Synthesis and antibacterial activity of N-[2-[5-(methylthio)thiophen-2-yl]-2-oxoethyl] and N-[2-[5-(methylthio)thiophen-2-yl]-2-(oxyimino)ethyl]piperazinylquinolone derivatives

Article abstract of DOI:10.1016/j.bmc.2005.12.058

A number of N-substituted piperazinylquinolone derivatives were synthesized and evaluated for antibacterial activity against Gram-positive and Gram-negative bacteria. Preliminary results indicated that most compounds tested in this study demonstrated comp

Full text of DOI:10.1016/j.bmc.2005.12.058

Bioorganic & Medicinal Chemistry 14 (2006) 3421–3427
Synthesis and antibacterial activity of
N-[2-[5-(methylthio)thiophen-2-yl]-2-oxoethyl] and
N-[2-[5-(methylthio)thiophen-2-yl]-
2-(oxyimino)ethyl]piperazinylquinolone derivatives
Alireza Foroumadi,a,d Mehdi Oboudiat,b Saeed Emami,c Alireza Karimollah,b
Lotfollah Saghaee,b Mohammad Hassan Moshafid and Abbas Shafieea,*
aFaculty of Pharmacy and Pharmaceutical Sciences Research Center, Tehran University of Medical Sciences, Tehran 14174, Iran
bDepartment of Medicinal Chemistry, Faculty of Pharmacy, Esfahan University of Medical Sciences, Esfahan, Iran
cDepartment of Medicinal Chemistry, Faculty of Pharmacy, Mazandaran University of Medical Sciences, Sari, Iran
dFaculty of Pharmacy, Kerman University of Medical Sciences, Kerman, Iran
Received 12 December 2005; revised 29 December 2005; accepted 29 December 2005
Available online 19 January 2006
Abstract—A number of N-substituted piperazinylquinolone derivatives were synthesized and evaluated for antibacterial activity
against Gram-positive and Gram-negative bacteria. Preliminary results indicated that most compounds tested in this study demon-
strated comparable or better activity against Staphylococcus aureus and Staphylococcus epidermidis than their parent piperazinylqu-
inolones as reference drugs. Among these derivatives, ciprofloxacin derivative 5a, containing N-[2-[5-(methylthio)thiophen-2-yl]-2-
oxoethyl] residue, showed significant improvement of potency against staphylococci, maintaining Gram-negative coverage.
ꢀ 2006 Elsevier Ltd. All rights reserved.
1. Introduction
field, there exists a continuous need for novel quinolones
to overcome the limitations of existing drugs.
The earliest antibacterial agents to be used clinically in
the 1920s were the synthetic sulfonamides. Since then,
quinolones were the only synthetic agents that play a
major role in the treatment of bacterial community or
hospital acquired diseases. The excellent pharmacoki-
netic properties, high antimicrobial activity, and few
side effects that most quinolones demonstrate explain
their widespread use in clinical practice.1 The com-
pounds have had good success against Gram-negative
bacteria, but resistance of Gram-positive pathogens,
such as Staphylococcus aureus, has become a prob-
lem.2–8 In addition, certain adverse events (e.g., CNS
side effects, phototoxicity, and arthropathy) became
apparent, although the more serious events are rare.9,10
Thus, despite many advances in the fluoroquinolone
Quinolones inhibit DNA synthesis by interacting with
two essential bacterial type II topoisomerases, DNA
gyrase and topoisomerase IV.11–13 They inhibit enzyme
function by binding to the catalytic intermediate en-
zyme–DNA complex. The stabilization of the resulting
quinolone–enzyme–DNA complex leads to the genera-
tion of double-strand DNA breaks that trigger a cascade
of events leading to cell death.12–15 The molecular orga-
nization of the complex is presently unknown although
several models have been suggested.16–18 According to
these models, differences in enzyme inhibitory potency
are mainly determined by the binding strength of the
drug to a DNA receptor site on the enzyme–substrate
complex, while the interaction of the C-7 substituent
with the enzyme plays a supporting role.
