Design, synthesis, and antibacterial evaluation of new quinoline-1,3,4-oxadiazole and quinoline-1,2,4-triazole hybrids as potential inhibitors of DNA gyrase and topoisomerase IV

Article abstract of DOI:10.1016/j.bioorg.2021.104920

DNA gyrase and topoisomerase IV (topo IV) inhibitors are among the most interesting antibacterial drug classes without antibacterial pipeline representative. Twenty-four new quinoline-1,3,4-oxadiazole and quinoline-1,2,4-triazole hybrids were developed and tested against DNA gyrase and topoisomerase IV from Escherichia coli and Staphylococcus aureus. The most potent compounds 4c, 4e, 4f, and 5e displayed an IC₅₀ of 34, 26, 32, and 90 nM against E. coli DNA gyrase, respectively (novobiocin, IC₅₀ = 170 nM). The activities of 4c, 4e, 4f, and 5e on DNA gyrase from S. aureus were weaker than those on E. coli gyrase. Compound 4e showed IC₅₀ values (0.47 μM and 0.92 μM) against E. coli topo IV and S. aureus topo IV, respectively in comparison to novobiocin (IC₅₀ = 11, 27 μM, respectively). Antibacterial activity against Gram-positive and Gram-negative bacterial strains has been studied. Some compounds have demonstrated superior antibacterial activity to ciprofloxacin against some of the bacterial strain studied. The most active compounds in this study showed no cytotoxic effect with cell viability>86%. Finally, a molecular docking analysis was performed to investigate the binding mode and interactions of the most active compounds to the active site of DNA gyrase and topoisomerase IV (topo IV) enzymes.

Full text of DOI:10.1016/j.bioorg.2021.104920

Bioorganic Chemistry 112 (2021) 104920
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Design, synthesis, and antibacterial evaluation of new
quinoline-1,3,4-oxadiazole and quinoline-1,2,4-triazole hybrids as
potential inhibitors of DNA gyrase and topoisomerase IV
,
d
Heba A. Hofnya, Mamdouh F.A. Mohameda, Hesham A.M. Gomaab, Salah A. Abdel-Azizc
,
,
,
f
,
,*
Bahaa G.M. Youssife *, Nawal A. El-koussid *, Ahmed S. Aboraiaf
a Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Sohag University, 82524 Sohag, Egypt
b Pharmacology Department, College of Pharmacy, Jouf University, Sakaka, Aljouf 72341, Saudi Arabia
c Department of Pharmaceutical Medicinal Chemistry, Faculty of Pharmacy, Al-Azhar University, Assiut 71524, Egypt
d Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Deraya University, Minia 61519, Egypt
e Pharmaceutical Organic Chemistry Department, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
f Medicinal Chemistry Department, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt
A R T I C L E I N F O
A B S T R A C T
Keywords:
Quinoline
Oxadiazole
Triazole
DNA gyrase and topoisomerase IV (topo IV) inhibitors are among the most interesting antibacterial drug classes
without antibacterial pipeline representative. Twenty-four new quinoline-1,3,4-oxadiazole and quinoline-1,2,4-
triazole hybrids were developed and tested against DNA gyrase and topoisomerase IV from Escherichia coli and
Staphylococcus aureus. The most potent compounds 4c, 4e, 4f, and 5e displayed an IC50 of 34, 26, 32, and 90 nM
against E. coli DNA gyrase, respectively (novobiocin, IC50 = 170 nM). The activities of 4c, 4e, 4f, and 5e on DNA
gyrase from S. aureus were weaker than those on E. coli gyrase. Compound 4e showed IC50 values (0.47 µM and
0.92 µM) against E. coli topo IV and S. aureus topo IV, respectively in comparison to novobiocin (IC50 = 11, 27
µM, respectively). Antibacterial activity against Gram-positive and Gram-negative bacterial strains has been
studied. Some compounds have demonstrated superior antibacterial activity to ciprofloxacin against some of the
bacterial strain studied. The most active compounds in this study showed no cytotoxic effect with cell
viability>86%. Finally, a molecular docking analysis was performed to investigate the binding mode and in-
teractions of the most active compounds to the active site of DNA gyrase and topoisomerase IV (topo IV)
enzymes.
Gyrase
Topoisomerase
1. Introduction
made efforts to expand new agents. Many natural and synthetic products
contain quinoline rings which show a variety of activity including
Despite significant developments in pharmaceutical and medicinal
chemistry, bacterial and fungal infectious diseases remain one of the
major health risks for the population. While many antimicrobial drugs
are used and successful in the clinic, as microorganisms quickly build
resistance to these drugs, they become less productive in a short time
[1]. It has been estimated that 700,000 people in the world die every
year from antibiotic-resistant infectious bacterial diseases. In the
absence of new prevention or treatment remedies, by 2050, it is esti-
mated that 10 million people worldwide will die of these infectious
diseases each year [2]. The discovery of new and more effective anti-
microbial drugs is therefore very important, and many studies have
antimicrobial [3,4]. DNA gyrase and topoisomerase IV are top-
oisomerases of type II present in bacteria. Although clearly related,
based on the similarity of the amino acid sequence, each plays a crucial
but distinct role in the cell. Gyrase is involved primarily in supporting
nascent chain elongation during replication of the chromosome,
whereas topoisomerase IV separates the topologically linked daughter
chromosomes during the terminal stage of DNA replication [5]. Quin-
olines are topoisomerase II (DNA gyrase) and topoisomerase IV in-
hibitors that play a pivotal role in the replication, transcription, and
recombination of bacterial cell DNA. Inhibiting this enzyme is an
important target for the discovery and development of new antibacterial
* Corresponding authors at: Medicinal Chemistry Department, Faculty of Pharmacy, Assiut University, Assiut 71526, Egypt (N. El-Koussi).
E-mail addresses: bahaa.youssif@pharm.aun.edu.eg, bgyoussif@ju.edu.sa (B.G.M. Youssif), nawal.abdelhalim@pharm.aun.edu.eg, nawal.abdelhalim@deraya.
edu.eg (N.A. El-koussi), ahmed.mohamed15@pharm.au.edu.eg (A.S. Aboraia).
https://doi.org/10.1016/j.bioorg.2021.104920
Received 26 January 2021; Received in revised form 12 March 2021; Accepted 14 April 2021
Available online 19 April 2021
0045-2068/© 2021 Elsevier Inc. All rights reserved.

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
drugs, as it prevents them from multiplying by dividing bacteria [6].
Recent studies have examined the antimicrobial activity of quinoline
ring-bearing compounds against existing bacteria and have reported
that certain derivatives are more effective than standard drugs [5,6].
1.3,4-oxadiazole heterocycles are on the other hand excellent bio-
isosteres of amides and esters, which contribute significantly to
increased pharmacological activity by involvement in hydrogen
bonding interactions with receptors [7]. A broad range of bioactivity,
such as antivirals [8], antimicrobials [9] and antimalarials [10], can be
found in oxadiazol derivatives, which play a major role in various
pharmaceutical applications.
the prepared compounds was confirmed by elemental analysis and the
results are in consistent with the molecular formula of the products.
Stirring compound 3 with (un)substituted phenacyl bromide, alkyl io-
dide, and aryl chloride in DMF/K2CO3 yields compounds 4c-j in good
yields.
The N-alkyl derivatives of 5-(2-phenylquinolin-4-yl)-1,3,4-oxadia-
zole-2(3H)-thione 5a-e were prepared by stirring a solution of com-
pound 3 with formaldehyde and appropriate amine in EtOH. The 1H
NMR spectrum of 5d revealed the appearance of a methylene signal of
the NH-CH2 group at δ 5.72 (s) ppm and ethyl group signals at δ 4.24
(2H, q, OCH2CH3) and δ 1.30 (3H, t, OCH2CH3). The 13C NMR spectrum
of 5d showed the characteristic methylene carbon (NH-CH2-N) at 60.22
In addition, due to their synthetic and competitive biological sig-
nificance, the chemistry of triazoles and their fused heterocyclic de-
rivatives received substantial attention. For example, a large number of
ring systems containing 1,2,4-triazole were integrated into a wide va-
riety of therapeutically interesting drug candidates including antibac-
terial, antimycobacterial, antifungal, and antiviral [11–13].
–
ppm and the C O of COOCH CH at 165.42 ppm. The olefinic and ar-
–
2
3
omatic carbons appeared at their expected chemical shifts
2-Phenyl-quinoline-4-carboxylic acid hydrazide 2 was reacted with
phenyl isothiocyanate in refluxing EtOH to yield 6 [21] which subse-
quently cyclised with NaOH to afford 1,2,4-triazole-3-thione 7 [22]. The
target compounds 8a-e and 9a-d were synthesized by the same pro-
cedures for 4a-j and 5a-e, respectively. Newly synthesized compounds
8a-e and 9a-d were distinguished by the presence of extra peaks do not
present in the starting material 1,2,4-triazole-3-thione 7 in both the 1H
NMR and 13C NMR spectra.
Molecular hybridization is currently seen as a promising technique in
which two or more biologically active scaffolds are combined to produce
novel agents against the desired drug target [14–17]. With a molecular
hybridization approach, we developed two new scaffolds A and B
(Fig. 1) to investigate their inhibitory activity against E. coli DNA gyrase.
Compounds with sub micromolar IC50 values will be evaluated against
S. aureus DNA gyrase, and E. coli and S. aureus topoisomerase IV.
Moreover, the antibacterial activity of the most active compounds will
be tested using the twofold serial dilution method with ciprofloxacin as a
reference. The most active compounds will be evaluated for cell viability
effect using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro-
mide (MTT) assay. Finally, a molecular docking analysis was performed
to investigate the binding mode and interactions of the most active
compounds to the active site of DNA gyrase and topoisomerase IV (topo
IV) enzymes.
2.2. Pharmacological evaluation
2.2.1. Inhibitory activity against E. Coli DNA gyrase
All final compounds were evaluated for their inhibitory activity
against E. coli DNA gyrase in a supercoiling assay [23]. Results are
presented as residual activities (RAs) of the enzyme at 1 µM of com-
pounds or as IC50 values for compounds with RA < 50% (Tables 1).
Generally, compounds 4c, 4e, 4f, 5e, and 8e showed inhibitory activities
stronger than that of novobiocin (IC50 = 170 nM) against E. coli DNA
gyrase, with low nanomolar inhibitory values (IC50 = 90 nM, except for
8e, IC50 = 180 nM). Four of the five most active compounds (4c, 4e, 4f,
and 5e) contained the 1,3,4-oxadiazole moiety in their backbone (X ¼
O, Fig. 1), which thus proved to be more active than derivatives of
phenyl-1,2,4-triazole backbone structures (X ¼ N-Ph, Fig. 1), probably
because the phenyl-1,2,4-triazole moiety is too large to fit into the
binding site of the enzyme. The most potent three compounds 4c, 4e and
4f with IC50 (34, 26 and 32 nM) and all containing (un)substituted
phenacyl group, 1,3,4-oxadiazole-5-thiol moiety, and phenyl quinoline
core. Also, presence of (un)substituted benzyl moiety with 1,3,4-oxadia-
zole-5-thiol, and phenyl quinoline cores enhance potency against DNA
gyrase as 4i and 4j with IC50 (400 and 380 nM), while presence of alkyl
group in the same nucleus showed moderate activity as 4 g (R ¼ Me)
and 4 h (R ¼ Ethyl) (RA = 58% and 64%). Compounds 4a [R ¼
CH2CH2–(1-morpholine)] and 4b [R ¼ –CH2 CH2-N(CH3)2] were almost
inactive at 1 µM concentration (RA = 89%, 100%). According to data
presented in Table 1, the only 1,3,4-oxadiazole-2-thione derivative with
activity in the low nanomolar range was compound 5e (R1 = NH-C6H4-
(3-F)) with an IC50 value of 90 nM.
2. Results and discussion
2.1. Chemistry
The preparation of target compounds 4a-j, 5a-e, 8a-e, and 9a-d was
described in Scheme 1. Aniline was reacted with benzaldehyde and
pyruvic acid in EtOH to yield 2-phenyl-quinoline-4-carboxylic acid 1
[18] which subsequently, after activation, reacted with hydrazine hy-
drate to afford 2-phenyl-quinoline-4-carboxylic acid hydrazide 2 [19].
Compound 2 was cyclized with CS2 and KOH in EtOH to give 5-(2-
phenyl-quinolin-4-yl)-1,3,4-oxadiazole-2-thione 3 [20]. Reflux com-
pound 3 with 4-(2-chloroethyl) morpholine hydrochloride or (2-chlor-
oethyl) dimethylamine in EtOH/sodium acetate gives compounds 4a
and 4b, respectively. 1H NMR spectrum of compound 4b showed three
common signals appeared as singlet at δ 2.39 ppm related to N(CH3)2,
triplet at 2.86 (2H) and triplet at 3.57 (2H) of (S-CH2CH2N). The aro-
matic protons appeared at their expected chemical shifts. The purity of
2.2.2. Inhibitory activity against S. Aureus DNA gyrase and topoisomerase
IV
Compounds with sub micromolar IC50 values were evaluated against
S. aureus DNA gyrase, and E. coli and S. aureus topoisomerase IV [23],
Table 3. In general, the activities on DNA gyrase from S. aureus were
weaker than those on E. coli gyrase, but compounds 4c, 4e and 4f that
were among the most potent inhibitors of E. coli gyrase also displayed
promising results on DNA gyrase from S. aureus (Table 2). 4c, 4e and 4f
have IC50 values in the sub micromolar range (<1 µM) against DNA
gyrase from S. aureus (IC50 = 0.79, 0.24, and 0.49, respectively), which
are much higher (less potent) than that for novobiocin (IC50 = 0.041
µM).
The activities of compounds 4c, 4e, 4f, 5e, and 8e on topo IV from
E. coli and S. aureus were superior to those of the reference novobiocin.
Fig. 1. Rational design of the new targets 4a-j, 5a-e, 8a-e, and 9a-d.
2

