Synthesis and structure-activity relationship of novel indene N-oxide derivatives as potent peroxisome proliferator activated receptor γ (PPARγ) agonists

Article abstract of DOI:10.1016/j.bmcl.2007.06.073

A series of novel indene N-oxide derivatives were prepared by various synthetic methods and evaluated for their ability to activate PPARγ. The best PPARγ agonist in this series was 9 h, which showed an EC₅₀ value of 15 nM.

Full text of DOI:10.1016/j.bmcl.2007.06.073

Bioorganic & Medicinal Chemistry Letters 17 (2007) 5239–5244
Synthesis and structure–activity relationship of novel indene
N-oxide derivatives as potent peroxisome proliferator
activated receptor c (PPARc) agonists
Jin Hee Ahn,a,* Mi Sik Shin,a Sun Ho Jung,a Jin Ah Kim,a Hye Min Kim,a Se Hoan Kim,a
Seung Kyu Kang,a Kwang Rok Kim,a Sang Dal Rhee,a Sung Dae Park,b Jae Mok Lee,c
Jeong Hyung Lee,d Hyae Gyeong Cheona,* and Sung Soo Kima,*
aBioorganic Science Division, Korea Research Institute of Chemical Technology, Yuseong-Gu, Daejeon 305-600, Republic of Korea
bJEIL Pharmaceutical Co., Ltd, R&D Center, Yongin 449-861, Republic of Korea
cR&D Center of Pharmaceuticals, CJ Corporation, Ichon 467-810, Republic of Korea
dKorea Research Institute of Bioscience and Biotechnology, Yuseong-Gu, Daejeon 305-333, Republic of Korea
Received 31 March 2007; revised 18 June 2007; accepted 27 June 2007
Available online 30 June 2007
Abstract—A series of novel indene N-oxide derivatives were prepared by various synthetic methods and evaluated for their ability to
activate PPARc. The best PPARc agonist in this series was 9 h, which showed an EC50 value of 15 nM.
Ó 2007 Elsevier Ltd. All rights reserved.
Peroxisome proliferator activated receptors (PPARs),
which are one of the attractive diabetes target pro-
teins, are members of the nuclear hormone receptor
superfamily, including three receptor isoforms,
PPARa, PPARc, and PPARd. Among them, PPARc
has been the subject of extensive research,1 and as a
result, its activation has played a prominent role in
the treatment for type 2 diabetes. The receptor is
widely distributed in the spleen, colon, adipose tissue,
and macrophages and found to a lesser extent in the
liver, pancreas, and skeletal muscle.2 Activation of
PPARc in the cell nucleus initiates heterodimeriza-
tion with another nuclear receptor, the retinoid X
receptor (RXR), with subsequent recruitment of
coactivators and induction of genes that are involved
in adipogenesis and insulin sensitivity. Target genes
that are upregulated or downregulated have been
identified from white and brown adipose tissues, skel-
etal muscle, and the liver.3 However, the details cor-
roborating the process through which the activation
leads to glucose homeostasis are not fully under-
stood. Convincingly, studies suggest that adipogene-
sis provides increased lipid metabolism and free
fatty acid uptake in adipose tissue, thereby leading
to increased insulin sensitivity and glucose metabo-
lism in the muscle and liver.1a,4,5
PPARc agonists containing thiazolidinedione (TZD)
structure for the treatment of type 2 diabetes have
proven successful for glucose control and reduction
of HbA1c, including the marketed compounds, Rosig-
litazone6 and Pioglitazone.7,6b However, side effects
such as edema, weight gain, and hepatotoxicity have
been reported in patients after treatment with PPARc
agonists.6b Recently, much attention has been focused
on PPARa/c dual agonists8 (mainly, carboxylic acid
derivatives), however, PPARa/c dual agonists so far
have side-effect issues.8c More recently, new classes
of selective PPARc modulators (SPPARc M, partial
agonist) have been reported.9 Indole derived PPARc
Ms exhibited glucose lowering with partial agonistic
activity compared to rosiglitazone. Although diverse
researches toward PPAR modulators are developing,
the discovery of a new class of PPARc agonists is nec-
essary to this area.
These situations prompted us to develop a new
PPARc agonist with a new skeleton, and we have re-
cently identified novel indenone skeleton,10 which pos-
sesses a new binding mode to PPARc in X-ray crystal
Keywords: PPARc; Indene N-oxide; Diabetes.
Corresponding authors. Tel.: +82 42 860 7076 (J.H.A.); e-mail:
jhahn@krict.re.kr
*
0960-894X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.06.073

