New 1,3-oxazolo[4,5-c]quinoline derivatives: Synthesis and evaluation of antibacterial and antituberculosis properties

Article abstract of DOI:10.1016/j.ejmech.2009.11.036

A new class of fused oxazoloquinoline derivatives was synthesized starting from 2-bromo-1-phenylethanones 1a-b through multi-step reactions. The newly synthesized compounds were evaluated for their in vitro antibacterial against Escherichia coli (ATTC-259

Full text of DOI:10.1016/j.ejmech.2009.11.036

European Journal of Medicinal Chemistry 45 (2010) 957–966
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
New 1,3-oxazolo[4,5-c]quinoline derivatives: Synthesis and evaluation
of antibacterial and antituberculosis properties
,
c
Sumesh Eswaran a, Airody Vasudeva Adhikari b , R. Ajay Kumar
*
a Anthem Biosciences Pvt. Ltd., 49 Bommasandra Industrial Area, Bommasandra, Bangalore 560099, Karnataka, India
b Department of Chemistry, National Institute of Technology Karnataka, Surathkal, Srinivasnagar, Mangalore 575025, Karnataka, India
c Department of Molecular Microbiology, Rajiv Gandhi Centre for Biotechnology Trivandrum 695014, Kerala, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new class of fused oxazoloquinoline derivatives was synthesized starting from 2-bromo-1-phenyl-
ethanones 1a-b through multi-step reactions. The newly synthesized compounds were evaluated for
their in vitro antibacterial against Escherichia coli (ATTC-25922), Staphylococcus aureus (ATTC-25923),
Pseudomonas aeruginosa (ATCC-27853) and Klebsiella pneumoniae (recultured) and antituberculosis
activity against Mycobacterium tuberculosis H37Rv (ATCC 27294). Preliminary results indicated that most
of the compounds demonstrated very good antibacterial and antituberculosis activities which are
comparable with the first line drugs. Compounds 6a, 6c, 6g, 6j, 6k and 6n emerged as the lead antitu-
Received 15 September 2009
Received in revised form
15 November 2009
Accepted 20 November 2009
Available online 26 November 2009
Keywords:
bercular agents with MIC, 1
6c, 6g, 6j, 6k and 6n were found to be more potent than INH (MIC: 1.5
m
g/mL and 99% bacterial inhibition while eight compounds, viz., 5a, 15k, 6a,
g/mL) with MIC 1 g/mL.
1,3-oxazolo[4,5-c]quinoline
Antibacterial activity
Antituberculosis activity
X-ray crystallography
m
m
Ó 2009 Elsevier Masson SAS. All rights reserved.
1. Introduction
Quinoline moiety is of great importance to chemists as well as
biologists as it is one of the key building elements for many natu-
rally occurring compounds. Among the numerous heterocyclic
moieties of biological and pharmacological interest, the quinoline
ring is endowed with various activities, such as antituberculosis [5],
anti-malarial [6], anti-inflammatory [7], anticancer [8], antibiotic
[9], antihypertensive [10], tyrokinase PDGF-RTK inhibiting agents
[11], and anti HIV [12,13]. In addition to the medicinal importance,
multi-substituted quinolines are valuable synthons used for the
preparation of nano- and mesostructures with enhanced electronic
and photonic properties [14–16].
It has been well-established that presence of aryl ring at 2nd
position of quinoline moiety gives a very good antibacterial prop-
erty to the target molecule and plays a significant role in devel-
opment of new antibacterials [17,18]. These derivatives were found
to be useful biological synthons and at present they are attracting
much attention in the development of new drugs [19–21]. In
addition, they are ideally suited for further modifications to obtain
more efficacious antibacterial and antituberculosis agents.
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 tubercu-
losis and there are around eight millions new cases each year, out of
which developing countries show major share [1]. Among HIV-
infected people with weakened immune system, TB is a leading
killer epidemic. Every year about two millions people living with
HIV/AIDS die from TB [2]. Furthermore, in recent times the
appearance of multidrug-resistant TB (MDR-TB), a form of TB that
does not respond to the standard treatments using first-line drugs
is a serious threat to TB control and treatment. It’s a shocking
revelation 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 infected with
the bacillus [3]. Keeping in view of the above statistics, WHO
declared TB as a global health emergency and aimed at saving 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 action
possibly different from that of existing drugs.
On the other hand, it has been well established that oxazole
derivatives possess a wide spectrum of chemotherapeutic activities
including antituberculosis [22], antibacterial [23], anti-inflammatory
(PDE4 inhibitor) [24], anticancer [25], antidepressant [26], and
anticonvulsant properties [27]. On the basis of these observations
and as a part of our general program in the continued research for
new antibacterials [28] and antitubercular agents, we have designed
* Corresponding author, Tel.: þ91 0 824 2474000x3203; fax: þ91 0 824 2474033.
E-mail addresses: avchem@nitk.ac.in, avadhikari123@yahoo.co.in (A.V. Adhikari).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.11.036

958
S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
some new fused oxazoloquinoline derivatives, wherein active 1,3-
oxazole is fused at its 4,5-positions to c-position of quinoline ring,
hoping that the newly designed molecules would exhibit enhanced
biological activity. Though several reports are there to support the
medicinal activity for condensed quinolines with various five and six
membered heterocycles [29–33], but there are very few reports on
the synthesis and evaluation of biological properties of fused
oxazoloquinolines. In the present work, all the new structures have
been designed on the basis of combinatorial synthesis, which is the
current trend being practiced in most of the drug discoveries. In this
communication, we report the synthesis of hitherto unknown title
compounds 5a-n and 6a-n, starting from 2-bromo-1-phenyl-
ethanones 1a-b and evaluation of their in vitro antibacterial activity
against Escherichia coli (ATTC-25922), Staphylococcus aureus (ATTC-
25923), Pseudomonas aeruginosa (ATCC-27853) and Klebsiella
pneumoniae and antitubercular activity against M. tuberculosis
H37Rv (ATCC 27294).
The formation of 2-aminoacetophenones, 2a-b from 2-bromo-
1-phenylethanones,1a-b was evidenced by its IR, 1H NMR and mass
spectra. Its IR spectrum showed strong bands at 3422 and
1678 cmꢁ1 indicating the presence of –NH2 and pC]O groups
respectively, while its 1H NMR spectrum showed one broad doublet
at
d
4.62 due to benzylic –CH2– protons and the presence of a broad
8.48 (which disappeared on D2O exchange) clearly
singlet at
d
confirmed the replacement of –Br by –NH2 group. In fact, the total
proton count for compounds 2a-b perfectly matched with their
proposed structures. The LCMS spectrum of 2a showed a molecular
ion peak at m/z 154(100%), which matches with its molecular
formula C8H8FNO.
The formation of anthranilamide, 3a-b from 2-amino-
acetophenones, 2a-b was confirmed by its FTIR and 1H NMR spectra.
The FTIR spectrum of 3a showed strong bands at 3426 and
3332 cmꢁ1 indicating the presence of amino and amidic –NH
groups; also the appearance of absorption bands at 1686 and
1652 cmꢁ1 of ketonic and amidic pC]O group, respectively, clearly
indicated the formation of 3a. In its 1H NMR spectrum the appear-
2. Results and discussion
ance of a broad singlet at
introduced –NH2 group and also the presence of four aromatic peaks
as multiplet at 7.12, 7.38 and 8.11 corresponding to four protons
d 6.44 confirmed the presence of newly
2.1. Chemistry
d
from the newly introduced phenyl ring confirmed the structure 3a.
The cyclization of anthranilamide 3a-b to the corresponding
3-amino-2-(3/4-fluorophenyl)quinolin-4-ol (4a-b) was evidenced
by its 1H NMR spectrum; the disappearance of one broad doublet of
The reaction sequences employed for synthesis of title
compounds are shown in Scheme 1. The starting materials viz.,
2-bromo-1-phenylethanones 1a-b were conveniently converted to
2a-b, by reacting them with sodium azide in dimethyl formamide
(DMF) at 0 ꢀC and subsequent reduction of the intermediates to the
corresponding amines using palladium in charcoal under hydrogen
atmosphere. The aminoacetophenones 2a-b, on heating at 80 ꢀC
with isatoic anhydride in basic medium gave 2-amino-N-[2-(3 or 4
fluorophenyl)-2-oxoethyl]benzamides 3a-b in good yield. The
compounds 3a-b were readily cyclized to 2-aryl aminoquinolines,
4a-b via, diazepinone intermediate in the presence polyphosphoric
acid (PPA) at 150 ꢀC. Further, the key intermediates, i.e., the urea
derivatives, 5a-n were obtained in excellent yield by refluxing the
corresponding 2-aryl aminoquinolines, 4a-b with different isocya-
nates in toluene. Finally, the target compounds, viz. 4-(3 and 4
fluorophenyl)-N-(substituted phenyl)[1,3]oxazolo[4,5-c]quinolin-
2-amines (6a-n) were synthesized in good yield from their precur-
sors 5a-n by refluxing them with POCl3 at 100 ꢀC. The structures of
all the newly synthesized compounds were confirmed by FTIR, 1H
and 13C NMR and LC mass spectral studies and elemental analysis.
benzylic (–CH2) protons from
from 6.44 clearly showed the smooth cyclization, also the
appearance of a broad singlet at 11.44 of –OH proton (which
d 4.67 and one broad singlet of –NH2
d
d
disappeared on D2O exchange) indicated the aromatization of
quinoline ring. Further, the total proton count for compounds 4a-b
perfectly matched with their structures, which further established
the cyclization. In its FTIR spectrum, compound 4a exhibited
a broad band at 3519 cmꢁ1 due to OH stretching. The LCMS of it
showed a molecular ion peak at m/z 255.2 (M þ 1), which matches
with its molecular formula C15H11FN2O.
