Synthesis and antibacterial activity of nitroaryl thiadiazole-gatifloxacin hybrids

Article abstract of DOI:10.1016/j.ejmech.2008.09.012

A number of gatifloxacin analogues containing a nitroaryl-1,3,4-thiadiazole moiety attached to the piperazine ring at C-7 position were prepared and evaluated as antibacterial agents against a panel of Gram-positive and Gram-negative bacteria. Among synth

Full text of DOI:10.1016/j.ejmech.2008.09.012

European Journal of Medicinal Chemistry 44 (2009) 1205–1209
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antibacterial activity of nitroaryl thiadiazole–gatifloxacin hybrids
Seyyedehsamira Jazayeri a, Mohammad Hassan Moshafi b, Loghman Firoozpour c, Saeed Emami d,
Saeed Rajabalian b, Mitra Haddad c, Farahnaz Pahlavanzadeh b, Manzarbanoo Esnaashari a,
,c,
Abbas Shafiee c, Alireza Foroumadi b
*
a Department of Chemistry, Islamic Azad University, Tehran North-Branch, Tehran, Iran
b Faculty of Pharmacy and Pharmaceutical Sciences Research Center and Kerman Neuroscience Research Center, Kerman University of Medical Sciences, Kerman, Iran
c Department of Medicinal Chemistry, Faculty of Pharmacy and Pharmaceutical Sciences Research Center, Tehran University of Medical Sciences, Tehran 14174, Iran
d Department of Medicinal Chemistry and Pharmaceutical Sciences Research Center, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 18 April 2008
Received in revised form 1 September 2008
Accepted 4 September 2008
Available online 19 September 2008
A number of gatifloxacin analogues containing a nitroaryl-1,3,4-thiadiazole moiety attached to the
piperazine ring at C-7 position were prepared and evaluated as antibacterial agents against a panel of
Gram-positive and Gram-negative bacteria. Among synthesized compounds, nitrofuran analog 6a
exhibited more potent inhibitory activity against Gram-positive bacteria including Staphylococcus epi-
dermidis (MIC ¼ 0.0078
m
g/mL), Bacillus subtilis (MIC ¼ 0.0039
mg/mL), Enterococcus faecalis
g/mL), with respect to other synthesized
(MIC ¼ 0.125
m
g/mL) and Micrococcus luteus (MIC ¼ 0.125
m
Keywords:
Quinolones
Gatifloxacin
1,3,4-Thiadiazole
Nitrothiophene
Nitrofuran
compounds and reference drug gatifloxacin. The target compounds were also assessed for their cytotoxic
activity against normal mouse fibroblast (NIH/3T3) cells using MTT assay. The results indicated that these
compounds exhibit antibacterial activity at non-cytotoxic concentrations.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Nitroimidazole
Antibacterial activity
1. Introduction
barriers to penetration. With these in mind, previously several
hybrids of 5-(nitroaryl)-1,3,4-thiadiazoles and different quinolones
During recent years much attention has been devoted to the
synthesis of new fluoroquinolones and to their antibacterial
activity. Antibacterial resistance is now well documented for many
pathogens, and studies with a variety of bacteria indicate that
resistance can develop within just a few years. Resistance against
many members of fluoroquinolones, particularly older ones, such as
ciprofloxacin 1, is increasing. Further advances in quinolone field
are likely to provide better compounds capable of dealing with the
resistant strains [1–3].
The inhibition of DNA gyrase or DNA topoisomerase IV and cell
permeability of the quinolones are greatly influenced by the nature
of the C-7 substituent on the standard structure of 4-quinolone-3-
carboxylic acids. In addition, the substitution of bulky groups is
permitted at the C-7 position [4–6]. Furthermore, it has been
proposed that for Gram-positive organisms, increasing molecular
mass and bulkiness of a substituent at the C-7 position are not
including ciprofloxacin 1, norfloxacin 2, enoxacin 3 and levofloxacin
4 have been synthesized with enhanced antibacterial activity
against some Gram-positive organisms compared to the parent
quinolones [7,8]. Gatifloxacin 5, is a novel extended-spectrum flu-
oroquinolone (fourth-generation) with improved Gram-positive
and anaerobe coverage compared with older agents such as
ciprofloxacin 1 [9]. However, dysglycemia has been noted as the
life-threatening adverse effect of gatifloxacin, which led to its
withdrawal from the market in the United States in 2006 [10]. Thus,
there exists continuous need for novel gatifloxacin derivatives, with
better activity profile and tolerability, to overcome the limitations
of gatifloxacin.
