α-Glucosidase inhibitory antihyperglycemic activity of substituted chromenone derivatives

Article abstract of DOI:10.1016/j.bmc.2009.10.047

Series of 3,4- and 3,6-disubstituted chromenones including new chromenone derivatives were synthesized applying various synthetic strategies including Pechmann condensation, Knoevenagel condensation, Reimer-Tiemann reaction and Suzuki coupling in very good yields. Synthesized compounds (4a-z) were screened for in vitro α-glucosidase inhibitory and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activities. Majority of compounds displayed varying degrees of α-glucosidase inhibitory and DPPH scavenging activity. Compound 4x emerged as the most potent α-glucosidase inhibitor in present series of compounds owing to the presence of 3-acetyl-6-(6-methoxy-3-pyridyl) group on chromenone; however, it could not display DPPH scavenging activity and was found to be mixed non-competitive type inhibitor of rat intestinal α-glucosidase. When tested in vivo for antihyperglycemic activity in starch loaded Wistar rats, it displayed significant antihyperglycemic property. This is the first report assigning rat intestinal α-glucosidase inhibitory property for this class of new chromenones and presents new family of compounds possessing α-glucosidase inhibitory activities and antihyperglycemic property. Compound 4x may serve as an interesting new compound for the development of therapeutics targeted against diet-induced hyperglycemia in diabetes.

Full text of DOI:10.1016/j.bmc.2009.10.047

Bioorganic & Medicinal Chemistry 18 (2010) 358–365
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
a-Glucosidase inhibitory antihyperglycemic activity of substituted
chromenone derivatives
b,
a
b
b
B. China Raju a, , Ashok K. Tiwari , J. Ashok Kumar , A. Zehra Ali , Sachin B. Agawane ,
*
*
G. Saidachary a, K. Madhusudana b
a Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500 607, India
b Pharmacology Division, Indian Institute of Chemical Technology, Hyderabad 500 607, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Series of 3,4- and 3,6-disubstituted chromenones including new chromenone derivatives were synthe-
sized applying various synthetic strategies including Pechmann condensation, Knoevenagel condensa-
tion, Reimer–Tiemann reaction and Suzuki coupling in very good yields. Synthesized compounds
Received 24 September 2009
Revised 23 October 2009
Accepted 24 October 2009
Available online 29 October 2009
(4a–z) were screened for in vitro
radical scavenging activities. Majority of compounds displayed varying degrees of
tory and DPPH scavenging activity. Compound 4x emerged as the most potent -glucosidase inhibitor in
a-glucosidase inhibitory and 1,1-diphenyl-2-picrylhydrazyl (DPPH) free
a
-glucosidase inhibi-
a
Keywords:
Substituted chromenone derivatives
Boronic acids
Suzuki coupling
Salicylaldehydes
b-Ketoesters
present series of compounds owing to the presence of 3-acetyl-6-(6-methoxy-3-pyridyl) group on
chromenone; however, it could not display DPPH scavenging activity and was found to be mixed non-
competitive type inhibitor of rat intestinal
activity in starch loaded Wistar rats, it displayed significant antihyperglycemic property. This is the first
report assigning rat intestinal -glucosidase inhibitory property for this class of new chromenones and
presents new family of compounds possessing -glucosidase inhibitory activities and antihyperglycemic
a-glucosidase. When tested in vivo for antihyperglycemic
a
Piperidine
Antihyperglycemic activity
a
property. Compound 4x may serve as an interesting new compound for the development of therapeutics
targeted against diet-induced hyperglycemia in diabetes.
a-Glucosidase inhibitory activity
DPPH scavenging activity
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
tion of starch digesting enzyme
tinal brush borders, have shown promise in reducing PPHGE,
hyperinsulinemia, burden of oxidative stress, and CVD.6 The
-glu-
cosidase inhibitors appear better therapeutic in controlling PPHGE
in Asian people7 presumably because of their specific food habits8
particularly Indians who demonstrate higher glycemic response to
all foods9 and present increased prevalence of PPHG10 than other
ethnic groups around the world.
a-glucosidase present at the intes-
With the admission of the fact that ‘diabetes is a cardiovascular
disease’ (CVD), rise in CVD is being cautioned due to the world
wide increase in prevalence of diabetes.1 Until recently, fasting
hyperglycemia has been the main therapeutic target for diabetes
mellitus. On the other hand, in recent years importance of post-
prandial hyperglycemia (PPHG) has been recognized as an impor-
tant cardiovascular risk factor.1e Furthermore, PPHG is also
identified as one of earliest detectable abnormalities expressed in
diabetes,2 better predictor of progression of diabetes3 and has been
implicated in inducing oxidative stress4 that is recognized as a ma-
jor pathophysiological link between CVD and diabetes.5 Therefore,
agents that hold the capacity of slowing down postprandial hyper-
glycemic excursion (PPHGE) and resultant oxidative stress may be-
come therapeutics of colossal importance.
a
In the course of our efforts in discovery and identification of tra-
ditional Indian medicinal plants11 and development of synthetic li-
brary of compounds12 possessing intestinal
a
-glucosidase
inhibitory and relevant antihyperglycemic activity, we observed
-glucosidase inhibitory potential in substituted new chromenone
a
derivatives. Natural as well as synthetic chromenones (2H-1-benz-
opyran-2-ones) have become important class of oxygenated het-
erocycles13 mainly due to their broad spectrum biological
activities such as antibiotics, antibacterial, antitumor, antiviral,
anticoagulants, antipsoriatic, and as anti-HIV.14 Compounds de-
rived from 4-hydroxycoumarin protect liver cells from damage
by peroxides.15
Food starches constitute a major source of energy in the diet
of many mammalian species, including humans. Slowing down of
digestion and absorption of dietary starches either by means of
dietary manipulation with low glycemic-index food or by inhibi-
In this study we report synthesis of number of substituted new
chromenone derivatives applying various synthetic strategies, their
* Corresponding authors. Tel.: +91 40 27191725; fax: +91 40 27160512 (B.C.R.).
E-mail addresses: chinarajuiict@yahoo.co.in (B.C. Raju), tiwari@iict.res.in (A.K.
Tiwari).
rat intestinal
a-glucosidase inhibitory potentials and DPPH free
radical scavenging activity as well as discuss the structure–activity
0968-0896/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2009.10.047

B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
359
relationship in relation to various substitutions and
inhibition. Furthermore, we also report antihyperglycemic activity
of most potent -glucosidase inhibitor in starch-induced hypergly-
a-glucosidase
O
O
O
O
R
CHO
OH
R
R2
O
R2
a
Piperidine
CH3CN
R1
cemia in normal Wistar rats.
