Design and synthesis of oxime ethers of α-acyl-β-phenylpropanoic acids as PPAR dual agonists

Article abstract of DOI:10.1016/j.bmcl.2006.11.050

Oxime ethers of α-acyl-β-phenylpropanoic acids were prepared to apply as PPARα and γ dual agonists. Among them, compound 11l proved to exhibit potent in vitro activities with EC₅₀ of 19 and 13 nM in PPARα and γ, respectively. It showed better g

Full text of DOI:10.1016/j.bmcl.2006.11.050

Bioorganic & Medicinal Chemistry Letters 17 (2007) 937–941
Design and synthesis of oxime ethers of a-acyl-b-phenylpropanoic
acids as PPAR dual agonists
Hee Oon Han, Seung Hae Kim, Kyoung-Hee Kim, Gwong-Cheung Hur, Hyeon Joo Yim,
Hee-Kyung Chung, Sung Ho Woo, Ki Dong Koo, Chang-Seok Lee,
Jong Sung Koh* and Geun Tae Kim*
Research and Development, LG Life Sciences, 104-1 Munji-dong, Yuseong-gu, Daejon 305-380, Republic of Korea
Received 21 September 2006; revised 9 November 2006; accepted 15 November 2006
Available online 18 November 2006
Abstract—Oxime ethers of a-acyl-b-phenylpropanoic acids were prepared to apply as PPARa and c dual agonists. Among them,
compound 11l proved to exhibit potent in vitro activities with EC50 of 19 and 13 nM in PPARa and c, respectively. It showed better
glucose lowering effects than rosiglitazone 1 and ameliorated the lipid profile like plasma triglyceride in db/db mice model.
Ó 2006 Elsevier Ltd. All rights reserved.
Type II diabetes has emerged as one of the biggest prob-
lems facing the world today. High glucose level in the
blood caused hyperglycemia and insulin resistance, which
resulted in the deterioration of the pancreatic b-cell func-
tion.1 Hyperglycemia should be controlled in a careful
manner, otherwise higher morbidity and mortality have
been found in the related diseases like retinopathy,
nephropathy, neuropathy, dyslipidemia, coronary heart
disease, hypertension, and obesity.2 Many targets have
been investigated to cure type II diabetes like dipeptidyl
peptidase IV,3 peroxisome proliferator-activated recep-
tors4 (PPARs), GLP-1 analog,5 glucokinase,6 and so on.
Among those targets, peroxisome proliferator-activated
receptors (PPARs) are known as a good target to lower
plasma glucose and to improve metabolic syndrome.
PPARs are members of the nuclear receptor superfamily,
which consists of three isoforms, PPARa, PPARc, and
PPARd.7 Heterodimer of PPARs with retinoid X recep-
tors binds to peroxisome proliferator response element
(PPRE) in the promoter region with cofactors, which
results in the regulation of many target genes. PPARc is
largely expressed in adipocytes and macrophages.8 In adi-
pocyte tissue, PPARc promotes the differentiation and
the lipid storage. PPARc agonists like rosiglitazone 1
and pioglitazone 2 ameliorate insulin sensitivity. In con-
trast with PPARc, PPARa is expressed in liver and heart.
Activation of PPARa induces fatty acid oxidation in the
liver, and reduces serum triglyceride (TG) and increases
HDL cholesterol.
PPARc agonists, rosiglitazone 1 and pioglitazone 2,
with thiazolidinediones (TZDs) have been marketed
with a sale of 1.9 billion dollars and 2.0 billion dollars,
respectively, in 2004.9 Recently, 3-year clinical study
indicated that pioglitazone reduced the risk of myocar-
dial infarction or stroke significantly.10 However, long
clinical treatment (3–4 months) of TZDs is required to
reach their full glucose reduction effect.11 Although
these agents have glucose lowering effect and improve
the lipid profile like TG, LDL cholesterols and HDL
cholesterol, the crucial side effects12 like congestive heart
failure, edema, fluid retention, and weight gain still re-
main unsolved. Until now, a large number of PPARa,
c dual agonists have been investigated in many research
groups but the successful PPARa, c dual agonists
including tesaglitazar 3 (AstraZeneca) and muraglita-
zar13 4 (BMS-Merck) have not been marketed. Never-
theless, PPARa, c dual agonist would be well suited
for treatment of diabetes and cardiovascular disease as
long as it could reduce side effects as mentioned above.
Many PPARa, c dual agonists contained a-alkoxy
acids, a-carbamate acids or thiazolidinediones as shown
in tesaglitazar 3, muraglitazar 4, rosiglitazone 1, and
pioglitazone 2. Acid group in PPAR agonists is known
Keywords: PPAR; Dual agonist; Oxime; Propanoic acid.
*
Corresponding authors. Tel.: +82 42 866 2247; fax: +82 42 861
2566; e-mail: gtakim@lgls.co.kr
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.11.050

