Design, synthesis and antibacterial evaluation of novel fluoroquinolone and its derivatives

Article abstract of DOI:10.14233/ajchem.2014.15572

Gatifloxacin isomers, [1-cyclopropyl-6-fluoro-1,4-dihydro-8-methoxy-7-(2- methyl-1-piperazinyl)-4-oxo-3-quinoline carboxylic acid] and a series of its derivatives were designed and synthesized and evaluated for their in vitro antibacterial activities. Pre

Full text of DOI:10.14233/ajchem.2014.15572

Asian Journal of Chemistry; Vol. 26, No. 1 (2014), 209-215
http://dx.doi.org/10.14233/ajchem.2014.15572
Design, Synthesis and Antibacterial Evaluation of Novel Fluoroquinolone and its Derivatives
1
1
1
2
2
2
1,*
KANG-MIN WANG , YUAN-CHENG QIN , GUAN-JUN CHENG , HUA-JUN ZHU , LONG LIANG , ZHI-PENG CHENG and MEI-MING LUO
1Key Laboratory of Green Chemistry and Technology of Ministry of Education at Sichuan University, College of Chemistry, Sichuan University,
No. 29 Wangjiang Road, Chengdu 610064, Sichuan Province, P.R. China
2Sichuan Kelun Pharmaceutical Co. Ltd, 18, 19/F, 2/Building, Jinjiang Times Garden, 107 Jinli West Road, Chengdu 610067, P.R. China
*Corresponding author: Tel/Fax: +86 28 85462021; E-mail: luomm@scu.edu.cn
Received: 3 April 2013;
Accepted: 25 May 2013;
Published online: 26 December 2013;
AJC-14506
Gatifloxacin isomers, [1-cyclopropyl-6-fluoro-1,4-dihydro-8-methoxy-7-(2-methyl-1-piperazinyl)-4-oxo-3-quinoline carboxylic acid] and
a series of its derivatives were designed and synthesized and evaluated for their in vitro antibacterial activities. Preliminary results
indicated that the tested compounds GI1, GI2, GI3 and GI4 demonstrated excellent activity against Staph. epidermidis. In addition,
compounds GI1, GI3 and GI4 show MIC 0.015 µg/mL against Klebsiella peneumoniae. It is worth noting that compound GI2 has been
found to exhibit the most prominent activity against all of the tested stains. On the basis of these promising results, some tested compounds
could be selected as potential drugs candidate for further evaluation.
Keywords: : Gatifloxacin isomers, 8-Methoxyfluoroquinolones, 2-Methylpiperazine, Antibacterial activities.
the nature of the C-7substituent5a-b. According to structure
activity relationship (SAR) analysis of fluoroquinolones,
modification of the substituents at the C-7 position is the most
INTRODUCTION
Since the discovery of norfloxacin in the early 1980s1,
adaptable site for chemical change and an area that could
affect their potency, spectrum and safety. At the C-7, the
piperazinyl groups have been utilized with optimal results.
Extensively investigated substituents are 3-substituted
piperazin-1-yl and 4-substituted derivatives. For example,
gatifloxacin is 3-methyl piperazin-1-yl derivative. Pefloxacin,
the 4-methylnorfloxacin and other 4-substituted piperazin-1-
yl prodrugs of norfloxacin were prepared to improve the
bioavailability of the parent6a-c. Furthermore, some studies have
demonstrated that increasing molecular mass and bulkiness
of a substituent at the C-7 position are not barriers to penetra-
tion and simply increasing the lipophilic character at C-7 in-
creased the potent activity7. The antiproliferative activity of
bis-quinolinium choline kinase inhibitors against the HT-29
colon cancer cell line has been improved with a higher
lipophilicity of the substituents8. It was reported that 8-OCH3
fluoroquinolones with N1-cyclopropyl substitution are much
more bactericidal activity than C-8 hydrogen analogs9.
Gatifloxacin (4th-generation, Fig. 1), having a particularly
strong in vitro activity and broad antimicrobial spectrum, could
be promising agents10a,b. 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
200611. Despite many advances in gatifloxacin, there exsist
fluoroquinolones (FQs) were found to have enhanced pharma-
cokinetics properties and potent bactericidal activity, when
compared to the previous existing bactericidal drugs. However,
the extensive clinical use of fluoroquinolones resulted in an
increased quinolone resistance among many pathogens2a-f. In
addition, certain adverse events (e.g. CNS, phototoxicity and
arthropathy) became apparent, although the more serious
events are rare3a-b. Consequently, great efforts have been devoted
towards the synthesis of novel fluoroquinolones in the recent years.
The search for new fluoroquinolones to overcome growing
bacterial resistance focuses largely on two approaches. One is
to identify novel targets where no pre-existing resistance exists4.