R1
O
3c-e
4d-j
2. Results and discussion
2.1. Chemistry
4d R = H; R1 = H; R2 = CH3
4e R = H; R1 = H; R2 = OEt
4f R = H; R1 = H; R2 = C6H5
4g R = Br; R1 = H; R2 = CH3
4h R = Br; R1 = H; R2 = C6H5
4i R = H; R1 = OH; R2 = OEt
4j R = H; R1 = OH; R2 = C6H5
In continuation of our efforts on synthesis and development of
synthetic methodologies for heterocycles16 we herein report the
synthesis of substituted chromenone derivatives applying various
synthetic strategies. Scheme 1 illustrates synthesis of 4-substituted
chromenones 4a–c by the Pechmann condensation of resorcinol 3a
and b with b-ketoesters in presence of p-TSOH (20 mol %) in dry
toluene under reflux conditions. Scheme 2 illustrates the synthesis
of 3-substituted chromenones 4d–j by Knoevenagel condensation
of salicylaldehydes 3c–e with b-ketoesters in presence of piperi-
dine in acetonitrile and 3,6-disubstituted-2H-2-chromenones 4k–
z were synthesized from 4-bromophenol 1 as the starting material.
The 4-bromophenol 1 was subjected for Reimer–Tiemann reaction
to give 5-bromosalicylaldehyde 2. Compound 2 was then subjected
for Suzuki coupling with various phenylboronic acids in presence
of Pd(PPh3)4 to give 5-substituted salicylaldehydes 3g–n. Applica-
tion of Suzuki coupling for the synthesis of 3f, 3h–n was made for
the first time in preparation of substituted salicylaldehyde inter-
mediates. Knoevenagel reaction of substituted salicylaldehydes
3g–n with various b-ketoesters in presence of piperidine in aceto-
nitrile solvent under mild conditions proceeded efficiently to give
3,6-disubstituted-2H-2-chromenones 4k–z in very good yields
(Scheme 3). Thus synthesized compounds (4a–z) were character-
ized by spectral data and results are presented in Table 1.
Scheme 2.
ter activity than 4-chloromethyl (4a), 3-chloro-4-methyl (4c),
ethyl-3-carboxylate (4i) and 3-benzoyl substituted chromenone
(4j).
The 3-acetyl-6-phenylchromenone (4m) could not display
a-
glucosidase inhibitory activity. However, introduction of tolyl
group at sixth position significantly added enzyme inhibitory
capacity (4p). On the contrary, ethyl-3-carboxy group (4q) reduced
the activity potential, whereas 3-benzoyl substitution (4o)
enhanced the activity level when compared with 4n bearing
ethyl-3-carboxylate group. It appears therefore that substitution
of 6-tolyl (4p) and 3-benzoyl (4o) has added advantage in improv-
ing a-glucosidase inhibitory activity than that of ethyl-3-carboxyl-
ate (4n and 4q). Introduction of 4-fluorophenyl group (4s) was
observed advantageous over 4-chlorophenyl (4r) in improving en-
zyme inhibitory potential. Substitution of ethyl-3-carboxylate (4t)
further increases the activity of 6-(4-fluorophenyl)-3-acetyl-
chromenone (4s). Morpholinophenyl group on 6-aryl (4z) was no
more advantageous over 6-(4-fluorophenyl)-3-acetylchromenone
(4s).
2.2. Biological activity
Compound 4x emerged as the most potent a-glucosidase inhib-
All the synthesized compounds were evaluated in vitro for their
potential for DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical
scavenging and rat intestinal a-glucosidase inhibitory activity. Val-
ues are presented in Table 1, the compounds 4b, 4c, 4f, 4l, and 4z
could display mild DPPH scavenging activity at primary screening
itor in present series of compounds owing to the presence of 3-
acetyl-6-(6-methoxy-3-pyridyl) group on chromenone, however
substitution of ethyl-3-carboxylate group drastically reduced the
activity (4y). 3-Acetyl-6-(6-methoxy-3-pyridyl) substitution (4x)
had advantage over 3-acetyl-6-(4-pyrimidinyl) chromenones (4v
and 4w). Furthermore, 3-acetyl-6-(6-methoxy-3-pyridyl) in com-
pound 4x was found an important substitution in improving the
activity when compared to 4u. The fact that 6-(6-methoxy-3-pyr-
concentration of 25
other exhibited varying degrees of
ity at primary screening concentration of 100
that displayed more than 60% -glucosidase inhibitory activity
l
g/mL. However, except compound 4m, all
-glucosidase inhibitory activ-
g/mL. Compounds
a
l
a
idyl) group improves a-glucosidase inhibition, is also evident from
the activity potential of 4l over 4k.
were selected for concentration dependent activity evaluation
and calculation of IC50 values.
Therefore, compound 4x was selected for the study of its mech-
anism of enzyme inhibition and evaluation of its potential in mit-
igating starch-induced hyperglycemia in normal Wistar rats.
Figure 1 presents Lineweaver–Burk plot which states that the slope
for 4x crosses slope of the control left to the intercept above x-
axis.17 Therefore, it may be designated as mixed non-competitive
Based on IC50 values we could observe some structure–activity
relationship. Though, 3-substituted chromenone derivatives (4d–f)
displayed moderate enzyme inhibition, substitution of bromine at
sixth position on aryl moiety reduced the activity (4g and 4h). In
case of 7-hydroxy substituted chromenones (4a–c, 4i, and 4j),
compound 4b with methyl group at eighth position displayed bet-
inhibitor of rat intestinal
a-glucosidase enzyme. The prior oral
administration of 4x in overnight fasted rats before inducing
hyperglycemia by starch feeding showed that it slowed down
digestion of starch significantly (Fig. 2). Calculation of area under
the curve (AUC)18 further disclosed the fact that it has strong abil-
ity of reducing starch-induced hyperglycemic burden (Fig. 3).
Though it appears from Figures 2 and 3 that 4x has better antihy-
perglycemic activity than a commercial antihyperglycemic drug
acarbose with tetrasaccharide structure, it is important to note that
the dose of 4x in this study was 10 times higher than that of the
acarbose. The blood glucose level in some of the rats tested with
4x decreased below their basal value (‘0’ h value) indicates that
compound may possess other mode of antihyperglycemic activity
also.
