Synthesis and antibacterial activity of 1-(2-fluorovinyl)-7-substituted-4- quinolone-3-carboxylic acid derivatives, conformationally restricted analogues of fleroxacin

Article abstract of DOI:10.1021/jm0402061

The novel 1-(2-fluorovinyl)-4-quinolone-3-carboxylic acid derivatives Z-15a-c, E-15a-c, Z-16a-c, and E-16a-c, conformationally restricted analogues of fleroxacin (5), were synthesized, and their in vitro antibacterial activity was evaluated. A dehydrosulf

Full text of DOI:10.1021/jm0402061

3194
J. Med. Chem. 2005, 48, 3194-3202
Synthesis and Antibacterial Activity of
1-(2-Fluorovinyl)-7-substituted-4-quinolone-3-carboxylic Acid Derivatives,
Conformationally Restricted Analogues of Fleroxacin
Yoshikazu Asahina,* Kazuhiko Iwase, Fujio Iinuma, Masaki Hosaka, and Takayoshi Ishizaki
Discovery Research Laboratories, Kyorin Pharmaceutical Co. Ltd., 2399-1, Nogi, Nogi-Machi,
Shimotsuga-Gun, Tochigi, 329-0114, Japan
Received November 24, 2004
The novel 1-(2-fluorovinyl)-4-quinolone-3-carboxylic acid derivatives Z-15a-c, E-15a-c, Z-16a-
c, and E-16a-c, conformationally restricted analogues of fleroxacin (5), were synthesized, and
their in vitro antibacterial activity was evaluated. A dehydrosulfenylation of a 2-fluoro-2-[(4-
methoxyphenyl)sulfinyl]ethyl group was employed as a key step for the construction of a
2-fluorovinyl group at the N-1 position. It appeared evident that the Z-isomers Z-15a-c and
Z-16a-c exhibited 2- to 32-fold more potent in vitro antibacterial activity than the corresponding
E-isomers E-15a-c and E-16a-c. Furthermore, since Z-15b showed in vitro antibacterial
activity and DNA gyrase inhibition comparable to that of 5, it was hypothesized that the
conformation of Z-15b would be equivalent to the active conformer of 5. The results revealed
that the antibacterial Z-1-(2-fluorovinyl)quinolone derivatives carry the novel N-1 substituent
of the fluoroquinolones.
Introduction
Since the development of norfloxacin (1),1 the first
new quinolone (fluoroquinolone) in which a fluorine
atom is attached at the C-6 position, other fluoroqui-
nolones (e.g., ciprofloxacin (2)2 and levofloxacin (3))3
have been developed and clinically used for the treat-
ment of various infectious diseases. A number of syn-
theses of fluoroquinolone analogues have been reported,
together with the corresponding structure-activity
relationship (SAR) studies.4 It is of particular note that
the N-1 substituent of fluoroquinolones plays an impor-
tant role in the antibacterial activity of the fluoroqui-
nolones, and alkyl groups such as ethyl, vinyl, cyclo-
propyl, and tert-butyl groups have been regarded as
suitable N-1 substituents. In addition, the stereochem-
Figure 1.
istry of the N-1 substituent of fluoroquinolones is also
known to be important for the antibacterial activity of
the fluoroquinolones, as is their bulkiness. For example,
in the case of 3, which possesses a rigid N-1 structure
restricted by a 1,8-annulated ring system, the 3S-
enantiomer of 3 was revealed as having 8-128 times
more potent activity than the 3R-enantiomer of 3.3 Even
in the case of 1-(2-fluorocyclopropyl)quinolone derivative
4, the conformation of the N-1 substituent possessing a
fluorine atom is restricted by a cyclopropane ring. It has
been reported that the cis isomer exhibited more potent
antibacterial activity than the trans isomer (Figure 1).5
These results indicated that the antibacterial potency
of fluoroquinolone would be optimized by restricting the
conformation of the N-1 substituent within narrow
limits. Thus, for the present study, we focused on the
2-fluoroethyl group, the N-1 substituent of fleroxacin
(5)6 (Figure 2). We designed and synthesized 1-(2-
fluorovinyl)quinolone derivatives 15 and 16 (Figure 2),
both bearing a 2-fluorovinyl group and the conformation
of which is restricted by the introduction of a double
bond into a 2-fluoroethyl group of 5. The Z-isomers
Z-15a-c and Z-16a-c appeared to exhibit a 2- to 32-
fold more potent in vitro antibacterial activity than the
corresponding E-isomers E-15a-c and E-16a-c. It was
also found that Z-15b, structurally related to 5, showed
comparable activity and DNA gyrase inhibition to that
of 5; thus, it is possible that the conformation of Z-15b
is in fact equivalent to the active conformer of 5.
In this paper, we present the synthesis and in vitro
antibacterial activity of the fluoroquinolone derivatives
15 and 16 carrying a Z- or E-(2-fluorovinyl) group as
novel N-1 substituents.
Results and Discussion
Chemistry. The synthetic strategy of the 1-(2-fluo-
rovinyl)-7-substituted-4-quinolone-3-carboxylic acid (15,
16) is given in Scheme 1. We employed a dehydrosul-
fenylation of 12, carrying a 2-fluoro-2-[(4-methoxy-
* To whom correspondence should be addressed. Phone: 81 (0)280
56 2201. Fax: 81 (0)280 57 1293. E-mail: yoshikazu.asahina@
mb.kyorin-pharm.co.jp.
10.1021/jm0402061 CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/02/2005

Analogues of Fleroxacin
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9 3195
Figure 2.
Scheme 1
Scheme 2a
a Reagents: (a) DAST, SbCl3, CH2Cl2 (91%); (b) MCPBA, CHCl3 (90%); (c) H2NNH2‚H2O (9a, 74%; 9b, 22%).
phenyl)sulfinyl]ethyl group7 of 12 as a key step in the
construction of the 2-fluorovinyl group at the N-1
position.
studies were performed on the basis of the reported
results for 1-(phenylsulfenyl)-1-fluoroethane.10 The ma-
jor anti isomer 9a was used as the starting material to
synthesize 12, which bears a 2-fluoro-2-[(4-methoxy-
phenyl)sulfinyl]ethyl group at the N-1 position (Scheme
2).
The synthesis of 2-fluoro-2-[(4-methoxyphenyl)sulfi-
nyl]ethylamine (9), used as the starting material, was
achieved by hydrazinolysis of the known sulfoxide 8,8
which was provided from 6 according to slightly modi-
fied previously reported procedures.9 After the treat-
ment of 8 with hydrazine monohydrate, separation of
the diastereomers of 9 by column chromatography gave
anti isomer 9a and syn isomer 9b. The ratio of 9a to 9b
was approximately 7:2. The stereochemistry of 9a and
9b was determined by comparison of 9a and 9b as
regards the chemical shifts of the C1 hydrogen atom in
1H NMR and the C1 carbon atom in 13C NMR. These
The synthetic route of 6,7-difluoro-1-(2-fluorovinyl)-
8-substituted-4-quinolones 13a-c is shown in Scheme
3. Treatment of benzoyl acetates 10a-c11 with dimeth-
ylformamide dimethylacetal12 followed by reaction with
9a gave enaminoesters 11a-c, respectively. Cyclization
of 11a-c under basic conditions afforded the 1-[2-fluoro-
2-(4-methoxyphenyl)sulfinyl]ethyl-4-quinolone deriva-
tives 12a-c. Thermal elimination of 4-methoxybenzen-
sulfinic acid from 12a-c in xylene gave the desired 6,7-

3196 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9
Asahina et al.
