Synthesis of Novel Ciprofloxacin-Based Hybrid Molecules toward Potent Antimalarial Activity

Article abstract of DOI:10.1021/acsmedchemlett.0c00196

Antimalarial drug resistance is a serious obstacle in the persistent quest to eradicate malaria. There is a need for potent chemical agents that are able to act on drug-resistant Plasmodium falciparum populations at reasonable concentrations without any related toxicity to the host. By rational drug design, we envisaged to address this issue by generating a novel hybrid drug possessing two pharmacophores that can act on two unique and independent targets within the cell. We synthesized a new class of ciprofloxacin-based hybrid molecules, which have been integrated with acridine, quinolone, sulphonamide, and cinnamoyl pharmacophores (1-4). We realized a potent chloroquinolone-ciprofloxacin-based antimalarial hybrid (2, CQ-CFX) whose mechanism of action is unlike that of its parent molecules indicating a unique biological target. CQ-CFX is not only potent against CQ-resistant and susceptible strains of Plasmodium falciparum at low nanomolar concentrations (IC50 values are 63.17 ± 1.2 nM and 25.52 ± 4.45 nM, respectively) but is also not toxic to mammalian and bacterial systems up to 20 μM and 1 μM, respectively.

Full text of DOI:10.1021/acsmedchemlett.0c00196

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Letter
Synthesis of novel Ciprofloxacin-based hybrid
molecules toward potent Antimalarial activity
Srikanta Dana, Praveesh Valissery, Sharvan Kumar, Sumiran Kumar
Gurung, Neelima Mondal, Suman Kumar Dhar, and Pritam Mukhopadhyay
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.0c00196 • Publication Date (Web): 04 Jun 2020
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Synthesis of novel Ciprofloxacin-based hybrid molecules toward po-
tent Antimalarial activity
Srikanta Dana,ab† Praveesh Valissery,b† Sharvan Kumar,a Sumiran Kumar Gurung,c Neelima Mondal,c
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Suman Kumar Dhar,b* Pritam Mukhopadhyaya*
a Supramolecular and Material Chemistry Lab, School of Physical Sciences, Jawaharlal Nehru University, New Delhi –
110067, India. bSpecial Center for Molecular Medicine, cSchool of Life Sciences, Jawaharlal Nehru University, New Delhi –
110067, India.
KEYWORDS: Hybrid drug design, Synthesis, Structure activity relationship, Antimalarial activity.
ABSTRACT: Antimalarial drug resistance is a serious obstacle in the persistent quest to eradicate malaria. There is a need for potent
chemical agents that are able to act on drug-resistant Plasmodium falciparum populations at reasonable concentrations without any
related toxicity to the host. By rational drug design, we envisaged to address this issue by generating a novel hybrid drug possessing
two pharmacophores that can act on two unique and independent targets within the cell. We synthesized a new class of ciprofloxacin-
based hybrid molecules, which have been integrated with acridine, quinolone, sulphonamide and cinnamoyl pharmacophores (1-4).
We realized a potent chloroquinolone-ciprofloxacin-based antimalarial hybrid (2, CQ-CFX) whose mechanism of action is unlike
that of its parent molecules indicating a unique biological target. CQ-CFX is not only potent against CQ-resistant and susceptible
strains of Plasmodium falciparum at low nanomolar concentrations (IC50 values are 63.17 ± 1.2 nM and 25.52 ± 4.45 nM, respectively)
but is also not toxic to mammalian and bacterial systems up to 20 μM and 1 μM respectively.
Malaria, caused by the apicomplexan Plasmodium falciparum,
is still a major threat to mankind. The most successful treatment
strategy that is currently employed involves the use of an arte-
misinin derivative in combination with a partner drug. The com-
bination of Artemether and lumefantrine have an overall treat-
ment efficacy of about 93.4% with certain places showing
greater than 10% failure rate.1 According to WHO global data-
base on antimalarial drug efficacy and resistance, the rate of Ar-
temisinin combination Therapy (ACT) failure has increased to
greater than 10% since 2010 in areas like Cambodia, Thailand,
Vietnam and Myanmar. The emergence and spread of these re-
sistant strains over the coming years may prove detrimental to
our goal to eradicate malaria. Therefore, there is a need for the
discovery and innovation of a new class of antimalarial com-
pounds that retain effective capabilities at low concentrations
and possess hitherto unexploited mechanisms of action to curb
the spread of resistant parasites.
ternary complex of enzyme-drug-DNA and consequently block
DNA replication.10 It has been seen that fluoroquinolones are
active against the in vitro culture of P. falciparum.11 This is at-
tributed to the presence of a prokaryotic organelle known as the
Apicoplast within the parasite.12 Among all the fluoroquino-
lone-based antibiotics tested against P. falciparum, grepafloxa-
cin, gatifloxacin, and moxifloxacin are among the most active.
