Synthesis, Docking, and Evaluation of Antimicrobial Activity of a New Series of Acyclo C-Nucleosides of 1, 2, 4-Triazolo[4, 3-a]quinoxaline Derivatives

Article abstract of DOI:10.1002/jhet.2396

(Chemical Equation Presented) In this study, 18 new 3-benzylquinoxalinyl hydrazones bearing carbohydrate moiety and their corresponding triazoloquinoxalines were synthesized in order to investigate their possible antibacterial and antifungal activities. S

Full text of DOI:10.1002/jhet.2396

Month 2015
Synthesis, Docking, and Evaluation of Antimicrobial Activity
of a New Series of Acyclo C-Nucleosides of 1, 2,
4-Triazolo[4, 3-a]quinoxaline Derivatives
Mohammed Salah Ayoup,a Hany Emary Ali Ahmed,b,c Abdel Moneim El Massry, Samir Senior,a,d
a,d
*
Sherine Nabil Khattab,a Seham Yassen Hassan,a and Adel Amera,e
*
aDepartment of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426 Ibrahimia, Alexandria, Egypt
bPharmacognosy and Pharmaceutical Chemistry Department, Pharmacy College, Taibah University, Al-Madinha
Al-Munawarah, Saudi Arabia
cPharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Al-Azhar University, Cairo, Egypt
dDepartment of Chemistry, College of Sciences and Arts, Rabigh Campus, King Abdulaziz University,
Jeddah, Saudi Arabia
eDepartment of Chemistry, Faculty of Science, Taibah University, Al-Madinha Al-Munawarah, Saudi Arabia
*
E-mail: adel.amer@alex-sci.edu.eg; heahmad@taibahu.edu.sa
Received August 19, 2014
DOI 10.1002/jhet.2396
Published online 00 Month 2015 in Wiley Online Library (wileyonlinelibrary.com).
In this study, 18 new 3-benzylquinoxalinyl hydrazones bearing carbohydrate moiety and their correspond-
ing triazoloquinoxalines were synthesized in order to investigate their possible antibacterial and antifungal
activities. Some of these compounds such as 4b, 4c, 7b, 7c, and 7d showed promising antibacterial and an-
tifungal activities and were found to have more potent activity compared with that of standard drugs. From
structure–activity relationship point of view, increasing the size of the substitutions at position 6 or 7 on the
quinoxaline nucleus decreased the antimicrobial activity, while the presence of the hydroxyl groups at C2
(R) and C3 (S) of sugar moieties enhanced the activity. Further, molecular docking studies of the active com-
pounds were performed on different targets belonging to different microorganisms and showed good scoring
with further understanding of the various interactions with the active sites of interesting enzymes compared
with the co-crystallized ligands.
J. Heterocyclic Chem., 00, 00 (2015).
INTRODUCTION
In common with other nitrogen heterocycles,
quinoxalines, as well as their fused-ring bio-isosteric ana-
logues, show marked activity in many biological systems.
A large number of compounds incorporating these ring
systems were found to possess antibacterial activities.
Thus, naturally occurring quinoxaline antibiotics are pro-
duced by several species of streptomycetes. They are char-
acterized by a heterodetic cyclic octadepsipeptide to
which two quinoxaline-2-carboxylic acid chromophores
are attached, for example, Echionomycin [1]. Further-
more, several synthetic quinoxalines such as [1,2,4]
triazolo[4,3-a]quinoxaline I [2–4] and quinoxalinone II
derivatives [5–8] have shown activity against Gram-
positive and Gram-negative microorganisms.
© 2015 HeteroCorporation

M. S. Ayoup, H. E. A. Ahmed, A. M. El Massry, S. Senior, S. N. Khattab,
S. Y. Hassan, and A. Amer
Vol 000
Although many antibiotics are available to clinicians,
many efforts have been invested in the search for novel
agents with new mechanisms of action to address the need
for new therapies to combat resistant organisms. Nucleosides
are one class of compounds worthy of further investigation
as antibacterial because some derivatives have shown mod-
erate to good activity against specific bacterial strains [9–11].
In the course of our ongoing studies aimed at the synthe-
sis heterocyclic compounds of potential pharmaceutical
relevance, we were interested in synthesizing novel cyclo
and acyclo C-nucleosides quinoxaline derivatives from
2-hydrazino-3-benzylquinoxaline 1 as the heterobase
builder because of its involvement in several biological ac-
tivities [12–15]. The antibacterial potency of these com-
pounds prompted us to continue our investigation on
quinoxalines in order to achieve additional data for a
structure–activity relationship (SAR) study. In this context,
we have prepared a new series of quinoxalin-2-yl sugar
hydrazones bearing either benzyl or phenyl group in 3, or
alternatively, chlorine atoms in 6 and 7 positions of
quinoxaline nucleus. Furthermore, we studied their trans-
formation to 1, 2, 4-triazolo-[4, 3-a]quinoxaline analogues
in order to verify if this type of biological activity was
maintained or not on the quinoxaline scaffold. The length
of the carbohydrate moiety (namely, hexoses and pentoses)
was also investigated. The procedures of preparation, iden-
tification, and screening the new series of compounds for
their preliminary antimicrobial activity are described in this
article.
7–9 were obtained by recrystallisation from appropriate
solvents (see the Experimental section). Their structural
proof was based on correct elemental analyses as well as
on IR and NMR spectral data.
In our attempt to transform 1 to triazoloquinoxaline in
one pot, D-mannose was selected as a prototype for a short
and a long period oxidative-cyclization duration. Thus,
when 1 was allowed to react with D-mannose in boiling
acidified ethanolic medium for 1 h, cooled to room tem-
perature then treated with methanolic bromine solution
for 2 h, it afforded 7a, which upon periodate oxidation
afforded the quinoxaline carbaldehyde 10. On the other
hand, leaving the reaction mixture in methanolic bromine
solution overnight gave after the work up (see the Exper-
imental section) colorless crystals of 11 with melting
points 227–228°C (Scheme 2). The 1H-NMR of 11
showed no signal for the benzylic protons, while in
13C-NMR spectrum, a signal at 190.91 ppm appeared for
a carbonyl carbon atom. This type of benzylic carbon ox-
idation was reported to proceed through one-pot tandem
halogenation-hydrolysis [16].
