Molecular modeling and protection against pentylenetetrazoleinduced seizure of new 1,4-dihydropyridines containing 5(4)-imidazolyl substituent

Article abstract of DOI:10.1007/s00044-011-9904-x

A group of symmetrical and asymmetrical esters of nifedipine analogs, in which the ortho-nitro phenyl group at position 4 was replaced by 2-ethyl(or H)-4(5)-chloro-5(4)-imidazolyl substituent, was designed and evaluated as anticonvulsant against pentylene

Full text of DOI:10.1007/s00044-011-9904-x

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:3767–3776
DOI 10.1007/s00044-011-9904-x
ORIGINAL RESEARCH
Molecular modeling and protection against pentylenetetrazole-
induced seizure of new 1,4-dihydropyridines containing
5(4)-imidazolyl substituent
•
Asghar Davood Hamed Shafaroodi
•
•
Maryam Iman Abbas Shafiee
Received: 16 January 2011 / Accepted: 9 November 2011 / Published online: 6 December 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A group of symmetrical and asymmetrical
esters of nifedipine analogs, in which the ortho-nitro phe-
nyl group at position 4 was replaced by 2-ethyl(or H)-4(5)-
chloro-5(4)-imidazolyl substituent, was designed and
evaluated as anticonvulsant against pentylenetetrazole
(PTZ)-induced seizure. Our molecular modeling studies
reveals that 4-chloro tautomeric form is the main one and
has good compatibility with nifedipine and that 4-H is syn-
perpendicular. Docking studies reveal that the oxygen
atoms of carbonyl group and the N30 of imidazole ring of
dihydropyridine form a hydrogen-bonding interaction with
the receptor. The time-course of anticonvulsant’ effect on
PTZ-induced seizure threshold was assessed, and it showed
that increasing the lipophilicity decreases the time need for
maximum effect. All those mice, treated with intraperito-
neal injection of 5, 10, and 20 mg/kg of these derivatives,
exhibited increased seizure threshold as compared with
control. Based on in vivo results of symmetrical and
unsymmetrical ester series, increasing the length of the
chain in C3- and C5-ester substituents increases the pro-
tection activity. The most active compounds were 2c and
3b, which were more active than the reference drug
nifedipine, and compound 2e had comparable activity with
nifedipine. QSAR studies indicate that size, hydrophobic-
ity, and topology of DHPs have main effects in the
respective biological activities of these compounds.
Keywords Calcium antagonists ꢀ Anticonvulsant ꢀ
Dihydropyridines ꢀ QSAR ꢀ Docking
Introduction
Epilepsy is a common neurological condition, affecting
0.5–1% of the population worldwide (more than 60 million
people) according to epidemiological studies. Every year
approximately 250,000 new cases are being added to this
figure. It is roughly estimated that there is a significant
group of patients (up to 30%) who are resistant to the
available medical therapies. Despite the development of
several new antiepileptic drugs (AEDs), the treatment of
epilepsy remains still inadequate, and the patients suffer
from a lot of unfavorable side effect. Although several new
anticonvulsants are already in clinical use, some types of
seizures are still not adequately treated with current therapy
and have limitations, such as intolerable side effects
(Ilangovan et al., 2010; Malawska, 2005). In response to
these limitations, the development of new drugs to opti-
mally manage seizures has been strongly advocated. Thus,
the search for new anticonvulsant drugs continues to be an
active area of investigation in medicinal chemistry. In the
recent literature, various dihydropyridines (calcium antag-
onist) with established pharmacophore requirements have
been reported as a novel class of anticonvulsant agents to
A. Davood (&)
Department of Medicinal Chemistry, Branch of Pharmaceutical
Sciences, Islamic Azad University, No 99, Yakhchal Ave.,
Shariatie Street, 19419 Tehran, Iran
e-mail: adavood@iaups.ac.ir; adavood2001@yahoo.com
H. Shafaroodi
Department of Pharmacology, Pharmaceutical Sciences Branch,
Islamic Azad University, Tehran, Iran
M. Iman
Department of Pharmaceutical Science, Faculty of Pharmacy
and Pharmaceutical Sciences, Mashad University of Medical
Sciences, Mashad, Iran
A. Shafiee
Department of Medicinal Chemistry, Faculty of Pharmacy,
Tehran University of Medical Sciences, Tehran, Iran
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Med Chem Res (2012) 21:3767–3776
be effective against the whole range of convulsive proce-
dures including electro- and pentylenetetrazole convulsions
and sound- and high pressure-induced seizures (Navidpour
et al., 2004; Samzadeh-Kermani et al., 2008; Errington
et al., 2005; Shafiee et al., 2004; Subudhi et al., 2009).
