Theoretical molecular predictions and antimicrobial activities of newly synthesized molecular hybrids of norfloxacin and ciprofloxacin

Article abstract of DOI:10.1002/jhet.3768

Antibiotics such as norfloxacin and ciprofloxacin are used to treat numerous bacterial infections. The present research work involves the molecular prediction, synthesis, characterization and in vitro antimicrobial activities of molecular hybrids of norfl

Full text of DOI:10.1002/jhet.3768

Received: 27 August 2019
DOI: 10.1002/jhet.3768
Revised: 17 September 2019
Accepted: 18 September 2019
A R T I C L E
Theoretical molecular predictions and antimicrobial
activities of newly synthesized molecular hybrids of
norfloxacin and ciprofloxacin
Gurmeet Kaur | Manpreet Kaur | Lakhvir Sharad | Manisha Bansal
Department of Chemistry, Punjabi
Abstract
University, Patiala, India
Antibiotics such as norfloxacin and ciprofloxacin are used to treat numerous
Correspondence
Manisha Bansal, Department of
bacterial infections. The present research work involves the molecular predic-
tion, synthesis, characterization and in vitro antimicrobial activities of molecu-
Chemistry, Punjabi University, Patiala,
India.
lar hybrids of norfloxacin and ciprofloxacin. First set of compounds involve
the substitutions of various amines at third position of ciprofloxacin and
norfloxacin. On the other hand, second set of molecular hybrids include the
substitution of different amines at seventh position along with linker
Email: jindal_manisha@yahoo.co.in
(
─COCH ─). These synthesized compounds were identified by TLC technique
2
and well characterized by various spectroscopic techniques such as IR, NMR,
and ESI-MS. Molecular prediction of these newly synthesized compounds have
been carried out using the SwissADME, ADMETLab software. Their cytotoxic-
ity parameters have also been studied using Osiris software. It was observed
that almost all these molecular hybrids suitable for their drug likeness proper-
ties. Further, these newly synthesized compounds were subjected to study their
antimicrobial activities in vitro. The third substituted as well as most of seventh
substituted molecular hybrids have shown 10-folds increase in their
antibacterial activity as compared to the standard drug ciprofloxacin. Some of
these compounds have also shown their potency when subjected to study their
cytotoxicity test against Escherichia coli AB 1157, proficient to prepare damage
in DNA.
1
| INTRODUCTION
UTI, pneumonia, diabetic foot infection, typhoid, fever,
[
2–7,10,11]
and so on.
The presence of two carbonyl groups
Infectious diseases are generated from various pathogenic
in these fluoroquinolones is important for binding with
DNA gyrase. Some researchers have also studied the che-
[
1]
microorganisms like bacteria, virus, fungi, and so on.
Fluoroquinolones have been widely used to cure such
lating process of these groups, which shows binding of
[2–7]
[12,13]
infections.
Ciprofloxacin and norfloxacin, second
these carbonyl groups with different cations.
But no
generation fluoroquinolones, are categorized as broad
clues are available which shows role of OH group of
COOH at third position in these processes of chelating or
[8,9]
spectrum antibiotics.
It is known to be the agent of
[
14,15]
choice for the treatment of various bacterial infections
like shigella species which causes diarrhea and also for
the treatment of tuberculosis, digestive disorder, anthrax,
binding with DNA gyrase.
Literature provides exces-
sive data about antibiotics which mainly differ in their
chemical structures having different substitution at fifth,
J Heterocyclic Chem. 2019;1–13.
wileyonlinelibrary.com/journal/jhet
© 2019 Wiley Periodicals, Inc.
1

2
KAUR ET AL.
FIGURE 1 Structure of fluoroquinolones
seventh, and eighth positions of fluoroquinolones.
Antibacterial activities are greatly affected by the various
substituents at different positions as shown in
molecules. ADMET studies and toxicological parameters
are preclinical properties which help in screening the
synthesis of new molecular hybrids before carrying out
their biological activities. SwissADME, ADMETLab, and
Osiris software are used to study and compare different
physicochemical properties like binding properties, drug
likeness, toxicity, and so on. Presently, we have synthe-
sized two set of compounds of both ciprofloxacin and
norfloxacin having substitutions at third position as well
as seventh position. The formation, identification and
characterization of the synthesized compounds have been
confirmed by melting point and spectroscopic techniques.
Broadly, the disappearance of stretching band
[12,13]
Figure 1.
Moreover, these fluoroquinolones behave
amphoterically due to the presence of basic group (sec-
[14–16]
ondary amine) and acidic group (carboxylic acid).
Research has revealed some coupled reactions of cip-
rofloxacin with aromatic amines some of which show
[17,18]
good antibacterial activity.
But the bacterial infec-
tions are becoming resistant to the fluoroquinolones
these days. To overcome such problems, there are basi-
cally two ways to enhance the activity of drug. First, the
new core molecules can be designed and synthesized
which may show enhanced antibacterial activities. Sec-
ond, new molecule hybrid of the existing fluoroquinolone
can be formed, which may show improve biological activ-
ities with minimum side effects. In the present piece of
work preclinical studies and molecular predictions of
newly synthesized molecular hybrids ciprofloxacin and
norfloxacin have been carried out to study various
ADMET and Toxicology parameters. Further, these com-
pounds have screened for antimicrobial activities and
cytotoxicity test in vitro.
−1
(3600-3400 cm ) for OH group of carboxylic moiety in
case of substitution at third position (Ia, Ib, IIa, IIb, Ic)
and
disappearance
of
NH
stretching
band
−
1
(3400–3200 cm ) in case of substitution at seventh posi-
tion (I a, I b, II a, II b), confirms the formation of coupled
compounds. Moreover, number of proton count and their
0
0
0
0
1
pattern for H-NMR spectra as well as that of molecular
ion peak in ESI-MS spectra further support the formation
of all these synthesized compounds.
All the synthesized compounds have subjected to
study these properties and compared with standard drug
ciprofloxacin and norfloxacin. The enhancement in the
2
2
| RESULTS AND DISCUSSION
.1 | Computational tools
0
binding properties has been observed for compounds II b,
0
0
I b, and I d. Presence of hetero atoms in the molecular
system affects the hydrogen bond acceptor and hydrogen
bond donor properties of the compound as shown in
Table 1. The physicochemical parameter like LogP, LogD,
and LogS provides data about the properties of Absorp-
tion, Distribution, and Solubility in the system as shown
An analysis of theoretical molecular predictions has pro-
vided strategy for physical properties and has been used
to get computational algorithms to calculate the CNS effi-
cacy as well as the toxicology of the newly synthesized