They have displayed IC50 values greater than 10 µM against dif-
ferent P. falciparum strains (3D7 and/or NF54-R).13 However,
we were interested in working with Ciprofloxacin (CFX). It is
a second generation fluoroquinolone, introduced in 1987, and is
included in the WHO list of essential medicines for adults as
well as children.14, 15 CFX treatment blocks apicoplast DNA
replication and causes the formation of abnormal apicoplast and
exerts “delayed death” phenotype in P. falciparum as well as T.
gondii.16, 17 Our group has previously characterized the nuclear-
encoded apicoplast targeted gyrase B and established it as a vi-
able target in malaria monotherapy using CFX.18, 19
In this context, the concept of hybrid drug design is at its in-
fancy and can be promising as one can use existing antimalarial
agents to generate combinations that possess two or more phar-
macophores that can act on multiple distinct targets within the
parasite.2-8 We conceptualized that a novel combination of such
molecules would be more potent than the parent drugs, and
would also be highly demanding for the parasites to become re-
sistant against. Fluoroquinolones, since their discovery in the
1970s have been used as broad-spectrum antibacterial agents
for the treatment of a wide variety of Gram-negative and Gram-
positive bacterial infections.9 They target the bacterial Gyrase
and Topoisomerase IV and exert their toxicity by forming a
The enhancement of antimalarial activity of CFX was achieved
by Dubar et al.20 In this work, ethyl ester derivatives of CFX
bearing a ferrocenyl substituent at N-1 or at the C-7 position of
the quinolone ring were synthesized. The introduction of ferro-
cenyl substituents and ethyl esterification of the carboxylic
group made these molecules more hydrophobic than their pre-
cursor drug CFX. In parallel to the enhancement of lipophilic-
ity, “prodrug” form of CFX was also achieved by esterification
of carboxylic group. These derivatives were 15-fold and 30-fold
more active than their precursor drug CFX as antimalarials.
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Scheme 1. Synthetic pathways to the ciprofloxacin derivatives 1-4.
However, despite the growing importance of CFX in clinical
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settings of bacterial infections, the lack of activity of CFX in
the 1st life cycle of malaria at clinically relevant concentration
prevents their use in monotherapy. All antibiotics, including
CFX, are slow acting antimalarials.21 However, the prokaryotic
apicoplast is a comparatively new target in malaria chemother-
apy and extensively divergent from existing targets of known
antimalarials. Therefore, in the search for the hybrid partner, we
restricted ourselves to possible pharmacophores that are active
in the first life cycle of the parasite.22, 23Additionally, such mod-
ifications could help to increase lipophilicity in hybrid mole-
cules. This increase in lipophilicity might help the hybrid mol-
ecule to traverse the multiple membranes of the parasite and its
plastid and reach the potential target sites as the biological
membranes are lipophilic in nature.24
1
with respect to the vinylic-H of 8 in the NMR spectra. The
ethyl ester of CFX (11) was prepared by an aromatic nucleo-
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Structure-activity relationship (SAR) studies have demon-
strated that structural modification at the C-7 position of the
fluoroquinolone ring including alkylation and acylation at the
secondary amine of the piperazine moiety results in the loss of
antibacterial activity.25, 26Therefore, we chose to functionalize
CFX at the terminal N atom of the piperazine moiety with var-
ious 1st life cycle active antimalarial scaffolds (acridine, quin-
oline, sulphonamide and cinnamoyl) to prepare CFX-based hy-
brid antimalarials 1-4.
philic substitution of the C-7 fluorine atom of difluoroquinolone
10 with piperazine in 98% yield. Finally, nucleophilic substitu-
tion reaction between secondary amine of piperazine moiety at
the C-7 position of 11 with corresponding chloro substituted 1st
life cycle active antimalarial scaffolds (ArCl) afforded the final
Ciprofloxacin-based hybrid compounds 1-4 in 30-40% yields.
The structures of 1-4 were confirmed by H NMR, 13C NMR,
1
FT-IR and mass spectrometric analysis. In addition, compounds
2 and 3 were characterized by single crystal X-Ray diffraction
analysis. A detailed account of the synthesis and characteriza-
tion has been given in the Supplementary Information (Figures
S6-S22).
