Synthesis of new series of quinoxaline based MAO-inhibitors and docking studies

Article abstract of DOI:10.1016/j.ejmech.2010.07.008

A series of 2-benzyl-3-(2-arylidenehydrazinyl)quinoxalines 3, 4-benzyl-1-aryl-[1,2,4]triazolo[4,3-a]quinoxalines 4 and phenyl(1-aryl-[1,2,4] triazolo[4,3-a]quinoxalin-4-yl)methanones 5 analogues were synthesized and investigated for their monoamine oxidas

Full text of DOI:10.1016/j.ejmech.2010.07.008

European Journal of Medicinal Chemistry 45 (2010) 4479e4489
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis of new series of quinoxaline based MAO-inhibitors and docking studies
,
a
Sherine N. Khattab a, Seham Y. Hassan a, Adnan A. Bekhit b , Abdel Moneim El Massry ,
**
,
Vratislav Langer c, Adel Amer a
*
a Department of Chemistry, Faculty of Science, P.O. Box 426 Ibrahimia, Alexandria University, Egypt
b Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Alexandria, Alexandria 21521, Egypt
c Department of Chemical and Biological Engineering, Chalmers University, SE-41296 Gothenburg, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 2-benzyl-3-(2-arylidenehydrazinyl)quinoxalines 3, 4-benzyl-1-aryl-[1,2,4]triazolo[4,3-a]qui-
Received 10 April 2010
Received in revised form
3 July 2010
Accepted 6 July 2010
Available online 21 July 2010
noxalines
4 and phenyl(1-aryl-[1,2,4]triazolo[4,3-a]quinoxalin-4-yl)methanones 5 analogues were
synthesized and investigated for their monoamine oxidase (MAO) inhibitory property. The inhibition
profile was found to be competitive for compounds 3k, 3m, 5f and 5n with MAO-A selectivity. Observation
of the docked positions of these compounds revealed interactions with many residues previously reported
to have an effect on the inhibition of the enzyme. The structural features of the new compounds have been
determined from the microanalytical, IR, 1H, 13C NMR spectral studies and X-ray crystalography.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Keywords:
Quinoxalines
[1,2,4]Triazolo[4,3-a]quinoxalines
Oxidation
Oxidative cyclization
Monoamine oxidase inhibitors
1. Introduction
compounds are heterocyclic hydrazines and hydrazides. Their
prototype, N0-propan-2-ylpyridine-4-carbohydrazide, was the first
Monoamine oxidase A and B (MAO-A and -B) are flavin adenine
dinucleotide (FAD) containing enzymes, which are localized in the
outer mitochondrial membranes of neuronal, glial, and other cells
[1,2] particularly abundant in the liver and brain [3]. These FAD
dependentenzymes catalyze the oxidativedeamination of a rangeof
endogenous and exogenous monoamines [4]. The two mammalian
isoforms are characterized by their different sensitivities to inhibi-
tors and their different specificities to substrates. Thus, MAO-A is
selectively inhibited by clorgyline and metabolizes serotonin pref-
modern antidepressant and was introduced into the market under
the trade names of ipronid, iprozid, marsilid, propilniazida and
rivivol. The discovery of this class of drugs has led to a considerable
increase in their preparation as potential therapeutic agents for the
treatment of central nervous system (CNS) depression.
In the course of our ongoing studies aimed at the synthesis of
heterocyclic compounds of potential pharmaceutical relevance
[6e10], we were interested in novel derivatives bearing a 2-ben-
zylquinoxalinyl core. Among these compounds is 2-benzyl-3-
hydrazinylquinoxaline 1 which was found to possess antimicrobial,
antifungal, MAO inhibition and CNS activity [11,12]. This compound
caused a significant and dose-dependent increase in pentobarbi-
tone-sleeping time in mice when it was given intraperitoneally and
orally [11]. The promising bioactive diversity of compound 1 urge
us to synthesize and biologically evaluate a series of its Schiff bases
and novel structural variants of [1,2,4]triazolo[4,3-a]quinoxalines
derivatives on the MAO inhibitory activity.
erentially, whereas MAO-B is inhibited by L-deprenyl and prefers
benzylamine and phenylethylamine as substrates. Selective MAO-A
inhibitors are used clinically as antidepressants and anxiolytics,
while MAO-B inhibitors are used for reduction of the progression of
Parkinson’s disease and of symptoms associated with Alzheimer’s
disease. Earlier MAO-inhibitors introduced into clinical practice for
the treatment of depression were abandoned due to adverse side-
effect, such as ‘cheese effect’ characterized by hypertensive crises
[5]. For this reason, research has been directed at the synthesis of
new potential agents with clinical practice. Among these targeted
2. Results and discussion
2.1. Chemistry
* Corresponding author. Tel.: þ20 122219463; fax: þ20 33911794.
** Corresponding author.
The synthesis of compounds 3e6 followed the general pathway
elicited in Scheme 1. Treatment of 1 with carbonyl compounds
E-mail address: aamer@sci.alex.edu.eg (A. Amer).
0223-5234/$ e see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.07.008

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S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
Compound
R1
R2
Compound
R1
R2
No.
No.
H
H
2-OCH3-C6H4
3,4-(OCH3)2-
C6H3
CH3
H
4-NO2-C6H4
4-HO-C6H4
3a
3b
3l
3m
H
3,4-(OCH2O)-
C6H3
3,4,5-(OCH3)3-
C6H2
H
4-N(CH3)2-C6H4
2-C5H4N
3c
3n
3o
CH3
CH3
3d
CH3
H
H
H
H
4-OCH3-C6H4
C6H5
4-Cl-C6H4
2-Cl-C6H4
4-OCH3-C6H4
C6H5
CH3
CH3
CH3
H
H
H
2-C4H3S
4-CH3-C6H4
4-NH2-C6H4
4-NO2-C6H4
3-Br-C6H4
3-CH3-(2-C4H2S)
H
3e
3f
3g
3h
3i
3j
3k
3p
3q
3r
3s
3t
3u
3v
CH3
CH3
4-HO-C6H4
H
* Same R1 and R2 are used for compounds 4, 5 and 6 with the same notation of 3
Scheme 1.
(namely, substituted benzaldehydes, acetophenones or formalde-
hyde) 2 afforded the corresponding Schiff bases 3 in good yield. The
structures of compounds 3 were found in agreement with the
assigned molecular structure confirmed by their consistent IR and
NMR spectra.
Attempt annelation of compounds 3 via pyrolysis in aprotic
polar solvent like dimethyl-formamide led to the formation of their
corresponding 1-aryl-4-benzyl-[1,2,4]triazolo[4,3-a]quinoxalines
4. Same products were obtained when compounds 3 were exposed
to acylation with acetic anhydride in pyridine. The structures of 4
were based on their NMR and elemental analysis.
which could be due to the solubility of the intermediate in each
case. Thus, compound 3f (R2 ¼ C6H5) afforded 4f which precipitated
out within 90 min stirring while in case of 3s (R2 ¼ 4-NO2eC6H4)
and 3v (R2 ¼ H) the oxidized compounds 5s and 5v were obtained.
Compounds 3h (R2 ¼ 2-CleC6H4) and 3n (R2 ¼ 4-Me2NeC6H4) fur-
nished the brominated products 6h and 6n (Fig. 3), respectively.
The sites of bromination were determined and secured by NMR
analyses.
2.2. Biological activity
On the other hand, using copper (II) chloride in dimethyl-
formamide as a promoter for the annelation reaction of type 3
compounds via double oxidation processes afforded compounds 5
in excellent yields. Their structures were confirmed by scrutiny of
their 1H NMR, 13C NMR, IR spectral data and elemental analyses.
Compound 5v showed unusual downfield shift of H-1 at
The newly synthesized compounds 3e6 were evaluated for their
MAO-A inhibitory activity in vitro by the method described by
Undenfriend et al. [13] by determining the MAO-A activity of rat
liver mitochondria [14] (Table 4). Furthermore, the synthesized
compounds 3e6 were tested to determine their activity toward
MAO-A and MAO-B selectivity in the presence of their specific
substrate serotonin or benzylamine, respectively [15]. Bovine brain
mitochondria were isolated according to Basford [15]. The
compounds 3e6 were tested to determine their activity toward
MAO-A and MAO-B according to the methods of Matsumoto et al.
[16] and Bradford [17]. The MAO-A and MAO-B results are expressed
as IC50 (Table 4). The selectivity index is also given in Table 4. The
results revealed that compounds 3k, 3m, 5f and 5n showed MAO-A
d
10.41 ppm and its structure was secured by X-ray crystallography
(Table 1 for crystal’s data). Perspective view of the molecule with
atom numbering and hydrogen bonding pattern are shown in
Figs. 1 and 2, respectively. Selected bond distances and angles are
given in Table 2 and hydrogen bonds are shown in Table 3.
Furthermore, our attempt to cyclize 3 with bromine in methanol
showed that the reaction product depends on the nature of R2

S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
4481
Table 1
Crystal data and structure refinement for 5v.
Empirical formula
Formula weight
Temperature
C16H10N4O
274.28
153(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Unit cell dimensions
Orthorhombic
Pna21
a ¼ 11.1840(8) Å a ¼ 90ꢀ
b ¼ 15.1398(11) Å b ¼ 90ꢀ
c ¼ 7.3035(5) Å g ¼ 90ꢀ
1236.65(15) Å3
4
Volume
Z
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta ¼ 32.00ꢀ
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
1.473 Mg/m3
0.097 mmꢁ1
568
Fig. 1. Numbering scheme with atomic displacement ellipsoids drawn at 50% proba-
bility level of compound 5v.
