6-Nitro-1-benzylquinolones exhibiting specific antitubercular activity

Article abstract of DOI:10.1111/cbdd.13747

In this study, we synthesized novel nitro quinolone-based compounds and tested them in vitro against a panel of Gram-positive and Gram-negative pathogens including Mycobacterium tuberculosis (MTB), Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumonia, Staphylococcus aureus, and Escherichia coli for antibacterial activities and also against HeLa cells for overt cytotoxicity. Compound 8e was identified as a non-toxic, potent hit with selective activity (MIC₉₀???0.24?μm) against MTB. 8e, however, showed no activity against DprE1 mutant, suggesting DprE1 as the likely target for this compound class.

Full text of DOI:10.1111/cbdd.13747

DR RICHARD MBI BETECK (Orcid ID : 0000-0002-6282-043X)
PROFESSOR LESETJA J LEGOABE (Orcid ID : 0000-0003-2440-4993)
Article type : Research Letter
6
Nitro-1-benzylquinolones exhibiting specific anti-tubercular activity
Richard M. Beteck *, Audrey Jordaan , Tarryn Swart , Frank Van Der Kooy , Digby F. Warnerb,d,e,
a
b
c
a
c,f
a
Heinrich C. Hoppe , Lesetja J. Legoabe *
aCentre of Excellence for Pharmaceutical Sciences, North-West University, Potchefstroom 2520,
South Africa.
bSAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology,
University of Cape Town, Observatory, 7925, South Africa.
cDepartment of Biochemistry and Microbiology, Rhodes University, Grahamstown 6140, South
Africa.
dInstitute of Infectious Disease and Molecular Medicine, University of Cape Town, Rondebosch 7701,
South Africa.
eWellcome Centre for Infectious Diseases Research in Africa (CIDRI-Africa), Faculty of Health
Sciences, University of Cape Town, Rondebosch 7701, South Africa.
This article has been accepted for publication and undergone full peer review but has not been
through the copyediting, typesetting, pagination and proofreading process, which may lead to
differences between this version and the Version of Record. Please cite this article as doi:
1
0.1111/CBDD.13747
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fCentre for Chemico- and Biomedicinal Research, Rhodes University, Grahamstown 6140, South
Africa.
*Corresponding Author: RMB- email; 25159194@nwu.ac.za, Tel.: +27 18992249, LJL- email;
lesetja.legoabe@nwu.ac.za, Tel.: +27182992182
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Abstract
In this study, we synthesized novel nitro quinolone-based compounds and tested them in vitro against
a panel of Gram-positive and Gram-negative pathogens including Mycobacterium tuberculosis
(MTB), Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumonia, Staphylococcus
aureus, and Escherichia coli for antibacterial activities and also against HeLa cells for overt
cytotoxicity. Compound 8e was identified as a non-toxic, potent hit with selective activity (MIC90
˂
0.24 µM) against MTB. 8e, however, showed no activity against DprE1 mutant, suggesting DprE1
as the likely target for this compound class.
Keywords: Quinolones, Mycobacterium tuberculosis, Nitro drugs, DprE1 enzyme.
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1
. Introduction
Although the genome of Mycobacterium tuberculosis (MTB), the causal agent of tuberculosis
(TB), has been completely sequenced and several drug targets identified (Cole et al., 1988), potent
inhibitors of many targets remain scarce. In part, this is because compounds identified via target-
based screening often fail to exhibit activity when tested against whole-cell MTB (Jansen and Rhee,
2
017). The notorious structural and pathophysiological features of MTB represent a major
confounder, precluding inhibitors from reaching their targets (Kana et al., 2014). For-example, MTB
possesses a cell wall core made up of mycolic acids esterified with arabinogalactan, which in turn is
covalently attached to peptidoglycan. This core is interspersed by various lipids, proteins, and
carbohydrates (Brennan, 2003). Underneath this core lies the usual lipid bilayer ─ the cell membrane,
which is found in all bacteria (gram +ve, and -ve inclusive) (Barak and Muchova, 2013). All these
collectively form an impermeable barrier against potential drug molecules. In addition, a definitive
pathophysiological hallmark of active MTB infection is the formation of granulomas, which result
from inflammatory response to MTB. In the simplest description, the granuloma consists of MTB-
containing macrophages, other immune cells, and dead cells, and is devoid of blood vessels
(Warsinske et al., 2017). These effectively shield MTB from the effect of xenobiotics in vivo
(Warsinske et al., 2017). Hence, in contrast to target-based drug discovery, whole cell-based screens
can be used to identify compounds able to penetrate MTB and affect its viability (Kana et al., 2014).