In continuing our efforts to find new quinolone–nitro-
arylthiadiazole hybrids, herein we report the synthesis and
antibacterial activity of gatifloxacin hybrids 6 carrying a 5-(nitroaryl)-
1,3,4-thiadiazol-2-yl group (Fig. 1).
2. Results and discussion
* Corresponding author. Pharmaceutical Sciences Research Center, Tehran
University of Medical Sciences, Tehran 14174, Iran. Tel.: þ98 21 66954708; fax: þ98
21 66461178.
Our synthetic route to target compounds 6a–f is presented in
Fig. 2. The requisite 2-chloro-5-(nitroaryl)-1,3,4-thiadiazole 7a–f,
E-mail address: aforoumadi@yahoo.com (A. Foroumadi).
0223-5234/$ – see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.09.012

1206
S. Jazayeri et al. / European Journal of Medicinal Chemistry 44 (2009) 1205–1209
O
O
F
COOH
F
COOH
N
X
N
R
N
N
HN
N
O
H3C
CH3
1, Ciprofloxacin X=CH; R = cyclopropyl
2, Norfloxacin X=CH; R= ethyl
3, Enoxacin X=N; R= ethyl
4, Levofloxacin
O
O
N
F
COOH
F
COOH
N
N
OCH3
N
N N
S
HN
NO2-Ar
N
OCH3
CH3
CH3
5, Gatifloxacin
6
Fig. 1. Chemical structures of some piperazinyl quinolones and target compounds nitroaryl thiadiazole–gatifloxacin hybrids 6.
was prepared according to the previously described method [7,8].
Reaction of gatifloxacin 5, with 2-chloro-5-(nitroaryl)-1,3,4-thia-
diazole 7a–f, in DMF in the presence of NaHCO3 at 85–90 ꢀC, gave
compounds 6a–f (Table 1) [11,12].
Furthermore, the data obtained indicate that all compounds have
more or equal inhibitory activity against B. subtilis (MIC ¼ 0.0039–
0.5
m
g/mL), in comparison to reference drug (MIC ¼ 0.5
mg/mL),
with the exception of 6e (MIC ¼ 32
mg/mL). Most tested compounds
Compounds 6a–f, were tested in vitro by the conventional agar
dilution method against a panel of microorganisms including
Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC
4940, Streptococcus pneumonia ATCC 1240, Bacillus subtilis
ATCC 6051, Enterococcus faecalis NCTC 6013, Micrococcus luteus
ATCC 1110, Escherichia coli ATCC 25922, Salmonella typhi ATCC
19430, Shigella flexneri NCTC 8516, Klebsiella pneumonia ATCC
10031, Serratia marcescens PTCC 1111 and Pseudomonas aeruginosa
ATCC 27853 [13]. The minimum inhibitory concentration values
(MICs) were determined by comparison to the parent quinolone,
gatifloxacin 5 as reference drug (Table 2).
had respectable in vitro activity against E. faecalis, but were
less active than reference drug, with the exception of 6a
(MIC ¼ 0.125
gatifloxacin. Compounds 6a, d and f possessed a comparable or
better activity against M. luteus (MIC ¼ 0.125–1 g/mL), with
g/mL).
mg/mL), which was fourfold more potent than
m
respect to gatifloxacin (MIC ¼ 1
m
Generally, compounds 6a–d and f showed moderate to good
activity against Gram-negatives including E. coli, S. typhi, S. flexneri,
K. pneumoniae and S. marcescens but were less active than reference
drug, with the exception of 6c for K. pneumoniae (MIC ¼ 0.5
mg/mL).
In contrast, all the synthesized compounds did not show significant
activity against another Gram-negative bacteria, P. aeruginosa
(MICs >64).