This approach, although sound in concept, has been met with
little success in identifying quality lead matter due to issues
associated with target validation and low hit rates from high
throughput screening. The second approach is to explore
existing clinically proven targets for new chemical matter or
modify existing matter with limited or no cross-resistance to
existing agents, eliminating the risk of target validation. This
approach has been used successfully by a number of researchers
to identify new series of fluoroquinolones.
The bactericidal activity of fluoroquinolones is caused
by the inhibition of bacterial type-2 topoisomerase (DNA
gyrase and topoisomerase IV), which is greatly influenced by

210 Wang et al.
Asian J. Chem.
continuous need for novel quinolones to overcome the limitation
of gatifloxacin.
fluoroquinolones with especially high in vitro activity against
Gram-positive bacteria16. These research results intensified our
interest, herein a number of new derivatives of fluoro-
quinolones were synthesized by introduction of diversified
substituents, including alkyl, acyl and sulfonyl, to the nitrogen
atom of the piperazine ring of the gatifloxacin isomer. More-
over, a SAR study is also explored to facilitate the further
development of the fluoro-quinolones. The synthesis of ethyl
ester derivative 2 has been reported earlier17 and serverd as
our key intermediate. We developed a practical and efficient
synthesis as a general route to gatifloxacin isomer GI-H
(Scheme-I).
O
O
O
OH
F
F
OH
O
N
N
HN
O
HN
O
Gatifloxacin
Fig. 1. Gatifloxacin and gatifloxacin isomer (GI-H)
GI-H
Gatifloxacin isomer (
)
2-Methylpiperazine was treated with di-tert-butyl
dicarbonate to produce Boc-protected 2-methylpiperazine (3)
prior to the substitution reaction to avoid the formation of
eonormous quanities of gatifloxacin as byproduct and improve
selection and purification of 7-C substituted gatifloxacin isomer.
Since direct nucleophilic aromatic substitution of inter-
mediate 2 and Boc-protected 2-methylpiperazine met with no
success, a new procedure have been designed, in which boron
chelate-type intermediate 4, prepared according to previously
published methods18, was treated with compound 3 to over-
come the diminished reactivity induced by the 8-methoxy
group and the steric hindrance induced by methyl neighbouring
electrophilic nitrogen atom. The subsequent cleavage step and
Boc deprotection could be combined to one-pot process.
Namely, refluxing compound 5 in methanol during for 12 h to
be sufficient to perform this cleavage, monitored by thin-layer
chromatography, then concentrated hydrochloric acid was
added and the Boc protective group of compound 6 was
removed to afford the novel compound GI-H. The whole
process is easy to workup without column chromatography
purification that makes it possible to scale up.
In an effort to discover new classes of antibacterial agents,
it was wisely decided to make structure modifications on
gatifloxacin. Sekine and his coworkers suggested that the
planar feature between the C-7 piperazinyl ring and the
naphthyridine nucleus of enoxacin may affect flouroquinolone
to interact with the narrow binding site of the enzyme12,13. Bulk
group on the 7-position, might restrict the free rotation around
the bond axis between the C-7 carbon and the piperazinyl
N-1 nitrogen in combination with the fluorine atoms at C-6
and methoxyl at C-8 and accordingly make the dihedral angle
change, thus possibly tracking the problem of bacterial resis-
tance and dysglycemic effects. Therefore, we here first reported
the synthesis of gatifloxacin isomer (Scheme-I) by introducing
methyl group at position 2 on the piperazin-1-yl ring, which
1
was determined by H NMR, 13C NMR, mass spectrometry
analysis. As expected, it show excellent antibacterial activity,
particularly against Klebsiella pneunoniae, when compared
to gatifloxacin. Furthermore, acylation and alkylation of
piperazine are important structural elements14, present in a
number of investigational and established drugs15. It is reported
that sulfonyl fluoroquinolones are a new class of antibacterial
CH3
O
O
O
CH3
a
+
HN
NH
N
NH
O
O
O
O
3
F2
B
O
O
N
c
F
O
O
N
OEt
F
F
b
O
F
OMe
OMe
2
4
F2
B
O
OH
O
N
OH
O
O
N
F
F
F
O
O
O
d
d
N
N
N
N
OMe
OMe
OMe
HN
N
N
o
o
5
6
GI-H
o
o
Scheme-I: Reactions and conditions: (a) di-tert-butyl dicarbonate (1 equiv), 2-methylpiperazine (1 equiv), CH2CI2, 0 °C, 1h, 93 % for 3; (b) BF3-Et2O (13
equiv), ethyl ester derivative (1 equiv), THF, reflux, 2d, 56 % for 4; (c) boron chelate-type intermediate (1 equiv), Boc-protected 2-methyl
piperazine (2.1 equiv), DMSO, 0 °C, 0.5 h, then 40 °C, 3d, 23 % for 5; (d) CH3OH, reflux, 12 h, then 0 °C, HCI(aq), 0.5 h, 40 % for GI-H

Vol. 26, No. 1 (2014)
Design, Synthesis and Antibacterial Evaluation of Novel Fluoroquinolone and its Derivatives 211
A series of novel GI-H derivatives (Fig. 2.) were achieved
through the versatile and efficient synthetic route as following.