It is estimated that approximately one-quarter of the world’s population harbour MTB in its
latent form, and almost 10 % of this cohort will develop active pulmonary TB in their life time
(Gideon and Flynn, 2011). At least 10 million active pulmonary TB cases and 1.6 million TB related
deaths were reported in 2018 (WHO, 2018). TB is a public health emergency owing to the existence
of several forms of drug(s) resistant MTB, including rifampicin resistance (RR), isoniazid resistance
(IR), multidrug resistance (MDR), and extensively drug resistance (XDR) (WHO, 2018), all of which
are transmissible (Leung et al., 2013). Increasing prevalence of drug-resistant MTB places current TB
treatments in jeopardy, and makes paramount the search for new compounds with novel modes of
action against the bacillus. Recently, a new regimen (comprising bedaquiline, pretomanid, and
linezolid) was approved by the US Food and Drug Administration (FDA) (FDA, 2019). However,
while very exciting, this success is inadequate given the global burden of drug resistant MTB. In
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addition to the safety concerns, other alternatives are needed to avoid over prescription of the new
regimen and to slow the emergence of drug-resistance.
Nitro benzenoids (see 1-2, Fig. 1) have recently been identified as new compounds showing
activity against both drug-susceptible and drug-resistant forms of MTB (Chikhale et al., 2018). They
exhibit potent inhibitory activity through a mode of action (MoA) that differs from that of anti-
tubercular agents in clinics. Most notably, the leading compound from this class of compounds,
PBTZ169, is reported to act as suicide inhibitor of the mycobacterial decaprenylphosphoryl-β-D-
ribose 2′-epimerase (DprE1) (Makarov et al., 2014). DprE1 is required for the synthesis of
arabinogalactan, an essential component of the mycobacterial cell wall (Chikhale et al., 2018). Leads
in this compound class have interesting attributes: they are pro-drugs activated by an enzyme peculiar
to MTB, hence reducing the probability of side effects (Trefzer et al., 2010). However, they also
suffer from poor drug-like properties such as short half-life and poor aqueous solubility (Zhang et al.,
2
019). These warrant further research in this area.
The quinolone class of antibiotics – which are characterized by carboxyl and amino moieties
attached at positions -3 and -7, respectively, of the quinolone nucleus and generally referred to as
fluoroquinolones (FQ) – has long served as mainstay antibiotic for a wide range of bacterial
infections, including TB (Asif, 2013). Their MoA involves targeting bacterial DNA gyrase and/or
topoisomerase IV (Aldred et al., 2014). The FDA currently recommends a black box label for all
fluoroquinolones (FDA, 2019b). While a structural alteration strategy could be used to mitigate off-
target effects of drugs (Kerns and Carter, 2009), this is difficult with the fluoroquinolones as the very
structural features that promote antibacterial activities are also implicated in off-target activities. For-
example, the amine moiety at position -7 of the quinolone nucleus which is crucial for antibacterial
activity has been reported to also promote genotoxicity and inhibition of GABA receptors (Pham et
al., 2019). Three studies have investigated 6- nitro-7-aminoquinolone-3-carboxylic acid for anti-TB
activity (Senthilkumar et al., 2009; Artico et al., 1999; Sbardella et al., 2004). The most active
compound from these studies (3, Fig. 1) shares significant structural similarity with ciprofloxacin (4,
Fig. 1), a FQ (Senthilkumar et al., 2009), and exhibits reduced activity against FQ resistant-TB (0.16
µM), which indicates cross resistance with fluoroquinolones (Beteck et al., 2018). Compounds in
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these studies were also active against Gram-positive and Gram-negative bacteria just like FQ (Artico
et al., 1999; Sbardella et al., 2004).