0.71 ꢂ 0.18 ꢂ 0.14 mm3
2.26e33.07ꢀ.
ꢁ15 ꢃ h ꢃ 17, ꢁ22 ꢃ k ꢃ21, ꢁ11 ꢃl ꢃ 10
16,065
to rationalize the obtained biological results. Structureeaffinity
relationships (SAR) and the hypothetical binding motif of these
compounds using human MAO-A crystal structure (PDB ID: 2BXR)
were carried as described earlier [6,18,19]. Compounds 3k, 3m, 5f
and 5n are the most active in this study, possessed good hydrogen
bonding interaction beside hydrophobic interactions with amino
acid residues of the active site of MAO-A enzyme. Docking of
compound 3k into the MAO-A active site revealed that several
molecular interactions were considered to be responsible for the
observed affinity. For instance, hydrophobic interaction was
observed with PHE208 and three hydrogen bonds to SER209 and
PRO72 residues (Fig. 4). Docking of compound 3m showed a hydro-
phobic interaction with PHE208 and three hydrogen bonds to
SER209, TYR 69 and GLN74 residues (Fig. 5). Dockingof compound 5f
showed five hydrophobic interactions with ILE335, LEU337, PHE208,
TYR444 and GLU216 and one hydrogen bond to SER209 (Fig. 6). On
the other hand, docking of compound 5n into the MAO-A active site
showed that the molecular interactions responsible for the observed
affinity were: (i) three hydrogen bond interactions with the
2401 [R(int) ¼ 0.0313]
99.9%
Multi-scan
0.9865 and 0.9341
Full-matrix least-squares on F2
2401/1/200
1.001
R1 ¼ 0.0385, wR2 ¼ 0.0980
R1 ¼ 0.0424, wR2 ¼ 0.1013
Not determined
0.284 and ꢁ0.303 e Åꢁ3
Absolute structure parameter
Largest diff. peak and hole
inhibition comparable to that of Clorgyline. In addition, compounds
3k and 5n possessed selectivity inhibition index toward MAO-A and
MAO-B comparable to those found with Clorgyline.
2.2.1. Modeling studies
Molecular modelingstudyand conformationalalignmentstudies
of the newly synthesized compounds 3e6 were performed in order
Fig. 2. Hydrogen bonding pattern of compound 5v.

4482
S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
Table 2
Bond lengths [Å] and angles [ꢀ] for 5v.
O1eC10
N1eC1
N1eC2
N1eC8
N2eC1
N2eN3
N3eC2
N4eC3
N4eC9
C1eH1
C2eC3
C3eC10
C4eC5
C4eC9
C4eH4
C5eC6
C5eH5
1.2197(17)
1.3654(17)
1.3787(16)
1.3941(16)
1.3134(18)
1.3861(18)
1.3224(16)
1.3058(16)
1.3936(15)
0.9500
1.4455(17)
1.5114(18)
1.3829(19)
1.4033(16)
0.9500
C6eC7
C6eH6
C7eC8
C7eH7
C8eC9
1.384(2)
0.9500
1.3952(18)
0.9500
1.4015(16)
1.4926(18)
1.3983(19)
1.4005(18)
1.3928(19)
0.9500
1.392(2)
0.9500
1.391(2)
0.9500
1.387(2)
0.9500
0.9500
C10eC11
C11eC12
C11eC16
C12eC13
C12eH12
C13eC14
C13eH13
C14eC15
C14eH14
C15eC16
C15eH15
C16eH16
1.400(2)
0.9500
C1eN1eC2
C1eN1eC8
C2eN1eC8
C1eN2eN3
C2eN3eN2
C3eN4eC9
N2eC1eN1
N2eC1eH1e
N1eC1eH1
N3eC2eN1
N3eC2eC3
N1eC2eC3
N4eC3eC2
N4eC3eC10
C2eC3eC10
C4eC5eC6
C4eC5eH5
C6eC5eH5
C7eC6eC5
C7eC6eH6
C5eC6eH6
C8eC7eC6
N4eC9eC4
C8eC9eC4
O1eC10eC11
O1eC10eC3
C5eC4eH4
104.98(11)
132.33(12)
122.64(11)
108.62(12)
106.30(11)
119.21(11)
109.75(13)
125.1
C5eC4eC9
C9eC4eH4
C8eC7eH7
C6eC7eH7
N1eC8eC7
N1eC8eC9
C7eC8eC9
N4eC9eC8
C11eC10eC3
120.07(12)
120.0
120.7
Fig. 3. The brominated products 6h and 6n.
120.7
122.61(11)
115.98(11)
121.40(11)
122.91(11)
120.01(11)
119.30(13)
123.59(12)
117.04(12)
119.90(13)
120.1
120.1
120.37(14)
119.8
119.8
119.90(14)
120.0
200 mg/kg, although no mortality was recorded at 300 mg/kg.
Moreover, these compounds were tested for their parenteral
toxicity and the results revealed that all the test compounds were
non-toxic up to 100 mg/kg. We could conclude that the synthesis
and biochemical evaluation of the newly synthesized compounds
led to the design of a novel class of MAO-A inhibitors with good
safety margins.
125.1
110.34(12)
132.51(12)
117.14(11)
122.09(11)
116.92(11)
120.71(11)
120.07(13)
120.0
C12eC11eC16
C12eC11eC10
C16eC11eC10
C13eC12eC11
C13eC12eH12
C11eC12eH12
C12eC13eC14
C12eC13eH13
C14eC13eH13
C15eC14eC13
C15eC14eH14
C13eC14eH14
C14eC15eC16
C14eC15eH15
C16eC15eH15
C15eC16eC11
C15eC16eH16
C11eC16eH16
Table 4
120.0
121.03(13)
119.5
Effect of some quinoxaline derivatives on the activity of MAO-A and MAO-B.
Compound
MAO-A IC50 (M)
MAO-B IC50 (M)
Selectivity
inhibition
index (SI)a
119.5
120.0
119.97(14)
120.0
120.0
120.52(14)
119.7
118.57(12)
118.22(11)
118.85(11)
122.25(12)
117.71(12)
120.0
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
8.3 ꢂ 10ꢁ8 ꢄ 0.12
5.6 ꢂ 10ꢁ8 ꢄ 0.14
6.3 ꢂ 10ꢁ9 ꢄ 0.22
2.9 ꢂ 10ꢁ8 ꢄ 0.13
8.9 ꢂ 10ꢁ8ꢄo.18
8.1 ꢂ 10ꢁ8 ꢄ 0.17
7.6 ꢂ 10ꢁ8 ꢄ 0.24
5.8 ꢂ 10ꢁ9 ꢄ 0.12
6.3 ꢂ 10ꢁ8 ꢄ 0.27
7.9 ꢂ 10ꢁ8 ꢄ 0.09
2.8 ꢂ 10ꢁ9 ꢄ 0.13
6.8 ꢂ 10ꢁ7 ꢄ 0.54
3.4 ꢂ 10ꢁ9 ꢄ 0.17
8.3 ꢂ 10ꢁ8 ꢄ 0.81
9.1 ꢂ 10ꢁ8 ꢄ 0.14
6.4 ꢂ 10ꢁ8 ꢄ 0.21
8.6 ꢂ 10ꢁ8 ꢄ 0.19
9.8 ꢂ 10ꢁ9 ꢄ 0.53
8.8 ꢂ 10ꢁ9 ꢄ 0.18
9.8 ꢂ 10ꢁ9 ꢄ 0.44
7.4 ꢂ 10ꢁ8 ꢄ 0.17
8.6 ꢂ 10ꢁ8 ꢄ 0.34
8.2 ꢂ 10ꢁ8 ꢄ 0.18
6.1 ꢂ 10ꢁ9 ꢄ 0.26
6.8 ꢂ 10ꢁ9 ꢄ 0.11
2.7 ꢂ 10ꢁ9 ꢄ 0.11
8.8 ꢂ 10ꢁ8 ꢄ 0.37
6.2 ꢂ 10ꢁ9 ꢄ 0.48
2.7 ꢂ 10ꢁ9 ꢄ 0.02
9.6 ꢂ 10ꢁ9 ꢄ 0.18
2.2 ꢂ 10ꢁ8 ꢄ 0.08
7.5 ꢂ 10ꢁ7 ꢄ 0.04
8.7 ꢂ 10ꢁ8 ꢄ 0.14
3.1 ꢂ 10ꢁ9 ꢄ 0.13
7.9 ꢂ 10ꢁ4 ꢄ 0.4
4.6 ꢂ 10ꢁ4 ꢄ 0.32
8.7 ꢂ 10ꢁ5 ꢄ 0.52
2.6 ꢂ 10ꢁ4 ꢄ 0.34
2.8 ꢂ 10ꢁ4 ꢄ 0.42
3.2 ꢂ 10ꢁ4 ꢄ 0.28
8.4 ꢂ 10ꢁ5 ꢄ 0.2
8.7 ꢂ 10ꢁ5 ꢄ 0.12
7.9 ꢂ 10ꢁ5 ꢄ 0.36
9.8 ꢂ 10ꢁ4 ꢄ 0.45
8.4 ꢂ 10ꢁ3 ꢄ 0.14
8.9 ꢂ 10ꢁ5 ꢄ 0.49
7.9 ꢂ 10ꢁ3 ꢄ 0.18
8.8 ꢂ 10ꢁ4 ꢄ 0.34
9.8 ꢂ 10ꢁ4 ꢄ 0.36
8.5 ꢂ 10ꢁ4 ꢄ 0.15
7.4 ꢂ 10ꢁ4 ꢄ 0.27
8.6 ꢂ 10ꢁ4 ꢄ 0.26
9.6 ꢂ 10ꢁ4 ꢄ 0.42
4.8 ꢂ 10ꢁ5 ꢄ 0.08
8.6 ꢂ 10ꢁ4 ꢄ 0.25
9.5 ꢂ 10ꢁ4 ꢄ 0.54
9.8 ꢂ 10ꢁ4 ꢄ 0.42
7.2 ꢂ 10ꢁ5 ꢄ 0.46
8.6 ꢂ 10ꢁ5 ꢄ 0.47
2.4 ꢂ 10ꢁ4 ꢄ 0.26
3.8 ꢂ 10ꢁ4 ꢄ 0.15
8.5 ꢂ 10ꢁ5 ꢄ 0.37
7.3 ꢂ 10ꢁ3 ꢄ 0.05
7.3 ꢂ 10ꢁ5 ꢄ 0.34
2.3 ꢂ 10ꢁ45 ꢄ 0.06
9.4 ꢂ 10ꢁ4 ꢄ 0.18
9.5 ꢂ 10ꢁ5 ꢄ 0.11
9.4 ꢂ 10ꢁ3 ꢄ 0.16
0.951 ꢂ 104
0.821 ꢂ 104
1.380 ꢂ 104
0.896 ꢂ 104
0.314 ꢂ 104
0.395 ꢂ 104
1.105 ꢂ 103
1.500 ꢂ 104
1.111 ꢂ X103
1.240 ꢂ 104
3.000 ꢂ 106
1.308 ꢂ 103
2.323 ꢂ 106
1.060 ꢂ 104
1.076 ꢂ 104
1.328 ꢂ X104
0.860 ꢂ 104
0.877 ꢂ 105
1.090 ꢂ 104
0.489 ꢂ 105
1.162 ꢂ 104
1.04 ꢂ 104
119.7
following residue: SER209, GLN74 and TYR444. (ii) Hydrophobic
interactions with PHE208 (Fig. 7). As a result, the inhibitory profile of
these compounds could be competitive. The hydrogen bonding
calculation and scoring through docking in active site of MAO-A
enzyme support the obtained experimental enzyme inhibitory
activities for these compounds. Compound 3k has three hydrogen
bondings with good scoring and it is the most active and selective
compound against MAO-A enzyme (Tables 4 and 5).
