Synthesis, antibacterial evaluation, and DNA gyrase inhibition profile of some new quinoline hybrids

Article abstract of DOI:10.1002/ardp.201900086

Antibiotic-resistant bacteria continue to play an important role in human health and disease. Inventive strategies are necessary to develop new therapeutic leads to challenge drug-resistance problems. From this perception, new quinoline hybrids bearing bioactive pharmacophores were synthesized. The newly synthesized compounds were evaluated for their in vitro antibacterial activity against nine bacterial pathogenic strains. The results revealed that most compounds exhibited good antibacterial activities. Seven compounds (2b, 3b, 4, 6, 8b, and 9c,d) displayed enhanced activity against methicillin-resistant Staphylococcus aureus compared to ampicillin. These compounds were subjected to an in vitro S. aureus DNA gyrase ATPase inhibition study, which revealed that compounds 8b, 9c, and 9d showed the highest inhibitory activity with IC₅₀ values of 1.89, 2.73, and 2.14 μM, respectively, comparable to novobiocin (IC₅₀, 1.636 μM). Compounds 2a–c, 3a, 7c, 9c,d, and 10a,b revealed half the potency of levofloxacin in inhibiting the growth of Pseudomonas aeruginosa. As an attempt to rationalize the observed antibacterial activity for the most active compounds 8b, 9c, and 9d, molecular docking in the ATP binding site of S. aureus gyrase B was performed using Glide. Such compounds could be considered as promising scaffolds for the development of new potent antibacterial agents.

Full text of DOI:10.1002/ardp.201900086

Received: 17 March 2019
Revised: 19 June 2019
Accepted: 2 July 2019
|
|
DOI: 10.1002/ardp.201900086
F U L L P A P E R
Synthesis, antibacterial evaluation, and DNA gyrase
inhibition profile of some new quinoline hybrids
1
,2
2
1
1
Ola H. Rizk
|
Mohamed G. Bekhit
|
Aly A. B. Hazzaa
|
El‐Sayeda M. El‐Khawass
|
3
Ibrahim A. Abdelwahab
1
Department of Pharmaceutical Chemistry,
Abstract
Faculty of Pharmacy, University of Alexandria,
Alexandria, Egypt
Antibiotic‐resistant bacteria continue to play an important role in human health and
disease. Inventive strategies are necessary to develop new therapeutic leads to
challenge drug‐resistance problems. From this perception, new quinoline hybrids
bearing bioactive pharmacophores were synthesized. The newly synthesized
compounds were evaluated for their in vitro antibacterial activity against nine
bacterial pathogenic strains. The results revealed that most compounds exhibited
good antibacterial activities. Seven compounds (2b, 3b, 4, 6, 8b, and 9c,d) displayed
enhanced activity against methicillin‐resistant Staphylococcus aureus compared to
ampicillin. These compounds were subjected to an in vitro S. aureus DNA gyrase
ATPase inhibition study, which revealed that compounds 8b, 9c, and 9d showed the
highest inhibitory activity with IC50 values of 1.89, 2.73, and 2.14 μM, respectively,
comparable to novobiocin (IC50, 1.636 μM). Compounds 2a‒c, 3a, 7c, 9c,d, and 10a,b
revealed half the potency of levofloxacin in inhibiting the growth of Pseudomonas
aeruginosa. As an attempt to rationalize the observed antibacterial activity for the
most active compounds 8b, 9c, and 9d, molecular docking in the ATP binding site of S.
aureus gyrase B was performed using Glide. Such compounds could be considered as
promising scaffolds for the development of new potent antibacterial agents.
2
Department of Pharmaceutical Chemistry,
Faculty of Pharmacy & Drug Manufacturing,
Pharos University in Alexandria, Alexandria,
Egypt
3
Department of Microbiology and
Immunology, Faculty of Pharmacy & Drug
Manufacturing, Pharos University in
Alexandria, Alexandria, Egypt
Correspondence
Ola H. Rizk, Department of Pharmaceutical
Chemistry, Faculty of Pharmacy, University of
Alexandria, Alexandria 21521, Egypt.
Email: ola.rizk@pua.edu.eg
K E Y W O R D S
antibacterial activity, DNA gyrase, quinoline, synthesis, thiazolidine
1
|
INTRODUCTION
binding site of DNA gyrase B or stabilization of the covalent enzyme‐
[5,6]
DNA complex; gyrase poisoning.
Although ATP competitive
Human struggle against infectious diseases is endless. The current
treatment of infectious diseases involves administration of a multi-
drug regimen over a long period of time. This has prompted a quick
rise of multidrug‐resistant strains in addition to an abnormal state of
inhibitors of DNA gyrase and topoisomerase IV have so far not
[7]
reached clinical use, they have pronounced therapeutic potential.
Quinolones are considered as very successful gyrase‐targeted drugs.
However, the continuous rise in bacterial resistance challenges us
not only for seeking new compounds, but also for discovering new
[
1,2]
patient resistance.
Among these drug‐resistant microbes are
[5]
methicillin‐resistant Staphylococcus aureus (MRSA), which became a
modes of inhibition of this enzyme. Novobiocin is considered the
[3,4]
serious global medical problem.
only ATPase inhibitor that has been clinically used. Hence, it was no
[
7]
Bacterial DNA gyrase is essential in all bacteria but absent from
higher eukaryotes, making it a validated target in the design of
antibacterial drugs. The main mechanism of these drugs is either
inhibition of the enzymatic activity of gyrase by blocking the ATP
longer used due to its toxicity and weak potency.
Among the wide variety of heterocyclic moieties that have been
explored for developing pharmaceutically important molecules, the
quinoline ring has played an important role in medicinal chemistry in
Arch. Pharm. Chem. Life Sci. 2019;e1900086.
wileyonlinelibrary.com/journal/ardp © 2019 Deutsche Pharmazeutische Gesellschaft
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https://doi.org/10.1002/ardp.201900086

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RIZK ET AL.
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FIGURE 1 Representative structures of
previously synthesized quinolines,
sulfamethizole, thiazoles, and thiazolidines
with antibacterial activity and the general
structures of the target compounds (a‒e)
the last few decades. Quinolines possess diverse biological activities
inhibitory activity on S. aureus DNA gyrase. Molecular docking study
was performed to gain further insights about active compounds.
Furthermore, the molecular docking of the active compounds was
performed in the ATP binding site of S. aureus gyrase B to investigate
their possible binding pattern, in order to rationalize their anti-
bacterial activity in a qualitative way.
[
8–11]
[12]
[13]
such as antimicrobial,
antiplasmodial,
[16]
antituberculosis,
[17]
[
14,15]
anti‐inflammatory,
antimalarial,
[19]
anticancer,
antioxi-
[
18]
dant,
and anti‐HIV.
Furthermore, several synthetic five‐
membered heterocyclic rings such as thiadiazoles, thiazoles, and
thiazolidines were found to have an extensive spectrum of
[20–25]
pharmacological activities among which is the antimicrobial.
The discovery of new antimicrobial scaffolds through consolidat-
ing at least two diverse antimicrobial pharmacophores together in
one molecule to get great synergistic impact became an important
2
2
|
RESULTS AND DISCUSSION
|
Chemistry
.1
[
26]
strategy.
