Synthesis, characterization, theoretical, anti-bacterial and molecular docking studies of quinoline based chalcones as a DNA gyrase inhibitor

Article abstract of DOI:10.1016/j.bioorg.2014.03.006

A series of fourteen (A₁-A₁₄) new qunioline based chalcones were synthesized by condensing 2,7-dichloro-8-methyl-3-formyl quinoline with acetophenone and acetylthiophenes, and subsequently characterized by IR, NMR and Mass spectroscopy. All the compounds were screened for antibacterial activities and found potentially active antibacterial agents. Bioassay, theoretical and dockings studies with DNA gyrase (the enzyme required for super coiling of DNA of bacteria) results showed that the type and positions of the substituents seemed to be critical for their antibacterial activities. The bromo and chloro substituted chalcone displayed high anti-bacterial activity. The A₄ and A₆ showed high interaction with DNA gyrase, contributing high free binding energy (ΔG -8.18 and -8.88 kcal).

Full text of DOI:10.1016/j.bioorg.2014.03.006

Accepted Manuscript
SYNTHESIS, CHARACTERIZATION, THEORETICAL, ANTI-BACTERI-
AL AND MOLECULAR DOCKING STUDIES OF QUINOLINE BASED
CHALCONES AS A DNA GYRASE INHIBITOR
Muhammad Imran Abdullah, Asif Mahmood, Murtaza Madni, Sara Masood,
Muhammad Kashif
PII:
S0045-2068(14)00018-2
DOI:
http://dx.doi.org/10.1016/j.bioorg.2014.03.006
YBIOO 1707
Reference:
Bioorganic Chemistry
To appear in:
Received Date:
19 January 2014
Please cite this article as: M.I. Abdullah, A. Mahmood, M. Madni, S. Masood, M. Kashif, SYNTHESIS,
CHARACTERIZATION, THEORETICAL, ANTI-BACTERIAL AND MOLECULAR DOCKING STUDIES OF
QUINOLINE BASED CHALCONES AS A DNA GYRASE INHIBITOR, Bioorganic Chemistry (2014), doi: http://
dx.doi.org/10.1016/j.bioorg.2014.03.006
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SYNTHESIS, CHARACTERIZATION, THEORETICAL, ANTI-
BACTERIAL AND MOLECULAR DOCKING STUDIES OF
QUINOLINE BASED CHALCONES AS A DNA GYRASE
INHIBITOR.
Muhammad Imran Abdullah,a* Asif Mahmood,b Murtaza Madni,c Sara Masood,d
and Muhammad Kashifa
aInstitute of Chemistry, University of the Punjab, Lahore, Pakistan
bDepartment of Chemistry, University of Sargodha, Sargodha, Pakistan
cDepartment of Chemistry, Quaid-e-Azam University, Islamabad, Pakistan
dSheikh Zayed Medical College&Hospital Rahim Yar Khan Pakistan
*E-mail: imranchemist.ali@gmail.com
Cell: +92-300-7476871
ABSTRACT: A series of fourteen (A1 – A14) new qunioline based chalcones were synthesized
by condensing 2,7-dichloro-8-methyl-3-formyl quinoline with acetophenone and
acetylthiophenes, and subsequently characterized by IR, NMR and Mass spectroscopy. All the
compounds were screened for antibacterial activities and found potentially active antibacterial
agents. Bioassay, theoretical and dockings studies with DNA gyrase (the enzyme required for
super coiling of DNA of bacteria) results showed that the type and positions of the substituents
seemed to be critical for their antibacterial activities. The bromo and chloro substituted chalcone
displayed high anti-bacterial activity. The A4 and A6 showed high interaction with DNA gyrase,
contributing high free binding energy (ΔG -8.18 and -8.88 Kcal).
KEYWORDS: Quinoline, chalcone, theoretical, acetophenone, anti-bacterial, DNA gyrase.
1

INTRODUCTION
Chalcones are α,β-unsaturated ketones, chalcones constitute an important class of natural
products that serve as the precursor for synthesis of various heterocyclic compounds like
pyrimidines, imidazoles [1], pyrazoles [2], 2-pyrazolines [3,4], and flavonoids [5]. Chalcones,
either natural or synthetic, are known to exhibit various biological activities such as anti-
inflammatory [6-7], antifungal [8-11], antioxidant [12-15], antimalarial [11-19], antituberculosis
[20], analgesic [21], anti-human immunodeficiency virus (HIV) [22], and antitumor activities
[23-24]. Some of them also act as anticancer [25], antiviral [26], and anti-AIDS agents [27].
Quinoline-based chalcones have been reported to possess antimalarial activity [28]. Chalcones as
well as some quinoline derivatives have already been recognized for their antimicrobial [29-30],
and antileishmanial activities [31-33].
Chalcones are considered the precursors of naturally-occurring compounds flavonoids
and isoflavonoids, but their true importance is extended in two branches: (i) The biological
activity associated with them (including anti-inflammatory, antimitotic, anti-leishmanial, anti-
invasive, anti-tuberculosis, anti-fungal, anti-malarial, anti-tumor), and (ii) anti-oxidant properties
[5,34-43].
2