3s
3t
2.2.2. Acute toxicity
3u
3v
4f
4h
5b
5f
5h
5i
5n
6n
5s
The test compounds 3k, 3m, 5f, 5n were further evaluated for
their oral acute toxicity in male mice using a literature method
[20e22]. The results indicated that test compounds proved to be
non-toxic and well tolerated by the experimental animals up to
1.195 ꢂ 104
1.180 ꢂ 104
1.264 ꢂ 104
0.888 ꢂ 105
0.431 ꢂ 104
1.370 ꢂ 104
2.703 ꢂ 106
0.812 ꢂ 105
1.045 ꢂ 104
1.253 ꢂ 103
1.091 ꢂ 103
3.032 ꢂ 106
Table 3
Hydrogen bonds for 5v [Å andꢀ].
D–H/A
d(DeH)
d(H/A)
d(D/A)
<(DHA)
5v
4v
Clorgyline
C7eH7/N2i
C7eH7/N3i
C12eH12/N4
0.95
0.95
0.95
2.43
2.55
2.43
3.2607(19)
3.4978(18)
2.9751(17)
146.0
176.8
116.3
The results were expressed as mean ꢄ S.E.M. Number of experiments was 6.
a
Symmetry transformations used to generate equivalent atoms: (i): xꢁ1/2, ꢁy þ 1/2,z.
SI_MAO-B IC50/MAO-A IC50.

S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
4483
Fig. 4. 3D view from a molecular modelling study, of minimum-energy structure of the complex of 3k (stick) docked in the active site of MAO-A (PDB ID: 2BXR). Dashed lines depict
hydrogen bond interactions. Viewed using Molecular Operating Environment (MOE) module.
3. Experimental protocols
NMR spectra) were recorded using a JEOL 500 MHz spectrometer
with the chemical shift values reported in units (part per million).
d
3.1. Chemistry
Infrared data were obtained using a PerkineElmer 1600 series
Fourier transform instrument as KBr pellets. The compounds were
named using Chem. Draw Ultra version 12, Cambridge soft Corpo-
ration. Elemental analyses were performed on PerkineElmer 2400
Melting points were determined with a Mel-Temp apparatus
and are uncorrected. Magnetic resonance spectra (1H NMR and 13
C
Fig. 5. 3D view from a molecular modelling study, of minimum-energy structure of the complex of 3m (stick) docked in the active site of MAO-A (PDB ID: 2BXR). Dashed lines
depict hydrogen bond interactions. Viewed using Molecular Operating Environment (MOE) module.

4484
S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
Fig. 6. 3D view from a molecular modelling study, of minimum-energy structure of the complex of 5f (stick) docked in the active site of MAO-A (PDB ID: 2BXR). Dashed lines depict
hydrogen bond interactions. Viewed using Molecular Operating Environment (MOE) module.
elemental analyzer, and the obtained values were within ꢄ0.3% of
the theoretical values. Follow up of the reactions and checking the
purity of the compounds were made by TLC on silica gel-protected
aluminum sheets (Type 60 GF254, Merck) and the spots were
ketones (1 mmol) which were dissolved in ethanol (10 mL), and
glacial acetic acid (2 drops) and the reaction mixture was then
refluxed with for 3 h. The product was separated out on cooling,
filtered off, recrystallized from ethanol and dried.
detected by exposure to UV-lamp at
l 254 nm for few seconds.
3.1.1.1. 3-Benzyl-2-(2-(2-methoxybenzylidene)hydrazinyl)quinoxa-
line (3a). This compound was obtained as yellow crystals (ethyl
alcohol), 0.32 g (86.96%) yield, mp (ꢀC) 130e131; IR (KBr): 3251
3.1.1. General procedure for the preparation of compound (3)
solution of 3-benzyl-2-hydrazinylquinoxaline (0.25 g,
1 mmol) in ethanol (10 mL) was added to substituted aldehydes or
A
1
(NH) cmꢁ1 1H NMR (CDCl3):
; d 3.91 (s, 3H, CH3), 4.28 (s, 2H, CH2),
Fig. 7. 3D view from a molecular modelling study, of minimum-energy structure of the complex of 5n (stick) docked in the active site of MAO-A (PDB ID: 2BXR). Dashed lines depict
hydrogen bond interactions. Viewed using Molecular Operating Environment (MOE) module.

S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
4485
Table 5
3.1.1.6. 3-Benzyl-2-(2-benzylidenehydrazinyl)quinoxaline (3f). This
compound was obtained as yellow needles (ethyl alcohol), 0.31 g
(91.72%) yield, mp (ꢀC) 145e146; IR (KBr): 3261 (NH) cmꢁ1; 1H NMR
Calculated docking hydrogen bonding results for compounds 3k, 3m, 5f and 5n.
Compound
Residue
Type
Score (%)
Distance
(DMSO-d6):
d
4.15 (s, 2H, CH2), 7.09 (t, 1H, AreH, J ¼ 6.9 Hz), 7.16 (t,
3k
PRO72
SER209
SER209
TYR69
GLN74
SER209
SER209
GLN74
SER209
TYR444
H-don
H-acc
H-acc
H-don
H-don
H-acc
H-acc
H-acc
H-acc
H-acc
46.3
78.0
26.4
51.3
68.6
12.9
13.5
22.9
20.9
21.4
1.07
2.73
2.59
2.92
1.67
2.82
2.46
3.04
1.81
2.83
1H, AreH, J ¼ 7.7 Hz), 7.26 (t, 2H, AreH, J ¼ 7.7 Hz), 7.33e7.46 (m,
6H, AreH), 7.53 (t, 2H, AreH, J ¼ 7.6 Hz),8.01 (d, 2H, AreH,
J ¼ 6.9 Hz), 8.55 (s, 1H, CeH), 11.00 (s, 1H, NH, D2O exchangeable).
3m
13C nmr (DMSO-d6):
d 39.50, 115.56, 122.77, 126.82, 127.21, 128.56,
128.79, 128.87, 129.13, 129.76, 129.98, 130.81, 132.32, 133.10, 135.59,
138.43, 146.13, 156.60, 159.60. Anal. Calcd for C22H18N4: C, 78.08; H,
5.36; N, 16.56. Found: C, 78.32; H, 5.09; N, 16.38.
5f
5n
3.1.1.7. 3-Benzyl-2-(2-(4-chlorobenzylidene)hydrazinyl)quinoxaline
(3g). This compound was obtained as reddish brown crystals (ethyl
alcohol), 0.26 g (69.90%) yield, mp (ꢀC) 159e160; IR (KBr): 3253
6.95 (t, 2H, AreH, J ¼ 9.2 Hz), 7.01, 7.11, 7.22 (3 t, 3H, AreH,
J ¼ 6.9 Hz), 7.28e7.31 (m, 3H, AreH), 7.39 (t, 1H, AreH, J ¼ 7.7 Hz),
7.54 (d, 2H, AreH, J ¼ 6.9 Hz), 7.63 (d, 1H, AreH, J ¼ 7.7 Hz), 8.07 (d,
1H, AreH, J ¼ 7.7 Hz), 9.02 (s, 1H, CeH), 9.39 (s, 1H, NH, D2O
exchangeable). Anal. Calcd for C23H20N4O: C, 74.98; H, 5.47; N,15.21.