Besides MTB, a good number of bacteria collectively referred to as “ESKAPE” pathogens are
of global public health concern because they have developed resistance against all clinically available
antibiotics and, more importantly, because these pathogens are responsible for healthcare-associated
infections (HAI) (Mulani et al., 2019). HAI are difficult to treat, necessitating longer stays in the
hospital, which ultimately increases treatment cost (Mulani et al., 2019). To this effect, we cross
screened compounds investigated for anti-tubercular activity against some ESKAPE pathogens in
order to identifying new hit compounds against these pathogens.
In this study, we synthesized novel 6-nitroquinolones and evaluated them in vitro for anti-
tubercular and antibacterial activities. Target compounds were achieved through simple synthetic
transformations illustrated in scheme 1, below. Briefly, a nucleophilic conjugate addition reaction
between 5 and 6 gave a condensed intermediate which underwent intramolecular Friedle-Craft
o
acylation reaction in Eaton’s reagent at 90 C to afford compound 7. Treatment of 7 with various
benzyl bromides using previously reported (Beteck et al., 2019) procedures effected N-alkylation of
the secondary amine to furnish target compounds 8a-8j in 70-85 % overall yields. Treatment of 8b in
refluxing hydroxylamine solution (50 % wt in H O) effected aminolysis of the ethyl ester to afford
2
compound 9, which is a hydroxamate, in 50 % yield. The NO - group in compounds 8b-8h and 8j
2
was selectively reduced to an NH - moiety using reduced iron powder and acetic acid. This
2
transformation afforded compound 10a-10h in 50-60 % yield.
All target compounds (8a-8j, 9, 10a-10h) were characterized using H and 13C NMR, and
1
1
HRMS. For compound 8a-8j, and 10a-10h, the H NMR spectra show a singlet peak appearing at ca
5
.7 ppm which is assignable to the –CH - of benzyl substituents. The quartet peak (J = 7.1) appearing
2
at ca 4.3 ppm is attributable to the –CH - of ethyl ester, while the triplet signal (J = 7.1) at ca 1.3 ppm
2
indicates the presence of the –CH of ethyl ester. The disappearance of the peaks at ca 4.3 and 1.3
3
1
ppm, and the appearance of singlet at 11.6 ppm (which is absent in 8b) in the H NMR spectrum of
compound 9 suggests that the ethyl ester was successfully transformed to a hydroxamate. The
1
appearance of a singlet peak at ca 5.4 ppm in the H NMR spectra of compound 10a-10h is indicative
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of the presence of aryl-NH ; this peak is absent in the spectra of the precursor compounds (8a-8j).
2
High-resolution mass spectrometry analysis further confirmed the desired molecular ions, which were
consistent with structures of target compounds.
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Scheme 1. Synthesis of target compoundsa
O
N
O
O
O
O
O N
2
OH
I
N
O N
2
O
O
H
+
NH2
5
6
iv
9; 50 %
i
O
N
O
O
N
O
O N
2
H N
2
O
O
iii
O
v
O
O N
2
O
N
R
R
10
H
8
7
8
8
8
8
8
8
8
8
8
8
a;72 %, R = benzyl
1
1
1
1
1
1
1
1
0a;60 %, R = 3-I-benzyl
0b;52 %, R = 4-Br-benzyl
0c;55 %, R = 3-Br-benzyl
0d;58 %, R = 3-Cl-benzyl
0e;50 %, R = 4-F-benzyl
0f;50 %, R = 3-F-benzyl
0g;56 %, R = 4-CN-benzyl
b;70 %, R = 3-I-benzyl
c;78 %, R = 4-Br-benzyl
d;80 %, R = 3-Br-benzyl
e;73 %, R = 3-Cl-benzyl
f;76 %, R = 4-F-benzyl
g;77 %, R = 3-F-benzyl
h;70 %, R = 4-CN-benzyl
i;72 %, R = 3-CN-benzyl
0h;57 %, R = 3-CH -benzyl
3
j;80 %, R = 3-CH -benzyl
3
a
Reagents and conditions. (i) EtOH, reflux, 2-3 hours, (ii) Eaton’s reagent, N atmosphere,
2
o
8
0-90 C, 12-15 hours, (iii) Benzyl bromide, K CO , DMF, reflux, 10-12 hours, (iv) NH OH (50% wt
2 3 2
in H O) (v) Fe/Acetic acid, EtOH, ultrasound irradiation, 3-6 hours.