Based on the above considerations, we focused on the develop-
ment of molecular hybrids through a combination of different active
antibacterial pharmacophores like quinolines with thiadiazoles,
thiazoles, or thiazolidines (Figure 1). Such strategy was employed
as an endeavor to enrich the chemical space for antibacterial activity
and to minimize antimicrobial resistance. Synthesized compounds
were evaluated in vitro for their antibacterial activities against
human pathogenic microbes including methicillin‐resistant S. aureus
and the most active compounds were further evaluated for their
The synthetic strategies adopted for the synthesis of the inter-
mediate and target compounds are illustrated in Schemes 1 and 2.
In Scheme 1, the starting material, 6‐bromo‐2‐methylquinoline‐4‐
carboxylic acid 1, was prepared by the condensation of 5‐bromoisatin
with acetone in potassium hydroxide solution followed by acidifica-
[27]
tion with glacial acetic acid according to a reported method.
The
amides 2a‒c and 3a,b were obtained by condensing 1 with the
selected aminothiadiazoles and amino‐5‐alkylthiothiadiazoles, re-
spectively, in the presence of N,N′‐carbonyldiimidazole (CDI). The

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SCHEME 1 Synthesis of quinoline
derivatives 2, 3
reaction was carried out in refluxing tetrahydrofuran and the target
and the appearance of signals assigned to C=CH proton. The
thiosemicarbazide derivatives 8a,b were prepared by refluxing the
acid hydrazide 5 with aryl isothiocyanate in absolute ethanol. IR
spectra of compound 8a,b were characterized by absorption bands
compounds 2a‒c and 3a,b were isolated according to the previously
[
28]
reported method.
It has been found that elemental analysis and
spectral data were in consistency with the proposed amide
structures. The IR spectra of compounds 2a‒c and 3a,b showed
absorption bands characteristic to NH, C=O as well as C=N and
1
corresponding to NH, C=O, and N–C=S thioamide. Their H‐NMR
spectra revealed the appearance of three deuterium exchangeable
signals assigned for the three NH protons. Cyclocondensation of 8a,b
with the selected phenacylbromide or ethyl bromoacetate in ethanol
containing anhydrous sodium acetate produced the respective
thiazoline derivatives 9a‒d, and thiazolidinone derivatives 10a,b,
respectively. The molecular structures of the prepared compounds
9a‒d and 10a,b were confirmed on the basis of their elemental
1
C–S–C functions at their expected regions. H‐NMR spectra of
2
compounds 2a‒c and 3a,b showed a D O exchangeable signal at
13.40–13.81 and 13.50–13.55, respectively, assigned to NH protons.
+
.
The MS spectra of 2b and 3b showed a molecular ion peak (M ) at
m/z 363 (9%) and 409 (7.84%) which matches their molecular
4 4 2
formula C14H11BrN OS and C15H13BrN OS , respectively.
1
13
Regarding Scheme 2, esterification of acid 1 with ethanol in the
presence of concentrated sulfuric acid yielded ethyl 6‐bromo‐2‐
methylquinoline‐4‐carboxylate 4, which on refluxing with 99%
hydrazine hydrate in ethanol, furnished the key intermediate quino-
microanalyses, IR, H‐NMR spectra for all compounds as well as C‐
1
NMR and mass spectra for some representative examples. H‐NMR
spectra of compounds 9a‒d and 10a,b revealed a deuterium‐
exchangeable signal assigned for one NH proton and signal assigned
[29]
line‐4‐carbohydrazide derivative 5.
N‐Substituted rhodanine
5
for thiazoline C ‐H proton in addition to signals assigned to quinoline
derivative 6 was adequately prepared by heating under reflux the
corresponding acid hydrazide 5 with bis(carboxymethyl)trithiocarbo-
nate in dioxane utilizing a previously reported procedure through
C‐2 methyl, phenyl, and quinolyl protons at their expected chemical
shifts. The mass spectrum of compound 9c showed a molecular ion
+
.
peak (M ) at m/z 529 (9.32%) corresponding to C27
H21BrN
4
OS.
[
30,31]
13
Holmberg’s method.
IR spectrum of 6 lacked the high‐frequency
Finally,
C‐NMR spectra of 9c and 10a provided a further
NH stretching absorption band and showed bands at 1759 and
2
confirmation for their intended structures.
−1
1
066 cm corresponding to (C=O) and (C–S–C) groups, respectively.
1
H‐NMR spectrum showed the disappearance of D
group and appearance of two doublets
at 4.53 and 4.62 ppm assigned for thiazolidinone C ‐H protons due to
2
O exchangeable
2.2
|
Biology
protons assigned to the NH
2
2
.2.1 | Antibacterial activity
5
germinal coupling in addition to signals assigned to NH, quinoline C‐2
All the newly synthesized target compounds were evaluated for their
in vitro antibacterial activities against the human pathogens:
methicillin‐resistant S. aureus (MRSA isolated from wound infection),
Staphylococcus epidermidis (RCMB 0100183), Streptococcus mutans
(RCMB 0100172), and Bacillus subtilis (RCMB 0100162) as examples
of Gram‐positive bacteria and Pseudomonas aeruginosa (RCMB
methyl and quinolyl protons at their expected chemical shifts.
Reacting the thiazolidinone derivative
6 with the appropriate
aromatic aldehyde in absolute ethanol containing anhydrous sodium
1
acetate afforded compounds 7a‒c. Their H‐NMR spectra visualized
5
the disappearance of signals assigned to thiazolidinone C protons

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SCHEME 2 Synthesis of quinoline derivatives 4‒10
0
100243), Escherichia coli (RCMB 010052), Salmonella typhi (RCMB
100104), Shigella dysenteriae (RCMB 0100542), and Proteus vulgaris
as standard Gram‐negative antibacterial. Dimethylformamide (DMF)
was used as blank and showed no antibacterial activity. As shown in
Table 2, all synthesized compounds except compound 9a exhibited
reasonable antibacterial activity. Concerning the activity against
Gram‐positive bacteria, nine compounds (2b, 3a,b, 4, 6, 8b, and 9b‒d)
displayed promising activity against the Gram‐positive bacterium
methicillin‐resistant S. aureus. Seven of them (2b, 3b, 4, 6, 8b, and
9c,d) showed superior activity (MIC = 25 µg/ml) than the reference
drug ampicillin (MIC = 32 µg/ml), whereas compounds 3a and 9b
showed approximately half the activity (MIC = 50 μg/ml) as that of
ampicillin. Moreover, compounds 2c, 7b, and 9b displayed half the
potency (MIC = 25 μg/ml) of the reference ampicillin (MIC = 12.5 μg/
0
(RCMB 010085) as examples of Gram‐negative bacteria. Agar‐
[
32]
diffusion technique
was used for the preliminary screening of
antibacterial activity and results were listed as the average diameter
of inhibition zones (IZs) of bacterial growth around the discs in mm
(
Table 1).