Figure 1. Molecular structures of CFX-based hybrid molecules
X-Ray Crystallography: The X-ray suitable single crystals of
2 and 3 were grown from MeCN solutions at room temperature.
The crystal structures of 2 belongs to monoclinic space group
‘P 21/n’ with one molecule per asymmetric unit.29 The quino-
lone moiety assumes a planer structure and the C=O bond
length of quinolone moiety was found to be 1.239 Å, while the
C=O bond of the ester group was found to be 1.208 Å. The
propyl group at the quinolone N1 forms obtuse geometry with
an angle of 119.70o (N1—C23—C24) and 120.60o (N1—
C23—C24) from N1 atom which allow H-bonding between H
atoms associated with C atoms of cyclopropyl and O and Cl at-
oms of the neighbouring moiety (Figure 2a).
Synthesis: The detailed synthetic pathway for the targeted
CFX-based hybrid molecules 1-4 (Figure 1) starting from com-
mercially available 2,4,5-trifluorobenzoic acid (6) is depicted in
Scheme 1. These molecules (1-4) were synthesized in seven
steps with 32-80% overall yield. The synthesis of the ethylester
of CFX 11 was adapted from the previous method reported else-
where.27 For the building of key quinolone cycle (10), 2,4,5-
trifluorobenzoic acid 6 was first reacted with Vilsmeier-Haack
reagent (oxalyl chloride and DMF) in dichloromethane to afford
acyl chloride (7) in quantitative yield, which was then con-
densed with ethyl 3-(diethylamino)acrylate (5) in a mixture of
triethylamine/toluene to obtain N,N-diethyl enaminone inter-
mediate (8) in 76% yield. Formation of enaminone intermediate
The crystal structures of CFX-based hybrid molecule 3 belongs
to the triclinic space group ‘P1’ with one molecule per asym-
1
̅
(8) was confirmed by recording the H NMR spectrum. The
ethyl 3-(diethylamino) acrylate (5) was synthesized by Michael
addition of diethylamine to ethyl propionate in acetonitrile with
88% yield as previously reported elsewhere.28 In a one-pot pro-
cess, transaminolysis of 8 with cyclopropylamine followed by
cyclization with potassium carbonate in DMF afforded difluo-
roquinolone (10) in 68% yield. The cyclization of 8 to fluoro-
quinolone 10 was confirmed by the ~ 0.9 ppm deshielding of
H-2 proton of 10
metric unit (Figure 2b). The quinolone moiety forms a planer
structure and the C=O bond length of quinolone moiety was
found to be distance of 1.236 Å, while the C=O bond of ester
was found to be 1.206 Å. The propyl group at the quinolone N1
forms obtuse geometry with an angle of 118.74o from N1 atom
allowing H-bonding between H atoms associated with C22
atom of cyclopropyl and O atoms of the neighbouring
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Table 1: In vitro antimalarial activity against CQ-
1
2
susceptible (3D7) and CQ-resistant (W2) P. falciparum
strains after 1st (48 h) and 2nd (96 h) life cycle.
3
4
5
IC50 (nM)a 1st life IC50(nM)a 2nd life RI
Log
Pb
Cycle (48 h)
Cycle (96 h)
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7
8
9
3D7
W2
3D7
W2
nd
359.40 ±
1.15
311.30
1.07
±
±
±
±
1
2
3
4
nd
-
6.31
5.02
4.29
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25.52
4.45
±
±
63.17
± 1.2
13.52
0.2
30.64
± 1.07
2.47
3.88
-
37.63
1.18
146.2
± 1.19
14.83
1.09
33.39
± 1.11
Figure 2: ORTEP representations of a) 2 and b) 3. Thermal ellip-
soids are shown at 50% probability.
9109.00
± 1.18
4786.00
1.05
nd
nd
moiety. The piperazine moiety adopts chair conformation. The
trifluoromethyl benzenesulfonyl group forms slightly obtuse
right angles with the N3 atom of the piperazine moiety (N3—
S1—C14 = 105.33 o).
3.81
1.32
C
F
X
37080.
00
1.04
22850.
