Design, molecular docking and synthesis of some novel 4-acetyl-1-substituted-3,4-dihydroquinoxalin-2(1H)-one derivatives for anticonvulsant evaluation as AMPA-receptor antagonists

Article abstract of DOI:10.1007/s00044-016-1723-7

A new series of 4-acetyl-1-substituted-3,4-dihydroquinoxalin-2(1H)-ones (2–13) were designed and synthesized in order to evaluate their AMPA-receptor antagonism as a potential mode of anticonvulsant activity. The structure of the synthesized compounds was

Full text of DOI:10.1007/s00044-016-1723-7

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-016-1723-7
ORIGINAL RESEARCH
Design, molecular docking and synthesis of some novel 4-acetyl-1-
substituted-3,4-dihydroquinoxalin-2(1H)-one derivatives for
anticonvulsant evaluation as AMPA-receptor antagonists
1
Abdel-Ghany A. El-Helby1 Rezk R. A. Ayyad1,2 Khaled El-Adl
Helmy Sakr1
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●
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●
Ashraf A. Abd-Elrahman1 Ibrahim H. Eissa1 Alaa Elwan1
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Received: 20 April 2016 / Accepted: 7 September 2016
© Springer Science+Business Media New York 2016
Abstract A new series of 4-acetyl-1-substituted-3,4-dihy-
droquinoxalin-2(1H)-ones (2–13) were designed and syn-
thesized in order to evaluate their AMPA-receptor
antagonism as a potential mode of anticonvulsant activity.
The structure of the synthesized compounds was confirmed
by elemental analysis and spectral data (IR, 1HNMR,
13CNMR and Mass). The molecular design was performed
for all the synthesized compounds to predict their binding
affinity to AMPA-receptor in order to rationalize their
anticonvulsant activity in a qualitative way. The data
obtained from the molecular modeling was strongly corre-
lated with that obtained from the biological screening which
revealed that; compounds 12b, 13, 12a and 7a showed the
highest binding affinities toward AMPA-receptor and also
showed the highest anticonvulsant activities against penty-
lenetetrazole -induced seizures in experimental mice. The
relative potencies of these compounds were 1.66, 1.66, 1.61
and 0.82 respectively, in comparing to diazepam.
Introduction
Extensive studies have been conducted on quinoxaline
derivatives to possess central nervous system (CNS)
depressant action (Rogawski 2006; Wagle et al. 2009;
Ibrahim et al. 2013; Elkaeed et al. 2014) with potent AMPA
receptor antagonist activity, which in some cases inhibit
AMPA-induced lethal convulsions in mice (Jin et al. 2003;
Jin and Gouaux 2003; Traynelis et al. 2010).
The quinoxalinedione derivatives are one of the most
important chemical classes of competitive AMPA receptor
antagonists. A great number of them have made it possible
to test the importance of AMPA receptors in different dis-
ease models. However, early pharmacological studies have
been hampered by the lack of potent and selective com-
pounds. CNQX (I) (Fig. 1) was, among the quinox-
alinedione series, the first potent and selective AMPA
receptor antagonist to be discovered (Rogawski 2013;
Catarzi et al. 2007). CNQX (I) and DNQX (II) showed to
be useful in developing and understanding of the pharma-
cology of AMPA receptor. However, these compounds also
have activity at the Gly/NMDA binding site, thus lacking
sufficient selectivity to be really useful tools for the char-
acterization of the AMPA receptors. Subsequently, NBQX
(III) was demonstrated to have improved AMPA receptor
selectivity with respect to CNQX and thus, it was used as
the antagonist of choice in many “in vitro” and “in vivo”
models (Catarzi et al. 2007). Moreover, the clinical devel-
opment of NBQX was prevented by its low-water solubility
at physiological pH (Faust et al. 2009). On the contrary,
YM90K (IV) showed to be systemically active, but it has a
short “in vivo” duration of action (Catarzi et al., 2007).
In fact, most simple quinoxalinedione derivatives
showed limited water solubility which restricted efforts to
formulate acceptable parenteral solutions. With this
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Keywords Quinoxaline Molecular docking AMPA
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antagonists Anticonvulsant agents
Electronic supplementary material The online version of this article
(doi:10.1007/s00044-016-1723-7) contains supplementary material,
which is available to authorized users.
* Khaled El-Adl
eladlkhaled74@yahoo.com
1
Pharmaceutical Chemistry Department, Faculty of Pharmacy,
Al-Azhar University, Cairo, Egypt
2
Pharmaceutical Chemistry Department, Faculty of Pharmacy,
Delta University, Gamasa, Dakahlia, Egypt

Med Chem Res
Fig. 1 Reported quinoxalines as
potent AMPA receptor
antagonists
problem to solve, new compounds such as PNQX (V) and
YM872 (VI) were prepared as possible AMPA receptor
antagonist candidates. Unfortunately, PNQX showed low
water solubility at physiological pH. YM872 is a very
water-soluble AMPA antagonist due to the presence of a
hydrophilic acetic acid side chain (Catarzi et al. 2007).
Taking YM90K as lead compound, compound VII
(1-ethyl-8-(1H-imidazol-1-yl)-7-nitro-[1,2,4]triazolo[4,3-a]
quinoxalin-4(5H)-one) was designed through replacement
of the oxygen atom, of the 2,3-dione moiety, at C-3 with a
bioisosteric nitrogen atom as a constituent of the fused
heterocyclic ring at C3-N4. This modifications exhibited
high-AMPA affinity and selectivity versus the Gly/NMDA
site (Catarzi et al. 2007).
On the other hand, it has been reported that a lot of com-
pounds containing, ester (Ibrahim et al. 2015), amide (El-Adl
2011), hydrazide (Ibrahim et al. 2013), pyrazole, oxadiazole,
semicarbazide, thiosemicarbazide, phthalimide (El-Helby et al.
2009; Ibrahim et al. 2015), isatin, and/or Schiff’s base (Alswah
et al. 2013; Bayoumi et al. 2012; Elhelby et al. 2011) moieties
possessed good anticonvulsant activity.
Based on that, it was decided to synthesize the title
compounds as hybrid molecules formed of quinoxaline
nucleus joined with the previously mentioned moieties in
hope of developing potent and safe new effective antic-
onvulsant agents. The hybrid of these pharmacophoric
features are designed to have different linkers at N-1 in
order to act as a supplementary interaction point which
reinforce the binding with the AMPA receptor which may
improve selectivity and binding affinity of our target com-
pounds toward AMPA receptor and overcome water solu-
bility problems.
structural modification made it possible to overcome the
solubility problems.
In addition, compound VII is the most potent 1,2,4-
triazolo[4,3-a]quinoxalin-4-one derivative with high-
AMPA affinity and selectivity (Catarzi et al. 2007).
Taking compounds YM872 (VI) and (VII) as lead
compounds, our target quinoxaline-2-one derivatives were
designed as hybrids to maintain the basic features of N-1
substituted lead compound YM872 and, at the same time,
the basic features of N-4 substituted lead compound VII.
Figure 2 represents the structure similarities and phar-
macophoric features of the lead compounds YM872 and
(VII) and our designed compounds. It also shows that
structure of our designed final compounds fulfilled all the
pharmacophoric structural requirements. These require-
ments include: the presence of quinoxalin-2-one moiety as
hydrophobic domain, the carboxylic acid (C=OO) moiety at
N-1 of YM872 was replaced by bioisosteric (C=ON or
C=NO) moieties as linkers in most derivatives to maintain
the same hydrogen bonding sites. As a result, our designed
derivatives maintained the improved AMPA receptor
binding affinities of the lead compound VI.
On the other hand, the nitrogen atom at position-2 of
compound VII was replaced by a bioisosteric oxygen atom
and the N atom at position-3 of the fused heterocyclic ring
was removed to obtain N-4 acetyl derivatives. As a result
the oxygen atom of the acetyl group in our derivatives
formed hydrogen bond with the same amino acid residue
Tyrosine220, while Proline89 formed hydrogen bond with
N-4 of compound VI.
Moreover, the presence of (un)substituted distal moieties
(e.g. ester, alkyl, cyclohexyl, phenyl, oxadiazole etc) as
another hydrophobic domain attached to the N-1 atom
through different linkers was responsible for controlling the
pharmacokinetic properties of the anticonvulsant activity.
The present study was carried out to prepare the target
compounds as hybrid molecules. These molecules formed
of quinoxaline-2-one ring system joined with the acetyl
group at 4-position and different substituents at position-1
with different electronic environments to study the SAR of
Results and discussion
Rationale and structure-based design
YM872 (VI) is a very water-soluble AMPA antagonist due
to the presence of a hydrophilic acetic acid side chain. This