Synaptosomal release of excitatory neurotransmitters is
dependent on calcium influx, and many established AEDs,
such as phenytoin and carbamazepine, inhibit this process
by inhibiting calmodulin activation of calmodulin kinase II
(Sohn and Ferrendelli, 1976; Crowder and Bradford, 1987).
Initiation of seizure activity is associated with synchroni-
zation of intrinsic burst-firing which is synapse mediated
(Meyer, 1989). The abnormal action potential (paroxysmal
depolarizing shift, PDS), which occurs when epileptogenic
activity begins, is also dependent on calcium cellular entry
(Goldensohn and Purpura, 1963; Wong and Prince, 1979).
Both burst-firing (Bingman and Speckman, 1989) and the
PDS (Witte et al., 1987) can be inhibited by calcium
antagonists or exacerbated by a calcium agonist (Walden
et al., 1986).
both nitrogen atoms probably can interact with receptor by
hydrogen binding (donor, acceptor), and so both tautomeric
forms should be pharmacologically active. In addition, it
has been shown that 4-aryl in DHPs have a lipophilic
pocket in DHP receptor (Goldmann and Stoltefuss, 1991);
in order to adjust lipophilic property of imidazole ring,
ethyl and chlorine groups were inserted in 2 and 4(5)
positions of imidazole, respectively.
The reported results (Roy and Roy, 2010; Dai et al.,
´
2010; Saız-Urra et al., 2011; Davood et al., 2010; Davood
and Iman, 2011; Nematollahi and Davood, 2010, Masanda
et al., 2011; Pana et al., 2006; Wang et al., 2009), dem-
onstrated the power of combining docking/QSAR approach
to explore the probable binding conformations of com-
pounds at the active sites of the protein target, and further
provided useful information in understanding the structural
and chemical features of ligands and lead compounds in
designing and finding new potential inhibitors. Progressive
docking, a hybrid QSAR/docking approach, was used
to accelerating in silico high throughput screening
(Cherkasov et al., 2006).
Worrisome neurological side effects with flunarizine
(Chouza et al., 1986) and the pharmacologic interactions of
other AEDs with verapamil (Macphee et al., 1986) and
diltiazem (Bordie and Macphee, 1986) promote the dihy-
dropyridines as candidates for investigation as AEDs in
clinical practice. Their lack of sedative side effects adds to
their benefits; with studies suggesting that the substitution
of C4 o-nitrophenyl with heterocycles retains pharmaco-
logic activity. We have found that bioisosteric replacement
of the 4-aryl moiety with an imidazolyl group yields
analogous 4-imidazolyl-1,4-dihydropyridines which exhi-
bit potent calcium antagonist activity (Davood et al., 2001,
2006; Pourmorad et al., 1997; Shafiee et al., 1987, 1996).
A major goal of the present research is to prepare
lipophilic 1,4-dihydropyridines with improved ability to
cross the blood–brain barrier with extra hydrogen binding
with receptor. Considering the tautomeric forms of
2-ethyl(or H)-4(5)-chloro-5(4)-imidazolyl moiety (Fig. 1),
In this study, we used the combined molecular docking
and QSAR approach to model the anticonvulsant activities
of DHP derivatives. In this study, a series of dihydropyri-
dine derivatives were evaluated as anticonvulsant agents
and was subjected to a molecular docking study followed
by quantitative structure–activity relationship (QSAR)
analyses in search of ideal physicochemical characteristics
of potential DHPs.
Materials and methods
Chemistry
Symmetrical and asymmetrical diesters analogues of
nifedipine were synthesized according to Scheme 1.