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
Scheme 1. Synthesis of target compounds 4a-j, 5a-e, 8a-e, and 9a-d. Reagents and conditions: (i) EtOH, Reflux, 3 h; (ii) ClCOOC2H5/TEA, DMF; (iii)
NH2NH2⋅H2O; (iv) CS2/KOH, EtOH, reflux; (v) K2CO3, DMF, RX (vi) HCHO 40%, different amines; (vii) C6H5NCS, EtOH, reflux; (viii) NaOH, reflux, HCl; (ix) K2CO3,
DMF, RX; (x) HCHO 40%, different amines.
Compounds 4c, 4e and 4f displayed promising results on both enzymes
(Table 2) with IC50 values in the sub micromolar range (<9 µM) against
E. coli topo IV, which is much lower than that for novobiocin (IC50 = 11
µM). Compound 4e with 4-methoxyphenacyl substituent showed IC50
values (0.47 µM and 0.92 µM) against E. coli topo IV and S. aureus topo
IV, respectively in comparison to novobiocin (IC50 = 11, 27 µM,
respectively). Compound 4f comes second in efficiency where it displays
a balanced activity against all four enzymes tested, with IC50 of 1.1 µM
against S. aureus topo IV (IC50 of novobiocin is 27 µM) and thus both 4e
and 4f appear to be promising dual target inhibitors. Compounds 5e and
8e did not display the same potency on the other three enzymes.
The results of the DNA gyrase and topoisomerase IV inhibitory assays
highlighted the importance of oxadiazole moiety for inhibitory activity,
which correlates to the previous study on the importance of oxadiazole
moiety as a balanced pharmacophore to inhibit DNA gyrase and
topoisomerase IV [24].
2.2.3. Antibacterial activity
The antibacterial activity of the most active compounds 4c, 4e, 4f,
5e, and 8e was tested using the twofold serial dilution method [25] with
ciprofloxacin as a reference. Overall, compounds 4c, 4e, 4f, 5e, and 8e
demonstrated greater Gram-positive inhibitory activity than Gram-
negative bacteria, Table 3. Compound 4e exhibited the strongest anti-
bacterial activity with a MIC value of 10 ng/ml against S. aureus, which
is three-fold lower than that of ciprofloxacin (30 ng/ml), and of 25 ng/
ml against E. coli in comparison to ciprofloxacin (MIC = 60 ng/ml).
Compound 4f showed MIC values comparable to that of ciprofloxacin
against the four tested species. Compounds 5e and 8e demonstrated
weak inhibitory activity against B. subtilis and P. aeruginosa with MIC
values>100 ng/ml. Finally, 4c showed no antibacterial activity against
3

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
the tested Gram-negative bacterial strains.
Table 1
Inhibitory activity of compounds 4a-j, 5a-e, 8a-e, 9a-i and novobiocin against
DNA gyrase from E. coli.
2.2.4. Cell viability assay
Compound
R
R1
IC50 (nM)a or RA
Cell viability testing was performed using the human mammary
gland cell line (MCF-10A) [26,27]. 4c, 4e, 4f, 5e, and 8e have been
incubated with MCF-10A cells for 4 days and MTT assay has been used to
determine cell viability. The test results showed no cytotoxic effects for
all the compounds reported and the viability of the cells for the tested
(%) b
E. Coli DNA
gyrase
4a
–CH2CH2-(1-
–
89%
morpholine)
compounds was>86% at 50 μM, Table 4.
4b
4c
4d
–CH2CH2-N(CH3)2
–
–
–
100%
–CH2-CO-C6H5
34 ± 1 nM
84%
–CH2-CO-NH-C6H4-(4-
2.3. Molecular docking study
2.3.1. E. Coli DNA gyrase B
COCH3)
4e
–CH2-CO-C6H4-(4-
–
26 ± 7 nM
OCH3)
4f
–CH2-CO-C6H4-(4-Br)
–
32 ± 9 nM
58%
Docking simulations were performed to study the binding pattern of
the newly synthesized compounds in E. coli DNA gyrase B active site to
predict their binding pattern and to investigate their ability to satisfy the
required structural features for binding interactions.
4 g
4 h
4i
–CH3
–
-C2H5
–
64%
–CH2-C6H5
–
400 ± 40 nM
380 ± 30 nM
69%
4j
–CH2-C6H4-(4-Cl)
–
5a
5b
5c
5d
–
–
–
–
1-morpholine
1-phenylpiperazine
–NH-C6H4-(4-COOH)
–NH-C6H4-(4-
COOC2H5)
The docking setup was first validated by performing redocking of the
co-crystalized thiazole inhibitor in the active site of E. coli DNA gyrase B
(PDB ID: 4DUH) [28,29]. The redocking validation reproduced the co-
crystallized thiazole indicating that the docking protocol used is suit-
able for the intended docking study. This is shown by the small RMSD
between the experimental co-crystallized inhibitor pose and the docked
pose of 0.566 Å; and by the capability of the docking pose to reproduce
all the key interactions achieved by the co-crystallized ligands in the
active site. the docking energy score was S = -17.25 kcal/mol. Arg76,
Arg136 interact with Ph-COO- through H-bonding and Arg76 interact
with Ph functional by arene-cation interaction. Lys103 interact with
thiazole moiety by arene-cation interaction. Lys101 interact with Ph-NH
function by H-bonding Gly77 with Asp73, and Thr165 with N3H thia-
zole by H-bonding through Water Bridge (Table 5 and Fig. 2).
69%
67%
89%
5e
8a
–
–NH-C6H4-(3-F)
–
90 ± 10 nM
–CH2CH2-(1-
84%
morpholine)
8b
8c
8d
8e
–CH2 CH2-N(CH3)2
–
–
–
–
100%
–CH3
57%
–CH2-C6H4-(4-Cl)
470 ± 70 nM
180 ± 20 nM
–CH2-CO-C6H4-(4-
OCH3)
9a
9b
9c
9d
–
–
–
–
1-morpholine
1-phenylpiperazine
–NH-C6H4-(4-COOH)
–NH-C6H4-(4-
COOC2H5)
87%
84%
89%
67%
Analysis of the molecular docking results showed that compounds
4e, and 4f could fit into the E. coli DNA gyrase B binding site with
docking energy scores ꢀ 15.99, and ꢀ 14.25 kcal/mol, respectively. The
two most active compounds 4e and 4f achieve hydrogen bonding and
hydrophobic interactions with the key amino acids Arg76 and Lys103,
Asn46. In compound 4e, Arg76 interacts with benzene and pyridine
rings of quinolone and oxadiazole rings by arene-cation interaction,
Arg136 interacts with Ph functional by arene-cation interactions.
Thr165 interact with oxygen carbonyl by H-bonding. Gly77 with Asp73,
and Thr165 interact with oxygen carbonyl by H-bonding through water
bridge. Methoxy oxygen interacts with Ala100. Asn46, and Val120 by H-
bonding through bridge of two water molecules. In compound 4f, Arg76
interact by arene-cation interaction with the benzene and pyridine rings
of quinoline, Lys103 interact by arene-cation interaction with oxadia-
zole ring. Asn46 and Lys103 interact with oxygen carbonyl by H-
bonding through water Bridge. Bromine of Ph-Br interacts by hydro-
phobic interaction with amino acids faced to it (Val43, Thr165) and
interacts by halogen bond with Val71 (θ1 angle 170.10) (Table 4 and
Figs. 3, 4).
Novobiocin
a
———
———
170 ± 20 nM
Concentration of compound that inhibits the enzyme activity by 50%.
b
Residual activity of the enzyme at 1 µM of the compound.
Table 2
Inhibitory activity of selected compounds 4c, 4e, 4f, 5e, and 8e against DNA
gyrase from S. aureus and topoisomerase IV from E. coli and S. aureus.
Compound
IC50 (µM)a or RA (%) b
S. aureus gyrase
E. coli topo IV
S. aureus topo IV
4c
0.79 ± 0.1 µM
0.24 ± 0.02 µM
0.49 ± 0.09 µM
1.4 ± 0.15 µM
1.1 ± 0.2 µM
9 ± 0.20 µM
0.47 ± 0.06 µM
6.8 ± 0.20 µM
89%
11 ± 0.20 µM
0.92 ± 0.10 µM
1.1 ± 0.10 µM
3.2 ± 0.20 µM
19 ± 0.20 µM
27 ± 7 µM
4e
4f
5e
8e
100%
Novobiocin
0.041 ± 0.07 µM
11 ± 2 µM
Table 3
Antibacterial activity of compounds 4c, 4e, 4f, 5e, 8e, and ciprofloxacin.
2.3.2. E. Coli topoisomerase IV
Minimum inhibitory concentration (MIC) in ng/ml
The docking setup was first validated by performing redocking of the
co-crystalized 2-benzimidazolylurea inhibitor in the active site of E. coli
DNA topoisomerase (PDB ID: PDB code: 3FV5) [30]. The redocking
Bacterial species
(G-)
Compound
(G+)
P. aeruginosa
E. coli
S. aureus
B. subtilis
Table 4
>100
40
>100
25
62
10
35
35
40
30
80
4c
Cell Viability assay of compounds 4c, 4e, 4f, 5e,
and 8e.
12
4e
64
62
10
4f
>100
>100
60
62
>100
>100
10
5e
Comp.
Cell viability %
>100
60
8e
4c
4e
4f
86
89
92
96
89
Ciprofloxacin
5e
8e
4