The 1,4-dihydro-4-oxopyridine-3-carboxylic acid associ-
ated with a 5,6-fused aromatic ring is the common
chemical feature of bactericidal quinolones (Fig. 1). In
the resulting bicyclic ring, the 1-, 5-, 6-, 7-, and 8-posi-
tions are the major targets of chemical variation but,
Keywords: Quinolones; N-Substituted piperazinylquinolones; In vitro
antibacterial activity.
*
Corresponding author. Tel.: +98 21 66406757; fax: +98 21
66461178; e-mail: ashafiee@ams.ac.ir
0968-0896/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.12.058

3422
A. Foroumadi et al. / Bioorg. Med. Chem. 14 (2006) 3421–3427
ethyl moiety attached to the piperazine ring in 7-
piperazinyl quinolones improved the overall antibacteri-
al activity against Gram-positive bacteria.25–28
R5
X
O
F
COOH
R7
N
In continuation of our research program to establish the
structure–activity relationships of N-[2-(thiophen-2-yl)-
2-oxoethyl] and N-[2-(thiophen-2-yl)-2-(oxyimino)eth-
yl]piperazinyl quinolones and their structural features
for anti-Gram-positive activity, we focused mainly on
5-(methylthio)thiophene as the side-chain aryl residue
that, in itself, shows some antimicrobial activity,29 and
investigation of its combination with other substitu-
tions. Thus, we herein report the synthesis and antibac-
terial activity of N-[2-[5-(methylthio)thiophen-2-yl]-2-
oxoethyl]piperazinylquinolones 5a–c and N-[2-[5-(meth-
ylthio)thiophen-2-yl]-2-(oxyimino)ethyl]piperazinylquino-
lone derivatives 6–8 (a–c) (Fig. 2).
R1
Figure 1. Common pharmacophore of quinolones and structure of
some piperazinylquinolones. 1, Ciprofloxacin; R1 = cyclopropyl,
R5 = H, R7 = piperazin-1-yl, X = CH. 2, Norfloxacin; R1 = ethyl,
R5 = H, R7 = piperazin-1-yl, X = CH. 3, Enoxacin; R1 = ethyl,
R5 = H, R7 = piperazin-1-yl, X = N.
synthetic efforts for improved potency have been the
main focus on 7-position.19–21 Both activity spectrum
and kinetic profile can be controlled at C-7. The most
common substituents are cyclic amino groups, for exam-
ple, piperazine or pyrrolidine rings; other groups have
been less successful. Piperazine rings are particularly
common (e.g., ciprofloxacin 1, norfloxacin 2 or enoxacin 3)
and confer potency against Gram-negative bacteria.19–21
The first generation of 7-piperazinyl quinolones,
exemplified by ciprofloxacin, norfloxacin, and enoxacin,
had high activity against Gram-negative species and
atypicals, but moderate activity against Gram-positive
bacteria.2
2. Chemistry
Our synthetic pathway to intermediates 11 and 12a–c,
and target compounds 5a–c and 6–8 (a–c) is presented
in Schemes 1 and 2. Compound 1-[5-(methylthio)thio-
phen-2-yl]ethanone 10 was obtained from 2-bromothio-
phene 9 according to the method reported in the
literature.30,31 Ketone 10 was brominated with copper
(II) bromide in refluxing CHCl3–EtOAc to give corre-
sponding a-bromoketone 11.32 Compound 11 was con-
verted to oxime derivative 12a by stirring with excess
HONH2ÆHCl in methanol at room temperature. Similar-
ly, the O-methyloxime ethers 12b and O-benzyloxime
ethers 12c were synthesized by reaction of compound
11 with O-methylhydroxylamine and O-benzylhydroxyl-
amine hydrochloride, respectively.27,28 Reaction of
quinolones 1, 2 or 3 with a-bromoketone 11 or a-bro-
mooxime derivatives 12a–c in DMF, in the presence of
NaHCO3 at room temperature, afforded corresponding
To explore the potential of tethered 7-piperazinylquinol-
ones as anti-Gram-positive agents, we have reported a
number of N-substituted piperazinylquinolones with
high activity against staphylococci.22–24 In addition, a
number of quinolones 4 with a 2-oxoethyl or a 2-oximi-
noethyl moiety attached to the piperazine ring at C-7
position were synthesized and evaluated for antibacteri-
al activity by us.25–28 The results demonstrated that the
introduction of thiophen-2-yl or 5-bromothiophen-2-yl
group instead of phenyl, substituted phenyl, and fur-
an-2-yl groups at 2 position of 2-oxoethyl or 2-oximino-
O
O
F
COOH
F
COOH
Y
N
X
N
R
N
X
N
R
Y
N
R1
N
H3CS
S
4
5-8
Figure 2. X = CH, N. Y = O, NOH, NOMe, NOCH2Ar. R = cyclopropyl, ethyl. R1 = Ph, substituted-Ph, furan-2-yl thiophen-2-yl, 5-bromothio-
phen-2-yl.