The structures of compounds 5a-n were elucidated by their
FTIR, NMR and LCMS analyses. The FTIR spectrum of 5a revealed the
presence of both –OH and –NH groups due to the appearance of
absorbance bands at 3508 and 3324 cmꢁ1 respectively, while that
of pC]O was observed at 1653 cmꢁ1. The 1H NMR spectrum of 5a
showed one singlet at
d
3.82 for three protons which correspond to
1
R
2
1
1
R
R
R
2
O
2
R
R
(a)
(b)
NH
Br
O
NH2
NH2
O
O
3a-b
1a-b
2a-b
H
HN
N
R
OH
O
N
O
O
N
R
H
NH2
(c)
NH
(d)
1
2
(e)
R
R
1
2
1
2
R
R
N
R
R
N
4a-b
5a-n
6a-n
R = alkyl/aralkyl/ aryl;
1
2
R /R = fluoro.
Scheme 1. Synthesis of substituted 1,3-oxazolo [4, 5-c]quinolin-2-amine. (a) i. NaN3, DMF, 0 ꢀC-RT, 8 h ii. Pd/C, MeOH, RT, 12 h, Yield: 58% (b) isatoic anhydride, Na2CO3, 80 ꢀC,
15 min, pH z 7 (c) PPA, 150 ꢀC, 1.5 h. (d) Substituted isocyanate, toluene, 110 ꢀC, 30 min (e) POCl3, 80 ꢀC, 2 h.

S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
959
newly introduced –OCH3, also the appearance of a sharp singlet at
8.07 that corresponds to –NH proton. Further, the LCMS showed
its molecular ion peak at 404.2 (98%), which is in accordance with
its molecular formula C23H18FN3O3.
The investigation of antibacterial screening data revealed that
all the tested compounds 5a-n and 6a-n showed moderate to very
good inhibitory activity. The compounds 5a, 5c-e, 5g, 5j, 5k, 5n, 6a-
d, 6g, 6j-l and 6n showed comparatively very good activity against
d
The formation of the title compounds, 6a-n from the corre-
sponding urea derivatives, 5a-n was evidenced by IR, 1H & 13C NMR
and mass spectral data. The IR spectrum of 6a showed a broad band
at 3345 cmꢁ1 due to –NH stretching, also the disappearance of –OH
stretching band from 3508 cmꢁ1 indicated the smooth cyclization
leading to condensed oxazole ring. Its 1H NMR spectrum indicated
all the bacterial strains with MIC 6.25 mg/mL. The good activity is
attributed to the presence of pharmacologically active moieties like
4-tolyl, 4-fluoro phenyl, 3-cyano phenyl and 2-methoxy phenyl
attached to –NH group of the title compounds.
2.2.2. Antituberculosis studies
the presence of one singlet at
disappearance of a broad singlet from
confirmed the cyclization. Further, the 13C NMR of 6a showed
signals at : 56.31, 112.2, 114.5, 116.2, 116.5, 117.8, 118.14, 119.9, 121.0,
d
10.41 of –NH proton and the
The encouraging results from the antibacterial studies impelled
us to go for the preliminary screening of the title compounds for
their in vitro antituberculosis activity. The compounds were eval-
uated against Mycobacterium tuberculosis H37Rv using broth micro
dilution method as per Martin et al with slight modification, with
Resazurin as indicator [36,37] and the observed MICs are presented
in Table 5. Isoniazid (INH) and Rifampicin (RIF) were used as
standard drugs.
The antituberculosis screening data revealed that all the tested
compounds 5a-n and 6a-n showed moderate to very good inhibi-
tory activity. The compounds 5a, 5k, 6a, 6c, 6g, 6j, 6k and 6n
showed very good antituberculosis activity. The good activity is
attributed to the presence of substituted aryl group at position-2 of
quinoline ring. Occurrence of pharmacologically active moieties
like 2-methoxy phenyl, 3-chloro phenyl and 4-fluoro phenyl at –NH
group of the title compounds enhances the activity. The structure–
activity relationship (SAR) study reveals that with the introduction
of 1,3-oxazole ring has tremendously increased the activity of the
title molecules. It has been observed that the urea derivatives 5c,
5g, 5j and 5n which were inactive against MTB, on cyclization to
1,3-oxazoloquinolines i.e., 6c, 6g, 6j and 6n showed enhanced
activity. It is interesting to note that eight compounds, viz., 5a, 15k,
6a, 6c, 6g, 6j, 6k and 6n were found to be more potent than INH
d
11.86 of –OH clearly
d
121.3, 125.4, 125.9, 126.9, 127.2, 128.7, 130.0, 131.13, 131.2, 134.9,
144.4, 150.6, 150.9, 160.1, 160.9 and 164.1 due to carbon atoms of
quinoline and other two aromatic rings. The structure of 6a was
confirmed by LCMS. It showed the molecular ion peak at m/z 386.2
(98%), which conforms to its molecular formula C23H16FN3O2.
Finally, the molecular structure of the compound 6j was deter-
mined by single crystal X-ray diffraction studies. The ORTEP view of
the molecular structure shows the spatial atomic positions of
compound 6j, as given in Fig. 1. The characterization data of newly
synthesized compounds are summarized in Tables 1 and 2.
2.2. Pharmacology
2.2.1. Antibacterial studies
The newly synthesized compounds 5a-n, 6a-n were screened
for their in vitro antibacterial activity against E. coli (ATTC-25922), S.
aureus (ATTC-25923), P. aeruginosa (ATCC-27853) and K. pneumo-
niae (recultured) bacterial strains by serial plate dilution method
[34,35] using ciprofloxacin as standard. The MICs and zone of
inhibition were determined for 5a-n and 6a-n and their results are
summarized along with that of ciprofloxacin in Tables 3 and 4.
(MIC: 1.5
viz., 5c, 5d, 5g, 5j, 5l, 5n, 6b, 6d, 6f, 6i and 6l showed moderate
activity at MIC 10 g/mL.
mg/mL) with MIC 1 mg/mL whereas eleven compounds,
m
Fig. 1. ORTEP diagram showing the X-ray crystal structure of 6j.

960
S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
Table 1
Characterization data of compounds 5a-n.
H
N
O
R
HO
NH
1
R
N
2
R
Compd
R
R1
R2
Molecular formula/
Mol. Weight
M.P (ꢀC)
Yield %
Analysis % found Found (Calc.)
C
H
N
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
2-methoxy phenyl
4-(methylthio) phenyl
Benzyl
Phenyl
3-cyano phenyl
Pentyl
4-fluoro phenyl
Phenylethyl
3,5 dimethyl phenyl
4-fluoro phenyl
2-methoxy phenyl
Benzyl
F
F
F
F
F
F
F
F
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
F
F
F
F
C23H18FN3O3/403
C23H18FN3O2S/419
C23H18FN3O2/387
245
247
249
254
232
259
265
250
275
290
255
256
261
264
98
95
87
95
92
85
95
81
96
92
95
82
80
94
68.48 (68.44)
65.86 (65.88)
71.31 (71.36)
70.77 (70.80)
69.34 (69.39)
68.65 (68.69)
67.52 (67.55)
71.81 (71.85)
71.81 (71.78)
67.52 (67.55)
68.48 (68.50)
71.31 (71.33)
68.65 (68.69)
64.79 (64.82)
4.50 (4.55)
4.33 (4.38)
4.68 (4.71)
4.32 (4.35)
3.80 (3.86)
6.04 (6.09)
3.86 (3.88)
5.02 (5.07)
5.02 (5.07)
3.86 (3.82)
4.50 (4.55)
4.68 (4.64)
6.04 (6.02)
3.71 (3.76)
10.42 (10.46)
10.02 (10.07)
10.85 (10.89)
11.25 (11.29)
14.06 (14.08)
11.44 (11.48)
10.74 (10.77)
10.47 (10.44)
10.47 (10.50)
10.74 (10.79)
10.42 (10.44)
10.85 (10.88)
11.44 (11.47)
10.30 (10.33)
C22H16FN3O2/373
C23H15FN4O2/398
C21H22FN3O2/367
C22H15F2N3O2/391
C24H20FN3O2/401
C24H20FN3O2/401
C22H15F2N3O2/391
C23H18FN3O3/403
C23H18FN3O2/387
C21H22FN3O2/367
C22H15ClFN3O2/407
Pentyl
3-chloro phenyl
F
2.3. X-ray crystallographic analysis of 6j
structure solution was solved by full matrix least-squares method
using SHELXL97. All the atoms were located in different Fourier
maps and refined isotropically, using a riding model and all the
projections were generated using ORTEP. The details of the crystal
data and refinement are shown in Table 6. Also the single crystal
images for compound 6j are given in Fig. 2.