Figure 1: Representation of different active part of newly synthesized drug against bacteria.
In the present study we have incorporated quinoline nucleus in the newly synthesized
anti-bacterial drugs which act as DNA gyrase inhibitor and efflux pumps inhibitor in bacteria
[44, 45]. To increase drug like properties of our compounds (A1 – A14) we have introduced
benzene and thiophene rings which contained high lipophilic groups like bromo, and chloro that
assist the drug molecule to enter into bacterial cell very easily. We have also changed the
position of substituent groups on benzene and thiophene rings in order to find out the substituent
effect on antimicrobial activities (Figure 1).
RESULTS AND DISCUSSION
The precursor 2,7-dichloro-8-methyl-3-formyl quinoline was prepared by the previously reported
method [46]. Synthesis of the title compounds (A1 – A14) were prepared through Claisen–
Schmidt reaction [36,42] by the condensation of formyl quinoline with commercially available
methyl aryl ketones in the presence of sodium hydroxide (Scheme 1 and Chart 1). All the newly
3

synthesized chalcones were in full agreement with the proposed structures. The E-configuration
1
was confirmed by the spectral data (IR, H-NMR and MS). Configuration of the double bond
was ascertained by coupling constants in 1H-NMR.
Scheme 1: Reaction protocol for the synthesis of chalcones (A1 – A14). (a) AcOH, H3PO4, reflux,
4-6 hrs, (b) POCl3, DMF, 80 °C, (c) Methyl Aryl Ketones, NaOH, rt, 2 hrs.
Chart 1: methyl Aryl (Ar) Moiety of Aromatic Ketones (A1 – A14).
4

ANTIBACTERIAL ACTIVITY: Antibacterial activities of the synthetic compounds were
tested against six bacterial species including Escherichia coli (Gram-negative), Klebsiella
aerogenes (Gram-negative), Salmonella typhimurium (Gram-negative), Staphylococcus aureus
(Gram-positive), Streptococcus pyogenes (Gram-positive) and Bacillus subtilis (Gram-positive)
by using method of Minimum Inhibitory Concentration (MIC). A commercial antibacterial
capsule Chloramphenicol and ciprofloxacin were used as a positive control for its comparative
study with all synthetic compounds
The bioactivity results indicate that substituted phenyl derivatives (A2 and A3) are less active
than A4 (IC50= 0.125mg/ml against Staphylococcus aureus, Staphylococcus aureus and
Escherichia coli, IC50=0.5mg/ml against Klebsiella aerogenes , Salmonella typhimurium and
Bacillus subtilis). The only difference between these molecules is the position of bromine on the
benzene ring. The activity is decreased considerably by the introduction of Br group at 3- and 2-
positions (A2 and A3, respectively) of phenyl ring whereas the activity is relatively increased on
moving the Br substituent to 4-position (A4) of phenyl ring. Conversely, replacing the bromo by
chloro (A6), and methoxy at 4-position of phenyl ring (A7) results in decrease activity. This may
be attributed to the greater hydrophobic effect of bromo group, than chloro, and methoxy at 4-
position.
The substituted hetero-aryl derivatives A8, A14 and A10 have shown promising antibacterial
activities against all the bacterial strains. Among the compounds, substituted thiophenyl
derivatives (A11, A12, A13,) exhibit almost equivalent antibacterial activities to that of the
standard (Table 1). Activity decreases considerably by the substitution of methyl on thiophene
ring (A11, A12, and A13). Incorporation of chlorine at 5-position of thiophene ring (A10) enhanced
the activity to a reasonable extent; it is further increased by the incorporation of another bromine
5