NOR1
Br
O
O
d
a, b
c
H3CS
H3CS
H3CS
S
Br
Br
S
S
CH3
S
12a;R1= H
12b;R1= Me
12c;R1= Bn
11
9
10
Scheme 1. Synthesis of a-bromoketone 11 and a-bromooxime derivatives12a–c. Reagents and conditions: (a) Mg, S8, CH3I, Et2O; (b) Ac2O, H3PO4;
(c) CuBr2, CHCl3–AcOEt, reflux; (d) hydroxylamine hydrochloride or O-methyl hydroxylamine hydrochloride or O-benzyl hydroxylamine
hydrochloride, MeOH, rt.

A. Foroumadi et al. / Bioorg. Med. Chem. 14 (2006) 3421–3427
3423
O
COOH
F
O
N
X
N
R
N
H3CS
S
a
O
5a-c
COOH
F
O
COOH
F
X
N
R
N
b
HN
NOR1
N
X
N
R
1-3
N
H3CS
S
6-8(a-c)
Scheme 2. Synthesis of compounds 5a–c and 6–8 (a–c). Reagents and conditions: (a) a-bromoketone 11, NaHCO3, DMF, rt; (b) a-bromooxime
derivatives 12a–c, NaHCO3, DMF, rt.
ketones 5a–c and oxime derivatives 6–8 (a–c),
respectively.27,28
individual minimum inhibitory concentrations (MICs,
lg/mL) obtained for compounds 5a–c and 6–8 (a–c)
are presented in Table 1.
3. Results and discussion
The MIC values of the test derivatives against Staphylo-
coccus strains indicate that most compounds possessed a
comparable or better activity (MIC = 0.03–1 lg/mL)
with respect to the reference drugs (MIC = 0.25–1
lg/mL). Compounds 7a, 5a, and 6a followed by 7b
and 5b are superior in inhibiting the growth of S. aureus
(MIC = 0.03–0.5 lg/mL). Compound 7a was the most
active compound against S. aureus, its activity
found to be 16–32 times better than reference drugs.
Derivatives 5a, 6a, and 7a were the most active against
S. epidermidis, showing MIC values of 0.03 lg/mL, their
activities 8- to 16-fold more than reference drugs.