2
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All target compounds were screened in vitro against Mtb::gfp reporter strain cultured in
Middlebrook 7H9 media supplemented with casitone, glucose and tyloxpol for anti-tubercular
evaluation. Each compound was screened at ten different concentration points (0.0002 – 10mM)
and a dose-response curve was generated at day 14, was constructed from which the MIC values
9
0
were determined. The MIC90 value refers to the minimum concentration of a test compound
required to inhibit 90 % of MTB growth. Rifampicin was included as the positive control in this
assay. Five out of the nineteen compounds inhibited MTB growth, demonstrating anti-MTB
activity in the range of 0.24 to 62.5 µM. Compound 8e exhibiting an MIC value of <0.24 µM
9
0
emerged as the most active compound in this study. Although the number of compounds showing
anti-MTB activity in this study was relatively small, precluding extensive structure activity
relationship (SAR) analysis, comparison of compounds showing anti-mycobacterial activity
suggests that meta substituted benzyl moieties at position -1 of the quinolone nucleus promote
activity better than para substituted benzyl moieties. For example, compound 8f (MIC : 8.4 µM)
9
0
bearing a para fluoro benzyl moiety at position -1 is two-fold less active than compound 8g
MIC : 4.1 µM) having a meta fluoro benzyl moiety at this position (see Table 1). Moreover,
(
9
0
comparing compound 8f (MIC : 8.4 µM) against 10e (MIC : ˃125 µM), compound 8g (MIC :
9
0
90
90
4
6
.1 µM) against 10f (MIC : 15.4 µM), and compound 8e (MIC : 0.24 µM) against 10d (MIC :
90 90 90
2.5 µM), shows that anti-MTB activity decreases multiple fold when the NO - moiety is replaced
2
by an NH - moiety. This suggests that the nitro group promotes anti-TB activity than amino
2
group─more analogues will be exploited to further confirm this.
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Table 1. Structural features, and anti-MTB activity of selected hit compounds compared
against rifampicin.
O
O
X
O
N
R
#a
X
R
MTB
MWb
XlogP3c
R5Vd
PAe
P-gp substrate?f
MIC90
(µM)
8
e
NO2
0.24
386
4.0
none
none
no
Cl
8
8
f
NO2
NO2
8.4
4.1
370
370
3.5
3.5
none
none
none
none
no
no
F
g
F
1
1
0d NH2
0f NH2
62.5
15.4
356
340
-
3.5
3.0
-
none
none
-
none
none
-
no
no
-
Cl
F
Rif
-
-
0.010
a: # = compound number. : Molecular weight (MW) generated using chem draw professional
b
c
d
e
version 12. : XlogP3, calculated lipophilicity. : R5V = Lipinski’s rule of five violation. : PA =
f
c,d,e,f
PAIN Alert. : P-gp = P-glycoprotein.
were predicted using SwissADME website . Rif =
Rifampicin.
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It is paramount to note that antibacterials (antimicrobials) are pivotal to the practice of modern
medicine, wherein they are deployed in surgery, organ(s) transplant, radiotherapy, sterilization,
medical implants, treatment and management of wounds and various types of infections (Yang et al.,
2
018). The years 1940-1960 referred to as the “golden age of antibiotics” saw an increase in the
discovery and development of several antibiotics, although centered around a few compound classes
including fluoroquinolones, β- lactams, aminoglycosides, tetracyclines, and macrolides (Davies,
2
006). With the emergence and spread of several forms of drug resistant bacteria, and pharmaceutical
companies opting out of antibacterial research (Pendleton et al., 2013), the practice of modern
medicine in the near future will face several limitations if new antibacterials are not identified and
developed. To this effect, all target compounds were also evaluated in vitro against five other bacteria
(E. coli, A. baumanni, K. pneumoniae, P. aeruginosa, S. aureus) for antibacterial activities
(Blaskovich et al., 2015). Bacteria were cultured in Cation-adjusted Mueller Hinton broth (CAMHB).