O
O
R1
R1
O
R2
O
R2
p-TSOH
HO
OH
HO
O
R
3a-b
R
4a-c
4a R = H; R1 = CH2Cl; R2 = H
4b R =CH3; R1 = CH2Cl; R2 = H
4c R = H; R1 = CH3; R2 = Cl
Scheme 1.

360
B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
Pd[PPh3]4
Toluene
B(OH)2
Br
Br
CHO
OH
CHO
CHCl3
NaOH
OH
OH
O
1
3g
2
O
H3C
OEt
Piperidine
O
O
O
4m
Scheme 3.
Table 1
Synthesis of chromenone derivatives and their activity profiles
Entry
Substrate (3)
Compound (4)
Yield* (%)
% DPPH scavenging
1.32
% AGH inhibition (IC50
, lM)
CH2Cl
HO
OH
OH
1
65
72
78.34 (242.8)
3a
HO
O
O
4a
CH2Cl
HO
2
28.47
72.7 (68.7)
HO
HO
O
4b
O
3b
Cl
O
HO
OH
3
4
56
90
20.75
0.83
77.82 (128.3)
O
O
3a
4c
CHO
53.19
OH
O
4d
O
O
3c
CHO
O
5
6
7
88
90
86
1.82
30.8
1.52
46.95
44.38
31.95
OH
O
O
O
3c
4e
4f
CHO
OH
3c
O
O
Br
Br
CHO
OH
O
Br
Br
3d
O
O
O
4g
CHO
OH
8
9
88
65
2.22
NA
18.14
3d
3e
O
O
4h
4i
CHO
OH
O
O
77.6 (91.0)
HO
HO
O
O

B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
361
Table 1 (continued)
Entry
Substrate (3)
Compound (4)
Yield* (%)
62
% DPPH scavenging
NA
% AGH inhibition (IC50
53.71
, lM)
CHO
OH
O
O
10
HO
Br
3e
HO
O
4j
CN
O
CN
O
11
12
70
72
10.39
34.98
95.5 (52.90)
93.06 (44.5)
O
O
3f
3f
4k
MeO
Br
CN
O
N
CN
O
O
O
O
4l
CHO
OH
13
14
15
16
17
95
85
90
82
75
19.56
4.80
2.45
NA
NA
O
4m
O
O
3g
3g
3g
CHO
OH
O
77.06 (185.90)
69.95 (52.20)
86.47 (52.60)
65.89 (111.50)
O
O
O
4n
CHO
OH
O
4o
O
O
CHO
OH
O
O
O
O
4p
3h
CHO
OH
O
NA
O
4q
3h
Cl
F
Cl
F
O
CHO
18
19
76
82
12.54
15.55
76.89 (96.40)
74.26 (53.10)
OH
O
O
3i
4r
O
CHO
OH
O
O
O
3j
4s
F
F
CHO
OH
O
20
21
86
80
NA
66.72 (37.60)
96.40 (58.10)
O
O
4t
3j
O
N
CHO
OH
N
3.72
O
O
3k
4u
(continued on next page)

362
B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
Table 1 (continued)
Entry
22
Substrate (3)
Compound (4)
Yield* (%)
85
% DPPH scavenging
% AGH inhibition (IC50
, lM)
N
N
O
N
N
CHO
OH
N
N
NA
83.52 (37.20)
O
O
O
O
3l
3l
4v
N
N
CHO
OH
O
23
24
72
85
NA
NA
80.39 (40.50)
O
4w
MeO
MeO
O
O
N
CHO
OH
N
85.98 (28.20)
O
O
3m
4x
MeO
MeO
O
O
N
N
CHO
OH
N
N
O
25
26
72
88
NA
76.92 (104.60)
85.06 (49.00)
3m
4y
O
O
O
O
20.50
CHO
OH
O
3n
4z
% DPPH scavenging activity is based on values obtained with primary screening concentration of 25 lg/mL and that for a-glucosidase inhibition concentration was 100 lg/
mL. NA: not active. Values in parentheses represent
Isolated and unoptimised yields.
lM IC50 value for the respective compound. AGH;
a
-glucosidase.
*
175
150
125
100
75
Control
4x
Acarbose
0.1
0.08
0.06
0.04
**
*
*
*
0.02
*
*
control
10.6 uM, compound 4x
*
0
*
-0.75
-0.5
-0.25
-0.02
0
0.25
0.5
1/S(uM)
0.75
1
50
-0.04
-0.06
0 min
30 min
60 min
90 min
120 min
Time in minutes
Figure 1. Lineweaver–Burk plot for the hydrolysis of substrate p-nitrophenyl-
a
-
D
-
Figure 2. Antihyperglycemic activity of test compound 4x in rats. Plasma glucose
levels of rats after starch tolerance test in various groups of animals at different
time points. One way ANOVA analysis followed by Bonferroni’s multiple compar-
ison tests was applied to find difference between the groups. Values represent
mean SD, n = 6, Ã and ÃÃ represent statistical comparisons between control and
test groups. *p <0.001, **p <0.01. The dose of compound 4x was selected 100 mg/kg
body weight and for standard drug acarbose 10 mg/kg body weight as per our
previous reports.
glucopyranoside (p-NPG) by rat intestinal -glucosidase. Experimental procedures
a
remain same as described earlier except that the Vmax kinetics was recorded with
10 s lag time after addition of the substrate for 10 min at the interval of 30 s, with or
without pre-incubation of 4x with different dilutions of substrate concentration. It
is evident from the figure that the slope for compound 4x at 10.6
crosses slope of the control left to the intercept of x-axis. Therefore, compound 4x
might be inhibiting enzyme -glucosidase by mixed non-competitive mechanism.
lM concentration
a

B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
363
4.1.1.1. 4-(Chloromethyl)-7-hydroxy-8-methyl-2H-2-chrome-
300
250
200
150
100
50
none (4b). Solid, mp 254–256 °C. IR (KBr): 3275, 2923, 2853,
1703, 1660, 1574, 1507, 1376, 1315, 1222, 1154, 1089, 975 cmÀ1
.
1H NMR (CDCl3): d 9.92 (s, 1H, OH), 7.34 (d, 1H, J = 8.2 Hz,
aromatic), 6.92 (d, 1H, J = 8.2 Hz, aromatic), 6.36 (s, 1H, aromatic),
4.64 (s, 2H, CH2Cl), 2.28 (s, 3H, CH3). Mass (LC–MS): m/z 225 [M+1].
*
*
4.1.1.2. 3-Chloro-4-methyl-7-hydroxy-2H-2-chromenone (4c).
