Design and synthesis of lupeol analogues and their glucose uptake stimulatory effect in L6 skeletal muscle cells

Article abstract of DOI:10.1016/j.bmcl.2014.04.059

Structure modifications of lupeol at the isopropylene moiety have been described via allylic oxidation using selenium dioxide. The antidiabetic efficacy of lupeol analogues were evaluated in vitro as glucose uptake stimulatory effect in L6 skeletal muscle cells. From all tested compounds, 2, 3, 4b and 6b showed significant stimulation of glucose uptake with respective percent stimulation of 173.1 (p <0.001), 114.1 (p <0.001), 98.3 (p <0.001) and 107.3 (p <0.001) at 10 μM concentration. Stimulation of glucose uptake by these compounds is associated with enhanced translocation of glucose transporter 4 (GLUT4) and activation of IRS-1/PI3-K/AKT-dependent signaling pathway in L6 cells. Structure-activity relationship analysis of these analogues demonstrated that the integrity of α,β-unsaturated carbonyl and acetyl moieties were important in the retention of glucose uptake stimulatory effect. It is therefore proposed that naturally occurring lupeol and their analogues might reduce blood glucose, at least in part, through stimulating glucose utilization by skeletal muscles.

Full text of DOI:10.1016/j.bmcl.2014.04.059

Bioorganic & Medicinal Chemistry Letters 24 (2014) 2674–2679
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of lupeol analogues and their glucose uptake
stimulatory effect in L6 skeletal muscle cells q
Mohammad Faheem Khan a, Chandan Kumar Maurya b, Kapil Dev a,c, Deepti Arha b,c, Amit Kumar Rai b,
Akhilesh Kumar Tamrakar b,c, Rakesh Maurya a,c,
⇑
a Medicinal and Process Chemistry Division, CSIR-Central Drug Research Institute, Lucknow 226031, India
b Biochemistry Division, CSIR-Central Drug Research Institute, Lucknow 226031, India
c Academy of Scientific and Innovative Research, New Delhi 110001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 December 2013
Revised 4 April 2014
Accepted 16 April 2014
Available online 24 April 2014
Structure modifications of lupeol at the isopropylene moiety have been described via allylic oxidation
using selenium dioxide. The antidiabetic efficacy of lupeol analogues were evaluated in vitro as glucose
uptake stimulatory effect in L6 skeletal muscle cells. From all tested compounds, 2, 3, 4b and 6b showed
significant stimulation of glucose uptake with respective percent stimulation of 173.1 (p <0.001), 114.1 (p
<0.001), 98.3 (p <0.001) and 107.3 (p <0.001) at 10 lM concentration. Stimulation of glucose uptake by
these compounds is associated with enhanced translocation of glucose transporter 4 (GLUT4) and activa-
tion of IRS-1/PI3-K/AKT-dependent signaling pathway in L6 cells. Structure–activity relationship analysis
of these analogues demonstrated that the integrity of a,b-unsaturated carbonyl and acetyl moieties were
important in the retention of glucose uptake stimulatory effect. It is therefore proposed that naturally
occurring lupeol and their analogues might reduce blood glucose, at least in part, through stimulating
glucose utilization by skeletal muscles.
Keywords:
Type 2 diabetes mellitus
Lupeol
Isopropylene moiety
Glucose uptake stimulation
Ó 2014 Elsevier Ltd. All rights reserved.
