Liver X receptor (LXR) modulators with dibenz[b,f]-[1,4]oxazepin-11-one, (Z)-dibenz[b,f]azocin-6-one, and 11,12-dihydrodibenz[b,f]azocin-6-one skeletons

Article abstract of DOI:10.3987/COM-09-11738

Conformationally restricted heterocyclic analogs of carba-T0901317 with dibenz[b,f][1,4]oxazepin-11-one, 11,12-dihydrodibenz[b,f)azocin-6-one, and (Z)-dibenz[b,f]-azocin-6-one skeletons were prepared as candidate for liver X receptor (LXR) agonists. In vitro transactivation assay revealed that the activity depends on the nature of the linking group.

Full text of DOI:10.3987/COM-09-11738

HETEROCYCLES, Vol. 78, No. 9, 2009
2209
HETEROCYCLES, Vol. 78, No. 9, 2009, pp. 2209 - 2216. © The Japan Institute of Heterocyclic Chemistry
Received, 17th April, 2009, Accepted, 28th May, 2009, Published online, 29th May, 2009.
DOI: 10.3987/COM-09-11738
LIVER X RECEPTOR (LXR) MODULATORS WITH DIBENZ[b,f]-
[1,4]OXAZEPIN-11-ONE, (Z)-DIBENZ[b,f]AZOCIN-6-ONE, AND
11,12-DIHYDRODIBENZ[b,f]AZOCIN-6-ONE SKELETONS
Atsushi Aoyama,a Hiroshi Aoyama,a Makoto Makishima,b Yuichi
Hashimoto,a and Hiroyuki Miyachia,c*
aInstitute of Molecular and Cellular Biosciences, The University of Tokyo. 1-1-1
Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan. bNihon University School of
Medicine. 30-1 Oyaguchi-kamicho, Itabashi-ku, Tokyo 173-8610, Japan.
cGraduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama
University. 1-1-1 Tsushima, Okayama 700-8530, Japan.
Abstract – Conformationally restricted heterocyclic analogs of carba-T0901317
with dibenz[b,f][1,4]oxazepin-11-one, 11,12-dihydrodibenz[b,f]azocin-6-one, and
(Z)-dibenz[b,f]-azocin-6-one skeletons were prepared as candidate for liver X
receptor (LXR) agonists. In vitro transactivation assay revealed that the activity
depends on the nature of the linking group.
INTRODUCTION
Liver X receptors (LXR) are members of the nuclear receptor superfamily and are involved in the
regulation of cholesterol, lipid, and glucose metabolism.1, 2 LXRs are ligand-dependent transcription
factors which bind to DNA as heterodimers with retinoid X receptor (RXR). There are two subtypes,
i.e., LXR and LXR, which have characteristic distribution patterns. LXR is mostly expressed in
liver, adipose tissue and macrophages, while LXR is ubiquitously distributed. The endogenous ligands
of LXRs are reported to be metabolites of cholesterol (oxysterols), as exemplified by
22(R)-hydroxycholesterol (1) and 24(S),25-epoxycholesterol (2).3 In macrophages, liver, and intestine,
activation of LXRs induces the expression of genes involved in cholesterol homeostasis.4 It may be
possible to prevent or even reverse atherosclerosis by modulating the expression or activity of LXRs,
which are therefore an attractive potential therapeutic target. However, the beneficial pharmacological
effects of LXR agonists are compromised by the LXR-mediated increase in the expression of genes that

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affect hepatic lipogenesis, including sterol regulatory element binding protein 1c (SREBP-1c) and fatty
acid synthase (FAS). Indeed, chronic treatment of rodents with pan-full-LXR agonists, such as
T0901317 (3), leads to the accumulation of hepatic triglycerides and causes steatosis.4 Recent studies
indicated a distinct role of the LXR subtype in lipogenesis, because LXR knockout mice are unable to
regulate lipid balance when they are given a high fat diet, and develop steatosis. On the other hand,
LXR knockout mice can manage a high fat diet as effectively as can wild-type mice.5, 6 Therefore,
there is great interest in subtype-selective LXR agonists, especially LXR-selective agonists and/or LXR
modulators that have beneficial effects on cholesterol transport and inflammation, but do not induce
hepatic lipogenesis.
We have studied the design and synthesis of ligands of various nuclear receptors, such as peroxisome
proliferator-activated receptor (PPAR) and farnesoid X receptor (FXR), and we recently expanded our
focus to include another metabolic nuclear receptor, LXR.7, 8 Previously, we have demonstrated that
5-substituted phenanthridin-6-one derivatives, which are conformationally restricted heterocyclic
analogues of carba-T0901317,9 exhibit no LXR-agonistic activity, but show LXR-antagonistic activity.10
This prompted us to speculate that the nature of the LXR-modulating activity elicited by the
conformationally restricted carba-T0901317 derivatives depends on the three-dimensional geometry of
their two phenyl ring moieties. Here, we would like to report the results of further structural
modification of carba-T0901317.
OH
F3C
O
O
N
S
F3C
HO
O
CF3
HO
HO
1; 22( )-hydroxycholesterol
2; 24( ),25-epoxycholesterol
3; T0901317
R
S
Figure 1. Structures of known LXR agonists, 22(R)HC (1), EPC (2) and T0901317 (3)
RESULTS AND DISCUSSION
In order to investigate the effects of the different degrees of conformational restriction, we planned to
synthesize dibenz[b,f][1,4]oxazepin-11-one 5, 11,12-dihydrodibenz[b,f]azocin-6-one 6, and
(Z)-dibenz[b,f]azocin-6-one 7 derivatives with one-atom and two-atom linkers.