Solid, 1H NMR (CDCl3): d 7.45 (d, 1H, J = 8.0 Hz, aromatic), 6.80 (d,
1H, J = 8.2 Hz, aromatic), 6.75 (s, 1H, aromatic), 2.54 (s, 3H, CH3).
Mass (LC–MS): m/z 211 [M+1].
4.1.2. General procedure for the synthesis of 5-substituted
salicylaldehydes (3g–n)
0
Pd(PPh3)4 (10 mol %) was added to a stirred solution of 5-
bromosalicylaldehyde (2, 1 mmol), phenylboronic acid (1 mmol),
K2CO3 (2.5 mmol) in dry toluene (5 mL) and ethanol (1 mL) at room
temperature under N2 atmosphere and the contents were stirred at
the same temperature for 20 min. The reaction mixture was slowly
heated to 75–80 °C for 2 h. After completion of the reaction (TLC),
the solvents were removed under reduced pressure, the reaction
mixture was extracted with ethylacetate (2 Â 20 mL) and washed
with water, the organic layer was separated, dried over sodium sul-
fate, solvent removed under reduced pressure and the obtained
crude product was purified by flash chromatography using silica
gel (60–120) with hexane/ethylacetate (98:2) as eluent to give 2-
hydroxy-5-phenylbenzaldehyde (3g) in 78% yield. Yellow solid,
mp 95–97 °C. IR (KBr): 3056, 2850, 1654, 1586, 1473, 1420,
Control
4x
Acarbose
Figure 3. Area under the curve (AUC) represents influence on blood glucose level
per hour. It was calculated applying following formula:18 AUC (mg/
dL h) = (BG0 + BG30) Â 0.5/2 + (BG30 + BG60) Â 0.5/2 + (BG120 + BG60) Â 1/2,
where
BG0, BG30, BG60, and BG120 represent blood glucose level at 0, 30, 60 and 120 min
after starch feeding to the rats. One way ANOVA analysis followed by Bonferroni’s
multiple comparison tests was applied to find difference between the groups. *p
<0.001 in comparison with control.
3. Conclusion
Compounds 4k–z were synthesized applying new synthetic ap-
proaches. Suzuki coupling for the synthesis of compounds 3h–n
has been applied for the first time in synthesizing chromenone
derivatives. Though compounds 4a–g, 4i, and 4j are known in the
literature along with the synthetic methodology applied in this re-
1373, 1296, 1233, 1176, 898, 767 cmÀ1 1H NMR (CDCl3): d 10.98
.
(s, 1H, OH), 10.00 (s, 1H, CHO), 7.75 (d, J = 8.2 Hz, 2H, aromatic),
7.50 (d, J = 8.4 Hz, 2H, aromatic), 7.42–7.38 (m, 2H, aromatic),
7.32–7.30 (m, 1H, aromatic), 7.08 (d, J = 8.8 Hz, 1H, aromatic). Mass
(LC–MS): m/z 197 [MÀ1].
port, the assignment of the a-glucosidase inhibitory activity to all
the chromenone derivatives in this report is new aspect. Com-
pound 4x is new and being reported in this study to possess intes-
4.1.2.1. 2-Hydroxy-5-(4-methylphenyl)-benzaldehyde (3h). Yield
65%. Yellow solid, mp 74–76 °C, IR (KBr): 3418, 2922, 2854, 1651,
tinal
for the first time. Therefore, it may serve as a model compound for
design and development of therapeutic based on -glucosidase
inhibitory antihyperglycemic activity. This study further presents
a-glucosidase inhibitory as well as antihyperglycemic activity
1
1591, 1478, 1262, 1169, 815, 723 cmÀ1. H NMR (CDCl3): d 10.88 (s,
a
1H, OH), 9.88 (s, 1H, CHO), 7.68–7.62 (m, 2H, aromatic), 7.33 (d,
J = 8.2 Hz, 2H, aromatic), 7.15 (d, J = 8.4 Hz, 2H, aromatic), 6.97 (d,
J = 8.0 Hz, 1H, aromatic), 2.32 (s, 3H, CH3). 13C NMR (75 MHz, CDCl3):
d 196.67, 160.73, 137.19, 136.41, 135.58, 133.25, 131.57, 129.66,
126.39, 120.66, 118.02, 21.05. Mass (LC–MS): m/z 211 [MÀ1].
chromenone derivatives as new class of a-glucosidase inhibitors.
4. Experimental
4.1. Chemistry
4.1.2.2. 2-Hydroxy-5-(4-chlorophenyl)-benzaldehyde (3i). Yield
76%. Yellow solid, mp 85–87 °C. IR (KBr): 3031, 2848, 2362, 1656,
1H NMR and 13C NMR spectra were recorded on a Varian Gemini
200 MHz and Avance 300 MHz spectrometer in CDCl3 using TMS as
internal standard. IR spectra were recorded on a Nicollet 740 FTIR
spectrometer. Mass spectra were obtained on Agilent LCMS instru-
ment. Melting points were determined in open glass capillary
tubes on a Metler FP 51 melting point apparatus and are uncor-
rected. All reactions were monitored by thin layer chromatography
(TLC) on pre-coated Silica Gel 60 F254 (mesh); spots were visualized
under UV light. Merck silica gel (60–120; 100–200 mesh) was used
for chromatography. All the reactions were carried out using re-
agent-grade solvents, and the reagents were purchased from Sig-
ma–Aldrich.
1588, 1476, 1394, 1266, 1172, 1092, 816 cmÀ1 1H NMR (CDCl3): d
.
10.98 (s, 1H, OH), 9.98 (s, 1H, CHO), 7.74–7.66 (m, 2H, aromatic),
7.48–7.36 (m, 4H, aromatic), 7.06 (d, J = 8.4 Hz, 1H, aromatic). Mass
(LC–MS): m/z 231, 233 [MÀ1].
4.1.2.3. 2-Hydroxy-5-(4-fluorophenyl)-benzaldehyde (3j). Yield
82%. Yellow solid, mp 91–93 °C. IR (KBr): 3449, 3062, 2852, 1659,
1592, 1478, 1221, 1170, 904, 829 cmÀ1 1H NMR (CDCl3): d 11.00
.
(s, 1H, OH), 9.96 (s, 1H, CHO), 7.74–7.69 (m, 2H, aromatic), 7.53–
7.47 (m, 2H, aromatic), 7.18–7.05 (m, 3H, aromatic). Mass (LC–
MS): m/z 217 [M+1].
