First identification of xanthone sulfonamides as potent acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.03.101

Inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT) would be useful anti-atherogenic agents, since an absence of ACAT affects the absorption and transformation of cholesterol, indirectly resulting in the reduction of cholesteryl ester accumulation in blood vessels. This report discloses xanthone sulfonamides as novel class small molecule inhibitors of ACAT. A series of xanthone sulfonamides were synthesized and evaluated to result in the identification of several potent ACAT inhibitors, among which 2n proved to be more potent than the positive control Sandoz58-35. Moreover, a molecular model for the binding between 2n and the active site of ACAT-2 was provided based computational docking results.

Full text of DOI:10.1016/j.bmcl.2010.03.101

Bioorganic & Medicinal Chemistry Letters 20 (2010) 3094–3097
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
First identification of xanthone sulfonamides as potent acyl-CoA:cholesterol
acyltransferase (ACAT) inhibitors
Honggang Hu a, , Hongli Liao c, , Jun Zhang a, Weifeng Wu a, Jufang Yan b, Yonghong Yan b, Qingjie Zhao a,
Yan Zou a, Xiaoyun Chai a, Shichong Yu a, Qiuye Wu a,
*
a Department of Organic Chemistry, School of Pharmacy, Second Military Medical University, Shanghai 200433, People’s Republic of China
b Pharmaceutical Institute of Chengdu Di-Ao Pharmaceutical Group, Chengdu, 610041, People’s Republic of China
c School of Pharmacy, Chengdu Medical College, Chengdu 610083, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Inhibitors of acyl-CoA:cholesterol acyltransferase (ACAT) would be useful anti-atherogenic agents, since
an absence of ACAT affects the absorption and transformation of cholesterol, indirectly resulting in the
reduction of cholesteryl ester accumulation in blood vessels. This report discloses xanthone sulfonamides
as novel class small molecule inhibitors of ACAT. A series of xanthone sulfonamides were synthesized and
evaluated to result in the identification of several potent ACAT inhibitors, among which 2n proved to be
more potent than the positive control Sandoz58-35. Moreover, a molecular model for the binding
between 2n and the active site of ACAT-2 was provided based computational docking results.
Ó 2010 Elsevier Ltd. All rights reserved.
Received 1 December 2009
Revised 2 March 2010
Accepted 27 March 2010
Available online 1 April 2010
Keywords:
Xanthone
Sulfonamide
Acyl-CoA:cholesterol acyltransferase (ACAT)
Inhibitor
Esterification of intracellular cholesterol has been proved to be
catalyzed by acyl-CoA:cholesterol acyltransferase (ACAT; EC
2.3.1.26).1 In hepatocytes and intestinal cells, cholesterol is esteri-
fied by ACAT and incorporated into apo B-containing lipoproteins,
which are subsequently secreted into circulation. After lipolytic
conversion, these lipoproteins are taken up by the cells of various
organs, where their cholesteryl esters are hydrolyzed in lysosomes
to liberate free cholesterol, which is re-esterified by ACAT again for
storage in cytoplasmic lipid droplets.2,3 Recent research shows that
ACAT could mediate foam cell formation, an initial event of athero-
sclerosis.4 Therefore, it is possible that inhibition of ACAT could re-
sult in a protective effect against atherosclerosis. In addition, ACAT
inhibitors could be useful for the treatment of Alzheimer’s disease,
for they can decrease the generation of amyloid b peptide in animal
models.5
positive control (Sandoz58-35, an ACAT inhibitor, from Sigma).
This finding prompted us to undertake further investigation. Here-
in, we describe our efforts to optimize the inhibitory effects of this
compound by analyzing structure–activity relationships.
Compounds required for the establishment of structure–activ-
ity relationship were prepared as shown in Scheme 1 starting
from 2,4,5-trimethoxybenzoic chloride (3). Friedel–Crafts acyla-
tion of the 1,3,5-trimethoxybenzene (4) afforded benzophenone
(5) and the free OH group in 5 was formed by demethylation
in extra amount of aluminium chloride.10 Treatment of 5 with
tetrabutylammonium hydroxide in pyridine and water under
A cell based high-throughput screening (HTS) assay has been
successfully developed by Rudel’s group to measure ACAT activity.6
In recent years, our group has been focusing on synthesizing and
evaluating the biological activities of novel xanthone com-
pounds.7,8 During the screening, compound 1 (Fig. 1), a xanthone
sulfonamide, was identified to show ACAT inhibitory activity.
Compound 19 showed a good inhibitory rate of 32.4% at 10
lg/
ml concentration in the cell based assay, compared to 55.0% for the
* Corresponding author. Tel./fax: +86 21 8187 1225.
E-mail addresses: wuqysmmu@sohu.com, huhonggang_fox@msn.com (Q. Wu).
Honggang Hu and Hongli Liao contributed equally to this work.
Figure 1. ACAT inhibitor identified through HTS.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.03.101

