Substituents at the naphthalene C3 position of (-)-Cercosporamide derivatives significantly affect the maximal efficacy as PPARγ partial agonists

Article abstract of DOI:10.1016/j.bmcl.2011.12.066

Peroxisome proliferator-activated receptor gamma (PPARγ) is a potential drug target for treating type 2 diabetes. The selective PPARγ modulators (SPPARMs), which partially activate the PPARγ transcriptional activity, are considered to improve the plasma glucose level with attenuated PPARγ related adverse effects. However, the relationships between desired pharmacological profiles and ligand specific PPARγ transcriptional profiles have been unclear. And there is also little knowledge of how to control ligand specific PPARγ transcriptional profiles. Herein, we present synthesis of novel derivatives containing substituent at naphthalene C3 position of compound 1. The novel derivatives showed various maximal efficacies as PPARγ partial agonist.

Full text of DOI:10.1016/j.bmcl.2011.12.066

Bioorganic & Medicinal Chemistry Letters 22 (2012) 1348–1351
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Substituents at the naphthalene C3 position of (À)-Cercosporamide
derivatives significantly affect the maximal efficacy as PPAR
c
partial agonists
a,
⇑
a
a
b
a
Akihiro Furukawa , Tsuyoshi Arita , Takehiro Fukuzaki , Susumu Satoh , Makoto Mori ,
a
a
b
a
a
a
Takeshi Honda , Yumi Matsui , Kenji Wakabayashi , Shinko Hayashi , Kazushi Araki , Jun Ohsumi
Shinagawa R&D Center, Daiichi Sankyo Co., Ltd, 1-2-58, Hiromachi, Shinagawa-ku, Tokyo, Japan
a
b
Daiichi Sankyo RD Novare Co., Ltd, 1-16-13, Kitakasai, Edogawa-ku, Tokyo, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Peroxisome proliferator-activated receptor gamma (PPAR
c
) is a potential drug target for treating type 2
Received 29 October 2011
Revised 11 December 2011
Accepted 13 December 2011
Available online 16 December 2011
diabetes. The selective PPAR
activity, are considered to improve the plasma glucose level with attenuated PPAR
effects. However, the relationships between desired pharmacological profiles and ligand specific PPAR
transcriptional profiles have been unclear. And there is also little knowledge of how to control ligand spe-
cific PPAR transcriptional profiles. Herein, we present synthesis of novel derivatives containing substi-
tuent at naphthalene C3 position of compound 1. The novel derivatives showed various maximal
efficacies as PPAR partial agonist.
c
modulators (SPPARMs), which partially activate the PPAR
c
transcriptional
c
related adverse
c
c
Keywords:
(
À)-Cercosporamide
Diabetes
PPAR modulator
SPPARM
SPPAR
c
Ó 2011 Elsevier Ltd. All rights reserved.
c
c
M
Peroxisome proliferator-activated receptor gamma (PPAR
member of a large family of ligand-activated nuclear hormone
c
) is a
sufficient plasma glucose lowering effect. Although the maximal
efficacies of SPPARMs on PPAR transcriptional activity are impor-
c
receptors, and is known to mediate adipocyte differentiation and
tant for their pharmacological profiles, there are few structure–
activity relationship studies.
1
13
improved plasma glucose levels. The PPAR
c
full agonists, Pioglit-
azone and Rosiglitazone, have been used to treat patient with type
We thought it would be valuable to extend our knowledge
about controlling the maximal efficacies of SPPARMs. Thus, we
2
diabetes. In spite of the beneficial effect, the use of these drugs
has been limited because of the adverse effects such as weight
undertook the structure–activity relationship studies of PPARc
gain, edema and anemia.2 Furthermore, additional concerns that
partial agonistic (À)-Cercosporamide derivatives. In this investiga-
tion, we intended to introduce various substituents at the naphtha-
lene C3 position of compound 1 with an expectation to be altering
the maximal efficacies. The reason we selected the naphthalene C3
position was that the X-ray crystal structure analysis of the
the use of PPARc full agonists elevates the risk of cardiovascular
3
4
events and fracture have been raised. Recently, the selective
PPAR modulators (SPPARMs), which partially activate the PPAR
transcriptional activity without activating PPAR fully, have been
considered efficacious to treat type 2 diabetes with attenuated
c
c
c
complex of PPARc–LBD (ligand binding domain) and compound
5
PPAR
c related adverse effects. Some SPPARMs, such as Fmoc-L-
leucine, FK614, T2384,8 INT-131,9 MBX-102, MK-0533, and
6
7
10
11
12
(
À)-Cercosporamide derivative 1 (Fig. 1), were reported to im-
prove plasma glucose level in hyperglycemic rodent models with-
out several undesirable side effects. Thus the developments of
novel SPPARMs as drug candidates attract a great deal of attention.
We thought that pharmacological profiles of SPPARMs were
determined by how much extent they activate PPAR
tional activity. A compound activating PPAR too much would
induce PPAR full agonist-related side effects. On the other hand
a compound activating PPAR at a much less level would lack
c transcrip-
c
c
c
⇑
Corresponding author. Tel.: +81 3 3492 3131; fax: +81 3 5436 8563.
E-mail address: furukawa.akihiro.zy@daiichisankyo.co.jp (A. Furukawa).
Figure 1. (À)-Cercosporamide derivative as selective PPAR
c modulator.
0
960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.12.066