KAUR ET AL.
3
TABLE 1 Parameters calculated by swissADME and ADMETlab
a
a
a
b
b
a
a
a
Compound
MW
HBA
HBD
LogP
1.583
1.268
2.511
1.357
2.196
1.042
0.694
3.335
2.308
1.154
1.993
0.84
LogD
LogS
TPSA
74.57
74.57
57.58
66.81
57.58
66.81
%ABS
83.274
83.274
89.077
85.883
89.077
85.883
71.24
BBB
No
No
Yes
No
Yes
No
No
No
No
No
No
No
No
No
No
No
GI
I
331.13
319.13
398.21
400.19
386.21
388.19
373.16
643.26
456.22
458.20
444.22
446.20
442.28
430.47
447.48
435.47
5
5
4
5
4
5
5
8
6
7
6
7
6
6
7
5
2
2
1
1
1
1
3
2
1
1
1
1
1
1
3
3
−0.705
−0.757
1.98
−1.32
−1.29
−3.20
−2.45
−3.17
−2.41
−2.55
−4.78
−2.35
−1.59
−2.31
−2.08
−2.04
−2.01
−2.71
−2.67
High
High
High
High
High
High
High
High
High
High
High
High
High
High
Low
Low
II
Ia
Ib
1.491
IIa
IIb
Ic
1.692
1.369
0.333
109.46
120.12
86.09
95.32
86.09
95.32
86.09
86.09
152.99
152.99
Id
0.997
67.56
II'a
II'b
I'a
I'b
I'c
II'c
I'd
II'd
0.126
79.212
76.12
−0.187
−0.096
−0.242
−0.156
−0.246
−0.675
−0.613
79.212
76.12
1.918
1.603
0.656
0.341
79.212
79.212
52.22
56.22
Abbreviations: %ABS = Percentage of absorption (%ABS = 109-0.345(TPSA); HBA, hydrogen bond acceptors; HBD, hydrogen bond donors; MW, molecular
[21]
weight; TPSA, topological polar surface area.
a
Calculated by using SwissADME.
b
Calculated by using ADMETlab.
in Table 1. Further the TPSA and solubility parameters
2.2 | Antimicrobial activities
[19]
inversely proportional to LogP.
leads to the good absorption in gastrointestinal
GI) track. Therefore, TPSA can be used as predefined
Also low TPSA value
All these coupled compounds have been subjected for
antimicrobial activities at six different concentration (2.5,
(
5, 10, 25, 50, 100 μg). Most of the synthesized compounds
tool to predict the transport path way of the particular
type of drug. It was seen that compound Ia and Ic which
were having TPSA value less than 70, have the tendency
to penetrate Blood brain barrier (BBB) and also increase
in hydrogen bonding causes the decrease in the BBB pen-
etration as shown in Table 1. Broadly, all the compounds
are having their TPSA value ranging from 57 to 120 which
have shown MIC value (2.5 μg), which shows 10-folds
more potency against gram positive and gram-negative
strains used, except (I'c and II'c), when compared with
ciprofloxacin. The zone of inhibition at minimum con-
centration 2.5 μg is greater for the synthesized com-
rd
pounds with substitution toward 3 position (Ia, Ib, IIa,
IIb, Ic, and Id) as shown in Tables 3 and 4, also represen-
ted graphically as shown in Figure 2 than for compound
[19,20]
justify the penetration of the drug in GI.
A uniform trend has been observed of the %ABS
parameter for both set of compounds having substitu-
tions at third position as well as seventh position. For the
first set of compounds which show 89% value for com-
pounds Ia and IIa having piperidine substitution at third
position. Similar trend we have seen from other mole-
cules having same substitution as shown in Table 1.
The studies have been extended by comparing the tox-
icities of all molecules using orisis software as shown in
Table 2. According to that most of the compounds are
showing very low toxic effects against (mutagenecity/car-
th
0
0
0
0
0
0
with substitution at 7 position (I a, I b, II a, II b, I c, II c,
0
0
I d, II d) as shown in Table 5 and Table 6. Exceptionally,
IIb compound has greater zone of inhibition even at min-
imum concentration for both gram positive and gram
negative strains as shown in Figure 3 graphically. Fur-
ther, it has been observed that these compounds are inac-
tive against fungi Candida albicans. In the cytotoxicity
analysis third substituted derivatives of ciprofloxacin
have significance minimum inhibitory concentration and
zone of inhibition as compared to standard drug cipro-
floxacin. Zone of inhibition increased with the increase
in concentration of the compound. These synthesized
[22]
cinogenic) except Ic.