The MIC values of compounds 6a–f against Staphylococcus strain
indicated that some compounds possess a comparable or better
activity with respect to gatifloxacin. Compound 6c, exhibited the most
Among synthesized compounds, nitrofuran analog 6a exhibited
the most potent inhibitory activity against Gram-positive
potent inhibitory activity against S. aureus (MIC ¼ 0.0313
compound 6a showed the most inhibitory activity against
g/mL), which were two and eightfold
mg/mL), and
bacteria including S. epidermidis (MIC ¼ 0.0078
(MIC ¼ 0.0039 g/mL), E. faecalis (MIC ¼ 0.125 g/mL) and M. luteus
(MIC ¼ 0.125 g/mL), with respect to other synthesized compounds
g/
g/mL) was equal to reference
mg/mL), B. subtilis
S. epidemidis (MIC ¼ 0.0078
m
m
m
more potent than their parent quinolone (gatifloxacin 5), respectively.
The MIC values of compounds 6a–f against S. pneumonia indicated
that 4-nitrophenyl analog 6f showed the most potent activity
m
and reference drug. Its inhibitory activity against E. coli (MIC ¼ 1
m
mL) and S. pneumonia (MIC ¼ 0.25
m
(MIC ¼ 0.0625
m
g/mL). Its activity was fourfold more than that
drug gatifloxacin.
of gatifloxacin. In addition, compounds 6a, b and d exhibited
The in vitro cytotoxic activity of the test compounds 6a–f against
potent activity (MIC ¼ 0.25
m
g/mL) comparable to gatifloxacin.
normal mouse fibroblast cell line (NIH/3T3) was investigated using
O
O
F
COOH
F
COOH
N
N
N
N
NaHCO3, DMF
N N
N
N
NO2-Ar
OCH3
N
HN
OCH3
S
CH3
6a-f
Cl
NO2-Ar
CH3
S
5
7a-f
Fig. 2. Synthetic route to target compounds 6a–f.

S. Jazayeri et al. / European Journal of Medicinal Chemistry 44 (2009) 1205–1209
1207
Table 1
Structural and physicochemical data of compounds 6a–f
O
N
F
COOH
N
N
N
NO2-Ar
N
OCH3
S
CH3
Compound
NO2-Ar
Mp (ꢀC)
Formula
Yield (%)
Anal. Calcd (Found) %
C
N
H
NO2
6a
263–265
C25H23FN6O7S
58
52.63 (52.88)
51.19 (51.31)
14.73 (14.71)
4.06 (4.03)
3.95 (4.02)
O
S
NO2
NO2
6b
6c
250–252
272–274
C25H23FN6O6S2
64
62
14.33 (14.35)
19.17 (19.17)
N
N
C25H25FN8O6S
51.36 (51.28)
55.86 (55.99)
4.31 (4.32)
CH3
6d
270–272
C27H25FN6O6S
69
14.48 (14.33)
4.34 (4.41)
NO2
6e
6f
168–170
267–269
C27H25FN6O6S
66
67
55.86 (55.90)
55.86 (55.77)
14.48 (14.45)
14.48 (14.53)
4.34 (4.48)
4.34 (4.30)
NO2
NO2
C27H25FN6O6S
MTT colorimetric assay [14]. The IC50 values obtained for these
compounds in comparison with reference drug gatifloxacin 5 are
shown in Table 3. All compounds did not show significant activity
against normal mouse fibroblast cell line at concentrations
negative bacteria. Similarly, N-[nitroaryl-1,3,4-thiadiazol-2-yl]
moieties are well tolerated at the piperazine ring of gatifloxacin and
the type of nitroaryl pendent on the 1,3,4-thiadiazole can modulate
the antibacterial activity. Structurally, these new series of
compounds distinct from ciprofloxacin derivatives solely by the
introduction of methoxy group to the C-8 position of quinolone core
and 3-methyl group to the piperazinyl residue at C-7 of the parent
drug. Comparison between MIC values of gatifloxacin derivatives
and corresponding ciprofloxacin derivatives reveal that these
modifications in nitroaryl thiadiazole–quinolone hybrids can
improve the antibacterial potency especially against Gram-positives.