atom at 5-position (A8). However, incorporation of bromo group at 2-positions (A9) decreases
activity. The incorporation of a second methyl group at 2-position (A11) have decreases the
activity than that of mono substituted one (A12, A13). In general, activity is enhanced by the
substitution of aromatic rings with electron withdrawing groups and is suppressed by the
incorporation of electron donating methyl groups. No systematic change has been observed in
antibacterial activities for the rest of the compounds. All the above results are also supported by
theoretically calculated LogP and bioassay studies.
Table 1: Anti-bacterial Activities of the Chalcones (A1 – A14) (IC50 mg/ml)
Compound
Bacillus
subtilis
1.0
Staphylococ Streptococc Escherichia Klebsiella Salmonella
cus aureus
us pyogenes coli
aerogenes typhimurium
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
A-9
A-10
A-11
A-12
A-13
1.0
1.0
1.0
0.125
0.5
0.125
1.0
0.125
1.0
1.0
1.0
0.5
0.5
0.125
1.0
0.5
1.0
1.0
0.5
0.125
0.5
0.5
1.0
0.125
1.0
0.5
1.0
1.0
1.0
0.125
1.0
1.0
1.0
1.0
0.125
0.5
0.5
1.0
0.5
1.0
0.5
0.5
1.0
0.5
0.125
1.0
1.0
1.0
0.5
0.5
0.5
0.125
1.0
0.5
1.0
0.5
1.0
0.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
0.5
0.5
1.0
0.125
1.0
0.5
1.0
1.0
0.5
1.0
1.0
1.0
1.0
1.0
0.5
0.5
0.5
1.0
0.5
1.0
0.125
1.0
1.0
1.0
0.5
1.0
1.0
A-14
Chloramphenicol
Ciproflxoacin
1.0
0.5
DNA gyrase inhibitory assay
To understand the mechanism by which the quinoline based chalcones derivatives induced
the anti-bacterial activity, the inhibitory activity of the selected compound were performed
against the DNA gyrase. The DNA gyrase was isolated from S.aureus, the result were shown in
6

the Table 2. The compound A4 and A6 with strong anti-bacterial activities powerfully inhibited
the S.aureus DNA gyrase with IC50 of 0.14 and 0.16ug/ml respectively. There was good
agreement between the docking experiment and DNA gyrase inhibitory MIC values, indicating
that the inhibition of the bacterial growth is due to the inhibition of DNA gyrase by quinoline
based chalcones. The inhibitory assay of DNA gyrase are good in agreement with docking
experiments.
Table 2: The inhibitory analysis of selected chalcones against DNA gyrase
Compounds
S.aureus DNA
gyrase IC50
µg/ml
A-4
A-6
A-7
A-8
A-14
0.14
0.16
5.15
1.01
0.95
0.22
Ciprofloxacin
Molecular descriptors-based SAR studies of Chalcones: From the data obtained by the
theoretical evaluation of the ADME properties, one can notice that hybrid compounds A1 – A14
do not break any point of the Lipinski’s rule of five, making them promising leads for drug
candidates [47]. LogP (Table 3) values are compatible with those described as a predictive
indicator of a drug’s capacity for membrane penetration [48]. The field template showed a good
similarity of the most active chalcone A4 with quinoline based drug ciproflaoxcin as shown in
Figure 2.
7

Figure 2: Representing the similarity of A4 with ciprofloxacin calculated by Field Templater.
For the comprehension of three-dimensional microscopic interactions and binding between a
ligand and a receptor, a detail analysis in SAR is important in drug design and synthesis. A
number of chemical parameters are reported to be responsible for their molecular interactions.
Although many reports on the structure activity relationships based on the biological properties
of chalcones have been the subject of a large number of investigations [49, 50], but the present
study is the first report of its nature on the antibacterial activity of chalcones against different
bacterial strain types of molecular descriptors. Calculations were performed by software
package, Namely ACDlabs, in order to derive a quantitative relation between bactericidal
8

activity and structural properties. The values of the calculated the parameters are given in Table
3.
Molecular descriptors
(1) Octanol-water partition coefficient (log P)
(2) Bioconcentraion Factor(BCF)
(3) Polar surface Area (PSA)
Regarding a correlation of the steric parameters with activity, all chalcones of both set were
found to correlate directly with the activity. The octanol-water partition coefficient (log P) is
representative of steric interactions and in the present study it showed a good correlation with the
bactericidal action of chalcones. A direct correlation of the activity with log P was indicative of
the fact that chalcones with a higher log P are expected to be more active as is reflected in the
activity of halogenated chalcones (Table 1).
The bromo and chloro groups’ containing compounds (A4, A6, A9, and A10) are more active
ones in the series of 14 compounds (Table 3). Their LogP values (6.42, 6.24, 614, and 6.00,
respectively) are higher than the other compounds. As stated earlier in this discussion that the
position of substitutent groups also affects the activity of the compounds e.g A2 (2-bromo) is less
active (LogP = 5.83) than A4 (5-bromo) (LogP = 6.42. This difference is caused by steric
difference in both molecules. Experimental and theoretical data indicates that the halogen group
is somewhat more active against bacteria than methyl group. This difference can be attributed to
the hydrophobic property that bromo is more hydrophobic than chloro and in turn it has greater
binding energy to bind with biomolecule and inhibit their life cycle and growth.
9

