L. Dinparast et al. / Journal of Molecular Structure 1114 (2016) 84e94
93
sample for final concentration of 50
m
g/mL in the reaction mixture.
stepwise regression method and the selected descriptors were used
to develop a linear model using multiple linear regression analysis
[62e64]. Regression coefficient, standard error of estimate and F
value along with the Leave one out cross-validation (LOOCV)
method was used to check the prediction capability of the devel-
oped model.
Acarbose was used as standard positive control. The mixture was
incubated at 37 ꢀC for 15 min and then enzymatic reaction was
initiated by adding 20
anoside (pNPG) in buffer. The plates were incubated at 37 ꢀC for
another 15 min and the reaction was stopped by addition of 80
mL of 5 mM 4-nitrophenyl-a-D-glucopyr-
mL
sodium carbonate solution (0.2 M). Finally, the absorbance of 4-
nitrophenol released from pNPG was measured at 405 nm. The
system without a-glucosidase was used as blank for correcting the
4. Conclusions
background absorbance. The increasing of absorbance was
compared with the control (buffer instead of sample solution) to
calculate the inhibitory activity. The enzyme inhibition rate of the
samples was calculated using the following formula:
A series of benzimidazole derivatives were synthesized selec-
tively using ZnO/MgO containing ZnO nanoparticles. The use of
non-toxic, recyclable and cheap catalyst and ionic liquid makes this
synthesis method green and economical. Other advantages of this
method were one-pot, solvent-free and mild reaction conditions
and high yields of products. The structure of the synthesized
compounds was investigated using spectroscopic data. Synthe-
% Inhibition ¼½ðAbsorbance control ꢁ Absorbance sampleÞ=
Absorbance controlꢂ ꢃ 100
sized benzimidazoles were evaluated for their
a-glucosidase
Afterward, derivatives with inhibition percent more than 50 in
above concentration were tested in lower concentrations (5, 10, 25
and 50 mg/mL) for calculation of IC50 values. All of the experiments
were carried out in triplicates. IC50 values were calculated and
expressed as mean SEM (Table 3).
inhibitory potential. Compounds 3c, 3e, 3l and 4n showed mod-
erate to high activity. In silico studies were also performed to
recognize the binding modes and molecular interactions of these
compounds. Good accordance was found between the experi-
mental data and docking results. A QSAR model was established to
find the correlation between observed bioactivity and structural
properties of synthesized derivatives. This model showed linear
relationship between the experimental inhibition percent of
compounds with molecular weight and density of the molecules.
Our findings indicated that this class of compounds could be
3.4. Computational methods
3.4.1. Software
The molecular geometry optimization of 3D structures of com-
pounds was carried out at the HartreeeFock (HF) level with 3-21G
basis set using Gaussian 03 program package [58]. The molecular
docking of synthesized benzimidazoles was performed using
AutoDock 4.2 software [59]. MLR model was developed using the
SPSS software. The dipole moment and stability energy of opti-
mized molecules was calculated by Gaussian 03 program. Physi-
cochemical properties i.e. log P, log D, molar refractivity, surface
tension, density and polarizability were calculated by ACD/Labs
program while the surface area was calculated using Hyper Chem 7
software.
considered as potent a-glucosidase inhibitors. So, further studies
on more derivatives and pharmacological evaluations are
warranted.
Disclosure of interest
The authors declare no conflicts of interest concerning this
article.
Acknowledgment
3.4.2. Molecular docking
The crystal structures of C-terminal domain of human intestinal
The partial financial assistance from the Research Vice Chan-
cellor of Azarbaijan Shahid Madani University is gratefully
acknowledged. In addition the authors would like to thank the Drug
Design Laboratory of Pharmacy Faculty of Tabriz University of
medical sciences for providing the software and hardware needed
for molecular docking and QSAR analysis.
a
-glucosidase (PDB code:3TOP, complex with acarbose) was
downloaded from Brookhaven protein database. Water molecules
were removed from enzyme structure whereas, the polar hydrogen
atoms, Kollman and Gasteiger charges were added to amino acid
residues of protein structure using Autodock Tools (ADT, version
1.5.6) [60]. The required pdbqt format of receptor and ligands were
obtained using the same software. Optimized structures of ligands
with the minimized energy were subjected for molecular docking
studies using Lamarckian genetic algorithm method (LGA) with 200
run for each docking. The population size and maximum number of
evaluation (medium) were set at 150 and 2500000, respectively.
The maximum number of generation was 27000. The grid box for
Abbreviations
ZnO
zinc oxide
MgO
QSAR
magnesium oxide
quantitative structure activity relationship
the C-terminal a-glucosidase was place at the center of acarbose
LOOCV leave one out cross-validation
MLR multiple linear regression
[bmim]Cl1-buthyl-3-methyl imidazolium chloride
with x, y, and z coordinates of ꢁ28.191, 32.654 and 24.654 Å [61].
The number of points in x, y and z dimensions was 32 ꢃ 32 ꢃ 32 in
C-terminal domain. The grid spacing was set in 0.375 Å.
NMR
FT-IR
LGA
nuclear magnetic resonance
fourier transform infrared
Lamarckian genic algorithm
3.4.3. Quantitative structure activity relationship (QSAR)
3.4.3.1. Data preparation. Synthesized bezimidazole compounds
(14 data point) with experimental enzyme inhibition percent was
used as a data set in the present QSAR study. The observed bioac-
tivity along with the calculated descriptors is given in the supple-
mentary material, Table S1.
pNPG
4-nitrophenyl-a-D-glucopyranoside
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
3.4.3.2. Model development. Best descriptors were selected using