The X-ray crystallographic analysis of 6j was determined on
a
colorless plate crystal, with approximate dimensions
0.30 mm ꢂ 0.25 mm ꢂ 0.15 mm, grown from the slow evaporation
of a dilute ethanol solution at room temperature. The crystal
Table 2
Characterization data of compounds 6a-n.
HN
R
O
N
1
2
R
N
R
Compd
R
R1
R2
Molecular formula/
Mol. Weight
M.P (ꢀC)
Yield %
Analysis % found Found (Calc.)
C
H
N
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
2-methoxy phenyl
4-(methylthio) phenyl
Benzyl
Phenyl
3-cyano phenyl
Pentyl
4-fluoro phenyl
Phenylethyl
3,5 dimethyl phenyl
4-fluoro phenyl
2-methoxy phenyl
Benzyl
F
F
F
F
F
F
F
F
H
H
H
H
H
H
H
H
H
H
H
H
H
H
F
F
F
F
F
C23H16FN3O2/385
C23H16FN3OS/401
C23H16FN3O/369
C22H14FN3O/355
223
233
198
249
274
162
257
223
285
280
220
168
182
293
92
71.68 (71.66)
68.81 (68.82)
74.78 (74.77)
74.36 (74.39)
72.6 (72.65)
72.19 (72.22)
70.77 (70.79)
75.18 (75.20)
75.18 (75.21)
70.77 (70.80)
71.68 (71.70)
74.78 (74.80)
72.19 (72.22)
67.79 (67.82)
4.18 (4.22)
4.02 (4.00)
4.37 (4.39)
3.97 (3.99)
3.44 (3.46)
5.77 (5.79)
3.51 (3.55)
4.73 (4.77)
4.73 (4.75)
3.51 (3.52)
4.18 (4.20)
4.37 (4.39)
5.77 (5.79)
3.36 (3.39)
10.90 (10.94)
10.47 (10.49)
11.38 (11.40)
11.82 (11.88)
14.73 (14.77)
12.03 (12.04)
11.25 (11.28)
10.96 (10.99)
10.96 (10.95)
11.25 (11.22)
10.90 (10.90)
11.38 (11.36)
12.03 (12.00)
10.78 (10.81)
96
81a
91
C23H13FN4O/380
98
C21H20FN3O/349
C22H13F2N3O/373
C24H18FN3O/383
C24H18FN3O/383
C22H13F2N3O/373
C23H16FN3O2/385
C23H16FN3O/369
82a
89
79a
97
97
92
77a
81a
92
Pentyl
3-chloro phenyl
C21H20FN3O/349
F
C22H13ClFN3O/389
a
Yield obtained after column purification.

S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
961
Table 3
Antibacterial activity of quinoline-urea derivative 5a-n.
Table 5
In vitro Antituberculosis evaluation of the synthesized compounds 5a-n, 6a-n.
Compound
MIC in
m
g/mL and zone of inhibition in mm
E. coli P. aeruginosa
Compd
MIC (
1
m
g/mL)
% Inhibition
5a
5b
5c
5d
5e
5f
5g
5h
5i
99
0
95
95
0
0
95
0
S. aureus K.pneumoniae
(ATCC 25923) (ATCC 25922) (ATCC 27853) (recultured)
>100a
10
5a
5b
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
5n
6.25 (19)
50 (<10)
6.25 (18)
6.25 (17)
6.25 (19)
12.5 (12)
6.25 (20)
50 (<10)
50 (<10)
6.25 (18)
6.25 (17)
6.25 (16)
50 (<10)
6.25 (18)
6.25 (22)
6.25 (22)
6.25 (21)
6.25 (20)
6.25 (23)
6.25 (22)
6.25 (21)
50 (<10)
50 (<10)
6.25 (24)
6.25 (21)
50 (<10)
6.25 (20)
6.25 (22)
6.25 (29)
6.25 (18)
50 (<10)
6.25 (20)
6.25 (18)
6.25 (19)
12.5 (11)
6.25 (19)
50 (<10)
50 (<10)
6.25 (17)
6.25 (16)
50 (<10)
50 (<10)
6.25 (20)
6.25 (25)
6.25 (19)
50 (<10)
6.25 (18)
6.25 (20)
6.25 (18)
12.5 (12)
6.25 (16)
50 (<10)
50 (<10)
6.25 (16)
6.25 (19)
50 (<10)
50 (<10)
6.25 (20)
6.25 (22)
10
>100a
>100a
10
>100a
>100a
10
0
5j
5k
5l
95
99
95
0
95
99
95
99
95
0
95
99
0
95
99
99
95
0
1
10
5m
5n
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
>100a
10
1
10
1
10
Ciprofloxacin 6.25 (24)
(Standard)
>100a
10
The MIC values where evaluated at concentration range, 6.25–50
in the table show the MIC values in
in mm.
m
g/mL. The figures
1
mg/mL and the corresponding zone of inhibition
>100a
10
1
1
10
3. Experimental section
6m
6n
>100a
1
99
3.1. General
Isoniazid (INH)
Rifampicin (RIF)
1.5
0.5
95
99
All reagents were purchased from Aldrich. Solvents used were
extra dried. Final purifications were carried out using Quad
biotage Flash purifier (A Dyax Corp. Company). TLC experiments
were performed on alumina-backed silica gel 40 F254 plates
(Merck, Darmstadt, Germany). The plates were illuminated under
UV (254 nm) and molybidinic acid. Melting points were deter-
mined using Buchi B-540 and are uncorrected. Elemental anal-
yses were carried out on an automatic Flash EA 1112 Series,
CHNSO Analyzer (Thermo). X-Ray diffraction studies where
carried on an Xcalibur E Oxford Diffraction system (Varian, Cal-
ifornia, USA). All 1H and 13C NMR spectra were recorded on
a Bruker AM-300 (300.12 MHz, 75.12 MHz), Bruker BioSpin Corp.,
Germany. Molecular weights of unknown compounds were
checked by LCMS 6200 series Agilent Technology. Chemical shifts
a
MIC > 100 mg/mL indicates that the strain is resistant to tested substance.
are reported in ppm (d) with reference to internal standard TMS.
The signals are designated as follows: s, singlet; d, doublet; dd,
doublet of doublets; t, triplet; m, multiplet; brs, broad singlet,
brt, broad triplet.
Table 6
Crystal data and measurement detail for compound 6j.
Crystal data
Empirical formula
Formula weight
Crystal system
Crystal dimension
Space group
a (Å)
C22H13F2N3O
373.35
Monoclinic
0.30 mm ꢂ 0.25 mm ꢂ 0.15 mm
p21c
13.8773(4)
7.04841(16)
19.7470(6)
1843.63(9)
90, 107.34(3), 90
8
1.197
680
0.08
Table 4
b (Å)
Antibacterial activity of fused quinoline–oxazole derivative 6a-n.
c (Å)
Volume (Å3)
Compound
MIC in
m
g/mL and zone of inhibition in mm
E. coli P. aeruginosa
Angle
Z
a, b, g
S. aureus K.pneumoniae
(ATCC 25923) (ATCC 25922) (ATCC 27853) (recultured)
Crystal density, g/cm3
F000
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6.25 (21)
6.25 (20)
6.25 (22)
6.25 (20)
12.5 (11)
12.5 (11)
6.25 (22)
50 (<10)
12.5 (11)
6.25 (20)
6.25 (22)
6.25 (21)
50 (<10)
6.25 (22)
6.25 (24)
6.25 (23)
6.25 (23)
6.25 (26)
12.5 (16)
6.25 (24)
6.25 (25)
50 (<10)
6.25 (24)
6.25 (28)
6.25 (27)
6.25 (24)
50 (<10)
6.25 (26)
6.25 (28)
6.25 (21)
6.25 (20)
6.25 (19)
6.25 (22)
12.5 (14)
12.5 (14)
6.25 (25)
50 (<10)
12.5 (14)
6.25 (22)
6.25 (19)
6.25 (24)
50 (<10)
6.25 (24)
6.25 (31)
6.25 (21)
6.25 (22)
6.25 (18)
6.25 (20)
12.5 (12)
12.5 (12)
6.25 (19)
50 (<10)
12.5 (12)
6.25 (20)
6.25 (23)
6.25 (19)
50 (<10)
6.25 (21)
6.25 (25)
m
(mmꢁ1
)
Absorption coefficient
Cut-off used in R-factor calculations
0.089
Fo2 > 2
0.0652
0.1796
293(2)
s
(Fo2)
R (Fo)
Rw (Fo2)
Temperature (T)
Radiation wavelength
Radiation type
Radiation source
Radiation monochromator
hmin
hmax
kmin
0.71073
MoK
a
Fine-focus sealed tube
Graphite
ꢁ17
17
ꢁ8
kmax
8
Ciprofloxacin 6.25 (26)
lmin
lmax
ꢁ24
(Standard)
24
The MIC values where evaluated at concentration range, 6.25–50
in the table show the MIC values in
in mm.
m
g/mL. The figures
Reflns (Fo)
Structure refinement
4871
SHELXL-97
mg/mL and the corresponding zone of inhibition

962
S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
Fig. 2. Single crystal images of compound 6j.