Med Chem Res
Fig. 2 Structural similarities and
pharmacophoric features of
reported potent AMPA
antagonists and our designed
compounds specially 12a–b, 13
and 7a as anticonvulsants
these compounds and the effect of each substituent on their
anticonvulsant activity.
5-sulfanyloxadiazole (11) derivatives respectively. Treat-
ment of 5-sulfanyloxadiazole derivative (11) with the
appropriate alkyl 2-chloroacetate and/or methyl chlor-
opropionate yielded the corresponding ester derivatives
(12a–b) and (13) respectively (Scheme 3).
Chemistry
The synthetic strategy for preparation of the target com-
pounds (2–13) is depicted in Schemes 1–3. The title com-
pounds were synthesized starting with ortho-
phenylenediamine by its reaction with 2-chloroacetic acid
to afford 3,4-dihydroquinoxalin-2(1H)-one (1), following
the reported procedure, which was then treated with acetyl
chloride and/or chloroacetyl chloride (Bonuga et al. 2013)
Docking studies
In the present work, all modeling experiments were per-
formed using Molsoft software. Each experiment used
AMPA (Loscher and Rogawski 2002) downloaded from the
Brookhaven Protein Databank (http://www.rcsb.org/pdb/
explore/explore.do?structureId=1FTL).
to afford the corresponding N-4 acetyl derivatives (2a−b
)
respectively. The obtained acetyl derivative 2a was refluxed
with ethyl chloroacetate to afford the corresponding ethyl
ester (3). Heating the ethyl ester (3) with hydrazine hydrate
furnished the corresponding acid hydrazide (4). On the
other hand, the reaction of chloroacetyl derivative 2b with
the appropriate aromatic amine, namely aniline, 4-
bromoaniline and/or 4-methylaniline resulted in the corre-
sponding derivatives (5a–c) respectively (Scheme 1).
Stirring of the acid hydrazide (4) with benzoyl chloride
yielded the corresponding benzoyl derivative (6). Heating
of acid hydrazide (4) with the appropriate isocyanates and/
or isothiocyanates under reflux afforded the corresponding
semicarbazide 7a–b and thiosemicarbazide 8a–b derivatives
respectively. Condensation of the acid hydrazide (4) with
the appropriate aldehyde, namly benzaldehyde, 2-
chlorobenzaldehyde and/or 2-methoxybenzaldehyde resul-
ted in the corresponding Schiff’s bases 9a–c respectively
(Scheme 2).
The obtained results indicated that all studied ligands
have similar position and orientation inside the putative
binding site of AMPA receptor (PDB code 1FTL) which
reveals a large space bounded by a membrane-binding
domain which serves as entry channel for substrate to the
active site (Fig. 3). In addition, the affinity of any small
molecule can be considered as a unique tool in the field of
drug design.
There is a relationship between the affinity of organic
molecules and the free energy of binding (Baum et al. 2009;
Englert et al. 2010; Ibrahim et al. 2015). This relationship
can contribute in prediction and interpretation of the activity
of the organic compounds toward the specific target protein.
The obtained results of the free energy of binding (ΔG)
explained that most of these compounds had good binding
affinity toward the receptor and the computed values
reflected the overall trend (Table 1).
The proposed binding mode of YM872 revealed affinity
value of −70.63 kcal/mol and 7 H-bonds. The carboxylate
group at position-1 formed 1 H-bond with Threonine143
(–O atom) with a distance of 2.92 Å. The carbonyl group at
The acid hydrazide (4) underwent cyclization by reaction
with acetic anhydride and/or carbon disulfide to afford
the corresponding 5-methyloxadiazole (10) and/or

Med Chem Res
Scheme 1 Synthetic route for
preparation of the target
compounds 2–6
position-2 formed one H-bond with Arginine96 (–NH
group) with a distance of 1.95 Å and another H-bond with
Threonine91 (–OH group) with a distance of 2.70 Å. The
other carbonyl group at position-3 was stabilized by for-
mation of 1 H-bond with Arginine96 (–NH group) with a
distance of 1.68 Å and 1 H-bond with Threonine91 (–NH
group) with a distance of 1.55 Å. NH group at position-4
formed 1 H-bond with proline89 (–O atom) with a distance
of 1.71 Å. The imidazole moiety at position-7 formed one
H-bond with Threonine174 (–OH group) with a distance of
1.77 Å and occupied the hydrophobic pocket formed by
Threonine174, Leucine192, Glutamate193 and Methio-
nine196. The quinoxaline nucleus occupied the hydro-
phobic pocket formed by Lysine60, Tyrosine61,
Arginine96, Threonine91, proline89, Lysine218, Tyr-
osine220, Glutamate193, Serine142 and Threonine143
(Fig. 4).
and the other N atom at position-3 of the fused triazole
group formed 2 H-bonds with Arginine96 (–NH groups)
with distances of 1.83 and 2.07 Å. The carbonyl group
formed 1 H-bond with Arginine96 (–NH group) with a
distance of 2.07 Å. The nitro group formed 1 H-bond with
Threonine174 (–OH group) with a distance of 1.54 Å. The
imidazole moiety at position-8 formed one H-bond with
Tyrosine16 (–OH group) with a distance of 1.83 Å and
occupied the hydrophobic pocket formed by Tyrosine61,
proline89, Tyrosine220, Tyrosine16, Glutamate193 and
Methionine196. The ethyl group at position-1 occupied the
hydrophobic pocket formed by Threonine91, Lysine218,
Tyrosine220 and proline89. The quinoxaline nucleus
occupied the hydrophobic pocket formed by Lysine60,
Tyrosine61,
Arginine96,
Threonine91,
proline89,
Lysine218, Tyrosine220, Glutamate193, Serine142 and
Threonine143 (Fig. 5).
The proposed binding mode of compound VII is vir-
tually the same as that of YM872 which revealed affinity
value of −67.74 kcal/mol and 6 H-bonds. The N atom at
position-2 of the fused triazole group formed one H-bond
with Threonine91 (–NH group) with a distance of 1.33 Å
The proposed binding mode of compound 12b is vir-
tually the same as that of YM872 and compounds VII
which revealed affinity value of −89.86 kcal/mol and 7 H-
bonds. The two nitrogen atoms of the distal oxadiazole
linker moiety at position-1 formed 2 H-bonds with

Med Chem Res
Scheme 2 Synthetic route for
preparation of the target
compounds 6–9a−c
ꢀ
Serine142 (–NH groups) with distances of 1.31 and 2.41 Å.
The carbonyl group of the ester moiety formed 1 H-bond
with Threonine143 (–OH group) with a distance of 2.10 Å
and the oxygen atom formed another H-bond with Threo-
nine174 (–OH group) with a distance of 2.95 Å. The car-
bonyl group at position-2 formed 2 H-bonds with
Arginine96 (–NH groups) with distances of 1.58 and
2.16 Å. The carbonyl group of acetyl moiety at position-4
formed 1 H-bond with Tyrosine220 (–OH group) with a
distance of 1.82 Å. The oxadiazole moiety occupied the
hydrophobic pocket formed by Threonine143, Serine142,
Lysine218 and Lysine60. The ethyl group of the distal ester
moiety occupied the hydrophobic pocket formed by
Threonine174, Leucine192, Glutamate193 and Methio-
nine196. The methyl group of acetyl moiety at position-4
occupied the hydrophobic pocket formed by Tyrosine61,
Threonine91, Tyrosine220, and proline89. The quinoxaline
nucleus occupied the hydrophobic pocket formed by
Lysine60, Tyrosine61, Arginine96, Threonine91, proline89,
Lysine218, Tyrosine220, Glutamate193, Serine142 and
Threonine143 (Fig. 6). These interactions of compound 12b
may explain the highest anticonvulsant activity.
The proposed binding mode of compound 13 is virtually
the same as that of 12b which revealed affinity value of
−86.09 kcal/mol and 7 H-bonds. The two nitrogen atoms of
the distal oxadiazole linker moiety at position-1 formed 2
H-bonds with Serine142 (–NH groups) with distances of
1.47 and 2.67 Å. The carbonyl group of the ester moiety
formed 1 H-bond with Threonine143 (–OH group) with a
distance of 1.84 Å and the oxygen atom formed another H-
bond with Threonine174 (–OH group) with a distance of
2.98 Å. The carbonyl group at position-2 formed 2 H-bonds
with Arginine96 (–NH groups) with distances of 1.56 and
2.08 Å. The carbonyl group of acetyl moiety at position-4
formed 1 H-bond with Tyrosine220 (–OH group) with a
distance of 1.75 Å. The oxadiazole moiety occupied the