Table 3: Calculated Molecular Discriptors
Compounds R
(LogP) LogKoc
(Koc)
LogBCF No. of
No.of H- PSA
acceptor
(BCF)
H-
Donor
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
A-9
A-10
A-11
A-12
A-13
A-14
3,4-OCH3 5.72
4.1(30712.00) 4.1(13040.45)
4.5(35322.38) 4.2(15854.16)
4.9(77083.59) 4.7(47165.41)
4.6(44596.77) 4.9(74054.95)
4.7(32737.98) 4.4(26168.79)
4.5(20229.20) 4.8(59355.09)
4.4(28074.36) 4.1(11502.72)
4.7(51823.04) 4.4(27084.16)
4.3(20229.20) 3.9(7277.05)
4.6(43889.70) 4.3(21473.55)
4.7(48218.08) 4.4(24448.88)
4.4(24667.63) 4.0(9600.87)
4.4(24667.63) 4.0(9600.87)
4.4(26078.77) 4.1(11505.26)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
2
2
2
3
2
3
2
2
2
2
2
2
4
48.40
29.94
29.95
29.96
39.19
29.96
39.19
58.20
58.20
58.20
29.09
29.08
58.20
48.22
2,-Br
3-Br
4-Br
5.83
6.14
6.42
2-Br, 4-OCH3 6.12
4-Cl
4-OCH3
3-Br
2-Br
5-Cl
2,5-CH3
4-CH3
3-CH3
1,4-
6.24
5.65
6.14
5.38
6.00
5.64
5.89
5.54
5.65
benzodioxane
Docking Studies: The docking experiments were performed using the bacterial DNA gyrase
structure with newly synthesized quinoline based chalcones (A1-A14) and with reference
compounds (Ciprofloxacin and Chloramphenicol). The DNA gyryase structure was obtained
from RCSB Portein data base (PDB ID 1Zi0). DNA gyrase is a unique type II topoisomerase
which is responsible for the surper-coiling activity of DNA in bacteria. We used the AutoDock to
determine the docked energy, the free energy of binding (ΔG) and the inhibition constant Ki
compared with experimental biological activity (Table 1 and Table 2). The calculated interaction
energies for (A1-A14) are good in agreement with experimental result which shows that A4, A6,
A8 and A14 are potent inhibitor of DNA gryase as compared to other chalcones and reference
standard (Table 4). The chain residue of DNA gryase to which the most potent inhibitors A4, A6,
A8 and A14 binds are LEU735, GLN788, ASP686, SER734, VAL737, VAL787, ARG739,
VAL685, LEU836 and VAL784 as shown in (Figure 3 and Figure 4).
10

Figure 3: Predicted binding conformations of chalcones A4 and A6 with catalytic portion of
DNA gyrase.
The close contact of quinoline ring of A4 and A6 with ILE736, VAL737 and VAL787 residue
(3.85, 3.69 and 3.62A0) suggested hydrophobic interaction. The nitrogen of quinoline make
interaction through hydrogen bonding with ASP686 and LEU735 residue (3.42 and 3.46A0
respectively). On the other hand –Cl of pyridine ring make interaction with VAL737 and
GLN788 residue (3.37 and 3.20 A0 respectively). The Br group on para position of benzene also
interact with VAl 784 (3.07) and the Cl group on para position of benzene interact with VAL784
and LEU836 (3.40 and 3,59 A0 respectively). These interactions stabilized the most potent
compound A4 and A6 in the active site of DNA gyrase as contributing favorable free binding
energy(ΔG -8.19 and -8.88 Kcal/mol respectively ).
11

Figure 4: Docking model derived for A4 and A6 with the catalytic portion of DNA gyrase.
Figure 4 predict the 3D model of DNA gyrase complexed with compounds A4 and A6 occupies
the same space which shows a great affinity with DNA gyrase. The result of the docking
experiment support the postulation that compounds A4 and A6 may act as potent inhibitor of the
DNA gyrase. These theoretical results were also supported by the experimental data (Table 2).
Table 4: Summary of calculated binding parameters of chalcones (A1-A14) docked with
DNA gyrase
Compounds
Free energy of
binding (ΔG)
Kcal/mol
-7.09
Docking
energy
Kcal/mol
-7.49
Ki (Inhibition
Constant) µM
A-1
A-2
A-3
A-4
A-5
A-6
A-7
A-8
A-9
A-10
A-11
A-12
6.37
10.84
1.24
992.57
4.36
310.99
5.12
11.91
5.96
2.29
2.37
2.88
-6.77
-7.04
-8.19
-7.31
-8.88
-7.22
-8.05
-6.62
-7.52
-8.01
-9.07
-7.81
-9.72
-8.36
-8.79
-7.40
-7.75
-7.09
-7.56
-8.45
-8.12
-8.34
12