3.2. General procedure for the synthesis of 2-amino-1-(substituted
fluorophenyl)ethanone 2a-b
(20 mmol) dissolved in water (100 mL) was stirred for 5 min, the
reaction mixture was gradually heated to 85 ꢀC over 30 min. At
30 ꢀC the mixture began to foam. On reaching 85 ꢀC it was stirred
for a further 10 min. After this, the solid phase was filtered off and
washed with a solution of sodium carbonate and water to neutral
pH. The solid was dried in vacuo and taken as such for the next step
without any further purification.
To
a solution of substituted 2-bromo-1-phenylethanone
1a-b (43.3 mmol) in 100 mL of DMF at 0 ꢀC, solid NaN3 (52 mmol)
was added portion wise while stirring and stirring was continued at
room temperature for 6 h. The completion of the reaction was
monitored by TLC. The reaction mixture was then poured into cold
water (200 mL) and the compound was extracted with ethyl acetate
(2 ꢂ100 mL). The combined organic layer was dried over sodium
sulphate and concentrated to get the crude product as yellowoil. The
crude product was taken as such for the next step without further
purification. The crude oil thus obtained was dissolved in methanol
(100 mL) and it was mixed with palladium in charcoal (10 mol%)
while stirring; the stirring was continued under H2 atmosphere
(2 kg/cm2) for 4 h. The reaction was monitored by TLC for comple-
tion. The reaction mixturewas filtered and concentrated togetcrude
product as colorless oil. This crude oil was made HCl salt with 50 mL
of 6 N HCl in 1,4 dioxane to get product as an off white solid.
3.3.1. 2-Amino-N-[2-(3-fluorophenyl)-2-oxoethyl]benzamide (3a)
Compound 3a was obtained as off white solid. Yield 85%. IR (KBr,
cmꢁ1 : 3426,3334 (pNH), 1686, 1652 (pC]O), 1164 (pC–F). 1H
) y
NMR (300 MHz, DMSO-d6)
d
; 4.67 (d, –CH2, 2H, J ¼ 5.7), 6.44 (brs,
–NH2, 2H, disappeared on D2O exchange), 6.52 (m, –CH, 1H), 7.12 (t,
–CH, 1H), 7.38 (m, –CH, 1H), 7.64 (m, –CH, 1H), 7.86 (m, –CH, 2H),
8.11 (m, –CH, 2H), 8.54 (brt, –NH, 1H, disappeared on D2O
exchange).
3.3.2. 2-Amino-N-[2-(4-fluorophenyl)-2-oxoethyl]benzamide (3b)
Compound 3b was obtained as off white solid. Yield 85%. IR (KBr,
cmꢁ1 : 3426,3334 (pNH), 1684, 1652 (pC]O), 1164 (pC–F). 1H
) y
3.2.1. 2-Amino-1-(3-fluorophenyl)ethanone (2a)
NMR (300 MHz, DMSO-d6)
d
; 4.68 (d, –CH2, 2H, J ¼ 5.7), 6.4 (brs,
Compound 2a was obtained as off white solid. Yield 77%. IR (KBr,
–NH2, 2H, disappeared on D2O exchange), 6.52 (m, –CH, 1H), 6.70
(d, –CH, 1H, J ¼ 8.1) 7.14 (t, –CH, 1H), 7.38 (m, –CH, 2H), 7.55 (d, –CH,
2H, J ¼ 8.4), 8.11 (m, –CH, 2H), 8.57 (brt, –NH, 1H, disappeared on
D2O exchange).
) y:
cmꢁ1 3422 (pNH), 1678 (pC]O), 1164 (pC–F). 1H NMR
(400 MHz, DMSO-d6) d; 4.62 (brd, –CH2, 2H), 7.36 (m, –CH, 1H), 7.64
(m, –CH,1H), 7.88 (m, –CH, 2H), 8.48 (brs, –NH2, 2H, disappeared on
D2O exchange).
3.4. General procedure for the synthesis of 3-amino-2-(substituted
3.2.2. 2-Amino-1-(4-fluorophenyl)ethanone (2b)
fluorophenyl)quinolin-4-ol 4a-b
Compound 2b was obtained as off white solid. Yield 81%. IR (KBr,
cmꢁ1
)
y:
3438 (pNH), 1688 (pC]O), 1162 (pC–F). 1H NMR
Freshly prepared PPA (50 g) was added to 2-amino-N-[2-
(substituted fluorophenyl)-2-oxoethyl]benzamides 3a-b (18 mmol)
and the reaction mixture was heated to 150–160 ꢀC. The heating
was continued for further 2 h at this temperature. Reaction
completion was monitored by TLC. The reaction mixture was then
poured onto solid sodium carbonate (60 g), and after foaming
stopped, water (600 mL) was added. After 30 min of stirring the
solid product obtained was filtered off and washed with plenty of
water and dried.
(400 MHz, DMSO-d6) d; 4.56 (brt, –CH2, 2H), 7.39 (m, –CH, 2H), 8.09
(m, –CH, 1H), 8.53 (brs, –NH2, 2H, disappeared on D2O exchange).
3.3. General procedure for the synthesis of 2-amino-N-
[2-(substituted fluorophenyl)-2-oxoethyl]benzamide 3a-b
A mixture of substituted 2-aminoacetophenone hydrochloride
2a-b (33 mmol), isatoic anhydride (36 mmol) and sodium carbonate

S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
963
3.4.1. 3-Amino-2-(3-fluorophenyl)quinolin-4-ol (4a)
J ¼ 8.1), 9.05 (brs, –NH,1H, disappeared on D2O exchange),11.91 (brs,
NH,1H, disappeared on D2O exchange). LC–MS (ESI) m/z 399 (M þ 1)
Compound 4a was obtained as green solid. Yield 93%. IR (KBr,
cmꢁ1
) y
: 3519 (O–H), 3449 (pNH), 1164 (pC–F). 1H NMR (300 MHz,
DMSO-d6)
d; 3.38 (brs, –NH2, 2H), 7.19 (m, –CH, 1H), 7.35(m, –CH,
3.5.6. 1-[2-(3-Fluorophenyl)-4-hydroxyquinolin-3-yl]-
1H), 7.64–7.50 (m, –CH, 5H), 8.11 (d, –CH, 1H, J ¼ 8.1), 11.44 (brs,
3-pentylurea (5f)
–OH, 1H).
Compound 5f was obtained as off white solid. IR (KBr, cmꢁ1
) y:
3496 (O–H), 3324 (pNH), 1623 (pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6)
–(CH2)3, 6H), 2.89 (m, –CH2, 2H), 6.1 (brt, NH, 1H), 6.95 (s, NH, 1H),
7.33 (m, –CH, 2H), 7.55–7.47(m, –CH, 3H), 7.67 (brs, –CH, 2H), 8.14
(d, –CH, 1H, J ¼ 6.9), 11.86 (brs, NH, 1H, disappeared on D2O
exchange).
3.4.2. 3-Amino-2-(4-fluorophenyl)quinolin-4-ol (4b)
d; 0.83 (t, –CH3, 3H, J ¼ 6.6), 1.23–1.15 (m,
Compound 4b was obtained as pale yellow solid. Yield 88%. IR
(KBr, cmꢁ1 : 3519 (O–H), 3449 (pNH), 1169 (pC–F). 1H NMR
) y
(400 MHz, DMSO-d6) d; 4.26 (brs, –NH2, 2H, disappeared on D2O
exchange), 7.22 (t, –CH, 1H, J ¼ 8.1), 7.44 (m, –CH, 2H), 7.52 (t, –CH,
1H, J ¼ 5.4), 7.57 (d, –CH,1H, J ¼ 8.4), 7.79–7.75 (m, –CH, 2H), 8.12 (d,
–CH, 1H, J ¼ 8.1), 11.45 (brs, –OH, 1H, disappeared on D2O
exchange).
3.5.7. 1-(4-Fluorophenyl)-3-[2-(3-fluorophenyl)-4-hydroxyquinolin-
3-yl]urea (5g)
Compound 5g was obtained as pale brown solid. IR (KBr, cmꢁ1
)
3.5. General procedure for the synthesis of quinoline urea 5a-n
y
: 3510 (O–H), 3334 (pNH), 1642 (pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6) ; 7.08–7.00 (m, –CH, 2H), 7.37–7.30 (m, –CH,
d
To
a
suspension of 3-amino-2-(substituted fluorophenyl)-
5H), 7.58–7.45 (m, –CH, 4H), 7.70 (s, –CH, 1H), 8.16 (d, –CH, 1H,
J ¼ 8.4), 8.76 (brs, –NH, 1H), 11.88 (brs, NH, 1H, disappeared on D2O
exchange). LC–MS (ESI) m/z 392 (M þ 1)
quinolin-4-ol 4a-b (2 mmol) in dry toluene (4 mL) equimolar
quantity of substituted isocyanate (2 mmol) was added slowly and
the reaction mixture was heated at 110 ꢀC for 2 h. The completion of
the reaction was monitored by TLC. The solid obtained on cooling
was filtered and washed with n-hexane (50 mL).