Compounds 5a–c and 6–8 (a–c) were evaluated for their
antibacterial activity against Gram-positive (S. aureus
ATCC 6538p, Staphylococcus epidermidis ATCC
12228, and Bacillus subtilis PTCC 1023) and Gram-neg-
ative (Escherichia coli ATCC 8739, Klebsiella pneumo-
niae ATCC 10031, andPseudomonas aeruginosa ATCC
9027) bacteria using conventional agar-dilution meth-
od.33 The MIC (minimum inhibitory concentration) val-
ues were determined by comparison to ciprofloxacin 1,
norfloxacin 2, and enoxacin 3 as reference drugs. The
Table 1. Structures and in vitro antibacterial activities of compounds 5a–c and 6–8 (a–c) against selected strains (MICs in lg/mL)
O
COOH
F
Y
N
X
N
R
N
H3CS
S
Compound
X
Y
R
S. aureus
S. epidermidis
B. subtilis
K. pneumoniae
E. coli
0.125
P. aeruginosa
5a
5b
5c
6a
6b
6c
7a
7b
7c
8a
8b
8c
1
CH
CH
N
O
Cyclopropyl
Ethyl
Ethyl
0.06
0.5
0.5
0.06
1
0.03
4
0.125
8
0.125
8
1
16
O
8
1
O
0.5
0.03
2
1
1
4
32
CH
CH
N
NOH
NOH
NOH
NOMe
NOMe
NOMe
NOBn
NOBn
NOBn
Cyclopropyl
Ethyl
Ethyl
2
64
2
1
>64
>64
2
>64
>64
1
>64
>64
16
>64
0.03
0.25
1
64
>64
0.5
8
CH
CH
N
Cyclopropyl
Ethyl
Ethyl
0.03
0.25
1
8
8
32
8
64
8
64
8
>64
>64
>64
>64
1
CH
CH
N
Cyclopropyl
Ethyl
Ethyl
16
32
32
64
>64
64
8
64
>64
64
>64
64
>64
0.5
1
(Ciprofloxacin)
(Norfloxacin)
(Enoxacin)
0.25
0.5
0.5
0.015
0.06
0.125
0.03
0.125
0.25
0.125
2
0.25
0.25
4
3
1
4

3424
A. Foroumadi et al. / Bioorg. Med. Chem. 14 (2006) 3421–3427
Antibacterial screening of compounds 5a–c and 6–8 (a–
c) against B. subtilis reveals that compounds 5a and 7a
possessed a significant activity. Derivative 5a was the
most potent against B. subtilis (MIC = 0.125 lg/mL),
being equipotent to enoxacin.
These organisms can be resistant to multiple antimicro-
bial agents, which severely limits therapeutic options in
selected instances. The susceptibility of an organism to a
particular quinolone is determined by both the ability of
the agent to penetrate the cell envelope and the inhibito-
ry activity of the agent against its target.34 It has been
reported that the activity of some quinolones against
staphylococci is dependent on the bulkiness of the sub-
stituents at C-7 position, demonstrating that molecular
mass is not a limiting factor for activity against staphy-
lococci.35 In addition, the C-7 substituent affects the
interaction with the target, and both activity spectrum
and kinetic profile can be controlled at C-7.2,16–18 There-
fore, our methodology to achieve a better antimicrobial
profile against staphylococci, by focusing on the func-
tionality at C-7 position and introducing a certain resi-
due on piperazine ring, would be useful.
Generally, most compounds showed poor or no activity
(MIC > 16 lg/mL) against Gram-negative bacteria.
However, compound 5a was the most potent against
all Gram-negative bacteria, with a MIC value of
0.125–1 lg/mL. Its activity was found to be comparable
to those of reference drugs.
The first information obtained in this study is that most
compounds exhibit high activity against Gram-positive
bacteria and less activity against Gram-negative bacte-
ria. Thus, introduction of 2-[5-(methylthio)thiophen-2-
yl]ethyl residue carrying 2-oxo- or 2-oxyimino groups
at the N-4 position of piperazine ring changes the anti-
bacterial profile of piperazinylquinolones. In general,
N-[2-[5-(methylthio)thiophen-2-yl]-2-oxoethyl]- and N-
[2-[5-(methylthio)thiophen-2-yl]-2-oximinooethyl] groups
are well tolerated in terms of Gram-positive activity.
In many cases, the compounds had activity superior to
the their parent quinolones. However, the improved
activity against Gram-positive bacteria can often be at
the expense of activity against Gram-negative bacteria.