4.1.3. General procedure for the synthesis of 3,6-disubstituted
chromenone derivatives (4d–z)
4.1.1. General procedure for the synthesis of 3-substituted
chromenones (4a–c)
Piperidine (5 mol %) was added to a stirred solution of 5-phe-
nyl-2-hydroxybenzaldehyde (3g, 1 mmol), ethylacetoacetate
(1.1 mmol) in CH3CN (4 mL) at room temperature. The contents
were stirred for 4 h at the same temperature. After completion of
the reaction (TLC), the solvent was removed under reduced pres-
sure and the crude product was subjected for column chromatog-
raphy purification using silica gel (60–120) with hexane/
The resorcinol (1 mmol), ethyl 4-chloro acetoacetate (1.1 mmol)
and p-TSOH (10 mol %) in dry toluene refluxed for 20 min. The
crude compound on flash chromatography using silica gel gave
4-(chloromethyl)-7-hydroxy-2H-2-chromenone (4a) in 65% yield.
Similarly the compounds 4b and 4c were prepared by using the
corresponding b-ketoesters.

364
B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
ethylacetate (8:2) as eluent to give 3-acetyl-6-phenyl-2H-2-
chromenone (4m) in 95% yield as yellow solid, mp 198–200 °C.
IR (KBr): 3067, 2922, 1743, 1679, 1565, 1483, 1359, 1208, 1109,
8.56 (s, 1H, aromatic), 7.85–7.76 (m, 2H, aromatic), 7.57–7.51 (m,
2H, aromatic), 7.45 (d, 1H, J = 8.4, aromatic), 7.22–7.15 (m, 2H, aro-
matic), 2.75 (s, 3H, CH3). 13C NMR (CDCl3): d 195.37, 164.44,
154.52, 147.38, 137.42, 133.16, 128.72, 128.61, 127.96, 124.83,
118.45, 117.11, 116.21, 115.92. Mass (LC–MS): m/z 283 [M+1].
970, 841, 765 cmÀ1 1H NMR (CDCl3): d 8.54 (s, 1H, aromatic),
,
7.85–7.81 (m, 2H, aromatic), 7.53 (d, J = Hz, 2H, aromatic), 7.45–
7.38 (m, 4H, aromatic), 2.72 (s, 3H, CH3). Mass (LC–MS): m/z 265
[M+1].
4.1.3.9. Ethyl-6-(4-fluorophenyl)-2-oxo-2H-chromene-3-carbox-
ylate (4t). Yellow solid, mp 180–182 °C. IR (KBr): 3061, 2983,
2923, 2852, 1742, 1710, 1575, 1482, 1265, 1161, 1033, 975,
4.1.3.1. 3-Benzoyl-2H-2-chromenone (4f). Solid, mp 132–
134 °C. IR (KBr): 3283, 3081, 2985, 2948, 1687, 1626, 1447, 1387,
830, 791 cmÀ1 1H NMR (CDCl3): d 8.56 (s, 1H, aromatic), 7.81,
.
1281, 1234, 1136, 1042, 916 cmÀ1
.
1H NMR (CDCl3): d 8.05 (s,
7.78 (d,d, 1H, J = 2.0, J = 8.6, aromatic), 7.22 (d, 1H, J = 2.0, aro-
matic), 7.55–7.49 (m, 2H, aromatic), 7.42 (d, 1H, J = 8.4, aromatic),
7.20–7.12 (m, 2H, aromatic), 4.43 (q, 2H, OCH2), 1.43 (t, 3H, CH3).
1H, aromatic), 7.84 (d, 2H, J = 7.16 Hz, aromatic), 7.65–7.55 (m,
3H, aromatic), 7.49–7.26 (m, 4H, aromatic). 13C NMR (CDCl3):
191.60, 154.69, 145.38, 136.14, 133.77, 133.59, 129.53, 128.55,
126.92, 124.93, 118.10, 116.87. Mass (LC–MS): m/z 251 [M+1].
13C NMR (CDCl3):
d 148.50, 133.08, 128.73, 128.62, 127.29,
117.24, 116.21, 115.92, 62.07, 29.62, 14.21. Mass (LC–MS): m/z
313 [M+1].
4.1.3.2. 3-Benzoyl-7-hydroxy-2H-2-chromenone (4j). Solid, mp
217–219 °C. IR (KBr): 3191, 1688, 1651, 1589, 1514, 1446, 1373,
4.1.3.10. 3-Acetyl-6-(3-pyridyl)-2H-2-chromenone (4u). Yellow
solid, mp 200–202 °C. IR (KBr): 3063, 2922, 2852, 1735, 1676,
1221, 1149, 930 cmÀ1 1H NMR (CDCl3): d 8.12 (s, 1H, aromatic),
.
7.86–7.82 (m, 2H, aromatic), 7.65–7.56 (m, 1H, aromatic), 7.52–
7.44 (m, 3H, aromatic), 6.86–6.78 (m, 2H, aromatic). Mass (LC–
MS): m/z 267 [M+1].
1561, 1361, 1207, 967, 802 cmÀ1 1H NMR (CDCl3): d 8.81 (d, 1H,
.
J = 2.2 Hz, heteroaromatic), 8.68, 8.66 (dd, 1H, J = 8.0 Hz, 2.0 Hz,
heteroaromatic), 8.58 (s, 1H, aromatic), 7.94–7.83 (m, 3H, aro-
matic + heteroaromatic), 7.48 (d, 1H, J = 8.2 Hz, aromatic), 7.46–
7.40 (m, 1H, aromatic), 2.78 (s, 3H, COCH3). 13C NMR (75 MHz,
CDCl3): d 196.05, 159.40, 155.44, 148.23, 147.70, 147.17, 135.94,
134.72, 133.51, 128.85, 125.38, 124.78, 119.09, 117.90, 30.60. Mass
(LC–MS): m/z 266, 288 [M+1, M+Na].
4.1.3.3. 4-Methyl-2-oxo-6-phenyl-2H-chromene-3-carbonitrile
(4k). Yellow solid, mp 185–187 °C. IR (KBr): 2922, 2852, 2224,
1721, 1607, 1561, 1481, 1448, 1378, 1288, 1249, 1084, 759 cmÀ1
.
1H NMR (CDCl3): d 7.92–7.84 (m, 2H, aromatic), 7.62–7.58 (m,
2H, aromatic), 7.56–7.40 (m, 4H, aromatic), 2.84 (s, 3H, CH3). Mass
(LC–MS): m/z 262 [M+1].