The symmetrical analogues were prepared by classical
Fig. 1 Two favoured
R
R
H
tautomeric forms for DHPs, A
when the imidazole substituent
at C-4 lies in a 4-chloro
tautomeric form, and B when
the imidazole substituent lies in
a 5-chloro tautomeric form
N
N
3
2
2
1
5
4
1
HN
Cl
O
5
3
N
Cl
O
4
O
O
"
'
R
R
R
R
"
'
O
O
O
O
H3C
N
H
CH3
H3C
N
H
CH3
B
A
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Med Chem Res (2012) 21:3767–3776
3769
Cl
Scheme 1 Synthesis of new
1,4-dihydropyridines containing
2-ethyl(or H)-4(5)-chloro-5(4)-
imidazolyl substituent
N
CHO
R
N
H
1a-b
a, b
b, c
R
NH
NH
N
Cl
O
N
Cl
O
O
O
R'
R''
R'
R'
O
O
O
O
N
N
H
H
3a-b
2a-e
a = amonium acetate
b = CH3COCH2COOR'
c =
CH3CH(NH2)CH2COOR''
R = H, Et
R' = Benzyl, phenethyl, phenpropyl
R'' = Me, Et
Hantzsch condensation (Davood et al., 2001, 2006) in
which 2-ethyl(or H)-4(5)-chloro-imidazole-5(4)-carboxal-
dehyde 1a–1b was reacted with 3-oxobutanoic acid ester
and ammonium acetate, and all compounds were readily
characterized by conventional spectral data.
transferred into Autodock (version 4.2.) program package,
and docking calculations were performed using Autodock
tools. In the L-type channel which was downloaded from
PDB bank server (PDB entry 1T0J), some amino acids’
side chain atoms were missing. A reconstruction of the
whole side chain was attempted using Swiss-PDB viewer
4.0.1.
Molecular modeling and docking studies
The Autodock 4.2 program starts with a ligand molecule
in an arbitrary conformation, orientation, and position and
finds favorable dockings in a protein-binding site using
both simulating annealing and genetic algorithms. The
program AutoDockTools (ADT), which has been released
as an extension suite to the Python Molecular Viewer, was
used to prepare the protein and the ligand. For the mac-
romolecule, crystal structure of L-type calcium channel,
polar hydrogens were added, and then Kollman United
Atom charges and atomic solvation parameters were
assigned. The grid maps of docking studies were computed
using the AutoGrid4.2 included in the Autodock4.2 dis-
tribution. Grid center that was centered on the active site
was obtained by using potential binding sites method
(Huey and Morris, 2008) and based on the previous studies
(Cosconati et al., 2007; Davood et al., 2009). and
60 9 60 9 60 points with grid spacing of 0.375 was
The chemical structures of desired compounds (Table 1)
were built using HYPERCHEM software (version 7,
Hypercube Inc.). Conformational analysis of the designed
compounds was performed through semi-empirical
molecular orbital calculation (PM3) methods using the
HYPERCHEM software. The molecular structures were
optimized using the Polak-Ribiere (conjugate gradient)
algorithm until the root mean square gradient was
0.01 kcal mol-1. Among all energy minima conformers,
the global minimum of two favored tautomeric forms of
DHPs was compared with the global minimum of nifedi-
pine used as a reference drug.