Scheme 3a
a Reagents and conditions: (a) Me2NCH(OMe)2; (b) 9a, EtOH; (c) K2CO3, DMF or NaH, THF; (d) reflux in xylene; (e) H2SO4, AcOH,
H2O; (f) 1-methylpiperazine, DMSO; (g) (i) 3-tert-butoxycarbonylaminopyrrolidine, DBU, MeCN; (ii) HCl.
ylpiperazinyl) derivative Z-15a. Reaction of Z-14a with
3-(tert-butoxycarbonylamino)pyrrolidine, followed by re-
moval of a tert-butoxycarbonyl (Boc) group, gave the
7-(3-aminopyrrolidinyl) derivative Z-16a as its hydro-
chloride. The geometric isomers E-15a and -16a were
synthesized from E-13a in the same manner as de-
scribed for Z-15a and -16a. The geometrical isomers of
13b and 13c were converted to the corresponding acids
14b and 14c in the same manner as described for the
synthesis of 14a. Reaction of 14b and 14c with 1-me-
Figure 3.
thylpiperazine followed by separation of the geometric
isomers gave the 7-(4-methylpiperazinyl) derivatives Z-
and E-15b, and Z- and E-15c, respectively. Reaction of
difluoro-1-(2-fluorovinyl)-8-substituted-4-quinolones
13a-c in a high yield as the mixture of geometrical
isomers Z-13a-c and E-13a-c. The ratio of the geo-
14b and 14c with 3-Boc-aminopyrrolidine, separation
metrical isomers Z and E was approximately 1:2, as
of the geometrical isomers, and subsequent deprotection
1
calculated from the integration value obtained by H
of the Boc groups furnished the 7-(3-aminopyrrolidinyl)
NMR. The geometric isomers of 8-fluoro and 8-methoxy
derivatives Z- and E-16b, and Z- and E-16c, respec-
derivatives 13b,c were inseparable at this stage by silica
tively.
gel column chromatography. On the other hand, the
Antibacterial Activity. The in vitro antibacterial
activity of the Z- and E-1-(2-fluorovinyl)quinolone de-
rivatives (15 and 16) against two Gram-positive strains
(Staphylococcus aureus Smith and Streptococcus pneu-
moniae type III) and against two Gram-negative strains
(Escherichia coli NIHJ JC-2 and Pseudomonas aerugi-
nosa IID 1210) are shown in Table 1 along with those
for 2 and 5. The Z-isomers Z-15a-c and Z-16a-c
geometrical isomers Z-13a and E-13a of the 8-hydrogen
derivative 13a were successfully separated by silica gel
column chromatography. Their geometries were deter-
mined by comparison of the coupling constants between
H1′ and F2′, as shown in Figure 3.
Hydrolysis of ester Z-13a under acidic conditions gave
acid Z-14a without geometric isomerization. Reaction
of Z-14a with 1-methylpiperazine gave the 7-(4-meth-

Analogues of Fleroxacin
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9 3197
Table 1. In Vitro Antibacterial Activity of Compounds Z- and
E-15 and Z- and E-16
MIC (µg/mL)
Gram-positive bacteria
Gram-negative bacteria
S. aureus St. pneumoniae
E. coli
NIHJ JC-2
P. aeruginosa
IID1210
compd
Smith
type III
Z-15a
E-15a
Z-15b
E-15b
Z-15c
E-15c
Z-16a
E-16a
Z-16b
E-16b
Z-16c
Z-16c
5
0.20
3.13
0.39
12.5
0.39
6.25
0.39
1.56
0.20
3.13
0.39
6.25
0.39
0.20
3.13
100
3.13
>50
3.13
50
3.13
6.25
0.78
12.5
1.56
12.5
3.13
0.78
0.025
0.20
0.025
0.39
1.56
6.25
1.56
12.5
3.13
25
0.78
3.13
0.39
1.56
1.56
6.25
1.56
0.20
Figure 4. NOE experiments in 1H NMR of E-15a and Z-15a.
0.025
0.20
0.05
0.20
0.05
0.20
0.0125
0.10
0.025
e0.0063
2
Table 2. Inhibitory Activity of Compounds of Z- and E-15b
against DNA Gyrase of S. aureus
Figure 5. NOE experiments in 1H NMR of E-15b and Z-15b.
compd
IC50 (µg/mL)
group. First, to confirm the position of the fluorine atom
on the 1-(2-fluorovinyl) group, we carried out NOE
experiments using 1H NMR analysis of the 8-hydrogen
derivatives Z-15a and E-15a. The results are shown in
Figure 4. The NOEs were observed between H1′ and
both H2 and H8 for both Z-15a and E-15a. From these
NOE data, it became apparent that the 2-fluorovinyl
groups of Z-15a and E-15a are oriented above (or below)
the plane of the quinolone ring. Furthermore, the NOE
was also observed between H2′ and H2 for E-15a; long-
range coupling (5J ) 1.0 Hz) with F2′ was also observed
in H2 for Z-15a. These 1H NMR data indicated that the
fluorine atoms on the 2-fluorovinyl groups of Z-15a and
E-15a existed on the side opposing H8.
Z-15b
E-15b
5
2
72.2
664
68.5
20.1
exhibited 2- to 32-fold more potent in vitro antibacterial
activity against both of the Gram-positive and both of
the Gram-negative strains than did the corresponding
E-isomers E-15a-c and E-16a-c. Our findings match
the case of 1-(2-fluorocyclopropyl)quinolone derivatives,
of which the cis isomers exhibited more potent anti-
bacterial activity than the trans isomers.5 In addition,
Z-15a-c and Z-16a-c exhibited comparable in vitro
antibacterial activity to that of 5. Among the compounds
tested, the 7-(3-aminopyrrolidinyl) derivative Z-16b,
which bears a fluorine atom at the C-8 position, exhib-
ited the most potent in vitro antibacterial activity of all
of the compounds, and Z-16b showed comparable in
vitro antibacterial activity against S. aureus Smith, St.
pneumoniae type III, and P. aeruginosa IID1210 to that
of 2, with the exception of its activity against E. coli
NIHJ JC-2.
Next, we evaluated the inhibition potencies of Z-15b
and E-15b, which are conformationally restricted ana-
logues of 5, and the inhibition potentials of 2 and 5 in
the presence of DNA gyrase of S. aureus. As shown in
Table 2, the IC50 value of Z-15b was 9-fold smaller than
that of E-15b and was comparable to that of 5. This
difference in the inhibition abilities of Z-15b, E-15b, and
5 reflected the differences in the in vitro antibacterial
activity of those compounds against S. aureus Smith.
The stereochemistry of the 2-fluorovinyl group, or the
position of the fluorine atom of the 2-fluorovinyl group
of Z-15a and E-15b, appeared to exert an influence on
both in vitro antibacterial activity and inhibition of the
target enzyme, DNA gyrase.
Additional NOE experiments were performed using
the 8-fluoro derivatives Z-15b and E-15b, which are
conformationally restricted analogues of 5. The NOEs
were observed between H1′ and H2 for both Z-15b and
E-15b and between H2′and H2 for E-15b, as shown in
Figure 5. In addition, long-range coupling (5J ) 1.5 Hz)
1
with F2′ was observed in H2 for Z-15b. These H NMR
results of Z-15b and E-15a were similar to those of the
corresponding 8-hydrogen derivatives Z-15a and E-15a.
It was therefore indicated that the 2-fluorovinyl groups
of Z-15b and E-15b have conformations similar to those
of Z-15a and E-15a, respectively.