HETEROCYCLES, Vol. 78, No. 9, 2009
2211
Et
Et
O
Et
O
Et
N
O
N
N
N
F3C
HO
O
F3C
HO
F3C
HO
F3C
HO
O
CF3
CF3
CF3
CF3
5
6
7
4; Carba-T0901317 analog
Figure 2. Structural development of conformationally restricted carba-T derivatives
We planned to synthesize compound 5 by the intramolecular aromatic nucleophilic substitution reaction
of a substituted phenol derivative as the key step.11 As shown in Scheme 1, Friedel-Crafts type reaction
of 2-methoxyaniline with hexafluoroacetone hydrate proceeded at the para-position of the amino group to
afford 1,1,1,3,3,3-hexafluoropropan-2-ol derivative 8, although the yield (41%) was moderate.
Compound 8 was amidated with 2-fluorobenzoyl chloride in the presence of triethylamine (95% yield),
and subsequent demethylation of the methoxy group with BBr3 afforded quantitatively the key
intermediate phenol derivative 10. The intramolecular aromatic nucleophilic substitution reaction of
compound 10 proceeded smoothly by use of K2CO3 as the base in DMF to afford the
dibenz[b,f][1,4]oxazepin-11-one skeleton in 81% yield. N-Ethylation of compound 11 afforded the
target dibenz[b,f][1,4]oxazepin-11-one derivative 5 in 42% yield.12
H
N
NH2
CF3COCF3
p-TsOH
H
2-fluorobenzoyl chloride
Et3N
NH2
N
BBr3
DCM
F3C
HO
O
F
F3C
HO
OH
OMe
F3C
HO
O
F
toluene
41%
DCM
95%
OMe
OMe
CF3
CF3
CF3
10
8
9
quant.
Et
H
N
O
O
EtI
NaH
N
K2CO3
DMF
81%
F3C
HO
F3C
HO
DMF
42%
O
O
CF3
CF3
5
11
Scheme 1. Synthetic routes to conformationally restricted carba-T0901317 derivatives 5
The preparation of 11,12-dihydrodibenz[b,f]azocin-6-one derivative 6 is summarized in Scheme 2. We
planned to construct this ring system by the intramolecular lactamation reaction of an amino-substituted
benzoic acid derivative as the key step.13 Wittig reaction of 2-nitrobenzyltriphenylphosphonium
bromide (12), which was prepared from 2-nitrobenzyl bromide and triphenylphosphine in toluene (93%
yield), and ethyl 2-formylbenzoate (13), which was prepared by the ethyl esterification of