In addition, ketones 5, oximes 6, and O-methyl
oximes 7 showed more potent antibacterial activity than
O-benzyl oximes 8 against both Gram-positive and
Gram-negative bacteria. Comparison between MIC
values of ketones 5, oximes 6, and O-methyl oximes 7
revealed that oximation of ketones seemed to have
different influence on the antibacterial activity against
various bacteria strains. For example, ketone 5a, oxime
6a, and O-methyl oxime 7a in ciprofloxacin series
showed equipotent activity against staphylococci, while
ketones 5 exhibited more potent activity than oxime
derivatives 6 against Gram-negative bacteria.
In conclusion, we have described the synthesis and
antibacterial evaluation of a new series of N-substitut-
ed piperazinylquinolones characterized by having N-[2-
[5-(methylthio)thiophen-2-yl]ethyl residue as a bulky
side-chain. Preliminary results indicated that most
compounds demonstrated comparable or better activi-
ty against S. aureus and S. epidermidis than their par-
ent piperazinylquinolones as reference drugs. Among
these derivatives, ciprofloxacin derivative 5a, contain-
ing N-[2-[5-(methylthio)thiophen-2-yl]-2-oxoethyl] resi-
due, showed significant improvement of potency
against staphylococci, maintaining Gram-negative
coverage.
4. Experimental
Chemicals and all solvents used in this study were
purchased from Merck AG and Aldrich Chemical. The
1-[5-(methylthio)thiophen-2-yl]ethanone 10 was pre-
pared according to the literature.30,31 Melting points
were determined on a Kofler hot stage apparatus and
are uncorrected. The IR spectra were obtained on a Shi-
madzu 470 spectrophotometer (potassium bromide
The results of MIC tests against both Gram-positive and
Gram-negative bacteria revealed that ciprofloxacin
derivatives (R = cyclopropyl and X = CH) were more
active than norfloxacine and enoxacine derivatives
(R = ethyl and X = CH or N). These data confirm that
the effect of changes in the side-chain of the 7-piperazi-
nyl ring mainly depends on the substituent at N-1
position.
1
disks). H NMR spectra were measured using a Bruker
FT-80 spectrometer, and chemical shifts are expressed as
d (ppm) with tetramethylsilane as internal standard. The
mass spectra were run on a Finnigan TSQ-70 spectrom-
eter (Finnigan, USA) at 70 eV. Elemental analyses were
carried out on a CHN-O rapid elemental analyzer
(GmbH-Germany) for C, H, and N, and the results
are within 0.4% of the theoretical values. Merck silica
gel 60 F254 plates were used for analytical TLC; column
chromatography was performed on Merck silica gel (70–
230 mesh). Yields are of purified product and were not
optimized.
First approach in the series of new 2-[5-(methyl-
thio)thiophen-2-yl]ethyl derivatives of piperazinyl quin-
olones bearing different structural features on the
quinolone ring and piperazine moiety points out that
the compound 5a exerts significant in vitro antibacterial
activity against staphylococci and it was more potent
than the reference drugs against S. aureus and S. epide-
rmidis, maintaining its Gram-negative coverage. Indeed,
the overall activity of compound 5a against Gram-posi-
tive (especially staphylococci) and Gram-negative bacte-
ria was the best among thiophene derivatives and other
aryl side chains in N-(2-oxoethyl) and N-[(2-(oxyimi-
no)ethyl]piperazinyl quinolone series 4.25–28 Staphylo-
cocci have been recognized as important pathogens.
