Design and synthesis of some new quinoline-3-carbohydrazone derivatives as potential antimycobacterial agents

Article abstract of DOI:10.1016/j.bmcl.2009.12.045

A series of 26 new quinoline derivatives carrying active pharmacophores has been synthesized and evaluated for their in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv (MTB), Mycobacterium smegmatis (MC²), and Mycobacterium fortuitum following the broth micro dilution assay method. Compounds 13e, 13i, 13k, 14a, 14c, 14i, and 14k exhibited significant minimum inhibition concentrations, when compared with first line drugs isoniazid (INH) and rifampicin (RIF) and could be ideally suited for further modifications to obtain more efficacious compounds in the fight against multi-drug resistant tuberculosis.

Full text of DOI:10.1016/j.bmcl.2009.12.045

Bioorganic & Medicinal Chemistry Letters 20 (2010) 1040–1044
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design and synthesis of some new quinoline-3-carbohydrazone derivatives
as potential antimycobacterial agents
c
c
Sumesh Eswaran a, Airody Vasudeva Adhikari b, , Nishith K. Pal , Imran H. Chowdhury
*
a Anthem Biosciences Pvt. Ltd, 49 Bommasandra Industrial Area, Bommasandra, Bangalore 560 099, Karnataka, India
b Department of Chemistry, National Institute of Technology Karnataka, Surathkal, Srinivasnagar, Mangalore 575 025, Karnataka, India
c Department of Bacteriology and Serology, Calcutta School of Tropical Medicine, Kolkata 700 073, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 July 2009
Revised 16 November 2009
Accepted 10 December 2009
Available online 14 December 2009
A series of 26 new quinoline derivatives carrying active pharmacophores has been synthesized and eval-
uated for their in vitro antituberculosis activity against Mycobacterium tuberculosis H37Rv (MTB), Myco-
bacterium smegmatis (MC2), and Mycobacterium fortuitum following the broth micro dilution assay
method. Compounds 13e, 13i, 13k, 14a, 14c, 14i, and 14k exhibited significant minimum inhibition con-
centrations, when compared with first line drugs isoniazid (INH) and rifampicin (RIF) and could be ide-
ally suited for further modifications to obtain more efficacious compounds in the fight against multi-drug
resistant tuberculosis.
Keywords:
Quinoline-3-carbohydrazone
TMC 207
Ó 2009 Elsevier Ltd. All rights reserved.
Antituberculosis activity
(3R)-3-Amino-N,N-dimethyl-4-
(phenylthio)butanamide
Tuberculosis (TB) is a worldwide pandemic caused by different
species of mycobacteria. The latest statistics reveals that around
two million people throughout the world die annually from tuber-
culosis and there are around 8 million new cases each year, out of
which developing countries show major share.1 Among HIV-in-
fected people with weakened immune system, TB is a leading killer
epidemic. Every year about 2 million people living with HIV/AIDS
die from TB.2 Furthermore, in recent times the appearance of mul-
tidrug-resistant TB (MDR–TB), a form of TB that does not respond
to the standard treatments, is more common. It is a shocking rev-
elation that MDR–TB is present in almost all countries as per the
recent survey, made by the World Health Organization (WHO)
and its partners. A recent estimation by WHO has revealed that
within next 20 years approximately 30 million people will be in-
fected with the bacillus.3 Keeping in view of the above statistics,
WHO declared TB as a global health emergency and aimed at sav-
ing 14 million lives between 2006 and 2015.4 All the above facts
reveal that there is an urgent need for development of new drugs
with divergent and unique structure and with a mechanism of ac-
tion possibly different from that of existing drugs.
biological activities. Amongst the various activities of their deriva-
tives, antimicrobial activity is noteworthy. Quinoline-based com-
pounds are known to exhibit excellent anti-TB properties.5–9 It is
O
N
O
HN
H
F
HO
Cl-
H
OH
H
N+
N
O
N
CF3
CF3
Moxifloxacin
Mefloquine
N
N
O
S
HO
NH
O
Br
N
R1
N
R
H
N
O
N
Quinoline moiety is of great importance to chemists as well as
biologists as it is found in a large variety of naturally occurring
compounds and also chemically useful molecules having diverse
A
TMC 207 (DARQ)
R = 8-CF3, 6-F
R1= Aromatic and aliphatic group
* Corresponding author. Tel.: +91 0824 2474000x3203; fax: +91 0824 2474033.
E-mail addresses: avadhikari123@yahoo.co.in, avchem@nitk.ac.in (A.V. Adhi-
kari).