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HETEROCYCLES, Vol. 78, No. 9, 2009
2-formylbenzoic acid in 98% yield, in the presence of sodium ethoxide in dichlomethane afforded
stilbene derivative 14 in 60% yield as a mixture of stereoisomers. Compound 14 was hydrogenated (15),
friedel-crafts type alkylated (16), hydrolysed with NaOH afforded the precursor acid derivative 17. The
intramolecular lactamation of 17 was proceeded EDCI-HOBt-DIPEA system in CH2Cl2 afforded
11,12-dihydrodibenz[b,f]azocin-6-one derivative 18 although the yield was poor (20% yield). In the
absence of HOBt or with the use of carbodiimidazole as the coupling reagent, we could obtain the lactam
18 in a trace amount. N-Ethylation of compound 18 as described for compound 11 afforded the target
11,12-dihydrodibenz[b,f]azocin-6- one derivative 6 in 63% yield.14
EtI
K2CO3
NO2
NO2
CHO
CHO
PPh3
toluene
CO2H
CO2Et
Br
P+Ph3Br-
DMF
rt, 98%
100 ºC, 93%
12
13
NO2
NH2
NH2
CF3COCF3
p-TsOH
10% Pd/C
H2
NaOEt
DCM
CO2Et
CO2Et
CO2Et
12
13
F3C
HO
AcOEt
rt, 3 h
94%
toluene
130 ºC, 12 h
70%
CF3
rt, 60%
14
15
16
EDCI
HOBt
DIPEA
Et
O
O
H
EtI
NaH
NH2
N
N
CO2H
1N NaOH aq.
F3C
F3C
HO
DMF
63%
EtOH
reflux, 2 h
99%
F3C
HO
CH2Cl2
rt, 28 h
20%
HO
CF3
CF3
CF3
6
17
18
Scheme 2. Synthetic routes to conformationally restricted carba-T0901317 derivatives 6
The preparation of (Z)-dibenz[b,f]azocin-6-one derivativ e 7 is summarized in scheme 3. We planned to
construct this ring system by means of intramolecular Stille coupling reaction of a vinyl-substituted
aromatic
iodide
derivative
as
the
key
step.15
The
Stille
coupling
of
2-(4-amino-3-bromophenyl)-1,1,1,3,3,3-hexafluoropropan-2-ol with tributyl(vinyl)tin in the presence of
Pd(PPh3)4 in toluene afforded 2-vinylaniline derivative 19 in 75% yield. Compound 19 was amidated
with 2-iodobenzoyl chloride in the presence of triethylamine to afford compound 20 in 73% yield. The
hydroxyl group of compound 20 was protected with 2-methoxyethoxymethyl chloride in the presence of
DBU as a base in DMF to afford the MEM- derivative 21 in 81% yield. The N-ethylation of compound
21 as described for compound 11 afforded the N-ethyl derivative 22 in 56% yield. The intramolecular
coupling reaction of compound 22 proceeded smoothly with the use of Pd(OAc)2 and PPh3 in the

HETEROCYCLES, Vol. 78, No. 9, 2009
2213
presence of AcONa as the base in DMF to afford the (Z)-dibenz[b,f]azocin-6-one skeleton in quantitative
yield. The MEM group was deprotected with TiCl4-DCM to afford the target
(Z)-dibenz[b,f]azocin-6-one derivative 7 in 63% yield.16
SnBu3
2-iodobenzoyl chloride
MEMCl
DBU
H
NH2
Br
NH2
H
N
N
Pd(PPh3)4
Et3N
F3C
HO
F3C
HO
DMF
F3C
O
I
DCM
F3C
HO
O
I
toluene
CF3
CF3
MEMO
rt, 81%
CF3
rt, 73%
CF3
100 ºC, 75%
20
21
19
Pd(OAc)2
PPh3
NaOAc
Et
N
Et
O
EtI
NaH
N
TiCl4
DMF
DMF
F3C
MEMO
O
I
F3C
HO
DCM
0 ºC to rt
56%
100 ºC
quant.
CF3
0 ºC
63%
CF3
22
7
Scheme 3. Synthetic routes to conformationally restricted carba-T0901317 derivatives 7
The values of in vitro transactivation activity of the compounds in the present series are summarized in
Table 1, along with that of carba-T0901317 analogue 4 as the positive control, and that of our previously
reported phenanthridin-6-one LXR antagonist. Compound 4 exhibited potent pan LXR-agonistic
activities, i.e., its EC50 values for LXR and LXR are 1.80 and 0.25 M, respectively.
As previously described, the directly linked carba-T0901317 analogue, the phenanthridin-6-one
derivative, did not exhibit LXR-agonistic activity, but did exhibit LXR-antagonistic activity. However,
the compound with the one-atom (oxygen) elongation linker, dibenz[b,f][1,4]oxazepin-11-one derivative
5, exhibited LXR-agonistic activity. It is of interest to note that it exhibited a decreased micromolar
order EC50 value for LXR as compared to compound 4, but still exhibited full agonistic activity (the
intrinsic activity of 5 is 73% of that of T0901317). In the case of LXR, it exhibited decreased potency
and efficacy, showing weak partial agonistic activity (32% of the activity of 10 M T0901317).
(Z)-Dibenz[b,f]azocin-6-one derivative 7, with the ethylidene linker (two-atom elongation linker), also
exhibited LXR-agonistic activity. It exhibited a more potent, sub-micromolar order EC50 value for
LXRas compared to 5 with the one-atom elongation linker, and showed full agonistic activity (the
intrinsic activity of 7 is 75% of that of T0901317). It also exhibited weak partial agonistic activity
towards LXR (67% of the activity of 10 M T0901317). The degree of partial agonism of compound
7 is greater than that of compound 5.