938
H. O. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 937–941
to play a key role in interacting with PPARa and c.4b In
an effort to search for the new PPAR agonist, this led us
to investigate isostere of a-substituent in acid. At the
beginning, introduction of oxime group at a-position
in acid was expected to provide a working scaffold for
the efficacious PPAR agonist. Therefore, we designed
a series of new phenylpropanoic acids containing the
oxime functionality as PPARa, c dual agonists. The syn-
thesis of phenylpropanoic acids having the oxime group
is described in Scheme 1. Most of the compounds were
synthesized in the recemic forms. Knoevenagel reaction
was employed for the synthesis of 6. Condensation of b-
keto ester 5 and 4-hyroxy benzaldehyde was carried out
with catalytic amounts of piperidine and acetic acid in
benzene using Dean-Stark trap. The yield of condensa-
tion was excellent (90–95%) and this type of reaction
allowed the modification of R1 group in 11 by simply
changing the commercially available b-keto esters 5.
Hydrogenation of 6 and the following reaction with
O-alkyl hydroxyl amine afforded phenols 8. The gener-
ated geometric (E)- and (Z)-isomers were not isolated
in this step but separated in the final step using HPLC.
Alkylation of phenols 8 with the commonly used
oxazoles 9 was carried out by refluxing with Cs2CO3
in acetonitrile to furnish esters 10 in good yields.
Oxazoles 9 could be prepared by using the published
procedures.14 Scheme 2 shows a simple synthetic route
to one of oxazoles 9 with phenyl group as R3 position.
Butane-2,3-dione mono-oxime was reacted with benzal-
dehyde and hydrochloric acid in dioxane to afford
oxazole N-oxide 14. Treatment of N-oxide 14 with phos-
phorus oxychloride in chloroform gave chloride 15. For
the one-carbon elongation, chloride 15 was subjected to
sodium cyanide in DMF at 80 °C and then alkaline
hydrolysis with KOH in aqueous THF to furnish the
corresponding acid. Reduction of the acid with borane
dimethylsulfide complex and the following reaction with
methanesulfonyl chloride afforded mesylate 18. Ester 10
was hydrolyzed with sodium hydroxide in aqueous THF
and methanol, and then the (E)- and (Z)-isomers were
separated with HPLC to give pure acid 11.15 Among
them, spectral data for the representative 11l are given
1
below. Spectra for 11l: H NMR (CDCl3) d 7.94–7.92
(1H, m), 7.38–7.33 (3H, m), 6.97 (1H, d, J = 8.6), 6.78
(1H, d, J = 8.6), 4.81(2H, s), 3.84–3.78 (1H, m), 3.79–
3.73 (1H, m), 3.38 (1H, dd, J = 12, 4.9 Hz), 3.15 (1H,
dd, J = 14, 4.9 Hz), 2.84 (1H, dd, J = 14, 12 Hz), 2.29
(3H, s), 1.75 (3H, s), 1.33–1.27 (2H, m), 0.66 (3H, t,
J = 7.6 Hz) 13C NMR (CDCl3) d 178.68, 159.90,
159.35, 156.87, 157.06, 132.43, 132.12, 130.08, 129.97,
O
O
O
O
b
c
a
O
1
R
O
O
N
O
HO
O
R1
HO
O
HO
R1
R1
O
O
R2
7
8
6
5
O
O
e
O
d
OH
N
O
O
N
O
N
O
O
N
O
R1
1
R
N
n
3
n
3
n
R
L
R
R3
R2
R2
O
n=1,2
n=1,2
10
L=OMs, Cl, Br
11
9
Scheme 1. Reagents and conditions: (a) 4-hydroxy benzaldehyde, AcOH (cat), piperidine (cat), benzene, Dean-Stark trap, 90–95%; (b) MeOH/ethyl
acetate 10:1, H2, Pd(OH)2, 95%; (c) MeOH, NaOAc, HClÆH2N–OR2, 90%; (d) Cs2CO3, CH3CN, reflux, n = 1, 80–90%, n = 2, 50–60%; (e) THF/
MeOH/1 N NaOH 1:1:1, 90%.
O
O
Cl
O
a
b
O
N+
O
N
+
N
O
15
14
13
12
c
d, e
f
O
O
O
CN
OMs
OH
N
N
N
17
18
16
Scheme 2. Reagents and conditions: (a) 4 M HCl in dioxane, rt, 99%; (b) CHCl3, POCl3, reflux, 99%; (c) NaCN, DMF, 80 °C, 95%; (d) KOH, aq.
THF, reflux; (e) BH3ÆSMe2, THF, rt, 68%; (f) MeSO2Cl, Et3N, CH2Cl2, 0 °C, 99%.

