Antihyperglycemic, α-glucosidase inhibitory and DPPH free radical scavenging activity of 5-bromosalicylaldehyde and schiff bases

Article abstract of DOI:10.1007/s00044-010-9377-3

α-Glucosidase inhibition and DPPH free radical scavenging by 5-bromosalicylaldehyde and some Schiff bases have been measured. 5-Bromosalicylaldehyde shows lowest IC₅₀ value (8.80 μM) for α-glucosidase inhibition and also shows good results in in vivo experiments for antihyperglycemic potential. Springer Science+Business Media, LLC 2010.

Full text of DOI:10.1007/s00044-010-9377-3

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2011) 20:1431–1437
DOI 10.1007/s00044-010-9377-3
ORIGINAL RESEARCH
Antihyperglycemic, a-glucosidase inhibitory and DPPH free
radical scavenging activity of 5-bromosalicylaldehyde and schiff
bases
•
Sristicheta Misra Krishna Bihari Pandeya Ashok Kumar Tiwari
•
•
•
Amtul Zehra Ali Thimmapatruni Saradamani
•
•
Sachin Bharat Agawane Kuncha Madhusudana
Received: 13 March 2010 / Accepted: 26 May 2010 / Published online: 10 June 2010
Ó Springer Science+Business Media, LLC 2010
Abstract a-Glucosidase inhibition and DPPH free radical
scavenging by 5-bromosalicylaldehyde and some Schiff
bases have been measured. 5-Bromosalicylaldehyde shows
lowest IC50 value (8.80 lM) for a-glucosidase inhibition
and also shows good results in in vivo experiments for
antihyperglycemic potential.
glycemia immediately following a meal (Slama et al.,
2006) (particularly those that contain starchy food), has
been implicated as an independent risk factor for cardio-
vascular disease (Gerich, 2003), not only in diabetic
patients, but also among subjects in general population
with mildly elevated postprandial glucose levels. In type-II
DM subjects (Maki et al., 2007), epithelial membrane
bound a-glucosidase in small intestine hydrolyses a-glu-
cosidic bond of carbohydrates and oligosaccharides to
release a-D-glucose. Inhibition of a-glucosidase has been
found to slow down digestion and absorption of carbohy-
drate, causing thereby lowering in the PPHG level (Dimi-
triadis et al., 1991; Lam et al., 1998; Raptis and
Dimitriadis, 2001). Slowing down of the digestion and
absorption of dietary carbohydrates using a-glucosidase
inhibitors has, thus, proved to be a promising therapeutic
strategy for reducing risk of diabetes and the consequential
diseases. Further, a rich meal also causes increased sus-
ceptibility of the organism toward oxidative damage,
known as postprandial oxidative stress (PPOS), character-
ized by overt generation of free radicals that induce oxi-
dative biological damage to biomolecules causing free
radical mediated diseases (Ceriello, 2008; Sies et al.,
2005), including diabetes. Antioxidants that scavenge free
radicals are now known to possess preventive as well as
therapeutic potential (Halliwell, 1994; Halliwell, 1999;
Noguchi and Nikki, 2000; Prasad et al., 1999; Tiwari,
1999; Visioli et al., 2000a; b; Winyard and Blake, 1997),
against free radical mediated diseases. A holistic thera-
peutic approach for combating ailments involving multiple
disorders would, therefore, be use of agents that reduce
both PPHG and PPOS. Intestinal a-glucosidase inhibitory
drugs like acarbose, Voglibose, or Miglitol have shown
promising results (Delorme and Chiasson, 2005; Maki,
2004; Maki et al., 2007), in this regard.