Colistin and vancomycin were used as standards for Gram-negative and Gram-positive bacteria,
respectively. At a single point concentration of 32 µg/ml, none of the compounds tested inhibited
bacterial growth above 50 % and, hence, were considered inactive against these bacteria. This result
suggests that the hit compounds exhibit selective anti-MTB activity probably through modulating a
target that is unique/vital only to MTB. It is important to mention that compounds exhibiting selective
anti-microbial activity are likely to have a large safety margin.
Since hit compounds showed specific antitubercular activity which seems to be depended on the
presence of the 6-nitro moiety, compound 8e was screened against DprE1 mutant to establish possible
mode of action. 8e, however, showed no activity (MIC : >125 µM) against DprE1 mutant,
9
0
suggesting DprE1 as the likely target for this compound class. The binding mode of 8e and its amino
derivative (10d) with the crystal structure of DprE1 enzyme were studied using Glide Ligand Docking
as implemented in Maestro in the Schrödinger package. The enzyme crystal structure (PDB: 4KW5)
was obtained from protein data bank (PDB). Both compound 8e and 10d showed good docking scores
of -6.267 and -5.579, respectively; which indicates binding with the enzyme. The Protein-ligand
interactions of both compounds shows the presence of intramolecular hydrogen bonding which are
essential for locking the ligand in the active site, and therefore a theoretical indication of inhibition. 8e
interacted with the enzyme through pi-pi stacking with TRP230 and hydrogen bonding with ASN385.
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1
0d interacted with the enzyme through pi-pi stacking with LYS418, halogen bonding with SER228
and hydrogen bonding with HIS132 and TYR60. The binding modes of 8e and 10d are presented in
figure 2a and 2b below.
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.
Potential cytotoxicity of these compounds was assessed in vitro against HeLa cells cultured in
Dulbecco’s modified Eagle’s medium (DMEM; Lonza) using a resazurin cell viability assay. Emetine
was included as a positive control. At 20 µM, none of the tested compounds inhibited HeLa cell
viability to below 50 %. This result indicates that the compounds exhibit low cytotoxicity against
human cells at 20 µM.
The drug-like properties of compounds showing anti-MTB activity were predicted online
through the swissADME website. Calculated lipophilicity (ClogP) values for these compounds were ≥
3
, but not more than 5 (see Table 1), and their water solubility profiles were predicted to be very
poor. These compounds were also predicted to have low risk of acting as pan-assay interference
PAIN) compounds ─ this is also evident in their selective anti-MTB activity. They all conform to
(
Lipinski’s rule of five, and are predicted not to act as substrate for P-glycoprotein. The aqueous
solubilities of compounds 8e and 8g were determined experimentally in phosphate buffered saline at
pH 7.4 to be < 5 µM, which is very poor. This result corroborated the solubility profiles predicted by
swissADME website.
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2
. Conclusion
In conclusion, this study has generated novel nitroquinolone and aminoquinolone based
compounds. The compounds were evaluated in vitro against a panel of bacteria, including
Mycobacterium tuberculosis, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella
pneumonia, Staphylococcus aureus, and Escherichia coli and five compounds were shown to exhibit
specific anti-MTB activity. SAR analyses of these hits suggest that a nitro moiety at position 6 of the
quinolone nucleus enhances anti-tubercular activity over an amino group─ more compounds are
needed to further confirm this. Compound 8e, the most active compound in this study, elicits a potent
activity profile (MIC : <0.2µM). This hit compound was inactive against DprE1 mutant, which
9
0
posits DprE1 as the most probable target. Compound 8e also exhibited good docking score of -6.267
against DprE1 enzyme, which further confirms possible interaction with the enzyme. Moreover, this
compound conforms to the Rule of Five and has no predicted PAIN liability structural features. 8e
however suffers from poor aqueous solubility (< 5 µM), an observation which motivates for further
research in this area.