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
co-crystallized ligands in the active site. The docking energy score was S
= -14.60 kcal/mol. Arg132 interact with N of pyridine through H-
bonding, Arg72 interact with pyridine ring by arene-cation interaction.
Asn42 interact with acetyl oxygen by H-bonding though water bridge.
Gly73, Thr163, and Asp69 interact with N3 benzimidazole by H-
bonding through Water Bridge. Asp69 interact with N1H, and NH3 urea
by H-bonding, Ser43 interact with NH3 urea by H-bonding (Table 6,
Fig. 5).
Table 5
Binding scores, amino acid interactions and bond lengths of the selected com-
pounds within the active site of E. coli DNA gyrase B.
Compound
Binding
scores
(kcal/
Ligand atom
Residue
Interaction
Bond
length
(A0)
molꢀ 1
)
4e
ꢀ 15.99
Benzene
ring of
Arg76
Arg76
Arg76
Lys103
Arg136
Thr165
H2O -
Arene-
cation
Arene-
cation
Arene-
cation
Arene-
cation
Arene-
cation
H-bond
H-bond
H-bond
H-bond
-
-
Analysis of the molecular docking results showed that compounds
4e, and 4f could fit into the E. coli DNA topoisomerase IV binding site
with docking energy scores ꢀ 15.84, and ꢀ 14.55 kcal/mol, respectively.
Compounds 4e, and 4f interact with key amino acids achieved hydrogen
bonding and hydrophobic interaction with the co-crystalized ligand
Arg72 and Asn42. 4e and 4f achieve hydrogen bonding by carbonyl
oxygen with Asn42 through water bridge, and hydrophobic arene-cation
interaction for benzene and pyridine rings of quinoline with Arg72.
Methoxy oxygen of compound 4e interacts with Ser43 through H-
bonding, and bromine of Ph-Br moiety in compound 4f interacts with
Val67 through halogen bond (θ1 angle 154.20). (Table 5, and Figs. 6, 7)
quinolone
Pyridine
ring of
-
-
-
quinoline
Oxadiazole
Oxadiazole
Ph of
2.71
2.8
2.88
2.59
H2O–
H2O–
Quinoline-
Ph
–
–
O of C
O
O
–
O of C
–
O of OMe
O of OMe
Benzene
ring of
4f
ꢀ 14.25
ꢀ 17.25
Arg76
Arene-
cation
Arene-
cation
H-bond
Halogen
bond
-
Arg76
-
3. Conclusion
quinolone
Pyridine
ring of
H2O–Val71
3.10
3.7
Overall, twenty-four compounds have been designed, synthesized,
and evaluated against DNA gyrase and only the most active compounds
against topoisomerase IV. The most potent three compounds 4c, 4e and
4f with IC50 (34, 26 and 32 nM) and all containing (un)substituted
phenacyl group, 1,3,4-oxadiazole-5-thiol moiety, and phenyl quinoline
core. Compound 4e had an IC50 value of 26 nM against E. coli gyrase and
0.24 µM against S. aureus gyrase and was active against E. coli topo IV
(IC50 = 0.47 µM) and S. aureus topo IV (IC50 = 0.92 µM) as well. Com-
pound 4f is second in efficiency, demonstrating a balanced activity
against all four tested enzymes, with IC50 of 1.1 µM against S. aureus
topo IV (IC50 of novobiocin is 27 µM) and thus both 4e and 4f appear to
be promising dual target inhibitors for further optimization. Based on
the promising in vitro inhibition results of compounds 4e, 4f against
E. coli DNA gyrase B and E. coli DNA topoisomerase IV, a molecular
docking study was performed. Compounds 4e and 4e revealed a good
fitting and favorable binding interactions with key amino acids bond to
native ligands.
quinoline
N of
oxadiazole
Br of Ph-Br
O- of Ph-
COO-
Ligand
Arg76
Arg76
Arg136
Arg136
Gly101
Lys103
H2O -
H-bond
Arene-
cation
2.83
-
inhibitor
Ph ring
2.49
2.71
2.01
-
–
O of C
–
O
H-bond
H-bond
H-bond
Arene-
cation
on of Ph-
COO-
–
–
O of C
O
1.88
on of Ph-
COO-
H-bond
NH of Ph-
NH
Thiazole
N3H of
Thiazole
validation reproduced the co-crystallized inhibitor indicating that the
docking protocol used is suitable for the intended docking study. This is
shown by the small RMSD between the experimental co-crystallized
inhibitor pose and the docked pose of 1.07 Å; and by the capability of
the docking pose to reproduce all the key interactions achieved by the
4. Experimental
4.1. Chemistry
General Details. See Appendix A
Fig. 2. 2D diagram representation of (left side) and 3D diagram representation (right side) of thiazole inhibitor docked into E. coli DNA gyrase B active site showing
his binding interactions with the amino acids binding site.
5

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
Fig. 3. 2D diagram representation of (left side) and 3D diagram representation (right side) of compound 4e docked into E. coli DNA gyrase B active site showing his
binding interactions with the amino acids binding site.
Fig. 4. 2D diagram representation of (left side) and 3D diagram representation (right side) of compound 4f docked into E. coli DNA gyrase B active site showing his
binding interactions with the amino acids binding site.
Compounds 1 [18], 2 [19], 3 [20], 6 [21], and 7 [22] were prepared
118.23, 122.53, 125.93, 128.98, 129.86, 130.38, 138.67,149.26, 156.76
(quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 127.46 (2C), 128.18
(2C), 128.37, 130.54 (phenyl C-2/6, 3/5, 4, 1 respectively), 164.40,
165.84 (oxadiazole C-5, 2 respectively). Anal. Calcd. For C23H22N4O2S
(418.51): C, 66.01; H, 5.30; N, 13.39; S, 7.66. Found: C, 65.89; H, 5.48;
N, 13.61; S, 7.84.
according to reported procedures.
4.1.1. General procedure for the preparation of S-alkyl derivatives of 5-(2-
phenylquinolin-4-yl)-1,3,4-oxadiazole-2(3H)-thione (4a,b).
A mixture of 3 (0.22 g, 0.72 mmol), sodium acetate (0.31 g, 3.8
mmol) and 4-(2-chloroethyl) morpholine hydrochloride or (2-chlor-
oethyl) dimethylamine (0.72 mmol) in 10 ml of EtOH was heated under
reflux for 10 h. The solvent was removed under reduced pressure and the
residue was triturated with water. The solid product formed was filtered
off and recrystalized from EtOH.
4.1.1.2. 2-(5-(2-Phenylquinolin-4-yl)-1,3,4-oxadiazol-2-ylthio)-N,N-
dimethyl ethanamine 4b. Recrystallization from ethanol; yield: 70%; mp:
ꢀ 1
112–114 ◦C. IR (KBr, ύ, cm ): 3030 (Ar–CH str), 2998 (aliph
– –
H C-
str), 1628 (C N), 1600–1450 (Ar-C C str). 1H NMR (400 MHz,
–
–
–
–
DMSO‑d6, δppm): 2.39 (s, 6H, N-(CH3)2), 2.86 (t, 2H, J = 8 Hz, S-CH2-
4.1.1.1. 4-(5-(2-Morpholinoethylthio)-1,3,4-oxadiazol-2-yl)-2-phenyl
CH2-N), 3.57 (t, 2H, J = 8 Hz, S-CH2-CH2-N), 7.52–7.60 (m, 3H, Ar-
quinoline 4a. Recrystallization from ethanol; yield: 60%; mp:
C3,4&5-H), 7.68 (t, 1H, J = 8 Hz, quinolyl-C6-H), 7.82 (t, 1H, J = 8 Hz,
ꢀ 1
144–146 ◦C. IR (KBr, ύ, cm ): 3015 (Ar–CH), 2998 (aliph
C- str),
quinolyl-C7-H), 8.23 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.28 (d, 1H, J = 8 Hz,
quinolyl-C5-H), 8.42 (s, 1H, quinolyl-C3-H), 9.16 (d, 1H, J = 8 Hz, qui-
nolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm): 30.95 (N-(CH3)2
(2C)), 45.08 (S-CH2-CH2-N), 57.64(S-CH2-CH2-N), 118.24, 122.56,
125.95, 128.96, 129.83, 130.34, 138.69, 149.23, 156.75 (quinoline C-3,
6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 127.47 (2C), 128.13 (2C), 128.43,
130.50 (phenyl C-2/6, 3/5, 4, 1 respectively), 164.32, 165.99 (oxadia-
zole C-5, 2 respectively). Anal. Calcd. For C21H20N4OS (376.47): C,
67.00; H, 5.35; N, 14.88; S, 8.52. Found: C, 66.88; H, 5.59; N, 14.65; S,
– –
H
1
–
–
–
–
1622 (C N); 1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d ,
6
δppm): 2.63 (s, 4H, N-(CH2)2), 2.94 (t, 2H, J = 8 Hz, S-CH2-CH2-N), 3.61
(t, 2H, J = 8 Hz, S-CH2-CH2-N), 3.77 (s, 4H, O-(CH2)2), 7.51–7.60 (m,
3H, Ar-C3,4&5-H), 7.69 (t, 1H, J = 8 Hz, quinolyl-C6-H), 7.82 (t, 1H, J =
8 Hz, quinolyl-C7-H), 8.24 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.27 (d, 1H, J =
8 Hz, quinolyl-C5-H), 8.43 (s, 1H, quinolyl-C3-H), 9.16 (d, 1H, J = 8 Hz,
quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm): 30.05 (N-CH2
(2C)), 53.25(S-CH2-CH2-N), 56.78 (S-CH2-CH2-N), 66.62 (O-CH2(2C)),
6

