Bioorganic & Medicinal Chemistry Letters
Benzoflavones as cholesterol esterase inhibitors: Synthesis, biological
evaluation and docking studies
Harbinder Singh a, Jatinder Vir Singh a, Manish K. Gupta b, Palwinder Singh c, Sahil Sharma a,
,
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Kunal Nepali a, , Preet Mohinder S. Bedi a,
⇑
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a Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar, Punjab 143005, India
b Lloyd Institute of Management and Technology, Greater Noida, UP, India
c Department of Chemistry, Guru Nanak Dev University, Amritsar, Punjab 143005, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A library of forty 7,8-benzoflavone derivatives was synthesized and evaluated for their inhibitory poten-
tial against cholesterol esterase (CEase). Among all the synthesized compounds seven benzoflavone
derivatives (A-7, A-8, A-10, A-11, A-12, A-13, A-15) exhibited significant inhibition against CEase in
in vitro enzymatic assay. Compound A-12 showed the most promising activity with IC50 value of
0.78 nM against cholesterol esterase. Enzyme kinetic studies carried out for A-12, revealed its mixed-type
inhibition approach. Molecular protein–ligand docking studies were also performed to figure out the key
binding interactions of A-12 with the amino acid residues of the enzyme’s active site. The A-12 fits well at
the catalytic site and is stabilized by hydrophobic interactions. It completely blocks the catalytic assem-
bly of CEase and prevents it to participate in ester hydrolysis mechanism. The favorable binding confor-
mation of A-12 suggests its prevailing role as CEase inhibitor.
Received 9 August 2016
Revised 30 December 2016
Accepted 9 January 2017
Available online xxxx
Keywords:
Benzoflavone
Baker Venkataraman rearrangement
Cholesterol esterase inhibition
Enzyme kinetics
Ó 2017 Elsevier Ltd. All rights reserved.
Docking studies
Cholesterol is a vital component of cell membrane and pos-
sesses many physiological functions. The greatest percentage of
cholesterol is used in cytoplasm for bile acid synthesis.1 Hyperc-
holesterolemia produced either by cholesterol feeding or by
cholesterol-free, purified diets (‘‘endogenous” Hypercholes-
terolemia) results in the accumulation of cholesterol in adipose tis-
sue. As there is a well-established link between plasma cholesterol
level and coronary artery disease, the reduction of cholesterol level
in plasma, particularly in low density lipoprotein (LDL) lowers the
risk of cardiovascular events.2 The contribution of elevated plasma
cholesterol specifically, LDL-cholesterol, to other diseases includ-
ing cancer, obesity, and diabetes has made control of plasma
cholesterol a major health aim.3
treating hypercholesterolemia and associated diseases such as
coronary heart disease.6
From the last decade, there are several classes of potent
CEase inhibitors have been developed,7 so far, including
6-chloro-2-pyrones,8 thieno[1,3]-oxazin-4-ones,9 carbamates,10
aryl phosphates and phosphonates,11 chloroisocoumarins,12
phosphaisocoumarins,13
flavonoids,14
thiazolidinediones,5
phosphorylated
2-(1H-Indol-3-yl)-4-phenylquinolines15 and 3-phenyl substituted
1,3,4-oxadiazol-2(3H)-ones16 (Fig. 1). However, most of these
inhibitors are not highly selective and they could also inhibit other
serine hydrolases, such as acetylcholinesterase (AChE), butyryl-
cholinesterase (BChE), Pseudomonas species lipase (PSL), chy-
motrypsin (CT) and trypsin.14
Pancreatic cholesterol esterase is the member of a/b hydrolase
family of proteins which catalyses the hydrolysis of dietary choles-
terol ester into free cholesterol in the lumen of small intestine.4 It
is also thought that the transport of cholesterol micelles to entero-
cytes is performed by this enzyme.5 As the combined role of CEase
in the absorption and transport of cholesterol, its inhibition is
important by the development of novel moieties which helps in
Flavonoids, including flavones, flavonols, isoflavones and fla-
vanones, are a large class of polyphenolic compounds widely dis-
tributed in herbs and foods of plant origin, and exhibit
diversified biological activities, such as antioxidant, anti-prolifera-
tive, anti-tumor, anti-microbial, estrogenic, acetyl cholinesterase,
anti-inflammatory activities and are also used in cancer, cardiovas-
cular disease, neurodegenerative disorders and enzyme inhibi-
tion.17 Among them, the flavones have been considerably
explored due to their ability to modulate several enzyme systems
involved in a number of diseases.14
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Corresponding authors.
0960-894X/Ó 2017 Elsevier Ltd. All rights reserved.