A-13
A-14
Ciprofloxacin
Chloramphenicol
-7.23
-8.00
-6.33
-4.20
-8.08
-8.88
-7.19
-6.44
2.79
30.98
23.10
15.66
1
Spectral data: Spectral data (IR, H-NMR and MS) of all the newly synthesized compounds
were found in good agreement with the proposed structures. IR spectra of the compounds A1 –
A14 showed an absorption band at 1659 cm-1, typical of the stretching vibrations of chalcone
moiety. No peaks were found due to starting material aldehydic functionality as impurity. In the
1H-NMR spectra of the chalcones two very sharp doublets were found around δ 7.61 – 7.63 ppm
for H and δ 8.17 – 8.13 ppm for H with J-value 15 – 16 Hz for the trans chalcones. The
α
β
molecular ion observed in the mass spectra for all the chalcones confirmed their molecular
masses. The base peak, in the mass spectra of most of the chalcones, was obtained possibly by
the cleavage of Ar─Cl bond. While in bromo and chloro substituted chalcones the base peak is
due to the cleavage of two bonds i.e. CO-phenyl and phenyl─ Cl/Br bonds.
CONCLUSIONS AND OUTLOOK
It is concluded from the above discussion that the chalcones (A4, A5, A6, A8, and A10) are
comparatively more active than (A1, A2, A3, A7, A9, A11, A12, and A13). We have divided these
compounds into four categories for their antibacterial activities and represented in Table 1 i.e.
IC50 = 0.125mg/mL or below as significantly active, 0.5mg/mL as good active, 1.0mg/mL as
moderately active and >1mg/mL as low active. The compounds (A4, A5, A6, A8 A10 and A14) are
found potentially active antibacterial agents. The activity depends on the position of substituent,
the hydrophobic effect of bromo group is greater at 4-position of benzene and thiophene as
exhibited in A4 and A8. On the other hand the hydrophobic effect of bromo group decreases at 2-
13

position of benzene and thiophene as in A2, A3 and A9 respectively. This is also supported by
docking experiment, bioassay the calculated LogP values of studied Compounds. The docking
experiment and bioassay tell us that compounds A4 and A6 are the most potent inhibitor of DNA
gyrase.
Category Compounds
Significant
Good
Moderate
A4, A6, A8
A5, A10 A14
A1, A2, A3, A7, A9
A11, A12, A13 and
A14
EXPERIMENTAL SECTION
General: Melting points were taken on Gallenkamp melting point apparatus. IR spectra were
1
recorded in KBr pellets on Perkin Elmer infrared spectrophotometer. H NMR spectra were
performed in CDCl3 on Brücker/XWIN NMR (300 MHz) and TMS was used as internal standard
(chemical shifts, δ in ppm) unless otherwise specified. Mass spectra were recorded on a Jeol MS
Route instrument. Thin layer chromatography (TLC) was performed with aluminium sheets -
Silica gel 60 F254 purchased from Merck. Purification of synthesized compounds was made by
recrystallization from appropriate solvents. Reagent grade chemicals such as phosphoryl
chloride, acetophenones, N,N-dimethylformamide (Sigma-Aldrich and Alfa Aesar) were used.
Bioassay conditions
Anti-bacterial activity
We have performed the anti-bacterial activity against Escherichia coli (Gram-negative),
Klebsiella aerogenes(Gram-negative), Salmonella typhimurium(Gram-negative), Staphylococcus
14

aureus (Gram-positive), Streptococcus pyogenes (Gram-positive) and Bacillus subtilis (Gram-
positive). We have used MH medium (Mueller-Hinton medium) which composed of 1.5g of beef
extract, 1.7g of starch and casein hydroxylate. All the stock solutions of new synthesized
chalcones were prepared in DMSO. The stock solutions of new synthesized chalcones were used
along with sterilized MH medium. The colorimetric method was used to determine the MIC
(minimum inhibitory concentration) values by using MMT dye.
Enzyme inhibition
We have been used the F.blanche [51] method for the purification of s.aureus DNA gyrase
enzyme form the crude extract of s.aureus. The s.aureus was grown in a medium which was
composed of 2g of yeast extract, 1.2g of (NH4)2SO4, 8g of Na2HPO4, 2g of K2H2PO4, 0.2g of
MgSO4, 4.0g of glucose per liter of the distilled water. According to F.blanche [59] the
decatenation and supercoiling were performed.
Docking protocol
The docking studies were performed by using the autodock docking software. The structures
of the studied compounds were drawn using ChemBio Ultra 11.0, then energies of all the
compounds were minimized by using Gaussian 09 at B3LYP/6-31(d). The Gasteiger-Huckel
method was used to assign the charges to the ligand. The DNA gyryase structure was obtained
from RCSB Portein data base (PDB ID 1Zi0).In order to prepare the enzymes the hydrogens
atoms were added at a PH range of (6.5-8.1). By the aid of AutoDock tools the salvation
parameters and kollman united atom type chargers were added (Morris, Goodsell et al., 1998).
The autogrid program was used to generate the affibity (gird) maps of 20x20x20 A0 gird points
and 0.375 A0 spacing. (Morris, Goodsell et al., 1998).
15