Preparation of N-alkyl-substituted GI: Compounds GI-
5, GI-7 and GI1-3 were easily prepared by alkylation of GI-
H by nucleophilic substitution with their corresponding
halohydrocarbons (Scheme-II). For example, compound GI-
5 was obained by treatment of GTFXS and triethylamine with
benzyl chloride in dichloromethane at room temperature.
Preparation of N-acyl and N-sulfonyl substituted GIS:
Reaction of GI-H with a suitable acyl chloride, (Scheme-III)
in the presence of triethylamine was performed in dichloro-
methane solution at room temperature, to afford derivatives
GI-8, GI-9, GI-10 and GI-11, respectively. Using a suitable
anhydride (Scheme-IV) instead of acyl chloride, the acetyl
derivative GI-1 and GI-2 was obtained. GI-H under the same
condition was treated with the selected sulfonyl chloride, pre-
pared from the corresponding sulfonic acid and thionyl
chloride, to provide derivatives (Scheme-IV) GI-3 and GI-6,
respectively.
EXPERIMENTAL
All non-aqueous reactions were performed under an
atmosphere of dry Ar (99.99 %) using oven-dried glassware
and anhydrous solvents. All reagents were obtained from
commercial sources and used without further purification.
Melting points were determined on an XRC-1 capillary melting
point apparatus and are uncorrected. Thin layer chromatography
was carried out by using Merck silica gel GF254 plates. Low-
resolution mass spectra were recorded on a Finnigan Surveyor
MSQ instrument. H NMR (400 MHz) and 13C NMR (100
1
MHz) spectra were determined on a Bruker-400 spectrometer
in DMSO-d6 or CDCl3 using tetramethylsilane (TMS) as an
internal standard.
1-Cyclopropyl-6-fluoro-1,4-dihydro-8-methoxy-7-(2-
methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic acid (GI-H).
Step-1 Boc Protection of 2-methylpiperazine: Di-tert-
butyl dicarbonate (16.35 g, 0.075 mol) in CH2Cl2 (50 mL)
was added to a solution of racemic 2-methylpiperazine (7.50 g,
O
O
O
F
COOH
F
COOH
F
COOH
N
N
N
N
N
N
O
N
O
N
O
HN
O
O
O
GI-1
GI-H
GI-2
O
O
N
O
N
F
COOH
F
COOH
F
COOH
N
N
N
N
O
N
O
N
O
N
S
O O
O
S
O
GI-3
GI-4
GI-5
O
N
O
N
O
O
N
O
F
COOH
F
F
OH
OH
N
N
N
N
N
O
N
O
N
O
N
GI-8
O
GI-6
GI-7
O
O
O
O
O
N
O
F
F
OH
F
OH
OH
F
N
N
N
N
N
Br
N
O
N
O
N
O
O
O
O
O
O
GI-9
GI-11
GI-10
O
N
O
F
OH
O
N
N
O
N
O
GI-12
Fig. 2. Structures of the novel fluoroquinolones

212 Wang et al.
Asian J. Chem.
O
O
N
O
O
N
F
F
OH
OH
CH2Cl2
Et3N
R1
X
R1
N
N
HN
N
+
OMe
GI-H
OMe
CH3
CH3
GI
GI-4:
GI-6:
GI-12:
Cl
Cl
R1X:
Cl
N
O
,
,
O
GI
7
8
9
GI
O
N
O
Scheme-II: Synthetic route of compound GI-4, GI-6, GI-12
O
O
O
O
N
F
F
OH
OH
CH2Cl2
O
SOCI2
R2COOH
N
RCOCI
N
N
+
HN
N
Et3N
R2
OMe
OMe
CH3
R2COOH:
N
CH3
F
N
GI-8:
GI
COOH
COOH
11
F
10
O
COOH
GI-9:
GI
O
Br
COOH
O
O
O
12
13
GI
GI-10:
GI-11:
O
O
O
Br
GI
Scheme-III: Synthetic route of compound GI-8, GI-9, GI-10 and GI-11
O
O
O
N
O
N
F
F
OH
OH
O
O
O
CH2Cl2
Et3N
R3
R3
C O C
+
N
N
HN
N
R3
OMe
OMe
CH3
CH3
R3 = CH3-, (CH3)3C-.