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HETEROCYCLES, Vol. 78, No. 9, 2009
Table 1. In vitro transactivation assay of the present series of compounds as LXR ligands.
LXR
IC50 (M)
LXR
EC50 (M)
Compd.
EC50 (M)
IC50 (M)
Et
N
O
4
N.A.
N.A.
1.80
0.25
F3C
HO
CF3
Et
N
O
5
7
6
32%@10
67%@10
M
M
1.2 (73%)

N.A.
N.A.
N.A.
N.A.
F3C
HO
O
CF3
Et
O
O
N
0.40 (75%)

F3C
HO
CF3
CF3
Et
N
0.95 (110%)
N.A.
N.A.
1.2
0.27 (109%)
N.A.
N.A.
8.2
F3C
HO
Et
N
O
F3C
HO
CF3

M
N.A.: No Activity @ 30
a) Compounds were screened for agonist activity on LXR-GAL4 chimeric receptors in transiently transfected HEK-293 cells. The EC50 value
is the molar concentration of the test compound that affords 50% of the maximal reporter activity. The IC50 value is the molar concentration
of the test compound that affords a 50% decrease in the maximal reporter activity of 100 nM T0901317.
In contrast to the compounds with the oxygen linker and the ethylidene linker, the compound with the
ethylene linker (two-atom elongation linker), 11,12-dihydro-dibenz[b,f]azocin-6-one derivative 6,
exhibited full LXR-agonistic activity towards both subtypes. In the case of LXR, it exhibited
comparable EC50 value to the positive control, carba-T analogue 4. In the case of LXR, it also
exhibited agonistic activity comparable to or somewhat superior to that of carba-T analogue 4. These
structure-activity relationship results clearly indicated the importance of the nature and/or length of the
bridging linker for both potency and efficacy in the present series of compounds.
In summary, we have developed LXR ligands with various degrees of intrinsic activity. We are
planning to conduct an X-ray crystallographic analysis in combination with molecular modeling studies
to understand the reason why these conformationally restricted carba-T analogues exhibit characteristic
activities towards LXRs. We are also planning an in vivo pharmacological evaluation of a representative
compound as a candidate antimetabolic syndrome agent.

HETEROCYCLES, Vol. 78, No. 9, 2009
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ACKNOWLEDGEMENTS
The work described in this paper was partially supported by a Grant-in-aid for Scientific Research from
The Ministry of Education, Culture, Sports, Science and Technology, Japan.
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1
mp 235—237 ℃; H NMR (500 MHz, d6–DMSO)  8.95 (s, 1H), 7.72 (dd, J = 7.8, 2.0 Hz, 1H),
7.68 (d, J = 8.3 Hz, 1H), 7.64 (d, J = 2.0 Hz, 1H), 7.58 (dd, J = 8.3, 7.3 Hz, 1H), 7.54 (d, J = 7.8 Hz,
1H), 7.42 (d, J = 7.8 Hz, 1H), 7.31 (dd, J = 7.8, 7.3 Hz, 1H), 4.09 (q, J = 6.8 Hz, 2H), 1.25 (t, J = 6.8
Hz, 3H); HRMS (FAB) calcd for C18H14F6NO3 406.0878; found: 406.0858 (M+H)+.
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14. 5-Ethyl-2-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)-11,12-dihydrodibenz[b,f]azocin-6-one (6).
mp 255—257 ℃; 1H NMR (500 MHz, CDCL3)  7.43–7.38 (m, 2H), 7.15 (dd, J = 7.3, 1.2 Hz, 1H),
7.11–7.02 (m, 3H), 6.88 (dd, J = 7.3, 1.2 Hz, 1H), 4.34–4.26 (m, 1H), 4.02 (s, 1H), 3.65–3.57 (m,

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HETEROCYCLES, Vol. 78, No. 9, 2009
1H), 3.46–3.39 (m, 1H), 3.36–3.28 (m, 1H), 2.98–2.89 (m, 2H), 1.24 (t, J = 7.3 Hz, 3H); HRMS
(FAB) calcd for C20H18F6NO2 418.1242; found: 418.1220 (M+H)+.
15. J. K. Stille, Angew. Chem., Int. Ed. Engl., 1986, 25, 508.
16. (Z)-5-Ethyl-2-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)-dibenz[b,f]azocin-6-one
(7).
mp
260—262 ℃; 1H NMR (500 MHz, CDCl3)  7.90 (dd, J = 7.9, 1.8 Hz, 1H), 7.63–7.60 (m, 2H), 7.45
(ddd, J = 7.9, 7.9, 1.8 Hz, 1H), 7.40–7.36 (m, 2H), 7.25 (dd, J = 7.9, 1.8 Hz, 1H), 5.52 (s, 1H), 5.48
(s, 1H), 4.40–4.32 (m, 1H), 3.98–3.90 (m, 1H), 3.61 (s, 1H), 1.31 (t, J = 7.3 Hz, 3H) ; HRMS (FAB)
calcd for C20H16F6NO2 416.1085; found: 416.1060 (M+H)+.