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J. H. Ahn et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5239–5244
structure. But, an improvement seemed to be needed
due to cytotoxic effects observed from some of the
indenone compounds.
published with full biological data, herein we report
the synthesis and a full SAR of indene N-oxide
derivatives.
Diverse indene N-oxide derivatives were synthesized by
Schemes 1–3. Synthesis of the initial hit compound 3 is
described in Scheme 1. Direct condensation from the
compound 2, which was prepared by our previous pa-
O-
O
N+
1
R6
O
6
CO Et
2
R2
2
per,10 with N-methyl hydroxylamine afforded
3
5
3
R3
(R = H). Also compound 3 and other indene N-oxides
could be prepared through the oxime intermediate 4.
Using hydroxylamine, the indenone 2 was converted to
the oxime 4, which was reacted with alkyl or benzyl ha-
lides to afford 3 as a minor product (5: major product).
4
Indenone
Indene N
-oxide
Synthesis of R6 substituted indene N-oxides is described
in Scheme 2. The compound 7 was converted to 8
through Mitsunobu reaction or alkylation, followed by
N-oxide formation with N-methyl hydroxylamine to af-
ford the compound 9.
Therefore, from the indenone skeleton, we have newly
identified indene N-oxide derivatives, which are not
cytotoxic. So we now report the synthesis and a full
SAR of indene N-oxide derivatives as PPARc agonists.
While the representative compound 9h,11 was recently
-O
N+
R
O
O
O
O
O
O
ref. 10
a
Cl
OEt
OEt
2
3
1
(R = H)
b
-O
HO
RO
N+
R
N
N
O
O
O
O
O
O
c
+
OEt
OEt
OEt
3
5
4
Scheme 1. Reagents and conditions: (a) MeNHOH, 2,6-lutidine, EtOH, 70 °C, 40 h, 25%; (b) NH2OH, pyridine, ethanol, 70 °C, 1 h, 65%; (c) MeI,
bromoethane, or benzyl bromide, K2CO3, DMF, rt, 2 h, 81–88% for 5, 7–10% for 3.
O
O
O
O
HO
O
R
HO
a
ref. 10
Cl
OEt
OEt
alkylation
8
6
7
Mitsunobu
reation
c
b
-O
N+
O
O
O
O
R
O
c
R
OEt
OEt
8
9
Scheme 2. Reagents and conditions: (a) R–X, NaH, KI, DMF, rt, 12 h, 81–95%; (b) ROH, triphenylphosphine, DIAD, THF/benzene 3:1, rt,
2 h, 56–93%; (c) MeNHOH, 2,6-lutidine, EtOH, 70 °C, 40 h, 17–36%.