Figure 1. New class of molecules focused on anti-TB therapy and target com-
pounds A.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.12.045

S. Eswaran et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1040–1044
1041
as a part of our general program in the continued research for new
antibacterials20 and antimycobacterial agents, we have designed
some new quinoline derivatives carrying active carbohydrazone
moiety and (3R)-3-amino-N,N-dimethyl-4-(phenylthio) butana-
mide group at positions 3 and 4 of core quinoline, respectively,
with the hope that newly designed molecules would exhibit en-
hanced activity. Here, the introduction of –N(CH3)2 group imparts
hydrophilic end, carbohydrazone provides hydrogen bonding do-
main and phenyl moiety gives a hydrophobic part to the active
base moiety quinoline carrying chiral centre (R) attached it. Fur-
ther, indirect type of molecular modeling study of newly designed
quinoline derivatives reveals that there exists 3D structural simi-
larity with that of TMC207, as given in Figure 2.
Thus, in this paper we herein report the synthesis of hitherto
unknown 26 (E)-4-((R)-1-(dimethylcarbamoyl)-3-(phenylthio)pro-
pan-2-ylamino)-N0-(2-fluoro-4-methoxybenzylidene)-6- or 8-(un)
substituted quinoline-3-carbohydrazides (13a–m and 14a–m)
starting from substituted anilines through multistep reactions.
The retrosynthetic approach as shown in Figure 3 has been fol-
lowed for the synthetic design of target compounds. Also, we
report their in vitro activity against Mycobacterium tuberculosis
H37Rv (MTB), Mycobacterium smegmatis (MC2), and Mycobacterium
fortuitum. It has been expected that the target molecules carrying
quinoline would inhibit mycobacterium membrane-bound ATP
synthase and hence follow the same mechanism, as shown by
TMC207.
Figure 2. 3D overlay of compound 14i with TMC206 showing the superimposition
of common pharmacophore.
interesting to note that quinoline is a core pharmacophore in the
recently developed anti tuberculosis drugs, viz. TMC207, a diaryl-
quinoline (DARQ),10 mefloquine,11 and moxifloxacin12 (Fig. 1).
The well-known TMC207, during its mechanism of action interacts
with the enzyme adenosine triphosphate (ATP) synthase by block-
ing the main energy source for bacterium.13
The total synthesis of the key reactant, that is, (3R)-3-amino-
N,N-dimethyl-4-(phenylthio)butanamide (6) was carried out in
six steps according to the literature procedure21 starting with opti-
cally pure
D(ꢀ)-aspartic acid, as shown in Scheme 1. The interme-
Further it has been well established that substituted butana-
mides is an important pharmacophore and are very good antibac-
terial agents.14 However, there is no literature report available on
antibacterial activity of (3R)-3-amino-N,N-dimethyl-4-(phenyl-
thio) butanamide, which is structurally similar to reported butana-
mide derivatives. Since it is an analog of an amino acid, it was
expected to show some biological activity. This moiety is predicted
to cause a reduction in clogP value and there by increasing lipo-
philicity of the molecule. Also substituted carbohydrazone moiety
has been reported to be a well known pharmacophoric group15–19
for antituberculosis activity. On the basis of these observations and
diate benzyl [(3R)-5-oxotetrahydrofuran-3-yl]carbamate (4) was
converted to compound 5 via two steps under microwave condi-
tion, wherein the reaction was completed in 20–25 min at a con-
stant power of 210 W with improved yields, whereas in the
reported procedure the reaction was completed in 18–24 h with
less yield. This is a significant achievement in the synthesis of
the compound 6.
The reaction sequences employed for synthesis of title com-
pounds are shown in Scheme 2. The starting materials 7a and b
were conveniently converted to diethyl phenyl amino methylidene
propanedioate derivatives 8a and b, by condensing them with
N
N
N
O
O
O
S
S
S
NH
O
NH
N
NH
O
N
R1
COOEt
NH2
N
N
R
H
R
R
H
N
N
Cl
N
O
NH2
COOEt
S
N
R
Key reactants
Figure 3. Design and retrosynthetic analysis of quinoline derivatives.

