A stereo-controlled synthesis of 2,4-dimethyl-4-hydroxy-16- phenylhexadecanoic acid 1,4-lactone and its PPAR activities

Article abstract of DOI:10.1016/j.bmcl.2010.08.069

A novel class of natural PPAR agonists, 2,4-dimethyl-4-hydroxy-16- phenylhexadecanoic acid 1,4-lactone (1), were discovered in marine natural product libraries. The synthesis of 1 was accomplished starting from vinylmethyl ketone. Ring formation of the α,γ dialkyl γ-lactone was achieved via the stereo-controlled reaction of a ketyl radical anion with a chiral methacrylate. In the PPAR agonistic assay, the most potent of the four stereoisomers had EC₅₀ values of 12 μM for mPPARα, 9 μM for mPPARδ and >100 μM for mPPARγ.

Full text of DOI:10.1016/j.bmcl.2010.08.069

Bioorganic & Medicinal Chemistry Letters 20 (2010) 6017–6019
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
A stereo-controlled synthesis of
2,4-dimethyl-4-hydroxy-16-phenylhexadecanoic acid
1,4-lactone and its PPAR activities
Jaeyoung Ko a, , Hoosang Hwang a, , Jungwook Chin a, Dongyup Hahn a, Jaehwan Lee a, Inho Yang a,
Kyoungjin Shin a, Jungyeob Ham b, Heonjoong Kang a, ,à
⇑
a Center for Marine Natural Products and Drug Discovery, School of Earth and Environmental Sciences, Seoul National University, NS-80, Seoul, 151-747, Republic of Korea
b KIST Gangneung Institute, Gangneung Techno Valley, 290 Daejeon-dong, Gangneung, Gangwon-do 210-340, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel class of natural PPAR agonists, 2,4-dimethyl-4-hydroxy-16-phenylhexadecanoic acid 1,4-lactone
Received 25 June 2010
Revised 11 August 2010
Accepted 13 August 2010
Available online 19 August 2010
(1), were discovered in marine natural product libraries. The synthesis of 1 was accomplished starting
from vinylmethyl ketone. Ring formation of the
trolled reaction of a ketyl radical anion with a chiral methacrylate. In the PPAR agonistic assay, the most
potent of the four stereoisomers had EC50 values of 12 M for mPPAR , 9 M for mPPARd and >100
for mPPAR
a,c dialkyl c-lactone was achieved via the stereo-con-
l
a
l
lM
c.
Keywords:
Nuclear receptor
Ó 2010 Elsevier Ltd. All rights reserved.
PPAR
a/d dual agonist
Marine agonist
PPARs are transcriptional factors that belong to the ligand-acti-
vated nuclear receptor superfamily and consist of three isotypes:
PPARa (NR1C1), PPARd (NR1C2), and PPARc (NR1C3). Upon activa-
Results from co-transfection assays using a PPRE-driven luciferase
reporter gene led to the discovery of several compounds that are
efficacious activators of PPARs.
tion by ligands, PPARs form heterodimers with the retinoid X
receptor (RXR). The PPAR/RXR heterodimers bind to the peroxi-
some-proliferator response element (PPRE) present in the pro-
moter regions of target genes and initiate the transcription of an
array of genes involved in glucose and lipid homeostasis in vivo.1
Compound 1, 2,4-dimethyl-4-hydroxy-16 phenyl hexadecanoic
acid 1,4-lactone, showed activity for a transfected PPAR promoter
(Fig. 1).6
We investigated the PPAR agonistic activity profile (subtype
selectivity) of compound 1, which was first isolated from the
deep-water sponge Plakortis nigra by the Faulkner group in
2002.7 However, due to its limited supply, we could not proceed
further with our PPAR research. In this Letter, we report the ste-
reo-controlled synthesis of four stereoisomers of compound 1
and the activity profile of this new class of PPAR agonists.