Scheme 2
RESULTS AND DISCUSSION
Chemistry. The sugar hydrazones 4–6 were obtained
by the condensation of quinoxaline hydrazine derivatives
1–3 with different monosaccharides under the same
reaction condition reported earlier [12]. Oxidative
cyclization of compounds 4–6 with bromine in methanol
gave corresponding fused triazoloquinoxalines 7–9 in good
yield (Scheme 1). Analytically pure triazoloquinoxalines
Scheme 1
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2015
Synthesis, Docking, and Evaluation of Antimicrobial Activity of a New Series of
Acyclo C-Nucleosides of 1, 2, 4-Triazolo[4, 3-a]quinoxaline Derivatives
In the present work, D-fructose hydrazone 12 was syn-
thesized as ketose prototype. Its tautomeric forms were
fully investigated by NMR and DFT quantum chemical
calculations. The 500MHz 1H-NMR of compound showed
the presence of only two isomeric forms in 1:3 ratio from
the integrated D2O exchangeable singlet peaks for N–H at
10.96 and 11.10ppm. Its 13C-NMR showed 10 signals
(2×5) in the aliphatic region of the sugar part in addition to
two signals at 171.32 and 169.54 ppm, which were assigned
to C¼N of open forms of syn and anti configurations.
polar sugar fragments might be essential for the activity.
Compound 4c bearing D-galactose moiety has a prominent
and potent antibacterial (Gmꢀve) and antifungal activities.
Its oxidative cyclization product 7c showed similar
activities. Compound 7b bearing D-glucose moiety showed
a potent and selective antifungal activity, while 7d with
D-xylose moiety possessed potent and selective antibacterial
(Gm+ve) activity. As a result the SAR analysis of the
synthesized compounds renders certain factors that affect
their biological activities such as substituents at the 3, 5
and 6 positions and the length of sugar moiety.
Molecular modeling studies. Potential energy distribution
of active compounds. Total molecular energy descriptors
were calculated to structurally compare the active
compounds. These energy descriptors accounted for
different types of energy like torsion, electrostatic, and
van der Waals (VDW) types. The comparison is reported
in (Table 2) and full overview about their stability was
given. Distribution of the energy of representative
compounds showed low potential energy for some
compounds like 4b, 7b, and 7d, while in some degrees,
the others are higher over 100kcal/mol. These
compounds with slight higher energy have some
instability performance in the active site because they
have higher extent of VDW energy and hence have low
tolerability in the enzyme active site (Table 2).
Docking. Different biological targets found in bacteria
and fungi are considered of medicinally interest. Because
of the pharmacological profile as primary investigation of
growth inhibition of microorganisms of test compounds
and structural similarities for reference ligands, we
decided to run molecular modeling studies using these
three different biological targets as promising and
pharmaceutical relevant targets for most of marketed
drugs. We assumed here that compound derivatives might
demonstrate their inhibition activity through interaction
with three microbial targets belonging to Gm+ve and
Gmꢀve bacteria, and finally fungi. These target enzymes
were chosen as major antimicrobial drug targets and
essential for biological process in the microorganism cell
life, and inhibition of such enzymes leads to overall cell
death. We assumed here that compound derivatives might
demonstrate their inhibition activity through interaction
with three microbial targets belonging to Gm+ve and
Gmꢀve bacteria, and finally fungi. These target enzymes
were chosen as major antimicrobial drug targets and
essential for biological process in the microorganism cell
life and inhibition of such enzymes leads to overall cell
death. Through the docking work, the representative
compounds showed different docking scores ranging
between ꢀ12.00 as low binding character to ꢀ17.66kcal/
mol as strong binding effect (Table 3). The difference in
the scores reflects the ability of the compounds to tolerate
the active site of the enzyme. However, they exhibit
According to the total energy calculation in DMSO, as a
solvent, the most stable two tautomers found are the open
syn-isomer and the open anti-isomer. It is found that the
open anti-isomer is more stable than the open syn-isomer
by 2.512 kcal/mol.
Biological evaluation (antimicrobial activity inhibition).
Final products were tested for their in vitro growth
inhibitory activity against human pathogens. The utilized
test organisms were Escherichia coli ATCC 8739,
Pseudomonas aeruginosa ATCC 9027 as Gram-negative
bacteria (Gmꢀve), Staphylococcus aureus ATCC 6583P
as an example of Gram-positive bacteria (Gm+ve), and
Candida albicans ATCC 2091 as yeast-like fungi.
Ampicillin, Ciprofloxacin, Clotrimazole, Dermatin,
Erythromycin, and Imipenam were used as control drugs.
The observed inhibition zone (IZ) antimicrobial data of
the compounds and the reference drugs are given in
Table 1. Lead compound 1 exhibited weak antibacterial
and antifungal activities with IZ ranges between 17 and
25. Slight modification on substituents of quinoxaline
moiety
from
benzyl-to-phenyl
as
2
and
hydrogen-to-chloro as 3 leads to slight improvement in
their antibacterial (Gmꢀve) and antifungal activities. The
hydrazones 4a–d showed significant increase in
antibacterial and antifungal activities. This means the
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

M. S. Ayoup, H. E. A. Ahmed, A. M. El Massry, S. Senior, S. N. Khattab,
S. Y. Hassan, and A. Amer
Vol 000
Table 1
Antimicrobial activity (inhibition zone profiles) of the synthesized compounds.
Inhibition zone
Antibacterial activity
Antifungal activity
G(+ve)
G(ꢀve)
Pseudomonas aeruginosa
Compound
Staphylococcus aureus
Escherichia coli
Candida albicans
1
2
3
25
23
23
8
17
23
18
7
15
17
10
20
8
21
19
11
18
22
20
25
20
18
21
17
18
19
17
18
18
38
—
20
19
22
25
32
35
12
22
9
—
39
31
20
24
21
21
20
19
19
17
20
21
18
18
18
25
—
20
25
24
27
31
34
29
—
28
—
39
30
37
—
22
25
24
25
22
19
24
20
19
18
19
—
29
4a
4b
4c
4d
4e
12
7a
7b
7c
7d
7e
5a
5b
8a
8b
8c
6a
6b
6c
9a
9b
9c
CPF
CZL
14
19
29
—
28
23
21
13
36
—
23
22
24
25
23
25
25
25
23
20
23
30
—
Gm(+ve), Gram-positive bacteria; G(ꢀve), Gram-negative bacteria; CPF. ciprofloxacin drug; CZL, clotrimazole.
mostly similar binding mode to the reference ligands that
makes these compounds possibly having the same
mechanism of action. The next sections explained their
binding mechanisms compared with the co-crystallized ligands.
Table 2
Potential energy for representative compounds.
Total
energy
Torsion
energy
Electrostatic
energy
Compound
VDW
Docking work against Gmꢀve bacteria (E. coli).
The
main goal of this docking work was to explore how
candidate molecules work and investigate their binding
modes at the active site. In the target protein, docking of
the reference ligand showed different types of
interactions, H-bonding with amino acid residues lle192,
Ala196, Asp64, and Lys163. In addition, the tight
4b
4c
4d
7b
7c
7d
102
104
123
93
106
91
9.06
10.8
5.66
12.96
13.27
10.2
60.50
62.80
54.09
61.29
69.07
50.3
0.00
0.00
34.76
ꢀ5.74
ꢀ1.00
6.8
VDW, van der Waals force.
Table 3
Docking scores for representative compounds.