Keywords a-Glucosidase inhibition Á DPPH free radical
scavenging Á Antihyperglycemic activity Schiff bases Á
5-Bromosalicylaldehyde
Introduction
Diabetes mellitus (DM) is one of the lifestyle-related dis-
eases, which has attained the status of world epidemic. The
number of patients that suffer from DM in the world has
been forecasted (King et al., 1998), to increase to *333
million in 2025 from 194 million in 2003. Postprandial
hyperglycemia (PPHG) has emerged (Carroll et al., 2003)
as a prominent and early defect in type-II diabetes. Post-
prandial hyperglycemic excursion, that is, the increase in
S. Misra Á K. B. Pandeya (&)
Department of Chemistry, University of Allahabad, Allahabad
211002, India
e-mail: kbpandeya@yahoo.com
A. K. Tiwari (&) Á A. Z. Ali Á T. Saradamani Á
S. B. Agawane Á K. Madhusudana
Division of Pharmacology, Indian Institute of Chemical
Technology, Hyderabad 500007, India
e-mail: astiwari@yahoo.com
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Med Chem Res (2011) 20:1431–1437
Fig. 1 Structures of the compounds
OH
1a
1b
1c
1d
1e
1f
Y=H
Y=H
Y=H
Y=H
Y=Br
Y=Br
Y=Br
X= H
X= Cl
X= -OCH3
X= -NO2
X= H
C = N
H
Y
X= Cl
X= -OCH3
1g
1h
Y=Br
X= -NO2
X
Z
Z
2a
2b
2c
X=H
X=H
X= CH3
Y=H Z=OH
Y=Br Z=OH
Y=H Z=H
N
C =
X
N =
C
Y
Y
X
OH
HO
C
3a
3b
Y=H
Y=Br
N
N =
C =
H
Y
Y
H
H C
3
N
C =
NH
C
4
5
O
CH
3
OH
CHO
Br
In the present communication, we report the synthesis
and rat intestinal a-glucosidase inhibitory and 1,1-diphe-
nyl-2-picrylhydrazyl (DPPH) generated free radical scav-
enging activities of 5-bromosalicylaldehyde and a series of
Schiff bases (Fig. 1). The Schiff bases 1 have been derived
from salicylaldehyde/5-bromosalicylaldehyde and anilines.
Schiff bases 2 have been derived from salicylaldehyde/5-
bromosalicylaldehyde/acetophenone and ethylene diamine.
Schiff bases 3 have been derived from salicylaldehyde/5-
bromosalicylaldehyde and phenylene diamine. Schiff base
4 has been derived from 4-methyl-acetophenone and ben-
zoylhydrazide. Similar experiments have also been carried
out on 5-bromosalicylaldehyde 5, which shows best results
in terms of IC50 value, and have, therefore, been chosen for
in vivo experiments.
Present work is an early part of our project on a-glucosi-
dase inhibition and antihyperglycemic properties of Schiff
bases and their oxovanadium(IV) complexes.
Materials and methods
Preparation of Schiff bases
The Schiff bases were prepared by refluxing, for 1–2 h, a
mixture of the aldehyde/ketone and aniline/substituted ani-
lines/ethtylenediamine/phenylenediamine/benzoin hydra-
zide in appropriate ratio in ethanolic medium. In most of the
cases, the Schiff bases precipitated out on cooling. Wherever
necessary, the excess solvent was evaporated to make the
Schiff base precipitate out. The product was filtered out and
dried in air at room temperature.
One of these Schiff bases, 2a, has earlier been used in
the form of its oxovanadium(IV) complex for in vivo an-
tihyperglycemic study (Durai and Saminathan, 1997).
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Med Chem Res (2011) 20:1431–1437
1433
Scheme for 1a to 1h (Pandeya and Khare, 1992a)
OH
OH
+
H2N
X
N
C
H
O
C
H
Y
Y
X
Y = H or Br
(10 mmol)
X = H or Cl or OCH3 or NO2
(10 mmol)
Schiff bases
Scheme for 2a, 2b, 2c, 3a, and 3b (Pandeya and Khare,
1992b)
Z
Y
Y
Z
N
N
H2N
H2N
NH2
NH2
X
X
Z
X
+
O
Y
Y
HO
Y
OH
N
N
H
H
X = H or CH3
Y = H or Br
Z = H or OH
(10 mmol)
(5 mmol)
Schiff bases
Scheme for 4
N
NH
C
O
H3C
C
+
O
NH2 NH
C
O
H3C
C
CH3
CH3
(10 mmol)
(10 mmol)
Schiff bases
Elemental analyses
NMR spectra
CHN analyses for all the Schiff bases were carried out at
Central Drug Research Institute (CDRI), Lucknow. The
results are presented in Table 1.