GI-1: CH3CO-GI
GI-2: (CH3)3CCO-GI
O
O
O
O
F
F
OH
OH
O
O
CH Cl
2
2
4
N
N
R
S
Cl
S
4
N
N
+
HN
N
Et N
3
OMe
R
OMe
O
O
CH
CH
3
3
R4 = CH3-, p-methylphenyl
GI-3: CH3SO2-GI
GI-5: Tosyl-GI
Scheme-IV: Synthetic route of compound GI-1, GI-2, GI-3 and GI-5

Vol. 26, No. 1 (2014)
Design, Synthesis and Antibacterial Evaluation of Novel Fluoroquinolone and its Derivatives 213
0.075 mmol) in CH2Cl2 (150 mL) under cooling with salt-ice
bath and the whole mixture was stirred at 0 °C for 1h. After
completion of the reaction, the organic layers was washed with
water (three times), dried over sodium sulfate and evaporated
in vacuo to give 14 g (93 %) of 3.
1H), 8.83 (s, 1H), 7.88 (d, 3JF-H = 12 Hz, 1H), 7.36-7.27 (m,
5H), 4.09-4.03 (m, 1H), 3.95 (s, 3H), 3.76-3.72 (m, 1H), 3.59-
3.54 (m, 2H), 3.42-3.98 (m, 1H), 3.27-3.24 (m, 1H), 2.81-
2.68 (m, 2H), 2.53-2.49 (m, 1H), 2.22-2.19 (m, 1H), 1.32-
1.28 (m, 1H), 1.21-1.05 (m, 5H), 0.95-0.90 (m, 1H). 13C NMR
1
Step-2 Chelation: BF3.Et2O (36 mL, 283.9 mmol) was
added to a suspension of 2 (7.56 g, 23.4 mmol) in THF (150
mL). After refluxing for 48 h, the clear reaction mixture was
evaporated under reduced pressure. The crude oily residue was
successively washed with Et2O, CHCl3 and water affording 4
as a white solid (4.5 g, 56 %).
(100 MHz, CDCl3): δ = 177.1, 166.7, 158.8 (d, JC-F = 253
Hz), 150.3, 148.6, 138.4 (d, 3JC-F = 13 Hz), 137.9, 133.4, 129.1,
128.3, 127.2, 123.8, 107.7 (d, 3JC-F = 23 Hz), 107.6, 63.1, 62.4,
60.5, 53.8, 53.4, 53.0, 50.4, 40.7, 29.7, 17.05, 9.9, 8.9.
Compound GI-6: m.p. 158-160 °C. MS: m/z calcd. for
C22H26N3O4F [M]+: 415.1; found [M+1]+: 416.1; 1H NMR (400
Step-3 Coupling: 4 (4.32 g, 12.6 mmol) was taken in
dimethyl sulfoxide (DMSO), cooled to 0-5 °C. A solution of 3
(5.4 g 27 mmol) in DMSO was slowly added keeping the
temperature below 5 °C. The mixture was allowed to stir at
0 °C for 0.5 h, then warmed to 40 °C for 3d. After the reaction
ended (TLC monitoring), the mixture was poured into water
(300 mL), forming a generous precipitate. The resulting gene-
rous suspension was then cooled at 0-5 °C and remained at
that temperature for an additional hour, then filtered and dried
under vacuum to obtain the crude product 5 (1.5 g, 27 %).
Step-4 deprotection: The above crude product 5 was
added methanol (100 mL) and the resulting yellow suspension
was heated to reflux (60-65 °C) for 12 h. The mixture was
then cooled to 0 °C and 40 mL of concentrated aqueous HCl
was carefully added under that temperature. The mixture was
stirred for 1 h at ambient temperature and the solvent was
distilled off under reduced pressure until the volume of residue
reached 40 mL. The solution was washed with CH2Cl2 and
made alkaline with saturated aqueous NaOH at 0 °C and then
the pH of the solution was adjusted to 7.4 with concentrated
aqueous HCl and dilute aqueous HCl. The resultant solution
was extracted with chloroform (4 × 50 mL) and the combined
organic layer was dried over anhydrous Na2SO4, filtered and
concentrated in vacuo. The residue was recrystallized from
EtOH to yield crude gatifloxacin isomer GI-H (0.36 g, 24 %) as
slightly yellowish white crystals. m.p. 163-164 °C. MS: m/z