Docking score
1KMM
Inhibition zone
Compound
AD4
1IYL
Staphylococcus aureus
Escherichia coli
Candida albicans
4b
4c
4d
7b
7c
7d
ꢀ15.25
ꢀ13.90
ꢀ14.70
ꢀ12.80
ꢀ13.40
ꢀ16.90
ꢀ17.66
ꢀ16.60
ꢀ13.50
ꢀ14.80
ꢀ15.70
ꢀ13.30
ꢀ17.13
ꢀ16.32
ꢀ15.04
ꢀ14.74
ꢀ14.9
—
14
19
29
21
13
36
32
35
12
39
31
20
31
34
29
39
30
—
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2015
Synthesis, Docking, and Evaluation of Antimicrobial Activity of a New Series of
Acyclo C-Nucleosides of 1, 2, 4-Triazolo[4, 3-a]quinoxaline Derivatives
a)
b)
c1)
c2)
Figure 1. 2D depiction of the docked conformation of the most active compound: (a) reference ligand bound to the target protein (enoyl-acyl carrier pro-
tein reductase (FabI) (PDB code 1C14)); (b) compound 4c in the active site of the enzyme; (c) compound 7b–c in the active site of the enzyme. Both
ligands reference and active compounds are aligned in the binding pocket and compared in each figure. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
positioning of pyridine ring in a hydrophobic pocket form of
lle92, lle192, Phe203, and Val14 gives good filing of ligand
in the active site. Compounds 4c, 7b, and 7c were docked
and compared. The phenylquinoxaline moiety adopted an
appropriate orientation to form a π–π stacking (hydrophobic
aromatic) with the lle92, lle192, and Phe203 residues pocket.
In addition, hydrogen-bonding interactions of sugar side
chain OHs of target compounds 4c, 7b, and 7c with Ser91,
Ala196, and Gly93 amino acid residues that similar to
reference ligand were detected. Finally, they could have a
strong resemblance to the reference ligand and thus might
have the same mode of action as antibacterial agents
(Fig. 1a–c).
Docking work against Gm+ve bacteria (S. aureus). In this
case, docking studies were also performed for compound
7d utilizing dihydropteroate synthetase as promising
target of S. aureus bacteria. The compound 7d was
reported most active against S. aureus. Docking of 7d
showed strong hydrogen-bonding interaction with Arg52
and Gln105 residues similar to the reference one. In
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

M. S. Ayoup, H. E. A. Ahmed, A. M. El Massry, S. Senior, S. N. Khattab,
S. Y. Hassan, and A. Amer
Vol 000
a)
b)
Figure 2. 2D depiction of the docked conformation of the most active compound: (a) reference ligand bound to the target protein (dihydropteroate syn-
thetase (PDB code 1 AD4)); (b) compound 7d in the aligned at the binding pocket. [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
addition, it exhibited indirect H2O-dependent metal
interaction through the backbone Val49. Also, the
appearance of hydrophobic stable binding of quinoxaline
moiety with the two amino acids Lys203 and Arg239
was detected. Thus, compound 4d could cause its activity
because of the similar adopting of binding mode of co-
CONCLUSIONS
In summary, we have synthesized a series of acyclo
C-nucleosides of 1, 2, 4-triazolo[4,3-a]quinoxaline deriv-
atives and evaluated for their in vitro antimicrobial activ-
ities that were successfully achieved. Five compounds
4c, 4d, 7b, 7c, and 7d showed excellent antibacterial ac-
tivities against all the tested strains with IZ value compa-
rable with those of ciprofloxacin and clotrimazole.
Specially, compound 7d displayed high Gm+ve antimi-
crobial and antifungal inhibitory activity. From SAR
point of view, increasing the size of the substitutions at
position 6 or 7 on the quinoxaline nucleus decreased
the antimicrobial activity, while the presence of the hy-
droxyl groups at C2 (R) and C3 (S) of sugar moieties en-
hanced the activity. Computational molecular analyses
were carried out and helped in exploring SARs of the
candidate molecules with comparative docking and po-
tential energy scores and proved that derivatives have
ability to inhibit a panel of microorganisms. Detailed
molecular docking studies further supported the inhibi-
tory activity of target compounds and further help in un-
derstanding the various interactions between the ligands
and enzyme active sites. As a result, three different activ-
ity profiles involving potent bivotal anti-Gm+ve antifun-
gal drugs, anti-Gmꢀve antifungal compounds, and
potent antifungal drugs have been introduced:
crystallized ligand (Fig. 2a–b).
Docking work against fungi (C. albicans). The binding
mode of the most compounds 4b, 4c, 7b, and 7c against
C. albicans with the active site of N-myristoyl transferase
(CaNmt) is shown in Figure 3. The benzyl quinoxaline
ring was located at the center of the active site,
surrounded by some hydrophobic residues, such as
Phe117, Phe339, Phe240, Val108, and Tyr335. Because
the OH groups of aliphatic sugar side chain was
important for the activity because of the ability to form
stable hydrogen-bonding interaction with Tyr107 and
Asn175 residues. However, it has been confirmed that
Leu451 is an important functional residue in the
catalytic cycle of CaNmt, and the docking results
revealed that the sugar side-chain OHs made a strong
hydrogen bond with C-terminal carboxylate of Leu451,
which was consistent with the binding mode of reference
ligand. An extra aromatic hydrophobic interaction was
exhibited through Tyr225 residue with the benzyl
quinoxaline fragment that strengthens the ligand
interaction (Fig. 3a–d).
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2015
Synthesis, Docking, and Evaluation of Antimicrobial Activity of a New Series of
Acyclo C-Nucleosides of 1, 2, 4-Triazolo[4, 3-a]quinoxaline Derivatives
a)
b)
c)
d)
Figure 3. 2D depiction of the docked conformation of the most active compounds: (a) compound 4b in the aligned at the binding pocket to the target
protein (N-myristoyl transferase (PDB code 1IYL); (b) compound 4c in the aligned at the binding pocket; (c) compound 7b in the aligned at the binding
pocket; and (d) compound 7c in the aligned at the binding pocket. Each compound is depicted in aligned form with the reference one. [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.com.]
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

M. S. Ayoup, H. E. A. Ahmed, A. M. El Massry, S. Senior, S. N. Khattab,
S. Y. Hassan, and A. Amer
Vol 000
4.43 (m, 1H,O H-6`, exchangeable with D2O), 4.52–4.57 (m, 5H,
H-3`, OH-2`, OH-3`, OH-4`, OH-5`, exchangeable with D2O),
5.50–5.53 (m, 1H, H-2`), 6.46 (d, JOH2`,2` 5.3 Hz, 1H, OH-1`,
exchangeable with D2O), 7.61 (bs, 3H, Ph-H,), 7.70–7.80 (m, 2H,
Ph-H, H-1`), 8.14–8.17 (m, 1 H, quin-H6), 8.73 (bs, 2H, quin-H7,
quin-H8), 8.81–8.79 (m, 1H, quin-H9), 10.20 (s, 1H, N–H,
exchangeable with D2O). Anal. Calcd for C20H22N4O5: C, 60.29;
compounds 7a, 7b, and 7d. They may be considered as a
promising leads for future design of potent and selective
antimicrobial agents.