00
1.04
45350.0
0 ± 1.18
26260.00 ±
0.99
1.62
34.2
±
±
The hybrid compounds are potent in vitro antimalarials :
3.93
Ciprofloxacin derivatives 1-4 were tested for their in vitro anti-
malarial activity against Chloroquine (CQ) sensitive (Pf 3D7)
as well as CQ resistant (Pf W2) strains. Ciprofloxacin and Chlo-
roquine were taken as controls and their IC50 values were deter-
mined (Table 1). All the dose-response curves are presented in
Supporting Information, Figure S1-S4.
C
Q
12.56
0.66
±
430.60
± 1.09
nd
nd
aIC50 values are from a single experiment with the duplicate
sample. CQ= chloroquine, CFX= ciprofloxacin: Resistance In-
dices (RI)= IC50 (W2)/ IC50(3D7) after 1st life cycle; calculated
using ChemDraw ultra 7.0; nd= not determined.
The synthesized hybrids 1-4 exhibited significant antimalarial
activity. Hybrids 1-3 exhibited IC50 values in nM ranges at both
cycles. Hybrid 4 bearing cinnamoyl moiety exhibited IC50 value
in µM range. The activity of hybrids 1-4 was improved in com-
parison to that of CFX. A remarkable increase in the antimalar-
ial activities (~103 -fold) at both the life cycle was observed es-
pecially for hybrids 2-3 in comparison to CFX. The higher ac-
tivities of hybrids 1-4 compared to CFX can be attributed to the
increased lipophilicity of hybrid molecules (log P values in Ta-
ble 1), as well as to the presence of two pharmacophores in the
hybrids. In the hybrids 2-4, the antiplasmodial activity (1st cycle
and 2nd cycle against Pf3D7 and PfW2) increased in the order
2>3>4. This is consistent with the increasing order of lipophilic-
ity [logP: 2 (5.02) >3 (4.09) >4 (3.81)]. However, Hybrid 1
bearing the acridine scaffold does not follow the order. The
most potent hybrids 2-3 were tested for their antimalarial activ-
ity against Pf W2 strain. Both the hybrids exhibited IC50 values
in nM ranges at 1st as well as 2nd life cycle against PfW2 strain.
The antimalarial activities of hybrids 2-3 at both the life cycle
were 2× 102 - 7×102 -fold higher in comparison to that of CFX.
Importantly, hybrids 2-3 were also more potent than CQ against
the CQ-resistant PfW2 strain. These hybrids exhibited 3 and 7-
fold higher activity, respectively, in the 1st cycle againstPfW2
strain than CQ. In addition, these hybrids also displayed 8 and
17-fold better resistance indices, respectively, than CQ.
Cytotoxicity Study of Most Potent Molecule, CQ-CFX:
The cytotoxicity of the most potent compound 2 (CQ-CFX) was
determined against mammalian fibroblast NIH3T3cells using
concentrations ranging from 0.3125 to 20 M by MTT assay.
The studies revealed that CQ-CFX did not produce any signifi-
cant cytotoxicity up to 10 M even when incubated for upto 72
hours (Figure 3). Further, it is noteworthy that molecules 1-4
did not show any hemolysis of infected RBCs or uninfected
RBCs at their highest tested concentrations (10-45 µM). There-
fore, these molecules may display minimal toxic effects in vivo.
Figure 3. Survivability of NIH3T3 cells in presence of 2 (CQ-
CFX)
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CQ-CFX shows stage specificity in inhibition: The life cycle
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of Plasmodiumis organized into discreet stages termed as Ring,
Trophozoite, and Schizont. Each stage is morphologically dis-
tinct and corresponds to a particular phase in the cell cycle
wherein various proteins are differentially expressed.30 We
found that CQ-CFX shows stage specificity in its action. The
compound was more effective during the Ring and the Schizont
stages compared to the Trophozoite stage (Figure 4). The bio-
logical target/s of CQ-CFX may be maximally expressed during
these stages.
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Figure 4. Stage-specific effects of CQ-CFX treatment. The drug-
treated groups were plotted as percentages calculated against the
untreated control group.
Figure 5. A. Synchronized ring stage parasites were treated with
various concentrations of CFX and CQ-CFX (as indicated at the
bottom) and the parasitemia was recorded at 48h and 96h and plot-
ted accordingly. B. The cell lysate from the 96h drug-treated para-
sites was probed with polyclonal antibodies specific for PfSSB
(Single-stranded binding protein). PfActin was used to ensure equal
loading of the untreated control and the vehicle (DMSO) treated
lysates. The arrowhead marks the unprocessed PfSSB specific band
that builds in the CFX treated lysate. C. Antibacterial activity of
CFX compared with CQ-CFX. An actively growing cultureof
DH10β strain of E.coli was aliquoted at OD600 of 0.2 into respective
treatment groups as indicated and treated with the corresponding
drug for 6h. The OD600 values were logged and the data were plot-
ted as a percentage of the untreated control group.