calcd. for C19H22N3O4F [M]+: 375.1; found [M+1]+: 376.1; 1H
NMR (400 MHz, CDCl3): δ = 8.85 (s, 1H), 7.90 (d, 3JF-H = 12
Hz, 1H), 4.11-4.05 (m, 1H), 3.99 (s, 3H), 3.66-3.62 (m, 1H),
3.37-3.34 (m, 1H), 3.22-3.16 (m, 2H), 3.11-3.03 (m, 2H), 2.71
(dd, J = 11.6 Hz, 8 Hz, 1H), 1.32-1.25 (m, 1H), 1.21-1.09 (m,
2H), 1.05 (d, J = 6.4 Hz, 3H), 0.95-0.90 (m, 1H). 13C NMR
MHz, CDCl3): δ = 14.69 (s, 1H), 8.84 (s, 1H), 7.88 (d, 3JF-H
=
11.6 Hz, 1H), 5.94-5.89 (m, 1H), 5.28-5.21 (m, 2H), 4.10-
4.04 (m, 1H), 3.95 (s, 3H), 3.77-3.75 (m, 1H), 3.40-3.29 (m,
2H), 3.15-3.02 (m, 2H), 2.86-2.79 (m, 2H), 2.55-2.45 (m, 1H),
2.16-2.02 (m, 1H), 1.28-1.26 (m, 1H), 1.15-1.05 (m, 5H), 0.93-
0.83 (m, 1H). 13C NMR (100 MHz, CDCl3): δ = 177.0, 166.5,
1
3
158.3 (d, JC-F = 253 Hz), 150.4, 149.0, 138.0 (d, JC-F = 13
3
Hz), 133.8, 133.4, 124.1, 124.0, 119.0, 107.6 (d, JC-F = 18
Hz), 62.7, 61.6, 60.3, 53.7, 52.6, 50.5, 40.8, 29.6, 17.1, 9.9, 8.9.
Compound GI-12: m.p. 96-98 °C. MS: m/z calcd. for
1
C25H31N4O6BrF [M]+: 502.2; found [M+1]+: 503.2; H NMR
(400 MHz, CDCl3): δ = 14.66 (s, 1H), 8.84 (s, 1H), 7.90 (d,
3JF-H = 11.6 Hz, 1H), 4.10-4.4.06 (m, 1H), 3.96 (s, 3H), 3.77-
3.63 (m, 9H), 3.50-3.40 (m, 1H), 3.27-3.24 (m, 3H), 2.86-
2.83 (m, 1H), 2.71-2.65 (m, 2H), 2.34-2.31 (m, 1H), 1.31-
1.28 (m, 1H), 1.21-1.11 (m, 5H), 0.95-0.90 (m, 1H). 13C NMR
(150 MHz, CDCl3): δ = 177.0, 167.9, 166.6, 159.4, 150.1,
148.7, 138.1 (d, 3JC-F = 12 Hz), 133.4, 124.0, 114.3,11.9, 107.7
3
(d, JC-F = 13 Hz), 67.0, 62.4, 61.5, 60.3, 53.8., 53.0, 49.9,
46.3, 42.2, 40.7, 16.8, 9.9, 8.9.
General procedure for the preparation of acyl chloride:
Acid (10, 11, 12 and 13 ) (12 mmol) was added thionyl chloride
(15 mL) and the mixture was stirred and refluxed for 2 h.
Redundant thionyl chloride was distilled off under reduced
pressure to afford quantitative yield of the corresponding
chloride which was used directly in the next step.
General procedure for the preparation of compounds GI-
1, GI-2, GI-3, GI-5, GI-7, GI-8, GI-9, GI-10 and GI-11. To
a suspension of gatifluoroxacin isomer (0.7 g, 1.8 mol), CH2Cl2
(50 mL) and triethylamine (0.84 mL, 1.8 mol) was dropped in
15 min a solution of fresh acyl chloride prepared by above
method or anhydride (1.8 mol) in CH2Cl2 (15 mL). The mixture
was stirred at 25 °C for 0.5 h and then was washed with dilute
aqueous HCl adjusting pH to 2-3 and water. The organic layer
was dried (anhydrous Na2SO4) and evaporated to dryness in
vacuo. The solid crystallized from 80 % EtOH to afford desired
product.
1
(100 MHz, CDCl3): δ = 177.1, 166.8, 158.8 (d, JC-F = 252
Hz), 150.1, 149.0, 138.3 (d, 3JC-F = 12 Hz), 133.4, 124.3, 124.2,
3
107.8 (d, JC-F = 24 Hz), 62.5, 53.8, 53.2, 51.5, 46.6, 40.7,
16.6, 9.9, 9.0.
General procedure for the preparation of compounds GI-
4, GI-6 and GI-12. To a stirred suspension of gatifluoroxacin
isomer (1 g, 2.5 mol), CH2Cl2 (25 mL) and triethylamine (0.84
mL, 1.8 mol) was added at room temperature. The correspon-
ding halogenated hydrocarbons (3 mmol) and the mixture was
stirred at room temperature for 6 h and then was washed with
dilute aqueous HCl to adjust pH to 2-3 and finally with water.