EXPERIMENTAL
H, 5.57; N, 14.06 Found: C, 60.44; H, 5.32; N, 13.82.
D-Glucose (3-phenylquinoxalin-2-yl) hydrazones (5b). This
Chemistry.
capillary tubes by using
Melting points were obtained in open
MEL-Temp II melting point
a
compound was obtained as deep red crystals, (0.94 g; 92%); mp
149–150°C; Rf 0.7 (7:3 ethylacetate: n-hexane). 1H-NMR
(DMSO-d6, 500 MHz): δ 2.99–3.66 (m, 3H, H-5`, H-6`a, H-6`b),
4.61–4.63 (dis. d, 1H, H-4`), 4.86–4.88 (m, 5H, H-3`, OH-3`,
OH-4`, OH-5`, OH-6`, exchangeable with D2O), 5.48–5.50 (d, J
5.3 Hz, 1H, H-2`), 5.64 (s, 1H, OH-2`, exchangeable with D2O),
7.14–7.17 (m, 1H, Ph-H,), 7.39–7.52 (m, 3H, Ph-H), 7.59–7.60
(m, 2H, H-1`, quin-H6), 7.67–7.79 (m, 2H, quin-H7, quin-H8),
8.70–8.77 (m, 1H, quin-H9), 10.17 (s, 1H, N–H, exchangeable
with D2O). Anal. Calcd for C20H22N4O5: C, 60.29; H, 5.57; N,
14.06. Found: C, 59.78; H, 5.29; N, 14.12.
apparatus (Cole Parmer, Dubuque, Iowa, USA) and are
uncorrected. TLC was performed using aluminum-backed
Merck Silica Gel 60 F254 plates (Sigma-Aldrich, Seelze,
Germany), with UV 254 nm, 20 × 20 cm, 2000 μm using
suitable solvent systems with spots being visualized by a
Spectroline UV Lamp (254 or 366 nm; Sigma-Aldrich, Seelze,
Germany) or staining by I2 vapor. IR spectra were recorded
on a Perkin-Elmer 1600 series Fourier transform instrument
(Perkin-Elmer, Waltham, MA, USA) as KBr pellets, the
absorption bands (ν max) cmꢀ1 1H-NMR and 13C-NMR were
.
recorded on JOEL 500 MHz spectrometers (JEOL, Tokyo,
Japan) at ambient temperature and reported for the major
isomer (when applicable). Mass spectra were recorded on a
JOEL JMS AX-500 spectrometer (JEOL) by using EI at
70 eV. Compounds 1–3 were synthesized following the
procedures described earlier [15,17]. Compounds 4a–c and
7a–c were prepared as previously reported [12].
D-Mannose (3-benzyl-6,7-dichloroquinoxalin-2-yl) hydrazones
(6a).
This compound was obtained as deep yellow crystals,
(0.80 g; 66.6%); mp 180–181°C; Rf 0.4 (7:3 ethylacetate: n-
hexane): 1H-NMR (DMSO-d6, 500MHz): δ 3.91–5.68 (m, CH
and OH of sugar moiety), 4.05 (bs, 2H, PhCH2), 7.29 (dist. t, 1H,
Ph-H), 7.53 (m, 4H, Ph-H), 7.80 (s, 1H, quin-H6), 7.92 (d, 1H, H-
1`), 8.06 (s, 1H, quin-H9), 9.20 (s, 1H, N–H, exchangeable with
D2O). Anal. Calcd for C21H22Cl2N4O5: C, 52.40; H, 4.61; N,
11.64 Found: C, 53.18; H, 5.69; N, 11.42.
General procedures for the preparation of D-sugar
(2-hydrazinoquinoxaline derivatives) hydrazones.
To a
solution of the hydrazine 1–3 (2.5 mmol) ethanol (25 mL), the
corresponding sugar (2.5 mmol) was added and one drop of HCl
(33%). The reaction mixture was heated under reflux for 1 h
then left to cool to room temperature. The solid that separated
out was filtered off, washed with ethanol, and dried.
D-Glucose (3-benzyl-6,7-dichloroquinoxalin-2-yl) hydrazones
(6b).
This compound was obtained as deep reddish yellow
crystals, (1.10 g, 91%); mp 225–226°C; Rf 0.77 (7:3 ethylacetate:
1
n-hexane): H-NMR (DMSO-d6, 500 MHz): 7.17 (dist. t, 1H, Ph-
H,), 7.23–7.26 (m, 5H, Ph-H, H-1`), 7.39 (s, 1H, quin-H6), 7.93
(s, 1H, quin-H9), 9.24 (s, 1H, N–H, exchangeable with D2O).
Anal. Calcd for C21H22Cl2N4O5: C, 52.40; H, 4.61; N, 11.64
D-Xylose (3-benzylquinoxalin-2-yl) hydrazone (4d).
This
compound was obtained as pale red crystals; (0.6 g, 63%); with
mp 179–180°C; Rf 0. 55 (7:3 ethylacetate to n-hexane). IR
(KBr); ν 3376 (NH, OH) and 1660 cmꢀ1 (C¼N); 1H-NMR
(DMSO-d6, 500 MHz): δ 3.52–3.62 (m, 3H, H-4`, H-5`a, H-5`b),
4.06 (s, 2H, PhCH2), 4.35–4.39 (m, 1H, H-2`), 4.46–4.61 (m,
4H, H-3`, OH-3`, OH-4`, OH-5`, exchangeable with D2O), 5.13
(d, JOH2`,2` 5.3 Hz, OH-2`, exchangeable with D2O), 7.15 (m,
1H, Ph-H,), 7.22–7.34 (m, 6 H, quin-H7, quin-H8, Ph-H), 7.48
(d, 1 H, J6,7 7.6 Hz, quin-H6), 7.68 (m, 1 H, quin-H9), 7.88 (d, 1H,
J1`,2` 4.5 Hz, H-1`), 10.97 (s, 1H, N–H, exchangeable with D2O),
13C-NMR (DMSO-d6, 125.7 MHz): δ 40.0 (PhCH2,), 63.02,
72.10, 72.37, 72.58, 122.55, 126.81, 128.55, 128.65, 128.75,
129.51, 129.73, 132.29, 132.65, 137.83, 137.59, 137.91, 138.30,
138.66, 140.17, 145.88, 147.78, 151.33(aromatic carbons for the
major isomer), 160.87 (C-1`). Anal. Calcd for C20H22N4O4: C,
62.82; H, 5.80; N, 14.65, Found: C, 62.96; H, 6.01; N, 14.82.