1H NMR spectra for the Schiff bases were recorded in
DMSO on 300 MHz spectrometer at CDRI, Lucknow. The
results are presented in Table 2.
Infrared spectra
Rat intestinal a-glucosidase inhibition
IR spectra of the samples were recorded on Perkin Elmer
spectrophotometer (500–4000 cm-1) in KBr at CDRI,
Lucknow. The results are presented in Table 2.
Rat intestinal acetone powder (Sigma chemicals, USA) was
sonicated properly in normal saline (100:1 w/v) and after
centrifugation at 3000 rpm 9 30 min the supernatant was
123

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Med Chem Res (2011) 20:1431–1437
Table 1 Elemental analyses
Table 2 NMR and IR spectral data
1
Compound no.
Formula
Calcd (found) %
1a: H NMR (300 MHz, DMSO) d13.10 (S, 1H, ArOH), 8.94 (S,
1H, CH), 7.62 (d, J = 1.5 Hz, 1H, ArH), 7.48–7.38 (m, 6H,
ArH), 7.35–7.28 (m, 1H, ArH), 7.00–6.95 (m, 2H, ArH).; IR
(KBr) 510, 682, 763, 814, 856, 908, 978, 1032, 1107, 1178, 1270,
1339, 1507, 1570, 1602, 1664, 1723, 2270, 2370, 2711, 3070,
C
H
N
1a
1b
1c
1d
1e
1f
C13H11NO
79.18
5.58
7.10
3473, 3653, 3692, 3780, 3906, 3978 cm-1
.
(78.03)
67.38
(5.23)
4.31
(7.01)
6.04
1
C
C
C
C
C
C
C
C
C
C
C
C
C
13H10NOCl
1b: H NMR (300 MHz, DMSO) d12.82 (S, 1H, ArOH), 8.95 (S,
1H, CH), 7.65 (d, J = 7.5 Hz, 1H, ArH), 7.52–7.39 (m, 5H,
ArH), 7.00–6.95 (m, 2H, ArH).; IR (KBr) 512, 556, 694, 755,
838, 903, 965, 1007, 1086, 1179, 1272, 1359, 1397, 1483, 1608,
1663, 1727, 1901, 2273, 2370, 2730, 2897, 2983, 3058, 3152,
3343, 3469, 3628, 3628, 3656, 3691, 3763, 3830, 3857,
(67.08)
74.00
(4.78)
5.72
(6.04)
6.16
14H13NO2
(73.73)
64.46
(6.56)
4.13
(6.15)
11.57
(11.77)
5.07
13H10N2O3
13H10NOBr
13H9NOBrCl
14H12NO2Br
13H9N2O3Br
16H16N2O2
16H14N2O2Br2
18H20N2
3915 cm-1
.
(63.55)
56.52
(4.56)
3.62
1
1c: H NMR (300 MHz, DMSO) d13.29 (S, 1H, ArOH), 8.93 (S,
1H, CH), 7.61 (d, J = 7.8 Hz, 1H, ArH), 7.42 (d, J = 9, 2H,
ArH), 7.37 (d, J = 8.1, 1H, ArH), 7.02 (d, J = 8.7, 2H, ArH),
6.96 (d, J = 8.7, 2H, ArH), 3.79 (S, 3H, OCH3).; IR (KBr) 465,
544, 671, 764, 835, 909, 980, 1032, 1111, 1187, 1246, 1283,
1364, 1413, 1495, 1615, 1810, 1899, 2054, 2368, 2843, 2961,
(56.68)
50.24
(3.98)
2.89
(5.06)
4.50
(51.41)
54.90
(3.01)
3.92
(4.56)
4.57
1g
1h
2a
2b
2c
3a
3b
4
3014, 3440, 3777, 3912 cm-1
.