CQ-CFX does not retain CFX like behaviour: Ciprofloxacin
exhibits a characteristic delayed-death phenotype in Plasmo-
dium falciparum.31 This is due to the fact that Ciprofloxacin tar-
gets the prokaryotic PfGyrase localized in a plastidlike orga-
nelle known as the apicoplast. Since there is an adequate pool
of apicoplast derived metabolites within the parasite, damage to
the apicoplast does not manifest any cellular toxicity in the first
life cycle of the parasite. Therefore, the parasitemia in the first
life cycle remains unaffected. It is however evident in the sec-
ond life cycle, where the now dysfunctional apicoplasts are un-
able to maintain the metabolic needs of the parasite. Thus, the
parasitemia in the second life cycle drops sharply compared to
the first life cycle. We wanted to check whether CQ-CFX shows
a similar pattern of inhibition.
We have previously observed that a nuclear-encoded apicoplast
targeted (NEAT) protein like PfSSB cannot successfully trans-
locate into a dysfunctional apicoplast and therefore accumulates
in the cytosol with the apicoplast targeting signal peptide in-
tact.32 This unprocessed protein can be seen as a higher molec-
ular weight band in an immunoblot probed with antibodies
against PfSSB. CFX treatment generated this unprocessed form
of PfSSB in the second life cycle by virtue of its mechanism of
action. This was not observed in CQ-CFX treated parasites (Fig.
5B). We failed to see the accumulation of this unprocessed form
of PfSSB in the parasites treated across an effective range of
concentrations of CQ-CFX (Supporting Information, Figure
S5). This suggests that the mechanism of CQ-CFX action is un-
like that of CFX.
We looked at the inhibition in the first and second life cycle
parasitemia across a range of concentrations below the IC50
value of CFX and CQ-CFX. In the CFX treated parasites a stark
statistically significant difference in parasitemia was seen. This
pattern was absent in the CQ-CFX treated parasites (Fig. 5A).
In order to corroborate the absence of delayed death on a protein
level, we looked at the accumulation of an unprocessed band of
the single-stranded DNA binding protein (PfSSB). The PfSSB
gene is located within the P.falciparum nucleus. Therefore, the
protein is synthesized outside the apicoplast and is targeted to
the organelle via a signal peptide.
Additionally, since Ciprofloxacin is an anti-bacterial agent, we
hypothesized that the compound could be toxic to prokaryotic
systems that are completely dependent on their DNA Gyrase for
replication. However, we saw that CQ-CFX fails to inhibit the
growth of E.coli at all concentrations tested (Fig., 5C); indicat-
ing that the CFX moiety in CQ-CFX is not functional. On a sep-
arate note, the lack of any anti-bacterial activity makes CQ-
CFX a better candidate than CFX for in vivo test as there would
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Figure 6. A. Panel shows the comparison of the reduction in hemo-
be minimal damage to the gut flora while maintaining an en-
hanced anti-malarial effect.
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zoin crystal size upon CQ and CQ-CFX treatment. B. The ratio of
hemozoin crystal to the cell size derived from images of parasites
treated with the indicated drugs for 24 hours. Image analysis and
estimation were done using ImageJ. C. Spectrophotometric titra-
tion of monomeric heme (blue dotted line) with increasing concen-
trations of (i)Ciprofloxacin (CFX), (ii) Chloroquine (CQ) and
(iii)CQ-CFX. The characteristic Soret band of heme ranges be-
tween 380 nm and 420 nm. The decreasing band between 380 and
420 nm in the Chloroquine titration is distinctive of the heme bind-
ing.