Despite the immense technological advancement, management
of diabetes mellitus without any side effects is still a challenge to
the medical science. This global pandemic is driven by type 2 dia-
betes mellitus1 (T2DM), a chronic and progressive metabolic disor-
der affecting approximately 4% population worldwide and is
expected to increase to 5.4% in 2025.2 The 2011 WHO data show
that T2DM affects >346 million patients worldwide.3 It is charac-
terized by abnormalities in carbohydrate, and lipid metabolisms
associated with insulin resistance and decreased pancreatic b-cell
function which causes hyperglycaemia as well as secondary com-
plications, such as hyperlipidemia, hyperinsulinemia, hyperten-
sion, and atherosclerosis.4 Currently, there is no absolute cure for
diabetes. T2DM is initially managed by regular exercise and dietary
modification. Nowadays, it is managed by therapeutic agents alone
or in combination with others or with insulin. Oral hypoglycemic
agents, such as sulfonylureas, metformin, glucosidase inhibitors,
troglitazone, etc. are using as the main means for T2DM but two
most popular agents now in use are the thiazolidinediones (TZDs)
and the biguanides.5 The TZDs are widely used but having undesir-
able side effects (weight gain, fluid retention and heart failure etc.).
The biguanide metformin does not cause weight gain but
mainly acts in liver rather than muscle and thus on its own is
not a complete therapy,6 and in addition, they are not suitable
for use during pregnancy.7 Therefore, the searches for the safer
and effective new therapies that can treat T2DM on a long term
basis without causing adverse events are highly desirable. As a part
of our interest in search of bioactive natural product derived ana-
logues,8 we have taken a targeted approach to investigate the ana-
logues of active triterpenoid molecule for the management of
T2DM.
Triterpenoid skeleton is readily available source of rigidity, chi-
rality and lipophilicity combined in a single aliphatic system which
not only possesses a high number of natural stereogenic centers
but also can be easily functionalized at two positions C-3 and C-
20, respectively. Lupane-type triterpenoids having four cyclohex-
ane rings, all in the chair conformation and one cyclopentane ring
in envelope conformation are the building blocks of the triterpe-
noids.9 Most of the compounds possess a hydroxylic group at car-
bon C-3 and showed different substitution (Ring A) patterns.10 In
the last two decades, hundreds of publications have been pre-
sented the broad spectrum of biological activities of triterpenoids,
such as anticancer,11 anti-inflammatory,12 antioxidatives,13
q
CDRI Comm. No. 8662
⇑
Corresponding author. Tel.: +91 (522) 2612411 18x4735; fax: +91 (522)
2623405/2623938/2629504.
E-mail address: mauryarakesh@rediffmail.com (R. Maurya).
http://dx.doi.org/10.1016/j.bmcl.2014.04.059
0960-894X/Ó 2014 Elsevier Ltd. All rights reserved.

M. F. Khan et al. / Bioorg. Med. Chem. Lett. 24 (2014) 2674–2679
2675
hepatoprotective,14 antidyslipidemic,15 antimalarial16 and anti-
HIV.17 Therefore, they are regarded as an important chemical pool
for further pharmaceutical development. Structural modifications
based on these skeleton, have been extensively explored to find
out more potent modified pentacyclic triterpenes as preventive
and therapeutic agents.18
and DCC (1.1 equiv.) in dry CH2Cl2, catalyzed by DMAP gave
respective esters 6a–6c in 70–80% yield. Compounds 6a, 6b and
6c were obtained as mixture of ester derivatives when we used
1.0 equiv of carboxylic acid. In contrast excess amount of acids
quantitatively afforded esterified compounds at both positions as
major one. Minor esters were not isolated. To obtain new deriva-
tives with modifications at C-30 position, the set of transforma-
tions presented in Scheme 2 was applied. In order to cyclise the
C-29 and C-30 positions, lupeol was first acetylated at C-3 position
as in 3 and the obtained product was then reduced into 7 with
sodium borohydride in ethanol at room temperature. The allylic
oxidation of the hydroxyl group of 30-hydroxy, compound 7 with
allyl bromide in dry CH2Cl2, first led to a compound 10 which
was subsequently converted to an appropriate compound 11 with
the use of Grubbs II generation catalyst23 in the presence of addi-
tive Ti(OiPr)4.