H. O. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 937–941
939
128.72, 127.48, 126.15, 114.56, 74.72, 62.23, 55.82,
34.84, 22.23, 12.68, 10.47, 10.32 mass (EI) m/z 437
(M++1) (Fig. 1).
pounds. We initiated to synthesize 11a, which was
found to be a potent agonist in PPARa and c. It was
so encouraging that we decided to scrutinize the influ-
ence of R2 groups. As the size of the substituent in-
creased, PPARa and c activities appeared to improve.
Modification of the chain in R2 group indicated that
the optimal size of the substituent was n-butyl group
in this study. As shown in Table 1, 11e had sub-nano-
molar activity on PPARc and 1.3 nM on PPARa. When
ethyl group was introduced to R1 in 11g and 11h, they
Compound 11 in our hand were screened for PPARa
and c agonist activity on PPAR-GAL4 chimeric recep-
tor in transfected HepG2 cells.16 Rosiglitazone 1, tesag-
litazar 3, and GW957817 were used as PPARc, PPARa/
c, and PPARa agonist controls. In Table 1, we summa-
rized functional transactivation data of all the com-
O
O
N
O
O
NH
O
N
N
NH
O
S
S
2
4
1
OH
O
N
O
O
O
OH
O
O
O
O
S
O
O
N
O
O
3
Figure 1. Structures of PPAR agonists.
Table 1. In vitro activity of oxime ethers of a-acyl-b-phenylpropanoic acids 11a
O
OH
O
N
O
N
O
R1
n
3
R
R2
Compound
Geometric isomer
N
R1
R2
R3
EC50(nM)b of hPPARc
EC50(nM)b of hPPARa
11a
11b
E
2
2
2
2
2
2
2
2
2
2
1
1
1
1
1
2
2
2
1
1
2
2
Me
Me
Me
Me
Me
Me
Et
Me
Et
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
2.1
1.0
0.55
0.3
0.19
0.36
0.31
0.1
0.54
5
19
12
E
11c
11d
E
n-Pr
CH2CHMe2
4.9
2.2
1.3
3.1
32
E
11e
11f
E
n-Bu
CH2-cyclopropyl
E
11g
11h
E/Z = 3/1
E/Z = 4/1
Me
Et
Et
26
11i
11j
E
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
4-F-PhenylCH2
4-F-PhenylCH2
10.6
596
91
Z
11k
11l
E/Z = 5/1
E
Et
Pr
4
13
19
12
11m
11n
E
Et
n-Pr
4-F-Phenyl
4-F-Phenyl
4-F-Phenyl
4-F-Phenyl
4-F-Phenyl
4-F-Phenyl
i-Propyl
6.8
28
E
11.7
23
11o
11p
E
2-F-Ethyl
Et
7.7
3.0
2.1
2.9
48
E
11.5
4
11q
11r
E
Pr
2-F-Ethyl
E
3.5
1237
105
139
10
11s
11t
E/Z = 5/1
E/Z = 5/1
Et
Pr
Et
Pr
i-Propyl
i-Propyl
i-Propyl
5
20
11u
11v
E
E
5.2
82
Rosiglitazone 1
Tesaglitazar 3
GW9578
3528
9798
78
a Agonist activities were measured in human PPAR-GAL4 chimeric HepG2 cells using the published procedure.16
b Concentration of the test compounds which produced 50% of the maximal reporter activity.

