Synthesis of novel triterpenoid (lupeol) derivatives and their in vivo antihyperglycemic and antidyslipidemic activity

Article abstract of DOI:10.1016/j.bmcl.2009.05.034

The triterpenoid, lupeol (1) has been isolated from the leaves extract of Aegle marmelos. Few novel derivatives (2-13) were synthesized from the naturally occurring lupeol (1) and screened for their antihyperglycemic activity (2-11) and antidyslipidemic a

Full text of DOI:10.1016/j.bmcl.2009.05.034

Bioorganic & Medicinal Chemistry Letters 19 (2009) 4463–4466
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of novel triterpenoid (lupeol) derivatives and their in vivo
antihyperglycemic and antidyslipidemic activity q
K. Papi Reddy a, A. B. Singh b, A. Puri b, A. K. Srivastava b, T. Narender a,
*
a Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226 001, UP, India
b Biochemistry Division, Central Drug Research Institute, Lucknow 226 001, UP, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The triterpenoid, lupeol (1) has been isolated from the leaves extract of Aegle marmelos. Few novel deriv-
atives (2–13) were synthesized from the naturally occurring lupeol (1) and screened for their antihyper-
glycemic activity (2–11) and antidyslipidemic activity (2–4 and 12–13). The derivative 4 lowered the
blood glucose levels by 18.2% and 25.0% at 5 h and 24 h, respectively, in sucrose challenged streptozoto-
cin induced diabetic rats (STZ-S) model at the dose of 100 mg/kg body weight. The compound 4 also sig-
nificantly lowered 40% (P <0.001) in triglycerides, 30% (P <0.05) in glycerol, 24% (P <0.05) in cholesterol
quantity and also improved the HDL–cholesterol by 5% in dyslipidemic hamster model at the dose of
50 mg/kg b.wt.
Received 5 February 2009
Revised 23 April 2009
Accepted 11 May 2009
Available online 15 May 2009
Keywords:
Lupeol ester derivatives
Antihyperglycemic activity
Antidyslipidemic activity
STZ-S model
Ó 2009 Elsevier Ltd. All rights reserved.
Diabetes mellitus is an independent risk factor for the
development of coronary artery diseases, myocardial infarction,
hypertension and dyslipidemia. Clinically diabetic patients are
characterized by marked increase in blood glucose level followed
by mild hyperlipidemia. Non-insulin dependent diabetes mellitus
(NIDDM) accounts for approximately 80–90% of all cases1 and it
is the fastest growing global threat to public health. If the current
trend continues, it is likely to result in an estimated 215 million
sufferers from NIDDM worldwide by the year 2010.2,3 This number
is expected to increase as medical advances extend life expectancy
and more widespread access to a calorie rich diet promotes the
prevalence of obesity. When carbohydrates are in low supply or
their breakdown is incomplete, fats become the preferred source
of energy. Fatty acids are mobilized into the general circulation
leading to secondary triglyceridemia in which total serum lipids
in particular triglycerides as well as in the levels of cholesterol
and phospholipids increases.
This rise is proportional to the severity of the diabetes. Uncon-
trolled diabetes is manifested by a very high rise in triglycerides
and fatty acid levels4 for one third of deaths in industrialized na-
tions.5 Therefore, a drug, having twofold properties is in great de-
mand. Several research groups are focusing to develop such dual-
acting agents (Fig. 1). Despite the remarkable progress in the man-
agement of diabetes mellitus by synthetic drugs,6 there has been a
renewed interest in medicinal plants because of the side effects of
synthetic drugs. The discovery of new drugs from traditional med-
icine is not a new phenomenon (Fig. 1). In continuation of our drug
discovery program on antidiabetic and antidyslipidemic agents, we
discovered antidyslipidemic activity in naturally occurring lupeol
(1), which was isolated from the leaves of Aegle marmelos.7 Re-
cently Sudhahar et al.8 also, reported hypercholesterolemia in lu-
peol and linoleate ester of lupeol. The linoleate ester of lupeol
appears to be a good prodrug of lupeol in Sudhahar et al. studies.9
Prodrugs play a major role in absorption, distribution, metabolism,
excretion (ADME) and improves the oral bioavailability. In our own
studies the lupeol (1) exhibited the dyslipidemic activity. We
therefore prepared few novel ester derivatives of lupeol (1) and
studied their in vivo antihyperglycemic activity in Streptozotocin
induced diabetic rats model and antidyslipidemic activity in ham-
ster model.
The syntheses of non-natural ester analogues 2–13 of lupeol (1)
were accomplished by subjecting various aromatic and aliphatic
acids with lupeol (Scheme 1) by employing DCC-DMAP esterifica-
tion protocol in dry CH2Cl2.
Ten novel ester derivatives 2–11 of lupeol were studied for their
antihyperglycemic activity in streptozotocin induced diabetic rats
(STZ-S model)10 at a dose of 100 mg/kg body weight. Out of these
10 derivatives nicotinic acid derivative 4 was the most potent
compound (À18.3% at 5 h and À25.0% at 24 h) followed by
2 (pyridin-2-yl) acetic acid 7 (À20.5% at 5 h and À18.2% at 24 h).
Extension of the alkyl chain between acid group and pyridine moi-
ety (6 and 8) led to decreased activity. Hippuric acid derivative 5
also showed good activity (À13.8% at 5 h and À23.6% at 24 h). p-
Chlorobenzoic acid derivative 2 and p-nitrobenzoic acid derivative
q
CDRI Communication 7654.
* Corresponding author. Tel.: +91 522 2612411x4440; fax: +91 522 2623405.
E-mail addresses: tnarender@rediffmail.com, t–narendra@cdri.res.in (T. Narender).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.05.034