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
8.78.
Table 6
Binding scores, amino acid interactions and bond lengths of the selected com-
pounds within the active site of E. coli DNA topoisomerase IV.
4.1.2. General method for synthesis of S-alkyl derivatives of 5-(2-phenyl
quinolin-4-yl)-1,3,4-oxadiazole-2(3H)-thione 4c-j
Compound
Binding
scores
(kcal/
Ligand atom
Residue
Interaction
Bond
length
(A0)
To the stirred solution of 3 (0.9 g, 3 mmol) and potassium carbonate
(0.45 g, 3 mmol) in DMF (20 ml), one-portion solution of substituted
phenacyl bromide (3 mmol) was added at room temperature. The re-
action mixture was stirred for 2 h. The precipitate formed was filtered
and washed with water. The same method was used for alkyl iodide, aryl
chloride.
molꢀ 1
)
4e
ꢀ 15.84
Benzene ring of
quinoline
Arg72
Arg72
H2O -
Ser43
Arene-
cation
-
-
Pyridine ring of
quinoline
Arene-
cation
2.87
2.95
O of CO
H-bond
H-bond
Arene-
cation
O of OMe
4.1.2.1. 2-(5-(2-Phenylquinolin-4-yl)-1,3,4-oxadiazol-2-ylthio)-1-phenyl-
4f
ꢀ 14.55
Benzene ring of
quinoline
Arg72
Arg72
H2O -
Val67
-
ethanone 4c. Recrystallization from EtOH; yield: 65%; mp: 185–187 ◦C.
-
IR (KBr, ύ, cmꢀ 1): 3030 (Ar–CH str), 1710 (C O), 1628 (C N),
–
–
–
–
Pyridine ring of
quinoline
Arene-
cation
2.95
3.30
1
–
–
1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d , δppm): 5.30 (s,
2H, S-CH2-CO),7.56–7.64 (m, 5H, (3H, Ar-C3,4&5-H) 6and (2H, CO-Ar-
O of CO
H-bond
Halogen-
bond
Br of Ph-Br
C
3&5-H)), 7.72–7.79 (m, 2H, (1H, quinolyl-C6-H) and (1H, CO-Ar-C4-
H)), 7.9 (t, 1H, J = 8 Hz, quinolyl-C7-H), 8.12 (d, 2H, J = 8 Hz, CO-Ar-
Ligand
ꢀ 14.60
Pyridine
Arg72
Arg132
H2O–
Arene-
cation
-
C
2&6-H), 8.21 (d, 1H, J = 8 Hz, quinolyl-C5-H), 8.27 (d, 2H, J = 8 Hz, Ar-
2&6-H),8.5 (s, 1H, quinolyl-C3-H), 9.00 (d, 1H, J = 8 Hz, quinolyl-C8-
inhibitor
N of Pyridine
O of acetyl
N3 of
2.95
2.64
2.64
1.64
2.05
2.23
C
H-bond
H-bond
H-bond
H-bond
H-bond
H-bond
H). 13C NMR (100 MHz, DMSO‑d6, δppm): 40.99 (S-CH2-CO), 118.70,
122.40, 125.94, 128.98, 129.44, 130.61, 138.13, 148.84, 156.12
(quinoline C-3, 6,5,4a,7,8,4,8a, 2 respectively), 127.72 (2C), 128.62
(2C), 128.89, 131.23 (phenyl C-2/6, 3/5,4,1 respectively), 129.45,
H2O–
benzimidazole
N1H of urea
N3H of urea
N3H of urea
Asp69
Asp69
Ser43
–
–
130.55,134.52, 135.61 (O C-C H ), 164.12, 165.12 (oxadiazole C-5, 2
6
5
–
–
respectively), 193.09 (C O). Anal. Calcd. for C25H17N3O2S (423.49):
C, 70.90; H, 4.05; N, 9.92; S, 7.57. Found: C, 71.04; H, 4.47; N, 10.18; S,
Fig. 5. 2D diagram representation of (left side) and 3D diagram representation (right side) of benzimidazol-2-ylurea inhibitor docked into E. coli DNA topoisomerase
IV active site showing his binding interactions with the amino acids binding site.
Fig. 6. 2D diagram representation of (left side) and 3D diagram representation (right side) of 4e docked into E. coli DNA topoisomerase IV active site showing his
binding interactions with the amino acids binding site.
7

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
Fig. 7. 2D diagram representation of (left side) and 3D diagram representation (right side) of 4f docked into E. coli DNA topoisomerase IV active site showing his
binding interactions with the amino acids binding site.
7.50
2H, S-CH2-CO), 7.54–7.62 (m, 3H, Ar-C3,4&5-H), 7.7–7.74 (m, 3H, (1H,
quinolyl -C6-H) and (2H, CO-Ar-C2&6-H)), 7.84 (t, 1H, J = 8 Hz, quinolyl-
C7-H), 7.97 (d, 2H, J = 8 Hz, CO-Ar-C3&5-H), 8.26 (d, 2H, J = 8 Hz, Ar-
4.1.2.2. 2-(5-(2-Phenylquinolin-4-yl)-1,3,4-oxadiazol-2-ylthio)-N-(4-ace-
C2&6-H), 8.32 (d, 1H, J = 8 Hz, quinolyl-C5-H), 8.46 (s, 1H, quinolyl-C3-
tylphenyl) acetamide 4d. Recrystallization from EtOH; yield: 51%; mp:
ꢀ 1
228–230 ◦C. IR (KBr, ύ, cm ): 3490 (NH), 3032 (Ar
– –
H C- str), 1715
H), 9.14 (d, 1H, J = 8 Hz, quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6,
δppm): 41.46 (S-CH2-CO), 118.76, 122.50, 125.89, 128.80, 129.41,
130.54, 138.28, 148.94, 156.46 (quinoline C-3, 6,5,4a,7,8,4,8a, 2
respectively), 127.72 (2C), 128.71 (2C), 129.40, 132.48 (phenyl C-2/6,
–
–
–
–
–
(O C-CH ), 1650 (O C-NH), 1664 and 1550 (C N), 1600–1450 (Ar-
–
3
1
–
–
–
–
C
C str). H NMR (400 MHz, DMSO‑d , δppm): 2.56 (s, 3H, O C-CH ),
5.30(s, 2H, S-CH2-CO), 7.58–7.65 (m,63H, Ar-C3,4&5-H), 7.79–7.82 (m,
3H, (1H, quinolyl-C6-H) and (2H, NH-Ar-C2&6-H),), 7.91 (t, 1H, J = 4 Hz,
quinolyl-C7-H), 8.03 (d, 2H, J = 8 Hz, NH-Ar-C3&5-H), 8.21 (d, 1H, J = 8
Hz, quinolyl-C5-H), 8.27 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.48 (s, 1H,
quinolyl-C3-H), 9.12 (d, 1H, J = 8 Hz, quinolyl-C8-H), 11.39 (s, 1H,
3
–
3/5, 4, 1 respectively), 128.62, 130.90, 131.15, 134.79 (O C-C H -
–
6
–
4
–
OCH ), 164.22, 164.95 (oxadiazole C-5, 2 respectively), 192.50 (C O).
Anal3. Calcd. for C25H16BrN3O2S (502.38): C, 59.77; H, 3.21; N, 8.36; S,
6.38. Found: C, 59.58; H, 3.47; N, 8.68; S, 6.50.
exchangeable, NH). 13C NMR (100 MHz, DMSO‑d , δppm): 26.63(O C-
–
–
CH3), 40.35(S-CH2-CO), 117.37, 117.94, 1286.66, 130.33, 130.52,
131.38, 131.62, 148.88, 156.60 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a , 2
respectively), 122.54, 129.14, 131.14, 143.01 (NH-C6H4), 126.03(2C),
4.1.2.5. 4-(5-(Methylthio)-1,3,4-oxadiazol-2-yl)-2-phenylquinoline 4 g.
◦
Recrystallization from EtOH; yield: 93%; mp: 150–152 C. IR (KBr, ύ,
cmꢀ 1): 3032 (Ar
H
C- str), 2980 (aliph
– –
– – –
H C str), 1650 and 1550
1
–
–
–
–
127.63(2C), 129.49, 138.41 (phenyl C-2/6, 3/5,4,1 respectively),
(C N), 1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d , δppm):
2.89 (s, 3H, CH3), 7.50–7.60 (m, 3H, Ar-C3,4&5-H), 7.69 (t, 1H, 6J = 4 Hz,
quinolyl-C6-H), 7.81 (t, 1H, J = 4 Hz, quinolyl-C7-H), 8.23 (d, 2H, J = 4
Hz, Ar-C2&6-H), 8.30 (d, 1H, J = 8 Hz, quinolyl-C5-H), 8.41 (s, 1H,
quinolyl-C3-H), 9.15 (d, 1H, J = 8 Hz, quinolyl-C8-H). 13C NMR (100
MHz, DMSO‑d6, δppm): 14.68 (S-CH3), 118.22, 122.55, 125.96, 128.97,
129.90, 130.37, 138.50, 149.06, 156.67 (quinoline C-3, 6, 5, 4a, 7, 8, 4,
8a, 2 respectively), 127.51, 128.20, 128.97, 130.42 (phenyl C-2/6, 3/5,
4, 1 respectively), 164.39, 166.22 (oxadiazole C-5, 2 respectively). Anal.
Calcd. for C18H13N3OS (319.38): C, 67.69; H, 4.10; N, 13.16; S, 10.04.
Found: C, 67.83; H, 4.14; N, 12.93; S, 9.87.
–
–
157.48, 157.58 (oxadiazole C-5, 2 respectively), 160.37 (O C-NH),
–
–
197.55 (O C-CH ). Anal. Calcd. for C27H20N4O3S (480.54): C, 67.48;
3
H, 4.20; N, 11.66; S, 6.67. Found: C, 67.30; H, 4.32; N, 11.78; S, 6.42.
4.1.2.3. 2-(5-(2-Phenylquinolin-4-yl)-1,3,4-oxadiazol-2-ylthio)-1-(4-
methoxy phenyl)ethanone 4e. Recrystallization from methylene chloride;
ꢀ 1
yield: 66%; mp: 222–224 ◦C. IR (KBr, ύ, cm ): 3030 (Ar
C- str),
– –
H
–
–
– –
H
2998 (aliph
C- str), 1710 (C O), 1664 and 1550 (C N),
–
–
C str). 1H NMR (400 MHz,
–
– –
1600–1450 (Ar-C C str), 1250–1050 (C
O
–
DMSO‑d6, δppm): 3.92 (s, 3H, O-CH3), 5.26 (s, 2H, S-CH2-CO), 7.15 (d,
2H, J = 8 Hz, CO-Ar-C2&6-H), 7.62–7.65 (m, 3H, , Ar-C3,4&5-H), 7.79 (t,
1H, J = 8 Hz, quinolyl-C6-H) , 7.94 (t, 1H, J = 8 Hz, quinolyl-C7-H), 8.14
(d, 2H, J = 8 Hz, CO-Ar-C3&5-H), 8.25 (d, 1H, J = 4 Hz, quinolyl-C5-H),
8.31 (d, 2H, J = 4 Hz, Ar-C2&6-H), 8.56 (s, 1H, quinolyl-C3-H), 9.02 (d,
1H, J = 12 Hz, quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm):
40.91(S-CH2-CO), 56.16 (OCH3), 114, 118.70, 122.43, 125.94, 128.48,
130.6, 138.16,148.87, 156.37 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2
4.1.2.6. 4-(5-(Ethylthio)-1,3,4-oxadiazol-2-yl)-2-phenylquinoline
4 h.
Recrystallization from EtOH; yield: 80%; mp: 90–92 ◦C. IR (KBr, ύ,
cmꢀ 1): 3032 (Ar
H
C- str), 2998 (aliph
– –
– –
H C- str), 1650, and 1550
1
–
–
–
–
(C N), 1450–1600 (Ar-C C str). H NMR (400 MHz, DMSO‑d , δppm):
1.59 (t, 3H, J = 8 Hz, S-CH2-CH3), 3.41(q, 2H, J = 8 Hz, S-C6H2-CH3),
7.50–7.59 (m, 3H, Ar-C3,4&5-H), 7.68(t, 1H, J = 4 Hz, quinolyl-C6-H),
7.81 (t, 1H, J = 4 Hz, quinolyl-C7-H), 8.23 (d, 2H, J = 8 Hz, Ar-C2&6-H),
8.27 (d, 1H, J = 8 Hz, quinolyl-C5-H), 8.40 (s, 1H, quinolyl-C3-H), 9.16
(d, 1H, J = 8 Hz, quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm):
14.69 (S-CH2-CH3), 27.18 (S-CH2-CH3), 118.19, 122.55, 125.00,
125.98, 128.95, 129.86, 130.37, 138.56, 149.10, 156.06 (quinoline C-3,
6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 127.49, 128.16, 128.50, 130.38
(phenyl C-2/6, 3/5, 4, 1 respectively), 164.24, 165.59 (oxadiazole C-5, 2
respectively). Anal. Calcd. for C19H15N3OS (333.41): C, 68.45; H, 4.53;
N, 12.60; S, 9.62. Found: C, 68.10; H, 4.34; N, 12.47; S, 9.41.
respectively), 127.73, 128.67, 128.89, 130.01 (phenyl C-2/6, 3/5, 4, 1
–
–
respectively), 129.44, 131.23, 131.43, 164.09 (O C-C H -OCH ),
6
–
4
3
–
164.34, 165.23 (oxadiazole C-5, 2 respectively), 191.37 (C O). Anal.
Calcd. for C26H19N3O3S (453.51): C, 68.86; H, 4.22; N, 9.27; S, 7.07.
Found: C, 69.14; H, 4.35; N, 9.49; S, 7.15.
4.1.2.4. 2-(5-(2-Phenylquinolin-4-yl)-1,3,4-oxadiazol-2-ylthio)-1-(4-
bromo phenyl)ethanone 4f. Recrystallization from methylene chloride;
ꢀ 1
yield: 83%; mp: 231–233 ◦C. IR (KBr, ύ, cm ): 3030 (Ar
– –
H C- str),
–
–
–
–
–
–
1710 (C O), 1664 and 1550 (C N), 1600–1450 (Ar-C C str),
O
C str). 1H NMR (400 MHz, DMSO‑d6, δppm): 5.01 (s,
4.1.2.7. 4-(5-(Benzylthio)-1,3,4-oxadiazol-2-yl)-2-phenylquinoline 4i.
– –
1250–1050 (C
8