3.5.8. 1-[2-(3-Fluorophenyl)-4-hydroxyquinolin-3-yl]-3-(2-
phenylethyl)urea (5h)
Compound 5h was obtained as pale brown solid. IR (KBr, cmꢁ1
)
3.5.1. 1-[2-(3-Fluorophenyl)-4-hydroxyquinolin-3-yl]-3-
y
: 3512 (O–H), 3298 (pNH), 1628 (pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6)
(2-methoxyphenyl)urea (5a)
d; 2.57 (t, –CH2, 2H, J ¼ 7.2), 3.14 (q, –CH2, 2H,
Compound 5a was obtained as off white solid. IR (KBr, cmꢁ1
)
y:
J ¼ 6.9), 6.20 (t, NH, 1H, J ¼ 6), 7.06 (s, NH, 1H), 7.28–7.11 (m, –CH,
5H), 7.39–7.31(m, –CH, 2H), 7.67–7.45 (m, –CH, 3H), 7.68 (s, –CH,
2H), 8.15 (d, –CH, 1H, J ¼ 8.1),11.76 (brs, NH,1H, disappeared on D2O
exchange). LC–MS (ESI) m/z 402 (M þ 1)
3508 (O–H), 3344 (pNH), 1653 (pC]O), 1169 (pC–F), 1112 (pC–O).
1H NMR (300 MHz, DMSO-d6)
d; 3.82 (s, –OCH3, 3H), 6.89–6.77 (m,
–CH, 2H), 6.97(d, –CH, 1H, J ¼ 9), 7.37–7.32 (m, –CH, 3H), 7.70–7.48
(m, –CH, 4H), 7.94 (d, –CH, 1H, J ¼ 7.8), 8.07 (s, –NH, 1H), 8.16 (d,
–CH, 1H, J ¼ 8.1), 8.22 (brs, –NH, 1H), 11.86 (brs, –OH, 1H, dis-
appeared on D2O exchange). LC–MS (ESI) m/z 404 (M þ 1)
3.5.9. 1-(3,5-Dimethylphenyl)-3-[2-(4-fluorophenyl)-4-hydroxy-
quinolin-3-yl]urea (5i)
Compound 5i was obtained as pale yellow solid. IR (KBr, cmꢁ1
) y:
3.5.2. 1-[2-(3-Fluorophenyl)-4-hydroxyquinolin-3-yl]-3-
3510 (O–H), 3340 (pNH), 1644 (pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6) ;2.17 (s, –(CH3)2, 6H), 6.53 (s, –CH,1H), 7.06 (s,
[4-(methylthio)phenyl]urea (5b)
d
Compound 5b was obtained as brown solid. IR (KBr, cmꢁ1
)
y:
–CH, 2H), 7.32 (s, –NH, 1H), 7.41–7.33(m, –CH, 3H), 7.74–7.65 (m,
–CH, 4H), 8.16 (d, –CH,1H, J ¼ 8.1), 8.54 (brs, –NH,1H, disappeared on
D2O exchange), 11.82 (brs, NH, 1H, disappeared on D2O exchange).
3494 (O–H), 3340 (pNH), 1645(pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6) ; 2.40 (s, –SCH3, 3H), 7.28–7.13 (m, –CH, 2H),
d
7.42–7.31(m, –CH, 5H), 7.69–7.49 (m, –CH, 3H), 7.70 (s, –CH, 2H),
8.13 (d, –CH, 1H, J ¼ 8.1), 8.75 (brs, –CH, 1H), 11.88 (brs, –OH, 1H,
disappeared on D2O exchange). LC–MS (ESI) m/z 420 (M þ 1)
3.5.10. 1-(4-Fluorophenyl)-3-[2-(4-fluorophenyl)-4-hydroxy-
quinolin-3-yl]urea (5j)
Compound 5j was obtained as off white solid. IR (KBr, cmꢁ1
) y:
3.5.3. 1-Benzyl-3-[2-(3-fluorophenyl)-4-hydroxyquinolin-3-yl]
3502 (O–H), 3338 (pNH), 1648 (pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6) ; 7.14–7.00 (m, –CH, 2H), 7.46–7.28 (m, –CH,
urea (5c)
d
Compound 5c was obtained as pale yellow solid. IR (KBr, cmꢁ1
)
6H), 7.74–7.65 (m, –CH, 4H), 8.16 (d, –CH,1H, J ¼ 8.1), 8.73 (brs, –NH,
1H, disappeared on D2O exchange), 11.84 (brs, NH, 1H, disappeared
on D2O exchange). LC–MS (ESI) m/z 392 (M þ 1)
y: 3504 (O–H), 3326 (pNH), 1650 (pC]O), 1169 (pC–F). LC–MS (ESI)
m/z 388 (M þ 1)
3.5.4. 1-[2-(3-Fluorophenyl)-4-hydroxyquinolin-3-yl]-3-
phenylurea (5d)
3.5.11. 1-[2-(4-Fluorophenyl)-4-hydroxyquinolin-3-yl]-3-(2-
methoxyphenyl)urea (5k)
Compound 5d was obtained as off white solid. IR (KBr, cmꢁ1
)
y:
Compound 5k was obtained as white solid. IR (KBr, cmꢁ1
) y:
3512 (O–H), 3339 (pNH), 1648 (pC]O), 1169 (pC–F). 1H NMR
3516 (O–H), 3334 (pNH), 1644 (pC]O), 1169 (pC–F). 1H NMR
(300 MHz, DMSO-d6) ; 3.82 (s, –OCH3, 3H), 6.89–6.79 (m, –CH,
(300 MHz, DMSO-d6)
d
; 6.89 (t, –CH, 1H, J ¼ 7.8), 7.20 (m, –CH, 2H),
d
7.38–7.31 (m, –CH, 5H), 7.62–7.50 (m, –CH, 3H), 7.62 (s, –CH, 2H),
8.17 (d, –CH, 1H, J ¼ 7.5), 8.74(brs, NH, 1H), 11.87 (brs, NH, 1H, dis-
appeared on D2O exchange).
2H), 6.97(m, –CH, 1H), 7.41–7.33 (m, –CH, 3H), 7.73–7.68 (s, –CH,
4H), 7.96 (m, –CH, 1H), 8.04 (s, –CH, 1H), 8.15 (d, –CH, 1H, J ¼ 8.1),
8.23 (brs, –NH, 1H), 11.83 (brs, NH, 1H, disappeared on D2O
exchange). LC–MS (ESI) m/z 404 (M þ 1)
3.5.5. 1-(3-Cyanophenyl)-3-[2-(3-fluorophenyl)-4-
hydroxyquinolin-3-yl]urea (5e)
3.5.12. 1-Benzyl-3-[2-(4-fluorophenyl)-4-hydroxyquinolin-3-
Compound 5e was obtained as off white solid. IR (KBr, cmꢁ1
)
y:
yl]urea (5l)
3498 (O–H), 3332 (pNH), 2224 (–CN), 1648 (pC]O),1169 (pC–F). 1H
NMR (300 MHz, DMSO-d6) ; 7.45–7.32 (m, –CH, 4H), 7.62–7.49 (m,
–CH, 5H), 7.71–7.70 (m, –CH, 2H), 7.82 (s, –CH, 1H), 8.16 (d, –CH, 1H,
Compound 5k was obtained as yellow solid. IR (KBr, cmꢁ1
) y:
d
3504 (O–H), 3326 (pNH), 1650 (pC]O), 1169 (pC–F). LC–MS (ESI)
m/z 388 (M þ 1)

964
S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
3.5.13. 1-[2-(4-Fluorophenyl)-4-hydroxyquinolin-3-yl]-3-
pentylurea (5m)
(75 MHz, DMSO-d6) d: 114.5, 116.0, 116.3, 118.3, 119.9, 123.4, 125.8,
127.5, 128.6, 129.6, 129.9, 131.1, 131.2, 134.7, 136.8, 138.4, 141.7, 144.5,
150.5, 159.0, 160.9, 164.2. LC–MS (ESI) m/z 356 (M þ 1).
Compound 5m was obtained as off white solid. IR (KBr, cmꢁ1
)
y:
3494 (O–H), 3322 (pNH), 1622 (pC]O), 1169 (pC–F).1H NMR
(300 MHz, DMSO-d6)
d
; 0.85 (t, –CH3, 3H, J ¼ 6.6), 1.29–1.14 (m,
3.6.5. 3-{[4-(3-Fluorophenyl)[1,3]oxazolo[4,5-c]quinolin-2-
yl]amino}benzonitrile (6e)
–(CH2)3, 6H), 2.87 (m, –CH2, 2H), 6.1 (t, NH, 1H,J ¼ 5.4), 6.92 (s, NH,
1H), 7.36–7.30 (m, –CH, 3H), 7.70–7.62 (m, –CH, 4H), 8.14 (d, –CH,
1H, J ¼ 7.8), 11.70 (brs, NH, 1H, disappeared on D2O exchange).
