Improvement of the transactivation activity of phenylpropanoic acid-type peroxisome proliferator-activated receptor pan agonists: Effect of introduction of fluorine at the linker part

Article abstract of DOI:10.1016/j.bmcl.2008.07.046

We developed a potent peroxisome proliferator-activated receptor pan agonist (a candidate drug for treatment of altered metabolic homeostasis) by introducing fluorine atoms at appropriate position(s) of the known phenylpropionic acid-type pan agonist TIPP

Full text of DOI:10.1016/j.bmcl.2008.07.046

Bioorganic & Medicinal Chemistry Letters 18 (2008) 4525–4528
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Bioorganic & Medicinal Chemistry Letters
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Improvement of the transactivation activity of phenylpropanoic acid-type
peroxisome proliferator-activated receptor pan agonists:
Effect of introduction of fluorine at the linker part
b
b
c
b
Jun-ichi Kasuga a, , Takuji Oyama , Yuko Hirakawa , Makoto Makishima , Kosuke Morikawa ,
*
Yuichi Hashimoto a, Hiroyuki Miyachi a,
*
a Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
b The Takara-Bio Endowed Division, Institute for Protein Research, Osaka University, 6-2-3 Furuedai, Suita, Osaka 565-0874, Japan
c Nihon University School of Medicine, 30-1 Oyaguchi-kamicho, Itabashi-ku, Tokyo 173-8610, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We developed a potent peroxisome proliferator-activated receptor pan agonist (a candidate drug for
treatment of altered metabolic homeostasis) by introducing fluorine atoms at appropriate position(s)
of the known phenylpropionic acid-type pan agonist TIPP-703.
Received 15 May 2008
Revised 1 July 2008
Accepted 11 July 2008
Available online 15 July 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
PPAR
Fluorine
PPAR pan agonist
Peroxisome proliferator-activated receptors (PPARs) are mem-
bers of the nuclear receptor (NR) superfamily, and three subtypes
(PPARa, PPARd, and PPARc) have been identified to date. The PPARs
are of great interest because they are considered to be the master
regulators of lipid and glucose homeostasis.1–5 PPARs are activated
by fatty acids and metabolites, and regulate the expression of var-
ious genes downstream of the PPAR response element. Each PPAR
subtype displays a distinct pattern of tissue distribution and a dis-
tinct pharmacological profile.
brate is a well-known PPAR pan agonist, which has been in clinical
use for a long time. Bezafibrate increases HDL cholesterol and re-
duces triglycerides, improves insulin sensitivity, and reduces blood
glucose level. Bezafibrate significantly lowers the incidence of car-
diovascular events.6
We have been engaged in structural development studies of no-
vel PPAR ligands based on the SAR results obtained from phenyl-
propanoic acid derivatives related to the PPAR
a-selective agonist
KCL.7 We have succeeded in the development of PPAR agonists
PPAR
as liver, heart, muscle, and kidney. It regulates genes associated
with fatty acid uptake and metabolism. Clinically, PPAR agonists,
a
is expressed in tissues involved in lipid oxidation, such
with characteristic subtype selectivity, that is, PPARa/d dual ago-
nist TIPP-401,8 PPARd-selective agonist TIPP-204,9 and PPAR pan
agonist TIPP-70310 (Fig. 1).
a
such as fenofibrate, are used for the treatment of dyslipidemia.
PPARd is expressed ubiquitously. Recently, the use of knock-out
animals and PPARd-selective agonists has revealed that PPARd is
associated with improved insulin sensitivity and elevated HDL lev-
During the development of TIPP-401, we found that the intro-
duction of fluorine at the ortho position of the amide carbonyl
group greatly enhanced PPARd activity. This was not unexpected,
because the introduction of fluorine can improve metabolic stabil-
ity by blocking metabolically labile sites, modulate physicochemi-
cal properties, such as lipophilicity or basicity, change molecular
conformation, and so on.11,12 Therefore, to evaluate the effect of
fluorine substitution more comprehensively, we designed and syn-
thesized a series of fluorinated phenylpropanoic acid PPAR ago-
nists. In this letter we present the SAR of these fluorinated
derivatives. We also report the creation of a potent PPAR pan ago-
nist based on the SAR obtained.