Methods of Preparation of Precursors for Chalcones
N-acetylation of Substituted Aniline
0.1 mole of substituted aniline, 0.2 mole of glacial acetic acid was added in a 250ml flask. To
this mixture, catalytic amount of phosphoric acid was added and the mixture was refluxed for 5-6
hours. After the completion of the reaction (by TLC monitoring), the mixture was poured in ice-
cold water and stirred well. The crude product was precipitated out at once. These precipitates
were filtered and washed with ice-cold water. The pure product was obtained by recrystallized
from boiling water.
Synthesis of 2-chloro-3-formyl quinoline (Conventional Thermal Method)
Vilsmeier reagent was prepared by adding POCl3 (107.4g, 64.4ml, 0.70 mol) dropwise in DMF
0
(18.6g, 19.2ml, 0.25 mol) at 0 C with constant stirring. To this solution acetanilide (0.10 mol)
was added and the mixture was stirred for 15mins at room temperature. Then this mixture was
0
stirred at 70-80 C for 16 hrs. After the completion of reaction (TLC monitoring), the mixture
0
0
was poured in ice-cold water (500 ml) and stirred vigorously (30mins at 0 C-10 C). The 2-
chloro-3-quinolinecarbaldehyde was precipitated out, which was filtered off and washed with
water (200ml), dried and recrystallized from ethanol.
General Method for the Synthesis of quinolinyl Chalcones (A1-A14)
A mixture of formylquinoline (1mmol) and an aromatic ketone (1mmol) in methanol (50 mL)
was stirred at room temperature, followed by dropwise addition of aq. NaOH (4 mL, 10%). The
stirring was continued for 2 h and the reaction mixture was then kept at 0 °C for 24 h.
Subsequently, it was poured onto ice-cold water (200 mL). The precipitates were collected by
filtration, washed with cold water followed by cold MeOH. The resulting chalcones were
recrystallized from CHCl3 and dried in vacuo..
16

(E)-3-(2,7-dichloro-8-methylquinolin-3-yl)-1-(3,4-dimethoxyphenyl)prop-2-en-1-one (A1)
Yield, 85%. M.p. 180-182 °C. IR (KBr, cm-1): 1652 (C=O), 1596 (C=C), 1156 (C=N of
quinoline ring). 1H-NMR (CDCl3) δ: 8.403 ( 1H, s, Ar-H), 8.152 (1H, d, J=15.6Hz, CH of
olefinic bond), 7.698 (1H, dd, J1=2 Hz, J2= 8.4Hz, Ar-H), 7.63 (3H, m, CH of olefinic bond and
Ar-H), 7.564 ( IH ,m, Ar-H ), 6.939 ( 1H, d, J=8.4Hz, Ar-H), 3.972 (6H, s, OCH3), 2.818 (3H, s,
CH3); Calc Mass 402.27 MS, 402.17 [M + H]+ (Molecular ion Peak) 366.25 [M + H]+ -Cl.
(E)-1-(2-bromophenyl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A2)
Yield, 78%. M.p. 198-200 °C. IR (KBr, cm-1): 1659 (C=O), 1598 (C=C), 1152 (C=N of
quinoline ring). 1H-NMR (CDCl3) δ: 8.139 ( 1H, s, Ar-H), 8.057 (2H, d, J=7.6Hz, CH of olefinic
bond and Ar-H), 7.629 (2H, d, J=8.8Hz ,CH of olefinic bond and Ar-H), 7.526 (3H, m, Ar-H),
7.24 ( 1H, s, Ar-H), 2.821 (3H, s, CH3); Calc Mass 421.11 MS, 421.92 [M + H]+ (Molecular ion
Peak) 388.17 [M + 2 + H]+ -Cl.
(E)-1-(3-bromophenyl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A3)
Yield, 80% white Color solid. M.p. 172-175 °C. IR (KBr, cm-1): 1654 (C=O), 1591 (C=C), 1157
(C=N of quinoline ring). 1H-NMR (CDCl3) δ: 8.428 (1H, s, Ar-H ), 8.180 (2H, m, CH of olefinic
bond and Ar-H), 7.96 ( 1H, d, J =7.6Hz, Ar-H), 7.734 (1H, d, J =8Hz, Ar-H), 7.658 (1H, d, J
=8.4Hz, Ar-H), 7.551 ( 2H, m, CH of olefinic bond and Ar-H), 7.406 (IH, t, J =8Hz Ar-H),
2.816 (3H, s, CH3); Calc Mass 421.11 MS, 421.92 [M + H]+ (Molecular ion Peak) 388.17 [M +
2 + H]+ -Cl.
(E)-1-(4-bromophenyl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A4)
Yield, 84% white Color solid. M.p 185-188 °C. IR (KBr, cm-1): 1651 (C=O), 1599 (C=C), 1153
1
(C=N of quinoline ring). H-NMR (CDCl3) δ: 8.408 ( 1H, s, Ar-H), 8.181 (1H, d, J =16Hz, CH
of olefinic bond), 7.906 (2H, d, J =8.8 Hz, Ar-H), 7.653 (3H , m, CH of olefinic bond and Ar-H),
17