Taking under consideration the above mentioned result of
Grubbs approach, the propargylic oxidation23 of 7 with propargyl
bromide in dry CH2Cl2 was also performed which was subse-
quently converted to an appropriate compound 9. Further, some
additional derivatives were synthesized via iron catalyzed cross
coupling reaction of alcohol and terminal alkene following the
reaction sequence shown in scheme 2. From known literature pro-
tocol24, C-20–C-29 double bond of compound 2 can be cross cou-
pled with benzyl alcohol in dichloro ethane catalyzed by FeCl3
(10 mol %) at reflux temperature for two hours and the compound
with b-hydroxy ketone functionality, is obtained as one of the
major product. It is also known, that the coupling of ketone and
hydroxyl groups of compound 12 with the use of NH2OHÁHCl in
ethanol at room temperature for 1 h, leads to a compound 13 with
isooxazoline ring containing an additional aromatic moiety.
All the compounds were evaluated for glucose uptake stimula-
tory effect in L6 myotubes. As shown in Table 1, from the tested
compounds 2, 3, 4b and 6b showed significant stimulation of glu-
cose uptake with respective percent stimulation of 173.1, 114.1,
The fundamental triterpenoid lupeol (1, Fig. 1) is accessible,
abundant, and valuable bioactive lupane type skeleton. The unique
structure and characteristic biological properties of 1 attracted
many research groups, and a number of synthetic reports on the
structural modification have been appeared.19 However, on the
basis of literature survey, modification in isopropylene functional-
ity in lupeol is not very much actively explored.20 In fact, develop-
ing versatile methods for the modification of isopropylene
functionality opens the door to an inextinguishable and structur-
ally diverse variety of lupeol for biological relevance. Therefore,
herein, we wish to report the design, synthesis and biological eval-
uation of lupeol analogues of a new class, exhibiting an in vitro glu-
cose uptake stimulatory effect in clonal skeletal muscle cells. The
structure of known and new compounds 8–12 and 13 were eluci-
dated on the basis of NMR as well as mass spectrometry methods
and their purity was determined by HPLC analysis for cellular
assay.
This approach relies on the allylic oxidation procedure that
ensures the introduction of formyl functionality at C-30 position
for subsequent derivatization on lupeol scaffold which was iso-
lated from Bombax ceiba stem bark in our laboratory21 and struc-
ture was confirmed on the basis of NMR data reported in the
literature.22 As depicted in scheme 1, SeO2 was chosen for the
preparation of allylic alcohol via allylic oxidation of isopropylene
moiety, which can be subsequently converted into a,b-unsaturated
aldehyde. Treatment of compound 1 with easily accessible SeO2 in
reflux ethanol furnished 30-formyl lupeol (2) in excellent yield.
The NMR spectrum of 2 showed a,b-unsaturated carbonyl moiety,
which was confirmed by long bond HMBC correlations between
the two singlet at d 6.30 (1H, br s, H-29a), 5.92 (1H, br s, H-29b)
and one multiplet at d 2.73 (1H, m, H-19) with the carbonyl carbon
at d 195.0 (CHO).
98.3 and 107.3 at 10
as positive control, which showed 112.4% percent stimulation of
glucose uptake at 10 M concentration. Remaining compounds
lM concentration. Rosiglitazone was used
l
This oxidation product having
a,b-unsaturated functionality
showed little or no stimulatory effect on glucose uptake in L6
may be considered as reactive motifs which are suitable for further
derivatization and thus acting as amenable building blocks of mol-
ecules. Treatment of 2 with Ac2O/pyridine yielded the correspond-
ing acetate 3, while esterification of 2 with different carboxylic acid
afforded compounds 4a–4c in the presence of Ac2O/pyridine. Com-
pound 3 was mixed with 10% KOH in ethanol, followed by addition
of hydrated hydroxyl amine at room temperature for 4 h to give 5
in quantitative yield. Reaction of 5 with different carboxylic acids
myotubes.
