Design, synthesis and evaluation of substituted phenylpropanoic acid derivatives as peroxisome proliferator-activated receptor (PPAR) activators: Novel human PPARα-selective activators

Article abstract of DOI:10.1016/S0960-894X(01)00672-2

A series of substituted phenylpropanoic acid derivatives was prepared as part of a search for subtype-selective human peroxisome proliferator-activated receptor (PPAR) activators. Structure-activity relationship studies indicated that the substituent at the α-position of the carboxyl group plays a key role in determining the potency and the selectivity for PPAR transactivation.

Full text of DOI:10.1016/S0960-894X(01)00672-2

Bioorganic & Medicinal Chemistry Letters 12 (2002) 77–80
Design, Synthesis and Evaluation of Substituted Phenylpropanoic
Acid Derivatives as Peroxisome Proliferator-Activated Receptor
(PPAR) Activators:Novel Human PPAR ꢀ-Selective Activators
Hiroyuki Miyachi,* Masahiro Nomura, Takahiro Tanase, Yukie Takahashi,
Tomohiro Ide, Masaki Tsunoda, Koji Murakami and Katsuya Awano
Discovery Research Laboratories, Kyorin Pharmaceutical Co., Ltd., 2399-1 Mitarai, Nogi-machi,
Shimotsuga-gun, Tochigi 329-0114, Japan
Received 18 August 2001; accepted 5 October 2001
Abstract—A series of substituted phenylpropanoic acid derivatives was prepared as part of a search for subtype-selective human
peroxisome proliferator-activated receptor (PPAR) activators. Structure–activity relationship studies indicated that the substituent
at the a-position of the carboxyl group plays a key role in determining the potency and the selectivity for PPAR transactivation.
# 2001 Elsevier Science Ltd. All rights reserved.
Introduction
Fibrate-class antihyperlipidemic drugs, such as clofi-
brate, bezafibrate, and fenofibrate (Chart 1), decrease
serum triglyceride and increase high-density lipoprotein
in humans.6 The exact molecular mechanism(s) of
action of these drugs are not known, though recent
molecular-pharmacological studies demonstrated that
fibrates not only activate, but also bind to PPARs.7
Although fibrates are ligands or activators of PPARs,
their affinity is weak and their subtype-selectivity is
poor.
The peroxisome proliferator-activated receptor (PPAR)
family of nuclear hormone receptors (NR1C’s) is het-
erogeneous, and its members have been classified into
three subtypes encoded by separate genes: PPARa
(NR1C1), PPARd (NR1C2), (also known as PPARb,
NUCI, FAAR) and PPARg (NR1C3).1 Each of the
PPAR subtypes appears to be differentially expressed in
a tissue-specific manner, and they play pivotal roles in
lipid and lipoprotein homeostasis. Upon ligand binding,
PPARs regulate specific gene expression by binding to
specific consensus DNA sequences, termed PPRE (per-
oxisome proliferator responsive element),2 which are
located in the regulatory regions of the target genes,
after heterodimerization with another nuclear receptor,
retinoid X receptor (RXR).3
Therefore, more potent and selective activators of
PPARa, especially human PPARa (fibrates exhibit spe-
cies-dependent PPARa transactivation, for example
fibrates are more potent activators of murine PPARa
than human PPARa8) are expected to have superior
therapeutic utility for the treatment of altered lipid
homeostasis in target organs, especially in the liver.9
PPARa, the first isoform to be identified,4 is expressed
at high density in tissues that have high levels of fatty
acid catabolism, such as liver, and regulates the expres-
sion of genes encoding for proteins involved in lipid and
lipoprotein metabolism.1 In addition, in mice lacking
PPARa (PPARaꢀ/ꢀ), inhibition of cellular fatty acid
flux caused massive hepatic and cardiac lipid accumu-
lation.5 These results clearly indicate a pivotal role for
PPARa in lipid homeostasis in vivo.
In order to develop structurally new human PPARa-
selective activators, we selected KRP-297 (Chart 1) as a
lead compound. Although KRP-297 belongs structu-
rally to the glitazones (thiazolidine-2,4-dione class insu-
lin sensitizers), it binds directly to and activates both
PPARg and PPARa isoforms with almost equal affi-
nity.9 This character is interesting, because the classical
glitazones, such as troglitazone,10 pioglitazone,11 and
rosiglitazone,12 were reported to bind to and activate
the PPARg isoform selectively.13 The reason why KRP-
297 exhibited co-ligand nature is not known, but we
anticipated that replacement of the thiazolidine-2,4-
*Correspondingauthor. Tel.: +81-280-56-2201x286; fax: +81-280-
57-1293; e-mail: hiroyuki.miyachi@mb2.kyorin-pharm.co.jp
0960-894X/02/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(01)00672-2