1042
S. Eswaran et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1040–1044
O
O
HN
O
O
OH NH2
OH HN
O
a
b
OH
OH
O
O
O
O
1
O
2
O
3
O
N
O
O
HN
O
O
O
NH2
O
NH
d,e
f
c
S
N
S
O
6
4
5
Scheme 1. Synthesis of enantiomerically pure (3R)-3-amino-N,N-dimethyl-4-(phenylthio) butanamide (6). Reagents and conditions: (a)
D
(ꢀ)-Aspartic acid, NaHCO3, Cbz-
ClꢁH2O/THF, 0 °C to rt, 8 h; (b) EtOAc, SOCl2, rt, 12 h; (c) NaBH4, THF, 0 °C to rt, 4 h; (d) N(CH3)2, THF, MW, 100 °C, 20 min; (e) Ph2S2, (Bu)3P, toluene, MW, 105 °C, 25 min; (f)
30% HBr in acetic acid, rt, 4 h.
OH
Cl
R
COOEt
a
b
COOEt
COOEt
COOEt
8 a-b
c
R
N
R
R
N
H
NH2
7 a-b
N
N
9 a-b
10 a-b
N
N
O
O
O
d
f
e
S
S
S
NH
O
NH
N
O
NH
N
N
R1
NH2
COOEt
N
N
R
R
H
R
H
N
11 a-b
13a-m , 14a-m
12 a-b
R = 8-CF3, 6-F
R1= Aromatic and aliphatic group
Scheme 2. Synthetic protocol of title compounds 13a–m, 14a–m. Reagents and conditions: (a) substituted-aniline, (COOEt)2C@CH–OEt, 110 °C, 4 h; (b) diphenylether,
260 °C, 4 h; (c) POCl3, 80 °C, 3 h; (d) (3R)-3-amino-N,N-dimethyl-4-(phenylthio) butanamide, K2CO3, CH3CN, 80 °C, 1 h; (e) NH2NH2, 80 °C, 2 h; (f) substituted aldehyde, EtOH,
AcOH, rt, 10 min.
diethyl ethoxymethylene malonate. The diesters 8a and b, on heat-
ing at 260 °C in Dowtherm medium, were readily cyclized to ethyl
4-hydroxy-substituted quinoline-3-carboxylate (9a and b), which
on refluxing with phosphorus oxychloride yielded the correspond-
ing 4-chloro quinoline derivatives 10a and b in very good yield.
The conversion of chloro derivatives 10a and b to the respective
amines 11a and b was carried out by treating them with (3R)-3-
amino-N,N-dimethyl-4-(phenylthio) butanamide at 80 °C in pres-
ence of potassium carbonate in acetonitrile. These amines, on con-
densation with hydrazine hydrate in alcoholic medium gave the
key intermediates quinoline-3-carbohydrazide derivatives 12a
and b in good yield. Finally, the target compounds, viz. (E)-4-
((R)-1-(dimethylcarbamoyl)-3-(phenylthio)propan-2-ylamino)-N0-
(benzylidene)-substituted quinoline-3-carbohydrazide (13a–m,
14a–m) were synthesized from their precursors 12a and b by con-
densing them with different bio-active aldehydes in ethanol/acetic
acid medium.
tubercular mycobacterial (NTM) species like M. smegmatis (MC2)
ATCC 19420, and M. fortuitum ATCC 19542 by Resazurin Assay
method22,23 and their MIC values were determined. The standard
drugs, viz. isoniazid (INH) and rifampicin (RIF) were used for com-
parison. The screening results of the title compounds and the stan-
dard drugs are reported in Table 1.
The compounds 13e, 13i, 13k, 14a, 14c, 14i, and 14k exhibited
moderate to good activity at 1 and 10 lg/mL, against all tested
Mycobacterium strains. The SAR study revealed that the presence
of –CF3 group at position-8 enhanced the activity while the intro-
duction of –F at position-6 partially lowered the activity. Amongst
the tested title compounds, –F and –OCH3 substituents (13a, 13c,
13d, 13f, 13g, 13i, 14a, 14c, 14d, 14g, and 14i) brought about in-
creased activity whereas presence of thiophene and –OH groups
(13h, 13f, 13l, 13m, 14f, 14h, 14l, and 14m) caused decrease in
activity when compared to standards. It is interesting to note that
eight compounds, viz. 13a, 13e, 13i, 13k, 14a, 14c, 14i, and 14k
were found to be more potent than INH (MIC: 50) against M.
