Modification at the acidic domain of RXR agonists has little effect on permissive RXR-heterodimer activation

Article abstract of DOI:10.1016/j.bmcl.2010.07.012

Retinoid X receptors (RXRs) function as homo- or heterodimers with other nuclear receptors, such as peroxisome proliferator-activated receptors (PPARs), which are targets for treatment of hyperlipidemia and type 2 diabetes, or liver X receptors (LXRs), wh

Full text of DOI:10.1016/j.bmcl.2010.07.012

Bioorganic & Medicinal Chemistry Letters 20 (2010) 5139–5142
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Modification at the acidic domain of RXR agonists has little effect on permissive
RXR-heterodimer activation
Shuji Fujii a, Fuminori Ohsawa a,b, Shoya Yamada a, Ryosuke Shinozaki a, Ryosuke Fukai a,
Makoto Makishima c, Shuichi Enomoto a,b, Akihiro Tai d, Hiroki Kakuta a,
*
a Division of Pharmaceutical Sciences, Okayama University, Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 1-1-1, Tsushima-Naka, Okayama 700-8530, Japan
b Multiple Molecular Imaging Research Laboratory, RIKEN Center for Molecular Imaging Science, Minatojima-minamimachi 6-7-3, Chuo-ku, Kobe, Hyogo 650-0047, Japan
c Division of Biochemistry, Department of Biomedical Sciences, Nihon University School of Medicine, Itabashi-ku, Tokyo 173-8610, Japan
d Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, 562 Nanatsuka, Shobara, Hiroshima 727-0023, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Retinoid X receptors (RXRs) function as homo- or heterodimers with other nuclear receptors, such as per-
oxisome proliferator-activated receptors (PPARs), which are targets for treatment of hyperlipidemia and
type 2 diabetes, or liver X receptors (LXRs), which are involved in glucose/lipid metabolism. PPAR/RXR or
LXR/RXR are known as permissive RXR-heterodimers because they are activated by RXR agonists alone.
Interestingly, the pattern of RXR-heterodimer activation is different depending on the RXR agonist struc-
ture, but the structure–activity relationship has not been reported. Here we show that modification or
replacement of the carboxyl group in the acidic domain of RXR agonists has little or no effect on permis-
sive RXR-heterodimer activation. Phosphonic acid (9), tetrazole (10), and hydroxamic acid (12) analogues
were synthesized from the common bromo intermediate 7. Except for 9, these compounds showed RXR
Received 23 May 2010
Revised 25 June 2010
Accepted 6 July 2010
Available online 8 July 2010
Keywords:
RXR agonists
Permissive heterodimers
PPAR
full-agonistic activities in the concentration range of 1–10
PPAR /RXR and LXR /RXR was the same as it was for RXR, that is, 11 > 10 > 12. These results should be
useful for the development of RXR agonists with improved bioavailability.
lM. The order of agonistic activity toward both
LXR
c
a
a
a
Carboxylic analogues
Docking simulation
Ó 2010 Elsevier Ltd. All rights reserved.
Retinoid X receptors (RXRs)1,2 function as transcription factors
either alone or as heterodimers with receptors such as PPAR
different patterns of activation of PPAR/RXR and LXR/RXR.16 There-
fore, we hypothesized that appropriate structural modification of
RXRs would eliminate the side effects. In addition, most RXR ago-
nists are lipophilic molecules, and their absorption, distribution,
metabolism, and excretion (ADME) characteristics are not optimal.
But, structural modification at the carboxylic moiety might alter
the pattern of permissive RXR-heterodimer activation.
Structural modifications at the carboxylic moiety of RAR ago-
nists have been reported.17,18 However, no structure–activity rela-
tionship (SAR) study of RXR agonists for activity toward permissive
heterodimers has been reported. RXR agonists generally consist of
a lipophilic domain, such as a 5,5,8,8-tetramethyl-5,6,7,8-tetrahy-
dronaphthyl moiety, an acidic domain, such as benzoic acid or nic-
otinic acid, and a linking domain. Although there have been SAR
studies on the linking domain (2 and 3) and on the lipophilic do-
main (NEt-3IP, 4a) (Fig. 1),19 modification of the acidic domain
has been limited to TZ335 (5) (Fig. 1), which has a thiazolidinedi-
one acidic group.20 Thus, modification of the acidic domain in
RXR agonists seemed worthy of investigation.
c
(the molecular target of thiazolidinediones, which are clinically
used to treat insulin resistance),3 and liver X receptors (LXRs; in-
volved in glucose/lipid metabolism).4,5 PPAR/RXR and LXR/RXR
are activated by PPAR and LXR agonists, respectively, but the ago-
nistic potency can be synergistically activated by RXR agonists.6
Interestingly, RXR agonists alone can also activate these heterodi-
mers (permissive heterodimers).7 Focusing on this permissive
mechanism, RXR agonists are expected to show comprehensive
therapeutic efficacy against insulin resistance or impaired glucose
metabolism in type 2 diabetes by modulating various RXR hetero-
dimers, such as PPAR/RXR and LXR/RXR. Thus, RXR agonists,
including LGD1069 (1) (TargretinÒ) (Fig. 1),8–10 which is used in
the USA to treat cutaneous T-cell lymphoma, are candidates for
the treatment of complex disorders such as metabolic syndrome.11
However, RXR agonists often cause side effects, such as weight
gain, plasma triglyceride elevation, and hypothyroidism.12–14
Among them, triglyceride elevation is reported to be based on
the transactivation of SREBP-1c by LXR/RXR.15 It is important to
note that the RXR agonists HX630 (2) and PA024 (3) (Fig. 1) show
Therefore, we synthesized RXR agonists possessing tetrazole,
hydroxamic acid, and phosphonic acid at the acidic domain from
a common bromo intermediate, and evaluated their RXR agonistic
activity and pattern of RXR-heterodimer activation activities to-
* Corresponding author. Tel./fax: +81 (0)86 251 7963.
E-mail address: kakuta@pharm.okayama-u.ac.jp (H. Kakuta).
ward PPARc/RXR and LXRa/RXR.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.07.012