4
KAUR ET AL.
TABLE 2 Predicted toxicity effects
using Orisis software
Compound
Mutagenic
None
None
None
None
None
None
Low
Tumorigenic
None
None
None
None
None
None
Low
Reproductive effective
Irritant
None
None
None
None
None
None
None
None
Low
I
None
None
High
High
High
High
Low
II
Ia
Ib
IIa
IIb
Ic
Id
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
None
High
None
None
None
None
None
None
None
None
II'a
II'b
I'a
I'b
I'c
II'c
I'd
II'd
None
Low
None
High
High
None
None
compounds have MIC value 25 μg which is fourfold more
potent than ciprofloxacin (100 μg) except II'c (250 μg) as
shown in Table 7.
using agar diffusion method against strain E. coli
AB 1157.
3
.2 | Synthesis of 1-alkyl-6-fluoro-
3
3
| EXPERIMENTAL
7-(piperazin-1-yl)-3-(substituted amine)
quinolin-4(1H)-one
.1 | Materials and methods
(
2.5 mmol, 0.827 g) of ciprofloxacin or (2.5 mmol, 0.80 g)
The 250 mg tablets of Norfloxacin were purchased
from the market under the brand Noxitef. Ciprofloxa-
cin was bought from Sigma-Aldrich. The melting
points were recorded by open capillary method. Meth-
anol, acetone, piperidine, and morpholine were used
of Lobachem. Sodium Hydroxide and Urea was used
from Merck chemicals. The IR spectra were obtained
by Bruker alpha-E and RC FT-IR KBr pellets on a
Perkin Elmer RXIFT Infrared spectrophotometer.
NMR spectra were recorded on Bruker Avance
of norfloxacin was refluxed after the addition of 15 mL of
methanol and 2 to 3 drops of concentrated sulphuric acid
for 8 to 10 hour at 35 C, respectively. After the formation
ꢀ
of ester derivatives of ciprofloxacin or norfloxacin,
(2.5 mmol) different aliphatic amines were added in the
reaction mixture and refluxed for 7 to 8 hours as shown
in Scheme 1. The product formation, as monitored by
thin layer chromatographic technique, was extracted
after the removal of solvent by vacuum rotary evaporator.
The solid product was extracted and washed with the
[
17]
4
00 MHz spectrophotometer with TMS as an internal
mixture of methanol-chloroform (2:8).
The pure sam-
standard. The mass spectra were recorded on the
Waters Micromass Q-T of Micro (ESI) spectrometer.
All the synthesized compounds have been evaluated
for their antibacterial and antifungal activity in vitro
by using agar diffusion method. Four bacterial strains
have been used namely, Bacillus subtilis, Staphylococ-
cus aureus (Gram positive) and Escherichia coli, Pseu-
domonas aeruginosa (Gram negative) and Candida
albicans strain were used for antifungal activity. Cip-
rofloxacin, norfloxacin, and fluconazole have been
used as standard drug for antibacterial and antifungal
activity. Cytotoxicity test has also been carried out by
ples were filtered, dried, and identified by using different
spectroscopic techniques.
3
7
.3 | Synthesis of 1-alkyl-6-fluoro-4-oxo-
-(4-(2-(substituted amine)acetyl)
piperazin-1-yl)-1,4-dihydroquinoline-
-carboxylic acid
3
(9 mmol, 2.98 g) of ciprofloxacin or (9 mmol, 2.87 g) of
norfloxacin was stirred with 40 mL dichloromethane and
trimethylamine in equimolar ratio (9 mmol), respectively,
ꢀ
for 20 minutes at 0 to 5 C followed by drop wise addition

KAUR ET AL.
5

6
KAUR ET AL.
rd
FIGURE 2 Graphical representation of 3 -substituted molecular hybrids
of 1.1 mL (14 mmol) of ɑ-chloroacetyl chloride. After the
complete addition of the ɑ-chloroacetyl chloride the mix-
ture was initially stirred at 0 to 5 C for 15 to 20 minutes
3.4 | Characterization data
3.4.1 | 1-cyclopropyl-6-flouro-7-(piperazin-
1-yl)-3-(piperidine-1-carbonyl)quinolin-
4-(1H)-one (Ia)
ꢀ
followed by stirring at room temperature for 36 hours.
The formation of the product has been monitored by sin-
gle spot on thin layer chromatography which differs from
that of reactant. The reaction mixture was then filtered
and the resulting solid was dissolved in dichloromethane.
The crude sample was given the washings of saturated
solution of sodium chloride (3 × 30 mL). Organic layer
was dried over anhydrous sodium sulphate and after the
removal of solvent pure sample was obtained as shown in
ꢀ
Pure creamish solid; yield 62% to 63%; mp 240 to 242 C
−
1
decompose; IR (KBr) cm : ν
3317.67 (N-H str.),
max
3045.45, 3014.52 (Ar C-H str.), 2961.58, 2909.60, 2846.53
(C-H str.), 1617.28, (C=O; keto), 1590.32 (C=O), 1331.46
1
(C-N); H-NMR (400 MHz, DMSO) δ (ppm): 8.66 (s, 1H,
H-2), 7.87 (d, 1H, H-5, JH-F = 13.44 Hz), 7.53 (d, 1H, H-8,
0
J = 7.56 Hz), 3.82 (d, 2H, H-4 , H-1 of cyclopropyl,
[8]
0 0
Scheme 2.
J = 3.6 Hz), 3.55 (s, 4H, H-2 , 4 ), 3.37 to 3.16 (m, 6H, H-
0
0
00
00
00
00
00
Thirty five micro liter of acetonitrile was added to
.2 mmol of chloroacetyl derivatives of Ciprofloxacin or
3 , 5 , 3 ), 2.90 (s, 6H, H-2 , 6 , 5 ), 1.58 (s, 2H, H-4 ),
1.30 (d, 2H, cyclopropyl, J = 6.12 Hz), 1.18 (m, 2H,
cyclopropyl); ESI-MS: Molecular ion peak = 398
1
norfloxacin. The reaction mixture was stirred after the
addition of 2.4 mmol triethylamine, 1.2 mmol of sodium
iodide, and 2.4 mmol of secondary aliphatic amines for
+
(M − NH) m/z = 382.
4
8 hours, respectively. The reaction was filtered and
3
3
1
.4.2 | 1-cyclopropyl-6-flouro-
-(morpholine-4-carbonyl)-7-(piperazin-
-yl)quinoline-4-(1H)-one (Ib)
resulting solid was dissolved in dichloromethane, which
was given the washings of saturated solution of sodium
chloride (3 × 30 mL). The organic layer collected and
dried over anhydrous sodium sulphate, pure sample was
obtained after the removal of solvent as shown in
ꢀ
Pure creamish solid; yield 58 to 59%; mp 246 to 248 C
decompose; IR (KBr) cm : ν
(Ar C-H str.), 2921.72, 2850.71 (C-H str.), 1621.55 (C=O;
−1
3355.67 (N-H str.), 3045.70
max
[23]
Scheme 2.