D-Arabinose (3-benzylquinoxalin-2-yl) hydrazone (4e). This
compound was obtained as deep yellow crystals that precipitated
out that was collected by filtration to yield (0.66 g; 69.45%);
with mp 175–176°C; Rf 0. 5 (7:3 ethylacetate to n-hexane). IR
(KBr); ν 3283 (NH, OH) and 1632 cmꢀ1 (C¼N). Anal. Calcd for
C20H22N4O4: C, 62.82; H, 5.80; N, 14.65, Found: C, 63.02; H,
Found: C, 51.88; H, 5.18; N, 12.02.
D-Galactose (3-benzyl-6,7-dichloroquinoxalin-2-yl) hydrazones
(6c).
This compound was obtained as pale orange crystals,
(1.0g; 83%); mp 145–146°C; Rf 0.54 (7:3 ethylacetate: n-hexane):
1H-NMR (DMSO-d6, 500 MHz): δ 3.46–3.77 (m, 5H, H-4`, H-5`,
H-6`a, H-6`b, OH-6`, exchangeable with D2O), 4.07 (bs, 2H,
PhCH2), 4.26–4.28 (m, 1H, H-3`), 4.17–4.48 (m, 3H, OH-3`, OH-
4`, OH-5`, exchangeable with D2O), 4.87 (dis. d, 1H, H-2`), 6.10
(bs, OH-2`, exchangeable with D2O), 7.17 (dist. t, 1H, J 7.6 Hz, J
6.9 Hz, Ph-H,), 7.23–7.28 (m, 4H, Ph-H), 7.33 (m, 1H, H-1`),
7.40 (s, 1H, quin-H6) 7.86 (s, 1H, quin-H9), 9.24 (s, 1H, N–H,
exchangeable with D2O). Anal. Calcd for C21H22Cl2N4O5: C,
52.40; H, 4.61; N, 11.64 Found: C, 53.11; H, 4.19; N, 11.92.
General procedure for the preparation of 1-(alditol-1-yl)-4-
substituted-[1,2,4]triazolo[4,3-a]quinoxaline derivatives. To
a
solution of 1–3 (2.50 mmol) in methanol (25 mL), the
corresponding sugar (2.50 mmol) and one drop of HCl (33%) were
added. The reaction mixture was heated under reflux on boiling water
bath for 1 h, left to cool at room temperature, and then a solution of
bromine (0.13 mL, 2.50 mmol) in methanol (5.0 mL) was added drop
wise with stirring, for 2 h. A mixture of ethanol (3 mL) and pyridine
(0.5 mL) was added, volatile components were evaporated in vacuum
at 60°C. The residue was treated with ethanol (95%, 10 mL), then left
to cool at room temperature. The crude product that precipitated out
was collected by filtration, washed by ethanol.
5.91; N, 14.35.
D-Mannose (3-phenylquinoxalin-2-yl) hydrazones (5a). This
compound was obtained as deep yellow crystals, (0.90 g; 89%); mp
242–243°C; Rf 0.6 (7:3 ethylacetate: n-hexane). 1H-NMR (DMSO-
d6, 500 MHz): δ 3.65–3.86 (m, 4H, H-4`, H-5`, H-6`a, H-6`b), 4.39–
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2015
Synthesis, Docking, and Evaluation of Antimicrobial Activity of a New Series of
Acyclo C-Nucleosides of 1, 2, 4-Triazolo[4, 3-a]quinoxaline Derivatives
1-(D-Xylo-tetritol-1-yl)-4-benzyl[1,2,4]triazolo[4,3-a]
quinoxaline (7d). The crude product was crystallized from
methyl alcohol to give colorless crystals, (0.4 g; 42.1%); mp
209–210°C; Rf
1-(D-Galacto-pentitol-1-yl)-4-phenyl[1,2,4]triazolo[4,3-a]
quinoxaline (8c). The crude product was recrystallized from
ethyl alcohol to give white crystals, (0.85 g, 85%); mp 230–
231°C; 1H-NMR (DMSO-d6, 500 MHz): δ 3.38–3.45 (m, 2H,
H-5`a, H-5`b), 3.71 (t, 1H, J 8.4 Hz, H-3`), 3.80 (m, 1H, H-4`),
4.22–4.26 (m, 2H, H-2`, OH-3`, exchangeable with D2O), 4.39
(d, 1H, JOH-4`,H4` 7.6 Hz, OH-4`, exchangeable with D2O) 4.49
(6:1 chloroform: methanol). IR (KBr); ν
0.66
3282 (OH), 1626 cmꢀ1 (C¼N); 1H-NMR (DMSO-d6,
500 MHz): δ 3.41 (dd, 1H, J 10.7 Hz, J 6.1 Hz,, H-4`a), δ 3.49
(dd, 1H, J 10.7 Hz, J 5.35 Hz,, H-4`b), 3.52–3.53 (m, 1H, H-3`),
4.30–4.34 (m, 1H, H-2`), 4.45–4.47 (m, 2H, OH-3`, OH-4`,
exchangeable with D2O), 4.54 (s, 2H, PhCH2), 4.92 (d, 1H,
JOH-2`,2` 6.1 Hz, OH-2`, exchangeable with D2O), 5.43 (t, 1H, J
(dist. t, 1H, JOH5`,
5.35 Hz, JOH5`,
6.1 Hz, OH-5`,
5`a
5`b
exchangeable with D2O), 4.91 (d, 1 H, JOH-2`,2` 5.35 Hz, OH-
2`, exchangeable with D2O), 5.67 (d, 1H, J 8.4 Hz, H-1`), 5.97
(d, 1H, J
7.6 Hz, OH-1`, exchangeable with D2O), 7.17
OH-1`,1`
6.9 Hz, J 7.6 Hz, H-1`), 6.13 (d, 1H, J
6.85 Hz, OH-1`,
OH-1`,1`
(dist. t, 1H, J 7.6 Hz, J 6.9 Hz, Ph-H), 7.61 (bs, 3H, Ph-H),
7.71 (t, 1H, J 7.6 Hz, Ph-H), 7.77 (t, 1H, J 7.6 Hz, Ph-H), 8.13
(d, 1H, J6,7 7.6 Hz, quin-H6), 8.72 (bs, 2H, quin-H7, quin-H8),
8.82 (d, 1H, J9,8 8.4 Hz, quin-H9), Anal. Calcd for
C20H20N4O5: C, 60.60; H, 5.09; N, 14.13; Found: C, 59.88; H,
5.61; N, 14.21.
exchangeable with D2O), 7.1 (t, 1H, J 7.6 Hz, Ph-H), 7.24 (t,
2H, J 7.6 Hz, Ph-H), 7.43 (d, 2H, J 7.6 Hz, Ph-H), 7.64–7.73
(m, 2H, quin-H7, quin-H8), 8.0 (dist. t, 1H, J 7.6 Hz, J 1.5 Hz,
quin-H6), 8.63 (d, 1H, J9.8 8.4 Hz, quin-H9). Anal. Calcd for
C20H20N4O4: C, 63.15; H, 5.30; N, 14.73. Found: C, 63.17; H,
5.60; N, 14.35.