The nonstereoselective synthesis of compound 1 was performed
in two steps from phenyldecyl bromide (Scheme 1). Ni0-mediated
conjugate addition of phenyldecyl bromide to vinylmethyl ketone
in pyridine (80 °C, 5 h) produced ketone 2 in a 48% yield.8 Through
a ketyl radical anion reaction promoted by SmI2, compound 1 was
successfully synthesized from ketone 2 with methyl methacrylate
PPAR
It regulates the expression of a number of enzymes that take part
in lipid oxidation. The fibrates, well-known PPAR agonists, have
exhibited therapeutic activities in the treatment of hypercholester-
olemia and mixed dyslipidemia.2 PPAR
, which is highly expressed
in adipose tissue, is a drug target for the treatment of diabetes. The
thiazolidinediones (TZDs), PPAR agonists, are insulin-sensitizing
a is mainly expressed in the liver, muscles, and kidney.
a
c
c
chemicals because they increase the expression of genes involved
in the homeostatic regulation of glucose.3 PPARd plays a key role
in regulating lipid metabolism and energy homeostasis in muscle
and adipose tissue. It also increases mitochondrial biogenesis and
fast-to-slow muscle transformation.4,5
Based on high-throughput screening from marine natural prod-
uct libraries, we tried to identify a novel class of PPAR agonists.
2
O
4
O
⇑
Corresponding author. Tel.: +82 2 880 5730; fax: +82 883 9289.
E-mail address: hjkang@snu.ac.kr (H. Kang).
These two authors contributed equally to the work.
Also affiliated with RIO/SNU.
à
Figure 1. Planar structure of compound 1.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.08.069

6018
J. Ko et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6017–6019
O
NiCl2.6H2O
Zn dust
O
Br
+
Pyridine, 80 ºC
48 %
2
O
O
SmI2, t-BuOH
O
O
THF, 0 ºC
56 %
1
cis /trans = 55/45
Scheme 1. Nonstereoselective synthesis of compound 1.
in a 56% yield.9 Because we did not use chiral auxiliaries for this
synthesis, diastereomeric products were obtained (cis/trans = 55/
45).10
The spectral data of synthesized compound 1 matched those re-
ported for the natural product.7 NOESY analysis confirmed that dia-
stereomeric products of compound 1 have relative configurations of
O
O
(
)
11
Ph
O
Ph
(
)
O
11
1a
(2R, 4S)
1b
(2S, 4R)
cis (2R*,4S*)-1 and trans (2S*,4S*)-1. The signals at d 2.19 and 1.68 in
1
*
*
the H NMR spectrum of cis (2R ,4S )-1 were assigned to H-3. The
NOESY spectra of cis (2R*,4S*)-1 showed strong correlations between
the Me-24 signal at d 1.35 and the H-3 signal at d 2.19, between the
H-2 signal at d 2.80 and the H-3 signal at d 2.19, and between Me-23
at d 1.26 and the H-3 signal at d 1.68, all supporting the cis product
with an absolute chemistry of (2R,4S) or (2S,4R). In the 1H NMR
O
O
(
)
11
(
)
11
Ph
O
Ph
(+/-)1c
(2R, 4R) or (2S, 4S)
O
*
*
spectrum of trans (2S ,4S )-1, the signals at d 2.35 and 1.62 were
assigned to H-3. The NOESY spectra of trans (2S*,4 S*)-1 showed
strong correlations between the two methyl signals (d 1.27 and
1.40) and the H-3 signal (d 1.62) and a weak correlation between
the H-2 signal at d 2.80 and the H-3 signal at d 2.35, all supporting
the trans configuration with an absolute chemistry of (2S,4S) or
(2R,4R). We then evaluated the PPAR agonistic activities of the cis/
transisomers(Table1). Interestingly,all ofthestereoisomers ofcom-
Figure 2. Absolute configurations of compound 1.
Table 2
In vitro PPAR activities of the four stereoisomers of 1
a
Compds
Transactivation EC50 (lM)
mPPAR
a
mPPARd
mPPARc
1a
1b
20
39
12
25
22
34
9
ia
ia
ia
ia
pound 1 had agonistic activities for both mPPAR
exhibited no activity for mPPAR
a and mPPARd, but
(À)-1c
c.