J. H. Ahn et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5239–5244
5241
O
O
A
X= O: a
X= NH: a,b
O
O
O
BnO
BnO
BnO
c
XR
XR
10
12
11
d
O-
N+
O
A
O
A
RO
f, g
O
HO
HO
e
O
O
XR
XR
XR
A
15
14
13
Scheme 3. Reagents and conditions: (a) diethyl carbonate, NaH, 80 °C, 2 h, 85%; (b) cyclopropyl amine or isopropyl amine, xylene, 140 °C, 44–70%;
(c) ACHO, piperidine, acetic acid, benzene, reflux, 6 h, 42–79%; (d) methane sulfonic acid, CH2Cl2, 0 °C, 2 h, 44–70%; (e) phenyl selenyl chloride,
pyridine, H2O2, CH2Cl2, 0 °C, 3 h, 25–72%; (f) R–X, NaH, KI, DMF, rt, 12 h, or ROH, triphenylphosphine, DIAD, THF/benzene 3:1, rt, 2 h, 56–
91%; (g) MeNHOH, 2,6-lutidine, EtOH, 70 °C, 40 h, 22–40%.
Diverse R2- and R3-substituted indene N-oxides were
obtained according to the Scheme 3. Benzyloxy ace-
tophenone 10 reacted with diethyl carbonate to give
b-ketoester, followed by amidation to afford 11.
The compound 11 was treated with several aldehydes
to produce the coupled compound 12, followed by
cyclization using methanesulfonic acid to give 13.
Oxidation of 13 with phenylselenyl chloride and
H2O2 furnished 14, and which was converted to the
final 15 according to the same adoption at R6 posi-
tion and N-oxide formation in a similar manner to
Scheme 2.
Table 1. The substituent effect at the 1-position of indene derivatives
a
Compound
Structure
EC50 (lM)
HO
N
N
O
O
O
4
>10
OEt
MeO
O
5
1.5
OEt
All the synthesized compounds were evaluated for
their activity of PPARc activation. The vector fused
with the ligand binding domain of a human PPARc
gene and the DNA binding site of a yeast GAL-4
gene, and luciferase reporter vector was simulta-
neously transfected in NIH/3T3 cells. Then, each
of the test compounds or the vehicle alone was
added thereto. After incubating for 24 h, the cells
were subjected to lysis. The luciferase activity of
the resultant was then measured, and the potency
of the test compound (EC50, the concentration at
which 50% of the maximum activation was ob-
served) was compared with the reference compound,
rosiglitazone.
O-
N+
O
O
O
3a
3b
0.3
OEt
O-
N+
O
>10
OEt
O-
N+
First, the substitutent effect of the C1 position was
evaluated as shown in Table 1. The oxime analogue
(4) was not active (>10 lM). Whereas, methyl oxime
(5) showed moderate potency with an EC50 value of
1.5 lM. N-methyloxide (3a) exhibited a good activity
(EC50 = 0.3 lM), so we further modified this N-oxide
by adoption of diverse substituents at R2, R3, R6 posi-
tion. N-ethyloxide (3b) and N-benzyloxide (3c) resulted
in a loss of the activity (>10 lM).
O
O
3c
>10
0.32
OEt
Rosiglitazone
a EC50 values were determined from direct regression curve analysis.
with an EC50 value of 50 nM. Other phenylpropylene-
oxy (9d) or phenylbutyloxy (9e) showed diminished
activities.
Next, the substituent effect of the R6 position was ex-
plored (Table 2). While methoxy (3c) and phenylethyl-
oxy (9a) analogues showed sub-micromolar activities,
adamantyl substituent (9b) was detrimental to the activ-
ity. Phenyl propyloxy (9c) seemed to be optimum length
In Table 3, the effects of the R3 position were inves-
tigated. The phenyl derivatives at the R3 (9c) had a

