefully acknowledge Kim Adkison, Kelli Plun-
ket, Raymond Merrihew and Lisa Leesnitzer, for their
help in pharmacokinetics, transient transfection and
binding determinations.
Early modeling studies,15 later confirmed by crystal-
lographic studies,13 showed that there is a lipophilic
pocket in the PPARd ligand-binding domain that could
accommodate small substituents at the ortho position of
the aromatic ring. The enhancement of PPARd activity
by methyl substitution at the ortho position can be seen
by comparing 7d with 7b (3-fold enhancement) and 7h
with 7g (15-fold enhancement). Comparable effects were
observed in the binding assay. Notably, the selectivity
versus PPARa and PPARg remained high.
References and Notes
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Replacement of the oxygen closest to the oxazole ring
with sulfur, led to compound 7i which showed similar
cellular PPARd activity (PPARd EC50=0.42 mM) and
better selectivity against PPARg and PPARa when
compared to 7g (PPARd EC50=0.47 mM). Combining
both of these modifications led to compound 7j, which
showed
a dramatic increase in PPARd activity
(EC50=0.006 mM) and selectivity (ꢂ400-fold against
PPARa and 250-fold against PPARg). Replacing oxa-
zole with thiazole (compound 7k) showed further
improvement in PPARd activity (EC50=0.001 mM) as
well as selectivity (1100 against PPARa, and 800 against
PPARg). Compound 7k also showed excellent selectiv-
ity on the murine receptors (EC50=2.5, 1.0, 0.02 mM for
PPARa, PPARg, and PPARd, respectively) and against
other nuclear or non-nuclear receptors.16 Finally com-
pound 7l demonstrated that addition of a fluorine ortho
to the CF3 group, maintained potency and selectivity on
the human and murine receptors (murine PPAR
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