The organic layer was dried (anhydrous Na2SO4) and evapo-
rated to dryness in vacuo. The solid crystallized from isopro-
panol to give the derivatives. Compound GI-4: m.p. 120-
122 °C. MS: m/z calcd. for C26H28N3O4F [M]+: 465.2; found
Compound GI-1: m.p. 176-178 °C. MS: m/z calcd. for
C21H24N3O5F [M]+: 417.1; found [M+1]+: 418.1; 1H NMR (400
MHz, CDCl3): δ = 14.60 (s, 1H), 8.83 (s, 1H), 7.90 (d, 3JF-H
=
11.6 Hz, 1H), 4.15-3.96 (m, 2H), 3.96 (s, 3H), 3.78-3.62 (m,
3H), 3.46-3.44 (m, 2H), 3.32-3.19 (m, 2H), 2.22 (s, 3H), 1.34-
1.28 (m, 1H), 1.20-1.08 (m, 5H), 0.96-0.92 (m, 1H). 13C NMR
(100 MHz, CDCl3): δ =177.21, 166.61, 154.83 (d, 1JC-F = 261
Hz), 150.17, 138.03 (d, 3JC-F = 9Hz), 133.49, 107.96 (d, 3JC-F
=
23 Hz), 80.09,62.5, 53.29, 40.68, 28.44, 16.00, 9.99, 9.04.
Compound GI-2: m.p. 158-160 °C. MS: m/z calcd. for
C24H30N3O6F [M]+: 475.2; found [M+1]+: 476.2; 1H NMR (400
1
[M+1]+: 466.2; H NMR (400 MHz, CDCl3): δ = 14.71 (s,

214 Wang et al.
Asian J. Chem.
MHz, CDCl3): δ = 14.64 (s, 1H), 8.84 (s, 1H), 7.90 (d, 3JF-H
=
7.44-7.40 (m, 2H), 7.34-7.30 (m, 1H), 4.29-4.03 (m, 2H), 3.98-
3.82 (m, 4H), 3.82-3.70 (m, 1H), 3.59-3.56 (m, 3H), 3.32-
3.30 (m, 1H), 1.32-1.30 (m, 1H), 1.21-1.11 (m, 5H), 0.95-
0.92` (m, 1H). 13C NMR (100 MHz, CDCl3): δ = 177.0, 176.9,
166.4, 160.0, 159.4, 156.9, 154.6, 150.2, 148.8, 137.7 (d, 3JC-F
= 14 Hz), 126.8, 126.6, 124.1, 124.0, 123.7, 122.3, 122.3,
112.5, 107.7 (d, 3JC-F = 20 Hz), 64.02, 62.6, 53.6, 49.6, 40.7,
25.3, 16.0, 9.9, 9.0.
14.4 Hz, 1H), 4.10-4.04 (m, 1H), 3.95 (s, 3H), 3.79-3.73 (m,
1H), 3.69-3.66 (m, 2H), 3.55-3.41 (m, 2H), 3.17-3.13 (m, 2H),
1.50 (s, 9H), 1.36-1.25 (m, 1H), 1.24-1.05 (m, 5H), 0.95-0.85
(m, 2H). 13C NMR (100 MHz, CDCl3): δ = 177.0, 169.3, 166.5,
158.2 (d, 1JC-F = 261 Hz), 150.25, 148.51, 137.6 (d, 3JC-F = 9
Hz), 133.5, 124.3, 124.2, 107.8 (d, 3JC-F = 23 Hz), 62.5, 52.8,
49.8, 49.2, 47.8, 47.1, 42.2, 40.7, 21.3, 21.2, 16.0, 10.0, 9.0.
Compound GI-3: m.p. 178-180 °C. MS: m/z calcd. for
C25H25N4O5F [M]+: 480.1; found [M+1]+: 481.1; 1H NMR (400
MHz, CDCl3): δ = 14.52 (s, 1H), 8.85 (s, 1H), 8.75 (d, J =
4 Hz, 2H), 7.93 (d, 3JF-H = 11.6 Hz, 1H), 7.39 (d, J = 4.8 Hz,
2H), 4.29-4.03 (m, 2H), 3.97 (s, 3H), 3.92-3.78 (m, 1H), 3.62-
3.53 (m, 3H), 3.40-3.19 (m, 2H), 1.31-1.26 (m, 1H), 1.21-
1.11 (m, 5H), 0.95-0.90 (m, 1H). 13C NMR (100 MHz, CDCl3):
δ = 177.0, 176.9, 168.0, 166.4, 150.3, 148.5, 143.2, 137.4 (d,
3JC-F = 13 Hz), 133.4, 124.4, 124.3, 107.6 (d, 3JC-F = 22 Hz),
62.6, 53.6, 53.7, 50.0, 48.9, 48.3, 42.7, 40.7, 30.9, 16.0, 15.8,
9.9, 9.0.