Thus, the superimposition of these conformers were
performed to confirm whether tautomeric form could
mimic the major conformation of reference drug to be used
in docking calculations, and the resulting geometry was
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Med Chem Res (2012) 21:3767–3776
Table 1 Calculated properties of DHPs using the Hyperchem software
R
N
3'
2'
4'
HN1'
Cl
O
5'
R
R
"
'
O
9
7
8O
O1o
CH3
4
3
2
5
6
1
H3C
N
H
DHP
R
R0
R00
HOMOa Volumeb Surface areac logpd b1e
b2f
b3g
b4h
92.83
b5i
-91.15
2a
2b
2c
2d
2e
3a
3b
a
H
H
H
Benzyl
Benzyl
-8.73
-8.97
1239.54
1394.19
1486.57
1349.52
1504.64
1250.51
1283.98
550.88
673.03
718.84
633.56
740.23
641.61
648.48
2.27
2.77
3.56
3.18
3.68
1.65
2.00
76.12 72.17 -0.28
Phenethyl
Phenethyl
106.53 34.49 -1.07 102.57 -103.45
108.94 71.13 -3.41 106.22 -105.84
Phenpropyl Phenpropyl -8.97
Et Benzyl
Benzyl
Phenethyl
Methyl
Ethyl
-8.56
-8.88
-8.76
-8.84
3.59 58.18
81.62 65.09 -1.95 104.56 -105.13
43.60 59.26 0.58 95.92 -96.54
1.80
88.01
-85.87
Et Phenethyl
Et Phenethyl
Et Phenethyl
75.57 73.10 -1.79 102.83 -103.53
Energies of the HOMO calculated by Hyperchem 7 (eV)
b
c
d
e
f
3
˚
Volume of the molecule, after minimization using the PM3 force field, calculated using the Hyperchem 7 program, in A
2
˚
Surface area of the molecule, after minimization using the PM3 force field, calculated using the Hyperchem 7 program, in A
Octanol–water partition coefficient according to Ghose, Pritvchett, and Crippen by Hyperchem software
C2–C3–C9–O10 dihedral angle
C6–C5–C7–O8 dihedral angle
g
h
i
N1–C2–C3–C4 dihedral angle
C2–C3–C4–C50 dihedral angle
C6–C5–C4–C50 dihedral angle
calculated. Four different docking algorithms are currently
available in AutoDock: SA, the original Monte Carlo-
simulated annealing; GA, a traditional Darwinian genetic
algorithm; LS, local search; and GA–LS, which is a hybrid
genetic algorithm with local search. The GALS is also
known as a Larmarckian genetic algorithm. Each search
method has its own set of parameters, and they must be set
before running the docking experiment itself. These
parameters include what kind of random number generator
to use, step sizes, etc. The most important parameters affect
how long each docking will run. In simulated annealing,
the number of temperature cycles, the number of accepted
moves and the number of rejected moves determine how
long a docking will take. In the GA and GA–LS, the
number of energy evaluations and the number of genera-
tions affect how long a docking will run. ADT enables us to
change all of these parameters (Huey and Morris, 2008).
The GA–LS method was adopted to perform the molecular
docking. The parameters for GA were defined as follows: a
maximum number of 250,000 energy evaluations; a
maximum number of generations of 27,000; mutation and
crossover rates of 0.02 and 0.8, respectively. Pseudo-Solis
& Wets parameters were used for the local search, and 300
iterations of Solis & Wets local search were imposed. The
number of docking runs was set to 50. Both Autogrid and
Autodock computations were performed on Cygwin. After
docking, all the structures generated were assigned to
˚
clusters based on a tolerance of 1 A all-atom RMSD
from the lowest-energy structure. Hydrogen bonding and
hydrophobic interactions between docked potent agents
and macromolecule were analyzed using ADT (Version
1.5.4). The best docking result can be considered to be the
one that bears conformation with the lowest (docked)
energy.
Computation of structural descriptors and descriptive
QSAR
The two-dimensional structures of molecules were drawn
using the Hyperchem 7.0 software. The final geometries
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Med Chem Res (2012) 21:3767–3776
3771
were obtained with the semi-empirical PM3 method in
the Hyperchem program. The molecular structures were
optimized using the Polak-Ribiere (conjugate gradient)
algorithm until the root mean square gradient was
0.01 kcal mol-1. The resulting geometry was transferred
into Dragon program package. SPSS software (version 17)
was used for the MLR regression method.
and all DHPs were administered intraperitoneally (i.p.).
Male NMRI mice (24–30 g, Pasteur Institute of Iran) were
used throughout this study.
The animals were housed in temperature-controlled
room (24 1°C) on a 12-h light/dark cycle with free
access to food and water. All procedures were carried out
in accordance with institutional guidelines for animal care
and use. Each mouse was used only once, and each treat-
ment group consisted of at least eight animals.