(+)-1c
24
*
*
*
*
The cis (2R ,4S )-1 and trans (2S ,4S )-1 enantiomers were fur-
ther separated by chiral HPLC using a Chiralcel OJ-H column,
resulting in a complete separation of the four diastereomers [1a,
1b, (À)-1c, (+)- 1c].10,11 The recent synthesis of (2R,4S)-1a allowed
us to conclude that the absolute configuration of 1b is (2S,4R).12
However, the stereochemistry of the two trans isomers could not
be determined (Fig. 2).
To investigate the mPPAR agonistic activities of compound 1, a
co-transfection assay was performed on all four stereoisomers
(Table 2). Structurally, compound 1 has essential pharmacophores
for PPAR agonist activity (acidic head and hydrophobic tail groups),
which are structurally consistent with all known PPAR agonists.13
a
The compounds were tested for agonist activity on PPAR in transiently trans-
fected CV-I cells. The EC50 value is the molar concentration of the test compound
with 50% of the maximal reporter activity. ‘ia’ means inactive (no apparent activity)
at a concentration of 100 lM.
Next, we developed a method for the synthesis of compound 1
in high enantioselectivity. In 1997, Fukuzawa and co-workers
reported a facile and effective method for the synthesis of optically
active
ephedrine chiral auxiliary were reacted with aldehydes or ketones
in the presence of SmI2 to give -butyrolactones with highly enan-
tioselective control of the chirality at the -position. Chiral auxilia-
ries derived from carbohydrates were used for the enantioselective
synthesis of -substituted
-butyrolactones by the Lin group.15
In 2004, Kerrigan and co-workers also showed that (1R,2S)-N-ben-
zyl ephedrinyl acrylate controls the chirality of the -position in
-butyrolactone, producing the R-configuration through reaction
with various aldehydes (66–81% ee).16
c a,b-Unsaturated esters bearing an
-butyrolactones.14
c
c
The activity pattern suggests the possibility that the
moiety can be a core skeleton as a substitute for the carboxylic acid
group of many PPAR agonists, suggesting the importance of the
chiralities of the a- and c-positions on the c-lactone.
c-lactone
a
,c
c
c
c
Table 1
We synthesized several N-benzyl ephedrinyl acrylates as chi-
ral auxiliaries to evaluate their diastereoselectivity and enanti-
In vitro PPAR activities of the stereoisomers of compound 1
a
Compds
Transactivation EC50 (lM)
oselectivity. Ephedrinyl auxiliaries 3,
4 and 5 were easily
mPPAR
a
mPPARd
mPPARc
synthesized from the corresponding starting materials in high
yields (Scheme 2). Using t-butyl alcohol as a proton source, we
investigated the reaction of these various methacrylates with
ketone 2. Specifically, a solution of ketone 2 in THF was slowly
added to a solution of SmI2 in THF at 0 °C. The reaction mixture
was stirred at that temperature for 1 h and warmed to room
temperature over a period of 5 h.
*
*
cis (2R ,4S )-1
24
13
22
16
ia
ia
*
*
trans (2S ,4S )-1
a
The compounds were tested for agonist activity on PPAR in transiently trans-
fected CV-I cells. The EC50 value is the molar concentration of the test compound
with 50% of the maximal reporter activity. ‘ia’ means inactive (no apparent activity)
at a concentration of 100 lM.

J. Ko et al. / Bioorg. Med. Chem. Lett. 20 (2010) 6017–6019
6019
O
O
O
Benzyl bromide
OH
OH
OH
O
N
H
Ph
N
Ph
N
CH2Cl2, TEA
2h. rt
DMF, 80 ºC
2 days
95 %
Ph
Ph
Ph
O
O
84 %
3
O
O
O
Boc2O
Boc
OH
Boc
H2N
H2N
N
N
H
CH2Cl2, TEA
2h. rt
CH2Cl2, TEA
3h. rt
H
Ph
Ph
Ph
Ph
O
O
99 %
88 %
O
O
4
O
Boc2O
OH
Boc
OH
Boc
O
N
H
N
H
CH2Cl2, TEA
2h. rt
CH2Cl2, TEA
3h. rt
Ph
Ph
5
95 %
81 %
Scheme 2. Synthesis of chiral auxiliary-methacrylates.