Compound GI-11: m.p. 176-178 °C. MS: m/z calcd. for
1
C24H23N3O6BrF [M]+: 547.1; found [M+1]+: 548.1; H NMR
(400 MHz, CDCl3): δ = 14.58 (s, 1H), 8.85 (s, 1H), 7.92 (d,
3JF-H = 11.6 Hz, 1H), 7.07 (d, J = 3.6 Hz, 1H), 6.47 (d, J = 3.2
Hz, 1H), 4.21-4.17 (m, 1H), 4.10-4.4.04 (m, 2H), 3.96 (s, 3H),
3.88-3.77 (m, 2H), 3.57-3.53 (m, 2H), 3.32-3.24 (m, 1H), 1.32-
1.30 (m, 1H), 1.21-1.11 (m, 5H), 0.95-0.90 (m, 1H). 13C NMR
(100 MHz, CDCl3): δ = 177.0, 176.9, 166.4, 159.4, 158.0,
3
156.9, 150.2, 149.4, 148.5, 137.6 (d, JC-F = 13 Hz), 133.5,
124.3, 124.0, 119.3, 113.5, 107.8 (d, 3JC-F = 20Hz), 77.3, 62.5,
53.5, 49.5, 40.7, 16.0, 10.0, 9.0.
Compound GI-5: m.p. 174-176 °C. MS: m/z calcd. for
C28H26N3O5F [M]+: 519.1; found [M+1]+: 520.1; 1H NMR (400
RESULTS AND DISCUSSION
MHz, CDCl3): δ = 14.60 (s, 1H), 8.85 (s, 1H), 7.92 (d, 3JF-H
=
Each compound was screened for in vitro antibacterial
activity against several representative Gram-positive bacteria
(S. aureus, S. aureus and S. epidermidis) and Gram-negative
bacteria (Escherichia coli, P. aeuginosa, K. peneumoniae,
Acinetobacter baumannii). The minimum inhibitory concen-
tration values (MICs) were determined by comparison to its
isomer, gatifloxacin as reference drug (Table-1)19.
11.6 Hz, 1H), 7.69 (d, J = 8 Hz, 1H), 7.54 (d, J = 8 Hz, 1H),
7.44-7.40 (m, 2H), 7.34-7.30 (m, 1H), 4.29-4.03 (m, 2H), 3.98-
3.82 (m, 4H), 3.82-3.70 (m, 1H), 3.59-3.56 (m, 3H), 3.32-
3.30 (m, 1H), 1.32-1.30 (m, 1H), 1.21-1.11 (m, 5H), 0.95-
0.92` (m, 1H). 13C NMR (100 MHz, CDCl3): δ = 177.0, 176.9,
166.4, 160.0, 159.4, 156.9, 154.6, 150.2, 148.8, 137.7 (d, 3JC-F
= 14 Hz), 126.8, 126.6, 124.1, 124.0, 123.7, 122.3, 122.3,
112.5, 107.7 (d, 3JC-F = 20 Hz), 64.02, 62.6, 53.6, 49.6, 40.7,
25.3, 16.0, 9.9, 9.0.
Generally, all of the synthesized compounds exhibited
potent antibacterial activity. Most tested compounds possess
good activity against E. coli and S. epidermidis, particularly
GI-1 and GI-II. The most prominent improvement was ob-
served against Klebsiella peneumoniae. The compounds GI-
H, GI-2 and GI-3 show MIC 0.015 µg/mL against Klebsiella
peneumoniae. It is worth noting that compound GI-1 displays
the most prominent activity against all of the tested stains (MIC:
0.015-16 µg/mL).
Compound GI-8: m.p. 178-180 °C. MS: m/z calcd. for
C25H25N4O5F [M]+: 480.1; found [M+1]+: 481.1; 1H NMR (400
MHz, CDCl3): δ = 14.52 (s, 1H), 8.85 (s, 1H), 8.75 (d, J = 4
3
Hz, 2H), 7.93 (d, JF-H = 11.6 Hz, 1H), 7.39 (d, J = 4.8 Hz,
2H), 4.29-4.03 (m, 2H), 3.97 (s, 3H), 3.92-3.78 (m, 1H), 3.62-
3.53 (m, 3H), 3.40-3.19 (m, 2H), 1.31-1.26 (m, 1H), 1.21-
1.11 (m, 5H), 0.95-0.90 (m, 1H). 13C NMR (100 MHz, CDCl3):
δ = 177.0, 176.9, 168.0, 166.4, 150.3, 148.5, 143.2, 137.4 (d,
3JC-F = 13 Hz), 133.4, 124.4, 124.3, 107.6 (d, 3JC-F = 22 Hz),
62.6, 53.6, 53.7, 50.0, 48.9, 48.3, 42.7, 40.7, 30.9, 16.0, 15.8,
9.9, 9.0.