<100
tives 6a–c and 4-nitrophenyl analog 6f showed inferior toxicity
with IC50 values of >200 M and there was no significant differ-
mM. Among the test compounds, 5-nitroheteroaryl deriva-
m
ences between the cytotoxicity of these compounds. As can be seen
from the results, these compounds display antibacterial activity at
non-cytotoxic concentrations.
In the previous works, we identified that the incorporation of 5-
(5-nitroheteroaryl)-1,3,4-thiadiazol-2-yl groups as
a particular
chemical modification at the piperazine residue of piperazinyl qui-
nolones such as ciprofloxacin, norfloxacin, enoxacin and levo-
floxacin allows manipulation of selectivity and potency of these
compounds [7,8]. As is evident from the data of present work, the N-
[nitroaryl-1,3,4-thiadiazol-2-yl]gatifloxacin derivatives 6a–f exhibit
high activity against Gram-positive and less activity against Gram-
3. Experimental
3.1. Chemistry
Chemical and all solvents used in this study were purchased
from Merck AG and Aldrich chemical. Melting points were

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S. Jazayeri et al. / European Journal of Medicinal Chemistry 44 (2009) 1205–1209
Table 2
In vitro antibacterial activities of compounds 6a–f and reference drug gatifloxacin against selected strains (MICs in mg/mL)
Microorganisms
6a
6b
6c
6d
32
0.0625
0.25
0.0625
2
0.5
16
16
16
64
6e
6f
32
0.0625
0.0625
0.0313
1
0.25
16
8
8
64
16
5a
Staphylococcus aureus ATCC 25923
Staphylococcus epidermidis ATCC 4940
Streptococcus pneumonia ATCC 1240
Bacillus subtilis ATCC 6051
Enterococcus faecalis NCTC 6013
Micrococcus luteus ATCC 1110
Escherichia coli ATCC 25922
Salmonella typhi ATCC 19430
Shigella flexneri NCTC 8516
Klebsiella pneumonia ATCC 10031
Serratia marcescens PTCC 1111
Pseudomonas aeruginosa ATCC 27853
0.125
0.0078
0.25
0.0039
0.125
0.125
1
1
0.5
1
8
0.5
0.125
0.25
0.5
2
0.0313
0.5
1
0.5
4
2
>64
0.25
0.0625
0.25
0.5
0.5
1
0.0313
1
32
>64
1
>64
>64
>64
>64
>64
>64
4
32
16
1
1
1
0.25
1
0.5
0.0625
0.0625
0.5
0.5
2
16
8
>64
64
>64
16
>64
>64
>64
a
Gatifloxacin.
determined on a Kofler hot stage apparatus and are uncorrected.
The IR spectra were obtained on a Shimadzu 470 spectrophotom-
eter (potassium bromide disks). 1H NMR spectra were recorded
using a Bruker 500 spectrometer and chemical shifts are expressed
and cyclopropyl), 3.72 (s, 3H, CH3O), 7.59 (s, 1H, H3-thiophen), 7.81
(d, 1H, H5-quinolone, J ¼ 12 Hz), 8.16 (s, 1H, H4-thiophen), 8.71 (s,
1H, H2-quinolone), 14.84 (s, 1H, COOH). IR (KBr, cmꢁ1): 1729 and
1618 (C]O), 1511 and 1347 (NO2). 13C NMR (125 MHz, DMSO-d6)
d:
as
d
(ppm) with tetramethylsilane as internal standard.
8.87, 13.69, 35.12, 45.24, 49.83, 53.88 (C5 piperazine), 63.83, 106.80
(d, C8 quinolone, 3JC-F ¼ 3.30 Hz), 113.12, 114.27 (d, C5 quinolone, 2JC-
3
¼ 22.20 Hz), 121.14 (d, C4a quinolone, JC-F ¼ 7.50 Hz), 127.98,
3.2. General procedure for the synthesis of compounds 6a–f
F
2
129.23, 137.19, 138.38, 139.28 (d, C7 quinolone, JC-F ¼ 9.75 Hz),
1
146.24 (d, C6 quinolone, JC-F ¼ 245.20 Hz), 149.11, 153.35, 154.69,
A mixture of compound 7 (0.5 mmol), gatifloxacin 5 (0.5 mmol),
and NaHCO3 (42 mg, 0.5 mmol) in DMF (10 mL), was heated at 85–
90 ꢀC for 12 h. After consumption of gatifloxacin (monitored by
TLC), H2O (20 mL) was added and the precipitate was filtered and
washed with water to give the crude 6. Purification was achieved by
passage through a short silica gel column (chloroform–ethanol;
95:5). The product was crystallized from DMF–H2O to give 6a–f.