Compound 6e was obtained as pale yellow solid. 1H NMR
(300 MHz, DMSO-d6) d; 7.45–7.39 (m, –CH, 1H), 7.58 (d, –CH, 1H,
J ¼ 6.6), 7.81–7.63 (m, –CH, 4H), 8.11–8.01 (dd, –CH, 2H), 8.23 (d,
–CH, 1H, J ¼ 8.4), 8.35 (s, –CH, 1H), 8.58 (dd, –CH, 1H), 8.63 (d, –CH,
1H, J ¼ 7.5), 11.72 (s, NH, 1H, disappeared on D2O exchange). 13C
3.5.14. 1-(3-Chlorophenyl)-3-[2-(4-fluorophenyl)-4-
hydroxyquinolin-3-yl]urea (5n)
Compound 5n was obtained as yellow solid. 3512 (O–H), 3342
NMR (75 MHz, DMSO-d6) d: 112.3, 114.6, 115.8 (CN), 116.1, 117.5,
(pNH), 1622 (pC]O), 1169 (pC–F). 1H NMR (300 MHz, DMSO-d6)
d;
117.8,119.1,119.7,120.5,122.6,125.4,126.5,128.2,128.4,129.6,130.9,
133.9, 139.4, 142.4, 144.8, 149.8, 158.0, 160.9, 164.2. LC–MS (ESI) m/z
381 (M þ 1)
6.95–6.91 (m, CH, 1H), 7.31–7.14 (m, –CH, 2H), 7.41–7.34 (m, –CH,
4H), 7.58 (s, –CH, 1H), 7.73–7.68 (m, –CH, 4H), 8.16 (d, –CH, 1H,
J ¼ 8.1), 8.89 (brs, –NH, 1H, disappeared on D2O exchange), 11.86
(brs, NH, 1H, disappeared on D2O exchange).
3.6.6. 4-(3-Fluorophenyl)-N-pentyl[1,3]oxazolo[4,5-c]quinolin-2-
amine (6f)
3.6. General procedure for the synthesis of oxazoloquinoline 6a-n
Compound 6f was obtained as pale yellow solid. 1H NMR
(300 MHz, DMSO-d6)
d
; 0.91 (t, –CH3, 3H, J ¼ 6.6), 1.40–1.35 (m,
A mixture of substituted urea derivatives of quinoline 5a-n
(2 mmol) and freshly distilled POCl3 (4 mL) was heated at 80 ꢀC for
2 h. The reaction was monitored by TLC. After completion of the
reaction, excess of POCl3 was distilled off. The residue thus obtained
was basified by saturated NaHCO3 solution. After this, the solid
phase was filtered and dried. Some of the final compounds were
purified by biotage column chromatography using pet ether/ethyl
acetate as the eluent.
–(CH2)2, 4H), 1.70–1.65 (m, –CH2, 2H), 3.45 (m, –N(CH2), 2H), 7.33
(brt, NH, 1H), 7.66–7.59 (m, –CH, 3H), 7.97 (d, –CH, 1H, J ¼ 7.5),
8.10 (d, –CH, 1H, J ¼ 7.5), 8.66–8.54 (m, –CH, 3H). 13C NMR
(75 MHz, DMSO-d6) d: 13.9, 22.3, 28.8, 29.3, 43.4, 115.2, 115.8,
116.15, 116.2, 118.8, 124.7, 124.8, 126.6, 127.3, 129.9, 130.0, 134.8,
139.9, 140.0, 143.9, 146.4, 149.6, 161.4, 161.8, 164.6. LC–MS (ESI)
m/z 350 (M þ 1)
3.6.7. 4-(3-Fluorophenyl)-N-(4-fluorophenyl)[1,3]oxazolo[4,5-
c]quinolin-2-amine (6g)
3.6.1. 4-(3-Fluorophenyl)-N-(2-methoxyphenyl)[1,3]oxazolo[4,5-
c]quinolin-2-amine (6a)
Compound 6g was obtained as pale yellow solid. 1H NMR
Compound 6a was obtained as pale yellow solid. 1H NMR
(300 MHz, DMSO-d6) d; 7.41–7.27 (m, –CH, 2H), 7.44–7.41 (m, –CH,
(300 MHz, DMSO-d6)
d
; 3.89 (s, –OCH3, 3H), 7.19–7.08 (m, –CH, 3H),
1H), 7.86–7.65 (m, –CH, 6H), 8.09–8.06 (m, –CH, 1H), 8.22 (d, –CH,
1H, J ¼ 7.5), 8.53 (d, –CH,1H, J ¼ 10.2), 8.64 (d, –CH,1H, J ¼ 7.8),11.32
(s, NH, 1H, disappeared on D2O exchange). 13C NMR (75 MHz,
7.41 (m, –CH, 1H), 7.80–7.68 (m, –CH, 3H), 8.09 (d, –CH, 1H, J ¼ 6.6),
8.17 (d, –CH, 1H, J ¼ 7.5), 8.27 (d, –CH, 1H, J ¼ 7.5), 8.59–8.50 (m,
–CH, 2H), 10.41 (s, NH, 1H). 13C NMR (75 MHz, DMSO-d6)
d: 56.31,
DMSO-d6) d: 114.8, 115.4, 115.7, 116.1, 116.4, 117.4, 119.6, 119.8, 119.9,
112.2,114.5,116.2,116.5,117.8,118.14,119.9,121.0,121.3,125.4,125.9,
126.9, 127.2, 128.7, 130.0, 131.13, 131.2, 134.9, 144.4, 150.6, 150.9,
160.1, 160.9, 164.1. LC–MS (ESI) m/z 386 (M þ 1)
125.3, 128.2, 129.0, 129.3, 131.1, 134.4, 135.1, 143.1, 145.1, 149.4, 156.6,
158.6, 161.1, 164.3. LC–MS (ESI) m/z 374 (M þ 1)
3.6.8. 4-(3-Fluorophenyl)-N-(2-phenylethyl)[1,3]oxazolo
[4,5-c]quinolin-2-amine (6h)
3.6.2. 4-(3-Fluorophenyl)-N-[4-(methylthio)phenyl][1,3]oxazolo[4,5-
c]quinolin-2-amine (6b)
Compound 6h was obtained as yellow solid. 1H NMR (300 MHz,
Compound 6b was obtained as pale yellow solid. 1H NMR
DMSO-d6)
d
; 3.00 (t, –CH2, 2H, J ¼ 7.2), 3.69 (q, –CH2, 2H, J ¼ 6.9),
(300 MHz, DMSO-d6)
d; 2.50 (s, –SCH3, 3H), 7.48–7.35 (m, –CH, 3H),
7.32–7.19 (m, –CH, 5H), 7.46–7.40 (m, –CH, 1H), 7.8–7.64 (m, –CH,
3H), 8.06 (d, –CH, 1H, J ¼ 8.1), 8.30 (d, –CH, 1H, J ¼ 8.4), 8.55 (m,
–CH, 2H), 8.93 (brt, NH, 1H). LC–MS (ESI) m/z 384 (M þ 1)
7.84–7.67 (m, –CH, 5H), 8.09 (d, –CH, 1H, J ¼ 6.6), 8.26 (d, –CH, 1H,
J ¼ 7.5), 8.46 (d, –CH, 1H, J ¼ 7.5), 8.48 (d, –CH, 1H, J ¼ 8.1), 11.35 (s,
NH, 1H). 13C NMR (75 MHz, DMSO-d6)
d: 16.1, 114.5, 115.9, 116.2,
117.7, 118.0, 119.8, 125.8, 127.6, 128.0, 128.5, 129.8, 131.2, 132.0, 134.7,
136.0, 141.7, 144.4, 150.4, 158.8, 160.9, 164.2. LC–MS (ESI) m/z 402
(M þ 1)
3.6.9. N-(3,5-dimethylphenyl)-4-(4-fluorophenyl)[1,3]oxazolo
[4,5-c]quinolin-2-amine (6i)
Compound 6i was obtained as off white solid. 1H NMR
(300 MHz, DMSO-d6) d; 2.31 (s, –(CH3)2, 6H), 6.74 (s, –CH, 1H), 7.44
3.6.3. N-benzyl-4-(3-fluorophenyl)[1,3]oxazolo[4,5-c]quinolin-2-
amine (6c)
(s, –CH, 2H), 7.56–7.50 (m, –CH, 2H), 7.87–7.76 (m, –CH, 2H), 8.09 (d,
–CH, 1H, J ¼ 8.4), 8.29 (d, –CH, 1H, J ¼ 8.4), 8.77–8.72(m, –CH, 2H),
11.24 (s, NH, 1H, disappeared on D2O exchange). LC–MS (ESI) m/z
384 (M þ 1)
Compound 6c was obtained as pale yellow solid. 1H NMR
(300 MHz, DMSO-d6)
d; 4.67 (d, –CH2, 2H, J ¼ 5.7), 7.48–7.28 (m,
–CH, 4H), 7.58–7.50 (m, –CH, 2H), 7.68–7.60 (m, –CH, 3H), 7.99 (d,
–CH, 1H, J ¼ 7.5), 8.11 (d, –CH, 1H, J ¼ 7.5), 8.59 (m, –CH, 1H), 8.65 (d,
–CH, 1H, J ¼ 8.1), 9.12 (t, NH, 1H, J ¼ 6). LC–MS (ESI) m/z 370 (M þ 1)
3.6.10. N,4-Bis (4-fluorophenyl)[1,3]oxazolo[4,5-c]quinolin-2-
amine (6j)
Compound 6j was obtained as pale yellow solid. 1H NMR
3.6.4. 4-(3-Fluorophenyl)-N-phenyl[1,3]oxazolo[4,5-c]quinolin-2-
amine (6d)
(300 MHz, DMSO-d6) d; 7.33–7.27 (m, –CH, 2H), 7.54–7.48 (m, –CH,
2H), 7.86–7.74 (m, –CH, 4H), 8.10 (d, –CH, 1H, J ¼ 7.8), 8.24 (d, –CH,
Compound 6d was obtained as yellow solid. 1H NMR (300 MHz,
1H, J ¼ 7.8), 8.78–8.75 (m, –CH, 2H),11.37 (s, NH,1H, disappeared on
DMSO-d6)
d; 7.36–7.08 (m, –CH, 1H), 7.47–7.37 (m, –CH, 3H), 7.77–
D2O exchange). 13C NMR (75 MHz, DMSO-d6)
d: 112.6, 116.1, 116.6,
7.65 (m, –CH, 3H), 8.06 (m, –CH, 2H), 8.30 (dd, –CH, 2H), 8.60 (m,
117.8, 119.9, 127.0, 128.5, 129.0, 129.5, 131.9, 133.2, 137.0, 147.1, 149.6,
152.9, 160.5, 161.5, 163.6, LC–MS (ESI) m/z 374 (M þ 1)
–CH, 1H), 8.30 (d, –CH, 1H, J ¼ 7.8), 11.23 (brs, NH, 1H). 13C NMR

S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
965
3.6.11. 4-(4-Fluorophenyl)-N-(2-methoxyphenyl)[1,3]oxazolo[4,5-