The biological data (Table 3) used in this study are
protection against pentylenetetrazole-induced seizure (in
terms of PPIS, percent of pentylenetetrazole to induced
seizure against 20 mg/kg of DHPs) of a set of DHPs
derivatives (2a–2e and 3a–3b). The large number of
molecular descriptors was calculated using Hyperchem,
E-dragon package, and Autodock tools. Some chemical
parameters including molecular volume (V), molecular
surface area (SA), hydrophobicity (LogP), hydration energy
(HE), refractivity (Rf), partial charge (PC), molecular
polarizability (MP), and different quantum chemical
descriptors including, dipole moment (DM), local charges,
and HOMO and LOMO energies were calculated using
Hyperchem Software (Table 1). Dragon software calcu-
lated different functional groups: topological, geometrical,
and constitutional descriptors for each molecule. Results
based on the docked conformations are the intermolecular
energy, Vdw-hb-desolv energy, electrostatic energy, total
internal energy, torsional energy, unbound energy, pre-
dicted binding energy, ligand efficiency, and inhibi-
tion_constant (Ki), which all were used as descriptors in
QSAR studies.
Threshold of PTZ-induced seizures was determined by
inserting a 30-gauge butterfly needle into the tail vein of
mice and the infusion of PTZ (0.5%) at a constant rate of
0.5 ml/min to unrestrained animals. Infusion was halted
when forelimb clonus followed by full clonus of the body
was observed. Minimal dose of PTZ (mg/kg of mice
weight) needed to induce clonic seizure was measured as
an index of seizure threshold.
Animals in experiment 1 received the highest doses of
DHPs (25 mg/kg), 2.5, 5, 10, 20, 30, 40, and 50 min before
PTZ in distinct groups of mice to determine the time of
maximal effect.
In experiment 2, different doses of the said derivatives
(5, 10, and 20 mg/kg) or vehicle was administered in
appropriate time that was obtained before the determina-
tion of seizure threshold (Loscher and Rundfeldt, 1991).
Results and discussion
Using Dragon software, the calculated descriptors were
first analyzed for the existence of constant or near-constant
variables, and those detected were removed. In addition, to
decrease the redundancy existing in the descriptor data
matrix, the correlations of descriptors with each other and
with the activity (PPIS) of the molecules were examined,
and collinear descriptors (i.e., r [ 0.9) were detected.
Among the collinear descriptors, the one that had the
highest correction with activity was retained, and the others
were removed from the data matrix. The calculated
descriptors were collected in a data matrix number of rows
and columns of which were the number of molecules and
descriptors, respectively. To select the set of descriptors
that are the most relevant to the IC50 of 1,4-DHP, the MLR
models were built, and the QSAR equations with stepwise
selection and elimination of variables were established by
MLR method.
Molecular modeling and docking
The effective properties of DHPs were calculated using
Hyperchem, and are presented in Table 1. Conforma-
tional studies of the designed compound were performed
through semi-empirical molecular orbital calculations
(PM3) method and we found two favored tautomeric forms
for this compound: labeled A when the imidazole substituent
at C-4 lies in a 4-chloro tautomeric form, and B when the
imidazole substituent lies in a 5-chloro tautomeric form
(Fig. 1). In A form, 4-H is syn-perpendicular (sp), but in B
form, 4-H is anti-perpendicular (ap). The heats of formation
for two possible tautomeric forms A and B were calcu-
lated,which showed that A tautomeric form was found to be
about 1.11 kcal more stable than B tautomeric form. Our
molecular modeling studies indicate that 4-chloro tauto-
meric form is the main form which is stabler than 5-chloro
tautomeric form. Superimposition with reference drug
nifedipine (Fig. 2) reveals that 4-chloro tautomeric form has
good compatibility (fitting), and 4-H is syn-perpendicular.
The relative position of the imidazolyl ring with respect to
the DHP ring is measured by the (b4, b5) (Table 1) dihedral
angle, and the deviation from planarity of DHP ring is
measured by the (b3) dihedral angle, indicating that, in both
Pharmacology, determination of anticonvulsant activity
Pentylenetetrazole (PTZ) was purchased from Sigma (UK).
It was dissolved in physiological saline solution, and all the
selected derivatives were dissolved in DMSO. In all
experiments, PTZ was administered intravenously (i.v.),
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Med Chem Res (2012) 21:3767–3776
tautomeric forms, the DHP ring showed a twisted boat
conformation and the imidazole ring occupies an axial
position perpendicularly bisecting the boat-like DHP ring.