The minimal inhibitory concentrations (MICs) and minimal
bactericidal concentrations (MBCs) were determined using two‐fold
[
33]
serial dilution
for compounds that showed significant growth
inhibition zones (>10 mm). Ampicillin was used as a reference
standard Gram‐positive antibacterial, while levofloxacin was used

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ml), while compounds 5, 6, and 9d showed 25% the activity of
ampicillin against S. mutans (MIC = 50 μg/ml). Compounds 5 and 9d
revealed half the potency (MIC = 25 μg/ml) of ampicillin (MIC =
TABLE 3 Inhibitory activities of the most active compounds
against Staphylococcus aureus DNA gyrase
a
Compounds
2b
IC50 (µM)
12.5 μg/ml) in inhibiting the growth of B. subtilis, whereas compounds
5.13 ± 0.14
3.24 ± 0.11
3.05 ± 0.095
5.83 ± 0.12
1.89 ± 0.04
2.73 ± 0.06
2.14 ± 0.02
1.636 ± 0.06
2c, 6, 7b, 9b, and 9d displayed 25% of the potency of ampicillin
3
4
6
8
9
9
b
against same organism with (MIC = 50 μg/ml). On the other hand,
compounds 2c, 6, 7c, and 10a showed 25% the activity of ampicillin
(MIC = 12.5 μg/ml) against S. epidermidis (MIC = 50 μg/ml).
b
c
By investigating the activity against Gram‐negative bacteria,
Compounds 2a–c, 3a, 7c, 9c,d, and 10a,b revealed half the potency
of levofloxacin (MIC = 12.5 µg/ml) in inhibiting the growth of P.
aeruginosa (MIC = 25 μg/ml), while compounds 4, 7b, 8a, and 9b
showed mild activity against P. aeruginosa with (MIC = 50 µg/ml).
Moreover, compounds 2c, 7a, 8a, and 10b displayed half the activity of
levofloxacin (MIC = 12.5 µg/ml) against P. vulgaris (MIC = 25 µg/ml),
while compounds 2a, 3b, 4, and 9a showed 25% the activity of
standard reference with MIC = 50 µg/ml. On the other hand, most
compounds showed a narrow spectrum of activity in inhibiting the
growth of Gram‐negative bacteria as it was inactive against Salmonella
typhi and Shigella dysenteriae and only two compounds 2a and 3b
showed 25% the activity of levofloxacin against E. coli (MIC = 25 µg/ml
vs. 6.25 µg/ml). It is worth mentioning that compounds 2b, 3a, 9c, and
d
Novobiocin
a
Concentration of compound (mean ± SD) that inhibits the enzyme
activity by 50%.
displayed a weak activity with IC50 values in the range of 3.05 to
5.83 μM.
2
.3 Molecular modeling
|
In order to investigate the possible binding modes of the most active
compounds (8b, 9c, and 9d), molecular docking in the ATP binding
site of S. aureus GyrB was performed using Glide (Schrödinger Inc.,
9d demonstrated a broad‐spectrum antibacterial activity.
[34]
NY).
The obtained docking pose of compound 8b (Figure 2a)
Structure–activity correlation of the target compounds revealed
shows that the quinoline moiety is embedded in a hydrophobic
region, where it undergoes van der Waals interactions with the side
chains of Ile541, Val79, Ile86, Ile102, and Ile175. The carbonyl group
of 8b was additionally able to undergo hydrogen bond interactions
with the conserved water molecule, while the thiourea moiety
showed two hydrogen bond interactions with Glu58. Furthermore,
the tolyl group displayed van der Waals interactions with Pro87.
Meanwhile, the analogous compounds 9c and 9d showed an identical
binding mode (Figure 2b). Interestingly, the quinoline moiety and the
tolyl group of these compounds were embedded in the same
hydrophobic region as observed for 8b. In addition, the carbonyl
group showed hydrogen bond interactions with the conserved water
molecule and the side chain of Thr173, while the hydrazone‐NH
displayed a hydrogen bond with the backbone of Asn54.
that among the thiadiazolylquinolines (2a–c and 3a,b), the methyl
and ethyl derivatives (2b and 3a,b) showed enhanced activity against
Gram‐positive bacteria (MRSA). While the unsubstituted and the
bromo derivatives (2a and 2c) displayed antibacterial activity against
the Gram‐negative P. aeruginosa. Replacement of thiadiazole moiety
with 4‐oxo‐2‐thioxothiazolidine moiety in compound 6 conserved the
antibacterial activity against MRSA. Introduction of the substituted
arylidenes at position 5 of the thioxothiazolidine moiety in compound
6
dramatically decreased the activity. It was observed that increasing
the length of atom spacer between the quinoline ring and the 3,4‐
diarylthiazoles as in compounds 9a–d enhanced the antibacterial
activity against MRSA and P. aeruginosa. Moreover, replacement of
3,4‐diarylthiazole moiety with 3‐arylthiazolidine moiety in com-
pounds 10a,b with the same atom spacers from quinoline ring
resulted in loss of the antibacterial activity against MRSA, while
retaining the activity against P. aeruginosa.
3
|
CONCLUSION
2
.2.2 | Inhibitory activities against Staphylococcus
aureaus DNA gyrase
The objective of the present study was to synthesize new molecular
hybrids through a combination of different active pharmacophores like
quinolines with thiadiazoles, thiazoles, or thiazolidines into one core
structure with the hope of discovering new potent and effective
antibacterial agents. The synthesized compounds were evaluated in
vitro for their antibacterial activities against human pathogenic
microbes to investigate the effect of such structural modification on
the biological effect. The results revealed that nine compounds (2b, 3a,
3b, 4, 6, 8b, and 9b‒d) displayed promising activity against the Gram‐
positive bacterium, methicillin‐resistant S. aureus. Seven compounds (2b,
3b, 4, 6, 8b, and 9c,d) exhibited superior antibacterial activity than the
Seven compounds (2b, 3b, 4, 6, 8b, and 9c,d) were evaluated for their
inhibitory activity against S. aureus DNA gyrase in Gyrase ATPase
[6,7]
assay utilizing novobiocin as internal standard.
The results are
presented as IC50 values (Table 3). Three compounds (8b, 9c, and 9d),
showed potent inhibition of S. aureaus DNA gyrase with IC50 values in
the range of 1.89 to 2.73 μM. Compound 8b was nearly equipotent to
the reference novobiocin (IC50, 1.89 μM vs. 1.636 μM). While
compounds 9c and 9d showed inhibitory activity with IC50 values
of 2.73 and 2.14 μM, respectively. Compounds 2b, 3b, 4, and 6

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RIZK ET AL.
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FIGURE 2 (a) Docking pose of compound 8b (green) in the adenosine triphosphate binding site of Staphylococcus aureus GyrB (PDB ID
[
35]
5
D7C).
green) and 9d (cyan). Protein residues in the binding site are shown as white sticks, the conserved water molecule as red sphere, and hydrogen
bonds as yellow dashed lines. (d) Ligand interaction diagram of the predicted binding mode of 9c in S. aureus GyrB
(b) Ligand interaction diagram of the predicted binding mode of 8b in S. aureus GyrB. (c) Overlay of the docking poses of compound 9c
(
reference drug ampicillin. Whereas compounds 2a‒c, 3a, 7c, 9c,d, and
0a,b revealed half the potency of levofloxacin in inhibiting the growth
novobiocin (IC50: 1.636 μM). To determine the possible binding modes
1
of compounds, molecular docking of most active compounds (8b, 9c, and
9d) was performed in the S. aureus GyrB binding site using Glide
(Schrödinger Inc.). Accordingly, such compounds deserve further
structure‐optimization studies hoping to discover new effective anti-
bacterial agents.
of P. aeruginosa. Compounds 2b, 3b, 4, 6, 8b, and 9c,d were subjected to
in vitro S. aureus DNA gyrase ATPase inhibition study, which revealed
that compounds 8b, 9c, and 9d showed the highest inhibitory activity
with IC50 values of 1.89, 2.73, and 2.14 μM, respectively, comparable to

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4
|
EXPERIMENTAL
The reaction mixture was heated under reflux for 75 min, whereupon
a white precipitate was separated out. Then a solution of equimolar
amount of 2‐amino and 2‐amino‐5‐substituted‐1,3,4‐thiadiazoles in
tetrahydrofuran (10 ml) was added to the stirred reaction mixture
and heating was continued under reflux for 3 hr. The reaction
mixture was allowed to attain room temperature, stirred with water
(100 ml), and acidified with glacial acetic acid to pH 4. The separated
precipitate was filtered, washed thoroughly with water, air dried, and
crystallized from dioxane.