KAUR ET AL.
7

8
KAUR ET AL.
1
keto), 1581.63 (C=O), 1334.70 (C-N), 1293.60 (C-O); H-
3063.49 (Ar C-H str.), 2807.52 (C-H str.), 1717.51 (C=O;
keto), 1690 53 (C=O; amide), 1629.42 (C=O; amide),
1494.42 (1 N-H), 1459.43 (2 N-H), 1381.59 (C-N). H-
NMR (400 MHz, DMSO) δ (ppm): 8.71 (s, 1H, H-2), 7.87 (d,
H, H-5, JH-F = 13.28 Hz), 7.50 (d, 1H, H-8, J = 7.36 Hz),
.78 (d, 1H, H-4 ), 3.64 (d, 2H, H-3 , J = 4.28 Hz), 3.62 (s,
H, H-2 , 6 ), 3.30 (t, 4H, H-3 , 5 ), 3.01 (t, 4H, H-2 , 6 ),
0
0
1
1
3
4
2
1
0
00
NMR (400 MHz, DMSO) δ (ppm): 14.88 (s, 1H, N-H, D O
2
0
0
0
0
00
00
exchangable proton), 8.89 (s, 2H, NH , D O exchange-
2
2
00
.84 (t, 1H, H-1 cyclopropyl), 1.38 (d, 2H, H-5 , J = 6.6 Hz),
able proton), 8.65 (s, 1H, H-2), 7.88 (d, 1H, H-5, JH-
13.02 Hz), 7.59 (d, 1H, H-8, J = 7.2 HZ), 3.84 (s, 1H,
13
.24 (s, 2H, cyclopropyl), 1.20 (s, 2H, cyclopropyl); C-
=
F
NMR (400 MHz, DMSO) δ (ppm): 176.26, 165.96, 154.21,
47.86, 145.54, 145.44, 139.15, 118.41, 110.95, 110.73,
06.64, 106.10, 50.09, 50.05, 44.94, 35.80, 7.51; ESI-MS:
0
H-4 , D O exchangeable proton), 3.72 (q, 1H, H-1 of
cyclopropyl), 3.65, 3.55 (d, 4H, H-2 , 6 ), 3.35 (dd, 4H,
H-3 , 5 ), 1.33 (d, 2H, cyclopropyl, J = 6.2 Hz), 1.18 (s,
H, cyclopropyl); C-NMR (400 MHz, DMSO) δ (ppm):
2
1
0
0
1
0
0
+
Molecular ion peak (M - Δ) m/z = 360.
13
2
176.29, 165.79, 154.05, 151.58, 148.09, 144.08, 143.98,
3
3
.4.3 | 1-ethyl-6-flouro-7-(piperazin-1-yl)-
-(piperidine-1-carbonyl)quinolin-4(1H)-
139.00, 119.30, 119.22, 111.22, 110.99, 106.88,106.76,
46.38, 46.33, 42.69, 35.94, 7.58; ESI-MS: Molecular ion
+
one (IIa)
peak = 373 (M − CH2 = CH ) m/z = 346, base
2
peak = 332
ꢀ
Pure creamish solid; yield 62 to 63%; mp 266 to 268 C
−1
decompose; IR (KBr) cm : ν
3392.94 (N-H str.), 2996.74
max
(Ar C-H str.), 2892.29, 2825.27 (C-H str.), 1678.12 (C=O;
keto), 1629.81 (C=O; amine), 1389.58 (C-N), 1360.02 (C-O);
H-NMR (400 MHz, DMSO) δ (ppm): 8.96 (s, 1H, H-2),
3.4.6 | 1-cyclopropyl-7-(4-(1-cyclopropyl-
6-flouro-4-oxo-7-(piperazin-1-yl)-
1
7
.93 (d, 1H, H-5, JH-F = 12.84 Hz), 7.25 (d, 1H, H-8,), 4.61
1,4-dihydroquinoline-3-carbonyl)piperazin-
1-yl)-6-flouro-4-oxo-1,4-dihydroquinoline-
3-carboxylic acid (Id)
0 0 0 0 0
s, 2H, -CH CH ), 3.51 (11H, H-2 , 3 , 4 , 5 , 6 ) 3.06 (8H, H-
2 3
(
0
0
00 00 00 00
, 3 , 4 , 5 , 6 ), 1.42 (s, 3H, -CH CH ); C-NMR
2 3
13
2
(
1
4
400 MHz, DMSO) δ (ppm): 176.07, 166.06, 148.57, 144.38,
37.04, 119.92, 111.44, 111.22, 107.08, 106.41, 52.93,49.14,
6.51, 42.75, 14.38; ESI-MS: m/z = 342.
ꢀ
Creamish yellow solid, yield 78 to 79% mp 298 to 300 C
−
1
decompose; IR (KBr) cm : ν
3418.30 (O-H str.),
022.26 (Ar C-H str.), 2826.28 (C-H str.), 1720.25 (C=O;
keto), 1629.23 (C=O; amine), 1340.35 (C-N); H-NMR
max
3
1
3
4
4
.4.4 | 1-ethyl-6-flouro-3-(morpholine-
-carbonyl)-7-(piperazin-1-yl)quinoline-
-(1H)-one (IIb)
(400 MHz, DMSO) δ (ppm):14.94 (1brs, 1H, OH), 8.92 (s,
0
0
1H, H-2), 8.69 (s, 1H, H-2 ), 7.91 (d, 1H, H-5, J
H-
=
13 Hz), 7.58 (d, 1H, H-8, J = 6.96 Hz), 3.83 to 3.35
F
0
0
0
0
0
ꢀ
(m, 10H, H-2 , 3 , 4 , 5 , 6 , H-1 of cyclopropyl), 1.35 (d,
2H, cyclopropyl, J = 6.4 Hz), 1.17 (s, 2H, cyclopropyl);
ESI-MS: Molecular ion peak (M + K) m/z = 684.
Pure creamish solid; yield 58 to 59%; mp 260 to 262 C
decompose; IR (KBr) cm : ν
−1
3405.76 (N-H str.),
max
+
2
988.59 (Ar C-H str.), 2827.11 (C-H str.), 1710.02 (C=O;
keto), 1628.92 (C=O; amine), 1389.80 (C-N), 1368.98 (C-
1
O); H-NMR (400 MHz, DMSO) δ (ppm): 8.96 (s, 1H, H-
2
4
6
),7.92 (d, 1H, H-5), 7.25 (s, 1H, H-8, JH-F = 13.04 Hz),
3.4.7 | 1-cyclopropyl-6-flouro-4-oxo-
7-(4-(piperidine-1-carbnyl)piperazin-1-yl)-
0
0
0
0
.61 (s, 2H, CH CH , J = 7.36 Hz), 3.43 (8H, H-2 ,3 ,4 , 5 ,
2
3
0
00
00
00
00
00
), 3.10 (9H, H-2 , 3 , 4 , 5 , 6 , J = 4.28 Hz), 1.42 (s, 3H,
1,4- dihydroquinoline-3-carboxylic acid (I'a)
13
s, 1H); C-NMR (400 MHz, DMSO) δ (ppm): 176.11,
ꢀ
Pure yellow solid; yield 60 to 61%; mp 248 to 250 C
1
1
4
66.00, 153.92, 151.44, 148.63, 144.43, 144.33, 137.06,
19.90, 111.44, 111.22, 107.12, 106.42, 52.85, 49.08, 46.72,
2.83, 14.42; ESI-MS: m/z = 334.
−
1
decompose; IR (KBr) cm : 3094 (Ar C-H str.), 1723
(
(
C=O; acid), 1645 (C=O; amide), 1630 (C=O; keto), 1253
C-N-C stretch of piperidine ring); H-NMR (400 MHz,
1
CDCl ) δ (ppm): 14.96 (brs, 1H, COOH), 8.75 (s, 1H, H-
3
3
4
1
.4.5 | N-carbamoyl-1-cyclopropyl-6-flouro-
-oxo-7-(piperazin-1-yl)-
,4-dihydroquinoline-3-carboxamide (Ic)
2
4
2
), 8.01 (d, 1H, H-5), 7.37 (s, 1H, H-8), 5.3 (s, 1H), 3.88 (d,
0
H, H-3, 5 ), 3.57 to 3.29 (7H, COCH , H-cyclopropyl, H-
2
0
0
00
00
, H-6 ), 2.48 (s, 4H, H-2 , 6 ), 1.86 (d, 2H), 1.60 (s, 4H,
0
0
Pure light brown solid, yield 69% to 70%, mp 276 to
cyclopropyl), 1.43 (d, 4H), 1.23 (d, 2H, H-4 ); ESI-MS:
Molecular ion peak (M + 1) m/z = 457.
ꢀ
−1
2
78 C decompose; IR (KBr) cm : N
3394.60 (N-H str.),
max