Further examination indicated a concentration dependent stim-
ulation of glucose uptake upon treatment with 2, 3, 4b, and 6b in
skeletal muscle cells (Fig. 2). It is further assessed whether the abil-
ity of these compounds to stimulate glucose uptake was mediated
by potentiation of insulin action or activation of cellular processes
independent of the hormone. Cells were treated with 2, 3, 4b, and
6b (10 lM) for 16 h with final three hour in serum-deprived med-
ium and a subset of cells was stimulated with insulin (100 nM) for
20 min before the measurement of glucose uptake.
As shown in Figure 3, insulin alone caused 2.2-fold (p <0.001)
stimulation of glucose uptake in L6 myotubes over basal state. Pre-
treatment with 2, 3, 4b or 6b (16 h) caused further increase in insu-
lin signal with respect to insulin treated control, but the gain in
transport was lower than that calculated from the independent
effect of insulin and test compounds (Fig. 3). These observations
suggest that both inputs might stimulate glucose uptake by differ-
ent sub cellular pathways, but some elements common to the
action of both agents may be finite.
In skeletal muscle, stimulation of glucose uptake is mostly
attributed to increased translocation and redistribution of the
GLUT4 to the plasma membrane, where they facilitate the entry
of glucose inside the cell.25 Thus, the effect of 2, 3, 4b, and 6b on
GLUT4 translocation was determined in L6-GLUT4myc cells. Simi-
lar to glucose uptake, treatment with 2, 3, 4b or 6b significantly
29
30
Two active
centres for chemical
modifications
20
H18
21
22
28
19
11
9
13
25
1
H17
26
15
H
5
3
27
7
HO
H
23
24
1
enhanced GLUT4myc translocation to cell surface at 10 lM concen-
Figure 1. Basic skeleton of starting compound (lupeol), showing the chemically
active centers.
tration (Fig. 4).

2676
M. F. Khan et al. / Bioorg. Med. Chem. Lett. 24 (2014) 2674–2679
H
R
O
O
N
N
N
H
N
H
H
H
a
d
e
H
H
H
H
H
HO
H
HO
H
H
O
H
HO
2
H
1
H
5
R
O
H
6a-c
c
b
O
O
H
H
H
H
O
H
H
R
O
AcO
H
4a-c
H
3
R
Br
4a
Cl
6a
and
4b
6b
4c
6c
and
and
Scheme 1. Reagents and conditions: (a) SeO2 (1.1 equiv), ethanol, reflux, 48 h (b) Ac2O (1.1 ca.), pyridine, dry CH2Cl2, rt, 1 h (c) DCC (1.1 equiv), DMAP (cat.), RCOOH
(1.0 equiv), dry CH2Cl2, rt, 6–8 h (d) NH2NH2.H2O (1.1 equiv), 10% KOH, ethanol, rt, 4 h (e) DMAP (cat.), RCOOH (1.0 equiv), dry CH2Cl2, rt, 6–8 h.
2'
3'
O
O
O
4'
5'
H
H
H
H
a
H
H
H
H
H
HO
AcO
AcO
H
H
H
3
2
11
b
g
f
HO
O
HO
O
H
H
H
H
e
H
H
H
H
AcO
AcO
H
h
H
H
HO
10
7
H
12
c
7'
2'
6'
3'
4'
O
O
O
N
5'
H
H
d
H
H
H
H
H
H
H
AcO
AcO
H
H
HO
9
H
8
13
Scheme 2. Reagents and conditions: (a) Ac2O (1.1 ca.), pyridine, dry CH2Cl2, rt, 1 h (b) NaBH4, ethanol, rt, 4 h (c) Propargyl bromide, dry CH2Cl2, K2CO3, , 0 °C to rt, 4 h (d)
Grubbs II (10 mol %), dry CH2Cl2, Ti(OiPr)4, 35 °C, 48 h (e) Allyl bromide, dry CH2Cl2, K2CO3, 0 °C to rt, 2 h (f) Grubbs II (10 mol %), dry CH2Cl2, Ti(OiPr)4, 35 °C, 48 h (g) FeCl3
(10 mol %), benzyl alcohol, dry DCE, 70 °C, 2 h (h) NH2OHÁHCl, ethanol, rt, 1 h.