Found: C, 75.22; H, 5.25; N, 14.98.
(NH) cmꢁ1 1H NMR (DMSO-d6):
; d 4.15 (s, 2H, CH2), 7.10e7.16 (m,
1H, AreH), 7.17e7.25 (m, 4H, AreH), 7.26 (t, 1H, AreH, J ¼ 6.9 Hz),
7.53 (d, 4H, AreH, J ¼ 8.4 Hz), 7.69 (m, 1H, AreH), 7.90 (d, 1H, AreH,
J ¼ 8.4 Hz), 8.03 (d, 1H, AreH, J ¼ 7.7 Hz), 8.54 (s, 1H, CH), 11.06 (s,
1H, NH, D2O exchangeable). 13C NMR (DMSO-d6):
d 39.50, 126.87,
128.42, 128.59, 128.80, 129.23, 129.29, 129.49, 129.73, 130.03,
130.21, 130.45, 131.69, 132.23, 133.16, 134.56, 135.25, 138.31, 146.30.
Anal. Calcd for C22H17ClN4: C, 70.87; H, 4.60; N, 15.03. Found: C,
71.05; H, 4.36; N, 14.82.
3.1.1.2. 3-Benzyl-2-(2-(3,4-dimethoxybenzylidene)hydrazinyl)qui-
noxaline (3b). This compound was obtained as yellow crystals
(ethyl alcohol), 0.373 g (93.72%) yield, mp (ꢀC) 95e96; IR (KBr):
3253 (NH) cmꢁ1 1H NMR (CDCl3):
; d 3.93 (s, 6H, 2 CH3), 4.26 (s,
2H, CH2), 6.90 (d, 1H, AreH, J ¼ 8.4 Hz), 6.94 (d, 1H, AreH,
J ¼ 9.2 Hz), 7.10 (t, 1H, AreH, J ¼ 8.4 Hz), 7.20 (t, 1H, AreH,
J ¼ 7.7 Hz), 7.27e7.31 (m, 4H, AreH), 7.43 (d, 1H, AreH, J ¼ 2.3 Hz),
7.51 (d, 2H, AreH, J ¼ 7.7 Hz), 7.63 (d, 1H, AreH, J ¼ 6.9 Hz), 8.54 (s,
1H, CeH), 9.45 (s, 1H, NH, D2O exchangeable). Anal. Calcd for
C24H22N4O2: C, 72.34; H, 5.57; N, 14.06. Found: C, 72.08; H, 5.41;
N, 14.33.
3.1.1.8. 3-Benzyl-2-(2-(2-chlorobenzylidene)hydrazinyl)quinoxaline
(3h). This compound was obtained as red crystals (ethyl alcohol),
0.32 g (86.02%) yield, mp (ꢀC) 160e161; IR (KBr): 3250 (NH) cmꢁ1
;
1H NMR (DMSO-d6):
d
4.17 (s, 2H, CH2), 7.12 (t,1H, AreH, J ¼ 6.9 Hz),
7.16 (t,1H, AreH, J ¼ 7.7 Hz), 7.26 (t, 3H, AreH, J ¼ 9.2 Hz), 7.36e7.38
(m, 3H, AreH), 7.43e7.45 (m, 2H, AreH), 7.50e7.52 (m, 1H, AreH),
7.55 (d, 1H, AreH, J ¼ 6.9 Hz), 8.50 (m, 1H, AreH), 8.79 (s, 1H, CH),
11.18 (s, 1H, NH, D2O exchangeable). Anal. Calcd for C22H17ClN4: C,
70.87; H, 4.60; N, 15.03. Found: C, 70.65; H, 4.42; N, 14.77.
3.1.1.3. 2-(2-(Benzo[d][1,3]dioxol-5-ylmethylene)hydrazinyl)-3-ben-
zylquinoxaline (3c). This compound was obtained as yellow crystals
(ethyl alcohol), 0.35 g (91.62%) yield, mp (ꢀC) 179e180; IR (KBr):
3.1.1.9. 3-Benzyl-2-(2-(4-methoxybenzylidene)hydrazinyl)quinoxa-
line (3i). This compound was obtained as yellow crystals (ethyl
alcohol), 0.32 g (86.96%) yield, mp (ꢀC) 170e171; IR (KBr): 3251
3249 (NH) cmꢁ1 1H NMR (CDCl3):
; d 4.25 (s, 2H, CH2), 6.03 (s, 2H,
CH2), 6.86, 6.98 (2d, 2H, AreH, J ¼ 8.4 Hz), 7.11 (t, 1H, AreH,
J ¼ 6.9 Hz), 7.17e7.22 (m, 2H, AreH), 7.27e7.31 (m, 3H, AreH), 7.45
(s, 1H, AreH), 7.51 (d, 2H, AreH, J ¼ 6.9 Hz), 7.63 (d, 1H, AreH,
J ¼ 6.9 Hz), 8.49 (s, 1H, CeH), 9.31 (s, 1H, NH, D2O exchangeable).
Anal. Calcd for C23H18N4O2: C, 72.24; H, 4.74; N, 14.65. Found: C,
71.97; H, 4.55; N, 14.81.
(NH) cmꢁ1 1H NMR (CDCl3):
; d 3.86 (s, 3H, CH3), 4.26 (s, 2H, CH2),
6.95e6.97 (m, 3H, AreH), 7.10 (t, 1H, AreH, J ¼ 8.4 Hz), 7.21 (t, 1H,
AreH, J ¼ 6.9 Hz), 7.27e7.31 (m, 3H, AreH), 7.53 (d, 2H, AreH,
J ¼ 7.7 Hz), 7.63 (d, 1H, AreH, J ¼ 6.9 Hz), 7.78 (d, 2H, AreH,
J ¼ 9.2 Hz), 8.55 (s, 1H, CeH), 9.35 (s, 1H, NH, D2O exchangeable).
Anal. Calcd for C23H20N4O: C, 74.98; H, 5.47; N, 15.21. Found: C,
75.22; H, 5.24; N, 14.99.
3.1.1.4. 3-Benzyl-2-(2-(1-(3,4,5-trimethoxyphenyl)ethylidene)hydra-
zinyl)quinoxaline (3d). This compound was obtained as yellow
crystals (ethyl alcohol), 0.419 g (94.69%) yield, mp (ꢀC) 120e121; IR
3.1.1.10. 3-Benzyl-2-(2-(1-phenylethylidene)hydrazinyl)quinoxaline
(3j). This compound was obtained as yellow crystals (ethyl
alcohol), 0.34 g (96.60%) yield, mp (ꢀC)- 140e141; IR (KBr): 3251
(KBr): 3370 (NH) cmꢁ1; 1H NMR (CDCl3):
d 2.48 (s, 3H, CH3), 3.90 (s,
3H, CH3), 3.93 (s, 6H, 2 CH3), 4.28 (s, 2H, CH2), 6.90 (d, 1H, AreH,
J ¼ 7.7 Hz), 7.06 (d, 2H, AreH, J ¼ 1.6 Hz), 7.11, 7.21 (2 t, 2H, AreH,
J ¼ 7.7 Hz), 7.27e7.32 (m, 3H, AreH), 7.51 (d, 2H, AreH, J ¼ 7.6 Hz),
7.66 (d, 1H, AreH, J ¼ 8.4 Hz), 9.08 (s, 1H, NH, D2O exchangeable).
Anal. Calcd for C26H26N4O3: C, 70.57; H, 5.92; N, 12.66. Found: C,
70.87; H, 6.19; N, 12.40.
(NH) cmꢁ1 1H NMR (DMSO-d6):
; d 2.41 (s, 3H, CH3), 4.16 (s, 2H,
CH2), 7.07 (t, 1H, AreH, J ¼ 7.7 Hz), 7.17 (t, 1H, AreH, J ¼ 7.7 Hz), 7.26
(t, 2H, AreH, J ¼ 7.7 Hz), 7.31 (t, 1H, AreH, J ¼ 6.9 Hz), 7.37e7.42 (m,
5H, AreH), 7.52 (d, 2H, AreH, J ¼ 7.7 Hz), 8.03 (dd, 1H, AreH, J ¼ 7.7,
J ¼ 1.5 Hz), 10.68 (s, 1H, NH, D2O exchangeable). 13C NMR (DMSO-
d6):
d 15.23, 39.50, 115.66, 122.59, 126.81, 127.57, 128.49, 128.71,
3.1.1.5. 3-Benzyl-2-(2-(1-(4-methoxyphenyl)ethylidene)hydrazinyl)
quinoxaline (3e). This compound was obtained as yellow crystals
(ethyl alcohol), 0.375 g (98.06%) yield, mp (ꢀC) 129e130; IR (KBr):
128.78, 129.60, 129.82, 129.98, 132.50, 133.03, 138.51, 138.96, 144.18,
160.17, 161.15. Anal. Calcd for C23H20N4: C, 78.38; H, 5.72; N, 15.90.
Found: C, 78.63; H, 5.98; N, 16.11.