KAUR ET AL.
9
th
FIGURE 3 Graphical representation of 7 -substituted molecular hybrids
TABLE 7 Cytotoxicity test (zone of inhibition in mm)
Strain
E. coli AB 1157
Conc.
25 μg
50 μg
100 μg
250 μg
500 μg
1000 μg
MIC μg
Compound
Ia
21
25
20
20
*
23
27
22
23
*
25
28
24
25
*
29
31
28
27
*
31
34
30
30
*
*
25
25
Ib
*
Ic
*
25
Id
40
*
25
IIb
25
I'c
8
10
0
8
12
8
14
10
20
21
8
16
12
21
23
*
25
II'c
0
0
250
25
I'd
12
12
-
16
18
-
16
20
1
18
21
3
II'd
25
Ciprofloxacin
100
Note. *Zones could not measure due to merging.

10
KAUR ET AL.
SCHEME 1 1-alkyl-6-fluoro-
-(piperazin-1-yl)-3-(substituted amine)
quinolin-4(1H)-one
7
3
7
1
3
.4.8 | 1-cyclopropyl-6-flouro-
acid), 1657 (C=O; amide), 1628 (C=O; keto), 1292 (C-N-C)
stretch of piperidine ring); H-NMR (400 MHz, DMSO) δ
(ppm): 15.11 (brs, 1H, COOH), 8.94 (s, 1H, H-2), 8.26 to
7.78 (1H, H-5), 7.13 to 7.09 (1H, H-8, JH-F = 7.28 Hz), 4.59
1
-(morpholine-4-carbonyl)-7-(piperazin-
-yl)quinoline-4-oxo-1,4-dihydroquninoline-
-carboxylic acid (I'b)
0 0 0
s, 2H, CH CH ), 3.78 to 3.14 (10H, COCH , H-3 , 5 , H-2 ,
2 3 2
(
ꢀ
Pure creamish solid; yield 58 to 59%; mp 252 to 254 C
decompose; IR (KBr) cm : ν
0
00 00
6
), 2.68 to 2.36 (4H, H-2 , 6 ), 1.49 (s, 2H), 1.40 (d, 4H, H-
−
1
3049.3 (Ar C-H str.),
max
0
0
00 00
, 4 , 5 ), 1.23 (s, 3H, CH CH ); ESI-MS: Molecular ion
2 3
3
2
907.9, 2851.0 (C-H str.), 1737.6 (C=O; acid), 1643.6
peak (M + 2) m/z = 446, (M + 1) m/z = 445.
(
(
(
C=O; amide), 1626.5 (C=O; keto), 1385.5 (C-N), 1297.7
C-O), 1117.6 (C-O-C); H-NMR (400 MHz, DMSO) δ
ppm): 15.24 (brs, 1H, COOH), 8.67 (s, 1H, H-2), 7.93 (d,
1
3.4.10 | 1-ethyl-6-flouro-3-(morpholine-
4
-carbonyl)-7-(piperazin-1-yl)quinoline-
1
5
H, H-5, JH-F = 13.28 Hz), 7.58 (d, 1H, H-8, J = 7.4 Hz),
0
0
00
00
0
0
00
4-oxo-1,4-dihydroquinoline-3-carboxylic
acid (II'b)
.74 to 3.33 (18H, COCH , H-3 , 5 , 3 , 5 , H-2 , 6 , 6 , H-
2
cyclopropyl), 1.31 (d, 2H, H-cyclopropyl), 1.19 (t, 2H);
ESI-MS: Molecular ion peak (M + Na) m/z = 481,
ꢀ
Mustard brown solid; yield 66 to 67%; mp 260 to 262 C
decompose; IR (KBr) cm : ν
(M + 1) = 459, (M + 2) m/z = 460.
−1
3069 (Ar C-H str.), 1626
max
1
(
C=O), 1628.92 (C=O), 1292 (C-N-C), 1127 (C-O-C); H-
NMR (400 MHz, DMSO) δ (ppm): 15.30 (brs, 1H, COOH),
3
7
1
.4.9 | 1-ethyl-6-flouro-4-oxo-
-(4-(piperidine-1-carbnyl)piperazin-1-yl)-
,4-dihydroquinoline-3-carboxylic
8
.96 (s, 1H, H-2), 7.93 (d, 1H, H-5, JH-F = 12 Hz), 7.07 (d,
H, H-8, J = 5.3 Hz), 4.59 (2H, CH CH ), 3.88 to 3.21
1
(
2
3
00 00 00 0 0 0 0
17H, H-3 , COCH , H-3 , 5 , H-3 , 5 , H-2 , 6 ), 2.44 to
3
acid (II'a)
00 00 00