Med Chem Res
Scheme 3 Synthetic route for
preparation of the target
compounds 10–14
Fig. 3 Superimposition of some
docked compounds inside the
binding pocket of 1FTL
hydrophobic pocket formed by Threonine143, Serine142,
Lysine218 and Lysine60. The methyl group of the distal
ester moiety occupied the hydrophobic pocket formed by
Threonine174, Leucine192 and Glutamate193. The methyl
group of acetyl moiety at position-4 occupied the hydro-
phobic pocket formed by Tyrosine61, Threonine91, Tyr-
osine220, and proline89. The quinoxaline nucleus occupied
the hydrophobic pocket formed by Lysine60, Tyrosine61,
Arginine96, Threonine91, proline89, Lysine218, Tyr-
osine220, Glutamate193, Serine142 and Threonine143
(Fig. 7). These interactions of compound 13 may explain
the high anticonvulsant activity.
The proposed binding mode of compound 12a is vir-
tually the same as that of 12b which revealed affinity value
of –82.12 kcal/mol and 5 H-bonds. The two nitrogen atoms
of the distal oxadiazole linker moiety at position-1 formed 2
H-bonds with Serine142 (–NH groups) with distances of
1.51 and 2.50 Å. The carbonyl group at position-2 formed 2
H-bonds with Arginine96 (–NH groups) with distances of
1.68 and 2.16 Å. The carbonyl group of acetyl moiety at

Med Chem Res
Table 1 The calculated ΔG (free energy of binding) and binding
affinities for the ligands (ΔG in Kcal/mole)
position-4 formed 1 H-bond with Tyrosine220 (–OH group)
with a distance of 1.67 Å. The oxadiazole moiety occupied
the hydrophobic pocket formed by Threonine143, Ser-
ine142, Lysine218 and Lysine60. The methyl group of the
distal ester moiety occupied the hydrophobic pocket formed
by Threonine174, Leucine192 and Glutamate193. The
methyl group of acetyl moiety at position-4 occupied the
hydrophobic pocket formed by Tyrosine61, Threonine91,
Tyrosine220, and proline89. The quinoxaline nucleus
occupied the hydrophobic pocket formed by Lysine60,
Compound
ΔG (kcal mol−1
)
Compound
ΔG (kcal mol−1
)
2a
2b
3
−48.39
−45.59
−64.03
−55.10
−65.06
−59.54
−67.61
−68.19
−81.02
−76.88
−75.31
8b
−75.38
−75.29
−72.97
−76.91
−65.29
−64.87
−82.42
−89.86
−86.09
−70.63
−67.45
9a
9b
4
9c
5a
5b
5c
6
10
11
12a
Tyrosine61,
Arginine96,
Threonine91,
proline89,
12b
Lysine218, Tyrosine220, Glutamate193, Serine142 and
Threonine143 (Fig. 8). These interactions of compound 12a
may explain the high anticonvulsant activity.
7a
7b
8a
13
YM872 (VI)
Comp. (VII)
Fig. 4 Predicted binding mode
for YM872 with 1FTL
Fig. 5 Predicted binding mode
for VII with 1FTL

Med Chem Res
Fig. 6 Predicted binding mode
for 12b with 1FTL
Fig. 7 Predicted binding mode
for 13 with 1FTL
Biological screening
respectively. Compound 8a exhibited relative potency of
50 % of diazepam. Other compounds exhibited relative
potencies higher than 50 % of diazepam (Fig. 9). Compounds
12a, 12b and 13 caused 100 % protection in a dose of 500
mcg/kg body weight. While compounds 5a, 7b and 8b caused
100 % protection in a dose of 1000 mcg/kg body weight.
Compounds 5b, 5c, 7a, 8a, 9a, 9b and 9c caused 83.33 %
protection at the same dose Table 2). Compounds 12a, 12b
and 13 caused 50 % protection in a dose of 125 mcg/kg body
weight while the remaining compounds showed 50 % pro-
tection at higher doses. The percent of protection per each
dose as well as the medium effective dose (ED50), the dose
which makes 50 % protection of animals, was calculated
using INSTAT 2 program (ICS, Philadelphia, PA, USA).
Structure activity relationship (SAR) studies indicated
that different substitution on the quinoxaline ring exerted
varied anticonvulsant activity. Substitution at 1-position
showed higher activities than those at 4-position. The
electronic nature of the substituent group attached to
In the present study, thirteen compounds of the newly syn-
thesized quinoxaline derivatives were selected to be screened
in vivo for their anticonvulsant activity against
pentylenetetrazole-induced convulsions in mice following a
reported procedure (Vogel 2008). Thirteen groups of six
mice each were given a range of i.p. doses of the selected
drug until at least four points were established in the range of
10–90 % seizure protection. From the plots of these data,
(ED50) was determined. The results were compared with
diazepam as a standard anticonvulsant drug. Most of the
tested compounds showed good anticonvulsant activities.
The tested compounds exhibited relative anticonvulsant
potencies ranged from 0.37 to 1.66 of diazepam. Compounds
12b, 13, 12a and 7a showed the highest anticonvulsant
activities in experimental mice with relative potencies of
1.66, 1.66, 1.61 and 0.82 respectively. Compounds 9a and 9b
exhibited the lowest relative potencies of 0.37 and 0.41

Med Chem Res
quinoxaline ring led to a significant variation in the antic-
onvulsant activity. From the structure of the substituted
compounds at 4-position, the presence of lipophilic electron
releasing group (CH3 at 5c) attached to phenyl moiety
slightly increased the activity when compared to the unsub-
stituted phenyl at 5a. While the presence of highly lipophilic
electron deficient group (Br at 5b) attached to phenyl moiety
decreased the activity. From the structure of the substituted
compounds at 1-position and the data shown in Table 2 we
can divide these tested compounds into four groups. The first
group is substituted semicarbazide derivatives 7a and 7b. In
this group, the presence of lipophilic electron releasing group
(cyclohehyl ring at 7a) attached to semicarbazide moiety
enhanced the activity when compared to the electron with-
drawing phenyl group at 7b. The second group is substituted
thiosemicarbazide derivatives 8a and 8b. The propyl group at
8b produced slightly increased activity in spite of high dif-
ference in lipophilicity. The third group is Schiff’s bases 9a,
9b and 9c. Among these compounds, 9c with electron
releasing group (2-OCH3) exhibited higher activity than 9b
with electron deficient group (2-Cl), which exhibited lower
activity. The fourth group is 1,3,4 Oxadiazole-5-sulfanyl
ester derivatives 12a, 12b and 13. The ethyl acetate derivative
12b and methyl propionate derivative 13 showed the same
highest activity. It was noticed that, the two derivatives also
have nearly the same lipophilicity. The methyl acetate deri-
vative 12a produced slightly decreased activity in spite of
high difference in lipophilicity.
compounds YM872 (VI) and VII. This indicated that, the
water solubility of our designed compounds, 12b, 13 and
12a were higher than that of the reference ligands YM872
(VI) and VII. The improved aqueous solubility may explain
the higher affinity and selectivity towards AMPA receptor.
In spite of compound 5b have lower anticonvulsant
potency than compounds 5a and 5c, it had higher C log P
value and had no correlation with the lipophilicity factor
while compounds 7a had higher C log P values than 7b
(1.06 and 0.85 respectively) and had good correlation with
the lipophilicity factor. Interestingly, the values of C log P
for compounds 8a and 8b were 0.07 and 0.57 respectively
and had no significant effect on biological activity. More-
over compounds 9a, 9b, and 9c showed C log P values of
1.71, 2.34 and 1.72 and relative potencies of 0.37, 0.41 and
0.80 respectively and also had no correlation of the lipo-
philicity factor with their potency levels.
Conclusion
The molecular design was performed to assess the binding
mode of the proposed compounds with AMPA receptor.
The data obtained from the docking studies showed that; all
the synthesized derivatives have considerable high affinity
towards the AMPA receptor in comparing to YM872 (VI)
and (VII) as reference ligands. The data obtained from the
biological screening fitted with that obtained from the
molecular modeling. All the tested compounds showed
variable anticonvulsant activities. Their potencies range
from 0.37 to 1.66 of that of diazepam. Compounds 12b, 13,
12a and 7a showed the highest anticonvulsant activities in
experimental mice with anticonvulsant potencies of 1.66,
1.66, 1.61 and 0.82 respectively in comparing to diazepam
as a reference drug. C log P values for compounds 12b, 13
and 12a were found to be less than that for compounds
YM872 (VI) and VII. This indicated that, the water solu-
bility of our designed compounds, 12b, 13 and 12a were
higher than that of the reference ligands which may explain
the higher affinity and selectivity towards AMPA receptor.
The obtained results showed that, the most active com-
pounds could be useful as a template for future design, opti-
mization, adaptation and investigation to produce more potent
and selective AMPA receptor antagonists with good physi-
cochemical properties and higher anticonvulsant analogs.
C log P correlation
As a trial for interpretation of the correlation between
chemical structure of compounds 5a, 5b, 5c, 7a, 7b, 8a, 8b,
9a, 9b, 9c, 12a, 12b and 13 and their biological activity, an
attempted correlation of anticonvulsant activity with C log P
data was calculated for the measurement of the lipophilicity
factor which could be attributed in their anticonvulsant
activity. Determination of lipid-water partitioning in vitro is
difficult, time-consuming, expensive, not always available
and not suitable to screen a large collection of new che-
micals. Therefore, an alternative method was used based on
computerized models. So, the C log P values were calcu-
lated for some derivatives to reflect the overall lipophilicity
of these compounds and compared. The C log P data for all
selected anticonvulsant compounds were explained in
Table 2 ranging from 0.07 to 3.01. C log P for diazepam,
YM872 (VI) and VII were calculated and were found to be
2.74, 0.89 and 0.65 respectively. It is worthwhile to note
that the C log P values for compounds 12b, 13 and 12a
which had higher potency were found to be 0.50, 0.49 and
0.12 respectively. It is noted that, C log P values for com-
pounds 12b, 13 and 12a were found to be less than that for
Experimental
Chemistry
All melting points were carried out by open capillary
method on a Gallen kamp Melting point apparatus at faculty