3.8. Antituberculosis activity broth micro dilution assay method
c]quinolin-2-amine (6k)
Compound 6k was obtained as yellow solid. 1H NMR (300 MHz,
DMSO-d6) d; 3.88 (s, –OCH3, 3H), 7.11–7.05 (m, –CH, 3H), 7.18 (m,
–CH, 2H), 7.49 (m, –CH, 2H), 7.83–7.72 (m, –CH, 2H), 8.09 (d, –CH,
1H, J ¼ 7.8), 8.17 (d, –CH, 1H, J ¼ 8.1), 8.27 (d, –CH, 1H, J ¼ 8.4), 8.78–
8.733 (m, –CH, 2H), 10.37 (s, NH, 1H). 13C NMR (75 MHz, DMSO-d6)
M. tuberculosis H37Rv was grown in Middlebrook 7H9 broth
(Difco BBL, Sparks, MD, USA) supplemented with 10% OADC (Bec-
ton Dickinson, Sparks, MD, USA). The culture was diluted to
McFarland 1 standard with the same medium. From this, 50
ml of
this culture were added to 150 l of fresh medium in 96 well
m
d
: 56.3, 112.1, 114.4, 116.0, 116.3, 119.9, 121.1, 125.2, 126.9, 130.8,
microtite plates. Stock solutions (2 mg/mL) of the test compounds
were prepared in Dimethyl Formamide (DMF). The compounds
132.3, 132.4, 134.7, 141.2, 145.1, 150.5, 150.8, 160.0, 162.4, 165.7. LC–
MS (ESI) m/z 386 (M þ 1)
were tested at 1, 10 and 100
had the same volumes of DMF without any compound. Isoniazid
(1.5 g/mL) and Rifampicin (0.5 g/mL) served as positive control.
After incubation at 37 ꢀC for 7 days, 15
l of 0.01% Resazurin (Sigma,
mg/mL concentrations. Control wells
3.6.12. N-benzyl-4-(4-fluorophenyl)[1,3]oxazolo[4,5-c]quinolin-2-
amine (6l)
m
m
m
Compound 6l was obtained as pale yellow solid. 1H NMR
St. Louis. MO.USA) in sterile water was added to the first growth
control wells and incubated for 24 hours. Once the first set of
growth controls turned pink, the dye solution was added to the
second set of growth controls and the test wells, and incubated for
24 hours at 37ꢀC. Resazurin, a redox dye, is blue in the oxidized
state and turns pink when reduced by the growth of viable cells.
The control wells showed change of colour from blue to pink after
24 h at 37 ꢀC. The compounds which prevented the change of
colour of the dye were considered to be inhibitory to M.
tuberculosis.
(300 MHz, DMSO-d6)
7.49–7.35 (m, –CH, 6H), 7.69–7.60 (m, –CH, 2H), 7.97 (d, –CH, 1H,
d
; 4.67 (d, –CH2, 2H, J ¼ 6), 7.28 (m, –CH, 1H),
J ¼ 7.5), 8.10 (d, –CH, 1H, J ¼ 7.5), 8.85 (m, –CH, 2H), 9.12 (t, NH, 1H,
J ¼ 6). 13C NMR (75 MHz, DMSO-d6)
d: 47.5, 115.0, 115.1, 115.4, 118.8,
126.3,127.3,127.7,128.0,128.8,129.9,131.1,133.6,134.2,137.3,144.0,
147.0, 149.6, 161.2, 162.0, 165.3. LC–MS (ESI) m/z 370 (M þ 1)
3.6.13. 4-(4-Fluorophenyl)-N-pentyl[1,3]oxazolo[4,5-c]quinolin-2-
amine (6m)
Compound 6m was obtained as pale yellow solid. 1H NMR
(300 MHz, DMSO-d6)
d
; 0.91 (t, –CH3, 3H, J ¼ 6.9), 1.37–1.34 (m,
4. Conclusion
–(CH2)2, 4H), 1.69–1.64 (m, –CH2, 2H), 3.47–3.35 (m, –N(CH2), 2H),
7.42–7.36 (m, –CH, 2H), 7.66–7.58 (m, –CH, 2H), 7.94 (d, –CH, 1H,
J ¼ 7.5), 8.10 (d, –CH, 1H, J ¼ 7.5), 8.49 (t, NH, 1H, J ¼ 5.4), 8.86–8.81
The present research study reports the successful synthesis,
antibacterial and antituberculosis studies of a new class of fused
1,3-oxazolo[4,5-c]quinolines carrying biologically active groups.
Their screening results revealed that all the compounds showed
moderate to very good activity against pathogenic strains. Study of
structure–activity relationship showed that the presence of aryl
group at position-2 and the existence of fused oxazole in quinoline
core are responsible for increased antibacterial and antitubercu-
losis activity of the newly synthesized condensed heterocycles. It
can be concluded that a combination of quinoline and oxazole has
caused an enhanced antimicrobial effect and hence they are ideally
suited for further modifications to obtain more efficacious anti-
bacterial and antituberculosis compounds.
(m, –CH, 3H). 13C NMR (75 MHz, DMSO-d6)
d: 14.1, 22.4, 28.9, 29.6,
44.2, 115.2, 115.8, 116.4, 116.6, 118.8, 124.7, 124.6, 126.7, 127.3, 130.7,
131.0, 134.2, 139.7, 140.0, 143.9, 146.4, 149.6, 161.4, 161.5, 163.2. LC–
MS (ESI) m/z 350 (M þ 1)
3.6.14. N-(3-chlorophenyl)-4-(4-fluorophenyl)[1,3]oxazolo[4,5-
c]quinolin-2-amine (6n)
Compound 6n was obtained as yellow solid. 1H NMR (300 MHz,
DMSO-d6) d; 7.18–7.14 (m, –CH, 2H), 7.53–7.43 (m, –CH, 2H), 7.83–
7.71 (m, –CH, 3H), 7.97 (s, –CH, 1H), 8.09 (d, –CH, 1H, J ¼ 8.4), 8.26
(d, –CH, 1H, J ¼ 8.4), 8.76–8.71 (m, –CH, 2H), 11.58 (s, NH, 1H, dis-
appeared on D2O exchange). 13C NMR (75 MHz, DMSO-d6)
d: 114.2,
116.3, 116.3, 116.7, 117.7, 120.1, 123.0, 126.0, 128.8, 129.5, 130.7, 131.2,
132.6, 133.9, 134.3, 139.7, 140.5, 145.0, 151.1, 158.6, 162.6, 165.9. LC–
MS (ESI) m/z 390 (M þ 1)
Acknowledgment
Authors are thankful to Dr. Ganesh Sambhasivam, CEO, Anthem
biosciences, Bangalore, India, for his invaluable support and allo-
cation of resources for this work. They are thankful to Dr. Suchetha
Shetty, Department of Biochemistry, Justice K.S. Hegde Medical
Academy, Deralakatte, India, for carrying out antibacterial
screening. They are also grateful to Dr. Guru Row, Solid State and
Structural Chemistry Unit (SSCU), Indian Institute Of Science, Ban-
galore, India, for carrying out single crystal X-ray diffraction studies.
3.7. Antibacterial testing by serial plate dilution method
Serial dilutions of the drug in Muller Hinton broth were taken in
tubes and their pH was adjusted to 5.0 using phosphate buffer. A
standardized suspension of the test bacterium was inoculated and
incubated for 16–18 h at 37 ꢀC. The minimum inhibitory concen-
tration (MIC) was noted by seeing the lowest concentration of the
drug at which there was no visible growth. A number of antimi-
crobial discs are placed on the agar for the sole purpose of
producing zones of inhibition in the bacterial lawn. Twenty milli-
liters of agar media was poured into each Petri dish. Excess of
suspension was decanted and plates were dried by placing in an
incubator at 37 ꢀC for an hour. Using an agar punch, wells were
made on these seeded agar plates and minimum inhibitory
concentrations of the test compounds in dimethylsulfoxide (DMSO)
were added into each labeled well. A control was also prepared for
the plates in the same way using solvent DMSO. The Petri dishes
were prepared in triplicate and maintained at 37 ꢀC for 3–4 days.