3377 (NH) cmꢁ1 1H NMR (CDCl3):
; d 2.50 (s, 3H, CH3), 3.86 (s, 3H,
CH3), 4.28 (s, 2H, CH2), 6.93e6.96 (m, 3H, AreH), 7.10 (t, 1H, AreH,
J ¼ 7.7 Hz), 7.20 (t, 1H, AreH, J ¼ 6.9 Hz), 7.29 (t, 3H, AreH,
J ¼ 7.7 Hz), 7.52 (d, 2H, AreH, J ¼ 6.9 Hz), 7.64 (dd,1H, AreH, J ¼ 7.7,
J ¼ 1.6 Hz), 7.84 (d, 2H, AreH, J ¼ 8.4 Hz), 9.17 (s, 1H, NH, D2O
exchangeable). Anal. Calcd for C24H22N4O: C, 75.37; H, 5.80; N,
14.65. Found: C, 75.61; H, 6.08; N, 14.50.
3.1.1.11. 3-Benzyl-2-(2-(1-(4-hydroxyphenyl)ethylidene)hydrazinyl)
quinoxaline (3k). This compound was obtained as yellow powder
(ethyl alcohol), 0.31 g (84.24%) yield, mp 185e186 ꢀC; IR (KBr):
3240 (NH) cmꢁ1; 1H NMR (DMSO-d6):
d 2.36 (s, 3H, CH3), 4.14 (s, 2H,
CH2), 6.78 (d, 2H, AreH, J ¼ 8.4 Hz), 7.04 (t, 1H, AreH, J ¼ 6.9 Hz),
7.16 (t, 1H, AreH, J ¼ 7.7 Hz), 7.23e7.30 (m, 3H, AreH), 7.37 (d, 2H,

4486
S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
AreH, J ¼ 7.7 Hz), 7.49 (t, 2H, AreH), 7.91 (d, 2H, AreH, J ¼ 8.4 Hz),
9.85 (br.s, 1H, OH, D2O exchangeable), 10.53 (s, 1H, NH, D2O
exchangeable). Anal. Calcd for C23H20N4O: C, 74.98; H, 5.47; N,15.21.
Found: C, 75.24; H, 5.72; N, 15.55.
AreH), 7.61 (d, 1H, AreH, J ¼ 5.4 Hz), 10.44 (s, 1H, NH, D2O
exchangeable). 13C NMR (DMSO-d6):
15.92, 39.50, 115.74, 122.65,
126.80, 128.20, 128.46, 128.76, 129.45, 129.61, 129.72, 129.80,
132.39,133.09,133.77,138.49,143.52,144.60, 152.22,156.94,160.03.
Anal. Calcd for C21H18N4S: C, 70.36; H, 5.06; N, 15.63. Found: C,
70.25; H, 5.32; N, 15.91.
d
3.1.1.12. 3-Benzyl-2-(2-(1-(4-nitrophenyl)ethylidene)hydrazinyl)qui-
noxaline (3l). This compound was obtained as yellow powder
(ethyl alcohol), 0.36 g (90.68%) yield, mp (ꢀC)- 135e136; IR (KBr):
3.1.1.17. 3-Benzyl-2-(2-(1-(p-tolyl)ethylidene)hydrazinyl)quinoxaline
3250 (NH) cmꢁ1
;
1H NMR (DMSO-d6):
d
2.40 (s, 3H, CH3), 4.19 (s,
(3q). This compound was obtained as orange crystals (ethyl alcohol),
2H, CH2), 7.11 (t, 1H, AreH, J ¼ 7.7 Hz), 7.17 (t, 1H, AreH,
J ¼ 7.7 Hz), 7.27 (t, 2H, AreH, J ¼ 6.9 Hz), 7.33e7.39 (m, 3H, AreH),
7.52 (d, 1H, AreH, J ¼ 8.4 Hz), 7.56 (d, 1H, AreH, J ¼ 7.7 Hz), 7.72 (t,
1H, AreH, J ¼ 7.7 Hz), 8.24 (d, 1H, AreH, J ¼ 6.9 Hz), 8.51 (d, 1H,
AreH, J ¼ 7.7 Hz), 8.72 (s, 1H, AreH), 10.91 (s, 1H, NH, D2O
0.33 g (90.16%) yield, mp (ꢀC)- 130e131; IR (KBr): 3249 (NH) cmꢁ1
;
1H NMR (DMSO-d6):
d 2.32 (s, 3H, CH3), 2.39 (s, 3H, CH3), 4.16 (s, 2H,
CH2), 7.06 (t, 1H, AreH, J ¼ 7.7 Hz), 7.16 (t, 1H, AreH, J ¼ 6.9 Hz),
7.21e7.27 (m, 4H, AreH), 7.31 (t, 1H, AreH, J ¼ 6.9 Hz), 7.38 (d, 2H,
AreH, J ¼ 7.7 Hz), 7.52 (d, 2H, AreH, J ¼ 7.7 Hz), 7.95 (d, 2H, AreH,
J ¼ 7.7 Hz),10.65 (s,1H, NH, D2O exchangeable). 13C NMR (DMSO-d6):
exchangeable). 13C NMR (DMSO-d6):
d 15.22, 31.26, 115.81, 121.84,
122.90, 124.32, 126.84, 128.60, 128.80, 129.60, 129.98, 130.25,
132.26, 133.17, 133.84, 138.44, 140.63, 144.59, 148.60, 159.10,
159.91. Anal. Calcd for C23H19N5O2: C, 69.51; H, 4.82; N, 17.62.
Found: C, 69.79; H, 5.11; N, 17.45.
d 15.13, 21.51, 39.50, 115.63, 122.51, 126.78, 127.55, 128.48, 128.76,
129.30, 129.59, 129.76, 132.57, 133.03, 136.24, 138.55, 139.62, 144.06,
160.24, 161.11. Anal. Calcd for C24H22N4: C, 78.66; H, 6.05; N, 15.29.
Found: C, 78.49; H, 5.88; N, 15.52.
3.1.1.13. 3-Benzyl-2-(2-(4-hydroxybenzylidene)hydrazinyl)quinoxa-
line (3m). This compound was obtained as yellow powder (ethyl
alcohol), 0.33 g (93.22%) yield, mp (ꢀC) 210e211; IR (KBr): 3249 (NH)
3.1.1.18. 3-Benzyl-2-(2-(1-(4-aminophenyl)ethylidene)hydrazinyl)
quinoxaline (3r). This compound was obtained as orange powder
(ethyl alcohol), 0.32 g (87.19%) yield, mp (ꢀC)- 152e153; IR (KBr):
cmꢁ1
;
1H NMR (DMSO-d6):
d
4.12 (s, 2H, CH2), 6.82 (d, 2H, AreH,
3261 (NH) cmꢁ1; 1H NMR (DMSO-d6):
d 2.33 (s, 1H, CH3), 4.12 (s, 2H,
J ¼ 8.4 Hz), 7.05 (t, 1H, AreH, J ¼ 6.9 Hz), 7.16 (t,1H, AreH, J ¼ 7.7 Hz),
7.25 (t, 2H, AreH, J ¼ 7.7 Hz), 7.31 (t,1H, AreH, J ¼ 7.7 Hz), 7.38 (d, 2H,
AreH, J ¼ 6.9 Hz), 7.48e7.52 (m, 2H, AreH), 7.84 (d, 2H, AreH,
J ¼ 8.4 Hz), 8.42 (s, 1H, CH), 9.95 (br.s, 1H, OH, D2O exchangeable),
CH2), 5.52 (s, 2H, NH2, D2O exchangeable), 6.55 (d, 2H, AreH,
J ¼ 8.4 Hz), 7.02 (t,1H, AreH, J ¼ 7.7 Hz), 7.16 (t, 1H, AreH, J ¼ 6.9 Hz),
7.23e7.28 (m, 3H, AreH), 7.37 (d, 2H, AreH, J ¼ 7.7 Hz), 7.47 (d, 2H,
AreH, J ¼ 8.4 Hz), 7.79 (d, 2H, AreH, J ¼ 8.4 Hz), 10.43 (s, 1H, NH, D2O
10.81 (s, 1H, NH, D2O exchangeable). 13C NMR (DMSO-d6):
d
39.5,
exchangeable). 13C NMR (DMSO-d6):
d 14.70, 39.50, 113.53, 115.37,
115.33, 116.03, 122.47, 126.70, 126.79, 128.46, 128.77, 128.95, 129.73,
129.84, 130.79, 132.56, 132.97, 138.49, 145.53, 156.69, 159.79, 160.30.
Anal. Calcd for C22H18N4O: C, 74.56; H, 5.12; N,15.81. Found: C, 74.34;
H, 4.89; N, 16.10.
122.16, 126.22, 126.76, 128.34, 128.75, 129.03, 129.59, 132.88, 132.96,
138.64, 143.41, 151.05, 160.55, 161.49. Anal. Calcd for C23H21N5: C,
75.18; H, 5.76; N, 19.06. Found: C, 74.90; H, 5.96; N, 18.82.
3.1.1.19. 3-Benzyl-2-(2-(4-nitrobenzylidene)hydrazinyl)quinoxaline
(3s). This compound was obtained as purple crystals (ethyl
alcohol), 0.34 g (88.77%) yield, mp (ꢀC) 140e141; IR (KBr): 3255
3.1.1.14. 3-Benzyl-2-(2-(4-dimethylaminobenzylidene)hydrazinyl)
quinoxaline (3n). This compound was obtained as red crystals
(ethyl alcohol), 0.31 g (81.36%) yield, mp (ꢀC) 170e171; IR (KBr):
(NH) cmꢁ1 1H NMR (DMSO-d6):
; d 4.18 (s, 2H, CH2), 7.17 (t, 2H,
3254 (NH) cmꢁ1; 1H NMR (DMSO-d6):
d
2.95 (s, 6H, 2CH3), 4.10 (s,
AreH, J ¼ 7.7 Hz), 7.26 (t, 3H, AreH, J ¼ 7.7 Hz), 7.40 (m, 2H, AreH),
7.57 (d, 2H, AreH, J ¼ 7.7 Hz), 8.28 (d, 3H, AreH, J ¼ 6.9 Hz), 8.67 (s,
1H, CH), 11.30 (s, 1H, NH, D2O exchangeable). 13C NMR (DMSO-d6):
2H, CH2), 6.71 (d, 2H, AreH, J ¼ 9.2 Hz), 7.03 (t, 1H, AreH,
J ¼ 8.4 Hz), 7.15 (t, 1H, AreH, J ¼ 7.6 Hz), 7.23e7.30 (m, 3H, AreH),
7.37 (d, 2H, AreH, J ¼ 7.7 Hz), 7.45 (d, 2H, AreH, J ¼ 7.7 Hz), 7.79 (d,
2H, AreH, J ¼ 9.2 Hz), 8.37 (s, 1H, CH), 10.72 (s, 1H, NH, D2O
exchangeable). Anal. Calcd for C24H23N5: C, 75.56; H, 6.08; N, 18.36.