4.1. 2-Bromo-1-[5-(methylthio)thiophen-2-yl]ethanone
(11)
A vigorously stirred solution of compound 10 (5.0 g,
29 mmol) in CHCl3–EtOAc (1:1, 50 mL) was refluxed
and then, pulverized copper (II) bromide (12.2 g,
55.0 mmol) was added portionwise during 4 h. The
resulting reaction mixture was refluxed with vigorous

A. Foroumadi et al. / Bioorg. Med. Chem. 14 (2006) 3421–3427
3425
stirring for additional 2 h to ensure complete exposure
of the copper (II) bromide to the reaction medium until
the reaction was completed as judged by a color change
of the solution from green to amber, disappearance of
all black solid, and cessation of HBr evolution. After
removal of the copper (I) bromide (white solid) by filtra-
tion, the solvents were evaporated from the filtrate
under reduced pressure. The residue was purified by col-
umn chromatography, eluting with hexane–chloroform
and crystallized from n-heptane to give compound 11
(4.3 g). Yield 62%; mp 58–59 ꢁC; mmax (KBr) 1660
0.3 mmol) in DMF (10 mL) was stirred at room temper-
ature for 8–10 h. After consumption of piperazinylqui-
nolone (monitored by TLC), H2O (20 mL) was added
and the precipitate was filtered, washed with water,
and crystallized from EtOH–CHCl3 to give compounds
5a–c.
4.5.1. 1-Cyclopropyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methyl-
thio)thiophen-2-yl]-2-oxoethyl]piperazin-1-yl]-4-oxo-3-quino-
lone carboxylic acid (5a). Yield 29%; mp 174–175 ꢁC
(dec); mmax (KBr) 1660, 1710 and 1725 (C@O) cmÀ1
;
(C@O) cmÀ1
;
1H NMR (CDCl3) d 2.60 (s, 3H,
1H NMR (CDCl3) 1.10–1.40 (m, 4H, cyclopropyl),
2.55 (s, 3H, S-CH3), 2.70 (br s, 4H, piperazine), 3.45
(br s, 4H, piperazine), 3.35–3.64 (m, 1H, cyclopropyl),
3.69 (s, 2H, COCH2N), 6.90 (d, 1H, J = 4.4 Hz,
thiophene), 7.30 (d,1H, H8, JH,F = 7.0 Hz), 7.81
(d, 1H, J = 4.4 Hz, thiophene), 7.90 (d, 1H, H5-quino-
line, JH,F = 12.5 Hz), 8.70 (s, 1H, H2-quinoline).
S-CH3), 4.30 (s, 2H, CH2Br), 6.95 (d, 1H, J = 4.4 Hz,
thiophene), 7.65 (d, 1H, J = 4.4 Hz, thiophene).
4.2. 2-Bromo-1-[5-(methylthio)thiophen-2-yl]ethanone
oxime (12a).
A solution of 11 (300 mg, 1.2 mmol), hydroxylamine
hydrochloride (4.8 mmol), and concentrated HCl
(0.7 mL) in CH3OH (20 mL) was stirred at room tem-
perature for 7 days. Then, H2O (25 mL) was added
and the precipitate was filtered, washed with water,
and crystallized from n-hexane to give compound 12a
(229 mg). Yield 72%; mp 150–151 ꢁC; mmax (KBr) 3200
4.5.2. 1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methylthio)
thiophen-2-yl]-2-oxoethyl]piperazin-1-yl]-4-oxo-3-quinolone
carboxylic acid (5b). Yield 65%; mp 197–198 ꢁC (dec);
mmax (KBr) 1660, 1715 and 1735 (C@O) cmÀ1 1H
;
NMR (CDCl3) 1.60 (t, 3H, J = 7.2 Hz, -CH3 ethyl),
2.60 (s, 3H, S-CH3), 2.90 (br s, 4H, piperazine), 3.41
(br s, 4H, piperazine), 3.70 (s, 2H, COCH2N), 4.45 (q,
2H, J = 7.2 Hz, -CH2- ethyl), 6.95 (d, 1H, J = 4.4 Hz,
thiophene), 7.00 (d,1H, H8, JH,F = 7.0 Hz), 7.85 (d,
1H, J = 4.4 Hz, thiophene), 7.99 (d, 1H, H5-quinoline,
JH,F = 12.5 Hz), 8.81 (s, 1H, H2-quinoline).