4
4
.1 Chemistry
|
.1.1 | General
All reagents and solvents were used as received from commercial
suppliers, unless indicated otherwise. Melting points were
determined in open‐glass capillaries using a Griffin melting point
apparatus and are uncorrected. Follow up of the reactions rates
were performed by thin‐layer chromatography (TLC) on silica gel
(
60 GF254) coated glass plates and the spots were visualized by
6‐Bromo‐2‐methyl‐N‐1,3,4‐thiadiazol‐2‐yl quinoline‐4‐
carboxamide (2a)
exposure to iodine vapors or UV‐lamp at λ 254 nm for a few
−1
seconds. Infrared spectra (IR) were recorded on Bruker Tensor
White needles; yield: 52%; Mp: 256–257°C. IR (KBr, cm ): 3117
1
3
7 FT‐IR spectrometer at the Central Laboratory Unit, Faculty of
(NH); 1679 (C=O); 1528 (C=N); 1264, 1076, 1048 (C–S–C). H‐NMR
Science, Cairo University. Nuclear magnetic resonance spectra,
(300 MHz, DMSO‐d
quinolyl‐C3,7,8‐H); 8.39 (s, 1H, quinolyl‐C
‐H); 13.48 (s, 1H, D O exchangeable, NH). C‐NMR (75.54 MHz,
DMSO‐d , δ ppm): 24.76, 120.04, 122.46, 123.40, 126.92, 130.95,
132.93, 137.29, 146.27, 149.26, 158.88, 159.23, 165.01. Anal. calcd.
for C13 BrN OS (349.21): C, 44.71; H, 2.60; N, 16.04; S, 9.18.
6
, δ ppm): 2.73 (s, 3H, CH
3
); 7.87–8.00 (m, 3H,
1
13
H‐NMR and C‐NMR, were scanned on Jeol spectrophotometer
5
‐H); 9.32 (s, 1H, thiadiazole‐
1
3
(
300 MHz) at Central Laboratory Unit, Faculty of Science, Cairo
C
5
2
University using deuterated dimethylsulfoxide as a solvent. The
data were reported as chemical shifts or δ values (ppm) relative
to tetramethylsilane (TMS) as internal standard. Signals are
indicated by the following abbreviations: s = singlet, d = doublet,
t = triplet, q = quartet, and m = multiplet. Electron impact mass
spectra (EI‐MS) were run on a gas chromatograph/mass spectro-
photometer Shimadzu GCMS/QP‐2010 plus (70 eV) at the
6
H
9
4
Found: C, 44.94; H, 2.63; N, 16.17; S, 9.26.
6‐Bromo‐2‐methyl‐N‐(5‐methyl‐1,3,4‐thiadiazol‐2‐yl)quinoline‐4‐
carboxamide (2b)
−1
Faculty of Science, Cairo University. Relative intensity
%
White needles; yield: 55%; Mp: 169–170°C. IR (KBr, cm ): 3116
1
corresponding to the most characteristic fragments were re-
corded. Elemental microanalyses were performed at the Micro-
analytical Center, Faculty of Science, Cairo University. The
results of the microanalyses were within ±0.4% of the calculated
values.
(NH); 1676 (C=O); 1539 (C=N); 1248, 1076 (C–S–C). H‐NMR
(300 MHz, DMSO‐d
6 3
, δ ppm): 2.69, 2.72 (two s, each 3H, 2xCH );
7.85–7.99 (m, 3H, quinolyl‐C3,7,8‐H); 8.39 (s, 1H, quinolyl‐C
5
‐H);
+
.
13.40 (s, 1H, D
2
O exchangeable, NH). MS (m/z, %): 365 (M +2)
+
.
+.
(5.70); 364 (M +1) (30.60); 363 (M ) (9.00); 220 (100). Anal. calcd.
for C14 11BrN OS (363.23): C, 46.29; H, 3.05; N, 15.42; S, 8.83.
Found: C, 46.37; H, 3.09; N, 15.67; S, 8.79.
The original spectra of the investigated compounds are provided
as Supporting Information, as are their InChI codes.
H
4
6
‐Bromo‐2‐methyl‐N‐(5‐bromo‐1,3,4‐thiadiazol‐2‐yl)quinoline‐4‐car-
4
.1.2 | Synthesis of 6‐bromo‐2‐methylquinoline‐4‐
boxamide (2c)
carboxylic acid (1)
−1
Brown needles; yield: 45%; Mp: 232–233°C. IR (KBr, cm ): 3110 (NH);
1
Acetone (24.2 ml, 0.33 mol) was gradually added to a stirred and
cooled solution of 5‐bromoisatin (5.00 g, 0.022 mol) in 33%
aqueous potassium hydroxide (19 ml). The reaction mixture was
heated under reflux while stirring for 16 hr and left to attain
room temperature, then acidified with glacial acetic acid to pH 4,
whereupon a beige precipitate was formed. The obtained product
was filtered, washed thoroughly with water, air dried, and
crystallized from ethanol. Yield: 64%; Mp: 266–267°C (reported
1675 (C=O); 1531 (C=N); 1163, 1038 (C–S–C). H‐NMR (300 MHz,
DMSO‐d
H); 8.40 (s, 1H, quinolyl‐C
Anal. calcd. for C13 Br
7.49. Found: C, 36.61; H, 1.85; N, 13.24; S, 7.53.
6
, δ ppm): 2.72 (s, 3H, CH
‐H); 13.81 (s, 1H, D
OS (428.10): C, 36.47; H, 1.88; N, 13.09; S,
3
); 7.86–7.98 (m, 3H, quinolyl‐C3,7,8
‐
5
2
O exchangeable, NH).
H
8
2 4
N
4
(
.1.4 | Synthesis of 6‐bromo‐2‐methyl‐N‐[5‐
substituted thio)‐1,3,4‐thiadiazol‐2‐yl]quinoline‐4‐
[
27]
2
59–260°C).
carboxamides (3a,b)
A solution of N,N'‐carbonyldiimidazole (0.81 g, 50 mmol) in tetrahydro-
furan (10 ml) was added to a stirred solution of 6‐bromo‐2‐methyl-
cinchoninic acid 1 (1.33 g, 50 mmol) in tetrahydrofuran (10 ml). The
reaction mixture was heated under reflux for 75 min, whereupon a
white precipitate was separated out. Then, a solution of equimolar
amount of 2‐amino‐5‐alkylthio‐1,3,4‐thiadiazole in tetrahydrofuran
(10 ml) was added to the stirred reaction mixture and heating was
4
.1.3 | Synthesis of 6‐bromo‐2‐methyl‐N‐(5‐
substituted‐1,3,4‐thiadiazol‐2‐yl)quinoline‐4‐
carboxamides (2a‒c)
A solution of N,N'‐carbonyldiimidazole (0.81 g, 50 mmol) in tetrahy-
drofuran (10 ml) was added to a stirred solution of 6‐bromo‐2‐
methylcinchoninic acid 1 (1.33 g, 50 mmol) in tetrahydrofuran (10 ml).