7.558 (1H, m, Ar-H), 7.519 (IH, s, Ar-H), 2.814 (3H, s, CH3); Calc Mass 421.11 MS, 421.92
[M + H]+ (Molecular ion Peak) 388.17 [M + 2 + H]+ -Cl.
(Z)-1-(2-bromo-4-methoxyphenyl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one
(A5)
Yield, 84% white Color solid. M.p. 190-192 °C. IR (KBr, cm-1): 1655 (C=O), 1593 (C=C), 1154
(C=N of quinoline ring). 1H-NMR (CDCl3) δ: 8.133 ( 1H, s, Ar-H), 8.048 (2H, d, J =8.8 Hz, CH
of olefin and Ar- H), 7.625 (1H, d, J =8.8 Hz, CH of olefin), 7.554 (1H, d, J =8.4Hz, Ar-H ),
7.240( 1H, s, Ar-H ), 6.965 (2H, d, J =8.8 Hz, Ar-H), 3.877 (3H, s, OCH3), 2.821 (3H, s,CH3 );
Calc Mass 451.14 MS, 451.08 [M + H]+ (Molecular ion Peak) 415.58 [M + H]+ -Cl.
(E)-1-(4-chlorophenyl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A6)
Yield, 75%. M.p. 168-170 °C. IR (KBr, cm-1): 1650 (C=O), 1590 (C=C), 1150 (C=N of
1
quinoline ring). H-NMR (CDCl3) δ: 8.410 ( 1H, s, Ar-H), 8.183 (1H, d, J =15.6Hz, CH of
olefin), 7.987 (2H, d, J =8.4 Hz, Ar-H), 7.645( 1H , d, J =8.8 Hz, Ar-H), 7.530(4H, m, CH of
olefin and Ar-H), 2.818 (3H, s, CH3); Calc Mass 376.66 MS, 376.00 [M + H]+ (Molecular ion
Peak) 340.00 [M + H]+ -Cl.
(E)-3-(2,7-dichloro-8-methylquinolin-3-yl)-1-(4-methoxyphenyl)prop-2-en-1-one (A7)
Yield, 70%. M.p 200-202 °C. IR (KBr, cm-1): 1662 (C=O), 1594 (C=C), 1160 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.402 ( 1H, s, Ar-H ), 8.153 (1H, d, J =16 Hz, CH of olefin), 8.065
(2H, d, J =1.6Hz, Ar-H), 7.629 (2H ,m, CH of olefin and Ar-H), 7.561 (1H, m, Ar-H), 6.995
(2H, d, J =8.4Hz, Ar-H), 3.893(3H, s, OCH3 ), 2.816 (3H, s, CH3); Calc Mass 372.14 MS, 372.08
[M + H]+ (Molecular ion Peak) 336.08 [M + H]+ -Cl.
(E)-1-(5-bromothiophen-2-yl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A8)
Yield, 56%. M.p. 162 °C. IR (KBr, cm-1): 1660 (C=O), 1592 (C=C), 1159 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.389 (1H, s, Ar-H), 8.209 (1H, d, J =15.6Hz, CH of olefin), 7.633
(2H, m, Ar-H), 7.56 (1H, d, J =8.8 Hz, CH of thiazole), 7.393 (1H, d, J =15.6Hz, CH of olefin),
7.171 (1H ,d, J =4Hz, CH of thiophene), 2.816 (3H, s, CH3); Calc Mass 427.14 MS, 428.00 [M
+ 4 + H]+ (Molecular ion Peak) 392.17 [M + 2 + H]+ -Cl.
18