A. Furukawa et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1348–1351
1349
112
extend to PPAR
of PPARc.
suggested that substituents at naphthalene C3 position would
helix12, which has an important role in activation
We synthesized the novel (À)-Cercosporamide deriva-
tives and tested their PPAR transcriptional activities in the cell-
based assay. Moreover, we carried out the X-ray crystal structure
analyses of complexes of PPAR –LBD and some derivatives, which
showed different maximal efficacies as PPAR partial agonist, to
reveal the relationships between the maximal efficacies and the
pattern of interacting with PPAR
c
1
4
c
c
c
c
.
Almost all of novel (À)-Cercosporamide derivatives were
synthesized by condensation reactions between methylated (À)-
Cercosporamide and 3-substituted-1-naphthaldehydes. The alde-
hydes were synthesized as shown in Scheme 1. 1,3-Dimethyl
naphthaldehyde 2 was oxidized by ceric ammonium nitrate to
1
5
3
-methyl-1-naphthaldehyde 3. A known 3-hydroxy-1-naphthal-
1
6
dehyde 4 was converted to compounds 5, 6, 7, and 8. The triflate
was treated with palladium catalyst and methanol under a car-
8
bon monoxide atmosphere to yield compound 9. Compound 10
was synthesized from compound 9 by 4 steps, acetal protection
of aldehyde, reduction of ester by lithium aluminum hydride,
methylation of alcohol, and hydrolysis of acetal protecting group.
Heck reaction of the triflate 8 and methyl acrylate afforded com-
pound 11. The triflate 8 was also treated with tetrakis(triphenyl-
phosphine)palladium and methyl 3-butanoate, pre-activated by
Scheme 2. Reagents and conditions: (a) (i) MeI, K
substituted-1-naphthoaldehyde, Et
79%; (b) K CO , MeOH–CH Cl , 25 °C, 1 h, 72%; (c) Pd-C, EtOAc–EtOH, 25 °C, 3.5 h
2
CO
3
, DMF, 25 °C, 24 h, 66%, (ii) 3-
3
SiH, TFA, acetonitrile, 25–50 °C, 3–10 d, 38–
2
3
2
2
2
under H , 72%; (d) LiOH aq, 25 °C, 1–4 h, 58%–quant.
palladium catalyzed hydrogenation. The esters 14, 18, 21, and 23
were hydrolyzed to carboxylic acid 15, 19, 22, and 24.
9
-BBN, to provide compound 12. All of these 3-substituted-1-
naphthaldehydes were condensed with methylated (À)-Cercos-
The PPAR
substituted derivatives were tested in the cell-based reporter assay
using MG-63 cells transiently transfected with pSG5–hPPAR
which is pSG5 vector inserted the full-length human PPAR gene,
and the results were summarized in Table 1. Compound 12 showed