CQ-CFX does not retain CQ like behaviour: During the in-
tra-erythrocytic stages of Plasmodium falciparum life cycle, the
parasite relies on the host erythrocyte’s hemoglobin as a nutri-
ent source.33 In the acidic food vacuole, dedicated proteases
break down hemoglobin into free amino acids. The heme com-
ponent, Fe(II)-protoporphyrin IX (FP), in hemoglobin is re-
leased as a by-product in these reactions. Free heme is toxic, as
it can generate free radicals via Fenton reactions and damage
the lipid bilayers in the parasite and the host erythrocyte. There-
fore, it is biocrystallized to an inert crystalline lattice known as
hemozoin.34 A vast array of protein complexes including Falci-
pain-2 and Heme Detoxification Protein (HDP) are involved in
this process of biomineralization.35 Chloroquine (CQ) has been
shown to disrupt the association of hemoglobin with Falcipain
2 and therefore inhibits hemozoin polymerization.36 Therefore,
one of the hallmarks of Chloroquine mediated toxicity is the re-
duction in the size of the hemozoin crystal compared to the un-
treated parasites. We decided to use this phenotype to screen
whether the CQ moiety in CQ-CFX is still functional. The par-
asites were treated with CQ and CQ-CFX separately and ob-
served for a duration of 48h (Figure, 6A). The CQ treated para-
sites showed a statistically significant reduction in the size of
the hemozoin (Figure, 6B). However, CQ-CFX treated parasites
did not show any impairment in their ability to form hemozoin
in the food vacuole. This suggests that perhaps the CQ related
function is absent or minimal in the hybrid molecule. In order
to corroborate this assumption, we looked at another facet of
Chloroquine’s physical chemistry. In addition to disrupting Fal-
cipain 2 and hemoglobin interaction, CQ also binds to Fe(II)-
protoporphyrin IX and forms a complex that sterically inhibits
its crystallization.37 We observed the ability of the hybrid to
bind to Fe(II)-protoporphyrin IX using UV-vis spectroscopy.
The concentration of Hemin was kept constant at 2.4 uM and
Chloroquine, Ciprofloxacin and CQ-CFX were added in small
increments. Chloroquine showed a clear
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concentration-dependent association with Hemin denoted by
the reduction in the characteristic Soret band of Hemin with in-
creasing amounts of Chloroquine. This pattern was absent
across a range of concentrations of CFX and CQ-CFX tested,
ranging from 100 nM to 4.5 μM (Fig. 6C). This suggests that
the CQ moiety in CQ-CFX does not retain its function.
Conclusion: In this study, we present a novel class of CFX-
based hybrid molecules whose antimalarial activities were
found to be remarkably higher than the precursor drug CFX;
due to their unique structural design. Hybrids (2-3) were found
to be much more potent than CQ against CQ-resistant Plasmo-
dium falciparum strains. It is intriguing that the CQ-CFX hybrid
compound is an effective anti-malarial agent that works at low
nanomolar concentrations. The hybrid is also not toxic to mam-
malian cells in its antimalarial range of concentrations, in vitro.
Presently, the limitation of this study is the lack of in vivo vali-
dation of the efficacy of CQ-CFX. Also, it is possible that the
ester prodrugs may not survive in vivo, hence, the efficacy of
the acid forms of the compounds need to be tested further for
their antimalarial activity. It is intriguing that CQ-CFX works
against CQ resistant parasites. It will be interesting to study the
stage specific effect of CQ-CFX that may allow us to explore
the mechanism of action of the molecule. To the best of our
knowledge, this is the first example of CFX-based hybrid mol-
ecules that exhibit nano-molar antimalarial activity in the 1st as
well as 2nd life cycle of the malaria parasite, Plasmodium falci-
parum.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website.
Details of biological assay protocols, synthetic procedures, in vitro
data is included in the supplementary data (PDF).
AUTHOR INFORMATION
Corresponding Author
m_pritam@mail.jnu.ac.in; skdhar@mail.jnu.ac.in
Author Contributions
The manuscript was written through contributions of all authors.
All authors have given approval to the final version of the manu-
script. ‡ SD and PV contributed equally to this work.
Funding Sources
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8. Bellot, F.; Coslédan, F.; Vendier, L.; Brocard, J.; Meunier, B.;
P.M. acknowledges financial support under the Swarna Jayanti
Fellowship (No. DST/SJF-02/CSA-02/2013-14) and DST-
PURSE II. SKD acknowledges University Potential of Excel-
lence 2 (University Grant Commission), Department of Science
and Technology (DST-PURSE II), Department of Biotechnol-
ogy (BT/PR21569/NNT/28/1234/2017), DST-DPRP and UGC-
SAP for funding. PV acknowledges UGC for fellowship.
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P.M. acknowledges financial support under the Swarna Jayanti Fel-
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ABBREVIATIONS
CFX, Ciprofloxacin; CQ, Chloroquine; CQ-CFX, Chloroquine-
Ciprofloxacin hybrid compound; HDP, Heme Detoxification Pro-
tein.
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Crystal data for 3: C26H25F4N3O5S, M = 567.55, triclinic, P1͞, a =
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