Med Chem Res
Fig. 8 Predicted binding mode
for 12a with 1FTL
of pharmacy Al-Azhar University and were uncorrected.
The infrared spectra were recorded on pye Unicam SP 1000
IR spectrophotometer at Pharmaceutical analytical Unit,
Faculty of Pharmacy, Al-Azhar University using potassium
bromide disk technique. Proton magnetic resonance
1HNMR spectra were recorded on a Bruker 400 MHZ-
NMR spectrometer at Microanalytical Center, Zagazig
University—Zagazig. 13CNMR spectra were recorded on an
Agilent 400 MHZ-NMR spectrometer at and Chemical
Laboratory—Ministry of Defense—Cairo. TMS was used
as internal standard and chemical shifts were measured in δ
scale (ppm). The mass spectra were carried out on Direct
Probe Controller Inlet part to Single Quadropole mass
analyzer in Thermo Scientific GCMS model ISQ LT using
Thermo X-Calibur software at the Regional Center for
Mycology and Biotechnology, Al-Azhar University. Ele-
mental analyses (C, H, N) were performed on a CHN
analyzer at Regional Center for Mycology and Bio-
technology, Al-Azhar University. All compounds were
within 0.4 of the theoretical values. The reactions were
monitored by thin-layer chromatography (TLC) using TLC
sheets precoated with UV fluorescent silica gel Merck 60
F254 plates and were visualized using UV lamp and dif-
ferent solvents as mobile phases.
for 1 h. The contents of the reaction flask were then
poured slowly into water with continuous stirring and the
resulting precipitate was filtered, washed with water,
dried and crystallized from ethanol to obtain the target
compound (2a).
Yield, 80 %; m.p.: 165–168 °C. Analysis for
C10H10N2O2 (m.w. 190); calcd.: C, 63.15; H, 5.30; N,
14.73. Found: C, 63.31; H, 5.36; N, 14.89. IR (KBr, cm−1):
3192 (NH), 3072 (C–H aromatic), 2992 (C–H aliphatic),
1672 (2C=O amidic overlapped). 1HNMR (DMSO, d6-400
MHz, ppm): 2.17 (s, 3H, CH3 acetyl), 4.32 (s, 2H, CH2
quinoxaline), 7.03 (m, 2H, H-6 and H-8 quinox.), 7.19 (m,
1 H, H-7 quinox.), 7.48 (d, 1H, H-5 quinox. J = 7.6 Hz),
10.68 (s, 1H, NH) (D2O exchangeable). 13CNMR (DMSO-
d6, 400 MHz): δ = 169.13 (C, CH3CO), 166.64 (C, C-2),
133.44 (C, C-8′), 129.45 (C, C-4′), 127.09 (CH, C-5),
125.03 (2CH, C-6, C-7), 123.15 (CH, C-8), 45.92 (CH2, C-
3), 22.12 (CH3, CH3CO). MS (m/z): 190 (M+, 35 %), 148
(82 %), 119 (100 %, base beak).
Ethyl 2-(4-acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetate (3)
A mixture of 4-acetyl-3,4-dihydroquinoxalin-2(1H)-one
(2a) (6.70 g, 0.03 mol) and ethyl chloroacetate (3.68 g, 0.03
mol) in dry acetone (30 ml) in the presence of anhydrous
K2CO3 (8.28 g, 0.06 mol) was refluxed for 13 h while stir-
ring. The reaction mixture was filtered, the solvent was
evaporated and the resulting product was collected by fil-
tration and re-crystallized from ethanol to give the target
compound (3).
3,4-Dihydroquinoxalin-2(1H)-one (1) and 4-(2-chlor-
oacetyl)-3,4-dihydroquinoxalin-2(1H)-one
(2b)
were
obtained according to the reported procedures (Bonuga
et al. 2013).
4-Acetyl-3,4-dihydroquinoxalin-2(1H)-one (2a)
Acetyl chloride (7.85 g, 0.1 mol) was added dropwise to the
stirred solution of 3,4-dihydro-quinoxalin-2(1H)-one 2
(14.8 g, 0.1 mol) in dry DMF (100 ml) in the presence of
potassium carbonate (13.8 g, 0.1 mol) using ice-bath.
After addition, the solution was stirred at room temperature
Yield, 80 %; m.p.: 73-–75 °C. Analysis for C14H16N2O4
(m.w. 276); calcd.: C, 60.86; H, 5.84; N, 10.14. Found: C,
61.02; H, 5.89; N, 10.31. IR (KBr, cm−1): 3072 (C–H
aromatic), 2990 (C–H aliphatic), 1741 (C=O ester), 1676
(2C=O amidic overlapped). 1HNMR (DMSO-d6, ppm):

Med Chem Res
Fig. 9 Relative potencies of the
tested compounds and diazepam
1.19 (t, 3H, CH2CH3, J = 7.2 Hz), 2.16 (s, 3H, CH3 acetyl),
4.15 (q, 2H, CH2CH3, J = 7.2 Hz), 4.46 (s, 2H, CH2 qui-
nox.), 4.69 (s, 2H, NCH2), 7.16 (m, 2H, H-6 and H-7
quinox.), 7.29 (d, 1H, H-8 quinox. J = 7.6 Hz), 7.56 (d, 1H,
H-5 quinox. J = 7.6 Hz). 13CNMR (DMSO-d6, 400 MHz):
δ = 169.12 (2C, CH3CO, COO), 166.65 (C, C-2), 133.43
(C, C-8′), 129.45 (C, C-4′), 125.05 (CH, C-6), 123.16 (CH,
C-7), 116.61 (2CH, C-5,C-8), 59.69 (CH2, OCH2), 45.95
(CH2, C-3), 42.93 (CH2, NCH2), 22.14 (CH3, CH3CO),
11.27 (CH3, CH2CH3).
(C, C-8′), 149.80 (C, C-4′), 124.89 (CH, C-6), 123.29
(CH, C-7), 118.34 (CH, C-5), 116.47 (CH, C-8), 44.17
(2CH2, C-3, NCH2), 22.31 (CH3, CH3CO). MS (m/z): 263
(M++1, 1.03 %), 262 (M+, 4.72 %), 231 (43 %), 190 (1.8
%), 147 (6 %), 133 (100 %, base beak).
4-(2-(4-Substitutedphenylamino)acetyl)-3,4-
dihydroquinoxalin-2(1H)-one (5a–c
)
General method To a stirred solution of compound 4-(2-
chloroacetyl)-3,4-dihydroquinoxalin-2(1H)-one (2b) (0.45 g,
0.002 mol) and NaHCO3 (0.34 g, 0.004 mol) in 2-propanol
(15 ml), the appropriate aromatic amine namely, aniline, 4-
bromoaniline and/or 4-methylaniline (0.002 mol) was added
followed by potassium iodide (20 mol%). The reaction
mixture was refluxed for12 h, cooled to room temperature
and filtered to remove the inorganic salts. The solvent was
evaporated and the resulting precipitate was re-crystallized
from ethanol to get the corresponding derivatives (5a–c),
respectively.
2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetohydrazide (4)
A mixture of the ester (3) (2.76 g, 0.01 mol) and hydrazine
hydrate (10 ml, 50 %) in ethanol (50 ml) was stirred well
and refluxed for 8 h. The reaction mixture was cooled and
the solid produced was collected by filtration, washed with
water, dried and re-crystallized from ethanol.
Yield, 80 %; m.p.: 230–231 °C. Analysis for
C12H14N4O3 (m.w. 262); calcd.: C, 54.96; H, 5.38; N,
21.36. Found: C, 55.12; H, 5.43; N, 21.49. IR (KBr, cm−1):
3299, 3229 (NH–NH2), 3044 (C–H aromatic), 2930 (C–H
aliphatic), 1672 (3C=O amidic overlapped). 1HNMR
(DMSO-d6, ppm): 2.16 (s, 3H, CH3 acetyl), 4.26 (s, 2H,
NH2) (D2O exchangeable), 4.45 (s, 2H, NCH2), 4.46 (s, 2H,
CH2 quinox.), 7.00–7.04 (m, 1H, H-6 quinox.), 7.11–7.15
(m, 1H, H-7 quinox.), 7.25–7.28 (d, 1H, H-8 quinox. J = 8
Hz), 7.53 (d, 1H, H-5 quinox. J = 8 Hz), 9.30 (s, 1H, NH)
(D2O exchangeable). 13CNMR (DMSO-d6, 400 MHz): δ =
169.34 (C, CH3CO), 166.71 (2C, CONH, C-2), 154.65
4-(2-Phenylaminoacetyl)-3,4-dihydroquinoxalin-2(1H)-one
(5a)
Yield, 70 %; m.p.: 220–222 °C. Analysis for C16H15N3O2
(m.w. 281); calcd.: C, 68.31; H, 5.37; N, 14.94. Found: C,
68.52; H, 5.44; N, 15.12. IR (KBr, cm−1): 3192, 3131
(2NH), 3063 (C–H aromatic), 2996 (C–H aliphatic), 1679
(2C=O amidic overlapped). 1HNMR (DMSO-d6, ppm):
4.08 (s, 2H, CH2 acetyl), 4.38 (s, 2H, CH2 quinox.),