To define the active conformer of 5, we then carried
out the molecular modeling of the 2-fluorovinyl group
of Z-15b. The dihedral angle of C2-N1-C1′-C2′ (denoted
as Θ in this paper) of Z-15b and that of 5 changed from
-180° to 180° by increments of 5°, and the energy of
each conformer was calculated by using AM1 param-
eters. The results are given in Figure 6. In the case of
Z-15b, it appeared that the two energy minima con-
formers existed. One of these conformers was energy
minimum conformer located above the plane of the
quinolone ring and was on the opposite side of a C8-
fluorine atom (Θ ) 45°, conformer A), and the other was
located under the plane of the quinolone ring (Θ ) -45°,
conformer B). There was very little energy difference
(0.195 kcal/mol) between the two. These results were
in good agreement with the results of the 1H NMR
experiments with Z-15b. In contrast, in the case of 5,
Conformation Analysis. Since Z-15b exhibited
equal ability to inhibit the target enzyme, DNA gyrase,
and also because it was revealed to have comparable in
vitro antibacterial activity to that of 5, Z-15b could be
regarded as an active conformer of 5. Therefore, we
performed a study to determine the active conformer of
5 by defining the conformation of the 1-(2-fluorovinyl)

3198 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9
Asahina et al.
Figure 6. Rotational energy map of N1-R1 bond and energy minima conformers of 1-(2-fluorovinyl) derivatives of Z-15b and 5
calculated by using AM1 parameters. Θ is defined as the C2-N1-C′1-C′2 dihedral angle.
although there existed the one energy minimum con-
former and it was located under the plane of the
quinolone ring (Θ ) -85°, conformer C), there was no
energy minimum conformer above the plane of the
quinolone ring. These calculation results showed that
the conformation of the 2-fluorovinyl group of Z-15b is
more restricted than that of the 2-fluoroethyl group of
5, especially within the range of the upper side of the
quinolone ring. Furthermore, according to a previous
study, which focused on the relationship between the
dihedral angle Θ of N1 substituents of fluoroquinolone
derivatives using molecular orbital calculation and the
in vitro antibacterial activity of this group, it appeared
that the active conformer of the N1 substituents of the
fluoroquinolones was located above the plane of the
quinolone ring.13 Consequently, conformer A of Z-15b
could be regarded as the active conformer of Z-15b.
On the basis of the results of the conformation
analysis of the 2-fluorovinyl group of Z-15b as described
above, it is likely that conformer A would be equivalent
to the active conformer of 5.
Conclusions
As described above, we succeeded in the design,
synthesis, and evaluation of in vitro antibacterial activ-
ity on the 4-quinolone-3-carboxylic acids Z-15a-c,
E-15a-c, Z-16a-c, and E-16a-c, which are conforma-
tionally restricted analogues of 5 carrying a 2-fluoroet-
hyl group as the novel N-1 substituent. The synthesis
of these compounds was achieved in five steps from
10a-c by a method featuring a dehydrosulfenylation
of the 2-fluoro-2-[(4-methoxyphenyl)sulfinyl]ethyl group
as the key step for the construction of the 2-fluorovinyl
group at the N-1 position. It appeared evident that the
Z-isomers Z-15a-c and Z-16a-c exhibited 2- to 32-fold
more potent in vitro antibacterial activity than the
corresponding E-isomers E-15a-c and E-16a-c. On the
basis of the in vitro antibacterial activity analysis, as

Analogues of Fleroxacin
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9 3199
chromatography (CH2Cl2/MeOH ) 10:1) of the residue gave
9a (2.16 g, 74%) as a pale-brown syrup and 9b (627 mg, 22%)
as a red-brown oil.
well as analysis of the DNA gyrase inhibitory ability of
Z-15b and 5, and the conformation analysis of Z-15b,
it can be concluded that the conformation of Z-15b is
most likely equivalent to the active conformer of 5.
Considering the results of the present study, the novel
Z-1-(2-fluorovinyl)-4-quinolone-3-carboxylic acid would
be an intriguing scaffold for the exploration of novel
quinolone antibacterials. Further investigation of the
Z-(1-fluorovinyl)quinolones is in progress.
1
9a. H NMR (CDCl3) δ: 3.35 (ddd, J ) 22.0, 15.1, 3.4 Hz,
1H, C1-H), 3.44 (ddd, J ) 27.3, 15.1, 4.9 Hz, 1H, C1-H), 3.87
(s, 3H, CH3), 4.81 (ddd, J ) 48.8, 4.9, 3.4 Hz, 1H, C2-H), 7.05-
7.09 (m, 2H, Ar-H), 7.62-7.66 (m, 2H, Ar-H). 13C NMR
(CDCl3) δ: 40.6 (J ) 20.2 Hz), 55.6, 107.6 (J ) 219 Hz), 115.0
(2C), 126.9 (2C), 130.9 (J ) 4.9 Hz), 162.7. MS (EI) m/z: 217
(M+). HRMS (EI) for C9H12FNO2S (M+): calcd, 217.0573;
found, 217.0546.
1
9b. H NMR (CDCl3) δ: 3.08 (ddd, J ) 17.1, 14.6, 6.3 Hz,
Experimental Section
1H, C1-H), 3.25 (ddd, J ) 22.5, 14.6, 4.9 Hz, 1H, C1-H), 3.87
(s, 3H, CH3), 4.97 (ddd, J ) 47.9, 6.3, 4.9 Hz, 1H, C2-H), 7.05-
7.09 (m, 2H, Ar-H), 7.61-7.64 (m, 2H, Ar-H). 13C NMR
(CDCl3) δ: 40.7 (J ) 22.1 Hz), 55.6, 106.4 (J ) 219 Hz), 114.9
(2C), 127.1 (2C), 129.3 (J ) 3.7 Hz), 162.7. MS (EI) m/z: 217
(M+). HRMS (EI) for C9H12FNO2S (M+): calcd, 217.0573;
found, 217.0562.
Melting points were determined with a Yanagimoto mi-
cromelting point apparatus and are uncorrected. Elemental
analyses are within (0.4% of the theoretical values and were
determined by a Yanaco CHN MT-5 instrument. Infrared
spectra (IR) were recorded with a JASCO FTIR-5300 spec-
trometer. Measurements of mass spectra (MS) and high-
resolution MS (HRMS) were performed with a JEOL JMS SX-
102A mass spectrometer. Proton nuclear magnetic resonance
(1H NMR) were measured with a JEOL EX-90 (90 MHz) or a
JEOL JMN-EX400 (400 MHz) spectrometer. The chemical
shifts are expressed in parts per million (δ value) downfield
from tetramethylsilane, using tetramethylsilane (δ ) 0) and/
or residual solvents such as chloroform (δ ) 7.26) as an
internal standard. Splitting patterns are indicated as follows:
s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; br,
broad peak. Column chromatography was carried out with
silica gel [silica gel 60 (Kanto)] as an absorbent. Merck
precoated thin-layer chromatography (TLC) plates (silica gel
60 F254, 0.25 mm, Art 5715) were used for the TLC analysis.
Solutions were dried over sodium sulfate, and the solvent was
removed by rotary evaporation under reduced pressure.
Ethyl 2-[2-(Fluoro-2-(4-methoxyphenylsulfinyl)ethyl-
amino)-1-(2,4,5-trifluorobenzoyl)]acrylate (11a). To a so-
lution of 10a (1.03 g, 4.18 mmol) in benzene (25 mL), N,N-
dimethylformamide dimethyl acetal (2.50 mL, 18.8 mmol) was
added. The mixture was heated under reflux for 1 h and then
concentrated in vacuo. To a solution of the residue in toluene
(12 mL), 9a (1.00 g, 4.60 mmol) was added. The mixture was
stirred at room temperature for 2 h and then concentrated in
vacuo. Flash chromatography (hexane/AcOEt ) 1:1) of the
residue gave 11a (1.57 g, 79%) as a yellow foam. 1H NMR
(CDCl3) δ: 1.40 (t, J ) 7.3 Hz, 3H, CH3), 3.91 (s, 3H, CH3),
4.38 (q, J ) 7.3 Hz, 2H, CH2), 4.66-4.81 (m, 2H, CH2), 5.15
(ddd, J ) 48.8, 7.8, 2.0 Hz, CHF), 6.78 (1H, dd, J ) 11.0, 6.3
Hz, Ar-H), 7.15 (d, J ) 8.8 Hz, 2H, Ar-H), 7.66 (d, J ) 8.8
Hz, 2H, Ar-H), 8.26 (dd, J ) 10.3, 8.8 Hz, 1H, Ar-H), 8.38
(s, 1H, CH).