940
H. O. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 937–941
Table 2. Pharmacokinetic data of 11l in SD ratsa
retained good PPARa and c activities. Comparison of
the activities of the geometric isomers 11i and 11j dem-
onstrated that (E)-isomer had more potent activities in
PPARa and c than (Z)-isomer. 11k and 11l, having
shorter linkers, exhibited well-balanced activities as well.
4-Fluorophenyl methyl group was installed in 11m–11r
because phenyl group is sometimes metabolically vul-
nerable. They were prepared for the pharmacokinetic
studies and in vivo experiment. We also attached isopro-
pyl group as R3. Compounds 11s and 11t with a short
linker turned out to decrease PPARa and c activities
as compared with compounds 11u and 11v. In general,
a series of oxime ethers of a-acyl-b-phenylpropanoic
acids 11 exhibited excellent PPARa and c activities,
which provide a useful scaffold for PPARa and c dual
agonist. Finally, X-ray crystallographic data of 11l were
obtained to verify which enantiomer was potent one in
PPARa and c, unequivocally. (R)-11l was found to be
a potent enantiomer as shown in Figure 2. Therefore,
we isolated a pure enantiomer (R)-11l by utilizing chiral
HPLC with a ChiracelÒ OD-RH column, which re-
vealed that it had EC50 of 11 and 5 nM in PPARa and c.
Pharmacokinetic parameters
po
iv
Dose (mg/kg)
10
5
6773
AUC0–24h(lg min/ml)
Cmax (lg/ml)
Tmax (min)
9708
22.6
30
T1/2 (min)
483
355.9
0.8
329
Clearance (ml/min/kg)
Vd (ml/kg)
Bioavailability (%)
75.5
a n = 2.
Table 3. In vivo data of compound 11l in db/db mice20
Compound
Dose
(mg/kg)
Plasma
glucosea (%)
Plasma
TGa (%)
Rosiglitazone 1b
Tesaglitazar 3c
11lc
10
1
65
68
8
65
38
43
41
58
0.1
1
56
73
10
a Reduction of plasma glucose and plasma TG were calculated as the
percent of reduction and increase with respect to control value.
b Blood samples were collected after 12 days.
c Blood samples were collected for glucose after 11days and for TG
after 14 days.
To investigate the interactions of these compounds with
the protein, the compound 11l was chosen to co-crystal-
lize with PPARa LBD (ligand binding domain) and the
co-activator peptide fragment (SRC-1).
and the nitrogen atom of the oxazole ring makes a
water-mediated hydrogen bond with Thr279.19 The
complex structure of the compound 11l with PPARc
LBD revealed similar binding interactions.
The U-shaped compound 11l binds to the PPARa LBD
using four hydrogen bonds and many van der Waals
contacts. The carboxylate group of the compound 11l
forms hydrogen bonds with Ser280 on helix 3, Tyr314
on helix 5, and Tyr464 on helix 12 as in the structure
of tesaglitazar 3.18 Its oxime group is located in the
so-called ‘benzophenone’ pocket and makes contacts
with Ile272, Phe273, Cys276, and Ile354. The oxime-
binding pocket can accommodate various sizes of func-
tional groups, which correlated well with SAR shown in
Table 1. The phenyl oxazole group fits into a hydropho-
bic pocket formed by helix 20; helix 3 and the b sheet,
Based on the cell-based activities and the pharmacoki-
netic studies in rats, 11l was selected to adjust the in vivo
experiment in male db/db mice for further evaluation. Its
pharmocokinetic behavior in Sprague–Dawley (SD) rats
is described in Table 2. When dosed orally at 0.1, 1,
10 mg/kg in db/db mice20 for 14 days, compound 11l
exhibited a does-dependent decrease in plasma glucose
and plasma triglyceride (TG) as depicted in Table 3.
Treatment of 10 mg/kg of 11l showed a glucose reduc-
tion of 73% as compared with that of 65% and 68% at
10 mg/kg of rosiglitazone 1 and 1 mg/kg of tesaglitazar
3, respectively. At the same time, 11l reduced plasma
TG by 58% at a dose of 10 mg/kg. Glucose lowering ef-
fect was also found at a dose of 1 mg/kg of 11l. Conse-
quently, compound 11l displayed better glucose
lowering effect than rosiglitazone 1, whereas it showed
diminished efficacy as compared with tesaglitazar 3.
Compound 11l turned out to have glucose lowering ef-
fect and ameliorate lipid profile like TG in db/db mice
model. In conclusion, we found that a series of oxime
ethers of a-acyl-b-phenylpropanoic acids were potent
agonists of PPARa and c, and exhibited good in vivo
efficacy, which will be further developed.
Acknowledgments
Figure 2. Crystal structure of the PPARa LBD in complex with
compound 11l. Compound 11l is shown in purple and Tyr464 from
˚
helix 12 is highlighted in red. All of the residues within 4 A from the
compound are labeled.
We thank Dr. Sunwha Lee for providing the pharmaco-
kinetic data and Ki-Sook Park for preparing the sam-
ples for in vivo experiment.

H. O. Han et al. / Bioorg. Med. Chem. Lett. 17 (2007) 937–941
941
´ ˇ
M.; Mokan, M.; Norkus, A.; Pirags, V.; Podar, T.;
Scheen, A.; Scherbaum, W.; Schernthaner, G.; Schmitz,
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