TABLE
in vitro ANTIBACTERIAL ACTIVITY OF
GT-H AND ITS DERIVATIVES
MIC (µg/mL)
Compound GI-9: m.p. 200-202 °C. MS: m/z calcd. for
C28H27N3O5F2 [M]+: 523.1; found [M+1]+: 524.1; 1H NMR (400
Strains
S. e.
E. coli
P. a.
K. p.
A. b.
S. a.
MHz, CDCl3): δ = 14.62 (s, 1H), 8.85 (s, 1H), 7.92 (d, 3JF-H
=
GI-H
GI-1
2
0.015
32
1
32
16
0.015
0.25
0.015
0.015
256
1
1
2
0.5
0.25
16
11.6 Hz, 1H), 7.71 (d, J = 15.2 Hz, 2H), 7.54 (dd, J = 8.4 Hz,
J = 5.6 Hz, 2H), 7.10 (t, 2H), 6.80 (d, J = 15.2 Hz, 1H), 4.29-
4.04 (m, 2H), 3.97-3.82 (m, 4H), 3.82-3.70 (m, 2H), 3.53-
3.25 (m, 3H), 1.32-1.26 (m, 1H), 1.21-1.11 (m, 5H), 0.95-
0.92 (m, 1H). 13C NMR (100 MHz, CDCl3): δ = 177.0, 176.9,
166.4, 165.5, 164.7, 162.3, 159.4, 156.9, 150.1, 148.5, 141.9,
GI-2
64
256
8
16
GI-3
6
2
0.5
0.5
GI-4
128
32
256
128
128
256
256
256
256
0.5
16
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
256
GI-5
256
GI-6
256
256
256
256
256
0.015
4
256
GI-7
256
3
GI-8
256
137.4 (d, JC-F = 13 Hz),, 130.9, 129.6, 124.2, 124.1, 116.4,
3
116.0, 107.7 (d, JC-F = 22 Hz), 77.3, 62.6, 48.4, 46.6, 40.7,
GI1-9
GI-10
GI-11
GI-12
256
256
25.3, 16.1, 10.0, 9.0.
Compound GI-10: m.p. 174-176 °C. MS: m/z calcd. for
C28H26N3O5F [M]+: 519.1; found [M+1]+: 520.1; 1H NMR (400
256
256
S.e. = Staphylococcus epidermidis; P.a. = Pseudomonas aeruginosa;
K.p. = Klebsiella peneumoniae; A.b. = Acinetobacter baumannii;
S.a. = Staphylococcus aureus R866.
MHz, CDCl3): δ = 14.60 (s, 1H), 8.85 (s, 1H), 7.92 (d, 3JF-H
11.6 Hz, 1H), 7.69 (d, J = 8 Hz, 1H), 7.54 (d, J = 8 Hz, 1H),
=

Vol. 26, No. 1 (2014)
Design, Synthesis and Antibacterial Evaluation of Novel Fluoroquinolone and its Derivatives 215
(e) D.T. Bearden and L.H. Danziger, Pharmacotherapy, 21, 224S
In order to further know an effect of varying the N-4'
substitution on activity, a series of novel synthesized quinolones
were investigated.An interest in an influence of N-substituent
GI-H derivatives and unsubstituents, thus N-substituted
compound GI-1 and GI-3 seems to have more inhibitory
activity than unsubstituents GI-H, while better than other
unsubstituents against both Gram-positive and Gram-negative
bacteria. When compared to bulkier N-acyl compound GI-2,
simple N-acyl compound 7a display 16 to 2000-fold increase
in activity against all of the tested bacteria. Furthermore, this
same trend can be seen in the comparison of N-sulfonyl substi-
tuted compounds GI-3 and GI-4.
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In summary, gatifluoroxacin isomers GI-H, [1-cyclopropyl-
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were designed and synthesized and evaluated for their in vitro
antibacterial activity against representative Gram-positive and
Gram-negative strains. Compounds GI1, GI2, GI3 and GI4
demonstrated excellent activity against both Gram-positive and
Gram-negative bacteria. Compound GI-1 has been found to
exhibit the most prominent activity against all of the tested
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ACKNOWLEDGEMENTS
17. J.P. Sanchez, R.D. Gogliotti, J.M. Domagala, S.J. Gracheck, M.D.
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Financial support is provided by Sichuan Kelun Pharma-
ceutical Co. and Natural Science Foundation of China
(J1103315/J0104).
18. G. Anquetin, J. Greiner, N. Mahmoudi, M. Santillana-Hayat, R.
Gozalbes, K. Farhati, F. Derouin, A. Aubry, E. Cambau and P. Vierling,
Eur. J. Med. Chem., 41, 1478 (2006).
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