N-[2-[2-Fluoro-(4-methoxyphenyl)thio]ethyl]phthali-
mide (7). Diethylaminosulfur trifluoride (4.21 mL, 31.9 mmol)
was added to a solution of N-[2-[(4-methoxyphenyl)sulfinyl]-
ethyl]phthalimide (6, 6.00 g, 18.2 mmol) and antiomonyl(III)
chloride (125 mg, 0.548 mmol) in anhydrous CH2Cl2 (42 mL)
under ice cooling, and the mixture was stirred at room
temperature for 3 h. After the reaction was quenched by
adding saturated aqueous NaHCO3 solution (36 mL) under ice
cooling, the mixture was extracted with CH2Cl2 (50 mL). The
combined CH2Cl2 extracts were washed with water (2 × 30
mL), dried over anhydrous Na2SO4, filtered, and then concen-
trated in vacuo to give 7 (5.52 g, 91%) as pale-brown crystals.
1H NMR (CDCl3) δ: 3.82 (s, 3H, CH3), 4.04 (ddd, J ) 40.2,
14.4, 4.9 Hz, 1H, CH2), 4.08 (ddd, J ) 42.0, 14.2, 8.1 Hz, 1H,
CH2), 5.94 (ddd, J ) 53.6, 8.1, 4.9 Hz, 1H, CH), 6.87-6.90 (m,
2H, Ar-H), 7.48-7.50 (m, 2H, Ar-H), 7.74 (dd, 2H, Ar-H),
7.87 (dd, 2H, Ar-H).
N-[2-Fluoro-2-[(4-methoxyphenyl)sulfinyl]ethyl]-
phthalimide (8). To a solution of 7 (5.51 g, 16.6 mmol) in
CHCl3 (100 mL), m-chloroperoxybenzoic acid (65%, 4.41 g, 16.6
mmol) was added at -50 to -40 °C for 40 min, and the mixture
was stirred at the same temperature for 20 min. The reaction
mixture was washed with saturated aqueous NaHCO3 solution
(2 × 100 mL), 10% aqueous Na2SO3 (2 × 100 mL) solution
and water (100 mL), dried over anhydrous Na2SO4, filtered,
and then concentrated in vacuo. Flash chromatography (hex-
ane/AcOEt ) 1:1 f AcOEt) of the residue gave 8 (5.18 g, 90%)
as a white solid. 1H NMR (CDCl3) δ: 3.85 (s, 2.4H, CH3), 3.86
(s, 0.6H, CH3), 4.08-4.20 (m, 1.2H, CH2), 4.39 (ddd, J ) 14.6,
12.7 , 7.8 Hz, 0.8H, CH2), 5.32 (ddd, J ) 48.8, 7.8, 4.4 Hz, 0.8H,
CH), 5.42 (dt, J ) 49.8, 5.9 Hz, 0.8H, CH), 7.03-7.08 (m, 2H,
Ar-H), 7.65-7.68 (m, 2H, Ar-H), 7.72-7.76 (m, 2H, Ar-H),
7.84-7.88 (m, 2H, Ar-H).
Ethyl 2-[2-(Fluoro-2-(4-methoxyphenylsulfinyl)eth-
ylamino)-1-(2,3,4,5-tetrafluorobenzoyl)]acrylate (11b). The
compound 11b (1.82 g, 99%) was prepared from 10b (1.00 g,
3.79 mmol) and 9a (948 mg, 4.36 mmol) by the same method
as that used for 11a. 1H NMR (CDCl3) δ: 0.99 and 1.40 (each
t, J ) 7.3 Hz, total 3H, CH3), 3.88 (s, 3H, CH3), 4.03-4.16 (m,
4H, CH2 × 2), 4.93-4.95 and 5.05-5.07 (each m, total 1H,
CHF), 6.99-7.11 (m, 3H, Ar-H), 7.63 (d, 2H, Ar-H), 7.99 and
8.11 (each d, total 1H, CH), 9.40-9.60 and 10.8-11.0 (each
br, total 1H, NH).
Ethyl 2-[2-(Fluoro-2-(4-methoxyphenylsulfinyl)eth-
ylamino)-1-(2,4,5-trifluoro-3-methoxybenzoyl)]acrylate
(11c). The compound 11c (1.62 g, 89%) was prepared from 10c
(1.00 g, 3.62 mmol) and 9a (905 mg, 4.17 mmol) by the same
method as that used for 11a. 1H NMR (CDCl3) δ: 0.98 and
1.10 (each t, J ) 7.3 Hz, total 3H, CH3), 3.88 (s, 3H, CH3),
4.00 (s, 3H, CH3), 4.03-4.16 (m, 2H, CH2 × 2), 4.91-5.07 (m,
1H, CHF), 6.86-6.92 and 6.98-7.04 (each m, total 1H, Ar-
H), 7.08-7.10 (m, 2H, Ar-H), 7.63 (d, J ) 8.8 Hz, 2H, Ar-H),
7.96 (d, J ) 14.2 Hz, 0.3H, CH), 8.08 (d, J ) 13.7 Hz, 0.7H,
CH), 9.41-9.54 and 10.8-10.9 (each br, total 1H, NH).
Ethyl 1-[2-Fluoro-2-(4-methoxyphenylsulfinyl)ethyl]-
6,7-difluoro-1,4-dihydro-4-oxo-3-quinolinecarboxylate
(12a). A solution of 11a (1.28 g, 2.70 mmol) in anhydrous THF
(13 mL) was added to a suspension of sodium hydride (60%
oil suspension, 108 mg, 2.70 mmol) in anhydrous THF (13 mL)
under cooling with ice. After the reaction mixture was stirred
at a constant temperature for 30 min, it was poured into ice/
water (30 mL). The resulting precipitates were collected by
filtration, washed with water, and then dried in vacuo to give
12a (945 mg, 77%). Mp: 191-193 °C (MeOH). 1H NMR
(CDCl3) δ: 1.40 (t, J ) 7.3 Hz, 3H, CH3), 3.89 (s, 3H, CH3),
4.38 (q, J ) 7.3 Hz, 2H, CH2), 4.62 (ddd, J ) 37.6, 16.6, 7.8
Hz, 1H, C1′-H), 4.75 (ddd, J ) 28.3, 16.1, 2.0 Hz, 1H, C1′-H),
5.15 (ddd, J ) 48.9, 7.8, 2.0 Hz, 1H, C2′-H), 6.79 (dd, J )
11.0, 6.3 Hz, 1H, C8-H), 7.15 (d, J ) 8.8 Hz, 2H, Ar-H), 7.66
(d, J ) 8.8 Hz, 2H, Ar-H), 8.26 (dd, J ) 10.3, 8.8 Hz, 1H,
C5-H), 8.38 (s, 1H, C2-H). IR (KBr) cm-1: 1732, 1602. MS
(EI) m/z: 453 (M+). Anal. (C21H18F3NO5S) C, H, N.
2-[2-Fluoro-2-(4-methoxyphenyl)sulfinyl]ethylamine
(9a, 9b). Hydrazine monohydrate (1.30 mL, 26.8 mmol) was
added to a solution of 8 (4.66 g, 13.4 mmol) in EtOH (50 mL),
and the mixture was heated under reflux for 1 h. After the
mixture was cooled, the precipitates that had formed were
filtered off and the filtrate was concentrated in vacuo. Flash

3200 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9
Asahina et al.