(55.33)
48.59
(4.35)
2.80
(4.38)
8.72
1
1d: H NMR (300 MHz, DMSO) d12.28 (S, 1H, ArOH), 9.00 (S,
1H, CH), 8.31(d, J = 9 Hz, 2H, ArH), 7.74 (d, J = 6.9, 1H,
ArH), 7.60 (d, J = 9, 2H, ArH), 7.50–7.45 (m, 1H, ArH).; IR
(KBr) 510, 682, 763, 814, 856, 908, 978, 1032, 1107, 1178, 1270,
1339, 1507, 1570, 1602, 1664, 1723, 2270, 2370, 2711, 3070,
(48.50)
71.64
(2.89)
5.97
(8.71)
10.44
(10.46)
6.57
(71.41)
45.07
(5.63)
3.28
3473, 3653, 3692, 3780, 3906, 3978 cm-1
.
1
1e: H NMR (300 MHz, DMSO) d13.04 (S,1H, ArOH), 8.93 (S,
1H, CH), 7.88 (d, J = 3 Hz, 2H, ArH), 7.55 (dd, J = 2.4 Hz, 1H,
ArH), 7.50–7.42 (m, 2H, ArH).; IR (KBr) 510, 556, 624, 806,
849, 908, 1173, 1272, 1350, 1439, 1477, 1608, 1661, 1724, 1812,
(45.03)
81.82
(3.44)
7.58
(6.54)
10.61
(10.24)
8.86
(79.60)
75.94
(7.98)
5.06
2272, 2371, 3402, 3629, 3629, 3654, 3690, 3777, 3909 cm-1
.
20H16N2O2
20H14N2O2Br2
16H16N2O
1
1f: H NMR (300 MHz, DMSO) d12.71 (S, 1H, ArOH), 8.92(S,
1H, CH), 7.87 (d, J = 2.4 Hz, 1H, ArH), 7.57 (dd, J = 2.4 Hz,
1H, ArH), 7.52 (d, J = 8.7 Hz, 2H, ArH), 7.43 (d, J = 8.7 Hz,
2H, ArH), 6.95 (d, J = 9 Hz, 1H, ArH).; IR (KBr) 531, 628, 711,
829, 910, 980, 1092, 1175, 1273, 1347, 1387, 1474, 1559, 1609,
(75.08)
50.63
(5.08)
2.95
(8.83)
5.90
(50.64)
76.19
(3.12)
6.35
(5.94)
11.11
(11.26)
–
1907, 2728, 3079, 3377, 3772 cm-1
.
(75.22)
41.79
(6.22)
2.49
1
1g: H NMR (300 MHz, DMSO) d13.28 (S, 1H, ArOH), 8.92 (S,
1H, CH), 7.83 (d, J = 2.1 Hz, 1H, ArH), 7.5 (dd, J = 2.1 Hz,
1H, ArH), 7.42 (d, J = 8.7 Hz, 2H, ArH), 7.03 (d, J = 8.7 Hz,
2H, ArH), 6.93 (d, J = 8.7 Hz, 1H, ArH).; IR (KBr) 469, 542,
628, 820, 909, 978, 1029, 1113, 1175, 1249, 1348, 1385, 1473,
1564, 1610, 1705, 1768, 1894, 2312, 2731, 2839, 2973, 3442,
5
C7H5O2Br
(41.78)
(2.45)
3692, 3776, 3821, 3878, 3974 cm-1
.
treated as crude intestinal a-glucosidase. Ten microliters of
test samples dissolved in DMSO (5 mg/ml solution) were
mixed and incubated with 50 ll of enzyme in a 96-well
microplate for 5 min. Reaction mixture was further incu-
bated for another 10 min with 50 ll substrate (5 mM, p-
nitrophenyl-a-D-glucopyranoside) prepared in 100 mM
phosphate buffer (PH *6.8) and release of nitrophenol was
read at, 405 nm spectrophotometrically (SPECTRAmax
PLUS384, Molecular devices, USA). Percent a-Glucosidase
inhibition was calculated as (1 - B/A) 9 100, where A
was the absorbance of reactants without test samples and B
was absorbance of reactants with test samples. All the
samples were run in triplicate, and acarbose was taken as
standard reference compound. Several dilutions of primary
solution (5 mg/ml DMSO) were made and assayed
accordingly to obtain concentration of the test sample
1
1h: H NMR (300 MHz, DMSO) d12.14 (S,1H, ArOH), 8.98 (S,
1H, CH), 8.30 (d, J = 8.7 Hz, 2H, ArH), 7.93 (d, J = 2.4 Hz,
1H, ArH), 7.65 (m, 1H, ArH), 7.55 (d, J = 8.7 Hz, 2H, ArH),
6.97 (d, J = 9 Hz, 1H, ArH).; IR (KBr) 513, 624, 691, 783, 866,
918, 987, 1106, 1174, 1271, 1339, 1470, 1513, 1589, 2276, 2372,
3069, 3432, 3621, 3690, 3762, 3872, 3950 cm-1
.