els. PPARc is expressed in adipose tissue, macrophages, and vascu-
lar smooth muscles, and it regulates genes related to adipogenesis
and lipid storage. Clinically, PPARc agonists, such as pioglitazone,
are used for the treatment of type 2 diabetes mellitus.1–4
In recent years, many PPAR dual and pan agonists have been
developed, as well as PPAR subtype-selective agonists.5,6 Bezafi-
* Corresponding authors.
E-mail addresses: jk817@msn.com (J. Kasuga), miyachi@iam.u-tokyo.ac.jp (H.
Miyachi).
The synthetic route to racemic compounds is depicted in
Scheme 1. Aldehydes 1a–e were treated with Horner–Emmons re-
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.07.046

4526
J. Kasuga et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4525–4528
O
O
O
O
O
O
F
O
O
O
O
OH
N
H
OH
N
H
OH
N
H
OH
F
F
F
F
N
H
O
O
R
F
F
Cl
α δ
TIPP-401 R = Me (PPAR
/
dual agonist)
α
Bezafibrate (PPAR pan agonist)
KCL (PPAR selective agonist)
TIPP-703 (PPAR pan agonist)
δ
TIPP-204 R = Bu (PPAR selective agonist)
Fig. 1. Structures of PPAR agonists.
O
O
O
O
X1
O
O
a)
c)
b)
H
OEt
H
OEt
N
OH
H
O
X3
O
X3
2
O
X3
R1
O
X3
R2
X2
R2
X2
R2
X2
R2 X2
R2 = Me, X2 = H, X3 = H
R2 = Me, X2 = F,*X3 = H
R2 = Me, X2 = H, X3 = F
R2 = Et, X2 = H, X3 = F
R2 = Pr, X2 = H, X3 = F
R
R
= Me, X = H, X3 = H
R
R
= Me, X = H, X3 = H
R
2a"R2 = Me,
3a"R2 = Me,
4c "R11 = CF ,
= CF33, X1 = H, R2 = Me, X2 = F,*X3 = H
2
2b R22 = Me,
3b R22 = Me,
4d
= Me, X = F,*X3 = H
= Me, X = F,*X3 = H
R1 = CF3, X1 = H, R2 = Me, X2 = H, X3 = F
4e R1 = Ad, X1 = H, R2 = Me, X2 = H, X3 = H
2
2
2c"R2 = Me, X2 = H, X3 = F
2d RR22 ==EEtt,, X2 = H, X3 = F
3c"R2 = Me, X2 = H, X3 = F
3d RR22 ==EEtt,, X2 = H, X3 = F
4f R1 = Ad,
X
1 = F,*R2 = Me, X2 = H, X3 = H
= Pr, X2 = H, X3 = F
R
= Pr, X2 = H, X3 = F
R1 = Ad, X1 = H, R2 = Me, X2 = F,*X3 = H
R1 = Ad, X1 = H, R2 = Me, X2 = H, X3 = F
2e"R2 = Pr,
3e"R2 = Pr,
4g
4h
4i
R
R1 = Ad,
X X
1 = H, R2 = Et, 2 = H, X3 = F
X1
O
5a
5b
R
R
R
1 = CF3, X1 = H
4j R1 = Ad, X1 = H, R2 = Pr, X2 = H, X3 = F
1 = Ad, X1 = H
4k R1 = Ad,
X
1 = F,*R2 = Et,
X
2 = H, X3 = F
NH2
5c" R11 = Ad, X11 = F
4l
= Ad, X = F
Ad : adamantan-1-yl
R1 = Ad, X1 = F,*R2 = Pr, X2 = H, X3 = F
R1
F
O
F
O
F
F
e)
f)
d)
OH
NH2
+
Br
Br
6
7
8
9
5c
Scheme 1. Synthetic route to racemic compounds. Reagents and conditions: (a) 1—triethyl-2-phosphonobutyrate, t-BuOK, THF, 84–96%; 2—10% Pd–C, H2, AcOEt, 95–100%;
(b) TiCl4, CHCl2OCH3, DCM, 77–89%; (c) 1—5a–c, Et3SiH, TFA, toluene, 42–92%; 2—HCl, dioxane, 54–84%; (d) Mg, Et2O, 49%; (e) Co(OAc)2, Mn(OAc)2, NaBr, O2, aq AcOH,
dioxane, 64%; (f) 1—SOCl2; 2—acetone, aq NH3, 90%.