Found: C, 75.84; H, 6.35; N, 18.07.
d
39.50, 115.83, 123.31, 124.35, 126.86, 128.68, 128.82, 129.55,
129.76, 130.24, 131.94, 133.42, 138.32, 141.92, 146.90, 148.37, 154.23,
159.33. Anal. Calcd for C22H17N5O2: C, 68.92; H, 4.47; N, 18.27.
Found: C, 69.11; H, 4.36; N, 18.02.
3.1.1.15. 3-Benzyl-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)qui-
noxaline (3o). This compound was obtained as orange crystals
(ethyl alcohol), 0.32 g (90.65%) yield, mp (ꢀC) 140e141; IR (KBr):
3.1.1.20. 3-Benzyl-2-(2-(3-bromobenzylidene)hydrazinyl)quinoxaline
(3t). This compound was obtained as yellow powder (ethyl
alcohol), 0.38 g (91.13%) yield, mp (ꢀC) 145e146; IR (KBr): 3253
3253 (NH)cmꢁ1; 1H NMR (DMSO-d6):
d
2.42 (s, 3H, CH3), 4.19 (s, 2H,
(NH) cmꢁ1 1H NMR (DMSO-d6):
; d 4.15 (s, 2H, CH2), 7.11 (t, 1H,
CH2), 7.11 (t, 1H, AreH, J ¼ 7.7 Hz), 7.16 (t, 1H, AreH, J ¼ 6.9 Hz), 7.26
(t, 2H, AreH, J ¼ 7.7 Hz), 7.33e7.40 (m, 4H, AreH), 7.52e7.57 (m, 2H,
AreH), 7.85 (dt, 1H, AreH, J ¼ 7.7, J ¼ 1.6 Hz), 8.54 (d, 1H, AreH,
J ¼ 8.4 Hz), 8.60 (d, 1H, AreH, J ¼ 4.6 Hz), 10.83 (s, 1H, NH, D2O
AreH, J ¼ 7.6 Hz), 7.17 (t, 1H, AreH, J ¼ 6.9 Hz), 7.26 (t, 2H, AreH,
J ¼ 7.7 Hz), 7.34e7.42 (m, 4H, AreH), 7.54 (t, 2H, AreH, J ¼ 7.6 Hz),
7.59 (d, 1H, AreH, J ¼ 7.7 Hz), 7.92 (d, 1H, AreH, J ¼ 7.7 Hz), 8.31 (s,
1H, AreH), 8.52 (s, 1H, CH), 11.11 (s, 1H, NH, D2O exchangeable). 13
C
exchangeable). 13C NMR (DMSO-d6):
d
14.11, 39.50, 115.75, 122.15,
NMR (DMSO-d6): d 39.50, 115.70, 122.76, 122.96, 126.83, 128.26,
122.86, 124.62, 126.83,128.60, 128.78, 129.65, 129.95, 132.29, 133.17,
138.43, 144.49, 149.14, 156.25, 160.02, 162.24. Anal. Calcd for
C22H19N5: C, 74.77; H, 5.42; N, 19.82. Found: C, 75.06; H, 5.21; N,
20.10.
128.60, 128.79, 128.97, 129.77, 130.06, 130.50, 131.27, 132.16, 133.19,
133.25, 138.05, 138.37, 143.14, 146.44, 155.01, 159.49. Anal. Calcd for
C22H17BrN4: C, 63.32; H, 4.11; N, 13.43. Found: C, 63.55; H, 4.32; N,
13.21.
3.1.1.16. 3-Benzyl-2-(2-(1-(thiophen-2-yl)ethylidene)hydrazinyl)qui-
noxaline (3p). This compound was obtained as yellow powder
(ethyl alcohol), 0.32 g (89.39%) yield, mp (ꢀC) 145e146; IR (KBr):
3.1.1.21. 3-Benzyl-2-(2-((3-methylthiophen-2-yl)methylene)hydra-
zinyl)quinoxaline (3u). This compound was obtained as yellow
powder (ethyl alcohol), 0.33 g (92.18%) yield, mp (ꢀC) 147e148; IR
3248 (NH) cmꢁ1; 1H NMR (DMSO-d6):
d
2.39 (s, 3H, CH3), 4.14 (s, 2H,
(KBr): 3250 (NH) cmꢁ1; 1H NMR (DMSO-d6):
d 2.36 (s, 3H, CH3), 4.13
CH2), 7.06e7.17 (m, 3H, AreH), 7.22e7.27 (m, 2H, AreH), 7.31 (t, 1H,
AreH, J ¼ 7.7 Hz), 7.34e7.40 (m, 2H, AreH), 7.48e7.56 (m, 3H,
(s, 2H, CH2), 6.96e6.99 (m, 1H, AreH), 7.05e7.10 (m, 1H, AreH), 7.16
(t,1H, AreH, J ¼ 6.9 Hz), 7.22e7.27 (m, 2H, AreH), 7.30e7.34 (m, 1H,

S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
4487
AreH), 7.37e7.41 (m, 2H, AreH), 7.47e7.54 (m, 2H, AreH), 7.6 (d,
1H, AreH, J ¼ 4.6 Hz), 8.69 (s, 1H, CH), 10.76 (s, 1H, NH, D2O
3.1.3.5. 4-Benzyl-1-(4-methoxyphenyl)-[1,2,4]triazolo[4,3-a]qui-
noxaline (4i). This compound was obtained as white powder (ethyl
exchangeable). 13C NMR (DMSO-d6):
d 14.31, 39.50, 115.73, 122.69,
alcohol), 0.27 g (73.77%) yield, mp (ꢀC) 145e146; 1H NMR (DMSO-
126.79, 128.44, 128.78, 128.98, 129.41, 129.45, 129.77, 129.84, 131.54,
138.48, 138.60, 141.41, 141.99, 144.22, 145.14, 149.82, 159.63. Anal.
Calcd for C21H18N4S: C, 70.36; H, 5.06; N, 15.63. Found: C, 70.11; H,
5.34; N, 15.89.
d6):
d
4.06 (2d, 2H, CH2, J ¼ 14.55 Hz), 6.61 (d, 1H, AreH, J ¼ 7.7 Hz),
6.86 (d, 2H, AreH, J ¼ 9.2 Hz), 7.00 (t, 1H, AreH, J ¼ 6.9 Hz), 7.17 (t,
1H, AreH, J ¼ 6.9 Hz), 7.23 (t, 1H, AreH, J ¼ 7.7 Hz), 7.33 (t, 3H,
AreH, J ¼ 9.2 Hz), 7.37e7.42 (m, 3H, AreH), 7.49 (d, 1H, AreH,
J ¼ 6.9 Hz). Anal. Calcd for C23H18N4O: C, 75.39; H, 4.95; N, 15.29.
Found: C, 75.12; H, 4.76; N, 15.57.
3.1.2. Procedure for the preparation of 2-benzyl-3-(2-
methylenehydrazinyl) quinoxaline (3v)
3.1.2.1. Method A. A solution of 3-benzyl-2-hydrazinylquinoxaline
3.1.3.6. 4-Benzyl-[1,2,4]triazolo[4,3-a]quinoxaline
compound was obtained as white powder (ethyl alcohol), 0.23 g
(88.46%) yield, mp (ꢀC) >320; 1H NMR (DMSO-d6):
4.41 (m, 2H,
CH2), 7.57 (t, 2H, AreH, J ¼ 7.7 Hz), 7.65 (t, 2H, AreH, J ¼ 7.7 Hz), 7.90
(t, 1H, AreH, J ¼ 7.7 Hz), 8.05 (d, 2H, AreH, J ¼ 7.7 Hz), 8.13 (d, 1H,
AreH, J ¼ 8.4 Hz), 8.55 (d, 1H, AreH, J ¼ 8.4 Hz), 10.29 (s, 1H, AreH).
Anal. Calcd for C16H12N4: C, 73.83; H, 4.65; N, 21.52. Found: C, 74.05;
H, 4.88; N, 21.26.
(4v). This
1
(0.25 g, 1 mmol) in ethanol (10 mL) was added to para-
formaldehyde (2 mmol) which was dissolved in ethanol
(10 mL),and glacial acetic acid (2 drops) and the reaction mixture
was then refluxed with for 3 hours. The product was separated
out on cooling, filtered off, recrystallized from ethanol, and dried.