.41 (7H, H-2 , 6 , H-5 , CH CH ); ESI-MS: Molecular
2 3
1
ꢀ
Dark brown solid; yield 61 to 62%; mp 262 to 264 C decom-
pose; IR (KBr) cm : ν
ion peak (M + Na) m/z = 469, (M + Na + 1) m/z = 470,
(M + 1) m/z = 447.
−1
3069 (Ar C-H str.), 1625 (C=O;
max

KAUR ET AL.
11
SCHEME 2 Synthesis of 1-alkyl-6-fluoro-4-oxo-7-(4-(2-(substituted amine)acetyl)piperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid
3
7
1
.4.11 | 1-cyclopropyl-6-flouro-4-oxo-
-(4-(2-(pyrrolidin-1-yl)acetyl)piperazin-
-yl)-1,4-dihydroquninoline-3-carboxylic
(C-H str.), 2727.6 (O-H str.), 1723.80 (C=O; keto), 1624.55
(C=O; amine), 1378.22 (C-N), 1258.78 (C-O); H-NMR
1
(400 MHz, DMSO) δ (ppm): 15.52 (s, 1H, 2” OH), 8.92 (s,
1H, H-2),7.92 (d, 1H, H-5, JH-F = 12.72 Hz), 7.18 (s, 1H,
H-8,), 4.57 (s, 2H, 3”CH CH ), 4.39 (2H, H-8’ COCH ),
acid (I'c)
2
3
2
ꢀ
Light yellow solid; yield 52 to 53%; mp 264 to 266 C
decompose; IR (KBr) cm : ν
str.), 2849.3 (C-H str.), 2723.4 (O-H str.),1739.4 (C=O;
carboxylic acid) 1720.38 (C=O; keto), 1643.45 (C=O;
0
0
0
0
0
0
0
3
1
.75 (t, H-2 , 3 , 5 , 6 ), 3.41 (4H, 10 , 13 ), 1.69 (s, 4H, 11 ,
−
1
3050, 2957.52 (Ar C-H
max
0
2 ), 1.29 (t, 3H, H-4” CH CH ); ESI-MS: Molecular ion
2
3
peak m/z = (M + 1) = 431.
1
amide), 1384.68 (C-N), 1248.66 (C-O);
H-NMR
3
.4.13 | 3.4.13 7-(4-(carbamothioylglycyl)
(
400 MHz, DMSO) δ (ppm): 8.96 (s, 1H, H-2),7.92 (d, 1H,
piperazin-1-yl)-1-cyclopropyl-6-fluoro-4-oxo-
1,4-dihydroquinoline-3-carboxylic acid (I'd)
H-5), 7.25 (s, 1H, H-8, J
CH and 2H, 8 ,), 3.51 (4H, H-,3 , 5 ,), 3.39 (4H, H-2 , 6 ,
J = 4.28 Hz), 3.25(s, 4H, 10 , 13 ) 1.69 (s, 4H, 10 , 13 );
ESI-MS: Molecular ion peak m/z = (M + 1) = 443.
= 13.04 Hz), 4.61 (s, 1H, 3”
H-F
0
0
0
0
0
2
0
0
0
0
ꢀ
Light green solid; yield: 46 to 47%; mp 274 to 276 C
decompose; IR (KBr) cm : ν
−1
3393.5 (N-H str.), 2917.35
max
(
(
(
Ar C-H str.), 2850.6 (C-H str.), 2617.3 (O-H str.), 1714
C=O; carboxylic acid), 1615.36 (C=O; ester), 1577.97
3
7
1
.4.12 | 1-ethyl-6-flouro-4-oxo-
-(4-(2-(pyrrolidin-1-yl)acetyl)piperazin-
-yl)-1,4-dihydroquninoline-3-carboxylic
C=O; amine), 1377.11(C=S), 1291.88 (C-N), 1255.81 (C-
1
O); H-NMR (400 MHz, DMSO) δ (ppm):8.67 (s, 1H, H-2),
7
.92 (d, 1H, H-5, JH-F = 13.2 Hz), 7.55 (d, 1H, H-8, J
H-
0
00
acid (II'c)
0
0
=
6.8 Hz), 3.84 (d, 2H, H-8 ), 3.36 to 2.33 (m, 8H, 2 , 3 ,
0
F
ꢀ
0
Creamish solid; yield 50 to 51%; mp 252 to 254 C decom-
pose; IR (KBr) cm : ν
5 , 6 ,), 1.25 to 1.92 (3H, -NH, -NH ), 0.94 to 0.93 (4H, 5 ,
6 ); ESI-MS: Molecular ion peak m/z = (M + K) = 486.
2
−1
00
2956.69 (Ar C-H str.), 2848.92
max