1-(D-Manno-pentitol-1-yl)-4-benzyl-7,8-dichloro[1,2,4]
1-(D-Arabino-tetritol-1-yl)-4-benzyl[1,2,4]triazolo[4,3-a]
triazolo[4,3-a]-quinoxaline (9a).
The crude product was
quinoxaline (7e).
The crude product was crystallized from
recrystallized from ethanol 95% to give colorless crystals,
ethanol 95% to give colorless crystals, (0.55 g; 57.6%); mp
205–206°C, Rf 0.67 (6:1 chloroform to methanol). IR (KBr); ν
3313 (OH), 1628 cmꢀ1 (C¼N); 1H-NMR (DMSO-d6,
500 MHz): δ 3.39 (dd, 1H, J 10.7 Hz, J 6.1 Hz, H-4`a), δ 3.46
(dd, 1H, J 10.7 Hz, J 5.35 Hz,, H-4`b), 3.52 (dist. t, J 6.9, J
5.35, 1H, H-3`), 4.31–4.35 (m, 1H, H-2`), 4.41–4.44 (m, 2H,
OH-3`, OH-4`, exchangeable with D2O), 4.55 (s, 2H, PhCH2),
4.90 (d, 1H, JOH-2`,2` 6.1 Hz, OH-2`, exchangeable with D2O),
5.41 (d, 1H, J 6.1 Hz, H-1`), 6.10 (s, 1H, OH-1`, exchangeable
with D2O), 7.18 (t, 1H, J 7.6 Hz, Ph-H), 7.26 (t, 2H, J 7.6 Hz,
Ph-H), 7.44 (d, 2H, J 7.6 Hz, Ph-H), 7.66 (t, 1H, J7,8 = J7,6
6.9 Hz, quin-H7), 7.73 (t, 1H, J8,7 = J8,9 6.9 Hz, quin-H8), 8.03
(d, 1H, J 7.6 Hz, quin-H6), 8.65 (d, 1H, J9.8 8.4 Hz, quin-H9).
Anal. Calcd for C20H20N4O4: C, 63.15; H, 5.30; N, 14.73.
Found: C, 63.56; H, 4.59; N, 14.79.
1-(D-Manno-pentitol-1-yl)-4-phenyl[1,2,4]triazolo[4,3-a]
quinoxaline (8a). The crude product was recrystallized from
ethanol 95% to give colorless crystals, (0.61 g; 61%); mp 245–
246°C; 1H-NMR (DMSO-d6, 500 MHz): δ 3.43–3.51 (m, 2H,
H-5`a, H-5`b), 3.57 (m, 1H, H-4`), 3.83 (t, 1H, J 8.4 Hz, H-4`),
4.39–4.41 (m, 2H, OH-4`, OH-5`, exchangeable with D2O),
4.46–4.51 (m, 2H, OH-3`, OH-2`, exchangeable with D2O),
4.55 (dist. t, 1H, J 7.6 Hz, J 9.1 Hz, H-2`), 5.52 (dd, 1H, J
6.1 Hz, J 9.9 Hz, H-1`), 6.44 (bd, 1H, OH-1`, exchangeable
with D2O), 7.61 (t, 3H, J 3.0 Hz, Ph-H), 7.70–7.75 (m, 2H, Ph-
H), 8.16 (dist. t, 1H, J 7.6 Hz, J 1.5 Hz, quin-H6), 8.72–8.74 (m,
2H, quin-H7, quin-H8), 8.80 (d, 1H, J9,8 8.4 Hz, quin-H9). Anal.
Calcd for C20H20N4O5: C, 60.60; H, 5.09; N, 14.13; Found: C,
1
(0.88 g; 74%); mp 201–202°C: H-NMR (DMSO-d6, 500 MHz):
δ 3.30–3.36 (m, 2H, H-5`a, H-5`b H-4`, H-3`), 3.68–3.74 (m,
2H, H-4`, H-3`), 4.04 (dist. t, 1H, JOH5`,
8.6 Hz, JOH5`,
5`a
5`b
6.1 Hz, OH-5`, exchangeable with D2O), 4.19 (d, 1H, JOH4`,H4`,
6.8 Hz, OH-4` `, exchangeable with D2O), 4.37 (d, 1H, JOH3`,
7.6 Hz, OH-3`, exchangeable with D2O), 4.52–4.60 (m, 3H,
H3`,
H-2`, PhCH2), 4.94 (d, 1H, J2`,
7.1 Hz, OH-2`,
OH2`
exchangeable with D2O), 5.63 (dist. d, 1H, H-1`), 6.23 (d, 1H,
J1`, OH1` 7.6 Hz, OH-1`, exchangeable with D2O), 7.17 (dist. t,
1H, J 6.9 Hz, J 7.6 Hz, Ph-H) 7.25 (t, 2H, J 7.6 Hz, Ph-H), 7.41
(d, 2H, J 6.8 Hz, Ph-H), 8.22 (s, 1H, quin-H6), 9.31 (s, 1H,
quin-H9). Anal. Calcd for C21H20Cl2N4O5, C, 52.62; H, 4.21;
N, 11.69. Found: C, 52.93; H, 3.86; N, 11.74.
1-(D-Gluco-pentitol-1-yl)-
4-benzyl-7,8-
dichloro[1,2,4]
triazolo [4,3-a]-quinoxaline (9b).
The crude product was
recrystallized from ethyl alcohol to give colorless crystals,
1
(0.70 g, 59%); mp 220–221°C; H-NMR (DMSO-d6, 500 MHz):
δ 3.28–3.34 (m, 2H, H-5`a, H-5`b), 3.49–3.53 (m, 2H, H-4`, H-
3`), 4.31 (dist. t, 1H, JOH5`, 5`a 5.35 Hz, JOH5`, 5`b 4.5 Hz, OH-5`,
exchangeable with D2O), 4.42–4.46 (m, 3H, H-2`, PhCH2),
4.53–4.54 (bd, 2H, OH-3`, OH-4`), 4.93 (d, 1H, J2`,
OH2`
6.10 Hz, OH-2`, exchangeable with D2O), 5.37 (dist. t, 1H, J1`,
6.1 Hz, J1`, 2` 7.6 Hz, H-1`), 6.36 (d, 1H, J1`, OH1` 5.3 Hz,
OH1`
OH-1`, exchangeable with D2O), 7.18 (dist. t, 1H, J 6.8 Hz, J
7.6 Hz, Ph-H) 7.26 (t, 2H, J 7.6 Hz, Ph-H), 7.42 (d, 2H, J
7.6 Hz, Ph-H), 8.29 (s, 1H, quin-H6), 8.92 (s, 1H, quin-H9).
Anal. Calcd for C21H20Cl2N4O5, C, 52.62; H, 4.21; N, 11.69.
Found: C, 52.01; H, 4.36; N, 11.77.
59.94; H, 5.52; N, 14.31.