M. F. Khan et al. / Bioorg. Med. Chem. Lett. 24 (2014) 2674–2679
2677
Table 1
The glucose uptake stimulation of luepol derivatives with isopropylene moiety
modifications
S. No.
Compound No.
Concentration (
l
M)
% Glucose uptake
stimulation (IC50
)
1
2
3
4
5
6
7
8
Control
Rosiglitazone
1
2
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
00
112.4 (4.8
26.8
173.1 (4.2
114.1 (5.2
3.1
98.3 (6.2
0.5
16.1
8.4
107.3 (4.9
2.8
22.2
19.2
2.1
l
M)
l
l
M)
M)
3
4a
4b
4c
5
6a
6b
6c
7
8
9
10
11
12
13
lM)
9
10
11
12
13
14
15
16
17
18
19
lM)
8.5
3.6
6.4
13.2
Figure 4. Effect of compounds (2, 3, 4b and 6b) on GLUT4 translocation in L6-
GLUT4myc myotubes. Cells were treated with test compounds (10 lM) for 16 h
with final three hour in serum free medium and a subset of cells was stimulated
with insulin (100 nM) for 20 min before the measurement of surface level of
GLUT4myc. Results are expressed as fold stimulation over control basal. Results
shown are mean SE of three independent experiments, each performed in
triplicate. ⁄p <0.05, ⁄⁄p <0.01, relative to respective control condition.
Figure 2. Dose-dependent effect of compounds (2, 3, 4b and 6b) on glucose uptake
in L6 myotubes. Cells were incubated with vehicle (Cont, DMSO), rosiglitazone
(Rosi, 10 lM) or different concentrations of test compounds (5, 10, 25 lM) for 16 h
and glucose uptake was as described. Results are expressed as fold stimulation over
control. Results shown are mean SE of three independent experiment, each
performed in triplicate. ⁄p <0.05, ⁄⁄p <0.01, relative to control.
Figure 5. Effect of compounds (2 and 6b) on insulin signaling pathway in L6
myotubes. Cells were treated with test compounds (10 lM) for 16 h with final three
hour in serum free medium and a subset of cells was stimulated with insulin
(100 nM) for 20 min. Cells were lysed and equal amount of protein was analyzed for
phosphorylation of the major components of insulin signaling pathway by western
blotting (A) and densitiometric quantification of pIRß/IRß (B), pAKT/AKT (C) and
pIRS-1/IRS-1 (D). Results of three independent experiments are presented as
mean SEM. ⁄p <0.05, ⁄⁄p <0.01, relative to respective control condition.
In skeletal muscle cells, insulin exerts its effect by binding to
its receptor on cell surface, resulting in the activation of the insulin
receptor (IR) tyrosine kinase followed by signaling through insulin
receptor substrate (IRS) proteins, Phosphatidylinositol-3-kinase
(PI-3-K) and the Ser/Thr kinase AKT.26 Since, our compounds
stimulated glucose uptake independently of insulin, we investigate
the effect of most active compounds (2 and 6b) on activation of the
Figure 3. Effect of compounds (2, 3, 4b and 6b) on insulin stimulated glucose
uptake in L6 myotubes. Cells were treated with test compounds (10 lM) for 16 h
with final three hour in serum free medium and a subset of cells was stimulated
with insulin (100 nM) for 20 min before the measurement of glucose uptake.
Results are expressed as fold stimulation over control basal. Results shown are
mean SE of three independent experiment, each performed in triplicate. ⁄⁄p <0.01,
relative to respective control condition.