4.1.3.11. 3-Acetyl-6-(4-pyrimidinyl)-2H-2-chromenone (4v). Yel-
low solid, mp 250–252 °C. Yield: 85%. IR (KBr): 3437, 3044, 2923,
4.1.3.4. 6-(6-Methoxy-3-pyridyl)-4-methyl-2-oxo-2H-chromene-
3-carbonitrile (4l). Yellow solid, mp 199–201 °C. IR (KBr): 2921,
2851, 2226, 1731, 1604, 1563, 1483, 1368, 1283, 1082, 997, 825,
2852, 1737, 1681, 1563, 1420, 1206, 975 cmÀ1 1H NMR (CDCl3): d
.
9.80 (s, 1H, heteroaromatic), 8.98 (s, 2H, heteroaromatic), 8.55 (s, 1H,
aromatic), 7.88–7.83 (m, 2H, aromatic), 7.56 (d, 1H, J = 8.2 Hz, aro-
matic), 2.74 (s, 3H, COCH3). Mass (LC–MS): m/z 267 [M+1].
763 cmÀ1 1H NMR (CDCl3): d 8.32 (s, 1H, heteroaromatic), 7.82–
.
7.72 (m, 3H, heteroaromatic + aromatic), 7.46 (d, 1H, J = 8.2 Hz, aro-
matic), 6.82 (d, 1H, J = 8.2 Hz, aromatic), 3.98 (s, 3H, OCH3), 2.84 (s,
3H, CH3). 13C NMR (75 MHz, CDCl3): d 145.13, 137.25, 133.58,
127.82, 123.52, 118.35, 111.32, 53.73, 29.66. Mass (LC–MS): m/z
293 [M+1].
4.1.3.12. Ethyl-2-oxo-6-(4-pyrimidinyl)-2H-chromene-3-carbox-
ylate (4w). Yellow solid, mp 194–196 °C. IR (KBr): 3508, 3061,
2925, 2854, 1742, 11709, 1625, 1400, 1269, 1025, 848 cmÀ1 1H
.
NMR (CDCl3): d 9.30 (s, 1H, heteroaromatic), 9.00 (s, 2H, heteroaro-
matic), 8.60 (s, 1H, aromatic), 7.89–7.80 (m, 2H, aromatic), 7.56 (d,
1H J = 8.0 Hz, aromatic), 4.45 (q, 2H, OCH2), 1.48 (t, 3H, CH3). 13C
NMR (CDCl3): d 162.91, 158.23, 156.23, 156.23, 155.65, 155.02,
147.92, 132.83, 131.47, 127.87, 119.84, 118.88, 118.35, 62.45,
14.43. Mass (LC–MS): m/z 297 [M+1].
4.1.3.5. 3-Benzoyl-6-phenyl-2H-2-chromenone (4o). Yellow so-
lid, mp 158–160 °C. IR (KBr): 3415, 2922, 2854, 1715, 1664, 1572,
1477, 1254, 1210, 1153, 924, 759 cmÀ1. 1H NMR (CDCl3): d 8.12 (s,
1H, aromatic), 7.90–7.82 (m, 3H, aromatic), 7.76 (d, 1H, J = 2.0 Hz,
aromatic), 7.64–7.35 (m, 9H, aromatic). 13C NMR (75 MHz, CDCl3):
d 145.47, 133.84, 132.56, 129.59, 129.11, 128.61, 128.04, 127.19,
127.03, 117.29. Mass (LC–MS): m/z 327 [M+1].
4.1.3.13. 3-Acetyl-6-(6-methoxy-3-pyridyl)-2H-2-chromenone
(4x). Yellow solid, mp 204–206 °C. IR (KBr): 2957, 1932, 1739,
1679, 1608, 1566, 1481, 1360, 1288, 1236, 1022, 973, 823 cmÀ1
.
4.1.3.6. 3-Acetyl-6-(4-methylphenyl-2H-2-chromenone (4p).
Yellow solid, mp 205–207 °C. 1H NMR (CDCl3): d 8.52 (s, 1H, aro-
matic), 7.84, 7.82 (dd, 1H, J = 8.2 Hz, 2.6 Hz, aromatic), 7.78 (d,
1H, J = 2.6 Hz, aromatic), 7.46–7.38 (m, 3H, aromatic), 7.26 (d,
2H, J = 8.0 Hz, aromatic), 2.78 (s, 3H, COCH3), 2.40 (s, 3H, CH3).
1H NMR (CDCl3): d 8.52 (s, 1H, heteroaromatic), 8.34 (s, 1H, aro-
matic), 7.82–7.70 (m, 3H, heteroaromatic + aromatic), 7.44 (d, 1H,
J = 8.0 Hz, aromatic), 6.82 (d, 1H, J = 8.0 Hz, aromatic), 3.98 (s, 3H,
OCH3), 2.74 (s, 3H, COCH3). 13C NMR (75 MHz, CDCl3): d 195.33,
164.07, 159.06, 154.57, 147.28, 145.02, 137.19, 135.20, 132.78,
127.86, 127.57, 124.95, 118.62, 117.33, 111.26, 53.68, 30.55. Mass
(LC–MS): m/z 296 [M+1].
13C NMR (CDCl3):
d 195.68, 159.47, 154.67, 147.79, 138.60,
138.26, 136.15, 133.43, 130.05, 128.05, 127.05, 124.92, 118.66,
117.20, 30.77, 21.32. Mass (LC–MS): m/z 279 [M+1].
4.1.3.14. Ethyl-6-(6-methoxy-3-pyridyl)-2-oxo-2H-chromene-3-
carboxylate (4y). Yellow solid, mp 161–163 °C. IR (KBr): 3432,
3060, 2979, 2930, 1741, 1710, 1481, 1289, 1264, 1022, 834,
4.1.3.7. 3-Acetyl-6-(4-chlorophenyl)-2H-2-chromenone (4r). Yel-
low solid, mp 232–234 °C. IR (KBr): 3426, 2919, 2850, 1725, 1681,
1612, 1562, 1230, 1123, 811, 768 cmÀ1
.
1H NMR (CDCl3): d 8.60 (s,
793 cmÀ1 1H NMR (CDCl3): d 8.56 (s, 1H, heteroaromatic), 8.34 (s,
.
1H, aromatic), 7.88–7.82 (m, 2H, aromatic), 7.56–7.42 (m, 5H, aro-
matic), 2.60 (s, 3H, CH3). Mass (LC–MS): m/z 299 [M+1].