The product was obtained as beige needles (ethyl alcꢁo1hol), 0.21 g
d
(80%) yield, mp (ꢀC) 205; IR (KBr): 3210 (NH) cm
;
1H NMR
(DMSO-d6):
d
4.54 (s, 2H, CH2), 7.18 (t, 1H, AreH, J ¼ 7.7 Hz), 7.27
(t, 2H, AreH, J ¼ 7.6 Hz), 7.43 (d, 2H, AreH, J ¼ 7.7 Hz), 7.74 (t, 2H,
AreH, J ¼ 7.7 Hz), 8.03 (d, 1H, AreH, J ¼ 7.6 Hz), 8.36 (d, 1H, AreH,
J ¼ 7.6 Hz), 9.99 (s, 1H, NH, D2O exchangeable). Anal. Calcd for
C16H14N4: C, 73.26; H, 5.38; N, 21.36. Found: C, 73.01; H, 5.12; N,
21.18.
3.1.4. General procedure for the preparation of compound (5)
Compound 3 (1 mmol) was dissolved in absolute DMF (5 mL) at
50 ꢀC and a warm solution of CuCl2 (2 mmol, 0.27 g) was added. The
reaction mixture was stirred at 50 ꢀC for 30 min and then heated at
100 ꢀC for 1 h under nitrogen. After the reaction mixture had been
cooled to ambient temperature, a solution of water (100 mL),
concentrated ammonia (50 mL), and NaCl (5 g) was added and the
mixture was stirred at 40 ꢀC for 20 min in the presence of air. The
precipitated solid was filtered off, washed with water and recrys-
tallized from ethanol, filtered and dried.
3.1.2.2. Method B. A solution of 3-benzyl-2-hydrazinylquinoxaline
1
(0.25 g, 1 mmol) in ethanol (10 mL) was added to ethyl-
orthoformate (1 mmol) which was dissolved in ethanol (10 mL),
and glacial acetic acid (2 drops) and the reaction mixture was then
refluxed with for 3 hours. The product was separated out on cool-
ing, filtered off, recrystallized from ethanol, and dried. The product
was obtained as beige needles (ethyl alcohol), 0.24 g (91.49%) yield.
3.1.4.1. 4-Benzoyl-1-(3,4-dimethoxyphenyl)-[1,2,4]triazolo[4,3-a]qui-
noxaline (5b). This compound was obtained as colorless crystals
(ethyl alcohol), 0.35 g (88.35%) yield, mp (ꢀC) 256e257; IR (KBr):
3.1.3. General procedure for the preparation of compound (4)
3.1.3.1. Method A. Compound 3 (1 mmol) was stirred in a mixture
of pyridine (3 mL)/acetic anhydride (1 mL) at room temperature for
3 h followed by 1 h reflux. The reaction mixture was poured onto
ice water with stirring and the solid that precipitated was collected
by filtration, washed with water, recrystallized from ethanol,
filtered and dried.
1686 (C]O), 1665 (C ¼ N) cmꢁ1
; d 3.74, 3.88 (2s,
1H NMR (CDCl3):
6H, 2 CH3), 7.24 (d, 1H, AreH, J ¼ 8.4 Hz), 7.32e7.35 (m, 2H, AreH),
7.55e7.69 (m, 5H, AreH), 7.78 (t, 1H, AreH, J ¼ 7.7 Hz),8.07 (d, 2H,
AreH, J ¼ 7.7 Hz), 8.12 (d, 1H, AreH, J ¼ 6.9 Hz). Anal. Calcd for
C24H18N4O3: C, 70.23; H, 4.42; N, 13.65. Found: C, 70.56; H, 4.69; N,
13.92.
3.1.4.2. 4-Benzoyl-1-phenyl-[1,2,4]triazolo[4,3-a]quinoxaline
(5f). This compound was obtained as white crystals (ethyl alcohol),
0.29 g (82.86%) yield, mp (ꢀC) 220e221; IR (KBr): 1690 (C]O)
3.1.3.2. Method B. Compound 3 (1 mmol) was dissolved in DMF
(5 mL). The solution was refluxed for 5 h. The reaction mixture was
poured onto ice water and the solid that precipitated was collected
by filtration, washed with water, recrystallized from ethanol,
filtered and dried.
cmꢁ1
;
1H NMR (DMSO-d6):
d
7.43 (d, 1H, AreH, J ¼ 8.4 Hz), 7.60 (t,
3H, AreH, J ¼ 7.7 Hz), 7.65e7.73 (m, 4H, AreH), 7.78 (t, 3H, AreH,
J ¼ 8.4 Hz), 8.08 (d, 3H, AreH, J ¼ 6.9 Hz), 8.13 (d, 1H, AreH,
J ¼ 8.4 Hz). 13C NMR (DMSO-d6):
d 116.28, 127.09, 128.47, 128.55,
3.1.3.3. 4-Benzyl-1-phenyl-[1,2,4]triazolo[4,3-a]quinoxaline
129.63, 129.83, 130.54, 131.01, 131.35, 131.73, 134.94, 135.66, 135.73,
143.41, 149.77, 149.88, 190.80. Anal. Calcd for C22H14N4O: C, 75.42;
H, 4.03; N, 15.99. Found: C, 75.66; H, 3.87; N, 16.13.
(4f). This compound was obtained as colorless crystals (ethyl
alcohol), 0.26 g (77.31%) yield, mp (ꢀC) 219e220; 1H NMR (DMSO-
d6):
d
4.58 (s, 2H, CH2), 7.20 (t, 1H, AreH, J ¼ 6.9 Hz), 7.29 (m, 3H,
AreH), 7.42 (t, 1H, AreH, J ¼ 8.4 Hz), 7.49 (d, 2H, AreH, J ¼ 6.9 Hz),
7.57 (t, 1H, AreH, J ¼ 7.7 Hz), 7.64 (m, 2H, AreH), 7.68 (d, 1H, AreH,
J ¼ 7.7 Hz), 7.75 (d, 2H, AreH, J ¼ 6.9 Hz), 8.03 (d, 1H, AreH,
J ¼ 7.7 Hz). Anal. Calcd for C22H16N4: C, 78.55; H, 4.79; N, 16.66.
Found: C, 78.28; H, 5.04; N, 16.87.
3.1.4.3. 4-Benzoyl-1-(2-chlorophenyl)-[1,2,4]triazolo[4,3-a]quinoxa-
line (5h). This compound was obtained as colorless crystals (ethyl
alcohol), 0.31 g (83.78%) yield, mp (ꢀC) 154e155; IR (KBr): 1692
(C]O) cmꢁ1
;
1H NMR (DMSO-d6):
d
7.19 (d, 1H, AreH, J ¼ 8.4 Hz),
7.61 (t, 2H, AreH, J ¼ 6.9 Hz), 7.64e7.73 (m, 3H, AreH), 7.77e7.85
(m, 4H, AreH), 8.11 (d, 2H, AreH, J ¼ 8.4 Hz), 8.17 (dd, 1H, AreH,
J ¼ 8.4, 1.6 Hz). Anal. Calcd for C22H13ClN4O: C, 68.67; H, 3.41; N,
14.56. Found: C, 68.89; H, 3.70; N, 14.42.
3.1.3.4. 4-Benzyl-1-(2-chlorophenyl)-[1,2,4]triazolo[4,3-a]quinoxa-
line (4h). This compound was obtained as white powder (ethyl
alcohol), 0.29 g (78.38%) yield, mp (ꢀC) 194e195; 1H NMR (DMSO-
d6):
d
4.62 (2d, 2H, CH2, J ¼ 13.8 Hz), 7.06 (d, 1H, AreH, J ¼ 8.4 Hz),
3.1.4.4. 4-Benzoyl-1-(4-methoxyphenyl)-[1,2,4]triazolo[4,3-a]qui-
noxaline (5i). This compound was obtained as coorless crystals
(ethyl alcohol), 0.29 g (86.96%) yield, mp (ꢀC) 182e183; IR (KBr):
7.21 (t,1H, AreH, J ¼ 6.9 Hz), 7.31 (t, 2H, AreH, J ¼ 6.9 Hz), 7.47e7.51
(m, 3H, AreH), 7.60e7.67 (m, 2H, AreH), 7.78e7.82 (m, 3H, AreH),
8.06 (d,1H, AreH, J ¼ 7.7 Hz). Anal. Calcd for C22H15ClN4: C, 71.25; H,
4.08; N, 15.11. Found: C, 71.43; H, 4.35; N, 14.90.
1685 (C]O) cmꢁ1; 1H NMR (DMSO-d6):
d
3.89 (s, 3H, CH3), 7.23 (d,
2H, AreH, J ¼ 8.4 Hz), 7.53 (d, 1H, AreH, J ¼ 8.4 Hz), 7.58e7.68 (m,

4488
S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
4H, AreH), 7.71 (d, 2H, AreH, J ¼ 8.4 Hz), 7.77 (t, 1H, AreH,
J ¼ 7.7 Hz), 8.07 (d, 2H, AreH, J ¼ 8.4 Hz), 8.12 (d, 1H, AreH,
J ¼ 8.4 Hz). Anal. Calcd for C23H16N4O2: C, 72.62; H, 4.24; N, 14.73.
Found: C, 72.91; H, 4.47; N, 14.88.
alcohol), 0.29 g (86.31%) yield. Melting point and spectral data are
identical to that of 4f.