4464
K. Papi Reddy et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4463–4466
O
O
O
O
OH
N
H
O
NH
S
Ph
O
F3C
H3CO
KRP - 297
OH
N
O
LY 465608
NH
NH
NH
NH2
OH
N
N
H
NH2
H2N
N
H
O
Metformin
4-Hydroxy isoleucine
Galegine
O
O iPr
Cl
O
O
Fenofibrate
Figure 1. Dual-acting agents in clinical trials (LY 465608 and KRP-297); synthetic antidiabetic agent (Metformin); naturally occurring antidiabetic agents (Galegine and 4-
Hydroxy isoleucine) and synthetic triglyceride lowering drug (Fenofibrate).
Appropriate acid
O
DCC-DMAP
CH2Cl2, rt., 4 h.
R
O
HO
1
2-13
Scheme 1. Synthesis of novel lupeol esters 2–13 using DCC-DMAP esterification protocol in dry CH2Cl2.
Table 1
In vivo antihyperglycemic activity of lupeol ester derivatives 2–11 in STZ- S model
O
R
O
Entry
1
Compound (R)
Test dose (mg/kg)
% Antihyperglycemic activity in STZS
24 h
5 h
100
100
À17.8
*
À19.6
*
Cl
2
*
2
À14.8
À21.1
O2N
3
*
**
3
4
100
100
À18.3
À13.8
À25.0
N
4
O
N
H
**
À23.6
5

K. Papi Reddy et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4463–4466
4465
Table 1 (continued)
Entry
Compound (R)
Test dose (mg/kg)
% Antihyperglycemic activity in STZS
24 h
5 h
*
5
6
100
100
100
100
100
100
100
À13.4
À20.5
À8.21
À15.8
À12.5
À16.9
À15.7
N
6
*
*
*
*
À18.2
N
7
7
À10.4
N
8
*
8
À18.5
O
9
9
À14.9
S
10
10
À21.5
*
S
11
11
Metformin (Fig. 1)
À23.5**
À26.5**
*
p <0.05 and **p <0.01. Control.
Table 2
Percentage decrease/increase in plasma lipids from baseline with the treatment of lupeol esters 2–4 and 12–13 in dyslipidemic hamsters (values are mean SD of eight hamsters
in each group)
O
R
O
Test sample
Vehicle
Food intake (g)
6.79
TG (mM)
CHO (mM)
HDL–C (mM)
2.59 1.06
GLU (mM)
GLY (mM)
1.35 0.30
H/C
12.14 2.14
12.51 2.99
87.94 5.24
0.21
7.10
+4
10.85 4.19
À11
9.18 4.78
À27
2.23 2.19
À14
93.2 15.21
+5
1.16 0.21
À14
0.24
+14
Cl
2
50 mg/kg
O2N
7.73
+4
9.76 1.74
8.27 2.47
1.81 1.44
À30
93.2 7.45
+6
1.07 0.09
À21
0.22
+4
À20
*
À34
*
3
50 mg/kg
(continued on next page)