1-(D-Gluco-pentitol-1-yl)-4-phenyl[1,2,4]triazolo[4,3-a]
1-(D-Galacto-pentitol-1-yl)-4-benzyl-7,8-dichloro[1,2,4]
triazolo[4,3-a]-quinoxaline (9c).
The crude product was
quinoxaline (8b). The crude product was recrystallized from
ethyl alcohol to give colorless crystals, (0.71 g, 71%); mp 165–
166°C; 1H-NMR (DMSO-d6, 500 MHz): δ 3.25–3.31 (m, 2H,
H-5`a, H-5`b), 3.48–3.54 (m, 2H, H-3`, H-4`), 4.25 (t, 1H, J
5.3 Hz, OH-5`, exchangeable with D2O), 4.33 (d, 1H, JOH-4`,H4`
5.3 Hz, OH-4`, exchangeable with D2O) 4.41 (d, 1H, JOH-3`,H3`
7.6 Hz, OH-3`, exchangeable with D2O), 4.92 (d, 1H, JOH-2`,2`
6.1 Hz, OH-2`, exchangeable with D2O), 5.49 (d, 1H, J 7.6 Hz,
H-1`), 6.18 (s, 1H, OH-1`, exchangeable with D2O), 7.61 (t,
3H, J 3.05 Hz, Ph-H), 7.76 (m, 2H, Ph-H), 8.17 (d, 1H, J6,7
7.6 Hz, quin-H6), 8.74 (m, 3 H, quin-H7, quin-H8, quin-H9).
Anal. Calcd for C20H20N4O5: C, 60.60; H, 5.09; N, 14.13;
Found: C, 60.12; H, 5.12; N, 14.23.
recrystallized from methyl alcohol to give bright gray crystals,
(0.90 g, 75%); mp 245–246°C; 1H-NMR (DMSO-d6,
500 MHz): δ 3.28–3.34 (m, 2H, H-5`a, H-5`b), 3.68–3.75 (m,
2H, H-4`, H-3`), 4.02 (dist. t, 1H, JOH5`, 5`a 8.6 Hz, JOH5`, 5`b
6.1 Hz, OH-5`, exchangeable with D2O), 4.37 (d, 1H, JOH3`,H3`,
7.6 Hz, OH-3`), 4.18 (d, 1H, JOH4`,H4`, 6.8 Hz, OH-4`), 4.48–
4.59 (m, 3H, H-2`, PhCH2), 4.94 (d, 1H, J2`, OH2` 7.1 Hz, OH-
2`, exchangeable with D2O), 5.63 (dist. t, 1H, J1`, OH1` 6.9 Hz,
J1`,
1.5 Hz, H-1`), 6.24 (d, 1H, J1`,
7.6 Hz, OH-1`,
2`
OH1`
exchangeable with D2O), 7.18 (dist. t, 1H, J 6.9 Hz, J 7.6 Hz,
Ph-H) 7.27 (t, 2H, J 7.6 Hz, Ph-H), 7.42 (d, 2H, J 6.8 Hz, Ph-
H), 8.27 (s, 1H, quin-H6), 9.37 (s, 1H, quin-H9). Anal. Calcd
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

M. S. Ayoup, H. E. A. Ahmed, A. M. El Massry, S. Senior, S. N. Khattab,
S. Y. Hassan, and A. Amer
Vol 000
for C21H20Cl2N4O5, C, 52.62; H, 4.21; N, 11.69. Found: C,
52.14; H, 3.96; N, 11.68.
D2O); 13C-NMR (DMSO-d6, 125.7 MHz): major isomer δ
40.0 (PhCH2), 58.58, 64.48, 69.08, 71.66, 71.88, 122.49,
126.73, 128.64, 128.70 129.75, 129.94, 132.36, 132.72,
138.24, 144.42, 159.75, aromatic carbons for the major
isomer, 171.32 (C-2`); minor isomer δ 40.0 (PhCH2), 63.07,
64.29, 70.56, 71.96, 73.21, 122.56, 126.58, 128.58, 128.46,
129.75, 130.01, 132.36, 132.72, 138.31, 144.42, 160.13,
aromatic carbons for the minor isomer, 169.54 (C-2`). Anal.
Calcd for C21H24N4O5: C, 61.15; H, 5.87; N, 13.58. Found:
C, 60.88; H, 6.69; N, 13.72.
4-Benzyl-[1,2,4]triazolo[4,3-a]quinoxaline-1-carbaldehyde
(10). A suspension of 7a (2 g, 3.0 mmol) in water (100 mL)
was treated with a solution of sodium metaperiodate (2.6 g,
12.5 mmol) in water (25 mL). The reaction mixture was
stirred at room temperature for 4 h and then left overnight in
the dark. The product (0.6, 70% was collected, washed with
water, dried, and crystallized from ethanol to give 12 as
colorless crystals mp 120–121°C, Rf 0.70 (4:1 ethylacetate: n-
hexane); IR (KBr); ν 1680 (C¼O), 2800–2900 (OC–H) cmꢀ1
;
Method of calculations. A geometry optimization method for
suitable conformers of the open and cyclic, syn-isomers and anti-
isomers of 12 was performed on the solution phase using the DMSO
as a solvent in the continuum solvation method [18,19] using the
DFT/B3LYP/6-31++G** level incorporated in Gaussian 03 package
[20]. This method and basis set were found to give accurate
molecular geometries [21]. Isomer populations were calculated from
the following equations using the calculated solution energy [12]:
1H-NMR (CDCl3, 500 MHz): δ 4.78 (s, 2H, PhCH2,), 7.17 (t,
1H, J 6.8 Hz, Ph-H), 7.29 (t, 2H, J 7.6 Hz, Ph-H), 7.61 (d,
2H, J 7.6 Hz, Ph-H), 7.75 (m, 2H, quin-H7, quin-H8), 8.19 (d,
1H, J6,7 7.6 Hz, quin-H6), 9.4 (d, 1H, J9,8 8.4 Hz, quin-H9),
10. 47 (s, 1H, CHO). Anal. Calcd for C17H12N4O: C, 70.82;
H, 4.20; N, 19.43. Found: C, 70.52; H, 4.41; N, 19.23.