1H, aromatic), 7.82–7.68 (m, 3H, aromatic + heteroaromatic), 7.42
(d, 1H, J = 8.2 Hz, aromatic), 6.82 (d, 1H, J = 8.0 Hz, aromatic), 4.48
(q, 2H, OCH2), 3.98 (s, 3H, OCH3), 1.44 (t, 3H, CH3). 13C NMR (CDCl3):
d 164.03, 162.94, 156.51, 154.41, 148.35, 144.99, 137.19, 135.02,
132.69, 127.91, 126.87, 118.83, 118.24, 117.42, 111.21, 62.05,
53.66, 14.19. Mass (LC–MS): m/z 326 [M+1].
4.1.3.8. 3-Acetyl-6-(4-fluorophenyl)-2H-2-chromenone (4s).
Yellow solid, mp 196–198 °C. IR (KBr): 3064, 2925, 1727, 1681,
1566, 1513, 1401, 1230, 1160, 974, 814 cmÀ1 1H NMR (CDCl3): d
.

B. C. Raju et al. / Bioorg. Med. Chem. 18 (2010) 358–365
365
4.1.3.15. 3-Acetyl-6-(4-morpholinophenyl)-2H-2-chromenone
(4z). Yellow solid, mp 158–160 °C. IR (KBr): 3056, 2923, 2853,
2366, 1745, 1709, 1622, 1573, 1476, 1365, 1268, 1029,
levels for basal (‘0’ h) value were measured by glucose–oxidase test
method using auto blood analyzer instrument (Bayer EXPRESS
PLUS). Test compound 4x and standard drug acarbose were sus-
pended in normal saline and administered orally through gastric
intubation. The control group of animals were treated sham with
normal saline. Fifteen minutes after treatment, animals were fed
with soluble-starch dissolved in normal saline at a dose of 2 g/kg
body weight. Thereafter, blood was collected at intervals of 30,
60, 90, and 120th min post starch feeding. Plasma was separated
out for glucose measurement as described above.
758 cmÀ1 1H NMR (CDCl3): d 8.55 (s, 1H, aromatic), 7.86, 7.82
.
(dd, 1H, J = 8.0 Hz, 2.0 Hz, aromatic), 7.78 (d, 1H, J = 2.0 Hz, aro-
matic), 7.52 (d, 2H, J = 8.0 Hz, aromatic), 7.42 (d, 1H, J = 8.2 Hz,
aromatic), 6.98 (d, 2H, J = 8.2 Hz, aromatic), 3.94–3.88 (m, 4H,
O(CH2)2), 3.28–3.20 (m, 4H, N(CH2)2), 2.74 (s, 3H, COCH3). Mass
(LC–MS): m/z 350 [M+1].
4.2. Biological activity evaluation
Acknowledgments
4.2.1. DPPH free radical scavenging activity
Assay for the scavenging of stable free radical 1,1-diphenyl-2-
The authors thank Dr. J. S. Yadav, Director, and Dr. J. Madhusu-
dana Rao, Head, Organic Chemistry Division-1, IICT for their con-
stant encouragement and support of this work. Financial
assistance to J.A.K. from UGC and G.S. from CSIR, New Delhi is
gratefully acknowledged.
picrylhydrazyl (DPPH) was done as reported earlier.11 Briefly, in a
96-well microplate, 25
lL of test sample dissolved in DMSO
(1 mg/mL), 125 L of 0.1 M Tris–HCl buffer (pH 7.4) and 125 lL
l
of 0.5 mM DPPH solution dissolved in absolute ethyl alcohol were
added. The reaction mixture was shaken well and incubated in
dark for 30 min and read at 517 nm spectrophotometrically (Spec-
tra Max plus384, Molecular Devices Corporation, Sunnyvale, CA,
USA). Percentage of DPPH scavenging was calculated as (1 À B/
A) Â 100, where A represents absorbance of control without test
samples, and B represents absorbance in presence of test samples.
References and notes
1. (a) Grundy, S. M.; Benzamin, I. J.; Burke, G. L.; Chait, A.; Eckel, R. H.; Howard, B.
V.; Mitch, W.; Smith, S. C.; Sowers, J. R. Circulation 1999, 100, 1134; (b) Gu, K.;
Cowie, C. C.; Harris, M. I. Diabetes Care 1998, 21, 1138; (c) Stamler, J.; Vaccaro,
O.; Nealon, J. D.; Wentworht, D. Diabetes Care 1993, 16, 434; (d) Haffner, S. M.;
Lehto, S.; Ronnemma, T.; Pyorala, K.; Laakso, M. N. Eng. J. Med. 1998, 339, 229;
(e) Fava, S. Expert Rev. Cardiovasc. Ther. 2008, 6, 859.
2. Gerich, J. E. Hormone Metab. Res. 1996, 28, 404.
3. Davidson, J. Diabetes Care 2003, 26, 1919.
4. Ceriello, A. Diabetes Vasc. Dis. Res. 2008, 5, 260.
5. Giugliano, D.; Ceriella, A.; Paolisso, G. Diabetes Care 1996, 16, 257.
6. (a) Maki, K. C. Am. J. Cardiol. 2004, 93, 12C; (b) Maki, K. C.; Carson, M. L.; Miller,
M. P.; Tutowski, M.; Bell, M.; Wildor, D. M.; Reeves, M. S. Diabetes Care 2007, 30,
1039; (c) Delorme, S.; Chiasson, J. L. Curr. Opin. Pharmacol. 2005, 5, 184.
7. Scheen, A. J. Lancet 2009, 373, 1570.
8. Chan, J. C.; Chan, K. W.; Ho, L. L., et al Diabetes Care 1998, 21, 1058.
9. Henry, C. J.; Lightowler, H. J.; Newens, K.; Sudha, V.; Radhika, G.; Satya, R. M.;
Mohan, V. Br. J. Nutr. 2008, 99, 840.
10. Milicevic, Z.; Raz, I.; Beattie, S. D.; Compaigne, B. N.; Sarwat, S.; Gromniak, E.;
Kowalska, I.; Galic, E.; Tan, M.; Hanefeld, M. Diabetes Care 2008, 31, S155.
11. Rao, R. R.; Tiwari, A. K.; Reddy, P. P.; Babu, K. S.; Ali, A. Z.; Madhusudana, K.;
Rao, J. M. Bioorg. Med. Chem. 2009, 17, 5170.