4466
K. Papi Reddy et al. / Bioorg. Med. Chem. Lett. 19 (2009) 4463–4466
Table 2 (continued)
Test sample
Food intake (g)
TG (mM)
CHO (mM)
8.25 2.9
HDL–C (mM)
GLU (mM)
GLY (mM)
0.94 0.24
H/C
7.34
+8
7.31 2.19
2.72 1.64
+5
89.73 23.1
+2
0.33
+57
N
***
*
*
À40
À24
À30
4
50 mg/kg
6.52
À4
14.66 5.9
+20
9.40 2.59
À25
2.47 1.70
À5
91.52 19.91
+4
1.25 0.21
À8
0.26
+24
MeO
12
50 mg/kg
N
13
7.51
+11
11.35 6.85
À7
9.10 4.01
À27
1.82 1.38
À30
81.22 15.02
À8
1.08 0.38
À20
0.20
À5
50 mg/kg
Fenofibrate 108 mg/kg (Fig. 1)
—
À42
*
À18
NC
—
À36**
+10
P <0.05 ( ), P <0.01 (**), P <0.001 (***); NC = no change.
*
3 lowered the blood glucose levels to À17.8%, À14.8% at 5 h and
À19.6%, À21.1% at 24 h, respectively. The five-membered furan
and thiophene ester derivatives 9, 10 and 11 were also lowered
the blood glucose levels to À15.8%, À12.5%, À16.9% at 5 h and
À18.5%, À14.9%, À21.5% at 24 h, respectively. The reference drug
metformin lowered the blood glucose levels À23.5% at 5 h and
À26.5% at 24 h in the same model (Table 1).
derivative 4 turned out to be dual-acting (antihyperglycemic
and antidyslipidemic activity) agent in our studies. Further work
is in progress to find out the mechanism of action of 4 in dyslip-
idemic activity.
Acknowledgments
Activity guided fractionation and isolation work on A. marmelos
led to identify the dyslipidemic activity in lupeol (1). Lupeol (1)
lowered the triglyceride by 26%, cholesterol by 9%, glycerol by
10%, free fatty acids by 23% and increased the HDL–cholesterol
by 44% (P <0.001) and the HDL/cholesterol ratio was 63% in ham-
ster model at 100 mg/kg body weight.10 Five novel ester deriva-
tives of lupeol (2–4, 12 and 13) were screened for their
antidylipidemic activity in the same model at a dose of 50 mg/kg
body weight. Nicotinic acid derivative 4 showed better lipid lower-
ing profile than other derivatives. It significantly lowered 40% (P
<0.001) in triglycerides, 30% (P <0.05) in glycerol, 24% (P <0.05)
in cholesterol quantity. It also improved the HDL–cholesterol by
5%. It is also noteworthy to mention here that 4 also exhibited good
Authors are grateful to the Director, Central Drug Research
Institute (CDRI), Lucknow, India for constant encouragement for
the drug development program on antihyperglycemic and antidy-
slipdemic agents, J. P. Chaturvedi for technical support and the
Sophisticated Analytical Instrumentation Facility (SAIF) of CDRI
for spectral data.
Supplementary data
The spectral data (1H, 13C NMR, ES and FAB Mass), experimental
procedure of novel synthetic derivatives and experimental proce-
dure of biological activity of lupeol are available. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.bmcl.2009.05.034.
antihyperglycemic activity. p-Nitrobenzoic acid derivative
3
showed good lowering in triglycerides (20%), cholesterol (34%),
glycerol (21%), however 3 also lowered the HDL–cholesterol, which
is undesired side effect in dyslipidimia treatment. Compound 2, 12
and 13 showed good cholesterol lowering property; mild effect in
lowering triglycerides, but these derivatives also possesses unde-
sired effect (HDL–C lowering). The reference drug fenofibrate low-
ered the triglycerides 42%, cholesterol 18% and glycerol 36% at a
dose of 108 mg/kg body weight in the same model (Table 2). There
is increasing evidence that hepatic insulin resistance is associated
with an increased production of free fatty acid and hypertriglycer-
idemia. The circulating triglycerides and free fatty acid are com-
monly elevated in obese and diabetic subjects and lower the
ability of insulin to suppress hepatic glucose production by activat-
ing gluconeogenesis yet inhibiting glycolysis.11 Reduction in the
circulating triglycerides and other fatty acid by ester derivative
such as 4 in our studies might be playing a major role to improve
the hyperglycaemia and strengthen the insulin response.
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In conclusion ester derivatives of abundantly available lupeol
(1) was prepared and screened for their in vivo antihyperglycemic
activity and also antidyslipidemic activity. Nicotinic acid