agents, followed by hydrogenation to afford esters 2a–e, which
were formylated at the ortho position of the alkoxyl group to afford
aldehydes 3a–e. In step b, from 2c, we had anticipated obtaining
the 2-fluoro benzaldehyde derivative, as well as the 4-fluoro benz-
aldehyde derivative 3c, but only 3c was formed. Compounds 3a–e
were amidealkylated with 5a–c, and then hydrolyzed to afford 4c–
l. Synthesis of 4a and 4b was previously reported.8 Compound 5c,
which was used in step c, was prepared in three steps. Compounds
6 and 7 were condensed13 to afford 8, which was oxidized14 and
amidated to afford 5c.
The synthetic route to the enantiomer of 41 is depicted in
Scheme 2. The synthetic scheme used for the preparation of
TIPP-70310 was not applicable for the synthesis of optically active
4l. According to the previous route, we had to prepare 4-fluoro-
5-formyl-2-hydroxybenzoic acid as a starting material, but unfor-
tunately we could not prepare it effectively. Therefore we adopted
scheme 2. Evans’ asymmetric aldol condensation15 of 1e with 10
followed by reductive dehydroxylation afforded 11, which was
treated with Ti(OEt)4 to afford 12. Then 12 was formylated, reduc-
tively amidated, and hydrolyzed to afford (S)-4l. The antipodal (R)
enantiomer was prepared similarly from (R)-4-benzyl-3-butyryl-
oxazolidin-2-one instead of 10 as the starting material.
First, we examined the effect of the introduction of fluorine at
different positions, that is, ortho to the amide carbonyl group of
the distal benzene ring (X1), and ortho (X2) and meta (X3) to the
methoxy group of the linker benzene ring (Table 1). In our previous
study, the introduction of fluorine at the X1 position of 4a en-
hanced PPARd activity, while PPARa activity was maintained
(4b–4a). This SAR is also applicable to adamantyl-substituted com-
pounds (4f–4e); PPARd transactivation activity of 4f (EC50; d
550 nM) is more potent than that of 4e (EC50; d 940 nM). Introduc-
tion of fluorine at the linker benzene ring (X2 and X3) had the
O
O
O
O
O
O
F
N
O
h)
N
O
OEt
g)
H
O
F
+
O
F
O
12
11
1e
10
F
O
O
O
O
j)
i)
N
H
OH
H
OEt
F
O
O
F
(S
)-4l
13
Scheme 2. Synthetic route to chiral compound (S)-4l. Reagents and conditions: (g) 1—Bu2BOTf, TEA, DCM, 98%; 2—Et3SiH, TFA, DCM, 82%; (h) Ti(OEt)4, EtOH, 53%; (i) TiCl4,
CHCl2OCH3, DCM, 84%; (j) 1—5c, Et3SiH, TFA, toluene, 63%; 2—HCl, dioxane, 68%.