smegmatis, while 13 compounds, viz. 13c, 13d, 13e, 13g, 13i, 13k,
The compounds were screened for their in vitro antimycobacte-
rial activity against M. tuberculosis H37Rv ATCC 27294, and non-

S. Eswaran et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1040–1044
1043
Table 1
Physical constants, preliminary results of antimycobacterial activities and cytotoxicity of the title compounds 13a–m, 14a–m
S
O
N
NH
N
O
1
N
R
N
H
R
R1
Mp range (°C)
Yielda (%)
MIC (
lg/mL)
% Inhibition
IC50 (lg/mL)
e
Compd
R
MTBb
MSc
MFd
13a
13b
13c
13d
13e
13f
13g
13h
13i
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
8-CF3
6-F
6-F
6-F
6-F
6-F
6-F
6-F
6-F
6-F
2-Fluoro phenyl
4-Methoxy phenyl
4-Fluoro phenyl
4-Trifluoro methoxy phenyl
3-Pyridyl
5-Bromo thiophene
3-Hydroxy-4-methoxy phenyl
5-Fluoro-2-hydroxy phenyl
3-(1,1,2,2-Tetrafluoro ethoxy) phenyl
2-fluoro-4-methoxy phenyl
Octyl
2-(Methylthio) phenyl
3-(Methylthio) propyl
2-Fluoro phenyl
4-Methoxy phenyl
4-Fluoro phenyl
4-Trifluoro methoxy phenyl
3-Pyridyl
5-Bromo thiophene
3-Hydroxy-4-methoxy phenyl
5-Fluoro-2-hydroxy phenyl
3-(1,1,2,2-Tetrafluoro ethoxy) phenyl
2-Fluoro-4-methoxy phenyl
Octyl
2-(Methylthio) phenyl
3-(Methylthio) propyl
Isoniazid (INH)
98–100
160–161
152
121–123
141–143
173–175
191
139–141
130–132
183–185
—
136–138
—
144–146
130–132
124–127
130–133
151–153
171–172
196–198
146–148
143–144
179–180
81–82
82
86
91
80
73
84
83
86
82
86
81
84
80
88
90
92
80
86
90
78
82
92
90
88
82
76
10
>100f
10
10
1
10
10
10
1
10
>100f
>100f
10
90
0
>62.5
ND
>100f
>100f
>100f
10
90
90
>95
90
90
0
>95
90
>95
0
90
>95
0
95
90
90
0
90
0
>95
0
>95
0
0
>62.5
>62.5
>62.5
>62.5
>62.5
ND
>62.5
ND
>62.5
ND
ND
>62.5
ND
>62.5
>62.5
>62.5
ND
>62.5
ND
10
1
>100f
>100f
>100f
10
>100f
10
>100f
10
13j
13k
13l
10
1
>100f
10
>100f
10
>100f
10
1
>100f
>100f
10
>100f
>100f
10
13m
14a
14b
14c
14d
14e
14f
14g
14h
14i
10
1
>100f
10
>100f
10
10
10
>100f
10
10
1
>100f
>100f
>100f
>100f
>100f
10
10
10
>100f
10
>100f
1
>62.5
ND
>62.5
ND
ND
>62.5
>62.5
14j
14k
14l
6-F
6-F
6-F
6-F
10
1
>100f
10
>100f
10
140–141
—
>100f
>100f
1
>100f
>100f
50
>100f
>100f
12.5
1.5
14m
>95
>95
Rifampicin (RIF)
0.5
1.5
—: Thick liquid.
ND: not determined.
a
After column purification.
b
c
d
e
f
Mycobacterium tuberculosis H37Rv.
Mycobacterium smegmatis (ATCC 19420).
Mycobacterium fortuitum (ATCC 19542).
Cytotoxicity in mammalian Vero cell lines.
MIC > 100 lg/mL indicates that the strain is resistant to tested substance.
14a, 14c, 14d, 14e, 14g, 14i, and 14k were found to be more potent
than INH (MIC:12.5) against M. fortuitum. In 13k, the enhanced
activity may be due to the presence of hydrophobic linear octyl
ond level anti tuberculosis screening of the title compound have
been incorporate in Table 2.
The structures of all the newly synthesized compounds were
confirmed by 1H & 13C NMR, LC–MS (ESI) studies, and elemental
analysis. The detailed experimental procedures and spectral data
for all the synthesized compounds are given in Supplementary
data. The chiral purity of the title compounds were >97% (ee)
which was determined using Agilent 1100 HPLC system (column-
group which may mimic the micolate
a-chain or mycolic acid b-
branch of protein, during its mode of action. Moreover, the linear
octyl group exerts electron releasing property in 13k. In conclu-
sion, compounds 13e and 14i showed exceptionally good activity
against both M. fortuitum and M. tuberculosis H37Rv and were more
potent than INH and they also showed better activity than RIF.