Med Chem Res
C log P
Table 2 Anticonvulsant activity of the selected compounds
Test comp.
Dose
(mcg/
kg)
No. of
Protection (%)
ED50
(mcg/
kg)
M.w
ED50
(mmol/
kg)
Relative
potency
protected
animal
5a
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
250
500
1000
75
3
5
6
2
4
5
3
4
5
3
4
5
2
5
6
2
4
5
2
5
6
1
3
5
1
3
5
3
4
5
5
6
6
5
6
6
5
6
6
1
3
6
50.00
83.33
100.00
33.33
66.67
83.33
50.00
66.67
83.33
50.00
66.67
83.33
33.33
83.33
100.00
33.33
66.67
83.33
33.33
83.33
100.00
16.67
50.00
83.33
16.67
50.00
83.33
50.00
66.67
83.33
83.33
100.00
100.00
83.33
100.00
100.00
83.33
100.00
100.00
16.67
50
250
375
250
250
375
375
375
500
500
250
125
125
125
150
281
360
295
387
381
349
363
350
384
380
376
390
390
284.5
0.89
1.04
0.85
0.65
0.98
1.07
1.03
1.43
1.30
0.66
0.33
0.32
0.32
0.53
0.60
0.51
0.62
0.82
0.54
0.50
0.51
0.37
0.41
0.80
1.61
1.66
1.66
1.00
2.20
3.01
2.65
1.06
0.85
0.07
0.57
1.71
2.34
1.72
0.12
0.50
0.49
2.74
5b
5c
7a
7b
8a
8b
9a
9b
9c
12a
12b
13
Diazepam
150
300
100
5.75 (s, 1H, NH-phenyl) (D2O exchangeable), 6.46 (m, 1H,
H-4 phenyl), 6.53 (m, 2H, H-2 and H-6 phenyl), 7.02 (m,
2H, H-6 and H-8 quinox.), 7.06 (m, 2H, H-3 and H-5
phenyl), 7.22 (m, 1 H, H-7 quinox.), 7.58 (d, 1H, H-5
quinox. J = 7.6 Hz), 10.71 (s, 1H, NH quinox.) (D2O
exchangeable).

Med Chem Res
4-(2-(4-Bromophenylamino)acetyl)-3,4-dihydroquinoxalin-
2(1H)-one (5b)
62.43; H, 4.98; N, 15.51. IR (KBr, cm−1): 3465 (NH), 3069
(C–H aromatic), 2930 (C–H aliphatic), 1650 (4C=O over-
lapped). 13CNMR (DMSO-d6, 400 MHz): δ = 169.34 (C,
CH2CONH), 168.21 (C, CH3CO), 167.43 (C, NHCOPh),
163.67 (C, C-2), 147.37 (2C, C-8′, C-4′), 144.27 (2C, C6H4
(C-1, CH-4)), 129.07 (2CH, C6H4 (C-3, C-5)), 128.97 (2CH,
C6H4 (C-2, C-6)), 127.06 (CH, C-6), 124.88 (CH, C-7),
116.75 (CH, C-5), 114.74 (CH, C-8), 55.74 (CH2, C-3),
44.23 (CH2, NCH2), 22.21 (CH3, CH3CO). MS (m/z): 366
(M+, 1.41 %), 189 (4.5 %), 77 (100 %, base beak).
Yield, 80 %; m.p.: 295–297 °C. Analysis for
C16H14BrN3O2 (m.w. 360); calcd.: C, 63.35; H, 6.98; N,
13.85. Found: C, 63.49; H, 7.05; N, 14.01. IR (KBr, cm−1):
3196, 3135 (2NH), 3057 (C–H aromatic), 2916 (C–H ali-
phatic), 1654 (2C=O amidic overlapped. 13CNMR (DMSO-
d6, 400 MHz): δ = 168.66 (C, C-2), 167.41 (C, CON),
143.36 (C, C6H4 (C-1)), 140.40 (C, C-8′), 133.43 (C, C-4′),
132.04 (C, 2CH, C6H4 (C-3, C-5)), 131.70 (CH, C-5),
130.34 (2CH, C-6, C-7), 127.29 (CH, C-8), 123.31 (CH, C-
6), 116.78 (2CH, C6H4 (C-2, C-6)), 44.75 (CH2, NHCH2),
44.28 (CH2, C-3). MS (m/z): 362 (M+2, 8.33 %), 360 (M+,
9.74 %), 207 (68.84 %), 147 (5.00 %), 133 (54.90 %), 87
(100 %, base beak).
2-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)-N-substituted-hydrazine-1-carboxamide (7a–b
)
General method A mixture of the acid hydrazide (4) (0.26 g,
0.001 mol) and the appropriate isocyanate namely cyclo-
hexyl and/or phenyl isocyanate (0.0015 mol) was refluxed
in ethanol (25 ml) for 2 h. the reaction mixture was cooled
and the formed solid was filtered and re-crystallized from
ethanol to obtain compounds (7a–b) respectively.
4-(2-(4-Tolylamino)acetyl)-3,4-dihydroquinoxalin-2(1H)-
one (5c)
Yield, 85 %; m.p.: 230–232 °C. Analysis for C17H17N3O2
(m.w. 295); calcd.: C, 69.14; H, 5.80; N, 14.23. Found: C,
69.28; H, 5.87; N, 14.35. IR (KBr, cm−1): 3196, 3143
(2NH), 3066 (C–H aromatic), 2916 (C–H aliphatic), 1685
(2C=O amidic overlapped). 1HNMR (DMSO-d6, ppm):
2.13 (s, 3H, CH3), 4.06 (s, 2H, CH2 acetyl), 4.37 (s, 2H,
CH2 quinox.), 5.56 (s, 1H, NH-phenyl) (D2O exchange-
able), 6.43 (d, 2H, H-2 and H-6 phenyl, J = 7.6 Hz), 6.85
(m, 2H, H-6 and H-8 quinox.), 7.06 (m, 2H, H-3 and H-5
phenyl), 7.21 (m, 1 H, H-7 quinox.), 7.63 (d, 1H, H-5
quinox. J = 8 Hz), 10.70 (s, 1H, NH quinox.) (D2O
exchangeable). 13CNMR (DMSO-d6, 400 MHz): δ = 170.16
(C, C-2), 168.02 (C, NCO), 146.27 (2C, C-8′, C-4′), 144.27
(C, C6H4 (C-1)), 129.68 (2CH, C6H4 (C-3, C-5)), 126.53
(C, C6H4 (C-4)), 125.11 (CH, C-6), 124.54 (CH, C-7),
116.80 (CH, C-5), 112.83 (3CH, C-8, C6H4 (C-2, C-6) ),
45.95 (CH2, NHCH2), 40.58 (CH2, C-3), 20.50 (CH3,
C6H4(4-CH3)).
2-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)-N-cyclohexylhydrazine-1-carboxamide (7a)
Yield, 70 %; m.p.: 255–257 °C. Analysis for C19H25N5O4
(m.w. 387); calcd.: C, 58.90; H, 6.50; N, 18.08. Found: C,
59.08; H, 6.57; N, 18.22. IR (KBr, cm−1): 3240, 3110 (3NH
overlapped), 3058 (C–H aromatic), 2930 (C–H aliphatic),
1
1669 (4C=O overlapped). HNMR (DMSO-d6, δ, ppm):
1.21–1.26 (m, 4H, C-3 and C-5 cyclohexyl), 1.52–1.55 (m,
2H, C-4 cyclohexyl), 1.63–1.72 (m, 4H, C-2 and C-6
cyclohexyl), 2.16 (s, 3H, CH3 acetyl), 3.34–3.36 (m, 1H,
cyclohexyl), 4.45 (s, 2H, N–CH2), 4.54 (s, 2H, CH2 qui-
nox.), 6.07 (s, 1H, CONH-cyclohexyl) (D2O exchangeable),
7.12 (m, 1H, H-6 quinox.), 7.16 (m, 1H, H-7 quinox.), 7.25
(d, 1H, H-8 quinox. J = 8 Hz), 7.54 (d, 1H, H-5 quinox. J =
8 Hz), 7.72 (s, 1H, CONHNHCO) (D2O exchangeable),
9.82 (s, 1H, CONHNHCO) (D2O exchangeable). 13CNMR
(DMSO-d6, 400 MHz): δ = 169.31 (C, CH3CO), 167.32
(2C, CONH, C-2), 157.54 (C, NHCONH), 155.84 (C, C-
8′), 154.73 (C, C-4′), 124.88 (CH, C-6), 123.67 (CH, C-7),
118.43 (CH, C-5), 116.73 (CH, C-8), 48.48 (CH2, C-3),
44.16 (CH2, NCH2), 33.38 (CH, C6H11), 25.76 (2CH2,
C6H11(C-2,6)), 25.08 (3CH2, C6H11(C-3,4,5)), 22.25 (CH3,
CH3CO).
N′-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)benzohydrazide (6)
Benzoyl chloride (0.14 g, 0.001 mol) was added dropwise to
the stirred solution of the acid hydrazide (4) (0.26 g, 0.001
mol) in dry DMF (30 ml) in the presence of potassium
carbonate (0.14 g, 0.001 mol) using ice-bath. After addition,
the solution was stirred at room temperature for 1 h. The
contents of the reaction flask were then poured slowly into
water with continuous stirring and the resulting precipitate
was filtered, washed with water, dried and crystallized from
ethanol to obtain compound (6).
2-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)-N-phenylhydrazine-1-carboxamide (7b)
Yield, 85 %; m.p.: 270–272 °C. Analysis for C19H19N5O4
(m.w. 381); calcd.: C, 59.84; H, 5.02; N, 18.36. Found: C,
59.98; H, 5.09; N, 18.57. IR (KBr, cm−1): 3288, 3110 (3NH
Yield, 70 %; m.p.: 290–292 °C. Analysis for C19H18N4O4
(m.w. 366); calcd.: C, 62.29; H, 4.95; N, 15.29. Found: C,