The b1 and b2 dihedral angles reveal that at least one of the
carbonyl ester orientations with respect to the olefinic double
bond is of cis orientation.
was -5.87 kcal/mol. Our docking studies reveal that,
based on the predicted binding energy, nifedipin with
-5.95 kcal/mol binding energy should be more active than
all compounds 2a–2e and compounds 3a–3b (Table 2)
except compounds 2c and 3b, which was confirmed
potentially by experimental data. Based on the predicted
binding energies, compounds 2c and 3b with -5.79 and
-5.10 kcal/mol binding energy, respectively, should
not be more active than nifedipin (binding energy =
-5.95 kcal/mol), but it could not be confirmed by experi-
mental data. We suggest this may be due to the higher
partition coefficients of compounds 2c and 3b with
logp 3.56 and 2, respectively, compared to nifedipin with
logp 0.38. These observations and experimental results
provide a good explanation for the respective activities of
these compounds.
Flexible docking of all datasets used for the computa-
tional study was carried out on the active site of L-type
calcium channel. The predicted binding energies and other
results of these inhibitors into the active site are listed in
Table 2.
The orientation of compound 2b in the active site of
L-type calcium channel was examined by a docking
experiment (Fig. 3). These docking studies show that the
oxygen (O8) of carbonyl group and the N30 of imidazole
ring form a hydrogen bonding interaction with the NH2 of
GLN 367 (distance = 1.99) and NH of GLU 240 (dis-
tance = 2.10), respectively, and the binding energy of 2b
Fig. 3 Docked structure of 2b in Model of LCC. DHPs are displayed
as sticks, and hydrogen bonds are represented by dashed green lines
(Docking study by using ADT program and LCC model obtained
from PDB server)
Fig. 2 Superimposition of 2b (cyan ball stick) with reference drug,
nifedipine (violet ball stick), reveals that 4-chloro tautomeric form has
good compatibility (fitting) and 4-H is syn-perpendicular
Table 2 Docking results of DHPs derivatives using AutoDock 4.2 software
Compounds Intermolecular Vdw-hb-desolv Electrostatic Total internal Torsional Unbound Ki
energy
Ligand
Binding
energy
energy
energy
energy
energy
(lm)a
efficiencyb energyc
2a
2b
2c
2d
2e
3a
3b
a
-7.95
-9.15
-9.67
-7.96
-8.47
-8.16
-8.09
-7.81
-9.13
-9.59
-7.95
-8.28
-8.15
-8.02
-0.14
-0.02
-0.08
-0.02
-0.20
-0.01
-0.06
-1.95
-0.91
-0.56
-2.45
-1.94
-1.66
-1.66
2.68
3.28
3.88
2.98
3.58
2.68
2.98
-1.95
-0.91
-0.56
-2.45
-1.94
-1.66
-1.66
137.31 -0.16
50.04 -0.16
57.07 -0.15
223.54 -0.14
259.03 -0.13
97.46 -0.18
181.16 -0.16
-5.27
-5.87
-5.79
-4.98
-4.89
-5.47
-5.10
Inhibition_constant is calculated in AutoDock as Ki = exp(DG 9 1000)/(Rcal 9 TK) where DG is docking energy, Rcal is 1.98719, and TK is
298.15
b
The ligand efficiency is defined as the calculated pKi divided by the number of heavy atoms in the. The smaller one may be more promising
one for the lead
c
The predicted binding energy (kcal/mol) is the sum of the intermolecular energy and the torsional free-energy penalty
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Med Chem Res (2012) 21:3767–3776
Pharmacology
3773
properties of R00 substituent increases the activity
(3b [ 3a). The most active compound was ethyl/phenethyl
(3b) derivative, being more active than nifedipine; indeed
compound 3b is the most active compound in symmetrical
and unsymmetrical derivatives. In general, increasing the
volume and surface area in each group had positive effect
on protection potency. As lipophilic ethyl substituents
attached to the C-2 position of imidazole ring are supposed
to improve penetration into brain, the activities of com-
pounds 2d and 2e against PTZ-induced seizure were
assessed compared to compounds 2a and 2b.