Ethyl 1-[2-Fluoro-2-(4-methoxyphenylsulfinyl)ethyl]-
6,7,8-trifluoro-1,4-dihydro-4-oxo-3-quinolinecarboxy-
late (12b). The compound 12b (1.36 g, 80%) was prepared
from 11b (1.77 g, 3.75 mmol) by the same method as that used
for 12a. Mp: 136-137 °C. 1H NMR (CDCl3) δ: 1.40 (t, J ) 7.3
Hz, 3H, CH3), 3.89 (s, 3H, CH3), 4.39 (q, J ) 7.3 Hz, 2H, CH2),
4.66-4.76 (m, 1H, C1′-H), 4.96 (ddt, J ) 27.6, 16.1, 2.9 Hz,
1H, C1′-H), 5.27 (dd, J ) 49.3, 8.3 Hz, 1H, C2′-H), 7.08-7.21
(m, 2H, Ar-H), 7.59-7.65 (m, 2H, Ar-H), 8.12 (dd, J ) 9.0,
2.4 Hz, 1H, C5-H), 8.37 (s, 1H, C2-H). IR (KBr) cm-1: 1732,
1701, 1602. MS (EI) m/z: 471 (M+). Anal. (C21H17F4NO5S) C,
H, N.
by filtration, washed with water, and then dried in vacuo to
give Z-14a (228 mg, 92%) as a white solid. Mp: 201-204 °C.
1H NMR (CDCl3) δ: 6.46 (dd, J ) 25.2, 3.4 Hz, 1H, C1′-H),
7.12 (dd, J ) 73.8, 3.4 Hz, 1H, C2′-H), 7.41 (dd, J ) 9.5, 6.4
Hz, 1H, C8-H), 8.32 (dd, J ) 9.8, 8.3 Hz, 1H, C5-H), 8.75 (d,
J ) 1.0 Hz, 1H, C2-H). IR (KBr) cm-1: 1720, 1618. MS m/z:
269 (M+). HRMS for C12H6F3NO3 (M+): calcd, 269.0300; found,
269.0302. Anal. (C12H6F3NO3) C, H, N.
6,7-Difluoro-1-[(E)-2-fluorovinyl]-1,4-dihydro-4-oxo-3-
quinolinecarboxylic Acid (E-14a). The compound E-14a
(413 mg, 93%) was prepared from E-13a (489 mg, 1.82 mmol)
by the same method as that used for Z-14a. Mp: 267-269
1
Ethyl 1-[2-Fluoro-2-(4-methoxyphenylsulfinyl)ethyl]-
6,7-difluoro-1,4-dihydro-8-methoxy-4-oxo-3-quinoline-
carboxylate (12c). The compound 12c (1.33 g, 88%) was
prepared from 11c (1.57 g, 3.12 mmol) by the same method as
°C. H NMR (CDCl3) δ: 7.12 (dd, J ) 10.5, 5.9 Hz, 1H, C1′-
H), 7.41 (dd, J ) 73.6, 10.3 Hz, 1H, C2′-H), 7.43 (dd, J ) 10.3,
6.4 Hz, 1H, C8-H), 8.32 (dd, J ) 9.5, 8.3 Hz, 1H, C5-H), 8.73
(s, 1H, C2-H). IR (KBr) cm-1: 1732, 1618. MS m/z: 269 (M+).
HRMS for C12H6F3NO3 (M+): calcd, 269.0300; found, 269.0328.
Anal. (C12H6F3NO3) C, H, N.
1
that used for 12a. Mp: 131-136 °C (MeOH/Et2O). H NMR
(CDCl3) δ: 1.40 (t, J ) 7.3 Hz 3H, CH3), 3.82 (d, J ) 2.4 Hz,
3H, OCH3), 3.89 (3H, s, OCH3), 4.39 (2H, m, CH2), 4.63 (1H,
ddd, J ) 15.3, 12.2, 9.3 Hz, C1′-H), 5.20 (1H, ddd, J ) 49.8,
9.3, 2.4 Hz, C1′-H), 5.33 (1H, ddd, J ) 49.8, 9.3, 2.4 Hz, C2′-
H), 7.10 (d, J ) 8.8 Hz, 2H, Ar-H), 7.62 (d, J ) 8.8 Hz, 2H,
Ar-H), 8.86 (dd, J ) 10.3, 8.8 Hz, 1H, C5-H), 8.32 (1H, s,
C2-H). IR (KBr) cm-1: 1730, 1618. MS m/z: 483 (M+). Anal.
(C22H20F3NO6S‚0.25H2O) C, H, N.
6,7,8-Trifluoro-1-(2-fluorovinyl)-1,4-dihydro-4-oxo-3-
quinolinecarboxylic Acid (14b). The compound 14b (123
mg, 93%) was prepared from 13b (145 mg, 0.460 mmol) by
the same method as that used for Z-14a. Mp: 268-271 °C.
1H NMR (CDCl3) δ: 6.67 (ddd, J ) 24.7, 9.8, 3.5 Hz, 0.5H,
Z-C1′-H), 7.00 (ddd, J ) 74.6, 3.5, 2.0 Hz, 0.5H, Z-C2′-H),
7.35 (dd, J ) 71.6, 9.8 Hz, 0.5H, E-C2′-H), 7.46 (ddd, J ) 10.1,
9.8, 6.8 Hz, 0.5H, E-C1′-H), 8.14-8.20 (m, 1H, C5-H), 8.62
(s, 1H, E-C2-H), 8.65 (d, J ) 1.5 Hz, 0.5H, Z-C2-H). IR (KBr)
Ethyl 6,7-Difluoro-1-(2-fluorovinyl)-1,4-dihydro-4-oxo-
3-quinolinecarboxylate (13a). A mixture of 12a (1.05 g, 2.32
mmol) and xylene (22 mL) was heated under reflux for 3.5 h
and then concentrated in vacuo. Flash chromatography (CH2-
Cl2/MeOH ) 10:1) of the residue gave Z-13a (235 mg, 34%)
and E-13a (427 mg, 62%) as white solids.
cm-1
:
1728, 1618. MS m/z: 287 (M+). Anal. (C12H5F4NO3‚
0.25H2O) C, H, N.
6,7-Difluoro-1-(2-fluorovinyl)-1,4-dihydro-8-methoxy-
4-oxo-3-quinolinecarboxylic Acid (14c). The compound 14c
(913 mg, 96%) was prepared from 13c (1.04 g, 3.18 mmol) by
the same method as that used for Z-14a. Mp: 230-232 °C.
1H NMR (DMSO-d6) δ: 3.93 (d, J ) 1.0 Hz, 2.1H, E-OCH3),
3.95 (d, J ) 1.5 Hz, 0.9H, Z-OCH3), 7.13 (ddd, J ) 28.9, 3.4
Hz, 0.3H, Z-C1′-H), 7.40 (ddd, J ) 76.8, 3.4 Hz, 0.3H, Z-C2′-
H), 7.70 (dd, J ) 16.1, 10.3 Hz, 0.7H, E-C1′-H), 7.81 (dd, J )
81.7, 10.3 Hz, 0.7H, E-C2′-H), 8.07 (dd, J ) 10.3, 8.3 Hz, 0.3H,
Z-C5-H), 8.09 (dd, J ) 10.3, 8.3 Hz, 0.7H, E-C5-H), 8.59 (d,
J ) 1.5 Hz, 0.3H, Z-C2-H), 8.63 (s, 0.7H, E-C2-H), 14.3 (br,
0.3H, COOH), 14.4 (s, 0.7H, COOH). IR (KBr) cm-1: 1736,
1617. MS m/z: 299 (M+). Anal. (C13H8F3NO4) C, H, N.
1
Z-13a. H NMR (CDCl3) δ: 1.41 (t, J ) 7.3 Hz, 3H, CH3),
4.40 (q, J ) 7.3 Hz, 2H, COOCH2), 6.36 (dd, J ) 26.4, 3.4 Hz,
1H, Z-C1′-H), 7.03 (dd, J ) 74.7, 3.4 Hz, 1H, Z-C2′-H), 7.25
(dd, J ) 10.7, 7.8 Hz, 1H, C8-H), 8.26 (dd, J ) 10.3, 8.8 Hz,
1H, C5-H), 8.45 (d, J ) 1.0 Hz, 1H, C2-H). MS (EI) m/z: 297
(M+). HRMS (EI) for C14H10F3NO3 (M+): calcd, 297.0613;
found, 297.0638. Anal. (C14H10F3NO3) C, H, N.