Med Chem Res
overlapped), 3061 (C–H aromatic), 2930 (C–H aliphatic),
1667 (4C=O overlapped). HNMR (DMSO-d6, δ, ppm):
CH2CH2CH3, J = 7.2 Hz), 4.46 (s, 2H, N–CH2), 4.61 (s,
2H, CH2 quinox.), 7.16 (m, 2H, H-6 and H-7 quinox.),
7.25 (d, H, H-8 quinox. J = 7.2 Hz), 7.54 (d, H, H-5
quinox. J = 7.6 Hz), 7.87 (s, 1H, CSNH–CH2CH2
CH3) (D2O exchangeable), 9.26 (s, 1H, NHNHCSNH)
(D2O exchangeable), 10.11 (s, 1H, NHNHCSNH) (D2O
exchangeable).
1
2.16 (s, 3H, CH3 acetyl), 3.83 (s, 2H, N–CH2), 4.57 (s, 2H,
CH2 quinox.), 6.70 (m, 1H, H-4 phenyl), 6.85 (m, 2H, H-3
and H-5 phenyl), 6.96 (m, 2H, H-2 and H-6 phenyl), 7.25
(m, 2H, H-6 and H-7 quinox.), 7.46 (m, 2 H, H-5 and H-8
quinox.), 8.17 (s, 1H, CONH-phenyl) (D2O exchangeable),
8.66 (s, 1H, CONHNHCO) (D2O exchangeable), 10.02 (s,
1H, CONHNHCO) (D2O exchangeable).
2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)-N
′-substitutedbenzylideneacetohydrazide (9a–c
)
2-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)-N-substituted-hydrazine-1-carbothioamide (8a–b
)
General method Equimolar amounts of (4) (0.52 g,
0.002 mol) and the appropriate aromatic aldehyde namely,
benzaldehyde, 2-chlorobenzaldehyde and/or 2-methoxy
benzaldehyde (0.002 mol) were refluxed in ethanol (25 ml)
for 4 h. The mixture was cooled and the formed solid was
filtered and re-crystallized from ethanol to furnish the cor-
responding compounds 9a–c, respectively.
General method A mixture of the acid hydrazide (4) (0.26 g,
0.001 mol) and the appropriate isothiocyanate namely ethyl
and/or propyl isothiocyanate (0.0015 mol) was refluxed in
ethanol (25 ml) for 2 h. the reaction mixture was cooled and
the formed solid was filtered and re-crystallized from ethanol
to obtain compounds (8a–b) respectively.
2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)-N
′-benzylideneacetohydrazide (9a)
2-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)-N-ethylhydrazine-1-carbothioamide (8a)
Yield, 80 %; m.p.: 250–252 °C. Analysis for C19H18N4O3
Yield, 70 %; m.p.: 195–196 °C. Analysis for C15H19N5O3S
(m.w. 349); calcd.: C, 51.56; H, 5.48; N, 20.04. Found: C,
51.73; H, 5.46; N, 20.19. IR (KBr, cm−1): 3253, 3110 (3NH
overlapped), 3058 (C–H aromatic), 2972 (C–H aliphatic),
(m.w. 350); calcd.: C, 65.13; H, 5.18; N, 15.99. Found: C,
65.32; H, 5.26; N, 16.13. HNMR (DMSO-d6, δ, ppm):
1
2.17 (s, 3H, CH3 acetyl), 4.47 (s, 2H, CH2 quinox.), 5.06 (s,
2H, N–CH2), 7.12 (m, 2H, H-3 and H-5 phenyl), 7.16 (m,
1H, H-4 phenyl), 7.27 (m, 2H, H-2 and H-6 phenyl), 7.45
(m, 2H, H-6 and H-7 quinox.), 7.71 (m, 2H, H-5 and H-8
quinox.), 8.05 (s, 1H, N=CH), 11.70 (s, 1H, NH) (D2O
exchangeable).
1
1668 (4C=O overlapped). HNMR (DMSO-d6, δ, ppm):
1.08 (t, 3H, CH2CH3, J = 6.8 Hz), 2.16 (s, 3H, CH3 acetyl),
3.47 (q, 2H, CH2CH3, J = 6.8 Hz), 4.46 (s, 2H, N–CH2),
4.62 (s, 2H, CH2 quinox.), 7.16 (m, 2H, H-6 and H-7
quinox.), 7.26 (d, H, H-8 quinox. J = 7.2 Hz), 7.54 (d, H, H-
5 quinox. J = 7.6 Hz), 7.88 (s, 1H, CSNH–CH2CH3) (D2O
exchangeable), 9.26 (s, 1H, NHNHCSNH) (D2O
exchangeable), 10.11 (s, 1H, NHNHCSNH) (D2O
exchangeable). 13CNMR (DMSO-d6, 400 MHz): δ = 167.26
(C, CH3CO), 166.45 (C, CONH), 164.06 (C, C-2), 155.34
(C, CS), 154.73 (C, C-8′), 150.30 (C, C-4′), 124.91 (CH, C-
6), 124.14 (CH, C-7), 116.84 (CH, C-5), 115.62 (CH, C-8),
44.11 (2CH2, C-3, NCH2), 37.76 (CH2, NHCH2), 22.24
(CH3, CH3CO), 14.74 (CH3, CH2CH3).
2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)-N′-(2-
chlorobenzylidene)acetohydrazide (9b)
Yield, 70 %; m.p.: 255–256 °C. Analysis for C19H17ClN4O3
(m.w. 384.5); calcd.: C, 59.30; H, 4.45; N, 14.56. Found: C,
59.53; H, 4.49; N, 14.67. IR (KBr, cm−1): 3210 (NH), 3082
(C–H aromatic), 2994 (C–H aliphatic), 1691, 1647 (3C=O
overlapped). 1HNMR (DMSO-d6, δ, ppm): 2.17 (s, 3H,
CH3 acetyl), 4.47 (s, 2H, CH2 quinox.), 5.07 (s, 2H,
N–CH2), 7.13 (m, 2H, H-3 and H-5 phenyl), 7.26 (m, 1H,
H-4 phenyl), 7.41–7.43 (d, 1H, H-6 phenyl, J = 8.4 Hz),
7.46 (m, 1H, H-7 quinox.), 7.53 (m, 1H, H-6 quinox.),
7.92–7.94 (d, 1H, H-8 quinox. J = 8 Hz), 8.03–8.05 (d, 1H,
H-5 quinox. J = 8 Hz), 8.43 (s, 1H, N=CH), 11.90 (s, 1H,
NH) (D2O exchangeable). 13CNMR (DMSO-d6, 400 MHz):
δ = 169.33 (C, CH3CO), 168.67 (C, CONH), 164.18 (C, C-
2), 143.36 (C, C-8′), 140.40 (C, C-4′), 133.60 (C, C–Cl),
131.80 (CH, N=CH), 130.35 (C, C6H4 (C-1)), 128.11 (CH,
C6H4 (C-6)), 128.02 (CH, C6H4 (C-4)), 127.45 (2CH, C6H4
(C-3, C-5)), 124.91 (CH, C-6), 123.32 (CH, C-7), 116.79
2-(2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)
acetyl)-N-propylhydrazine-1-carbothioamide (8b)
Yield, 70 %; m.p.: 200–202 °C. Analysis for C16H21N5O3S
(m.w. 363); calcd.: C, 52.88; H, 5.82; N, 19.27. Found: C,
53.12; H, 5.89; N, 19.45. IR (KBr, cm−1): 3253, 3110 (3NH
overlapped), 3058 (C–H aromatic), 2972 (C–H aliphatic),
1
1668 (3C=O overlapped). HNMR (DMSO-d6, δ, ppm):
0.85 (t, 3H, CH2CH2CH3, J = 7.2 Hz), 1.50 (m, 2H,
CH2CH2CH3), 2.16 (s, 3H, CH3 acetyl), 3.39 (t, 2H,