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M. F. Khan et al. / Bioorg. Med. Chem. Lett. 24 (2014) 2674–2679
Figure 6. Effect of wortmannin on insulin- and compounds (2 and 6b)-induced
glucose uptake in L6 myotubes. Cells were treated with test compounds (10 M) for
l
16 h without or with wortmannin (50 nM) followed by insulin treatment and
determination of glucose uptake and described earlier. Results are expressed as fold
stimulation over control basal. ⁄p <0.05, ⁄⁄p <0.001 relative to respective control
condition.
Figure 8. Effect of compounds (2, 3, 4b and 6b) on glucose uptake in 3T3 L1
adipocytes (A) and HepG2 hepatic cells (B). Cells were treated with test compounds
(10 lM) for 16 h with final three hour in serum free medium and a subset of cells
was stimulated with insulin (100 nM) for 20 min before the measurement of
glucose uptake. Results are expressed as fold stimulation over control basal. Results
shown are mean SE of three independent experiment, each performed in
triplicate. ⁄p <0.05, ⁄⁄p <0.01, relative to respective control condition.
HN
N
O
Synthesis of pyrazoline
ring is devoid
Insertion of α, β-unsaturated
carbonyl carbon
required for potent
activity
of activity
H
H
Cyclization of isopropylene
H
lost the acivity
HO
H
O
O
O
N
At this position, aliphatic ester
linkage lost the activity
but α, β-unsaturated ester
retain the acivity
Figure 7. Effect of compounds (2, 3, 4b and 6b) on phosphorylation of AMPK
172). L6 myotubes were treated with teat compounds (10 M) for 16 h followed by
lysis and western analysis. Shown are representative immunoblots and densito-
metric quantification of phosphor-AMPK (Thr-172) relative to total AMPK
Results of three independent experiments are presented as mean SEM.
a (Thr-
O
l
R
Figure 9. Structure activity relationship.
a
a.
major components of insulin signaling pathway. As shown in
Figure 5, Insulin alone significantly increased the phosphorylation
of IR-b, IRS-1and AKT. Treatment with 2 or 6b significantly stimu-
lated the phosphorylation of IRS-1 and AKT, without affecting IR-b
phosphorylation, under basal condition. Furthermore, stimulation
of glucose uptake by 2 or 6b was abolished in presence of
wortmannin, which is a specific inhibitor for PI-3-K (Fig. 6). Results
indicate the involvement of IRS-1/PI-3-K/AKT-mediated signaling
pathway under biological effects of these compounds.
Involvement of PI-3-kinase independent pathways has also
been established to stimulate glucose utilization in skeletal muscle
cells. Activation of AMPK pathway has been shown to facilitate glu-
cose uptake and GLUT4 translocation. To delineate the possible
contribution of AMPK in observed glucose uptake stimulatory
effect of 2, 3, 4b and 6b, we determine effect on activation of AMPK
by measuring the phosphorylation of Thr-172, the principle acti-
vating phosphorylation site within AMPK
a. Treatment with 2, 3,
4b or 6b had no effect on AMPK activation (Fig. 7). We further

M. F. Khan et al. / Bioorg. Med. Chem. Lett. 24 (2014) 2674–2679
2679
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(3.1%), 6c (2.8%), 7 (22.2), 8 (19.2%), 9 (2.1%), 10 (8.5%), 11 (3.6%),
12 (6.4%), 13 (13.2%) except the compound 4b and 6b which dis-
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S.; Raj, K.; Singh, K.; Puri, S. K.; Kundu, B. Bioorg. Med. Chem. Lett. 2002, 12,
2803.
20. Gutiérrez-Nicolás, F.; Gordillo-Román, B.; Oberti, J. C.; Estévez-Braun, A.;
Ravelo, A. G.; Joseph-Nathan, P. J. Nat. Prod. 2012, 75, 669.