10 of 14
RIZK ET AL.
|
continued under reflux for 3 hr. The reaction mixture was allowed to
attain room temperature, stirred with water (100 ml), and acidified with
glacial acetic acid to pH 4. The separated precipitate was filtered,
washed thoroughly with water, air dried, and crystallized from dioxane.
hydrazine hydrate (5 ml, 100 mmol). The reaction mixture was heated
under reflux for 2 hr, whereupon white crystals started to separate
out. After attaining room temperature, the crystalline product was
filtered, washed thoroughly with water, air dried and recrystallized
from ethanol. White needles; yield: 98%; Mp: 240–241°C (reported
[
29]
−1
6
4
‐Bromo‐2‐methyl‐N‐[5‐(methylthio)‐1,3,4‐thiadiazol‐2‐yl]quinoline‐
‐carboxamide (3a)
254–255°C).
IR (KBr, cm ): 3258, 3147 (NH
1586 (C=N). H‐NMR (300 MHz, DMSO‐d , δ ppm): 2.67 (s, 3H, CH
4.68 (s, 2H, NH , D O exchangeable); 7.49 (s, 1H, quinolyl‐C ‐H);
7.86–7.94 (m, 2H, quinolyl‐C7,8‐H); 8.34 (s, 1H, quinolyl‐C ‐H); 9.92
(s, 1H, NH, D O exchangeable). Anal. calcd. for C11 10BrN
2
, NH); 1639 (C=O);
1
6
3
);
−
1
White needles; yield: 50%; Mp: 210–212°C. IR (KBr, cm ): 3112
2
2
3
1
(
(
NH); 1675 (C=O); 1542 (C=N); 1169, 1076 (C–S–C). H‐NMR
5
300 MHz, DMSO‐d
.86 (s, 1H, quinolyl‐C
s, 1H, quinolyl‐C ‐H); 13.50 (s, 1H, D
11BrN OS (395.29): C, 42.54; H, 2.81; N, 14.17; S,
6
, δ ppm): 2.72, 2.77 (two s, each 3H, 2xCH
‐H); 7.91–7.99 (m, 2H, quinolyl‐C7,8‐H); 8.40
O exchangeable, NH). Anal.
3
);
2
H
3
O
7
3
(280.13): C, 47.17; H, 3.60; N, 15.00. Found: C, 47.35; H, 3.64; N,
15.23.
(
5
2
calcd. for C14
H
4
2
1
6.22. Found: C, 42.69; H, 2.88; N, 14.25; S, 16.34.
4
.1.7 | Synthesis of 6‐bromo‐2‐methyl‐N‐(4‐oxo‐2‐
thioxothiazolidin‐3‐yl)quinoline‐4‐carboxamide (6)
6
‐Bromo‐2‐methyl‐N‐[5‐(ethylthio)‐1,3,4‐thiadiazol‐2‐yl]quinoline‐4‐
carboxamide (3b)
To a stirred solution of acid hydrazide 5 (0.28 g, 1 mmol) in dioxane,
was added an equimolar amount of bis(carboxymethyl)trithiocarbo-
nate (0.23 g, 1 mmol). The reaction mixture was heated under reflux
with stirring for 5 hr and then left to attain room temperature. The
obtained precipitate was filtered, washed with water, air dried, and
crystallized from ethanol. Yellow crystals; yield: 74%; Mp:
−
1
White needles; yield: 51%; Mp: 143–145°C. IR (KBr, cm ): 3107
1
(
(
NH); 1670 (C=O); 1535 (C=N); 1167, 1070 (C–S–C). H‐NMR
300 MHz, DMSO‐d
H, CH ); 3.25 (q, J = 7.2 Hz, 2H, CH
H); 7.90–7.99 (m, 2H, quinolyl‐C7,8‐H); 8.39 (s, 1H, quinolyl‐C
6
, δ ppm): 1.39 (t, J = 7.2 Hz, 3H, CH
CH ); 7.85 (s, 1H, quinolyl‐C
‐H);
O exchangeable, NH). C‐NMR (75.54 MHz, DMSO‐
, δ ppm): 14.69, 24.77, 28.08, 120.09, 122.48, 123.36, 126.95,
30.94, 132.94, 136.92, 146.27, 158.78, 159.19, 159.48, 164.89. MS
2 3
CH ); 2.72 (s,
3
3
2
3
3
‐
5
1
3
−1
1
d
1
3.55 (s, 1H, D
2
124–125°C. IR (KBr, cm ): 3164 (NH); 1759, 1699 (C=O); 1597
1
6
(C=N); 1066 (C–S–C). H‐NMR (300 MHz, DMSO‐d
6
, δ ppm): 2.75 (s,
); 7.66 (s, 1H, quinolyl‐C
H); 7.93–8.01 (m, 2H, quinolyl‐C7,8‐H); 8.50 (s, 1H, quinolyl‐C ‐H);
O exchangeable). C‐NMR (75.54 MHz, DMSO‐
, δ ppm): 25.14, 34.15, 120.37, 121.64, 123.76, 127.27, 131.31,
33.53, 137.97, 146.50, 159.74, 164.68, 170.52, 200.27. Anal. calcd.
10BrN (396.280): C, 42.43; H, 2.54; N, 10.60; S, 16.18.
Found: C, 42.51; H, 2.51; N, 10.76; S, 16.27.
3H, CH
3
); 4.53, 4.62 (2d, J = 6.6 Hz, 2H, CH
2
3
‐
+.
+.
+.
(
m/z, %): 411(M +2) (6.26); 410 (M +1) (29.99); 409 (M ) (7.84); 250
100). Anal. calcd. for C15 13BrN OS (409.32): C, 44.02; H, 3.20; N,
3.69; S, 15.67. Found: C, 44.26; H, 3.25; N, 13.86; S, 15.74.
5
1
3
(
H
4
2
12.04 (s, 1H, NH, D
2
1
d
6
1
for C14
H
3 2 2
O S
4
.1.5 | Synthesis of ethyl 6‐bromo‐2‐
methylquinoline‐4‐carboxylate (4)
A solution of 6‐bromo‐2‐methylcinchoninic acid 1 (8.50 g, 32 mmol)
4
.1.8 | Synthesis of N‐(5‐arylidene‐4‐oxo‐2‐
thioxothiazolidin‐3‐yl)‐6‐bromo‐2‐methylquinoline‐4‐
carboxamides (7a‒c)
in absolute ethanol (60 ml) containing concentrated sulfuric acid
(7 ml) was heated under reflux for 15 hr. The reaction mixture was
concentrated to half its volume under reduced pressure, allowed to
attain room temperature and then carefully poured with stirring onto
excess 10% sodium hydrogen carbonate solution. The obtained ester
was filtered, washed several times with cold water, air dried and
crystallized from ethanol. Brown crystals; yield: 85%; Mp:
A solution of the appropriate aldehyde (0.5 mmol) in absolute ethanol
was gradually added to a well stirred solution of 6‐bromo‐2‐methyl‐
N‐(4‐oxo‐2‐thioxothiazolidin‐3‐yl)quinoline‐4‐carboxamide 7 (0.2 g;
0.5 mmol) in absolute ethanol (10 ml) containing anhydrous sodium
acetate (0.08 g, 0.5 mmol). The reaction mixture was heated under
reflux for 2 hr. The resulting precipitates were filtered, washed with
cold ethanol, air dried, and crystallized from dioxane.