1
2a: H NMR (300 MHz, DMSO) d13.37 (S, 1H, ArOH), 8.58
(S,1H, CH), 7.41 (d, J = 7.5 Hz, 2H, ArH), 7.34–7.29 (m, 1H,
ArH), 6.90–6.84 (m, 2H, ArH); IR (KBr) 671, 766, 979, 1047,
1124, 1153, 1217, 1280, 1338, 1461, 1498, 1633, 2362, 3022,
3446, 3832 cm-1
.
2b: 1H NMR (300 MHz, DMSO) d 13.4(S, 1H, ArOH), 8.57(S, 2H,
CH), 7.66(d, J = 2.4 Hz, 2H, ArH), 7.4(dd, J = 2.4 Hz, 2H,
ArH), 6.84 (d, J = 8.7 Hz, 2H, ArH), 3.92(S, 4H, 2 9 CH2).; IR
(KBr) 479, 557, 627, 671, 767, 897, 978, 1032, 1079, 1216, 1276,
1362, 1390, 1476, 1567, 1634, 2365, 2402, 2906, 3022,
3450 cm-1
.
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Med Chem Res (2011) 20:1431–1437
1435
solvent and B is absorbance of decolorized DPPH in the
presence of test compound. All the analysis was done in
duplicate; trolox was taken as reference compound. Several
dilutions of primary solution (1 mg/ml in DMSO)were made
and assayed accordingly to obtain concentration of the
sample required to scavenge 50% (SC50) of DPPH free
radical applying suitable regression analysis.
Table 2 continued
2c: 1H NMR (300 MHz, DMSO) d7.80 (m, 4H, ArH), 7.38 (m, 6H,
ArH), 3.81 (S, 4H, 2 9 CH2), 2.24 (S, 6H, 2 9 CH3).; IR (KBr)
576, 670, 763, 926, 1027, 1086, 1217, 1278, 1369, 1440, 1636,
2363, 2939, 3021, 3450, 3866 cm-1
1
.
3a: H NMR (300 MHz, DMSO) d 12.93 (S, 1H, ArOH), 8.93 (S,
2H, CH), 7.67 (d, J = 6.6 Hz, 2H, ArH), 7.48–7.38 (m, 6H,
ArH), 7.00 (m, 4H, ArH).; IR (KBr) 671, 763, 910, 980, 1034,
1111, 1154, 1216, 1280, 1484, 1576, 1620, 2362, 3022, 3421,
3840, 3905 cm-1
.
In vivo experiment
1
3b: H NMR (300 MHz, DMSO) d12.92(S, 1H, ArOH), 8.91(S,
1H, CH), 7.69–6.93 (m, 10H, ArH); IR (KBr) 498, 541, 568, 627,
670, 769, 872, 914, 974, 1072, 1111, 1183, 1216, 1273, 1347,
1383, 1471, 1561, 1612, 1737, 1880, 2363, 2403, 2628, 2737,
Male Wistar rats (weight 195 10) were used for in vivo
experiments. Animals were allowed for alternating 12 h
light dark cycle at 22 1°C room temperature. Animals
were kept for overnight fasting and next morning basal
glucose value was measured by auto blood analyzer (Bayer
Express Plus). Compound 5 was tested for blood glucose
lowering measurements. Experiments were performed as
per the animal ethical committee rules in Pharmacology
Division, IICT Hyderabad.
2928, 3022, 3426, 3692, 3774, 3812, 3904 cm-1
.