21. We have isolated lupeol (1) from n-Butanol fraction of ethanol extract (200 g)
of Bombax ceiba stem bark. n-Butanol fraction (100 g) was fractionated by gel
filtration chromatography over sephadex LH-20 and followed by sephadex G-
25 using a H2O/MeOH as eluent gradient (100:00, 90:10, 75:25, 50:50 and
00:100). It was packed over silica gel (60–120 mesh) bed using CHCl3 and
MeOH eluent system with increasing polarity of methanol. This afforded
fifteen fractions (F1–F8). Similar fractions were combined into eight major
fractions on the basis of TLC profile. First fraction (F1, 25 g) was
rechromatographed over silica gel (230–400 mesh, 300 g) using n-hexane/
ethyl acetate (98:2) as eluent system in isocratic manner. Fractions of 100 ml
each were collected. Fraction having same TLC profile, combined together,
concentrated which afforded solid material. It was recrystalized in chloroform
at room temperature. White microcrystalline solid of 1 was obtained.
22. Jean, F. D.; Scott, B.; Mara, L. L.; Elias, G.; Rukunga, G.; Augustin, N. E. J. Nat.
Prod. 2006, 69, 62. Physiochemical and NMR spectroscopic data of lupeol.
White fine crystalline solid; IR vmax (KBr) cmÀ1: 3431, 3021, 1646; ESI-MS: m/z
426 [M]+; 1H (CDCl3, 300 MHz; d, ppm): 4.70 (1H, br s, H-29a), 4.58 (1H, br s, H-
29b), 3.19 (1H, dd, J = 4.6, 11.5 Hz, H-3), 2.38 (1H, dt, J = 4.1, 9.5 Hz, H-19),
1.90–0.80 (25H, all peaks merged with each others), 1.72 (3H, s, H-30), 1.05
(3H, s, H-26), 0.98 (3H, s, H-23), 0.97 (3H, s, H-27), 0.83 (3H, s, H-25), 0.80 (3H,
s, H-28), 0.77 (3H, s, H-24). 13C (CDCl3, 75 MHz; d, ppm): 151.1(C-20), 109.5 (C-
29), 79.2 (C-3), 55.4 (C-5), 50.6 (C-9), 48.3 (C-19), 48.1 (C-18), 43.2 (C-17), 43.0
(C-14), 41.1 (C-8), 40.4 (C-22), 39.1 (C-4), 38.9 (C-1), 38.2 (C-13), 37.5 (C-10),
35.7 (C-16), 34.5 (C-7), 29.8 (C-21), 28.1 (C-23), 27.6 (C-2, 15), 25.4 (C-12), 21.2
(C-11), 19.6 (C-30), 18.4 (C-6), 18.1 (C-28), 16.4 (C-25), 16.2 (C-26), 15.4 (C-24),
14.8 (C-27).
compared with reference compound 1. Compounds without oxo
functionality at C-30 position did not show any remarkable activ-
ity. Results are presented in (Figs. 2–8 and Table 1).
In conclusion, a set of isopropylene modified analogues of
lupeol were synthesized and tested for anti-diabetic activity in
L6 skeletal muscle cells. Among the compounds tested 2, 3, 4b
and 6b containing
a,b-unsaturated carbonyl moiety showed the
potent in vitro glucose uptake stimulatory effect. This work sug-
gests that lupeol can further provide additional lead compounds
on the route to unravel physiological and therapeutic implications
of glucose uptake stimulatory effect. In vivo biological evaluation
of the title compounds and further derivatization of this triterpe-
noid scaffold are currently in progress and will be reported in
due course.
Acknowledgements
We thank the University Grant Commission (UGC) and Council
of Scientific and Industrial Research (CSIR), New Delhi, India for
financial support as Senior Research Fellowship (SRF) and Junior
Research Fellowship (JRF). Authors are also grateful to SAIF divi-
sion, CDRI, Lucknow, India for providing analytical data.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2014.
04.059.
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