J. Kasuga et al. / Bioorg. Med. Chem. Lett. 18 (2008) 4525–4528
4527
Table 1
PPARs transactivation activity of the present series of compounds
X1
O
O
N
H
OH
R1
X3
O
X2
Compound
Structure
Activity (EC50 SE/nM)a
R1
X1
X2
X3
PPAR
10
7.9 1.5
54 15
3.6 0.8
a
PPARd
PPAR
c
4a
4b
4c
4d
4e
4f
CF3
CF3
CF3
CF3
Adb
Adb
Adb
Adb
H
F
H
H
H
F
H
H
F
H
H
H
F
H
H
H
F
H
H
H
F
1
130 20
2600 100
2600 200
>10,000
1100 100
110 10
29
59
20
5
6
2
53
5
940 30
550 70
2200 300
280 30
60 14
260 30
140 20
190 30
4g
4h
H
H
Fig. 2. Three-dimensional structure of TIPP-401 complexed with human PPARd
ligand binding domain (LBD). (A) Whole structure. (B) Zoomed view of TIPP-401.
The interacting amino acids are colored pink.
H
13
4
36
6
a
Compounds were screened for agonist activity on PPAR–GAL4 chimeric recep-
tors in transiently transfected HEK-293 cells. EC50 value is the concentration of the
test compound that affords 50% of the maximal reporter activity.
b
‘Ad’ means adamantyl.
opposite effect. Introduction of fluorine at the X2 position is not tol-
erated for PPARs activity (4c and 4g). On the other hand, the intro-
duction of fluorine at the X3 position enhanced PPARs activity (4d
and 4h). 4d (EC50
;
a
3.6 nM, d 20 nM,
c 1100 nM) is more potent
than 4a (EC50 10 nM, d 130 nM, c
;
a
2600 nM) for PPARs of all sub-
types. Likewise, adamantyl-substituted derivatives exhibited the
same SAR (4h–4e).
Based on the same tendency of the effect of introduction of
fluorine, we hypothesized that the SAR could be extended to
other compounds. To test this hypothesis, we planned to design
a more potent PPAR pan agonist than TIPP-703. Based on the
SAR, we fixed X3 as F, X1 as H or F, and R2 as ethyl or propyl
for the compounds tested. The results are summarized in Table
2. All the compounds (4i–l) exhibited more potent activities than
TIPP-703. In particular, compound 4l exhibited the most potent
and well-balanced PPAR activity. When the activity of optically
active 4l was tested, we found that (S)-4l is more potent than
the antipodal R-enantiomer, as expected from previous stud-
ies.8–10
Fig. 3. Zoomed view of the fluorine at X1 position of TIPP-401 and amino acids
Cys285 and Leu339. Lengths of the yellow lines are shorter than 4 Å.
The structure reveals that the two amino acids (Cys285 and
Leu339) are positioned within 4 Å around fluorine atom at the X1
position of TIPP-401(Fig. 3). This indicates the possibility of some
interaction(s) between fluorine and these amino acids, and the
possible interaction(s) might be one reason why fluorine at the
X1 position enhanced PPARd activity. Further structural analysis
is in progress.
Although the reason(s) why fluorine at the X1 and X3 positions
enhanced PPARd activity is uncertain, recently the X-ray crystallo-
graphic structure of TIPP-401 complexed with human PPARd is
solved16 (Figs. 2 and 3).
In summary, introduction of fluorine at appropriate position(s)
enhances the activity of the present phenylpropionic acid-type
PPAR agonists. Based on this SAR, we developed a potent PPAR
pan agonist, which is a candidate drug for the treatment of altered
metabolic homeostasis.
Table 2
PPARs transactivation activity of the present series of compounds
X1
O
O
N
H
OH
O
F
Acknowledgments
R2
Compound
Structure
R2
Activity (EC50 SE/nM)a
The work described in this letter was partially supported by a
Grant-in-aid for Scientific Research from the Ministry of Education,
Culture, Sports, Science and Technology, Japan, and grant from
Keimeikai Foundation.
X1
Stereo
PPAR
13
7.1 1.1
17
7.5 1.5
a
PPARd
PPARc
4h
4i
4j
4k
4l
(S)-4l
(R)-4l
H
H
H
F
F
F
Me
Et
Pr
Et
Pr
Pr
Pr
rac.
rac.
rac.
rac.
rac.
S
4
280 30
36
24
15
22
35
38
6
2
2
3
3
3
94
60
55
28
25
9
7
3
2
2
2
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