1
E-13a. H NMR (CDCl3) δ: 1.40 (t, J ) 7.3 Hz, 3H, CH3),
4.36 (q, J ) 7.3 Hz, 2H, COOCH2), 7.03 (dd, J ) 10.3, 5.9 Hz,
1H, E-C1′-H), 7.25 (dd, J ) 10.7, 6.4 Hz, 1H, C8-H), 7.47 (dd,
J ) 74.5, 10.3 Hz, 1H, E-C2′-H), 8.16 (dd, J ) 10.3, 8.3 Hz,
1H, C5-H), 8.37 (s, 1H, C2-H). MS (EI) m/z: 297 (M+). HRMS
(EI) for C14H10F3NO3 (M+): calcd, 297.0613; found, 297.0638.
Anal. (C14H10F3NO3) C, H, N.
6-Fluoro-1-[(Z)-2-fluorovinyl]-1,4-dihydro-7-(4-methyl-
1-piperazinyl)-4-oxo-3-quinolinecarboxylic Acid (Z-15a).
A mixture of Z-14a (60 mg, 0.223 mmol), N-methylpiperazine
(54.0 µL, 0.487 mmol), and DMSO (1 mL) was stirred at 60 °C
for 1 h and then concentrated in vacuo. Flash chromatography
(CH2Cl2/MeOH/25% NH4OH ) 20:5:1) of the residue gave
Ethyl 6,7,8-Trifluoro-1-(2-fluorovinyl)-1,4-dihydro-4-
oxo-3-quinolinecarboxylate (13b). The compound 13b (780
mg, 93%) was prepared from 12b (1.25 g, 2.65 mmol) by the
same method as that used for 13a. Mp: 141-143 °C. 1H NMR
(CDCl3) δ: 1.39-1.42 (m, 3H, CH3), 4.36-4.42 (m, 2H,
COOCH2), 6.67 (ddd, J ) 25.9, 9.3, 3.4 Hz, 0.5H, Z-C1′-H),
6.91 (ddd, J ) 75.2, 3.4, 2.0 Hz, 0.5H, Z-C2′-H), 7.39 (ddd, J
) 10.3, 10.0, 4.4 Hz, 0.5H, E-C1′-H), 7.43 (dd, J ) 74.5, 10.3
Hz, 0.5H, E-C2′-H), 8.05-8.13 (m, 1H, C5-H), 8.05 (s, 1H,
1
Z-15a (21 mg, 27%) as a white powder. Mp: 196-199 °C. H
NMR (CDCl3) δ: 2.38 (s, 3H, CH3), 2.62-2.65 (m, 4H, CH2 ×
2), 3.33-3.38 (m, 4H, CH2 × 2), 6.42 (dd, J ) 25.9, 3.4 Hz,
1H, C1′-H), 6.77 (d, J ) 6.4 Hz, 1H, C8-H), 7.06 (dd, J ) 74.3,
3.4 Hz, 1H, C2′-H), 8.05 (d, J ) 12.7 Hz, 1H, C5-H), 8.65 (d,
J ) 1.0 Hz, 1H, C2-H), 14.5-15.0 (br, 1H, COOH). IR (KBr)
cm-1: 1728, 1628. MS m/z: 349 (M+). HRMS for C17H17F2N3O3
(M+): calcd, 349.1238; found, 349.1203. Anal. (C17H17F2N3O3)
C, H, N.
E-C2-H), 8.36 (d, J ) 1.5 Hz, 0.5H, C2-H). IR (KBr) cm-1
:
1730, 1691, 1628. MS m/z: 315 (M+). Anal. (C14H9F4NO3) C,
H, N.
6-Fluoro-1-[(E)-2-fluorovinyl]-1,4-dihydro-7-(4-methyl-
1-piperazinyl)-4-oxo-3-quinolinecarboxylic Acid (E-15a).
The compound E-15a (96 mg, 74%) was prepared from E-14a
(100 mg, 0.371 mmol) by the same method as that used for
Z-15a. Mp: 249-251 °C. 1H NMR (CDCl3) δ: 2.39 (s, 3H, CH3),
2.62-2.65 (m, 4H, CH2 × 2), 3.35-3.38 (m, 4H, CH2 × 2), 6.77
(d, 1H, J ) 6.8 Hz, C8-H), 7.12 (dd, J ) 10.3, 6.4 Hz, 1H,
C1′-H), 7.13 (dd, J ) 74.6, 10.3 Hz, 1H, C2′-H), 8.04 (d, J )
13.2 Hz, 1H, C5-H), 8.61 (s, 1H, C2-H). IR (KBr) cm-1: 1721,
1630. MS m/z: 349 (M+). HRMS for C17H17F2N3O3 (M+): calcd,
349.1238; found, 349.1278. Anal. (C17H17F2N3O3) C, H, N.
6,8-Difluoro-1-[(Z)-2-fluorovinyl]-1,4-dihydro-7-(4-meth-
yl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic Acid (Z-
15b) and 6,8-Difluoro-1-[(E)-2-fluorovinyl]-1,4-dihydro-
7-(4-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic
Acid (E-15b). A mixture of 14b (50 mg, 0.174 mmol), N-
methylpiperazine (43.0 µL, 0.387 mmol), and DMSO (1 mL)
Ethyl 6,7-Difluoro-1-(2-fluorovinyl)-1,4-dihydro-8-meth-
oxy-4-oxo-3-quinolinecarboxylate (13c). The compound
13c (1.09 g, 81%) was prepared from 12c (2.00 g, 4.14 mmol)
by the same method as that used for 13a. Mp: 177-178 °C.
1H NMR (CDCl3) δ: 1.47 (t, J ) 7.3 Hz, 3H, CH3), 3.95 (d, J
) 1.0 Hz, 1H, OCH3), 3.98 (d, J ) 1.5 Hz, 2H, OCH3), 4.36-
4.42 (m, 2H, CH2), 6.78 (s, 0.3H, Z-C1′-H), 6.91 (dd, J ) 51.3,
3.9 Hz, 0.3H, Z-C2′-H), 7.26 (dd, J ) 75.6, 10.3 Hz, 0.7H,
Z-C2′-H), 7.55 (dd, J ) 10.3, 6.8 Hz, 0.7H, E-C1′-H), 8.00-
8.09 (m, 1H, C5-H), 8.29 (s, 0.7H, E-C2-H), 8.35 (d, J ) 2.0
Hz, 0.3H, C2-H). IR (KBr) cm-1: 1730, 1617. MS m/z: 327
(M+). Anal. (C15H12F3NO4) C, H, N.
6,7-Difluoro-1-[(Z)-2-fluorovinyl]-1,4-dihydro-4-oxo-3-
quinolinecarboxylic Acid (Z-14a). A mixture of Z-13a (273
mg, 1.01 mmol), concentrated H2SO4 (0.7 mL), AcOH (3.5 mL),
and water (3.5 mL) was stirred at 100 °C for 1 h and then
poured into ice/water. The resulting precipitates were collected

Analogues of Fleroxacin
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9 3201
was stirred at 60 °C for 1 h and then concentrated in vacuo.