Table 3
Synthesis of 1 using various chiral auxiliaries
References and notes
Entry Methacrylates
Diastereoselectivitya Enantioselectivityb Yieldc
(%)
1. Berger, J.; Moller, D. E. Annu. Rev. Med. 2002, 53, 409.
2. Rosenson, S. R. Expert Rev. Cardiovasc. Ther. 2008, 6, 1319.
3. Picard, F.; Auwerx, J. Annu. Rev. Nutr. 2002, 22, 167.
cis-1/trans-1
1a/1b (À)/(+)-1c
4. Wang, Y.; Zhang, C.; Yu, R. T.; Cho, H. K.; Nelson, M. C.; Bayuga-Ocampo, C. R.;
Ham, J.; Kang, H.; Evans, R. M. PLoS Biol. 2004, 2, e294.
5. Narkar, V. A.; Downes, M.; Yu, R. T.; Embler, E.; Wang, Y.; Banayo, E.;
Mihaylova, M. M.; Nelson, M. C.; Zou, Y.; Juguilon, H.; Kang, H.; Shaw, R. J.;
Evans, R. M. Cell 2008, 134, 405.
6. CV-1 cells were cultured in Dulbecco’s modified Eagle’s medium (DMEM). Cells
were transfected with plasmid mixture containing b-galactosidase expression
vector and TK-PPRE-luc vector by Superfect reagent (QIAGEN). Transfected
cells were incubated with compounds (marine natural products). Luciferase
activity was analyzed after incubation for 24 h at 37 °C.
1
Methyl
55/45
51/49 49/51
56
methacrylate
(1R,2S)-3
(1R)-4
2
3
4
50/50
50/50
49/51
45/55 26/74
70/30 27/73
28/72 81/19
45
60
54
(1S,2R)-5
trans and cis configurations were confirmed by 1H–1H NOESY, and the ratio of
trans/cis was determined by HPLC.
Enantioselectivity was determined by HPLC analysis on
column.
a
b
a Chiralcel (OJ-H)
7. Sandler, J. S.; Colin, P. L.; Hooper, J. N. A.; Faulkner, D. J. J. Nat. Prod. 2002, 65,
1258.
c
Total isolated yields of trans and cis products.
8. (a) Manchand, P. S.; Yiannikouros, G. P.; Belica, P. S.; Madan, P. J. Org. Chem.
1995, 60, 6574; (b) Garraffo, H. M.; Jain, P.; Spande, T. F.; Daly, J. W.; Jones, T. H.;
Smith, L. J.; Zottig, V. E. J. Nat. Prod. 2001, 64, 421; (c) Sustmann, R.; Hopp, P.;
Holl, P. Tetrahedron Lett. 1989, 30, 689.
In all cases, diastereoselectivity was not observed (Table 3). In
terms of enantioselectivity, methyl methacrylate showed no effect,
as demonstrated by the resulting racemic mixture (entry 1). On the
other hand, when methacrylate (1R,2S)-3 was used as a chiral aux-
iliary, (+)-1c predominated, while no enantioselectivity between
1a and 1b was achieved (entry 2). However, both 1a and (+)-1c
were the major products when using methacrylate (1R)-4, thus
affecting the enantioselectivity of the cis product (1a and 1b) de-
spite the absence of substituents on its 2-position (entry 3). Based
on these results, we expected that the S-configuration of the 1-po-
sition of the ephedrinyl auxiliary would produce the most active
stereoisomer (entry 4) and concluded that the stereochemistry of
each diastereomer was influenced by the configuration of the chi-
ral auxiliary.
In summary, we found that the four diastereomers of compound
1 comprise a novel class of natural PPAR agonists. Their PPAR activ-
ities suggested that compound 1 could form a new class of PPARa/d
dual agonists. We also achieved the stereo-controlled synthesis of
1 starting from vinylmethyl ketone with enantioenrichment using
chiral auxiliaries in a ketyl radical anion reaction.