1-(D-Manno-pentitol-1-yl)-4-benzoyl[1,2,4]triazolo[4,3-a]
quinoxaline (11). To a solution of 1-(2-benzylquinoxalin-3-yl)
hydrazine 1 (2.50mmol) in methanol (25 mL), D-mannose sugar
(0.625g, 2.50mmol) and one drop of HCl (33%) were added. The
reaction mixture was heated under reflux on boiling water bath for
1 h, left to cool at room temperature, and then a solution of
bromine (0.13 mL, 2.50 mmol) in methanol (5.0mL) was added
drop wise with stirring for one day. A mixture of ethanol (3 mL)
and pyridine (0.5 mL) was added, volatile components were
evaporated in vacuum at 60°C. The residue was treated with
ethanol (95%, 10mL), then left to cool at room temperature. The
crude product that precipitated out was collected by filtration, then
washed by ethanol. The crude product was crystallized from
ethanol to afford colorless crystals, (0.61 g; 59.5%); mp 227–228°
C; 1H-NMR (DMSO-d6, 500 MHz): δ 3.52–3.85 (m, 5H, H-3`, H-
4`, H-5a`, H-5`b, OH-5`, exchangeable with D2O), 4.42–4.51(m,
4H, H-2`, OH-2`, OH-3`, OH-4`, exchangeable with D2O), 5.51
(m, 1H, H-1`), 6.49 (d, 1H, J OH-1`,1` 6.1 Hz, OH-1`, exchangeable
with D2O), 7.55–7.58 (m, 2H, Ph-H), 7.73–7.76 (m, 2H, Ph-H),
7.86 (dis. t, 1H, J 7.4 Hz, J 6.8 Hz Ph-H), 8.0–8.02 (m, 2H, quin-
H7, quin-H8), 8.13 (d, 1H, J 8.4 Hz, quin-H6), 8.85 (d, 1H, J
8.4 Hz, quin-H9). 13C-NMR (DMSO-d6, 125.7MHz): δ 64.25,
66.55, 69.40, 69.83, 71.17, 119.91, 126.85, 128.58, 129.67,
130.86, 130.94, 131.50, 134.82, 135.70, 143.55, 149.71, 153. 16,
190.91(C¼O). EI-MS: m/e 424.14 [M+]. Anal. Calcd for
C21H20N4O6: C,59.43; H, 4.75; N, 13.20. Found: C, 59.21; H,
ꢀ
ꢁ
ΔGi
RT
ni ¼ exp ꢀ
ΔGi ¼ Gi ꢀ Gj
N ¼ nA þ nB þ nC
ni
%i ¼ *100
N
where ni is the ratio number of isomers of type i and j, ΔGi is the
energy difference of isomers i and j; j is an isomer chosen arbi-
trary; R is the gas constant (1.987 cal molꢀ1 Kꢀ1), and T is the
absolute temperature (289.15 K).
Biology.
Agar-diffusion method was used for the
determination of antibacterial and antifungal activity. From each
of the test compounds in DMF (1mg/mL), 75μL was placed in
a 6-mm-diameter well in gar plate seeded with the appropriate
test organism in triplicates. Ampicillin trihydrate (10.0μg/disc),
Ciprofloxacin (5.0μg/disc), Impenam (10.0μg/disc) and
Clotrimazole (100.0 μg/disc) were used as standard antibacterial
and antifungal agents, respectively. DMF alone showed no IZ.
The plates were incubated at 37°C for 24h. The results were
recorded for each tested compound and the reference drugs as
the average diameter of IZ of bacterial growth in mm (Table 1).
4.71; N, 13.45.
D-Fructose (3-benzylquinoxalin-2-yl) hydrazones (12). To
Molecular docking.
Molecular docking studies were
a solution of 1 (2.50 mmol) and fructose (2.50 mmol) in
methanol (25 mL), one drop of HCl was added. The mixture
was heated under reflux on water-bath for 1 h and left to
cool. The pale red crystals that precipitated out was collected
by filtration (0.94 g; 91.6%); mp 185–186°C. Rf 0.51 (7:3
ethylacetate to n-hexane). IR (KBr); ν 3297 (NH, OH) and
1660 cmꢀ1 (C¼N); 1H-NMR (DMSO-d6, 500 MHz): δ 3.45–
3.69 (m, 5H, H-1`a, H-1`b, H-5`, H-6`a, H-6`b), 4.05 (s, 2H,
PhCH2), 4.31 (d, 1H, JOH4`,4` 7.6 Hz, OH-4`, exchangeable
with D2O), 4.36–4.42 (m, 2H, H-4`, OH-6` exchangeable with
D2O), 4.56 (d, 1H, JOH5`,5` 5.3 Hz, OH-5`, exchangeable with
D2O), 4.73 (d, 1H, JOH3`,3` 7.6 Hz, OH-3`, exchangeable with
D2O), 4.86 (d, 1H, J 7.6 Hz, H-3`), 5.11 (dist. t, 1H, J
6.1 Hz, J 4.6 Hz, OH-1`, exchangeable with D2O), 7.07, 7.15
(2 t, 2H, Ph-H), 7.23 (t, 3H, J 7.6 Hz, Ph-H), 7.28–7.35 (m,
3H, quin-H6, quin-H7, quin-H8), 7.50–7.54 (m, 1H, J 5.3 Hz,
J 12.9 Hz, quino-H9), 10.96 (s, 1H, N–H, exchangeable with
carried out to understand the molecular binding modes of the
active synthesized compounds toward three different biological
targets belonging to focused microorganisms. Target
compounds were docked against three biological targets
including the crystal structures of enoyl-acyl carrier protein
reductase (FabI) (Protein Data Bank (PDB) code 1C14) as E.
coli promising target, dihydropteroate synthetase (PDB code
1 AD4) as S. aureus promising target, and N-myristoyl
transferase (PDB code 1IYL) as C. albicans promising target
[22]. The proteins were considered without co-crystallized
ligands for the purpose of the docking simulations. Before
screening the active compounds, the docking protocol was
validated by running the simulation only using the bound
ligands and low rmsd between docked and crystal
conformations. AutoDock 3.0 [23] and MOE [24] softwares
were used for all docking calculations. The AutoDockTools
package [24] was employed to generate the docking input files
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2015
Synthesis, Docking, and Evaluation of Antimicrobial Activity of a New Series of
Acyclo C-Nucleosides of 1, 2, 4-Triazolo[4, 3-a]quinoxaline Derivatives
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and to analyze the docking results. A grid box size of 90 × 90 × 90
points with a spacing of 0.375 Å between the grid points was
generated that covered almost the entire protein surface. Ligands
were fully flexibly docked. All non-polar hydrogens and
crystallographic water molecules were removed prior to the
calculations. The docking grid was centered on the mass center of
the bound trichostatin A (TSA). In each case, 100 docked
structures were generated using genetic algorithm searches. A
default protocol was applied with an initial population of 50
randomly placed conformations, a maximum number of 2.5 × 105
energy evaluations, and
a maximum number of 2.7 × 104
generations. A mutation rate of 0.02 and a crossover rate of 0.8
were used. Heavy atom comparison rmsd values were calculated,
and initial ligand binding modes were plotted. Protein-ligand
interaction plots were generated using MOE 2008.10.
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Zhu, X. Tetrahedron Lett 2014, 55, 4458.
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Acknowledgment. HA gratefully acknowledge the support from
the Deanship of Scientific Research at Taibah University,
Al-Madinah Al-Munawarah, Saudi Arabia. The authors would
like to thank chemical computing group for use of the MOE
software.
REFERENCES AND NOTES
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Journal of Heterocyclic Chemistry
DOI 10.1002/jhet