78
H. Miyachi et al. / Bioorg. Med. Chem. Lett. 12 (2002) 77–80
Chart 1. Chemical structures of the fibrate drugs and KRP-297.
dione ringof KRP-297 with other acidic functionalities,
such as the carboxyl group usually used in fibrates,
would decrease the affinity for PPARg and thereby
afford PPARa-selective ligands. In this paper, we present
our discovery of human PPARa-selective activators.
characterized by 1H NMR, mass spectral, and elemental
analyses (details and physicochemical data of the com-
pounds will be published elsewhere).14
In Vitro Studies
Analysis of transient transactivation activity towards
human PPARa and human PPARg was done by using
the previously described method.9 The activity was
expressed as EC50, which is the concentration of the test
Synthesis
The compounds prepared in this study were synthesized
by standard procedures as outlined in Chart 2, and were
Chart 2. Synthetic routes to the phenylpropanoic acids and related compounds. Reagents and Conditions: (a) OHꢀ, MeOH; (b) 4-
(CF3)PhCH2NH2, ClCO2Et, NEt3, THF; (c) CrO3–H2SO4, acetone; (d) (1) NaBH4, MeOH; (2) SOCl2; (3) KCN, n-Bu3N+ Clꢀ, CHCl3; (e) (1) same
as in (a); (2) same as in (b); (f) (1) 30% H2O2, 0.1 N NaOH, EtOH,; (2) 1 N NaOH, EtOH; (g) (1) (Ph)3P+CH2OMeClꢀ, LDA, THF; (2) p-TosOH,
MeOH; (h) (1) same as in (a); (2) same as in (b); (i) (1) 6 N HCl, AcOEt; (2) (Ph)3P¼CHCO2Me, CH2Cl2; (3) H2, 10% Pd/C, EtOH; (4) same as in
(a); (j) (1) (EtO)2POCH(R1)CO2Et, NaH, THF [or (Ph)3P¼CHCO2Me, toluene]; (2) same as in (i) (3); (k) same as in (b); (l) same as in (a); (m) (1)
same as in (d) (2), Ac2O, pyridine, DMAP, CH2Cl2; (n) (1) (R)2C¼C(OTMS)OMe (R¼Me or Et), Mg(ClO4)2, CH2Cl2; (2) same as in (i) (3); (o) (1)
same as in (b); (2) same as in (a).