[
29]
−1
106–107°C.
IR (KBr, cm ): 1717 (C=O); 1589 (C=N); 1243, 1168
ppm): 1.49 (t, 3H,
); 4.52 (q, 2H, J = 6.9 Hz,
); 7.68 (d, 1H, J = 9 Hz, quinolyl‐C ‐H); 7.85 (s, 1H, quinolyl‐
‐H); 8.03 (d, 1H, J = 9 Hz, quinolyl‐C ‐H); 8.79 (s, 1H, quinolyl‐C
H). Anal. calcd. for C13 12BrNO (294.15): C, 53.08; H, 4.11; N, 4.76.
Found: C, 53.19; H, 4.18; N, 4.85.
1
(
C–O–C). H‐NMR (300 MHz, DMSO‐d
6
,
δ
2 3 3
J = 6.9 Hz, ‐CH CH ); 2.80 (s, 3H, CH
‐
CH CH
2
3
7
C
3
8
5
‐
N‐(5‐Benzylidene‐4‐oxo‐2‐thioxothiazolidin‐3‐yl)‐6‐bromo‐2‐methyl-
quinoline‐4‐carboxamide (7a)
H
2
−1
Yellow crystals; yield: 55%; Mp: 265–266°C. IR (KBr, cm ): 3048
1
(
(
NH); 1729, 1648 (C=O); 1522 (C=N); 1116, 1025 (C–S–C). H‐NMR
6 3
300 MHz, DMSO‐d , δ ppm): 2.76 (s, 3H, CH ); 7.59–8.02 (m, 8H,
4
.1.6 | Synthesis of 6‐bromo‐2‐methylquinoline‐4‐
phenyl‐C2,3,4,5,6‐H and quinolyl‐C3,7,8‐H); 8.07 (s, 1H, C=CH); 8.53 (s,
H, quinolyl‐C ‐H); 12.33 (s, 1H, D O exchangeable, NH). Anal. calcd.
for C21 14BrN (484.39): C, 52.07; H, 2.91; N, 8.68; S, 13.24.
Found: C, 52.14; H, 2.98; N, 8.75; S, 13.41.
carbohydrazide (5)
1
5
2
A
solution of ethyl 6‐bromo‐2‐methylcinchoninate
4
(2.94 g,
H
3 2 2
O S
1
0 mmol) in absolute ethanol (30 ml) was added to a stirred 99%

RIZK ET AL.
11 of 14
|
6
2
‐Bromo‐N‐[5‐(4‐chlorobenzylidene)‐4‐oxo‐2‐thioxothiazolidin‐3‐yl]‐
‐methylquinoline‐4‐carboxamide (7b)
(415.31): C, 52.06; H, 3.64; N, 13.49; S, 7.72. Found: C, 52.19; H, 3.71;
N, 13.67; S, 7.90.
−
1
Pale yellow crystals; yield: 54%; Mp: 255–256°C. IR (KBr, cm ):
3
1
146 (NH); 1759, 1646 (C=O); 1509 (C=N); 1169, 1074 (C–S–C).
2
‐(6‐Bromo‐2‐methylquinoline‐4‐carbonyl)‐N‐(p‐tolyl)hydrazine‐1‐
carbothioamide (8b)
White needles; yield: 86%; Mp: 246–247°C. IR (KBr, cm ): 3213
H‐NMR (300 MHz, DMSO‐d
‐H); 7.55 (d, J = 8.1 Hz, 2H, 4‐chlorophe-
nyl‐C3,5‐H); 7.72 (s, 1H, 4‐quinolyl C ‐H)); 7.81 (d, J = 8.1 Hz, 2H,
‐chlorophenyl‐C2,6‐H); 7.86–8.36 (m, 3H, quinolyl‐C5,8‐H and
6 3
, δ ppm): 2.72 (s, 3H, CH ); 7.33 (d,
J = 8.1 Hz, 1H, quinolyl C
7
−1
3
(NH); 1678 (C=O); 1594, 1287, 1179, 961 (N–C=S thioamide I, II, III,
4
1
IV bands respectively). H‐NMR (300 MHz, DMSO‐d
6
, δ ppm): 2.31 (s,
); 7.16 (d, J = 7.5 Hz, 2H, p‐tolyl‐C2,6
H); 7.32 (d, 2H, J = 7.8 Hz, p‐tolyl‐C3,5‐H); 7.78 (s, 1H, quinolyl‐C ‐H);
.88–7.98 (m, 3H, quinolyl‐C5,7,8‐H); 9.75, 9.85, 10.78 (three s, each
H, D O exchangeable, NH). Anal. calcd. for C19 17BrN OS (429.34):
1
3
C=CH); 12.29 (s, 1H,
75.54 MHz, DMSO‐d , δ ppm): 24.77, 119.67, 121.15, 123.83,
26.97, 128.19, 128.43, 128.91, 130.96, 132.53, 132.81, 134.89,
38.84, 143.90, 145.08, 147.71, 159.34, 162.33. Anal. calcd. for
13BrClN (518.83): C, 48.62; H, 2.53; N, 8.10; S, 12.36.
Found: C, 48.74; H, 2.52; N, 8.19; S, 12.42.
D
2
O
exchangeable, NH).
C‐NMR
3H, C
6
H
4 3
‐CH ); 2.71 (s, 3H, CH
3
‐
(
6
3
1
1
7
1
2
H
4
C
21
H
3 2 2
O S
C, 53.15; H, 3.99; N, 13.05; S, 7.47. Found: C, 53.22; H, 4.07; N, 13.21;
S, 7.53.
6
‐Bromo‐N‐[5‐(4‐methoxybenzylidene)‐4‐oxo‐2‐thioxothiazolidin‐3‐
4
.1.10 | 6‐Bromo‐N'‐(3,4‐di‐arylthiazol‐2(3H)‐
yl]‐2‐methyl quinoline‐4‐carboxamide (7c)
−
1
ylidene)‐2‐methylquinoline‐4‐carbohydrazides (9a‒d)
Yellow crystals; yield: 50%; Mp: 215–217°C. IR (KBr, cm ): 3110
1
(
(
NH); 1759, 1646 (C=O); 1535 (C=N); 1173, 1076 (C–S–C). H‐NMR
To a stirred suspension of the appropriate thiosemicarbazone 8a,b
300 MHz, DMSO‐d
6 3 3
, δ ppm): 2.72 (s, 3H, CH ); 3.83 (s, 3H, OCH );
(
1 mmol) in absolute ethanol (20 ml), an equimolar amount of
phenacyl bromide or p‐bromophenacyl bromide in absolute ethanol
10 ml) was added. The reaction mixture was heated under reflux for
hr and then allowed to attain room temperature. The pH of the
solution was adjusted to pH 8 by adding a cooled saturated solution
of sodium acetate (10 g/10 ml H O). After standing for an overnight
7.03 (d, J = 8.4 Hz, 2H, 4‐methoxyphenyl‐C2,6‐H); 7.53 (s, 1H,
quinolyl‐C
3
‐H); 7.70‐8.34 (m, 6H, 4‐methoxyphenyl‐C3,5‐H, quinolyl‐
O exchangeable, NH). Anal.