1
4: H NMR (300 MHz, DMSO) d10.72 (S, 1H, ArOH), 7.87–
7.23(m, 10H, ArH), 2.34(S, 6H, 2 9 CH3).; IR (KBr) 562, 670,
763, 893, 929, 976, 1026, 1135, 1217, 1276, 1375, 1530, 1646,
2364, 3021, 3428 cm-1
.
1
5: H NMR (300 MHz, DMSO) d 10.95 (S, 1H, ArOH), 10.22 (S,
1H, CHO), 7.71 (d, J = 2.7, 1H, ArH), 7.63 (dd, J = 2.7 Hz, 1H,
ArH), 6.98(d, J = 8.7 Hz, 1H, ArH).; IR (KBr) 538, 624, 671,
767, 830, 889, 928, 1015, 1074, 1116, 1175, 1217, 1278, 1369,
1468, 1570, 1615, 1670, 1910, 2072, 2362, 2402, 2743, 2858,
3022, 3417, 3823, 3946 cm-1
.
Results and discussion
All the compounds show satisfactory elemental analyses
(Table 1) and exhibit well-resolved sharp infrared bands
confirming their purity. The two Schiff bases derived from
nitroaniline (1d and 1h) show IR bands due to NO2 group
of the nitroaniline. These band appear at 1507 cm-1 (1d)
and 1513 cm-1 (1h) and at 1339 cm-1 (both 1d and 1h),
which are evidently due to ms(NO2) and ma(NO2), respec-
required to inhibit 50% activity (IC50) of the enzyme
applying suitable regression analysis.
DPPH free radical scavenging activity
DPPH free radical scavenging activity was tested with 25 ll
of test sample (1 mg/ml DMSO), 125 ll of 0.1 M Tris–HCl
buffer (PH *7.4) and 125 ll of 0.5 mM DPPH (1,1-diphe-
nyl-2-picrylhydrazyl; Sigma chemicals, USA, dissolved in
absolute ethyl alcohol) were mixed and shaken well. After
incubating 20 min in dark, absorbance was recorded spec-
trophotometrically (SPECTRAmax PLUS384, Molecular
devices, USA) at 517 nm. The free radical scavenging
potential was determined as the percent decolourisation of
DPPH due to the test samples and calculated as (1 - B/
A) 9 100, where A is absorbance of DPPH control with
1
tively. IR and H NMR data for all the compounds are
presented in Table 2.
Figure 2 presents a-glucosidase inhibition and free
radical scavenging activity of the compounds at fixed
screening concentrations.
a-Glucosidase activity inhibition
All the Schiff bases of anilines (except 1f) show a-gluco-
sidase activity inhibition property; percentage inhibition
Fig. 2 DPPH free radical
100
75
50
25
0
DPPH-rs (250 uM)
AGH-i (200 uM)
scavenging and rat intestinal a-
glucosidase inhibitory (AGH-i)
activities of the compounds at
primary screening level.
Concentrations of the reagents
are shown in parenthesis except
that in the case of AGH-i the
concentration of 5 was 300 lM
1a 1b 1c 1d 1e 1f
1g 1h 2a 2b 2c 3a 3b
4
5
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Med Chem Res (2011) 20:1431–1437
(for 200 lM Schiff base) ranging from 6.63 (for 1b) to 95.6
(for 1d). 1f shows no inhibition of a-glucosidase activity at
this concentration. Among the Schiff bases formed with
salicylaldehyde and the anilines the trend is:
1b \ 1c \ 1a \ 1d, while for the Schiff bases formed with
bromosalicylaldehyde and the anilines the trend is:
1f \ 1e \ 1h \ 1g. If the Schiff bases formed with
methoxy anilines are kept apart Schiff bases of salicylal-
dehyde and bromosalicylaldehyde both show the following
trend of anilines: chloroanilines \ anilines \ nitroanilines.
The Schiff base of bromosalicylaldehyde with methoxy
aniline shows much higher inhibition (67.21%) compared
to the Schiff base of salicylaldehyde with methoxy aniline
(11.45%). In all other cases, the salicylaldehyde Schiff base
shows higher inhibition compared to corresponding
bromosalicylaldehyde Schiff base.