that methyl substituent did not affect the PPAR transcriptional
c transcriptional activities of napthlene C3 position
poramide using triethylsilane and trifluoroacetic acid as shown in
1
7
Scheme 2. Compound 20 was converted to compound 21 by
c,
c
c
activity, both the affinity and the maximal efficacy. Interestingly,
the hydroxyl group and alkoxy groups decreased the maximal effi-
cacies. The compounds 15, 16, and 17 showed low Emax values 29%,
3
2%, and 22%, respectively. This effect would be attributed to the
oxygen atom directly bonding to the naphthalene ring because
compound 13, which is an oxygen position isomer of compound
1
7, did not show a decreased Emax value. On the other hand, ester
and carboxylic acid groups combined with alkyl linkers increased
the maximal efficacies. Compound 21 showed a moderately high
Table 1
PPARc transcriptional activities in the cell-based assay
Compound
3-Substituent
Transactivationa
EC50 (nM) max (%)
E
1
–H
–Me
–CH OMe
2
–OAc
–OH
–OMe
–OEt
–CO
–CO
–(CH
–(CH
–(CH
–(CH
180
210
200
680
130
94
240
880
>1000
130
320
42
47
51
44
50
29
32
22
55
12
13
14
15
16
17
18
19
21
22
23
24
2
Me
H
N.D. b
79
2
2 2
) CO
2 2
) CO
2 3
) CO
2 3
) CO
2
2
2
2
Me
H
Me
H
109
99
105
106
67
11
Rosiglitazone
Scheme 1. Reagents and conditions: (a) Ce(NH
0%; (b) R-I, NaH, DMF, 0–25 °C, 1 h, 45–49%; (c) Ac
d) PhNTf , NaH, THF, 0 °C, 1.5 h, quant.; (e) Pd(OAc)
0 °C, 3 h under CO, 95%; (f) (i) 1,3-propandiol, TsOH, toluene reflux, 4 h, (ii) LiAlH
O, 0–25 °C, 1.5 h, (iii) MeI, NaH, DMF; 0–25 °C, 1.5 h, (iv) AcOH–H O, 50 °C, 2 h,
9% in foursteps; (g) methyl acrylate, Pd(OAc) , dppf, Et N, DMF, 60 °C, 22 h, 52%;
h) (i) methyl 3-butenoate was hydroborated by 9-BBN, (ii) Pd(PPh , K PO , 1,4-
dioxane, 85 °C, 20 h, 51%.
4
)
2
(NO
O, pyridine, 25 °C, 4 h, quant.;
, dppf, MeOH, Et N, DMF,
3 6 2
) , AcOH–H O, 80 °C, 0.5 h,
a
The transactivation in the presence of an in-house potent PPAR
c
full agonist
3
(
6
Et
8
(
2
(
3.3 nM) was defined as 100%, while that in the vehicle alone was defined as zero.
The maximum transactivation in the presence of the test compound was defined as
max (%). The concentration of the test compound indicating Emax/2 value was
2
2
3
4
,
E
2
2
defined as EC50. The values of each parameter were determined by nonlinear curve
fitting using Delta Graph.
2
3
)
3 4
3
4
b
The data was not determined because the transactivation did not reach plateau.