12
KAUR ET AL.
3
.4.14 | 3.4.14 7-(4-(carbamothioylglycyl)
piperazin-1-yl)-1-ethyl-6-fluoro-4-oxo-
,4-dihydroquinoline-3-carboxylic
acid (II'd)
the plates incubated and zone of inhibition noted in
diameter (mm) after 96 hours.
[
24,25]
1
ꢀ
3.7 | Cytotoxic assay
Light brown solid; yield: 45 to 46%; mp 268 to 270 C
−
1
decompose; IR (KBr) cm : ν
2
3401.59 (N-H str.),
max
The wild-type strain E. coli AB 1157 was used for the
cytotoxicity studies. For the solid cultural media 10 g
tryptone, 10 g sodium chloride, 5 g yeast extract and 20 g
agar were dissolved in 1000 mL distilled water. Initially,
918.09 (Ar C-H str.), 2849.98 (C-H str.), 1707.39 (C=O;
carboxylic acid), 1615.36 (C=O; ester), 1577.97 (C=O;
amine), 1377.11(C=S), 1291.88 (C-N), 1255.81 (C-O); H-
NMR (400 MHz, DMSO) δ (ppm):15.31 (s, 1H, OH), 8.96
s, 1H, H-2), 7.94 (s, 1H, H-5), 7.21 (s, 1H, H-8,), 4.60 (2H,
0 0 0 0 0
CH CH ), 3.69 (2H, 8 ), 3.69 to 1.42 (8H, 2 , 3 , 5 , 6 ,),
2 3
.42 (3H, -NH, -NH ), 1.12 (3H, -CH CH ); ESI-MS:
2 2 3
Molecular ion peak m/z = (M + K) = 474.
1
the stock culture of bacteria was revived by inoculating
ꢀ
(
-
1
in broth medium and grown at 37 C for 18 hours. All the
compounds were dissolved in DMSO. The LB agar plates
were prepared and wells were made in the solidified LB
agar plate. Each plate was inoculated with 18 hours old
cultures and spread evenly on the plates. After
20 minutes, the wells were filled with compounds at dif-
3
.5 | Antibacterial assay
ferent concentration. All the plates were incubated at
ꢀ
3
7 C to 24 hours and zone of inhibition measured in
Antibacterial activity was studied against two gram-
positive strains B. subtilis and S. aureus and two gram-
negative strains E. coli and P. aeruginosa. For the analy-
sis, agar diffusion method was carried out. For the solid
cultural media 10 g peptone, 10 g sodium chloride, 5 g
yeast extract and 20 g agar were dissolved in 1000 ml of
distilled water. The stock cultures were inoculating in
broth media and grown at 37 C for 18 hours and also
revived. The above stock solution poured in the petri
plates and wells were made in the plate. For 18 hours old
cultures (100 μL 10 cfu) inoculated for each plate and
spread consistently on the plates. The wells were filled
after 20 minutes containing different concentrations of
samples and antibiotic. After that at 37 C all the plates
incubated and zone of inhibition in diameter (mm) noted
[
24,25]
diameter mm.
4 | CONCLUSIONS
The molecular predictions for almost all the synthesized
compounds were evaluated and have shown highly effi-
cient results except Ia and IIa, which entered in the blood
brain barrier due to their low TPSA value. The molecular
hybrids at third position of ciprofloxacin and norfloxacin
are showing promising antibacterial activity as compared
to seventh substituted molecular hybrids. But all the
molecular hybrids are inactive against fungal strain Can-
dida albicans. Moreover, IIb compound have shown
highest antibacterial activity. Enhanced cytotoxicity
results of all the synthesized compounds have been
observed as compared to ciprofloxacin. It is further long
way to study and synthesized more molecular hybrid
with substitution toward third position and to find their
efficiency for binding with DNA gyrase.
ꢀ
−4
ꢀ
[24,25]
after 24 hours.
3.6 | Antifungal assay
These coupled compounds were also subjected to study
antifungal activity against fluconazole as standard. The
Agar diffusion method was used for studying the results
against the fungi Candida albicans. The solid culture
media Czapek-Dox Agar prepared which is the composi-
ACKNOWLEDGMENTS
tion of 30 g sucrose, 2 g sodium nitrite, 1 g K HPO , 0.5 g
2
4
We highly thankful to RSIC, Panjab University, Chandi-
garh, and IIT Ropar for spectroscopic analysis and
Sophisticated Instrument Centre, Punjabi University,
Patiala. Also, we are highly thankful to Biogenics, Hubli,
Karnataka for Antimicrobial and cytotoxicity studies.
MgSO .7H O, 0.5 g KCl, 0.01 g FeSO , and 20 g agar dis-
4
2
4
solved in 1000 mL of distilled water. This stock culture is
ꢀ
inoculated in broth media and grown at 27 C for 48 hours
and also revived. The above stock solution poured in the
petri plate and wells were made in each petri plate. For
4
4
8 hours old cultures (100 μL 10 CFU) inoculated for
each plate and spread consistently on the plate. The wells
were filled after 20 minutes containing different concen-
trations of samples and antibiotic. After that at 27 C all
ORCID
ꢀ
Manisha Bansal https://orcid.org/0000-0002-1490-8015