The Schiff bases of salicylaldehyde, bromosalicylalde-
hyde, and acetophenone with ethylenediamine (2a, 2b, and
2c) are all inactive toward DPPH free radical scavenging at
the experimental concentration. However, the correspond-
ing Schiff bases of phenylene diamine show strong free
radical scavenging activity (3a, 75.27%; 3b, 25.55%). In-
fact, sal–phn (3a) is the strongest free radical scavenger
(75.27%) among the compounds studied and shows SC50
value of 115.36 lM.
IC50 value (a-glucosidase inhibition)
Compounds showing more than 60% a-glucosidase inhi-
bition, viz., 1d, 1g, and 5 were chosen for IC50 value
determination. The results are as under:
The Schiff bases of salicylaldehyde/bromosalicylalde-
hyde and aceteophenone with ethylene diamine (2a, 2b,
and 2c) show moderate inhibition of the a-glucosidase;
order being 2c [ 2a [ 2b. The phenylene diamine Schiff
bases (3a and 3b) show stronger inhibition (3a, 57.94%;
3b, 58.77%) compared to corresponding ethylene diamine
Schiff bases (2a, 29.11%; 2b, 14.38%). In going from
salicylaldehyde to bromosalicylaldehyde, the inhibition is
decreased in the case of ethylene diamine Schiff bases. In
phenylene diamine Schiff bases, no such decrease is,
however, observed. Schiff base of 4-methyl-acetophenone
with benzoyl hydrazide, 4 also show moderate a-glucosi-
dase inhibition (31.55%).
Compound
IC50
1d
1g
5
22.72
74.11
8.80
In vivo study
Compound 5, which shows the lowest IC50 value for
a-glucosidase inhibition, was selected for validation of its
actual antihyperglycemic potential in animal model Wistar
200
Compound 5 (300 lM) shows 85.81% inhibition of the
a-glucosidase and exhibits lowest IC50 value (8.80 lM).
The IC50 value of acarbose (Hari Babu et al., 2008) for a-
glucosidase inhibition is 6.38 lM. It implies that in in vitro
experiments 5 is, at least, as strong an inhibitor of a-glu-
cosidase as acarbose. Lee (2005) has evaluated the inhib-
itory activity of cuminaldehyde, a biologically active
constituent of Cuminum cyminum seed oil, to find that
cuminaldehyde is nearly 1.8 times less in inhibitory
activity than acarbose. In conclusion, 5 is stronger inhibitor
of a-glucosidase in comparison to cuminaldehyde.
In-vivo experiments have been carried out on Com-
pound 5.
150
a
b
100
a
b
a
b
50
0
Control
5
Acarbose
0 hr
30 min
60 min
90 min
120 min
Time in minutes
DPPH free radical scavenging activity
Fig. 3 Plasma glucose level under the influence of compound 5 after
starch feeding. Compound 5 (50 mg/kg body weight) and standard a-
glucosidase inhibitory antihyperglycemic drug acarbose (10 mg/kg
body weight) were administered 15 min before starch (2 g/kg body
weight) feeding to respective group of animals. Plasma glucose levels
were measured at different time points post starch feeding. One-way
ANOVA followed by Bonferroni’s multiple comparison tests was
applied to find differences between the groups. Values represent
mean SD, n = 5, a and b represent statistical comparisons between
Among the Schiff bases of anilines, the trend of free radical
scavenging activities is as follows: 1a (9.29%) & 1e
(9.27%) \ 1f (13.52%) \ 1g (48.71%). All other Schiff
bases (1b, 1d, and 1h) of this group show no free radical
scavenging. There appears to be no correlation between the
trends of a-glucosidase activity inhibition and free radical
scavenging activities for the compounds under study.
a
b
control and test groups. p \ 0.001, p \ 0.01
123

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0
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Acknowledgments The authors thank Dr. J. S. Yadav, the Director,
Indian Institute of Chemical Technology, Hyderabad, for providing
necessary facilities for biological activity screening and evaluation of
the compounds presented in this report, Director Central Drug
Research Institute, Lucknow, for elemental analysis, IR and NMR
data and the University Grants Commission, New Delhi, for financial
assistance in the form of a research project (F. No. 31-109/2005(SR)).
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