Antibacterial activity was determined by measuring the diameter of
inhibition zone in mm. Activity of each compound was compared
with ciprofloxacin as standard [38,39].
References
[1] WHO Global Tuberculosis Control Report, 2008.
[2] R. Jain, B. Vaitilingam, A. Nayyar, P.B. Palde, Bioorg. Med. Chem. Lett. 13 (2003)
1051–1054.
[3] WHO Weekly epidemiological record No. 15. 78 (2003)121–128.
[4] M. Zignol, M.S. Hosseini, A. Wright, C.L. Weezenbeek, P. Nunn, C.J. Watt,
C.G. Williams, C. Dye, J. Infect. Dis. 194 (2006) 479–485.
[5] A. Lilienkampf, J. Mao, B. Wan, Y. Wang, S.G. Franzblau, A.P. Kozikowski, J. Med.
Chem. 52 (2009) 2109–2118.
[6] P. Nasveld, S. Kitchener, Trans. R. Soc. Trop. Med. Hyg. 99 (2005) 2–5.
[7] P.A. Leatham, H.A. Bird, V. Wright, D. Seymour, A. Gordon, Eur. J. Rheumatol.
Inflamm. 6 (1983) 209–211.
[8] W.A. Denny, W.R. Wilson, D.C. Ware, G.J. Atwell, J.B. Milbank, R.J. Stevenson,
U.S Patent 7064117 (2006).
[9] A. Mahamoud, J. Chevalier, A. Davin-Regli, J. Barbe, Jean-Marie Pages, Curr.
Drug Targ. 7 (2006) 843–847.

966
S. Eswaran et al. / European Journal of Medicinal Chemistry 45 (2010) 957–966
[10] N. Muruganantham, R. Sivakumar, N. Anbalagan, V. Gunasekaran, J.T. Leonard,
Biol. Pharm. Bull. 27 (2004) 1683–1687.
[11] M.P. Maguire, K.R. Sheets, K. McVety, A.P. Spada, A. Zilberstein, J. Med. Chem.
37 (1994) 2129–2137.
[12] W.D. Wilson, M. Zhao, S.E. Patterson, R.L. Wydra, L. Janda, L. Strekowski, Med.
Chem. Res. 2 (1992) 102–110.
[27] A. Drabczyn´ ska, C.E. Mu¨ller, B. Schumacher, S. Hinz, J.K. Wojciechowska,
B.Michalak, E.Pe˛kala, K.K.Kononowicz, Bioorg.Med.Chem.12(2004)4895–4908.
[28] S. Eswaran, A.V. Adhikari, N.S. Shetty, Eur. J. Med. Chem. 44 (2009) 4637–4647.
[29] V. Colotta, F. Capelli, O. Lenzi, D. Catarzi, F. Varano, D. Poli, F. Vincenzi,
K. Varani, P.A. Borea, D.D. Ben, R. Volpini, G. Cristalli, G. Filacchioni, Bioorg.
Med. Chem. 17 (2009) 401–410.
[13] L. Strekowski, J.L. Mokrosz, V.A. Honkan, A. Czarny, M.T. Cegla, S.E. Patterson,
R.L. Wydra, R.F. Schinazi, J. Med. Chem. 34 (1991) 1739–1746.
[14] A.K. Aggarwal, S.A. Jenekhe, Macromolecules 24 (1991) 6806–6808.
[15] X. Zhang, A.S. Shetty, S.A. Jenekhe, Macromolecules 32 (1999) 7422–7429.
[16] S.A. Jenekhe, L. Lu, M.M. Alam, Macromolecules 34 (2001) 7315–7324.
[17] M.E. Jason, W.C. Robert, C. Mark, G.C. Gary, H.H. Peter, A.J. Brian, A. MacLeod,
M. Rose, M.L. Georgina, M. Elena, M. Fraser, R. Michael, R. Inmaculada,
G.N.R. Michael, S. Bindi, L.T. Kwei, W. Brian, Bioorg. Med. Chem. Lett. 50 (2006)
5748–5751.
[18] J. Nilsson, E.Ø. Nielsen, T. Liljefors, M. Nielsen, O. Sterner, Bioorg. Med. Chem.
Lett. 18 (2008) 5713–5716.
[19] M. Simeon, N. John, L. Georgia, K. Eleni, G. Vasiliki, T. Dimitrios, N. Pavlos, Int. J.
of Antimicrob. Agents 29 (2007) 738–748.
[20] N. Kaila, K. Janz, S. DeBernardo, P.W. Bedard, R.T. Camphausen, S. Tam,
D.H.H. Tsao, J.C. Keith Jr., C.N. Nutter, A. Shilling, R.Y. Sciame, Q. Wang, J. Med.
Chem. 50 (2007) 21–39.
[21] K.E. Andersen, B.F. Lundt, A.S. Jørgensen, C. Braestrup, Eur J Med Chem. 31
(1996) 417–425.
[22] H. Sasaki, Y. Haraguchi, M. Itotani, H. Kuroda, H. Hashizume, T. Tomishige,
M. Kawasaki, M. Matsumoto, M. Komatsu, H. Tsubouchi, J. Med. Chem. 49
(2006) 7854–7860.
[23] K. Mohamed, N.K. Venugopala, R. Mohana, R.G. Krishna, Lett. Drug Des. Discov.
6 (2009) 21–28.
[30] J.F. Gerster, K.J. Lindstrom, R.L. Miller, M.A. Tomai, W. Birmachu,
S.N. Bomersine, S.J. Gibson, L.M. Imbertson, J.R. Jacobson, R.T. Knafla,
P.V. Maye, N. Nikolaides, F.Y. Oneyemi, G.J. Parkhurst, S.E. Pecore, M.J. Reiter,
L.S. Scribner, T.L. Testerman, N.J. Thompson, T.L. Wagner, C.E. Weeks,
J.D. Andre, D. Lagain, Y. Bastard, M. Lupu, J. Med. Chem. 48 (2005) 3481–3491.
[31] M. Dinakaran, P. Senthilkumar, P. Yogeeswari, A. China, V. Nagaraja, D. Sriram,
Bioorg. Med. Chem. 16 (2008) 3408–3418.
[32] A. Marco, Loza-Mejı´a, S. Olvera-Va´zquez, K. Maldonado-Herna´ndez,
T.G. Salgado, I. Gonza´lez-Sa´nchez, F. Rodrı´guez-Herna´ndez, J.D. Solano,
R. Rodrı´guez-Sotres, A.L. Rocha, Bioorg. Med. Chem. 17 (2009) 3266–3277.
[33] T. Izumi, J. Sakaguchi, M. Takeshita, H. Tawara, Ken-ichi Kato, H. Dose,
T. Tsujino, Y. Watanabe, H. Kato, Bioorg. Med. Chem. 11 (2003) 2541–2550.
[34] A.L. Barry, Procedure for testing antimicrobial agents in agar media. in:
V.L. Corian (Ed.), Antibiotics in Laboratory Medicine. Williams and Wilkins,
Baltimore, MD, 1980, pp. 1–23.
[35] D. James, Mac. Lowry, J.M. Jaqua, T.S. Sally, Appl. Microbiol. 20 (1970) 46–53.
[36] A. Martin, M. Camacho, F. Portaels, J.C. Palomino, Resazurin microtiter assay
plate testing of Mycobacterium tuberculosis susceptibilities to second-line
drugs: rapid, simple, and inexpensive method. Antimicrob. Agents Chemother.
47 (2003) 3616–3619.
[37] A.Y. Coban, C.C. Cekic, K. Bilgin, M. Uzun, A. Akgunes, E. Cetinkaya,
B. Durupinar, Rapid susceptibility test for Mycobacterium tuberculosis to
isoniazid and rifampin with resazurin method in screw-cap tubes. J Chemo-
ther. 18 (2006) 140–143.
[24] R. Kuang, Ho-Jane Shue, D.J. Blythin, Neng-Yang Shih, D. Gu, X. Chen,
J. Schwerdt, L. Lin, P.C. Ting, X. Zhu, R. Aslanian, J.J. Piwinski, L. Xiao,
D. Prelusky, P. Wu, J. Zhang, X. Zhang, C.S. Celly, M. Minnicozzi, M. Billah,
Bioorg. Med. Chem. Lett. 17 (2007) 5150–5154.
[25] C. Jeong-woo, L. Sang-chul, M. Cheol-young, H. Sun-gwan, B. Sung-jin, K. Eun-
ae, WO Patent 075888 A1 (2006).
[38] C.H. Fenlon, M.H. Cynamon, Comparative in vitro activities of cipro-
floxacin and other 4-quinolones against Mycobacterium tuberculosis and
Mycobacterium intracellulare. Antimicrob. Agents Chemother 29 (1986)
386–388.
[39] R. Davis, A. Markham, J.A. Balfour, Ciprofloxacin, An updated review of its
pharmacology, therapeutic efficacy and tolerability. Drugs 51 (1996)
1019–1074.
[26] D.A. Evrard, D. Zhou, G.P. Stack, A.M. Venkatesan, A.A. Failli, S.C. Croce, US
Patent 7153849 B2 (2006).