165.47, 165.85, 176.42 (d, C4 quinolone, 4JC-F ¼ 2.30 Hz).
3.2.3. 1-Cyclopropyl-6-fluoro-7-[4-[5-(1-methyl-5-nitro-1H-
imidazol-2-yl)-1,3,4-thiadiazol-2-yl]-3-methylpiperazin-1-yl]-8-
methoxy-4-oxo-quinoline-3-carboxylic acid (6c)
1H NMR (500 MHz, DMSO-d6)
d: 1.04–1.53 (m, 4H, cyclopropyl),
1.41 (d, 3H, CH3-piperazine, J ¼ 6.5 Hz), 3.30–3.98 (m, 8H, piperazine
and cyclopropyl), 3.75 (s, 3H, CH3O), 4.35(s, 3H, CH3-imidazole), 7.80
(d,1H, H5-quinolone, J ¼ 11.5 Hz), 8.23 (s,1H, imidazole), 8.73 (s,1H,
H2-quinolone), 14.78 (s, 1H, COOH). IR (KBr, cmꢁ1): 1736 and 1623
3.2.1. 1-Cyclopropyl-6-fluoro-7-[4-[5-(5-nitrofuran-2-yl)-1,3,4-
thiadiazol-2-yl]-3-methylpiperazin-1-yl]-8-methoxy-4-oxo-
quinoline-3-carboxylic acid (6a)
(C]O), 1516 and 1357 (NO2). 13C NMR (125 MHz, DMSO-d6)
d:
1H NMR (500 MHz, DMSO-d6)
d: 0.95–1.58 (m, 4H, cyclopropyl),
8.99, 13.75, 18.65, 35.08, 45.30, 49.75, 53.90, 63.80, 106.80 (d, C8
1.40 (d, 3H, CH3-piperazine, J ¼ 6.5 Hz), 3.33–3.90 (m, 8H, pipera-
zine, and cyclopropyl), 3.72 (s, 3H, CH3O), 7.48 (s,1H, H3-furan), 7.80
(d, 1H, H5-quinolone, J ¼ 12 Hz), 8.10 (s, 1H, H4-furan), 8.73 (s, 1H,
H2-quinolone), 14.82 (s, 1H, COOH). IR (KBr, cmꢁ1): 1724 and 1619
3
2
quinolone, JC-F ¼ 3.30 Hz), 113.00, 114.20 (d, C5 quinolone, JC-
3
¼ 22.00 Hz), 121.30 (d, C4a quinolone, JC-F ¼ 7.00 Hz), 132.90,
F
134.10,138.40,139.30 (d, C7 quinolone, 2JC-F ¼ 9.50 Hz),146.20 (d, C6
quinolone, 1JC-F ¼ 245.10 Hz), 149.21, 153.25, 165.70, 165.70, 171.42,
176.42 (d, C4 quinolone, 4JC-F ¼ 2.30 Hz).
(C]O), 1521 and 1351 (NO2). 13C NMR (125 MHz, DMSO-d6)
d: 8.93,
13.44, 34.98, 45.56, 49.66, 53.85, 63.79, 106.59 (d, C8 quinolone, 3JC-
¼ 3.24 Hz),112.99,114.21 (d, C5 quinolone, 2JC-F ¼ 22.35 Hz),121.32
F
(d, C4a quinolone, 3JC-F ¼ 7.45 Hz), 122.34, 122.87, 138.43, 138.98 (d,
3.2.4. 1-Cyclopropyl-6-fluoro-7-[4-[5-(2-nitrophenyl)-1,3,4-
thiadiazol-2-yl]-3-methylpiperazin-1-yl]-8-methoxy-4-oxo-
quinoline-3-carboxylic acid (6d)
2
1
C7 quinolone, JC-F ¼ 9. 60 Hz), 146.38 (d, C6 quinolone, JC-
¼ 245.00 Hz), 148.91, 149.19, 153.40, 154.83, 165.34, 165.98, 176.56
F
1H NMR (500 MHz, DMSO-d6)
d: 1.04–1.50 (m, 4H, cyclopropyl),
(d, C4 quinolone, 4JC-F ¼ 2.25 Hz).