Med Chem Res
(2CH, C-5, C-8), 44.75 (CH2, NCH2), 44.29 (CH2, C-3),
22.21 (CH3, CH3CO).
Yield, 90 %; m.p.: 246–248 °C. Analysis for
C13H12N4O3S (m.w. 304); calcd.: C, 51.31; H, 3.97; N,
18.41. Found: C, 51.53; H, 3.93; N, 18.67. IR (KBr, cm−1):
3068 (C–H aromatic), 2913 (C–H aliphatic), 2590 (SH),
2-(4-Acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-yl)-N′-(2-
methoxybenzylidene)acetohydrazide (9c)
1
1684, 1621 (2 C=O amide). HNMR (DMSO-d6, δ, ppm):
2.16 (s, 3H, CH3 acetyl), 4.50 (s, 2H, CH2 quinox.), 5.23 (s,
2H, N–CH2), 7.19 (m, 1 H, H-7 quinox.), 7.31 (m, 1 H, H-6
quinox.), 7.42 (d, 1H, H-5 quinox.), 7.57 (d, 1H, H-
8quinox.), 14.57 (s, 1H, SH) (D2O exchangeable). 13CNMR
(DMSO-d6, 400 MHz): δ = 169.37 (2C, CH3CO, C-2),
159.84 (2C, CN2, CSH), 154.27 (C, C-8′), 150.36 (C, C-4′),
130.37 (CH, C-6), 127.18 (CH, C-7), 116.82 (CH, C-5),
115.33 (CH, C-8), 37.85 (2CH2, C-3, NCH2), 22.23 (CH3,
CH3CO).
Yield, 86 %; m.p.: 263–265 °C. Analysis for C20H20N4O4
(m.w. 380); calcd.: C, 63.15; H, 5.30; N, 14.73. Found: C,
63.24; H, 5.37; N, 14.89. IR (KBr, cm−1): 3182 (NH), 3055
(C–H aromatic), 2940 (C–H aliphatic), 1675 (3C=O over-
lapped). 13CNMR (DMSO-d6, 400 MHz): δ = 169.34 (C,
CH3CO), 168.21 (C, CONH), 163.67 (C, C-2), 147.36 (C,
C6H4 (C-2)), 144.27 (2C, C-8′, C-4′), 129.14 (2CH, C6H4
(C-4, C-6)), 129.07 (CH, N=CH), 128.97 (CH, C6H4 (C-
5)), 127.06 (C, C6H4 (C-1)), 124.88 (CH, C-6), 123.24 (CH,
C-7), 116.75 (CH, C-5), 114.76 (CH, C-8), 114.74 (CH,
C6H4 (C-3)), 55.74 (CH3, OCH3), 44.60 (CH2, C-3), 44.23
(CH2, NCH2), 22.21 (CH3, CH3CO). MS (m/z): 380 (M+,
37.32 %), 231 (21.00 %), 177 (75.50 %), 133 (100 %, base
beak).
Alkyl 2-((5-((4-acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-
yl)methyl)-1,3,4-oxadiazol-2-yl)sulfanyl)acetate (12a–b
)
General method A mixture of 11 (0.61 g, 0.002 mol) and
the appropriate alkyl chloroacetate, namely methyl chlor-
oacetate and/or ethyl chloroacetate (0.002 mol) in dry
acetone (50 ml) in the presence of anhydrous K2CO3 (0.83 g,
0.006 mol) was refluxed for 13 h while stirring. The reaction
mixture was filtered, the solvent was evaporated and the
resulting product was collected by filtration and re-
crystallized from ethanol to furnish the corresponding ester
derivatives (12a–b) respectively.
4-Acetyl-1-((5-methyl-1,3,4-oxadiazol-2-yl)methyl)-3,4-
dihydroquinoxalin-2(1H)-one (10)
The acid hydrazide (4) (0.52 g, 0.002 mol) was refluxed
with acetic anhydride (5 ml) for 3 h. The reaction mixture
was allowed to attain room temperature, and then poured
carefully onto an ice-water (100 ml). The formed precipitate
was filtered and crystallized from ethanol to give the target
compound (10).
Methyl 2-((5-((4-acetyl-2-oxo-3,4-dihydroquinoxalin-1
(2H)-yl)methyl)-1,3,4-oxadiazol-2-yl)sulfanyl)acetate (12a)
Yield, 75 %; m.p.: 270–272 °C. Analysis for
C14H14N4O3 (m.w. 286); calcd.: C, 58.74; H, 4.93; N,
19.57. Found: C, 59.01; H, 5.02; N, 19.72. IR (KBr, cm−1):
3012 (C–H aromatic), 2963 (C–H aliphatic), 1676 (2C=O
amidic overlapped). 1HNMR (DMSO-d6, ppm): 2.17 (s, 3H,
CH3 acetyl), 2.33 (s, 3H, CH3), 4.47 (s, 2H, CH2 quinox.),
5.14 (s, 2H, CH2), 7.01 (m, 1 H, H-7 quinox.), 7.14–7.18
(m, 1 H, H-6 quinox.), 7.25–7.27 (d, 1H, H-5 quinox. J = 8
Hz), 7.56–7.58 (d, 1H, H-8quinox. J = 8 Hz).
Yield, 82 %; m.p.: 140–142 °C. Analysis for C16H16N4O5S
(m. w. 376); calcd.: C, 51.06; H, 4.28; N, 14.89. Found: C,
51.30; H, 4.32; N, 15.03. IR (KBr, cm−1): 3068 (C–H
aromatic), 2986 (C–H aliphatic), 1731 (C=O ester), 1660
1
(2C=O amide). HNMR (DMSO-d6, δ, ppm): 1.14 (s, 3H,
CH3 ester), 2.16 (s, 3H, CH3 acetyl), 4.06 (s, 2H, SCH2),
4.15 (s, 2H, CH2 quinox.), 5.72 (s, 2H, N–CH2), 7.43–7.89
(m, 4H, aromatic protons).
4-Acetyl-1-((5-sulfanyl-1,3,4-oxadiazol-2-yl)methyl)-3,4-
dihydroquinoxalin-2(1H)-one (11)
Ethyl 2-((5-((4-acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-
yl)methyl)-1,3,4-oxadiazol-2-yl)sulfanyl)acetate (12b)
The acid hydrazide (4) (2.62 g, 0.01 mol) was dissolved in a
solution of potassium hydroxide (0.56 g, 0.01 mol) in
ethanol/water mixture (20:2 ml). Carbon disulphide (0.76 g,
0.01 mol) was then added while stirring, and the reaction
mixture was refluxed for 18 h. The reaction mixture was
concentrated, cooled to room temperature and acidified with
diluted hydrochloric acid. The obtained solid was filtered,
washed with water and re-crystallized from ethanol to
produce compound (11).
Yield, 85 %; m.p.: 145–147 °C. Analysis for C17H18N4O5S
(m. w. 390); calcd.: C, 52.30; H, 4.65; N, 14.35. Found: C,
52.47; H, 4.71; N, 14.49. IR (KBr, cm−1): 2999 (C–H
aromatic), 2950 (C–H aliphatic), 1728 (C=O ester), 1660
1
(2C=O amide). HNMR (DMSO-d6, δ, ppm): 1.09 (t, 3H,
CH2CH3, J = 6.8 Hz), 2.16 (s, 3H, CH3 acetyl), 4.02 (q, 2H,
CH2CH3, J = 6.8 Hz), 4.04 (s, 2H, SCH2), 4.09 (s, 2H, CH2
quinox.), 5.68 (s, 2H, N–CH2), 7.43 (m, H, H-7 quinox.),
7.65 (m, 2H, H-5 and H-6 quinox.), 7.88 (d, H, H-8 quinox.