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
◦
Recrystallization from EtOH; yield: 67%; mp: 138–140 C. IR (KBr, ύ,
(t, 1H, J = 4 Hz, -N-Ar-C4-H), 6.94 (d, 2H, J = 8 Hz, -N-Ar-C2&6-H), 7.21
(t, 2H, J = 8 Hz, -N- Ar-C3&5-H), 7.57–7.64 (m, 3H, Ar-C3,4&5-H), 7.83 (t,
1H, J = 4 Hz, quinolyl-C6-H), 7.95 (t, 1H, J = 4 Hz, quinolyl-C7-H), 8.24
(d, 1H, J = 8 Hz, quinolyl-C5-H), 8.34 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.49
(s, 1H, quinolyl-C3-H), 8.89 (d, 1H, J = 8 Hz, quinolyl-C8-H). 13C NMR
(100 MHz, DMSO‑d6, δppm): 48.92 (2C) (N-(CH2)2), 50.19 (2C) (Ar-N-
(CH2)2), 71.28 (N-CH2-N), 118.24, 122.33, 125.76, 128.53 ,128.68,
130.48, 138.40, 148.95, 156.46 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2
respectively), 116.18, 119.49, 129.44, 130.57 (-N-C6H5), 127.72 (2C),
127.74 (2C), 129.41, 131.05 (phenyl C-2/6, 3/5, 4, 1 respectively),
158.21, 178.82 (oxadiazole C-5, 2 respectively). Anal. Calcd. for
cmꢀ 1): 3032 (Ar
– –
H C- str), 2998 (aliph
– –
H C- str), 1650 and 1550
1
–
–
–
–
(C N), 1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d , δppm):
6
4.52 (s, 2H, S-CH2-C6H5), 7.21–7.30 (m, 3H, Ar-C3,4&5-H), 7.39–7.48 (m,
5H, S-CH2-C6H5), 7.57 (t, 1H, J = 4 Hz, quinolyl-C6-H), 7.70 (t, 1H, J =
8 Hz, quinolyl-C7-H), 8.11 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.17 (d, 1H, J =
8 Hz, quinolyl-C5-H), 8.26 (s, 1H, quinolyl-C3-H), 9.03 (d, 1H, J = 4 Hz,
quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm): 36.95 (S-CH2-
C6H5), 118.30, 122.54, 125.56, 129.26, 129.95, 130.30, 138.40,148.97,
156.65 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 127.56,
128.25, 128.54, 130.49 (phenyl C-2/6, 3/5, 4, 1 respectively), 128.90,
128.98, 129.16, 135.43 (S-CH2-C6H5), 164.39, 165.13 (oxadiazole C-5,
2 respectively). Anal. Calcd. for C24H17N3OS (395.48): C, 72.89; H,
4.33; N, 10.63; S, 8.11. Found: C, 73.08; H, 4.17; N, 10.72; S, 8.20.
C
28H25N5OS (479.6): C, 70.12; H, 5.25; N, 14.60; S, 6.69. Found: C,
70.14; H, 5.34; N, 14.89; S, 6.78.
4.1.3.3. 4-((5-(2-Phenylquinolin-4-yl)-2-thioxo-1,3,4-oxadiazol-3(2H)-
4.1.2.8. 4-(5-(4-Chlorobenzylthio)-1,3,4-oxadiazol-2-yl)-2-phenyl quino-
yl)methyl- amino)benzoic acid 5c. Recrystallization from EtOH; yield:
line 4j. Recrystallization from EtOH; yield: 65%; mp: 136–138 C. IR
88%; mp: 233–235 ◦C. IR (KBr, ύ, cmꢀ 1): 3500–2500 (br, COOH), 3032
◦
(KBr, ύ, cmꢀ 1): 3032 (Ar
C- str), 2998 (aliph
C- str), 1650 and
(Ar
H
C- str), 1650 and 1550 (C N), 1600–1450 (Ar-C C str). H
1
–
–
–
– –
H
– –
H
– –
–
1
–
–
–
–
1550 (C N), 1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d ,
NMR (400 MHz, DMSO‑d6, δppm): 5.29 (s, 2H, NH-CH2-N), 7.07 (d, 1H,
J = 12 Hz, quinolyl-C6-H), 7.58–7.60 (m, 3H, Ar-C3,4&5-H), 7.74 (t, 1H,
J = 4 Hz, quinol-yl-C7-H), 7.80 (d, 2H, J = 8 Hz, HOOC-Ar-C2&6-H),
7.92–7.94 (m, 2H, HOOC– Ar-C3&5-H), 8.23 (d, 1H, J = 8 Hz, quinolyl-
C5-H), 8.32 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.48 (s, 1H, quinolyl-C3-H),
8.77 (d, 1H, J = 8 Hz, quinolyl-C8-H), 12.21 (s, 1H, exchangeable,
COOH). 13C NMR (100 MHz, DMSO‑d6, δppm): 58.24 (N-CH2-NH),
113.12, 118.87, 131.28, 150.26 (-N-C6H4), 118.59, 120.64, 122.77,
125.38, 128.84, 129.50, 130.67, 131.62, 148.83 (quinoline C-3, 6, 5, 4a,
7, 8, 4, 8a, 2 respectively), 127.77 (2C), 128.19 (2C), 131.45, 138.08
(phenyl C-2/6, 3/5, 4, 1 respectively), 157.43 (COOH), 156.37, 167.65
(oxadiazole C-5, 2 respectively). Anal. Calcd. for C25H18N4O3S (454.5):
C, 66.07; H, 3.99; N, 12.33; S, 7.05. Found: C, 65.89; H, 4.17; N, 12.57;
S, 7.31.
δppm): 4.70 (s, 2H, S-CH2-C6H5), 7.42–7.44 (m, 3H, Ar-C3,4&5-H6),
7.59–7.61 (m, 4H, S-CH2-C6H4), 7.78 (t, 1H, J = 8 Hz, quinolyl-C6-H),
7.90 (t, 1H, J = 8 Hz, quinolyl-C7-H), 8.20 (d, 1H, J = 8 Hz, quinolyl-C5-
H), 8.31 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.52 (s, 1H, quinolyl-C3-H), 8.98
(d, 1H, J = 4 Hz, quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm):
35.60 (S-CH2-C6H4), 118.76, 122.41, 125.99, 129.03, 130.52, 130.60,
138.32, 148.80, 156.37 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respec-
tively), 127.77 (2C), 128.65 (2C), 128.86, 131.20 (phenyl C-2/6, 3/5, 4,
1 respectively), 129.46, 131.43, 132.93, 136.32 (S-CH2-C6H4), 164.34,
164.96 (oxadiazole C-5, 2 respectively). Anal. Calcd. for C24H16ClN3OS
(429.92): C, 67.05; H, 3.75; N, 9.77; S, 7.46. Found: C, 67.24; H, 3.42; N,
9.59; S, 7.47.
4.1.3. General method for synthesis of N-alkyl derivatives of 5-(2-
phenylquinolin-4-yl)-1,3,4-oxadiazole-2(3H)-thione 5a-e
4.1.3.4. Ethyl4-((5-(2-phenylquinolin-4-yl)-2-thioxo-1,3,4-oxadiazol-3
Formaldehyde (38%; 1.5 ml, 0.02 mol) was added to a stirred solu-
tion of 3 (2.7 g, 0.02 mol) in EtOH (20 ml). The appropriate amine (0.02
mol) in EtOH (5 ml) was added dropwise to the reaction mixture, stirred
for 10–15 h and then left overnight at room temperature. The resulting
solid was collected, washed with cold EtOH, dried, and crystallized from
EtOH to get the desired compounds.
(2H)-yl)methylamino)benzoate 5d. Recrystallization from EtOH; yield:
ꢀ 1
◦
– –
H
89%; mp: 212–214 C. IR (KBr, ύ, cm ): 3032 (Ar
C- str), 2998
1
–
–
– –
(aliph
H
C- str), 1650 and 1550 (C N), 1600–1450 (Ar-C C str). H
–
–
NMR (400 MHz, DMSO‑d6, δppm): 1.30 (t, 3H, J = 8 Hz, –CH2-CH3),
4.24 (q, 2H, J = 8 Hz, –CH2-CH3), 5.72 (s, 2H, NH-CH2-N), 7.08 (d, 1H, J
= 8 Hz, quinolyl-C6-H), 7.56–7.60 (m, 3H, Ar-C3,4&5-H), 7.73 (t, 1H, J =
8 Hz, quinolyl-C7-H), 7.82 (d, 2H, J = 12 Hz, HOOC-Ar-C2&6-H),
7.94–7.98 (m, 2H, HOOC– Ar-C3&5-H), 8.22 (d, 1H, J = 8 Hz, quinolyl-
C5-H), 8.32 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.47 (s, 1H, quinolyl-C3-H),
8.76 (d, 1H, J = 8 Hz, quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6,
δppm): 14.55 (CH3), 60.22 (N-CH2-NH), 61.53(CH2), 112.94, 119.53,
130.39, 142.14 (-N-C6H4), 123.94, 125.84, 127.68, 128.18, 130.63,
131.22, 138.49, 141.14, 148.94 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2
respectively), 126.27 (2C), 126.48 (2C), 129.43, 138.22 (phenyl C-2/6,
3/5, 4, 1 respectively), 165.42 (COOC2H5), 156.38, 167.99 (oxadiazole
C-5, 2 respectively). Anal. Calcd. for C27H22N4O3S (482.55): C, 67.20;
H, 4.60; N, 11.61; S, 6.64. Found: C, 67.43; H, 4.69; N, 11.89; S, 6.72.
4.1.3.1. 3-(Morpholinomethyl)-5-(2-phenylquinolin-4-yl)-1,3,4-oxadia-
zole-2(3H)-thione 5a. Recrystallization from EtOH; yield: 74%; mp:
– –
H C- str), 2998
242–244 ◦C. IR (KBr, ύ, cmꢀ 1): 3032 (Ar
–
–
–
– – –
H C str), 1650 and 1550 (C N), 1600–1450 (Ar-C C str).
–
(aliph
1H NMR (400 MHz, DMSO‑d6, δppm): 2.97 (t, 4H, J = 8 Hz, N-(CH2)2),
3.76 (t, 4H, J = 8 Hz, O-(CH2)2), 5.22 (s, 2H, N-CH2-N), 7.52–7.61 (m,
3H, Ar-C3,4&5-H), 7.69 (t, 1H, J = 8 Hz, quinolyl-C6-H), 7.83 (t, 1H, J =
8 Hz, quinolyl-C7-H), 8.25 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.29 (d, 1H, J =
8 Hz, quinolyl-C5-H), 8.49 (s, 1H, quinolyl-C3-H), 8.86 (d, 1H, J = 8 Hz,
quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm): 50.69 (2C) (N-
(CH2)2), 66.80 (2C) (O-(CH2)2), 71.00 (N-CH2-N), 118.62, 121.91,
124.81, 126.77, 130.04, 130.39, 138.29, 149.22, 156.86 (quinoline C-3,
6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 127.50 (2C), 128.36 (2C), 128.98,
130.91 (phenyl C-2/6, 3/5, 4, 1 respectively), 157.45, 177.92 (oxadia-
zole C-5, 2 respectively). Anal. Calcd. for C22H20N4O2S (404.48): C,
65.33; H, 4.98; N, 13.85; S, 7.93. Found: C, 65.01; H, 4.77; N, 13.85; S,
8.15.
4.1.3.5. 3-((3-fluorophenylamino)methyl)-5-(2-phenylquinolin-4-yl)-
1,3,4-oxadiazole-2(3H)-thione 5e. Recrystallization from EtOH; yield:
ꢀ 1
–
84%; mp: 170–172 ◦C. IR (KBr, ύ, cm ): 3032 (Ar
– – –
H C str), 2998
–
–
– – –
H C str), 1650 and 1550 (C N), 1600–1450 (Ar-C C str).
–
(aliph
1H NMR (400 MHz, DMSO‑d6, δppm): 5.64 (s, 2H, NH-CH2-N),
6.47–6.49 (m, 1H, quinolyl-C6-H), 6.78–6.80 (m, 2H, Ar-C3&5-H),
7.17–7.20 (m, 1H,Ar-C4-H), 7.57–7.60 (m, 2H,F-Ar –C2&6-H), 7.72–7.74
(m, 1H,F-Ar–C4-H),7.90 (t, 1H, J = 8 Hz, quinolyl-C7-H), 8.19 (d, 1H, J
= 8 Hz,quinolyl-C5-H), 8.29 (d, 3H, J = 8 Hz,Ar-C2&6-H, F-Ar–C5-H),
8.46 (s, 1H,quinolyl-C3-H), 8.77 (d, 1H,J = 8 Hz,quinolyl-C8-H). 13C
NMR (100 MHz, DMSO‑d6, δppm): 58.73 (N-CH2-NH),110.00, 113.61,
113.81, 131.27, 148.83, 156.36 (-N-C6H4), 118.56, 118.85, 122.00,
122.16 ,125.60, 128.83, 130.65, 130.97, 143.29 (quinoline C-3, 6, 5, 4a,
4.1.3.2. 3-((4-Phenylpiperazin-1-yl)methyl)-5-(2-phenylquinolin-4-yl)-
1,3,4-oxadiazole-2(3H)-thione 5b. Recrystallization from aq. EtOH;
ꢀ 1
–
yield: 69%; mp: 202–204 ◦C. IR (KBr, ύ, cm ): 3032 (Ar
– –
H C- str),
–
–
– –
H C- str), 1650 and 1550 (C N), 1600–1450 (Ar-C C
–
2998 (aliph
str). 1H NMR (400 MHz, DMSO‑d6, δppm): 3.04 (t, 4H, J = 4 Hz, N-
(CH2)2), 3.20 (t, 4H, J = 4 Hz, Ar-N-(CH2)2), 5.28 (s, 2H, N-CH2-N), 6.78
9