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Acknowledgements
RMB, LJL, FVK thank North-West University for financial support. The authors acknowledge
the South African Medical Research Council (SHIP grant to DFW) for financial support of the anti-
mycobacterial testing work. We appreciate Dr D. Otto, and Dr J. Jordaan of Chemical Resource
Beneficiation unit, Potchefstroom for generation of NMR and HRMS data. Molecular docking data
were generated by Dr T. Tshiwawa, Rhodes University. The antimicrobial screening performed by
CO-ADD (The Community for Antimicrobial Drug Discovery) was funded by the Wellcome Trust
(UK) and The University of Queensland (Australia), while cytotoxicity evaluation was supported by
the SA Medical Research Council.
Conflict of interest.
The authors have no conflict of interest to declare
Data Availability Statement
1
13
Detailed characterization data together with H, C and HRMS spectra for compounds 8a-j, 9
and 9a-h are available in the supplementary file. Samples of compounds can be obtained from
corresponding authors upon request.
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References
Aldred, K.J., Kerns, R.J., Osheroff, N. (2014). Mechanism of quinolone action and resistance.
Biochemistry, 53, 1565–1574.
Artico, M., Mai, A., Sbardella, G., Massa, S., Musiu, C., Lostia, S., Demontis, F., La Colla, P. (1999).
Nitroquinolones with broad-spectrum antimycobacterial activity in vitro. Bioorganic and Medicinal
Chemistry Letters, 9, 1651-1656.
Asif, M. (2013). Antimicrobial and anti-tubercular activity of quinolone analogues. Science
International, 1, 336-349.
Barák, I. and Muchová, K. (2013). The role of lipid domains in bacterial cell processes. International
Journal of Molecular Sciences, 14, 4050-4065.
Beteck, R.M., Seldon, R., Coertzen, D., van der Watt, M.E., Reader, J.,… (2018). Accessible and
distinct decoquinate derivatives active against Mycobacterium tuberculosis and apicomplexan
parasites. Communications Chemistry 1, 62, 1-11.
Beteck, R.M., Seldon, R., Jordaan, A., Warner, D.F., Hoppe, H.C., Laming, D., Khanye, S.D. (2019).
New quinolone-based thiosemicarbazones showing activity against plasmodium falciparum and
mycobacterium tuberculosis. Molecules, 24, 1740.
Blaskovich, M.A., Zuegg, J., Elliott, A.G., Cooper, M.A. (2015). Helping chemists discover new
antibiotics. ACS Infectious Diseases, 1, 285-287.
Brennan, P.J. (2003). Structure, function, and biogenesis of the cell wall of Mycobacterium
Tuberculosis. Tuberculosis, 83, 91–97.
Chikhale, R.V., Barmade, M.A., Murumkar, P.R., Yadav, M.R. (2018). Overview of the development
of Dpre1 inhibitors for combating the menace of tuberculosis. Journal of Medicinal Chemistry, 61,
8
563−8593.
Cole, S.T., Brosch, R., Parkhill, J., Garnier, T., Churcher, C., Harris, D., Gordon, S.V., Eiglmeier,
K.,…(1988). Deciphering the biology of Mycobacterium tuberculosis from the complete genome
sequence. Nature, 393, 537-44.
This article is protected by copyright. All rights reserved

Davies, J. (2006). Where have all the antibiotics gone? Canadian Journal of Infectious Diseases and
Medical Microbiology, 17, 287–290.
Di, L., Kerns, E.H., Carter, G.T. (2009). Drug-like property concepts in pharmaceutical design.
Current Pharmaceutical Design, 15, 2184-2194.
Gideon, H.P. and Flynn, J.L. (2011). Latent tuberculosis: what the host “sees”? Immunologic
Research,
50, 202–212.
https://www.fda.gov/news-events/press-announcements/fda-approves-new-drug-treatment-
resistant-forms-tuberculosis-affects-lungs. Accessed on 04/10/2019.
https://www.fda.gov/news-events/press-announcements/fda-updates-warnings-fluoroquinolone-
antibiotics-risks-mental-health-and-low-blood-sugar-adverse. Accessed on 04/10/2019.