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J. H. Ahn et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5239–5244
Table 3. The substituent effect at the 3-position of indene N-oxide
derivatives
potent activity (50 nM). Ethyl and other alkyl sub-
stituents (15a and 15b) resulted in the decrease of
the activities compared to phenyl. Also, heteroaryl
derivatives (15c and 15e), except furyl (15d), showed
diminished activities. The introduction of substituents
on phenyl ring did not provide improved activity
(15f–15i).
a
Compound
Structure
EC50 (lM)
O-
N+
O
O
9c
0.05
OEt
To improve aqueous solubility and bioavailability by
reducing the overall lipophilicity of indene N-oxide,
the basic nitrogen was introduced at the R6 position
(Table 4). Among the derivatives (9f–9j), morpholino-
ethyloxy analogue (9h) exhibited the most potent
activity with an EC50 value of 15 nM. So we further
modified with morpholinoethyloxy group at the R6
position.
O-
N+
O
O
15a
15b
0.08
0.08
OEt
O-
N+
O
O
O
OEt
The compounds substituted with H, ester and amide
functional groups at R2 position were prepared.
(Table 5) While ethyl ester (9h) at the R2 position
O-
N+
O
15c
15d
15e
0.19
0.05
>1
OEt
Table 2. The substituent effect at the 6-position of indene N-oxide
derivatives
S
a
O-
Compound
Structure
EC50 (lM)
N+
O-
N+
O
O
O
O
O
OEt
3a
0.3
OEt
O
O-
N+
O-
N+
O
O
O
OEt
9a
9b
9c
9d
9e
0.2
N
OEt
HN
O-
N+
O
O
O-
N+
15f
0.66
OEt
O
O
0.84
0.05
0.2
OEt
O-
N+
O-
N+
O
O
O
15g
0.3
O
OEt
O
OEt
O-
N+
O
O-
N+
OEt
O
15h
0.25
O
OEt
O
O
O-
N+
O-
N+
O
O
O
O
OEt
OEt
15i
0.07
0.15
Cl
a EC50 values were determined from direct regression curve analysis.
a EC50 values were determined from direct regression curve analysis.

J. H. Ahn et al. / Bioorg. Med. Chem. Lett. 17 (2007) 5239–5244
5243
Table 4. The substituent effect at the 6-position of indene N-oxide
derivatives
Table 5. The substituent effect at the 2-position of indene N-oxide
derivatives
a
a
Compound
Structure
EC50 (lM)
Compound
Structure
EC50 (lM)
O-
N+
O-
N+
O
O
O
O
N
N
O
9f
0.07
9h
0.015
OEt
OEt
O-
N+
O-
N+
O
O
N
O
O
O
N
N
15j
0.14
0.025
0.20
0.02
0.15
O
9g
9h
9i
0.03
0.015
0.09
0.03
OEt
O-
N+
O-
N+
O
O
O
O
N
O
O
O
N
O
15k
O
OEt
O-
N+
O-
N+
O
N
O
O
N
O
OEt
15l
HN
O-
N+
O-
N+
O
N
O
N
O
O
15m
HN
9j
OEt
O-
N+
a EC50 values were determined from direct regression curve analysis.
O
N
O
15n
showed a good activity (15 nM), methyl ester (15j)
exhibited a decrease of activity. Cyclopropyl amide
analogue (15m) is another potent compound with an
EC50 value of 20 nM. The decarboxylated compound
(15n) was detrimental to the potency.
a EC50 values were determined from direct regression curve analysis.
Table 6. The isomeric effect of indene N-oxide derivatives
Finally, the isomeric effect of compound 9h, which is the
most potent in this series, was explored (Table 6). The
compound 16, which is a stereoisomer of 9h, resulted
in 3-fold less potent than 9h.
a
Compound
Structure
EC50 (lM)
O-
N+
O
O
O
N
O
9h
0.015
OEt
Attempting to optimize the ring substitution of indene
N-oxide with adoptions of various substituents led to
successful improvement in potency. From these SAR
data, we had selected the compound 9h as a representa-
tive compound for evaluating pharmacological profiles,
and we described the results including selectivity toward
other PPARs, glucose uptake, PK, and in vivo study in a
separate paper.11
-
N+
O
O
N
O
16
0.040
OEt
a EC50 values were determined from direct regression curve analysis.
In summary, a series of the novel indene N-oxide deriv-
atives have been synthesized12 and evaluated for their
ability to activate PPARc. The indene N-oxide skeleton
was derivatized at the R1, R2, R3, and R6 positions. The
full SAR study was investigated. The compound 9h
emerged as the most active compound, which showed
an EC50 value of 15 nM.
Acknowledgments
This research was supported by the Center for Biologi-
cal Modulators of the 21st Century Frontier R&D Pro-
gram, the Ministry of Science and Technology, Korea.

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Triantafillou, J.; Cowan, D.; Pennink, B. G. A.; Connolly,
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2005100303).