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
7, 8, 4, 8a, 2 respectively), 125.37 (2C), 127.77 (2C), 129.49, 138.07
(phenyl C-2/6, 3/5, 4, 1 respectively), 157.42, 176.19 (oxadiazole C-5, 2
respectively). Anal. Calcd. for C24H17FN4OS (428.48): C, 67.27; H,
4.00; N, 13.08; S, 7.48. Found: C, 67.46; H, 3.89; N, 13.37; S, 7.32.
14.20; S, 8.13. Found: C, 73.40; H, 4.73; N, 14.46; S, 8.25.
4.1.5.2. 4-(5-(4-chlorobenzylthio)-4-phenyl-4H-1,2,4-triazol-3-yl)-2-
phenyl quinoline 8d. Recrystallization from EtOH; yield: 70%; mp:
– –
186–188 ◦C. IR (KBr, ύ, cmꢀ 1): 3032 (Ar
H
C- str), 2998
1
–
–
4.1.4. General method for synthesis of S-alkyl derivatives of 4-
Phenyl-5-(2-phenylquinoline-4-yl)-4H[1,2,4]triazole-3-thiol 8a,b
8a and 8b were prepared by using the same procedure as mentioned
in 4a,b.
– –
(aliph
H
C- str), 1650 and 1550 (C N), 1600–1450 (Ar-C C str). H
–
–
NMR (400 MHz, DMSO‑d6, δppm): 4.56 (s, 2H, S-CH2-C6H5), 7.09(d, 2H,
J = 4 Hz, S-CH2-C6H4 (C2&6-H)), 7.34 (d, 2H, J = 4 Hz,S-CH2-C6H4
(C3&5-H)), 7.36–7.40 (m, 5H,N-C6H5), 7.44–7.46 (m, 3H,Ar-C3,4&5-H),
7.55–7.57 (m, 2H, quinolyl-C3&6-H) 7.74 (t, 1H, J = 8 Hz, quinolyl-C7-
H), 7.82–7.85 (m, 2H,Ar-C2&6-H), 8.22 (d, 1H, J = 4.2 Hz, quinolyl-C5-
H), 8.30 (d, 1H, J = 4.2 Hz,quinolyl-C8-H). 13C NMR (100 MHz,
DMSO‑d6, δppm): 36.18 (S-CH2-C6H4), 120.82, 125.07, 125.98, 131.41,
133.69, 133.80, 138.32, 148.34, 152.26 (quinoline C-3, 6, 5, 4a, 7, 8, 4,
8a, 2 respectively), 127.46 (2C), 127.80 (2C), 129.37, 136.81 (phenyl C-
2/6, 3/5, 4, 1 respectively), 127.91, 128.91, 129.35, 132.69 (S-CH2-
C6H4), 130.02, 130.07, 130.36, 130.93(N-C6H5), 152.38, 155.71 (oxa-
diazole C-5, 2 respectively). Anal. Calcd. for C30H21ClN4S (505.03): C,
71.35; H, 4.19; N, 11.09; S, 6.35. Found: C, 71.58; H, 4.37; N, 11.38; S,
6.41.
4.1.4.1. 4-(5-(2-morpholinoethylthio)-4-phenyl-4H-1,2,4-triazol-3-yl)-2-
phenyl quinoline 8a. Recrystallization from aq. EtOH; yield: 92%; mp:
ꢀ 1
208–210 ◦C. IR (KBr, ύ, cm ): 3015 (Ar–CH), 2998 (aliph
– –
H C- str),
1
–
–
–
–
1622 (C N); 1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d ,
δppm): 2.63 (s, 4H, N-(CH2)2), 2.76 (t,2H, J = 16 Hz, S-CH2-CH2-N6),
3.62 (t, 2H, J = 8 Hz, S-CH2-CH2-N), 3.76 (s, 4H, O-(CH2)2), 7.24 (d, 3H,
Ar-C3,4&5-H), 7.43–7.46 (m, 5H,-N-C6H5), 7.54–7.59(m, 2H, quinolyl-
C3&6-H), 7.74 (t, 1H, J = 8 Hz, quinolyl-C7-H), 7.84 (d, 2H, J = 8 Hz, Ar-
C
2&6-H), 8.18 (d, 1H, J = 8 Hz,quinolyl-C5-H), 8.31 (d, 1H, J = 8 Hz,
quinolyl-C8-H). 13C NMR (100 MHz, DMSO‑d6, δppm): 33.78 (N-CH2
(2C)), 48.43(S-CH2-CH2-N), 52,61 (S-CH2-CH2-N), 61.55 (O-CH2(2C)),
115.47, 115.96 , 120.11, 120.87, 122.04, 122.53, 124.83,125.24,
147.64 (quinoline C-3, 6,5,4a,7,8,4,8a, 2 respectively), 124.05, 125.19,
125.42, 134.07 (N-C6H5), 126.41 (2C), 128.02 (2C), 128.83, 144.13
(phenyl C-2/6, 3/5, 4, 1 respectively), 148.78, 151.45 (oxadiazole C-5, 2
respectively). Anal. Calcd. for C29H27N5OS (493.62): C, 70.56; H, 5.51;
N, 14.19; S, 6.50. Found: C, 70.43; H, 5.67; N, 14.42; S, 6.63.
4.1.5.3. 2-(4-phenyl-5-(2-phenylquinolin-4-yl)-4H-1,2,4-triazol-3-ylthio)-
1-(4-methoxyphenyl)ethanone 8e. Recrystallization from methylene
chloride; yield: 75%; mp: 138–140 ◦C. IR (KBr, ύ, cmꢀ 1): 3030
–
– –
– –
– –
H C- str), 1710 (C O), 1664 and 1550
(Ar
H
C- str), 2998 (aliph
–
–
–
–
(C N), 1600–1450 (Ar-C C str), 1250–1050 (C
–
O
C str). 1H NMR
(400 MHz, DMSO‑d6, δppm): 3.91 (s, 3H, O-CH3), 5.1 (s, 2H, S-CH2-CO),
7.01 (s, 3H, Ar-C3,4&5-H), 7.30 (s, 2H, CO-Ar-C3&5-H), 7.47–7.50 (m, 5H,
N-C6H5), 7.60 (s, 2H, CO-Ar-C2&6-H), 7.82 (s, 3H, quinolyl-C3,6&7-H),
8.02–8.09 (m, 2H, quinolyl-C5&8-H), 8.39 (s, 2H, Ar-C2&6-H). 13C NMR
(100 MHz, DMSO‑d6, δppm): 39.56 (S-CH2-CO), 56.15 (OCH3), 114.62,
120.18, 125.05, 126.00, 127.94, 128.74, 130.45, 130.92, 148.35
(quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 124.07, 127.49,
129.36, 133.32 (N-C6H5), 127.82, 130.02, 130.23, 138.32 (phenyl C-2/
4.1.4.2. 2-(4-phenyl-5-(2-phenylquinolin-4-yl)-4H-1,2,4-triazol-3-ylthio)-
N,N-dimethylethanamine 8b. Recrystallization from aq. EtOH; yield:
89%; mp: 178–180 ◦C. IR (KBr, ύ, cmꢀ 1): 3030 (Ar–CH str), 2998
–
–
–
–
– –
(aliph
H
C- str), 1628 (C N), 1600–1450 (Ar-C C str). 1H NMR
(400 MHz, DMSO‑d6, δppm): 2.18 (s, 6H, N-(CH3)2), 2.63 (t, 2H, J = 8
Hz, S-CH2-CH2-N), 3.44 (t, 2H, J = 8 Hz, S-CH2-CH2-N), 7.42–7.43 (m,
4H, Ar-C3,4&5-H, quinolyl-C6-H), 7.58–7.60 (m, 2H, -N-C6H5 (C3&5-H),
7.71 (d, 1H, J = 8 Hz, -N-C6H5 (C4-H)), 7.80 (t, 2H, J = 8 Hz, -N-C6H5
(C2&6-H)), 8.02–8.05 (m, 3H,Ar-C2&6-H, quinolyl-C3-H) 8.09 (d, 1H, J =
8 Hz, quinolyl-C7-H), 8.16 (d, 1H, J = 8 Hz, quinolyl-C5-H), 8.28 (d, 1H,
J = 8 Hz, quinolyl-C8-H).13C NMR (100 MHz, DMSO‑d6, δppm): 31.05
(N-(CH3)2 (2C)), 45.22 (S-CH2-CH2-N), 57.98 (S-CH2-CH2-N), 117.77,
120.86, 122.77, 127.45, 130.48, 130.99, 133.82, 148.29, 152.07
(quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 125.04 (2C), 126.12
(2C), 130.18, 138.25 (phenyl C-2/6, 3/5, 4, 1 respectively), 127.61,
127.92, 129.42, 129.97(N-C6H5), 153.53, 155.64 (oxadiazole C-5,2
respectively). Anal. Calcd. for C27H25N5S (451.59): C, 71.81; H, 5.58;
N, 15.51; S, 7.10. Found: C, 71.62; H, 5.66; N, 15.79; S, 7.04.
–
–
6, 3/5, 4, 1 respectively), 126.62, 131.07, 131.32, 152.49 (O C-C H -
6
–
4
–
OCH ), 155.73, 164.18 (oxadiazole C-5, 2 respectively), 191.92 (C O).
Anal3. Calcd. for C32H24N4O2S (528.62): C, 72.71; H, 4.58; N, 10.60; S,
6.07 Found: C, 72.98; H, 4.76; N, 10.91; S, 6.15.
4.1.6. General method for synthesis of N-alkyl derivatives of 4-
phenyl-5-(2-phenylquinoline-4-yl)-4H[1,2,4]triazole-3-thiol 9a-d
9a-d were prepared by using the same procedure as mentioned in 5a-
e.
4.1.6.1. 2-(morpholinomethyl)-4-phenyl-5-(2-phenylquinolin-4-yl)–2H-
1,2,4-triazole-3(4H)-thione 9a. Recrystallization from EtOH; yield: 84%;
ꢀ 1
mp: 190–192 ◦C. IR (KBr, ύ, cm ): 3032 (Ar
C- str), 2998
– –
H
–
–
–
–
4.1.5. General method for synthesis of S-alkyl derivatives of 4-Phenyl
ꢀ 5-(2-phenylquinoline-4-yl)-4H-[1,2,4]triazole-3-thiol 8c-e
8c-e were prepared by using the same procedure as mentioned in 4c-
j.
– –
H C- str), 1599 and 1581 (C N), 1600–1450 (Ar-C C str)
(aliph
1
–
–
,1338–1321 (C S). H NMR (400 MHz, DMSO‑d , δppm): 3.03 (t, 4H, J
6
= 8 Hz, N-(CH2)2), 3.78 (t, 4H, J = 8 Hz, O-(CH2)2), 5.41 (s, 2H, N-CH2-
N), 7.28–7.30 (m, 2H, -N-C6H5 (C2&6-H)), 7.39–7.40 (m, 3H, -N-
C6H5(C3&5-H), quinolyl-C6-H), 7.48–7.50 (m, 3H, Ar-C3,4&5-H),
7.59–7.60 (m, 2H, -N-C6H5(C4-H), quinolyl-C3-H), 7.78–7.79 (m, 1H,
quinolyl-C7-H), 7.86–7.88 (m, 2H, Ar-C2&6-H), 8.08 (d, 1H, J = 4 Hz,
quinolyl-C5-H), 8.20 (d, 1H, J = 8 Hz, quinolyl-C8-H). 13C NMR (100
MHz, DMSO‑d6, δppm): 50.98 (2C) (N-(CH2)2), 66.97 (2C) (O-(CH2)2),
70.32 (N-CH2-N), 120.72, 124.31, 127.33, 128.96, 129.92, 130.55,
131.55, 146.82, 148.73 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respec-
tively), 124.45 (2C), 127.63 (2C), 129.67, 134.33 (N-C6H5), 127.81
(2C), 129.84 (2C), 130.49, 138.38 (phenyl C-2/6, 3/5, 4, 1 respectively),
156.33, 170.53 (oxadiazole C-5, 2 respectively). Anal. Calcd. for
4.1.5.1. 4-(5-(methylthio)-4-phenyl-4H-1,2,4-triazol-3-yl)-2-phenyl quin-
oline 8c. Recrystallization from EtOH; yield: 69%; mp: 220–222 ◦C. IR
(KBr, ύ, cmꢀ 1): 3032 (Ar
C
str), 2980 (aliph
– – –
H
– – –
H C str), 1650
and 1550 (C N), 1600–1450 (Ar-C C str). 1H NMR (400 MHz,
–
–
–
–
DMSO‑d6, δppm): 2.86 (s, 1H, CH3), 7.23–7.28 (m, 2H, Ar-C3&5-H),
7.41–7.49 (m, 6H, N-C6H5, Ar-C4-H), 7.57–7.64 (m, 2H, quinolyl-C6&7
-
H), 7.77–7.84 (m, 3H, quinolyl-C3,5&8-H), 8.38 (d, 2H, J = 4 Hz, Ar-
C2&6-H). 13C NMR (100 MHz, DMSO‑d6, δppm): 15.01(S-CH3), 120.81,
122.37, 125.09, 126.11, 130.38, 130.90, 133.82, 148.38, 152.27
(quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 127.46, 127.82,
130.18, 138.36 (phenyl C-2/6, 3/5, 4, 1 respectively), 127.48, 127.87,
129.35, 129.99 (N-C6H5), 153.80, 155.71 (oxadiazole C-5, 2 respec-
tively). Anal. Calcd. for C24H18N4S (394.49): C, 73.07; H, 4.60; N,
C
28H25N5OS (479.6): C, 70.12; H, 5.25; N, 14.60; S, 6.69. Found: C,
70.34; H, 5.39; N, 14.87; S, 6.58.
10