9. (a) Molander, G. A.; Harris, C. R. Chem. Rev. 1996, 96, 307; (b) Otsubo, K.;
Inanaga, J.; Yamaguchi, M. Tetrahedron Lett. 1986, 27, 5763; (c) Kawatsura, M.;
Matsuda, F.; Shirahama, H. J. Org. Chem. 1994, 59, 6900.
10. Data for cis (2R ,4S )-1: 1H NMR (500 MHz, CDCl3) d 7.15–7.29 (m, 5H), 2.80 (m,
1H), 2.59 (t, 2H, J = 7.7 Hz), 2.19 (dd, 1H, J = 9.1, 12.5 Hz), 1.68 (m, 1H), 1.64 (m,
4H), 1.35 (s, 3H), 1.26 (d, 3H, J = 7.6 Hz), 1.25–1.40 (m, 18H); 13C NMR
(125 MHz, CDCl3) d 179.5, 143.2, 128.6, 128.4, 125.7, 84.4, 42.0, 41.9, 36.2, 35.2,
31.7, 30.0, 29.8, 29.7, 29.6, 29.5, 24.9, 23.9, 15.7; HRMS calcd for C24H38O2 (M+)
*
*
358.29; found 358.2870; 1a [a]D = À4.1 (c 0.003, CHCl3), 1b [a]D = +3.6 (c 0.003,
CHCl3).
Data for trans (2S*,4S*)-1: 1H NMR (500 MHz, CDCl3) d 7.15–7.29 (m, 5H), 2.80
(m, 1H), 2.59 (t, 2H, J = 7.7 Hz), 2.35 (dd, 1H, J = 9.3, 12.8 Hz), 1.62 (m, 1H), 1.59
(m, 4H), 1.40 (s, 3H), 1.27 (d, 3H, J = 7.2 Hz), 1.25–1.40 (m, 18H); 13C NMR
(125 MHz, CDCl3) d 179.7, 143.2, 128.6, 128.4, 125.7, 84.6, 42.0, 40.5, 36.2, 35.7,
31.7, 30.1, 29.8, 29.7, 29.6, 29.5, 27.2, 24.3, 16.3; HRMS calcd for C24H38O2 (M+)
358.29; found 358.2869; (À)-1c [
a]D = À6.3 (c 0.005, CHCl3); (+)-1c [a]D = +7.4
(c 0.004, CHCl3).
11. HPLC conditions: Chiralpak OJ-H (10 Â 250 mm) eluent, hexane/isopropyl
alcohol = 97/3; detection, UV at 209 nm. Retention time; 1a (7.2 min), 1b
(11.1 min), (À)-1c (8.7 min) and (+)-1c (12.5 min).
12. Garnier, J.-M.; Robin, S.; Guillot, R.; Rousseau, G. Tetrahedron: Asymmetry 2007,
18, 1434.
13. (a) Markt, P.; Petersen, R. K.; Flindt, E. N.; Kristiansen, K.; Kirchmair, J.; Spitzer,
G.; Distinto, S.; Schuster, D.; Wolber, G.; Laggner, C.; Langer, T. J. Med. Chem.
2008, 51, 6303; (b) Wei, Z.; Petukhov, P. A.; Bizik, F.; Teixeira, J. C.; Mercola, M.;
Volpe, E. A.; Glazer, R. I.; Wilson, T. M.; Kozikowski, A. P. J. Am. Chem. Soc. 2004,
126, 16714.
Acknowledgements
14. Fukuszwa, S.; Seki, K.; Tatsuzawa, M.; Mutoh, K. J. Am. Chem. Soc. 1997, 119,
1482.
15. (a) Wang, W.; Zhong, Y.; Lin, G. Tetrahedron Lett. 2003, 44, 4613; (b) Huang, L.;
Xu, M.; Lin, G. J. Org. Chem. 2005, 70, 529.
16. Kerrigan, N. J.; Hutchison, P. C.; Heightman, T. D.; Procter, D. Org. Biomol. Chem.
2004, 2, 2476.
H.H., J.H., D.H., and I.Y. were in part supported by the BK21 pro-
gram, Ministry of Education, Science and Technology, Korea. This
work was supported by the Marine Biotechnology Program, Minis-
try of Land, Transport and Maritime Affairs, Korea.