5140
S. Fujii et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5139–5142
Figure 1. Chemical structures of known RXR agonists.
Scheme 1. Reagents and conditions: (a) 2,5-dibromopyridine, p-TsOH, KI, dioxane, reflux, 60%; (b) EtI, NaH, DMF, 0 °C, q.y; (c) methyl 6-chloronicotinate, p-TsOH, dioxane,
reflux, 80%; (d) diethyl phosphite, Pd(PPh3)4, Cs2CO3, THF, microwave irradiation (140 °C), 61%; (e) Me3SiBr, CH2Cl2, rt 76%; (f) CuCN, DMF, reflux, 88%; (g) NaN3, NH4Cl, DMF,
reflux, 43%; (h) NaOH aq, EtOH, reflux, 92%; (i) NaOH aq, MeOH, THF, 60 °C, 98%; (j) O-benzylhydroxylamine, HOBt, EDC, TEA, DMF, rt 82%; (k) H2, 10% Pd-C, EtOAc, rt 76%.
RXRα
As shown in Scheme 1, after coupling reaction of 5,5,8,8-tetra-
methyl-5,6,7,8-tetrahydronaphthylamine (6)21 and 2,5-dibromo-
1.0
0.8
0.6
0.4
LGD1069 (1)
pyridine or methyl 6-chloronicotinate in the presence of
a
R = PO(OH) (9)
2
catalytic amount of p-toluenesulfonic acid, N-ethylation of the
linking nitrogen was performed to afford the common intermedi-
ates 7 and 8. Compound 7 was reacted with diethyl phosphite in
the presence of a palladium catalyst and cesium carbonate in
THF under microwave irradiation at 140 °C,22 and then deprotec-
tion of the esters with trimethylsilyl bromide in methylene chlo-
ride gave the phosphonic derivative 9.23 The bromo atom of 7
was substituted to a cyano group by coupling reaction of interme-
diate 7 and copper cyanide in DMF,24 and then [3 + 2]cycloaddition
reaction was performed with sodium azide to give tetrazolyl deriv-
ative 10.25 Carboxy derivative 11 was synthesized by hydrolysis of
the cyanide derivative or ester 8. Hydroxamic acid 12 was
H
N
R =
(10)
N
N
N
R = CO H (11)
2
0.2
0
R = CONHOH (12)
10-10 10-9 10-8 10-7 10-6 10-5
Concentration (M)
Figure 2. Transactivation dose-response curves of 1 (s), 9 (4), 10 (h), 11 (d), and
12 (N) against RXR in COS-1 cells. The vertical scale is normalized with respect to
M 1, taken as 1.0. The assays were carried out in triplicate at least three times.
a
1
l