12. (a) Tiwari, A. K.; Kumbhare, R. M.; Agawane, S. B.; Ali, A. Z.; Kumar, K. V. Bioorg
Med. Chem. Lett. 2008, 18, 4130; (b) Hari Babu, T.; Rao, V. R. S.; Tiwari, A. K.;
Babu, K. S.; Srinivas, P. V.; Ali, A. Z.; Rao, J. M. Bioorg. Med. Chem. Lett. 2008, 18,
1659.
4.2.2.
a-Glucosidase inhibitory assay
a
-Glucosidase inhibitory activities were determined as per ear-
lier reported methods.11,12 Rat intestinal acetone powder in normal
saline (100:1; w/v) was sonicated properly and the supernatant
was used as a source of crude intestinal
fugation. In brief, 20 L of test samples (5 mg/mL DMSO solution)
were reconstituted in 100 L of 100 mM-phosphate buffer (pH
6.8) in 96-well microplate and incubated with 50 L of crude intes-
tinal -glucosidase for 5 min before 50 L substrate (5 mM, p-
nitrophenyl- -glucopyranoside prepared in same buffer) was
a-glucosidase after centri-
l
l
l
a
l
a
-D
added. Release of p-nitrophenol was measured at 405 nm spectro-
photometrically (Spectra Max plus 384), Molecular Devices Corpo-
ration, Sunnyvale, CA, USA) 5 min after incubation with substrate.
Individual blanks for test samples were prepared to correct back-
ground absorbance where substrate was replaced with 50
lL of
buffer. Control sample contained 10 L DMSO in place of test
l
13. O’Kennedy, R.; Thomas, R. D. Coumarins: Biology, Applications, and Mode of
Action; Wiley: Chichester, UK, 1997; Murray, R. D. H.; Mendez, J.; Brown, S. A.
The Natural Coumarins; Wiley: New York, 1982.
samples. Percentage of enzyme inhibition was calculated as
(1 À B/A) Â 100, where [A] represents absorbance of control with-
out test samples, and [B] represents absorbance in presence of test
14. (a) Maxwell, A. Mol. Microbiol. 1993, 9, 681; (b) Musicki, B.; Periers, A. M.;
Laurin, P.; Ferroud, D.; Benedetti, Y.; Lachaud, S.; Chatreaux, F.; Haesslein, J. L.;
Iltis, A.; Pierre, C.; Khider, J.; Tessot, N.; Airault, M.; Demassey, J.; Dupuis-
Hamelin, C.; Lassaigne, P.; Bonnefoy, A.; Vicat, P.; Klich, M. Bioorg. Med. Chem.
Lett. 2000, 10, 1695; (c) Chimichi, S.; Boccalini, M.; Cosimelli, B.; Viola, G.;
Vedaldi, D.; Dall’Acqua, F. Tetrahedron Lett. 2002, 43, 7473; (d) Yoakim, C.;
Bonneau, P. R.; De´ziel, R.; Doyon, L.; Duan, J.; Guse, I.; Landry, S.; Malenfant, E.;
Naud, J.; Ogilvie, W. W.; O’Meara, J. A.; Plante, R.; Simoneau, B.; Thavonekham,
B.; Bo, S. M.; Cordingley, M. G. Bioorg. Med. Chem. Lett. 2004, 14, 739; (e)
Uchiumi, F.; Hatano, T.; Ito, H.; Yoshida, T.; Tanuma, S. Antiviral Res. 2003, 58,
89; (f) Yu, D.; Suzuki, M.; Xie, L.; Morris-Natschke, S. L.; Lee, K. H. Med. Res. Rev.
2003, 23, 322; (g) Jeddy, A. S.; Gleason, B. L. Ann. Pharmacother. 2003, 37, 1502;
(h) Pineo, G.; Hull, R. D. Hematol. Oncol. Clin. North Am. 2003, 17, 201; (i)
Guiotto, A.; Chilin, A.; Manzini, P.; Dall’Acqua, F.; Bordin, F.; Rodighiero, P.
Farmaco 1995, 50, 479.
samples. For calculation of 50% enzyme inhibitory activity (IC50%
)
more than five dilutions of primary screening concentration
(5 mg/mL DMSO solution) of test compounds were prepared. The
IC50 values were calculated applying logarithmic regression
analysis.
4.2.3. Animal experiment
Antihyperglycemic activity study was done according to the
method reported earlier.11,12 Wistar rats of either sex weighing be-
tween 195 and 215 g were obtained from National Institute of
Nutrition (CPCSEA Reg. No. 154, Government of India), Hyderabad.
The animals were housed in standard polyvinyl cages. The room
temperature was maintained at 22 1 °C with an alternating
12 h light dark cycle. Food and water were provided ad libitum.
Experiments were performed as per the Institutional Animal Ethi-
cal Committee norms. The rats were divided into various groups’
viz. control, test compound 4x group (100 mg/kg body weight)
and a group with standard drug acarbose (10 mg/kg body weight).
Five rats in each group were taken. All the animals were kept for
overnight fasting. Next day forenoon blood was collected from ret-
ro orbital plexus in EDTA containing tubes, and plasma glucose
15. Rollinger, J. M.; Hornick, A.; Langer, T.; Stuppner, H.; Prast, H. J. Med. Chem.
2004, 47, 6248–6254.
16. (a) Gangadasu, B.; Janaki Ram Reddy, M.; Ravinder, M.; Bharath Kumar, S.;
China Raju, B.; Pranay Kumar, K.; Murthy, U. S. N.; Jayathirtha Rao, V. Eur. J.
Med. Chem. 2009, 44, 4661.; (b) Gangadasu, B.; China Raju, B.; Jayathirtha Rao,
V. J. Heterocycl. Chem., in press, doi:10.1002/jhet.208.; (c) Narender, P.;
Ravinder, M.; Partha Sarathi, S.; China Raju, B.; Ramesh, Ch.; Jayathirtha Rao,
V. Helv. Chim. Acta 2009, 92, 959; (d) Kumar, A. J.; Tiwari, A. K.; Ali, A. Z.;
Madhusudana, K.; Reddy, B. S.; Ramakrishna, S.; China Raju, B. J. Enz. Inhib. Med.
Chem. 2009. doi:10.1080/14756360903017122.; (e) China Raju, B.; Dharma
Theja, N.; Ashok Kumar, J. Synth. Commun. 2009, 39, 175.
17. Babu, K. S.; Tiwari, A. K.; Srinivas, P. V.; Ali, A. Z.; China Raju, B.; Rao, J. M.
Bioorg. Med. Chem. Lett. 2004, 14, 3841.
18. Ye, F.; Shen, Z.; Xie, M. Phytomedicine 2002, 9, 161.