(514.41): C, 51.37; H, 3.14; N, 8.17; S,
2.46. Found: C, 51.45; H, 3.16; N, 8.24; S, 12.55.
(
C
5,7,8‐H and C=CH); 12.06 (s, 1H, D
2
2
calcd. for C22 16BrN
H
3 3 2
O S
1
2
in a refrigerator, the separated products were filtered, washed
several times with water, air dried and crystallized from dioxane/
ethanol mixture (1:1).
4
.1.9 | Synthesis of N‐aryl‐2‐(6‐bromo‐2‐
methylquinoline‐4‐carbonyl)hydrazine‐1‐
carbothioamides (8a,b)
6‐Bromo‐N'‐(3,4‐diphenylthiazol‐2(3H)‐ylidene)‐2‐methylquinoline‐
A solution of the selected aryl isothiocyanate (10 mmol) in absolute
ethanol (5 ml) was gradually added to a well stirred solution of an
equimolar amount of the acid hydrazide 5 (2.8 g, 10 mmol) in
absolute ethanol (20 ml). The reaction mixture was heated under
reflux for 2 hr, concentrated to half its volume under reduced
pressure and set aside for an overnight in refrigerator for complete
precipitation of the product. The formed beige precipitates were
filtered, washed with cold 50% ethanol, air dried, and crystallized
from ethanol.
4‐carbohydrazide (9a)
−1
Pale yellow needles; yield: 88%; Mp: 211–212°C. IR (KBr, cm ):
1
3280 (NH); 1637 (C=O); 1239, 1069 (C–S–C). H‐NMR (300 MHz,
DMSO‐d , δ ppm): 2.60, 2.67 (two s, each 3H, 2xCH , Z and E); 6.25,
6
3
6.57 (two s, each 1H, 2x thiazoline‐C ‐H, Z and E); 6.94–7.92 (m, 14H,
5
thiazoline‐C ‐phenyl‐C2,3,4,5,6‐H and thiazoline‐N‐phenyl‐C2,3,4,5,6‐H,
4
quinolyl‐C3,7,8‐H and NH, Z and E); 8.71, 8.88 (two s, each 1H,
quinolyl‐C ‐H, Z and E). Anal. calcd. for C26H19BrN OS (515.43): C,
5
4
60.59; H, 3.72; N, 10.87; S, 6.22. Found: C, 60.71; H, 3.69; N, 10.98; S,
.18.
6
2
‐(6‐Bromo‐2‐methylquinoline‐4‐carbonyl)‐N‐phenylhydrazine‐1‐
carbothioamide (8a)
White needles; yield: 85%; Mp: 248–250°C. IR (KBr, cm ): 3115
6‐Bromo‐N'‐[4‐(4‐bromophenyl)‐3‐phenylthiazol‐2(3H)‐ylidene]‐2‐
methylquinoline‐4‐carbohydrazide (9b)
−
1
−1
(NH); 1682 (C=O); 1594, 1285, 1178, 962 (N–C=S thioamide I, II, III,
White needles; yield: 90%; Mp: 225–227°C. IR (KBr, cm ): 3104
1
1
IV bands, respectively). H‐NMR (300 MHz, DMSO‐d
6
, δ ppm): 2.72
‐H); 7.39 (t, J = 7.5 Hz,
H, phenyl‐C3,5‐H); 7.50 (d, J = 7.5 Hz, 2H, phenyl‐C2,6‐H); 7.88–7.97
m, 3H, quinolyl‐C3,7,8‐H); 8.57 (s, 1H, quinolyl‐C ‐H); 9.84, 9.95,
0.82 (three s, each 1H, exchangeable, NH).
75.54 MHz, DMSO‐d , δ ppm): 24.88, 119.60, 121.52, 123.93,
25.23, 127.70, 128.28, 130.78, 132.81, 133.40, 138.80, 139.05,
46.24, 159.12, 165.91, 181.90. Anal. calcd. for C18 15BrN OS
(NH); 1636 (C=O); 1238, 1070 (C–S–C). H‐NMR (300 MHz, DMSO‐
(s, 3H, CH
3
); 7.20 (t, J = 7.5 Hz, 1H, phenyl‐C
4
d
6
, δ ppm): 2.60, 2.68 (two s, each 3H, 2xCH
(two s, each 1H, 2x thiazoline‐C ‐H, Z and E); 6.94–7.91 (m, 13H,
thiazoline‐C ‐phenyl‐C2,3,4,5,6‐H and thiazoline‐N‐phenyl‐C2,3,4,5,6‐H,
quinolyl‐C3,7,8‐H and NH, Z and E); 8.51, 8.84 (two s, each 1H,
quinolyl‐C ‐H, Z and E). Anal. calcd. for C26 18Br OS (594.33): C,
3
, Z and E); 6.32, 6.67
2
5
(
5
4
1
3
1
D
2
O
C‐NMR
(
6
5
H
2 4
N
1
1
52.54; H, 3.05; N, 9.43; S, 5.39. Found: C, 52.78; H, 3.02; N, 9.62; S,
5.47.
H
4

12 of 14
RIZK ET AL.
|
6
‐Bromo‐2‐methyl‐N'‐[4‐phenyl‐3‐(p‐tolyl)thiazol‐2(3H)‐ylidene]qui-
163.21, 172.90. Anal. calcd. for C20
H15BrN
4 2
O S (455.33): C, 52.76;
noline‐4‐carbohydrazide (9c)
H, 3.32; N, 12.30; S, 7.04. Found: C, 52.93; H, 3.40; N, 12.41; S, 7.11.
−
1
White needles; yield: 91%; Mp: 220–221°C. IR (KBr, cm ): 3112
1
(
NH); 1665 (C=O); 1237, 1070 (C–S–C). H‐NMR (300 MHz, DMSO‐
6‐Bromo‐2‐methyl‐N'‐[4‐oxo‐3‐(p‐tolyl)thiazolidin‐2‐ylidene]quino-
line‐4‐carbohydrazide (10b)
d
2
1
6
, δ ppm): 2.27, 2.29 (two s, each 3H, 2xCH
.60, 2.67 (two s, each 3H, 2xCH , Z and E); 6.23, 6.54 (two s, each
H, 2x thiazoline‐C ‐H, Z and E); 6.99–7.91 (m, 13H, thiazoline‐C
, C
3 6
4 3
H ‐CH , Z and E);
−1
3
White needles; yield: 85%; Mp: 247–248°C. IR (KBr, cm ): 3090
1
5
4
‐
(NH); 1671 (C=O); 1076 (C–S–C). H‐NMR (300 MHz, DMSO‐d
6
, δ
); 3.55 (s, 2H,
‐H); 7.33–7.75 (m, 4H, phenyl‐C2,3,5,6‐H); 8.21 (s,
‐H); 8.35–8.78 (m, 3H, quinolyl‐C5,7,8‐H); 12.79 (s, 1H,
O exchangeable, NH). Anal. calcd. for C21 17BrN S (469.36): C,
phenyl‐C2,3,4,5,6‐H and thiazoline‐N‐phenyl‐C2,3,4,5,6‐H, quinolyl‐
3,7,8‐H and NH, Z and E); 8.70, 8.84 (two s, each 1H, quinolyl‐C
ppm): 2.57 (s, 3H, C
thiazolidinone‐C
1H, quinolyl‐C
6
H
4
3 3
‐CH ); 2.73 (s, 3H, CH
C
5
‐
5
13
H, Z and E). C‐NMR (75.54 MHz, DMSO‐d
6
, δ ppm): 20.65, 24.81,
19.02, 120.66, 120.99, 124.20, 127.68, 128.09, 128.27, 129.50,
29.59, 130.91, 132.20, 135.20, 137.08, 139.67, 140.80, 141.30,
3
1
1
1
D
2
H
4 2
O
53.74; H, 3.65; N, 11.94; S, 6.83. Found: C, 53.90; H, 3.71; N, 12.13; S,
6.92.