3.1.5.7. 4-Benzoyl-1-(3-bromo-4-(N,N-dimethylaminophenyl))-
[1,2,4]triazolo[4,3-a]quinoxaline (6n). This compound was obtained
as colorless crystals (ethyl alcohol), 0.35 g (76.42%) yield, mp (ꢀC)
3.1.4.5. 4-Benzoyl-1-(4-(dimethylamino)phenyl)-[1,2,4]triazolo[4,3-
a]quinoxaline (5n). This compound was obtained as pale yellow
powder (ethyl alcohol), 0.33 g (861.98%) yield, mp (ꢀC) 216e217; IR
224e225; 1H NMR (DMSO-d6):
d 4.07 (s, 2H, CH2), 7.20 (t, 1H, AreH,
J ¼ 6.9 Hz), 7.29 (t, 2H, AreH, J ¼ 7.6 Hz), 7.34 (d, 1H, AreH,
J ¼ 8.4 Hz), 7.47 (m, 4H, AreH), 7.59 (t, 1H, AreH, J ¼ 6.9 Hz), 7.69 (d,
1H, AreH, J ¼ 7.7 Hz), 7.96 (s, 1H, AreH), 8.03 (d, 1H, AreH,
J ¼ 7.7 Hz). Anal. Calcd. for C24H20BrN5: C, 62.89; H, 4.40; N, 15.28.
Found: C, 63.14; H, 4.31; N, 15.02.
(KBr): 1686 (C]O) cmꢁ1; 1H NMR (DMSO-d6):
d 3.03 (s, 6H, 2CH3),
6.74 (d, 1H, AreH, J ¼ 8.4 Hz), 6.92 (d, 1H, AreH, J ¼ 8.4 Hz), 7.45 (d,
1H, AreH, J ¼ 8.4 Hz), 7.55e7.67 (m, 5H, AreH), 7.72 (t, 1H, AreH,
J ¼ 8.4 Hz), 7.77 (t, 1H, AreH, J ¼ 7.7 Hz), 8.08 (m, 3H, AreH). Anal.
Calcd for C24H19N5O: C, 73.27; H, 4.87; N, 17.80. Found: C, 72.99; H,
5.07; N, 17.55.
3.2. Biology
3.1.4.6. 4-Benzoyl-
[1,2,4]triazolo[4,3-a]quinoxaline
(5v). This
The newly synthesized compounds 3e6 tested to determine
their activity toward MAO-A and MAO-B selectivity in the presence
of the specific substrate, serotonin or benzylamine, respectively.
Bovine brain mitochondria were isolated according to Basford [15].
The activities of MAO-A and MAO-B were determined using
a fluorimetric method described by Matsumoto et al. [16]. The
mitochondrial fractions were incubated at 38 ꢀC for 30 min with
the substrate following the inhibition of one of the MAO isoforms
compound was obtained as colorless needles (ethyl alcohol),
0.22 g (80.29%) yield, mp (ꢀC) 243e244; IR (KBr): 1685 (C]O)
cmꢁ1
;
1H NMR (DMSO-d6):
d
7.57 (t, 2H, AreH, J ¼ 7.7 Hz), 7.75 (t,
2H, AreH, J ¼ 8.4 Hz), 7.92 (t, 1H, AreH, J ¼ 7.7 Hz), 8.05 (d, 2H,
AreH, J ¼ 8.4 Hz), 8.13 (d, 1H, AreH, J ¼ 8.4 Hz), 8.50 (d, 1H, AreH,
J ¼ 8.4 Hz), 10.24 (s, 1H, AreH). 13C NMR (DMSO-d6):
d 117.40,
126.00, 128.64, 129.52, 130.90, 131.07, 131.85, 134.89, 135.01,
135.47, 137.90, 149.03, 190.71. Anal. Calcd for C16H10N4O: C, 70.06;
H, 3.67; N, 20.43. Found: C, 70.23; H, 3.54; N, 20.67.
with the specific inhibitor, L-deprenyl (l0.5 mM) to determine
MAO-A activity and clorgyline (10.5 mM) to determine MAO-B
activity. The incubation mixture contained 0.1 ml phosphate buffer
(0.25 M, pH 7.4), mitochondrial suspension (6 mg/ml), the specific
substrate for MAO-A or MAO-B (0.1 mM) and test compounds at
five different concentrations ranging from 0.5 nM to 0.1 M (0,
3.1.5. General procedure for the bromination of compound (3)
3.1.5.1. Method A. Compound 3 (1 mmol) was dissolved in meth-
anol (5 mL). Bromine (0.5 mL) in methanol (10 mL) was added
dropwise for 30 min. The reaction mixture was stirred at room
temperature overnight. The solvent was evaporated under vacuum
and the crude solid obtained was dried and recrystallized from
ethanol, filtered and dried.
0.5 nM, 5 nM,
5 mM, 5 mM and 100 mM) were dissolved in
propylene glycol. The mixture was incubated in a shaking water-
bath at 37 ꢀC for 60 min. The reaction was quenched by adding
perchloric acid. The samples were centrifuged at 10,000g for 5 min
and the supernatant was completed to 2.7 ml using 1 N NaOH and
measured with a PerkineElmer Lf 45 Spectrofluorimeter. The
values were from 6 independent samples that were measured in
duplicate. The average value of the duplicate measurements was
used for the statistical analysis. Protein concentration was deter-
mined according to a previously reported method [17]. The MAO-A
and MAO-B results are expressed as IC50 (Table 4). Propylene glycol
was used as negative control and did not show any effect on the
enzyme activity.
3.1.5.2. 4-Benzoyl-1-(5-bromo-2-chlorophenyl)-[1,2,4]triazolo[4,3-a]
quinoxaline (6h). This compound was obtained as colorless crystals
(ethyl alcohol), 0.38 g (81.95%) yield, mp (ꢀC) 195e196; IR (KBr):
1691 (C]O) cmꢁ1; 1H NMR (DMSO-d6):
d 7.19 (s, 1H, AreH), 7.61 (t,
2H, AreH, J ¼ 6.9 Hz), 7.73 (t, 1H, AreH, J ¼ 7.7 Hz), 7.77e7.91 (m,
5H, AreH), 8.11 (dd, 1H, AreH, J ¼ 8.4, 3.8 Hz). Anal. Calcd for
C22H12BrClN4O: C, 56.98; H, 2.61; N, 12.08. Found: C, 57.25; H, 2.80;
N, 11.86.
The test compounds were further evaluated for their oral acute
toxicity in male mice (20 g each obtained from Medical Research
Institute, Alexandria University) according to previously reported
methods [18,19]. The animals were divided into groups of six mice
each. The compounds were suspended in 1% gum acacia and given
orally in doses of 1, 10, 100, 200, 250, 300 mg/kg. The mortality
percentage in each group was recorded after 24 h. Additionally the
test compounds were investigated for their parenteral acute
toxicity in groups of mice of six animals each. The compounds or
their vehicle, propylene glycol (control), were given by intraperi-
toneal injection in doses of 10, 25, 50, 75, 100 mg/kg. The
percentage survival was followed up to 7 days [20].
3.1.5.3. 4-Benzoyl-1-(4-nitrophenyl)-[1,2,4]triazolo[4,3-a]quinoxa-
line (5s). This compound was obtained as pale yellow crystals
(ethyl alcohol), 0.32 g (81.01%) yield, mp (ꢀC) 124e125; IR (KBr):
1687 (C]O) cmꢁ1; 1H NMR (DMSO-d6):
d 7.18e7.21 (m, 1H, AreH),
7.32e7.42 (m, 4H, AreH), 7.53 (t, 1H, AreH, J ¼ 8.4 Hz), 7.61e7.68
(m, 2H, AreH), 7.84 (d, 2H, AreH, J ¼ 7.7 Hz), 8.08 (d, 2H, AreH,
J ¼ 8.4 Hz), 8.14 (d,1H, AreH, J ¼ 7.7 Hz). Anal. Calcd for C22H13N5O3:
C, 66.83; H, 3.31; N, 17.71. Found: C, 67.13; H, 3.08; N, 17.45.
3.1.5.4. 4-Benzoyl-[1,2,4]triazolo[4,3-a]quinoxaline
(5v). This
compound was obtained as colorless needles (ethyl alcohol), 0.25 g
(91.24%) yield. Melting point and spectral data are identical to that
of 5v.
3.2.1. Modeling studies
Computer-assisted simulated docking experiments were carried
out under MMFF94X in human MAO-A crystal structure (PDB ID:
2BXR). Docking simulation study of the synthesized compounds
3e6 using MOE dock [18] with the following protocol.
3.1.5.5. Method B. One millimole of compound 3 was dissolved in
5 mL methanol, 0.5 mL Bromine in 10 mL methanol was added
dropwise for 30 min. The reaction mixture was stirred at room
temperature for 1 h. The formed precipitate was filtered off, dried
and recrystallized from ethanol, filtered and dried.
(1) Enzyme structures were checked for missing atoms, bonds and
contacts.
3.1.5.6. 4-Benzyl-1-phenyl-[1,2,4]triazolo[4,3-a]quinoxaline
(4f). This compound was obtained as colorless cystals (ethyl
(2) Hydrogen atoms were added to enzyme structure. Water
molecules and bound ligands were manually deleted.

S.N. Khattab et al. / European Journal of Medicinal Chemistry 45 (2010) 4479e4489
4489
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University-Bozeman.
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Y. Katsumata, I. Takahashi, Clin. Biochem. 18 (1985) 126e129.
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[18] Molecular Operating Environment (MOE), Version 2006e08.http//www.
chemcomp.com.
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A. Yesilada, Bioorg. Med. Chem. 17 (2009) 675e689.
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941e946.
(3) The ligand molecules were constructed using the builder
module and were energy minimized.
(4) The active site was generated using the MOE-Alpha Site Finder.
(5) Dummy atoms were created from the obtained alpha spheres.
(6) Ligands were docked within the MAO-A active site using the
MOEDock with simulated annealing used as the search
protocol and MMFF94X molecular mechanics forcefield for
8000 iterations.
(7) The lowest energy conformation was selected and subjected to
an energy minimization using MMFF94X force field.
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