The protections against pentylenetetrazole-induced seizure
of these inhibitors in mice are shown in Figs. 4, 5, 6, 7, 8,
9, 10, 11. Based on in vivo results of symmetrical ester
series, we find that in 2a–2c, 2d, and 2e (Figs. 4, 5, 6, 7, 8;
Table 3), by increasing the length of the chain in C3- and
C5-ester substituents increases the protection activity in the
order (2e [ 2d, 2c [ 2b [ 2a). The most active compound
was the diphenylpropyl ester derivative (2c), which was
more active than the reference drug nifedipine, while
compound 2e had comparable activity with nifedipine.
In unsymmetrical diester, 3a and 3b (Figs. 9, 10;
Table 1), when R0 is phenethyl, increasing the lipophilic
Based on the partition coefficient (logp) of the DHPs 2a–
3b (Table 3), we suggest that all of them are more liphophile
than nifedipine, and are supposed toimprove penetrationinto
Fig. 4 Effect of different dosages of 2a (5, 10, and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 2a was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
*P \ 0.05 compared to vehicle group
Fig. 6 Effect of different dosages of 2c (5, 10, and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 2c was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
***P \ 0.001 compared to vehicle group
Fig. 5 Effect of different dosages of 2b (5, 10, and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 2b was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
**P \ 0.01 compared to vehicle group
Fig. 7 Effect of different dosages of 2d (5, 10 and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 2d was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
**P \ 0.01 compared to vehicle group
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Med Chem Res (2012) 21:3767–3776
Fig. 8 Effect of different dosages of 2e (5, 10, and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 2e was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
**P \ 0.01 compared to vehicle group
Fig. 10 Effect of different dosages of 3b (5, 10, and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 3b was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
***P \ 0.001 compared to vehicle group
Fig. 11 Comparison of the highest dosage (20 mg/kg) of DHPs on
PTZ-induced seizure threshold *P \ 0.05, **P \ 0.01, ***P \ 0.001
compared to vehicle group
Fig. 9 Effect of different dosages of 3a (5, 10, and 20 mg/kg) on
PTZ-induced seizure threshold in mice: 3a was administrated 30 min
before PTZ. Data are expressed as mean SEM of eight mice.
**P \ 0.01, ***P \ 0.001 compared to vehicle group
The compounds in the study are not large enough to help
us find which descriptors affect the biological response;
hence, we have perfrormed only descriptive QSAR, and not
predictive. The stepwise multiple linear regression method
used in the study reveals that two descriptors, ATS3p and
‘‘surface area’’ (SA), affect anticonvulsant activity. The
ATS3p descriptor corresponds to Broto-Moreau autocor-
relation of a topological structure, that autocorrelated
function to the topology of molecular structures and the SA
descriptor corresponds to van der Waals, and the solvent-
accessible surface areas are carried out by an approximate
method.
brain and result in less cardiovascular side effect, faster onset
of action, and longer half-life than nifedipine.
Descriptive QSAR studies
To test the validity of the QSAR equations, there are two
methods: predictive, based on the test set molecules; and
descriptive, based on whole dataset as training set of
molecules, especially in cases where the compounds in our
study to QSAR studies are not more. In the predictive
QSAR we can build the reliable QSAR model to prediction
but, in the descriptive QSAR, the compounds in the study
are not enough to build the reliable model to prediction,
and we can only distinguish which descriptors affect the
biological response.
Based on these results, it seems that size, hydropho-
bicity, and topology of substituent and DHPs can affect the
biological activities of these compounds.
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Med Chem Res (2012) 21:3767–3776
3775
recommended that we keep the DHP structure, but in order
to achieve better potency, we can change imidazole ring
with other nitrogen-containing heterocyclic ring with an
additional more liphophilic group. The results from this
study are presently being used for the design of newer
compounds with better anticonvulsant activity.
Table 3 Structure and protection against pentylenetetrazole-induced
seizure of DHPs (2a–2e and 3a–3b)
R
NH
N
Cl
O
O
R'
R''
Acknowledgment This research was supported by grants from the
research council of Tehran Azad University.
O
O
N
H
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