KAUR ET AL.
13
REFERENCES
[17] N. Sultana, M. S. Arayne, S. B. S. Rizvi, Bull. Korean Chem.
Soc. 2011, 32, 483.
[
1] S. S. Panda, O. S. Detistov, A. S. Girgis, P. P. Mohapatra,
[18] N. N. A. Jafar, N. Sadiqmajeed, Int. J. Chemtech. Res. 2016,
A. Samir, A. R. Katritzky, Bioorg. Med. Chem. Lett. 2016, 26,
9
, 387.
2
198.
[
[
[
19] H. Pajouhesh, R. Lenz, Neuro Therapeutics 2005, 2, 541.
20] Z. Rankovic, J. Med. Chem. 2015, 58, 2584.
21] N. C. Desai, G. M. Kotadiya, A. R. Trivedi, Bioorg. Med. Chem.
Lett. 2014, 24, 3126.
[
[
[
[
[
[
[
2] C. M. Oliphant, G. M. Green, K. Permanent, Am. Fam. Physi-
cian. 2002, 65, 455.
3] G. D. Singh, K. C. Gupta, Int. J. Curr. Microbiol. App. Sci. 2014,
3
, 641.
[
[
22] A. A.-M. Abdel-Aziz, A. A. El-Azab, A. M. Alanazi, Y. A. Asiri,
I. A. Al-Suwaidan, A. R. Maarouf, R. R. Ayyad, T. Z. Shawer,
J. Enzyme Inhib. Med. Chem. 2016, 3, 796.
23] M. Qandil, L. O. Al-Zoubi, A. G. Al-Bakri, H. A. Amawi,
Q. A. Al-Balas, A. M. Alkatheriand, A. M. Albekairy, Antibi-
otics 2014, 3, 244.
4] M. G. Rabbani, M. R. Islam, M. Ahamad, A. M. Hossion,
Bangladesh J. Pharmacol. 2011, 6, 8.
5] K. J. Aldred, R. J. Kerns, N. Osheroff, Biochemistry 2014, 53,
1
565.
6] G. Cheng, H. Hao, M. Dai, Z. Liu, Z. Yuan, Eur. J. Med. Chem.
013, 66, 555.
7] Y. Q. Hu, Z. Xu, M. Qiang, Z. S. Lv, J. Heterocyclic Chem. 2018,
5, 187.
2
[
[
24] E. J. Threlafall, I. S. T. Fisher, L. Ward, H. Tschape, P. Gerner-
smidt, Microb. Drug Resist. 1999, 5, 195.
25] R. D. Walker, J. F. Prescott, J. D. Baggot, Antimicrobial Ther-
apy in Veterinary Medicine, University Press, Iowa State
5
8] J. Azema, B. Guidetti, J. Dewelle, B. Le Calve, T. Mijatovic,
A. Korolyov, J. Vaysee, R. Malet-Martino, R. Kiss, Bioorg. Med.
Chem. 2009, 17, 5396.
2000 12.
[
9] R. Bartzatt, S. L. G. Cirillo, J. D. Cirillo, J. Pharm. 2013,
2
013, 1.
10] Z. Xu, Z. S. Lv, X. F. Song, M. Qiang, J. Heterocyclic Chem.
018, 55, 97.
SUPPORTING INFORMATION
[
Additional supporting information may be found online
in the Supporting Information section at the end of this
article.
2
[
[
11] Z. Xu, X. F. Song, J. Fan, Z. S. Lv, J. Heterocyclic Chem. 2018, 55, 77.
12] G. G. Zhanel, A. Walkty, L. Vercaigne, J. A. Karlowsky,
J. Embil, A. S. Gin, D. J. Hoban, Can. J. Infect. Dis. 1999,
1
0, 207.
13] S. Emami, A. Shafiee, A. Foroumadi, Iran. J. Pharm. Res. 2005,
, 123.
[
How to cite this article: Kaur G, Kaur M,
Sharad L, Bansal M. Theoretical molecular
predictions and antimicrobial activities of newly
synthesized molecular hybrids of norfloxacin and
ciprofloxacin. J Heterocyclic Chem. 2019;1–13.
https://doi.org/10.1002/jhet.3768
3
[
14] G. Sarkozy, Vet. Med-Czech. 2001, 46, 257.
[
15] F. Varanda, M. J. Pratas de Melo, A. I. Caco, R. Dohrn,
F. A. Makrydaki, E. Voutsas, D. Tassios, I. M. Marrucho, Ind.
Eng. Chem. Res. 2006, 45, 6368.
[
16] P. C. Sharma, A. Jain, S. Jain, Polish Pharmacol. Soc. 2009,
6
6, 587.