Preparative TLC (CH2Cl2/MeOH ) 10:1) of the residue gave
E-15b (Rf ) 0.40, 34 mg, 53%) as a white solid and Z-15b (Rf
) 0.36, 18 mg, 26%) as a pale-brown solid.
MS (EI) m/z: 335 (M+). HRMS for C16H15F2N3O3 (M+): calcd,
335.1081; Found, 335.1063. Anal. (C16H15F2N3O3 HCl 0.5 H2O)
C, H, N.
7-(3-Amino-1-pyrrolidinyl)-6,8-difluoro-1-[(Z)-2-fluo-
rovinyl]-1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid
Hydrochloride (Z-16b) and 7-(3-Amino-1-pyrrolidinyl)-
6,8-difluoro-1-[(E)-2-fluorovinyl]-1,4-dihydro-4-oxo-3-
quinolinecarboxylic Acid Hydrochloride (E-16b). A mix-
ture of 14b (200 mg, 0.696 mmol), 3-Boc-aminopyrrolidine (156
mg, 0.836 mmol), 1,8-diazabicyclo[5.4.0]undec-7-ene (105 µL,
0.703 mmol), and MeCN (5 mL) was heated under reflux for 1
h and then concentrated in vacuo. The residue was dissolved
in CH2Cl2 (5 mL) and successively washed with water (2 mL),
aqueous 10% citric acid solution (2 × 2 mL), and water (2 mL).
The mixture was then dried over anhydrous Na2SO4 and
concentrated in vacuo. Flash chromatography (CH2Cl2/AcOEt
) 1:1) of the residue gave the Z-Boc-amino derivative of Z-16b
(72 mg, 23%) as a yellow solid and the E-Boc-amino derivative
of E-16b (174 mg, 55%) as a yellow solid. A suspension of the
Z-Boc derivative (53 mg, 0.118 mmol) in saturated HCl in
AcOEt solution (1 mL) was stirred at room temperature for 1
h and then concentrated in vacuo. After MeOH (2 mL) was
added to the residue, the resulting precipitates were collected
by filtration, washed with MeOH, and then dried in vacuo to
give Z-16b (24 mg, 53%) as yellow crystals. Following the same
procedure, the E-Boc-amino derivative (151 mg, 0.333 mmol)
was converted to E-16b (89 mg, 69%), giving a yellow
powder.
1
Z-15b. Mp: 203-205 °C. H NMR (CDCl3) δ: 2.37 (s, 3H,
CH3), 2.57 (br, 4H, CH2 × 2), 3.43 (br, 4H, CH2 × 2), 6.72 (ddd,
J ) 25.9, 10.8, 3.4 Hz, 1H, C1′-H), 6.91 (dd, J ) 74.3, 3.4, 2.0
Hz, 1H, C2′-H), 7.29 (dd, J ) 12.7, 2.0 Hz, 1H, C5-H), 8.56
(d, J ) 1.5 Hz, 1H, C2-H), 14.5-14.7 (br, 1H, COOH). IR (KBr)
cm-1: 1657. MS m/z: 367 (M+). Anal. (C17H16F3N3O3‚0.75H2O)
C, H, N.
1
E-15b. Mp: 248-251 °C. H NMR (CDCl3) δ: 2.37 (s, 3H,
CH3), 2.57 (br, 4H, CH2 × 2), 3.44 (br, 4H, CH2 × 2), 7.26 (ddd,
J ) 73.6, 10.3, 3.4 Hz, 1H, C2′-H), 7.44 (ddd, J ) 11.9, 10.3,
6.4 Hz, 1H, C1′-H), 7.92 (dd, J ) 13.2, 2.0 Hz, 1H, C5-H),
8.56 (s, 1H, C2-H). IR (KBr) cm-1: 1725, 1620. MS m/z: 367
(M+). Anal. (C17H16F3N3O3‚0.25H2O) C, H, N.
6-Difluoro-1-[(Z)-2-fluorovinyl]-1,4-dihydro-8-methoxy-
7-(4-methyl-1-piperazinyl)-4-oxo-3-quinolinecarboxylic
Acid (Z-15c) and 6-Difluoro-1-[(E)-2-fluorovinyl]-1,4-
dihydro-8-methoxy-7-(4-methyl-1-piperazinyl)-4-oxo-3-
quinolinecarboxylic Acid (E-15c). The compounds Z-15c
(15.0 mg, 12%) and E-15c (30.4 mg, 24%) were prepared from
14c (100 mg, 0.334 mmol) by the same method as that used
for Z-15c and E-15c.
1
Z-15c. Mp: 172-175 °C. H NMR (CDCl3) δ: 2.39 (s, 3H,
CH3), 2.52-2.63 (br, 4H, CH2 × 2), 3.43-3.49 (br, 4H, CH2 ×
2), 3.71 (s, 3H, CH3), 6.78 (dd, J ) 17.6, 3.4 Hz, 1H, C1′-H),
6.91 (dd, J ) 66.5, 3.4 Hz, 1H, C2′-H), 7.92 (d, J ) 12.2 Hz,
1H, C5-H), 8.58 (d, J ) 2.0 Hz, 1H, C2-H), 14.4-14.8 (br,
1H, COOH). IR (KBr) cm-1: 1733, 1619. MS (EI) m/z: 379
(M+). HRMS (EI) for C18H19F2N3O4 (M+): calcd, 379.1344;
found, 379.1340. Anal. (C18H19F2N3O4‚0.25H2O) C, H, N.
Z-16b. Mp: 240-244 °C. 1H NMR (DMSO-d6) δ: 2.00-2.08
(m, 1H, CH2), 2.19-2.28 (m, 1H, CH2), 3.66-3.81 (m, 2H, CH2),
3.84-4.02 (m, 3H, CH, CH2), 7.08 (ddd, J ) 28.7, 10.5, 3.4
Hz, 1H, C1′-H), 7.38 (dt, J ) 76.2, 2.9 Hz, 1H, C2′-H), 7.79
(dd, J ) 13.7, 1.5 Hz, 1H, C5-H), 8.51 (d, J ) 1.0 Hz, 1H,
C2-H). IR (KBr) cm-1: 1723, 1628. MS (EI) m/z: 353 (M+).
Anal. (C16H14F3N3O3‚HCl‚2H2O) C, H, N.
1
E-15c. Mp: 229-232 °C. H NMR (CDCl3) δ: 2.39 (s, 3H,
CH3), 2.57-2.59 (br, 4H, CH2 × 2), 3.43-3.45 (br, 4H, CH2 ×
2), 3.73 (s, 3H, CH3), 7.27 (dd, J ) 74.8, 10.3 Hz, 1H, C2′-H),
7.60 (dd, J ) 10.3, 6.8 Hz, 1H, C1′-H), 7.90 (d, J ) 11.7 Hz,
1H, C5-H), 8.52 (s, 1H, C2-H), 14.4-14.7 (br, 1H, COOH).
IR (KBr) cm-1: 1624. MS (EI) m/z: 379 (M+). HRMS (EI) for
C18H19F2N3O4 (M+): calcd, 379.1344; found, 379.1327. Anal.
(C18H19F2N3O4‚0.25H2O) C, H, N.
E-16b. Mp: 258-263 °C. 1H NMR (DMSO-d6) δ: 2.02-2.10
(m, 1H, CH2), 2.19-2.28 (m, 1H, CH2), 3.69-3.75 (m, 2H, CH2),
3.75-4.02 (m, 3H, CH, CH2), 7.67 (ddd, J ) 13.0, 10.3, 8.3
Hz, 1H, C1′-H), 7.80 (dd, J ) 13.7, 1.5 Hz, 1H, C5-H), 7.86
(ddd, J ) 80.2, 10.3, 1.5 Hz, 1H, C2′-H), 8.53 (s, 1H, C2-H).