Med Chem Res
J = 7.6 Hz). MS (m/z): 390 (M+, 0.71 %), 332 (26.87 %),
227 (100 %, base beak). 13CNMR (DMSO-d6, 400 MHz): δ
= 169.35 (C, COO), 166.87 (C, CH3CO), 165.97 (C, C-2),
154.69 (2C, CN2, CS), 150.55 (2C, C-4′, C-8′), 131.42
(CH, C-8), 130.12 (CH, C-5), 124.87 (CH, C-6), 123.94
(CH, C-7), 59.69 (CH2, CH2CH3), 45.34 (CH2, NCH2),
44.65 (CH2, C-3), 31.54 (CH2, SCH2), 22.28 (CH3,
CH3CO), 14.08 (CH3, CH3CH2).
binding mode and to rationalize the observed biological
activity.
Anticonvulsant screening
The animal studies were undertaken with approval from the
Ethics Committee (approval # 23PD/3/12/8R) of Al-Azhar
University, Nasr City, Cairo, Egypt. All the trials were
carried out according to the respective internationally
guidelines. Swiss albino adult male mice, weighing 20–25 g,
were used as experimental animals. They were obtained from
an animal facility (Animal house, Department of Pharma-
cology and Toxicology, Faculty of Pharmacy, Al-Azhar
University). Mice were housed in stainless steel wire-floored
cages without any stressful stimuli. Animals were kept under
well-ventilated conditions at room temperature (25–30 °C).
They were fed on an adequate standard laboratory chow (El-
Nasr Co., Abou-Zabal, Egypt) and allowed to acclimatize
with free access to food and water for 24 h period before
testing except during the short time they were removed from
the cages for testing. Albino mice were randomly arranged in
groups, each of six animals. Diazepam (Sigma-Aldrich
Chemical Co, Milwaukee, WI, USA) was used as a reference
drug for comparison. Pentylenetetrazole (Sigma-Aldrich
Chemical Co, Milwaukee, WI, USA) was used to induce
convulsions in the experimental animals.
The selected derivatives of the newly synthesized com-
pounds were suspended in normal saline using Tween 80
(2 %) and were given intraperitoneally (i.p.) in doses ranging
from 250–1000 mcg/kg animal weight using the same dosing
volume of 0.2 ml per 20 g. The chosen dose was based on
preliminary experimental work. Pentylenetetrazole (PTZ,
Sigma) was dissolved in normal saline in 2 % concentration
and was given intraperitoneally (i.p.) in a dose of 60 mg/kg
body weight (dose that could induce convulsions in at least
80 % of the animals without death during the following 24 h).
Diazepam was suspended in normal saline using Tween 80
(2 %) and was i.p. given in doses of 75, 150 and 300 mcg/kg
using the same dosing volume. All drugs were freshly pre-
pared to the desired concentration just before use.
Methyl 2-((5-((4-acetyl-2-oxo-3,4-dihydroquinoxalin-1(2H)-
yl)methyl)-1,3,4-oxadiazol-2-yl)sulfanyl)propionate (13)
General method A mixture of 12 (0.61 g, 0.002 mol) and
methyl chloropropionate (0.61 g, 0.002 mol) in dry acetone
(50 ml) in the presence of anhydrous K2CO3 (0.83 g, 0.006
mol) was refluxed for 12 h while stirring. The reaction
mixture was filtered, the solvent was evaporated and the
resulting product was collected by filtration and re-
crystallized from ethanol to furnish the corresponding
methyl ester derivative (13). Yield, 80 %; m.p.: 154–156 °
C. Analysis for C17H18N4O5S (m. w. 390); calcd.: C, 52.30;
H, 4.65; N, 14.35. Found: C, 52.43; H, 4.70; N, 14.52. IR
(KBr, cm−1): 3020 (C–H aromatic), 2980 (C–H aliphatic),
1730 (C=O ester), 1660 (2 C=O amide). 13CNMR (DMSO-
d6, 400 MHz): δ = 178.27 (C, COO), 169.37 (C, CH3CO),
167.18 (C, C-2), 160 (2C, CN2, CS), 154.27 (C, C-8′),
150.36 (C, C-4′), 125.17 (CH, C-8), 124.25 (CH, C-5),
116.82 (CH, C-6), 115.33 (CH, C-7), 56.47 (CH3, OCH3),
45.83 (CH, CHOO), 37.85 (2CH2, C-3, NCH2), 22.22
(CH3, CH3CO), 19.00 (CH3, CH3CHCOO). MS (m/z): 390
(M+, 1.89 %), 235 (22.90 %), 199 (20.22 %), 148 (21.87 %),
45 (100 %, base beak).
Docking studies
In the present work, all the target compounds were sub-
jected to docking study to explore their binding mode to
AMPA-receptor. All modeling experiments were performed
using molsoft program which provides a unique set of tools
for the modeling of protein/ligand interactions. It predicts
how small flexible molecule such as substrates or drug
candidates bind to a protein of known 3D structure repre-
sented by grid interaction potentials (http://www.molsoft.
com/icm_pro.html). Each experiment used the biological
target AMPA-receptor downloaded from the Brookhaven
Groups of six mice were administered the graded doses
of the test compounds intraperitoneally. Control animals
received an equal volume of saline (10 ml/kg). After one
hour, the animals were subcutaneously injected with the
convulsive dose of pentylenetetrazole (60 mg/kg). The cri-
terion of anticonvulsant activity is complete protection
against convulsions of any kind. Observations were made at
least 60 minutes after the administration of pentylenete-
trazole. Doses that gave full protection against the induced
convulsions and that which exhibited 50 % protection in
addition to the relative potencies of the test compounds to
diazepam were recorded.
Protein
Databank
(http://www.rcsb.org/pdb/explore/
explore.do?structureId=1FTL). In order to qualify the
docking results in terms of accuracy of the predicted
binding conformations in comparison with the experimental
procedure, the reported AMPA-receptor antagonist drugs
(YM872 (VI) and (VII)) were used as reference ligands.
The docking study has been conducted to predict the

Med Chem Res
Elhelby AA, Ayyad RR, Zayed MF (2011) Synthesis and biological
evaluation of some novel quinoxaline derivatives as antic-
onvulsant agents. Arzneimittelforschung 61(7):379–381
Elkaeed E, Ghiaty A, El-Morsy A, El-Gamal K, Sak H (2014)
Synthesis and biological evaluation of some quinoxaline-2-one
derivatives as novel anticonvulsant agents. Chem Sci Rev Lett 3
(12):1375–1387
Englert L, Biela A, Zayed M, Heine A, Hangauer D, Klebe G (2010)
Displacement of disordered water molecules from hydrophobic
pocket creates enthalpic signature: binding of phosphonamidate
to the S10-pocket of thermolysin. Biochim Biophys Acta
1800:1192–1202
The percentage protection per each dose and the ED50 of
each compound (in mcg/kg and millimole/kg) were calcu-
lated and presented in (Table 2). Finally the relative
potencies of the test compounds compared to Diazepam
were calculated and used for comparison among com-
pounds under test as shown in (Table 2).
Acknowledgments The authors extend their appreciation and
thanking to Prof. Dr. Ahmed M. Mansour, Pharmacology & Tox-
icology Department, Faculty of Pharmacy, Al-Azhar University,
Cairo, Egypt for helping in the pharmacological screening.
Faust K, Gehrke S, Yang Y, Yang L, Beal MF, Lu B (2009) Neuro-
protective effects of compounds with antioxidant and anti-
inflammatory properties in a Drosophila model of Parkinson’s
disease. BMC Neurosci 10:109–125
Compliance with ethical standards
Conflict of interest The authors declare that they have no conflict of
interests.
Ibrahim M-K, Abd-Elrahman AA, Ayyad RRA, El-Adl K,
Mansour AM, Eissa IH (2013) Design and synthesis of some
novel 2-(3-methyl-2-oxoquinoxalin-1(2H)-yl)-N-(4-(substituted)
phenyl)-acetamide derivatives for biological evaluation as antic-
onvulsant agents. Bull Fac Pharm Cairo Univ 51:101–111
Ibrahim M-K, El-Adl K, Zayed MF, Mahdy HA (2015) Design,
synthesis, docking, and biological evaluation of some novel 5-
chloro-2-substituted sulfanylbenzoxazole derivatives as antic-
onvulsant agents. Med Chem Res 24(1):99–114
Jin R, Banke TG, Mayer ML, Traynelis SF, Gouaux E (2003) Struc-
tural basis for partial agonist action at ionotropic glutamate
receptors. Nat Neurosci 6(8):803–810
Jin R, Gouaux E (2003) Probing the function, conformational plasti-
city, and dimer–dimer contacts of the GluR2 ligand-binding core:
studies of 5-substituted willardiines and GluR2 S1S2 in the
crystal. Biochemistry 42(18):5201–5213
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