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
4.1.6.2. 4-phenyl-2-((4-phenylpiperazin-1-yl)methyl)-5-(2-phenyl quino-
4.2. Pharmacological evaluations
lin-4-yl)–2H-1,2,4-triazole-3(4H)-thione
9b. Recrystallization
from
ꢀ 1
–
EtOH; yield: 78%; mp: 134–136 ◦C. IR (KBr, ύ, cm ): 3032 (Ar
H
C-
4.2.1. Assay of inhibitory activities on E. Coli and S. Aureus DNA gyrase
IC50 assay determination was carried out in accordance with the
procedures previously stated [23]. See Appendix A
– –
– –
H C- str), 1650 and 1550 (C N), 1600–1450 (Ar-
–
str), 2998 (aliph
1
–
–
C
C str). H NMR (400 MHz, DMSO‑d , δppm): 3.04 (t, 4H, J = 4 Hz, N-
6
(CH2)2), 3.20 (t, 4H, J = 4 Hz, Ar-N-(CH2)2), 5.50 (s, 2H, N-CH2-N),
6.89–6.99 (m, 3H, piperazine N-C6H5 (C3,4&5-H)), 7.28–7.32 (m, 5H, N-
C6H5), 7.39–7.40 (m, 2H, piperazine N-C6H5 (C2&6-H)), 7.48–7.50 (m,
3H, Ar-C3,4&5-H), 7.59–7.65 (m, 2H, quinolyl –C3&6-H), 7.80 (t, 1H, J =
2 Hz, quinolyl-C7-H), 7.89 (d, 2H, J = 2 Hz, Ar-C2&6-H), 8.11 (d, 1H, J =
4.2 Hz, quinolyl-C5-H), 8.21 (d, 1H, J = 4.2 Hz, quinolyl-C8-H). 13C NMR
(100 MHz, DMSO‑d6, δppm): 48.91 (2C) (N-(CH2)2), 50.47 (2C) (Ar-N-
(CH2)2), 69.82 (N-CH2-N), 116.10, 117.91, 121.57, 128.90, 130.11,
130.53, 131.11, 132.59, 151.57 (quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a , 2
respectively), 115.91, 119.41, 129.89, 146.85 (-N-C6H5piperazine),
124.72, 127.50, 129.38, 134.95 (-N-C6H5), 125.46 (2C), 128.26 (2C),
129.53, 138.13 (phenyl C-2/6, 3/5, 4, 1 respectively), 155.72, 170.17
(oxadiazole C-5, 2 respectively). Anal. Calcd. for C34H30N6S (554.71):
C, 73.62; H, 5.45; N, 15.15; S, 5.78. Found: C, 73.80; H, 5.66; N, 15.42;
S, 5.89.
4.2.2. Assay of inhibitory activities on E. Coli and S. Aureus topoisomerase
IV
IC50 assay determination was carried out in accordance with the
procedures previously stated [23]. See Appendix A
4.2.3. Antibacterial activity assay
The antibacterial activities against selected bacterial strains were
performed according to previously reported procedures [24]. See
Appendix
4.2.4. Cell viability and MTT assay
MTT assay was conducted to explore the effect of the synthesized
compounds on the viability of mammary epithelial cells (MCF-10A)
[25,26]. See Appendix A
4.1.6.3. 4-((4,5-dihydro-4-phenyl-3-(2-phenylquinolin-4-yl)-5-thioxo-
1,2,4-triazol-1-yl)methylamino)benzoic acid 9c. Recrystallization from
EtOH; yield: 80%; mp: 198–200 ◦C. IR (KBr, ύ, cmꢀ 1): 3500–2500 (br,
4.3. Molecular docking studies
From the protein data bank, the co-crystallized structures of E. coli
DNA gyrase B co-crystallized with a thiazole inhibitor and Topoisom-
erase IV co-crystallized with benzimidazole urea inhibitor (PDB codes:
4DUH and 3FV5) were downloaded, respectively [26,27]. See Appen-
dix A.
–
– –
H C- str), 1650 and 1550 (C N), 1600–1450 (Ar-
–
COOH), 3032 (Ar
1
–
–
C
C str). H NMR (400 MHz, DMSO‑d , δppm): 5.82 (s, 2H, NH-CH -N),
7.08 (t, 1H, J = 8 Hz, quinolyl-C6-H),67.43–7.44 (m, 3H, Ar-C3,4&52-H),
7.49–7.63 (m, 5H, N-C6H5), 7.72 (t, 1H, J = 4 Hz, quinol-yl-C7-H), 7.91
(s, 2H, HOOC-Ar-C2&6-H), 8.05–8.11 (m, 2H, HOOC– Ar-C3&5-H), 8.20
(d, 1H, J = 8 Hz, quinolyl-C5-H), 8.27 (d, 2H, J = 8 Hz, Ar-C2&6-H), 8.46
(s, 1H, quinolyl-C3-H), 9.15 (d, 1H, J = 8 Hz, quinolyl-C8-H), 12.27 (s,
1H, exchangeable, COOH). 13C NMR (100 MHz, DMSO‑d6, δppm): 57.72
(N-CH2-NH), 113.09, 117.94, 131.11, 150.79 (–NH-C6H4), 120.22,
121.37, 128.87, 130.11, 130.50, 131.48, 132.23, 146.97, 148.27
(quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 124.61, 125.47,
129.36, 134.64 (-N-C6H5), 127.44 (2C), 128.07 (2C), 129.64, 138.08
(phenyl C-2/6, 3/5, 4, 1 respectively), 155.65, 167.75 (oxadiazole C-5, 2
respectively), 168.67 (COOH). Anal. Calcd. for: C31H23N5O2S (529.61):
C, 70.30; H, 4.38; N, 13.22; S, 6.05. Found: C, 69.96; H, 4.56; N, 13.43;
S, 6.21.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.bioorg.2021.104920.
References
4.1.6.4. Ethyl 4-((4,5-dihydro-4-phenyl-3-(2-phenylquinolin-4-yl)-5-thi-
oxo-1,2,4-triazol-1-yl)methylamino)benzoate 9d. Recrystallization from
EtOH; yield: 72%; mp: 160–162 ◦C. IR (KBr, ύ, cmꢀ 1): 3032
[1] J.M.A. Blair, M.A. Webber, A.J. Baylay, D.O. Ogbolu, L.J.V. Piddock, Molecular
mechanisms of antibiotic resistance, Nat. Rev. Microbiol. 13 (1) (2015) 42–51.
[2] K.U. Jansen, C. Knirsch, A.S. Anderson, the role of vaccines in preventing bacterial
antimicrobial resistance, Nat. Med 24 (2018) 10.
–
– – –
– – –
(Ar
H
C
str), 2998 (aliph
H
C
str), 1650 and 1550 (C N),
–
1
–
1600–1450 (Ar-C C str). H NMR (400 MHz, DMSO‑d , δppm): 1.38 (t,
–
[3] K. Kaur, M. Jain, T. Kaur, R. Jain, Antimalarials from nature, Bioorg. Med. Chem.
17 (2009) 3229–3256.
6
3H, J = 8 Hz, –CH2-CH3), 4.35 (q, 2H, J = 8 Hz, –CH2-CH3), 5.89 (s, 2H,
[4] R. Musiol, J. Jampilek, V. Buchta, L. Silva, H. Niedbala, B. Podeszwa, A. Palka,
K. Majerz-Maniecka, B. Oleksyn, J. Polanski, Antifungal properties of new series of
quinoline derivatives, Bioorg. Med. Chem. 14 (10) (2006) 3592–3598.
[5] C. Levine, H. Hiasa, K.J. Marians, DNA gyrase and topoisomerase IV: biochemical
activities, physiological roles during chromosome replication, and drug
sensitivities, Biochim Biophys Acta 1400 (1998) 29–43.
NH-CH2-N), 7.08 (d, 1H, J = 8 Hz, quinolyl-C6-H), 7.28–7.30 (m, 3H, Ar-
C
3,4&5-H), 7.39–7.46 (m, 5H, N-C6H5), 7.51(s, 1H, quinolyl-C7-H),
7.56–7.63 (m, 2H, C2H5OOC-Ar-C2&6-H), 7.78–7.82 (m, 2H, C2H5OOC-
Ar-C3&5-H), 7.95 (s, 1H, quinolyl-C3-H), 8.01 (m, 2H,Ar-C2&6-H), 8.14
(d, 1H, J = 8 Hz, quinolyl-C5-H), 8.27 (d, 1H, J = 8 Hz, quinolyl-C8-H).
13C NMR (100 MHz, DMSO‑d6, δppm): 14.40 (CH3), 60.43 (N-CH2-NH),
65.51 (CH2), 113.67, 120.52, 130.16, 148.81 (–NH-C6H4) , 114.29,
120.64, 121.66, 124.59, 129.99, 130.70, 131.48, 146.81, 148.33
(quinoline C-3, 6, 5, 4a, 7, 8, 4, 8a, 2 respectively), 124.29, 127.38,
129.68, 134.10 (-N-C6H5), 127.82 (2C), 128.90 (2C), 129.87, 137.91
(phenyl C-2/6, 3/5, 4, 1 respectively), 166.51 (COOC2H5), 156.01,
169.63 (oxadiazole C-5, 2 respectively). Anal. Calcd. for C33H27N5O2S
(557.66): C, 71.07; H, 4.88; N, 12.56; S, 5.75. Found: C, 71.34; H, 5.12;
N, 12.79; S, 5.69.
[6] F. Collin, S. Karkare, A. Maxwell, Exploiting bacterial DNA gyrase as a drug target:
current state and perspectives, Appl Microbiol Biotechnol. 92 (3) (2011) 479–497.
[7] M. H. El-Shershaby, K. M. El-Gamal, A. H. Bayoumi, K. El-Adl, H. E. Ahmed, H. S.
Abulkhair. Synthesis, antimicrobial evaluation, DNA gyrase inhibition, and in silico
pharmacokinetic studies of novel quinoline derivatives. Arch. Pharm. 2020:
2000277.
[8] T.M.C. Tan, Y.u. Chen, K.H. Kong, J. Bai, Y. Li, S.G. Lim, T.H. Ang, Y. Lam,
Synthesis and the biological evaluation of 2-benzenesulfonylalkyl-5-substituted-
sulfanyl[1,3,4]-oxadiazoles as potential anti-hepatitis B virus agents, Antivir. Res.
71 (1) (2006) 7–14.
[9] M.A. Ali, M. Shaharyar, Oxadiazole mannich bases: Synthesis and
antimycobacterial activity, Bioorg. Med. Chem. Lett. 17 (2007) 3314–3316.
[10] I.A.M. Radini, T.M. Elsheikh, E.M. El-Telbani, R.E. Khidre, New Potential
Antimalarial Agents: Design, Synthesis and Biological Evaluation of Some Novel
Quinoline Derivatives as Antimalarial Agents, Molecules 21 (2016) 909.
[11] A.M. Mohassab, H.A. Hassan, D. Abdelhamid, M. Abdel-Aziz, K.N. Dalby, T.
S. Kaoud, Novel quinoline incorporating 1, 2, 4-triazole/oxime hybrids: Synthesis,
molecular docking, anti-inflammatory, COX inhibition, ulceroginicity and
histopathological investigations, Bioorg. Chem. 75 (2017) 242–259.
11