1.42 (d, 3H, CH3-piperazine, J ¼ 6.5 Hz), 3.30–4.31 (m, 8H, pipera-
zine and cyclopropyl), 3.76 (s, 3H, CH3O), 7.62 (m, 2H, phenyl), 7.70
(m, 1H, phenyl), 7.95 (d, 1H, H5-quinolone, J ¼ 12 Hz), 8.05 (d, 1H,
phenyl, J ¼ 6.5 Hz), 8.86 (s, 1H, H2-quinolone), 14.82 (s, 1H, COOH).
IR (KBr, cmꢁ1): 1731 and 1623 (C]O), 1541 and 1372 (NO2). 13C
3.2.2. 1-Cyclopropyl-6-fluoro-7-[4-[5-(5-nitrothiophen-2-yl)-1,3,4-
thiadiazol-2-yl]-3-methylpiperazin-1-yl]-8-methoxy-4-oxo-
quinoline-3-carboxylic acid (6b)
1H NMR (500 MHz, DMSO-d6)
d: 0.90–1.54 (m, 4H, cyclopropyl),
NMR (125 MHz, DMSO-d6) d: 8.54, 13.56, 34.88, 45.23, 49.77, 53.92,
1.41 (d, 3H, CH3-piperazine, J ¼ 6.5 Hz), 3.30–3.99 (m, 8H, piperazine
63.74, 106.80 (d, C8 quinolone, 3JC-F ¼ 3.25 Hz), 113.22, 114.12 (d, C5
2
3
Table 3
quinolone, JC-F ¼ 22.25 Hz), 121.00 (d, C4a quinolone, JC-
Cytotoxic activity of compounds 6a–f in comparison with gatifloxacin 5, against
mouse fibroblast (NIH/3T3) cell line
¼ 7.38 Hz),121.58,128.58,129.03,135.65, 138.43, 139.02,139.32 (d,
F
2
1
C7 quinolone, JC-F ¼ 9.75 Hz), 146.24 (d, C6 quinolone, JC-
Compound
IC50 (m
M)a
¼ 245.20 Hz), 149.11, 149.43, 153.50, 165.49, 165.79, 176.34 (d, C4
F
6a
6b
6c
6d
6e
6f
5
238 ꢂ 27
243 ꢂ 35
246 ꢂ 37
168 ꢂ 32
161 ꢂ 4.8
223 ꢂ 31
596 ꢂ 42
quinolone, 4JC-F ¼ 2.28 Hz).
3.2.5. 1-Cyclopropyl-6-fluoro-7-[4-[5-(3-nitrophenyl)-1,3,4-
thiadiazol-2-yl]-3-methylpiperazin-1-yl]-8-methoxy-4-oxo-
quinoline-3-carboxylic acid (6e)
1H NMR (500 MHz, DMSO-d6)
d: 0.99–1.48 (m, 4H, cyclopropyl),
a
1.43 (d, 3H, CH3-piperazine, J ¼ 6.5 Hz), 3.35–4.33 (m, 8H, pipera-
IC50 is the concentration required to inhibit 50% of cell growth. The values
represent mean ꢂ SD.
zine and cyclopropyl), 3.75 (s, 3H, CH3O), 7.81 (d, 1H, H5-quinolone,

S. Jazayeri et al. / European Journal of Medicinal Chemistry 44 (2009) 1205–1209
1209
J ¼ 12 Hz), 7.83 (t, 1H, phenyl, J ¼ 8 Hz), 8.30–8.31 (m, 1H, phenyl),
8.39–8.41 (m, 1H, phenyl), 8.43–8.54 (m, 1H, phenyl), 8.73 (s, 1H,
H2-quinolone), 14.90 (s, 1H, COOH). IR (KBr, cmꢁ1): 1738 and 1618
MTT colorimetric assay. Briefly, cultures in the exponential
growth phase were trypsinized and diluted in complete growth
medium to give a total cell count of 5 ꢃ104 cells/mL. The cell
(C]O), 1531 and 1347 (NO2). 13C NMR (125 MHz, DMSO-d6)
d: 8.52,
suspension (100
After plating, 50
m
m
L) was added to wells of sterile 96-well plates.