IR (KBr) cm-1
:
1680, 1626. MS (EI) m/z: 353 (M+). Anal.
(C16H14F3N3O3‚HCl‚0.75H2O) C, H, N.
7-(3-Amino-1-pyrrolidinyl)-6-fluoro-1-[(Z)-2-fluorovinyl]-
1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid Hydro-
chloride (Z-16a). A mixture of Z-14a (60 mg, 0.223 mmol),
3-Boc-aminopyrrolidine (50 mg, 0.268 mmol), 1,8-diazabicyclo-
[5.4.0]undec-7-ene (34 µL, 0.227 mmol), and MeCN (2 mL) was
heated under reflux for 1 h and concentrated in vacuo. After
dilution of the residue with CH2Cl2 (20 mL), the mixture was
successively washed with water (5 mL), aqueous 10% citric
acid solution (2 × 5 mL), and water (5 mL). The mixture was
then dried over anhydrous Na2SO4 and concentrated in vacuo.
The residue was suspended in saturated HCl in AcOEt solution
(2 mL), and the mixture was allowed to stand at room
temperature for 30 min. The resulting precipitates were
collected by filtration, washed with AcOEt, and then dried in
vacuo to give Z-16a (76 mg, 92%) as yellow crystals. Mp: 263-
270 °C. 1H NMR (DMSO-d6 + CF3COOD) δ: 2.09-2.16 (m,
1H, CH2), 2.27-2.36 (m, 1H, CH2), 3.57-3.97 (m, 5H, CH, CH2
× 2), 6.61 (d, J ) 7.3 Hz, 1H, C8-H), 7.07 (dd, J ) 9.3, 3.4 Hz,
1H, C1′-H), 7.49 (dd, J ) 76.2, 3.4 Hz, 1H, C2′-H), 7.87 (d, J
) 14.2 Hz, 1H, C5-H), 8.59 (d, J ) 1.0 Hz, 1H, C2-H). IR
(KBr) cm-1: 1688, 1634. MS (EI) m/z: 335 (M+). HRMS for
C16H15F2N3O3 (M+): calcd, 335.1081; found: 335.1040. Anal.
(C16H15F2N3O3‚HCl‚2.75H2O) C, H, N.
7-(3-Amino-1-pyrrolidinyl)-6-fluoro-1-[(E)-2-fluorovinyl]-
1,4-dihydro-4-oxo-3-quinolinecarboxylic Acid Hydro-
chloride (E-16a). The compound E-16a (66 mg, 48%) was
prepared from E-14a (100 mg, 0.371 mmol) by the same
method as that used for Z-16a. Mp: 276-285 °C. 1H NMR
(DMSO-d6+CF3COOD) δ: 2.10-2.18 (m, 1H, CH2), 2.28-2.37
(m, 1H, CH2), 3.59-4.02 (m, 5H, CH, CH2 × 2), 6.62 (d, J )
7.3 Hz, 1H, C8-H), 7.74 (dd, J ) 10.3, 8.3 Hz, 1H, C1′-H),
7.87 (d, J ) 14.2 Hz, 1H, C5-H), 7.92 (dd, J ) 75.7, 10.3 Hz,
1H, C2′-H), 8.62 (s, 1H, C2-H). IR (KBr) cm-1: 1680, 1626.
7-(3-Amino-1-pyrrolidinyl)-6-fluoro-1-[(Z)-2-fluorovinyl]-
1,4-dihydro-8-methoxy-4-oxo-3-quinolinecarboxylic Acid
Hydrochloride (Z-16c) and 7-(3-Amino-1-pyrrolidinyl)-
6-fluoro-1-[(E)-2-fluorovinyl]-1,4-dihydro-8-methoxy-4-
oxo-3-quinolinecarboxylic Acid Hydrochloride (E-16c).
The compounds Z-16c (14.3 mg, 6%) and E-16c (86 mg, 34%)
were prepared from 14c (200 mg, 0.668 mmol) by the same
method as that used for Z-16b and E-16b.
Z-16c. Mp: 211-219 °C. 1H NMR (DMSO-d6) δ: 1.91-2.08
(m, 1H, CH2), 2.23-2.39 (m, 1H, CH2), 3.51 (s, 3H, OCH3),
3.56-3.67 (m, 1H, CH2), 3.68-3.90 (m, 4H, CH, CH2 × 2), 7.03
(dd, J ) 29.3, 3.4 Hz, 1H, C1′-H), 7.34 (dd, J ) 76.8, 3.4 Hz,
1H, C2′-H), 7.76 (d, J ) 13.7 Hz, 1H, C5-H), 8.27 (br, 3H,
NH‚HCl), 8.49 (d, J ) 1.0 Hz, 1H, C2-H), 14.0-15.5 (br, 1H,
COOH). IR (KBr) cm-1: 1725, 1620. MS (EI) m/z: 365 (M+).
HRMS (EI) for C17H17F2N3O4 (M+): calcd, 365.1187; found,
365.1177. Anal. (C17H17F2N3O4‚HCl‚0.5H2O) C, H, N.
E-16c. Mp: 180-188 °C. 1H NMR (DMSO-d6) δ: 1.91-2.10
(m, 1H, CH2), 2.22-2.34 (m, 1H, CH2), 3.50 (s, 3H, OCH3),
3.58-3.67 (m, 1H, CH2), 3.70-3.96 (m, 4H, CH, CH2 × 2), 7.65
(dd, J ) 10.3, 8.3 Hz, 1H, C1′-H), 7.76 (d, J ) 14.2 Hz, 1H,
C5-H), 7.87 (dd, J ) 76.5, 10.3 Hz, 1H, C2′-H), 8.36 (br, 3H,
NH‚HCl), 8.49 (s, 1H, C2-H), 15.0 (br, 1H, COOH). IR (KBr)
cm-1
:
1722, 1620. MS (EI) m/z: 365 (M+). HRMS (EI) for
C17H17F2N3O4 (M+): calcd, 365.1187; found, 365.1214. Anal.
(C17H17F2N3O4‚HCl‚0.75H2O) C, H, N.
In Vitro Antibacterial Activity. The MIC (µg/mL) was
determined by the agar dilution method14 using Muller-
Hinton agar (Difco Laboratories, Detroit, MI). The MIC was
defined as the lowest concentration of an antibacterial agent
that inhibited visible growth after incubation at 35 °C for 18
h.

3202 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 9
Asahina et al.
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Inhibitory Activity against DNA Gyrase of S. aureus.
The supercoiling activity of DNA gyrase was determined by a
previously reported procedure.15 The inhibitory activity was
assayed by determining the concentration required to inhibit
50% of the enzyme reaction.
Acknowledgment. We thank Dr. Keiji Hirai,
Kyorin Pharmaceutical Co. Ltd., for his encouragement
and support of this project. We are also grateful to Dr.
Yasumichi Fukuda, Kyorin Pharmaceutical Co. Ltd.,
and Drs. James V. Heck and Milton L. Hammond,
Merck Research Laboratories, for their close readings
of this manuscript and for their helpful comments on
the study. We also thank Mr. Masaya Takei and Ms.
Hinako Gomori, Kyorin Pharmaceutical Co. Ltd., for
providing the antibacterial data.
(8) McCarthy, J. R.; Peet, N. P.; LeTourneau, M. E.; Inbasekaran,
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Supporting Information Available: Purity data for
compounds 12-16. This material is available free of charge
via the Internet at http://pubs.acs.org.
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