Some of the compounds listed in Table 1 were further examined
chiralcel AD-H 4.6 ꢂ 250 mm, 5
lm, flow; 1.0 mL/min, wave-
length: 230 nm, mobile phase: n-hexane: IPA (80:20)).
for toxicity (IC50) in a mammalian Vero cell line till 62.5
l
g/mL
In conclusion, the present study described the design, synthesis,
and evaluation of antitubercular activities of new quinoline deriva-
tives against sensitive strains of M. tuberculosis namely M. tubercu-
losis H37Rv (MTB), M. smegmatis (MC2), and M. fortuitum. All
tested compounds were found to be nontoxic and some of the com-
pounds displayed significant and promising anti-tuberculosis activ-
ity. The results of biological activity clearly indicate that the
presence of substituted hydrazones and potent (3R)-3-amino-N,N-
dimethyl-4-(phenylthio)butanamide (6) respectively at positions-
3 and -4 of quinoline skeleton has tremendously enhanced the
concentrations. After 72 h of exposure, viability was assessed on
the basis of cellular conversion of (3-(4,5-dimethylthiazol-2-yl)-
2,5-diphenyltetrazolium bromide (MTT) into a formazan product
using the Promega Cell Titer 96Ò non-radioactive cell proliferation
assay.24 None of them were found to be toxic. Hence the activities
of the newly synthesized compounds are not due to cytotoxicity of
compounds. The physical constants, results of antimycobacterial
activities and cytotoxicity of the newly synthesized title com-
pounds 13a–m, 14a–m are summarized in Table 1. While the sec-

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S. Eswaran et al. / Bioorg. Med. Chem. Lett. 20 (2010) 1040–1044
Table 2
References and notes
Second level antituberculosis screening of the title compounds
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MTB
MS
MF
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13a
13b
13c
13d
13e
13f
13g
13h
13i
2.5
—
5
5
—
—
10
5
1.25
—
10
—
2.5
—
5
—
—
5
—
5
5
10
—
5
—
1.25
—
—
—
—
2.5
—
—
—
5
—
10
—
—
10
—
10
—
—
—
—
—
2.5
—
10
—
—
5
0.625
10
5
10
1.25
10
1.25
—
10
1.25
10
1.25
2.5
5
13j
13k
13l
13m
14a
14b
14c
14d
14e
14f
14g
14h
14i
13. Karl, D.; Xilin, Z.; Barry, K. Lancet Infect. Dis. 2008, 8, 273–275.
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—
5
10
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1.25
—
ˇ
ˇ
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5
—
—
14m
—
— indicates that MIC > 10
l
g/mL.
pharmacological property. Thus, the compounds 13e and 14i are
ideally suited for further modifications to obtain more efficacious
and potent antituberculosis drugs. The evaluation of in vivo anti-
tuberculosis activity of most promising analogues is currently
underway in our laboratory and results will be reported in due
course of time.
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23. M. tuberculosis strains were grown in Middlebrook 7H9 broth (Difco BBL,
Sparks, MD, USA) supplemented with 10% OADC Becton Dickinson, Sparks, MD,
USA). The culture was diluted to McFarland 2 standard with the same medium.
From this, 50 lL of this culture was added to 150 lL of fresh medium in 96 well
microtitre plates. Stock solutions (2 mg/mL) of the test compounds were
prepared in dimethyl formamide (DMF). The compounds were tested at 1, 10
Acknowledgment
and 100
lg/mL concentrations. Further the second level testing was carried out
at concentrations 0.3125, 0.625, 1.25, 2.5, and 5
lg/mL. Control tubes had the
same volumes of DMF without any substrate. Rifampicin (RIF) and isoniazid
(INH) was used as the reference compounds. After incubation at 37 °C for
7 days, 20 lL of 0.01% Resazurin (Sigma, St. Louis. MO, USA) in water was
added to each tube. Resazurin, a redox dye, is blue in the oxidized state and
turns pink when reduced by the growth of viable cells. The control tubes
showed a colour change from blue to pink after 1 h at 37 °C. Compounds which
prevented the change of colour of the dye were considered to be inhibitory to
M. tuberculosis.
Authors are thankful to Dr. Ganesh Sambhasivam, CEO, Anthem
biosciences, Bangalore, India, for his invaluable support and alloca-
tion of resources for this work. They are also grateful to the Head,
Chemistry Department, NITK for providing necessary laboratory
facilities for the research work and valuable support.
24. Gundersen, L. L.; Nissen-Meyer, J.; Spilsberg, B. J. Med. Chem. 2002, 45, 1383.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.12.045.