H. Hu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3094–3097
3095
Scheme 1. Synthesis of compounds 2a–w. Reagents and conditions: (a) AlCl3, Et2O, rt, 48 h, 72%; (b), TBAOH (25% in H2O), Py-H2O (1:1), reflux, 4 h, 95%; (c) HSO3Cl, 0 °C,
30 min, 80%; (d) amine, 1,4-dioxane, rt, 1 h, 90–98%.
Figure 2. The main HMBC correlations of compound 7.
Figure 3. Computed binding geometry of 2n in the active site of ACAT-2.

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H. Hu et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3094–3097
reflux gave 6 in high yield (95%).11 Chlorosulfonic acid was added
dropwise into the flask containing 6 at 0 °C to give key interme-
diate 7 as a brown powder, which was characterized by 1D and
2D NMR. The main HMBC correlations of 7 are shown in Figure 2.
Reaction of 6 with different amines formed the final xanthone
sulfonamides 2a–w in quantitative yield.12,13 The reactions were
carried out in parallel. All new compounds were characterized by
NMR and MS.
The effect of the synthesized compounds on ACAT was first
studied at a concentration of 10 g/mL. As shown in Table 1, except
l
compounds 2a–c and 2t, all tested compounds showed certain
ACAT inhibitory activity (5.13–64.8%). Compounds 2d–h which
had five- or six-member rings possessed moderate inhibitory activ-
ities. Compounds containing 1-(substituted-aryl)-piperazines
(2m–o) showed strong inhibition to ACAT. It should be noted that
their aryl groups at one position of piperazine led to a significant
enhancement of potency. With the similar replacement groups of
2m–o, compound 2p also had a good potency. Among all these
compounds, compound 2n showed higher inhibitory activity than
the positive control.
To explain the results, we proposed a likely binding mode for 2n
to the active site of ACAT-2 based on computational docking re-
sults (Fig. 3).14 The designed compound could fit into the hydro-
phobic pocket formed by Gln186, Arg223, Ser226, Asn227,
Ala230, Met231, Leu234, Thr247, Ala249, Ile349 and Ala350 (PDB
structure 1WL4). Moreover, the sulfonamide group and xanthone
Table 1
Structure and ACAT inhibition rate of 2a–w at 10 lg/mL concentration
Sample
R
%Inh.
55.00
Sandoz58-35a
b
2a
—
2b
2c
—
—
ring would generate
a hydrogen bond interaction with the
2d
10.53
Arg223. These results may provide some guidance for the develop-
ment of novel ACAT inhibitory lead structures.
In summary, a series of 1,3,6,7-tetramethoxyxanthone-4-sul-
fonamide derivatives 2a–w as potential ACAT inhibitors were syn-
thesized in high yields. The biological screening of these
compounds resulted in the identification of several potent ACAT
inhibitors, particularly compound 2n which is more potent than
the established ACAT inhibitor Sandoz58-35. This observation
was explainable by a molecular model resulting from the compu-
tational docking simulation, which showed that 2n could fit into
the hydrophobic pocket of ACAT-2. Effort aimed at further optimi-
zation, as well as in-depth biological investigations, of the identi-
fied lead compounds is continuing in our laboratories, and
results will be reported in due course.
2e
7.99
2f
12.59
2g
2h
14.50
20.96
2i
8.84
2j
10.24
25.00
Acknowledgment
2k
This work was supported by a grant from Science & Technology
Commission of Shanghai Municipality (Nos. 054319909 and
08JC1405500).
2l
15.76
36.92
2m
Supplementary data
2n
64.80
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2010.03.101.
2o
2p
2q
43.56
51.34
10.78
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