+.
46.34, 149.00, 150.50, 158.79, 159.16. MS (m/z, %): 531 (M +2)
+
.
+.
(
9.02); 530 (M +1) (30.09); 529 (M ) (9.32); 91 (100). Anal. calcd. for
21BrN OS (529.46): C, 61.25; H, 4.00; N, 10.58; S, 6.06. Found:
C, 61.44; H, 4.12; N, 10.67; S, 6.15.
C
27
H
4
4.2
|
Biology
4
.2.1 | Antibacterial activity
Inhibition‐zone measurements
6
‐Bromo‐N'‐[4‐(4‐bromophenyl)‐3‐(p‐tolyl)thiazol‐2(3H)‐ylidene]‐2‐
All the newly synthesized compounds were tested by the agar cup
methylquinoline‐4‐carbohydrazide (9d)
[
32]
−1
diffusion technique
using a 1 mg/ml solution in DMSO. The
Pale yellow; yield: 93%; Mp: 240–241°C. IR (KBr, cm ): 3107 (NH);
1
organisms used were methicillin‐resistant S. aureus (MRSA
isolated from wound infection), S. epidermidis (RCMB 0100183),
S. mutans (RCMB 0100172), and B. subtilis (RCMB 0100162) as
examples of Gram‐positive bacteria and P. aeruginosa (RCMB
1
666 (C=O); 1237, 1071 (C–S–C). H‐NMR (300 MHz, DMSO‐d
6
, δ
, Z and E); 2.61,
, Z and E); 6.23, 6.60 (two s, each 1H, 2x
‐H, Z and E); 6.98–7.91 (m, 12H, thiazoline‐C ‐phenyl‐
2,3,4,5,6‐H, thiazoline‐N‐phenyl‐C2,3,4,5,6‐H, quinolyl‐C3,7,8‐H and NH,
Z and E); 8.70, 8.90 (two s, each 1H, quinolyl‐C ‐H, Z and E). Anal.
calcd. for C27 20Br OS (608.35): C, 53.31; H, 3.31; N, 9.21; S, 5.27.
Found: C, 53.41; H, 3.28; N, 9.28; S, 5.33.
ppm): 2.27, 2.30 (two s, each 3H, 2xCH
.66 (two s, each 3H, 2xCH
thiazoline‐C
, C
3 6
H ‐CH
4
3
2
3
5
4
0
0
100243), E. coli (RCMB 010052), Salmonella typhi (RCMB
100104), Shigella dysenteriae (RCMB 0100542) and Proteus
C
5
vulgaris (RCMB 010085) as examples of Gram‐negative. Each
00 ml of sterile molten agar (at 45°C) received 1 ml of 6 h‐broth
H
2 4
N
1
culture and then the seeded agar was poured into sterile Petri
dishes. Cups (8 mm in diameter) were cut in the agar. Each cup
received 0.1 ml of the 1 mg/ml solution of the test compounds.
The plates were then incubated at 37°C for 24 hr. A control using
dimethylformamide (DMF) without the test compound was
included for each organism. Ampicillin was used as Gram‐positive
antibacterial reference drug, while levofloxacin was used as
Gram‐negative antibacterial reference drug. The resulting inhibi-
tion zones are recorded in Table 1.
4
3
.1.11 | Synthesis of 6‐bromo‐2‐methyl‐N'‐(4‐oxo‐
‐arylthiazolidin‐2‐ylidene)quinoline‐4‐
carbohydrazides (10a,b)
To a stirred suspension of the appropriate 8a,b (1 mmol) in absolute
ethanol (20 ml), an equimolar amount ethyl bromoacetate (0.11 ml) in
absolute ethanol (10 ml) was added and heated under reflux for 2 hr.
The reaction mixture was left to attain room temperature and then
left for an overnight in a refrigerator. The separated products were
filtered, washed several times with water, air dried, and crystallized
from dioxane/ethanol mixture (1:1).
Minimal inhibitory concentration measurement
The MIC of the compounds were measured using the two‐fold
[33]
serial broth dilution method.
The test organisms were grown
in their suitable broth: 24 hr at 37°C. Two‐fold serial dilutions of
solutions of the test compounds were prepared using 200, 100,
50, 25, 12.5, 6.25, and 3.125 μg/ml. The tubes were then
inoculated with the test organisms; each 5 ml received 0.1 ml of
the above inoculum and were incubated at 37°C for 48 hr. Then,
the tubes were observed for the presence or absence of microbial
growth. The MIC values of the prepared compounds are listed in
Table 2.
6
‐Bromo‐2‐methyl‐N'‐(4‐oxo‐3‐phenylthiazolidin‐2‐ylidene)quino-
line‐4‐carbohydrazide (10a)
−
1
Pale yellow needles; yield: 91%; Mp: 264–265°C. IR (KBr, cm ):
1
3
d
1
7
7
093 (NH); 1671 (C=O); 1033 (C–S–C). H‐NMR (300 MHz, DMSO‐
6
, δ ppm): 2.75 (s, 3H, CH
H, J = 7.5 Hz, phenyl‐C ‐H); 7.41 (t, J = 7.5 Hz, 2H, phenyl‐C3,5‐H);
.66 (d, J = 8.1 Hz, 2H, phenyl‐C2,6‐H); 7.84 (s, 1H, quinolyl‐C ‐H);
.97–7.98 (m, 2H, quinolyl‐C7,8‐H); 9.32 (s, 1H, quinolyl‐C ‐H); 10.93
O exchangeable, NH). C‐NMR (75.54 MHz, DMSO‐d , δ
ppm): 24.71, 34.16, 121.17, 123.13, 126.98, 128.01, 128.20, 128.40,
28.90, 132.54, 134.70, 136.80, 138.89, 143.90, 148.08, 159.73,
3
); 3.57 (s, 2H, thiazolidinone‐C
5
‐H); 7.07 (t,
4
3
5
1
3
(s, 1H, D
2
6
Minimal bactericidal concentration measurements
MIC tests were always extended to measure the MBC as follows: A
loop‐full from the tube that did not show visible growth (MIC) was
1

RIZK ET AL.
13 of 14
|
spread over a quarter of Müller–Hinton agar plate. After 18 hr of
incubation, the plates were examined for growth. Again, the tube
containing the lowest concentration of the test compound that failed
to yield growth on subculture plates was judged to contain the MBC
of that compound for the respective test organism. The MBC values
are listed in Table 2.
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