Jansen, R.S. and Rhee, K.Y. (2017). Emerging approaches to tuberculosis drug development: At
home in the metabolome. Trends in Pharmacological Sciences, 38, 393–405.
Kana, B.D., Karakousis, P.C., Parish, T., Dick, T. (2014). Future target-based drug discovery for
tuberculosis? Tuberculosis (Edinb), 94, 551–556.
Leung, E. C., Leung, C.C., Kam, K.M., Yew, W. W., Chang, K.C., Leung, W.M., Tam, C.M. (2013).
Transmission of multidrug-resistant and extensively drug-resistant tuberculosis in a metropolitan city.
The European Respiratory Journal, 41, 901–908.
Makarov, V., Lechartier, B., Zhang, M., Neres, J., van der Sar, A.M.,…(2014). Towards a new
combination therapy for tuberculosis with next generation benzothiazinones. EMBO Molecular
Medicine, 6, 372-383.
Mulani, M.S., Kamble, E.E., Kumkar, S.N., Tawre, M.S., Pardesi, K.R. (2019). Emerging strategies
to combat ESKAPE pathogens in the era of antimicrobial resistance: a review. Frontiers in
Microbiology, 10, 539.
Pendleton, J.N., Gorman, S.P., Gilmore, B.F. (2013). Clinical relevance of the ESKAPE pathogens.
Expert Review of Anti-infective Therapy, 11, 297-308.
This article is protected by copyright. All rights reserved

Pham, T.D.M., Ziora, Z.M.M., Blaskovich, A.T. (2019). Quinolone antibiotics. Medicinal Chemistry
Communication, 10, 1719-1739.
Sbardella, G., Mai, A., Artico, M., Setzu, M.G., Poni, G., La Colla, P. (2004). New 6-nitroquinolones:
synthesis and antimicrobial activities. IL FARMACO, 59, 463–471.
Senthilkumar, P., Dinakaran, M., Yogeeswari, P., Sriram, D., China, A., Nagaraja, V. (2009).
Synthesis and antimycobacterial activities of novel 6-nitroquinolone-3-carboxylic acids. European
Journal of Medicinal Chemistry, 44, 345-358.
Trefzer, C., Rengifo-Gonzalez, M., Hinner, M.J., Schneider, P., Makarov, V., Cole, S.T., Johnsson, K.
(
2010). Benzothiazinones: prodrugs that covalently modify the decaprenylphosphoryl-β – d-ribose 2′-
epimerase DprE1 of Mycobacterium tuberculosis. Journal of America Chemical Society, 132, 13663–
3665.
1
Warsinske, H.C., DiFazio, R.M., Linderman, J.J., Flynn, J.L., Kirschner, D.E. (2017). Identifying
mechanisms driving formation of granuloma-associated fibrosis during Mycobacterium tuberculosis
infection. Journal of Theoretical Biology, 429, 1–17.
WHO. Global tuberculosis report 2018. 2018, PP1-2.
Yang, X., Xiao, X., Wang, L., Ao, Y., Song, Y., Wang, H., Wang, H. (2018). Application of
antimicrobial
drugs in perioperative surgical incision. Annals of Clinical Microbiology and
Antimicrobials, 17, 2.
Zhang, G., Howe, M., Aldrich, C.C. (2019). Spirocyclic and bicyclic 8-nitrobenzothiazinone for
tuberculosis with improved physicochemical and pharmacokinetic properties. ACS Medicinal
Chemistry Letters, 10, 348-351.
This article is protected by copyright. All rights reserved

cbdd_13747_f1.pdf
Figure 1. Structures of nitro benzenoids with anti-tubercular activity, and fluoroquinolone
(4).
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cbdd_13747_f2a.pdf
Figure 2a. Binding orientation of 8e with DprE1 enzyme.
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cbdd_13747_f2b.pdf
Figure 2b. Binding orientation of 10d with DprE1 enzyme
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