S. Fujii et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5139–5142
5141
Figure 3. Proposed structures of RXR agonists 11 (A), 10 (B), and 12 (C) bound to the RXR
a
LBD (pdb code: 1mvc), calculated with AutoDock 4.0.29 Green broken lines indicate
hydrogen bonds.
PPARγ
PPARγ/RXRα
H
1.0
1.0
N
R =
(10)
N
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
N
N
R = CO2H (11)
R = CONHOH (12)
10-8
10-7
10-6
10-5
10-8
10-7
10-6
10-5
Concentration (M)
Concentration (M)
LXRα
LXRα/RXRα
1.0
0.8
0.6
0.4
0.2
0
1.0
0.8
0.6
0.4
0.2
0
10-8
10-7
10-6
10-5
10-8
10-7
10-6
10-5
Concentration (M)
Concentration (M)
Figure 4. Relative transactivation data of 10 (s), 11 (d), and 12 (N) toward PPAR
c
, PPAR
c
/RXR
a
, LXR
a
and LXR
a
/RXR
a
. One micromolar TIPP-703 (PPAR-pan agonist) and
, respectively.
carba-T0901317 (LXR-pan agonist) were used as positive controls for PPAR
c
and PPAR
c
/RXR
a, and LXR
a
and LXR
a/RXRa
produced by coupling of 11 and O-benzylhydroxylamine, followed
RARa activities even at 10 lM (data shown in Supplementary
by deprotection.
data). Figure 2 shows dose–response curves of transactivation
RXRa
and RAR
a
activities of compounds 9–12 were evaluated
activity against RXRa compared to that of 1 lM 1 as a positive
by reporter gene assay in COS-1 cells. All of them did not show
control.

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S. Fujii et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5139–5142
RXR-agonistic activity of compound 11 possessing a carboxy
group reached a plateau at 0.1 M, and 11 (EC50 = 5.28 1.23 nM)
was as potent as 1 (EC50 = 19.8 3.4 nM). Phosphonic acid 9 did not
show RXR-agonist activity up to 10 M. Tetrazole 10 (EC50 = 205
The authors are grateful to Ms. Mariko Nakayama and Mr. Kohei
Kawata for helpful discussions during the preparation of this
manuscript.
l
l
22 nM) and hydroxamic acid 12 showed RXR full-agonistic activity,
though they were less potent than 11. The reason why 10 and 12
show RXR-agonist activities may be the planarity of their acidic
moieties. On the other hand, the lower potency of 12 as compared
with 10 may reflect the acidic character: the pKa values of phenyl-
tetrazole and benzohydroxamic acid are 4.526 and 8.8,27,28 respec-
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.07.012.
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and RXR- heterodimer activation activities toward PPAR
c/RXR
and LXR /RXR indicated that modification of the acidic domain
a
of RXR agonists has little influence on permissive RXR-heterodimer
activation. This information may be useful for the creation of RXR
agonists with superior bioavailability.
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authors are also grateful to Professor Miyachi for presenting
TIPP-703 and carba-T0901317. This work was partially supported
by a Grant-in-Aid for Scientific Research on Priority Areas from
the Ministry of Education, Science, Culture and Sports of Japan.
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