L of a serial dilution of every agent was added.
13.66, 35.02, 45.29, 49.83, 54.08, 63.68, 106.92 (d, C8 quinolone, 3JC-
2
¼ 3.30 Hz), 113.22, 114.23 (d, C5 quinolone, JC-F ¼ 22.30 Hz),
Each compound dilution was assessed in triplicate. Three wells
containing only normal mouse fibroblast (NIH/3T3) cells sus-
F
3
120.89 (d, C4a quinolone, JC-F ¼ 7.50 Hz), 122.08, 123.07, 128.23,
2
129.88,138.38, 139.33 (d, C7 quinolone, JC-F ¼ 9. 75 Hz), 139.59,
pended in 150
cell viability. The plates were then incubated for 72 h. After
incubation, 30 L of a 5 mg/mL solution of MTT was added to
each well and the plate was incubated for another 1 h. After
incubation, the culture medium was replaced with 100 L of
mL of complete medium were used as control for
1
146.29 (d, C6 quinolone, JC-F ¼ 245.15 Hz), 149.21, 153.43, 165.50,
165.77, 176.41 (d, C4 quinolone, 4JC-F ¼ 2.25 Hz).
m
3.2.6. 1-Cyclopropyl-6-fluoro-7-[4-[5-(4-nitrophenyl)-1,3,4-
thiadiazol-2-yl]-3-methylpiperazin-1-yl]-8-methoxy-4-oxo-
quinoline-3-carboxylic acid (6f)
m
DMSO. Then, the absorbance of each well was measured by
using a microplate reader at 492 nm wavelengths. For each
compound, dose–response curve was measured with different
drug concentrations, and the concentration causing 50% cell
1H NMR (500 MHz, DMSO-d6)
d: 1.00–1.59 (m, 4H, cyclopropyl),
1.52 (d, 3H, CH3-piperazine, J ¼ 6.5 Hz), 3.42–4.32 (m, 8H, pipera-
zine and cyclopropyl), 3.79 (s, 3H, CH3O), 7.80 (d, 1H, H5-quinolone,
J ¼ 11.5 Hz), 8.07 (d, 2H, phenyl, J ¼ 8.5 Hz), 8.40 (d, 2H, phenyl,
J ¼ 8.5 Hz), 8.72 (s, 1H, H2-quinolone), 14.85 (s, 1H, COOH). IR (KBr,
cmꢁ1): 1726 and 1623 (C]O), 1521 and 1332 (NO2). 13C NMR
growth inhibition (IC50
calculated.
) compared with the control was
(125 MHz, DMSO-d6) d: 8.58,13.59, 34.92, 45.14, 49.88, 53.92, 63.78,
Acknowledgments
3
106.84 (d, C8 quinolone, JC-F ¼ 3.32 Hz), 113.13, 114.32 (d, C5 qui-
2
3
nolone, JC-F ¼ 22.25 Hz), 121.09 (d, C4a quinolone, JC-F ¼ 7.45 Hz),
We would like to thank the Cipla Pharmaceutical Company for
providing gatifloxacin. This work was supported by grants from the
Research Council of Kerman University of Medical Sciences and Iran
National Science Foundation (INSF).
2
122.08, 129.03, 138.38, 139.28 (d, C7 quinolone, JC-F ¼ 9. 75 Hz),
1
139.02, 146.24 (d, C6 quinolone, JC-F ¼ 245.20 Hz), 149.11, 149.43,
153.34, 165.54, 165.84, 176.40 (d, C4 quinolone, 4JC-F ¼ 2.28 Hz).
3.3. Antibacterial activity [13]
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