H.A. Hofny et al.
Bioorganic Chemistry 112 (2021) 104920
[12] T. Kochikyan, M. Samvelyan, V. Arutyunyan, A. Avetisyan, R. Tamazyan,
A. Aivazyan, Synthesis of 1, 2, 4-triazole-3-thiols and their S-substituted
derivatives, Russ. J. Org. Chem. 46 (2010) 551–555.
[21] A.A. Radwan, F.K. Alanazi, M.H. Al-Agamy, 1, 3, 4-Thiadiazole and 1, 2, 4-triazole-
3(4H)-thione bearing salicylate moiety: synthesis and evaluation as anti-Candida
albicans, Braz. J. Pharm. 53 (2017) 1–18.
[13] S¸.G. Küçükgüzel, P. Çıkla-Süzgün, Recent advances bioactive 1, 2, 4-triazole-3-
thiones, Eur. J. Med. Chem. 97 (2015) 830–870.
[22] P. Kaur, R. Kaur, M. Goswami, A review on methods of synthesis of 1,2,4-triazole
derivatives, Int. Res. J. Pharm. 9 (7) (2018) 1–35.
[14] A.M. Mohassa, H.A. Hassan, D. Abdelhamid, A.M. Gouda, B.G.M. Youssif,
H. Tateishi, M. Fujita, M. Otsuka, M. Abdel-Aziz, Design and Synthesis of Novel
quinoline/chalcone/1,2,4-triazole hybrids as potent antiproliferative agent
targeting EGFR and BRAFV600E kinases, Bioorg. Chem. 106 (2021), 104510.
[15] H.A. Abou-Zied, B.G.M. Youssif, M.F.A. Mohamed, A.M. Hayallah, M. Abdel-Aziz,
EGFR inhibitors and apoptotic inducers: Design, synthesis, anticancer activity and
docking studies of novel xanthine derivatives carrying chalcone moiety as hybrid
molecules, Bioorg. Chem. 89 (2019), 102997.
[23] M. Durcik, P. Tammela, M. Barancokova, T. Tomasic, J. Ilas, D. Kikelj, N. Zidar,
Synthesis and evaluation of N-phenylpyrrolamides as DNA gyrase B inhibitors,
ChemMedChem 13 (2018) 186–198.
ˇ
ˇ
ˇ
´
[24] Z. Jakopin, J. Ilas, M. Barancokova, M. Brvar, P. Tammela, M. Sollner Dolenc,
ˇ ˇ
T. Tomasic, D. Kikelj, discovery of substituted oxadiazoles as a novel scaffold for
DNA gyrase inhibitors, Eur. J. Med. Chem 130 (2017) 171–184.
[25] P. Lakshmana Swamy, T. Srinivasa Rao, C.A. Kumar, C. Srinivasa Prasad, G.S. Rao,
In vitro antimicrobial activity of cashew (Anacardium occidentale, L.) nuts shell
liquid against methicillin resistant staphylococcusaureus (MRSA) clinical isolates,
Int. J. Pharm. Pharm. Sci. 3 (2011) 436–440.
[16] M.S. Abdelbaset, G.-D. Abuo-Rahma, M.H. Abdelrahman, M. Ramadan, B.G.
M. Youssif, S.N.A. Bukhari, M.F.A. Mohamed, M. Abdel-Aziz, Novel pyrrol-2(3H)-
ones and pyridazin-3 (2H)-ones carrying quinoline scaffold as anti-proliferative
tubulin polymerization inhibitors, Bioorg. Chem. 80 (2018) 151–163.
[17] T.S. Kaoud, A.M. Mohassab, H.A. Hassan, C. Yan, S.X. Van Ravenstein,
D. Abdelhamid, K.N. Dalby, M. Abdel-Aziz, NO-releasing STAT3 inhibitors
suppress BRAF-mutant melanoma growth, Eur. J. Med. Chem. 186 (2020), 111885.
[18] X. Wang, X. Xie, Y. Cai, X. Yang, J. Li, Y. Li, Design, synthesis and antibacterial
evaluation of some new 2-phenyl-quinoline-4-carboxylic acid derivatives,
Molecules 21 (2016) 340.
[26] L.H. Al-Wahaibi, A.M. Gouda, O.F. Abou-Ghadir, O.I.A. Salem, A.T. Ali, H.
S. Farghaly, M.H. Abdelrahman, L. Trembleau, H.H.M. Abdu-Allah, B.G.M. Youssif,
Design and synthesis of novel 2,3-dihydropyrazino[1,2-a]indole-1,4-dione
derivatives as antiproliferative EGFR and BRAFV600E dual inhibitors, Bioorg. Chem.
104 (2020), 104260.
[27] M. Hisham, B.G.M. Youssif, E.E.A. Osman, A.M. Hayallah, M. Abdel-Aziz, Synthesis
and biological evaluation of novel xanthine derivatives as potential apoptotic
antitumor agents, Eur. J. Med. Chem 176 (2019) 117–128.
[19] M.F. Mohamed, B.G.M. Youssif, M.S.A. Shaykoon, M.H. Abdelrahman, B.
E. Elsadek, A.S. Aboraia, Utilization of Tetrahydrobenzo[4, 5]thieno[2, 3-d]
pyrimidinone as a Cap Moiety in Design of Novel Histone Deacetylase Inhibitors,
Bioorg. Chem. 91 (2019), 103127.
[28] Molecular Operating Environment (MOE), Version 2008.10, Chemical Computing
Group, Inc. Montreal, Quebec, Canada. http://www.chemcomp.com.
[29] M. Brvar, A. Perdih, M. Renko, G. Anderluh, D. Turk, T. Solmajer, Structure-based
discovery of substituted 4,5’-bithiazoles as novel DNA gyrase inhibitors, J. Med.
Chem 55 (14) (2012) 6413–6426.
[20] H.A.A. El-Aal, T.I. El-Emary, Efficient synthesis, characterization and biological
evaluation of some new atophan carbohydrazide derivatives, J. chem. Pharm. 6
(2014) 90–99.
[30] Y. Wei, P. Charifson, A. Letiran, Crystal Structure of E. coli Topoisomerase IV co-
complexed with inhibitor. https://www.rcsb.org/structure/3FV5.
12