(E)-1-(3-bromothiophen-2-yl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A9)
Yield, 60%. M.p. 170 °C. IR (KBr, cm-1): 1648 (C=O), 1593 (C=C), 1161 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.406 (1H, s, Ar-H ), 8.22 (1H, d, J =15.6Hz, CH of olefin), 7.831
(1H, d, J =15.6Hz, CH of olefin), 7.657(1H, d, J =8.8 Hz, Ar-H ), 7.575 (2H, m, CH of thiazole),
7.164 (1H, d, J =8.8 Hz, Ar-H), 2.814 (3H, s, CH3); Calc Mass 427.14 MS, 427.92 [M + H]+
(Molecular ion Peak) 392.08 [M + H]+ -Cl.
(E)-1-(5-chlorothiophen-3-yl)-3-(2,7-dichloro-8-methylquinolin-3-yl)prop-2-en-1-one (A10)
Yield, 53%. M.p. 148 °C. IR (KBr, cm-1): 1656 (C=O), 1594 (C=C), 1158 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.383 (1H, s, Ar-H ), 8.202 (1H, d, J =15.6Hz, CH of olefin), 7.747
(2H, m, Ar-H), 7.66(1H, m, CH of olefin), 7.425 (1H, d, J =10 Hz, CH of thiophene), 7.024 (1H,
d, J =4Hz, CH of thiophene), 2.812 (3H, s, CH3); Calc Mass 380.95 MS, 382.99 [M + H]+
(Molecular ion Peak) 347.49 [M + H]+ -Cl
(E)-3-(2,7-dichloro-8-methylquinolin-3-yl)-1-(2,5-dimethylthiophen-3-yl)prop-2-en-1-one
(A11)
Yield, 60%. M.p. 158 °C. IR (KBr, cm-1): 1658 (C=O), 1595 (C=C), 1157 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.353 (1H, s, Ar-H), 8.076 (1H, d, J =15.6Hz, CH of olefin), 7.627
(1H, d, J =8.8 Hz, Ar-H), 7.542 (1H, d, J =8.8 Hz, Ar-H ), 7.339 (1H, d, J =16Hz, CH of olefin),
7.096 (1H, s, CH of thiophene), 2.811 (3H, s,CH3), 2.721 (3H, s, CH3), 2.442 (3H, s, CH3); Calc
Mass 376.30 MS, 376.17 [M + H]+ (Molecular ion Peak) 340.17.08 [M + H]+ -Cl.
(E)-3-(2,7-dichloro-8-methylquinolin-3-yl)-1-(4-methylthiophen-2-yl)prop-2-en-1-one(A12)
Yield, 50%. M.p. 140 °C. IR (KBr, cm-1): 1654 (C=O), 1589 (C=C), 1149 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.395 (1H, s, Ar-H), 8.198 (1H, d, J =15.6Hz, CH of olefin), 7.707
(1H, s, CH of thiazole), 7.645 (1H, d, J =8.8 Hz, Ar-H), 7.553 (1H, d, J =8.8 Hz, Ar-H), 7.454
(1H, d, J =15.6 Hz, CH of olefin), 7.315 (1H, s, CH of thiophene), 2.814 (3H, s, CH3), 2.330
(3H, s, CH3); Calc Mass 362.27 MS, 362.17 [M + H]+ (Molecular ion Peak) 326.25 [M + H]+ -
Cl.
(E)-3-(2,7-dichloro-8-methylquinolin-3-yl)-1-(5-methylthiophen-2-yl)prop-2-en-1-one(A13)
19

Yield, 67%. M.p. 130 °C. IR (KBr, cm-1): 1654 (C=O), 1598 (C=C), 1160 (C=N of quinoline
1
ring). H-NMR (CDCl3) δ: 8.380 (1H, s, Ar-H), 8.172 (1H, d, J =15.6 Hz, CH of olefin), 7.715
(1H, d, J =4Hz, CH of thiazole), 7.637 (1H, d, J =8.8 Hz, Ar-H), 7.547(1H, d, J =8.8 Hz, Ar-H ),
7.436 (1H, d, J =15.6Hz, CH of olefin), 6.868 (1H, d, J =4Hz, CH of thiophene), 2.811 (3H, s,
CH3), 2.572 (3H, s, CH3); Calc Mass 362.27 MS, 362.11.08 [M + H]+ (Molecular ion Peak)
364.11 [M + H]+ -Cl.
(E)-3-(2,7-dichloro-8-methylquinolin-3-yl)-1-(2,3-dihydrobenzo[b][1,4]dioxin-5-yl)prop-2-
en-1-one (A14)
Yield, 45%. M.p. 158-160 °C. IR (KBr, cm-1): 1658 (C=O), 1595 (C=C), 1156 (C=N of
1
quinoline ring). H-NMR (CDCl3) δ: 8.391 (1H, s, Ar-H ), 8.147 (1H, d, J =15.6Hz, CH of
olefin), 7.606 (4H, m, CH of olefin and Ar-H ), 7.542 (1H,m, Ar-H ), 6.961 (1H, d, J =8.8 Hz,
Ar-H ), 4.319 (4H, dd, J1=5.2Hz, J2=13.2Hz, CH2 of acetal), 2.811 (3H, s, CH3); Calc Mass
400.25 MS, 400.17 [M + H]+ (Molecular ion Peak) 364.17 [M + H]+ -Cl.
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24

Graphical Abstract
25

SYNTHESIS, CHARACTERIZATION, THEORETICAL,
ANTI-BACTERIAL STUDIES AND MOLECULAR DOCKING
OF QUINOLINE BASED CHALCONES AS A DNA GYRASE
INHIBITOR.
Highlights
ꢀ A series of quinoline based chalcones A1-A14 were synthesized.
ꢀ Their anti-bacterial activity by using method of Minimum Inhibitory
Concentration (MIC). Activities were evaluated.
ꢀ Tested compounds displayed potential anti-bacterial activity against all bacterial
strain
ꢀ Docking studies of chalcones A1-A14 with DNA gyrase were performed
ꢀ Better binding affinities were achieved with novel inhibitors than commercial ones.
26