H. Miyachi et al. / Bioorg. Med. Chem. Lett. 12 (2002) 77–80
79
compound that affords half-maximum transactivation
activity. PPARd transactivation activity was not exam-
ined, since the lead compound (4) shows very weak
PPARd transactivation activity.
Since compound (18) exhibited potent and subtype-
selective human PPARa activation, we selected 18 as
the next lead compound and performed further chemi-
cal modification focused on the a-position of the car-
boxyl group of 18 (although compound 14 exhibited
comparable PPARa transactivation activity, we were
not interested in this compound because it is a dual
activator of human PPARa and human PPARg). We
anticipated that the introduction of a hydrophobic sub-
stituent at the a-position of the carboxyl group of 18
might enhance the human PPARa transactivation
activity, based on the result of an X-ray crystallographic
analysis of human PPARg–rosiglitazone complex.16
Results and Discussion
The transactivation activity of the present series of
compounds is summarized in Table 1, together with the
results for a representative fibrate, bezafibrate. Bezafi-
brate exhibited weak and non-selective PPAR activa-
tion. These results are consistent with reported data.8
The distance between the carboxyl group and the right-
side benzene ringis important for human PPAR a
transactivation potency. The benzoic acid and phenyla-
cetic acid derivatives (8 and 11) were inactive at the
concentration of 10 mM, but the phenylpropanoic acid
derivative (18) exhibited potent activity, comparable to
that of the lead compound (4). Further elongation of
the methylene chain to give the phenylbutanoic acid
derivative (14) decreased the activity to some extent.
As also indicated in Table 1, the introduction of appro-
priate substituents at the a-position of the carboxyl
group of 18 strikingly affected human PPARa transac-
tivation activity and subtype-selectivity. Introduction of
a methyl group (19) enhanced human PPARa transac-
tivation activity, and the introduction of an ethyl group
(20) afforded maximum activity. Bulkier substituents
generally decreased the activity, that is the potency
decreased in the order of n-pr (21)=i-pr (22)>n-bu
(23)>Ph (24). These data suggest that there are distinct
steric requirements to exhibit potent human PPARa
transactivation activity, and the ethyl group appears to
be the most favorable.
On the other hand, these compounds (8, 11, 18, and 14)
were inactive (8, 11, 18) or weak activators (14) of
human PPARg compared with the lead compound (4).
These results are consistent with the prevailinghypoth-
esis that the thiazolidine-2,4-dione ringstructure is
important for potent PPARg transactivation activity.15
Introduction of a further substituent at the a-position of
the a-monosubstituted phenylpropanoic acid derivatives
is unfavorable, that is the a,a-dimethyl- and the
a,a-diethyl-substituted derivatives (30, 31) exhibited
decreased human PPARa transactivation activity as
compared to those of the corresponding a-mono-
substituted compounds (19, 20).
Table 1. PPAR transactivation activities of the present series of
compounds
The same steric tendency was seen in a series of a-alkoxy-
substituted derivatives (25–27), though to a lesser extent
than a series of a-alkyl-substituted derivatives.
Structure
R
Transactivation (EC50, mM)a
No.
mp (ꢁC)
PPARa
PPARg
As regards human PPARg transactivation, only com-
pound 20, which has an ethyl group at the a-position of
the carboxyl group, exhibited more potent transactiva-
tion activity than the lead compound (4). Other a-sub-
stituted derivatives (19, 21–31) exhibited weak activities.
Thus, these a-substituted derivatives retained moderate
or high human PPARa selectivity, except for the com-
pounds 23 and 26.
4
8
CH2TZDb
CO2H
CH2CO2H
(CH2)2CO2H
(CH2)3CO2H
177–178
236–237
167–168
157–158
107–108
1.0
iac
0.8
ia
11
18
14
19
20
21
22
23
24
ia
1.3
ia
ia
2.2
3.0
ia
0.40
ia
ia
2.5
ia
CH2CH(Me)CO2Hd 155–156
CH2CH(Et)CO2Hd 145–147
0.24
0.040
0.36
0.29
1.0
CH2CH(n-Pr)CO2Hd
147
CH2CH(i-Pr)CO2Hd 174–175
CH2CH(n-Bu)CO2Hd
150
CH2CH(Ph)CO2Hd 159–161
In conclusion, we have developed a potent human
PPARa activator (20; KCL1998001079) with high
selectivity for PPARa over PPARg, as compared with
the fibrates. The structure–activity relationship study
indicated that the substituent at the a-position of the
carboxyl group plays a key role in determining the
potency of PPARa transactivation, and the ethyl group
is the most effective.
ia
25 CH2CH(OMe)CO2Hd 161–163
0.23
1.6
ia
2.9
ia
2.8
ia
26
27
30
31
CH2CH(OEt)CO2Hd 146–148
CH2CH(OPh)CO2Hd 142–143
CH2C(Me)2CO2H
CH2C(Et)2CO2H
Bezafibrate
151–152
156–157
ia
2.8
ia
>78
>137
aCompounds were screened for agonist activity on PPAR-GAL4 chi-
meric receptors in transiently transfected CHO-K1 cells as described in
the text. EC50 value is the molar concentration of the test compound
that causes 50% of the maximal reporter activity (n=3).
bKRP-297, TZD means thiazolidine-2,4-dione ring. The data were
taken from ref 9a.
Further pharmacological evaluation of KCL1998001079,
and a more detailed structure–activity relationship study
of the present series of a-substituted phenylpropanoic
acid derivatives are in progress, including investigations
of enantio-dependency and species-selectivity.
cia, inactive at 10 mM.
dAssayed as a racemate.

80
H. Miyachi et al. / Bioorg. Med. Chem. Lett. 12 (2002) 77–80
11. (a) Momose, Y.; Meguro, K.; Ikeda, H.; Hatanaka, C.;
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Suzuki and T. Nakazawa of Kyorin Pharmaceutical
Co., Ltd., for their technical assistance.
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