1
350
A. Furukawa et al. / Bioorg. Med. Chem. Lett. 22 (2012) 1348–1351
E
max value at 79% and compounds 22, 23, and 24 showed high Emax
values around 100% same as Rosiglitazone, which meant they
turned from SPPARMs into PPAR full agonists. In regard to the al-
kyl linkers, the n-propylene (compound 24, EC50: 67 nM) had five
times higher affinity than the ethylene (compound 22, EC50
c
:
3
20 nM). However, direct bonded ester or carboxylic acid groups,
compounds 14, 18 and 19, decreased their affinity to PPARc. These
results revealed that small substituents at the naphthalene C3 po-
sition of (À)-Cercosporamide derivatives significantly affect the
affinities to PPARc and the maximal efficacies as PPARc partial
agonist.
To properly understand the effects of the substituents, we car-
ried out the X-ray crystal structure analyses of complexes of
PPARc–LBD with characteristic compounds, full agonistic com-
pound 24, moderately high Emax compound 21, and low Emax com-
1
8
pound 17. The cercosporamide scaffolds and the naphthalene
Figure 3. Crystal structure of the complex of PPARc–LBD with compound 21
(shown in orange stick representation).
rings of these compounds take almost the same position as those
1
2
of compound 1. The cercosporamide scaffolds occupy a space be-
tween helix3 and b-sheet, making water-mediated hydrogen
bonds with backbone carbonyl oxygen of Leu340 and amide NH
of Ser342. The naphthalene rings are embedded in a hydrophobic
region formed by helix3, helix5, b-strand2, and helix7.
The butanoic acid group of full agonistic compound 24 extends
to helix12 and forms a hydrogen bonding network with the hydro-
xyl group of Ser289, imidazol rings of His323 and His449, and phe-
nol group of Tyr473, functioning the same as the thiazolidinedione
moiety of Rosiglitazone (Fig. 2). This type of hydrogen bonding net-
work is important for stabilizing a PPAR
common among PPAR full agonists. Thus, it is reasonable that
compound 24 acted as a PPAR full agonist. The propionic acid
c active conformation and
c
c
group of compounds 22 and the methyl butanoate group of 23
would also have similar hydrogen bonding networks.
On the other hand, the methyl propionate group of moderately
high Emax compound 21 does not extend to helix12 (Fig. 3). The
methyl propionate group occupies a space surrounded by Ile326,
Tyr327, His323, and His449. To the best of our knowledge, no SPP-
ARMs occupying this space have been reported. It is unclear why
Figure 4. Crystal structure of the complex of PPARc–LBD with compound 17
(
shown in green stick representation).
the methyl propionate group increased maximal efficacy of PPAR
c
transcriptional activity without a hydrogen bonding for stabilizing
helix12, but occupying this space might have some effects of stabi-
lizing helix12.
The oxygen atom adjacent to naphthalene C3 carbon of the
compound 17 makes hydrogen bonding with the hydroxyl group
of Ser289 (Fig. 4). We speculate that this hydrogen bonding has
have a oxygen atom in the same position as compounds 17 and 13,
in which methoxymethyl group is an oxygen position isomer of
ethoxy group in compound 17, did not show decreased Emax value.
However, it should be reminded that the hydroxyl group of Ser289
is involved in the hydrogen bonding network for stabilizing he-
an important role to decreasing the maximal efficacy as PPAR
c
par-
lix12 in the case of PPARc full agonists. To elucidate the controver-
tial agonist. Because the other low Emax compounds 15 and 16 also
sial role of the hydrogen bonding between PPARc ligands and the
Ser289, more careful studies would be needed.
In conclusion, we synthesized several (À)-Cercosporamide
derivatives containing substituents at naphthalene C3 position
for clarifying structure–activity relationships as PPARc partial ago-
nist. The PPAR transcriptional activities of these compounds were
c
tested in the cell-based reporter assay. These derivatives showed
various profiles. Compounds 15, 16, and 17, which contain an oxy-
gen atom adjacent to naphthalene C3 carbon, showed low maximal
efficacy. Compound 21 indicated moderately high maximal effi-
cacy with occupying the unknown space without direct interaction
with Tyr473. Compounds 22, 23, and 24 have full agonistic profiles.
We believe that the knowledge of structure–activity relationships
on the maximal efficacies as PPARc partial agonists is useful for
creating novel SPPARMs as drug candidates.
Acknowledgments
We thank Mr. Takashi Suzuki and his co-workers at Onahama
Plant, Daiichi Sankyo Propharma Co. Ltd, for providing the purified
(À)-Cercosporamide.
Figure 2. Crystal structure of the complex of PPAR
in cyan stick representation) is superimposed on that of Rosiglitazone (shown in
magenta stick representation, derived from 2PRG.pdb ).
c–LBD and compound 24 (shown
1
4

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