1
(OH), 1610 (C@N) cmÀ1; H NMR (CDCl3) d 2.55 (s,
3H, S-CH3), 4.50 (s, 2H, CH2Br), 7.00 (d, 1H,
J = 4.5 Hz, thiophene), 7.45 (d, 1H, J = 4.5 Hz, thio-
phene). MS (m/z) 265 (M+), 267 (M++2).
4.3. 2-Bromo-1-[5-(methylthio)thiophen-2-yl]ethanone
O-methyloxime (12b)
4.5.3. 1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methylthio)-
thiophen-2-yl]-2-oxoethyl]
piperazin-1-yl]-4-oxo-1,8-
naphthyridine-3-carboxylic acid (5c). Yield 71%; mp
155–156 ꢁC (dec.); mmax (KBr) 1660, 1710 and 1730
A solution of 11 (400 mg, 1.6 mmol) and O-methylhydr-
oxylamine hydrochloride (266 mg, 3.2 mmol) in CH3OH
(15 mL) was stirred at room temperature for 7 days.
Water (40 mL) was added and extracted with CHCl3.
The organic layer was washed (H2O), dried (Na2SO4),
and evaporated in vacuo to give 12b as a viscous oil. Yield
85%; 1H NMR (CDCl3) d 2.55 (s, 3H, S-CH3), 4.10 (s, 3H,
O-CH3), 4.50 (s, 2H, CH2Br), 6.95 (d, 1H, J = 4.5 Hz,
thiophene), 7.20 (d, 1H, J = 4.5 Hz, thiophene).
(C@O) cmÀ1
;
1H NMR (CDCl3) 1.45 (t, 3H,
J = 7.2 Hz, -CH3 ethyl), 2.62 (s, 3H, S-CH3), 2.75 (br
s, 4H, piperazine), 3.70 (s, 2H, COCH2N), 3.95 (br s,
4H, piperazine), 4.35 (q, 2H, J = 7.2 Hz, -CH2-ethyl),
6.91 (d, 1H, J = 4.4 Hz, thiophene), 7.75 (d, 1H,
J = 4.4 Hz, thiophene), 8.01 (d, 1H, H5-quinoline,
JH,F = 12.6 Hz), 8.65 (s, 1H, H2-quinoline).
4.4. 2-Bromo-1-[5-(methylthio)thiophen-2-yl]ethanone
O-benzyloxime (12c)
4.6. General procedure for the synthesis of N-[2-[5-
(methylthio)thiophen-2-yl]-2- hydroxyiminoethyl]piper-
azinylquinolones 6a–c
A solution of 11 (251 mg, 1.0 mmol) and O-benzylhydr-
oxylamine hydrochloride (240 mg, 1.5 mmol) in CH3OH
(20 mL) was stirred at room temperature for 48 h. Water
(30 mL) was added and extracted with CHCl3. The
organic layer was washed (H2O), dried (Na2SO4), and
evaporated in vacuo to give 12c as a viscous oil. Yield
A mixture of compound 12a (88 mg, 0.33 mmol), piper-
azinylquinolone 1–3 (0.3 mmol), and NaHCO3 (26 mg,
0.3 mmol) in DMF (10 mL) was stirred at room tempera-
ture for 6 h. After consumption of piperazinylquinolone
(monitored by TLC), water (20 mL) was added and the
precipitate was filtered, washed with water, and crystal-
lized from EtOH–DMF to give compounds 6a–c.
1
92%; H NMR (CDCl3) d 2.50 (s, 3H, S-CH3), 4.50 (s,
2H, CH2Br), 5.25 (s, 2H, O-CH2), 6.95 (d, 1H,
J = 4.4 Hz, thiophene), 7.15 (d, 1H, J = 4.4 Hz, thio-
phene), 7.20–7.50 (m, 5H, phenyl).
4.6.1.
1-Cyclopropyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-
(methylthio)thiophen-2-yl]-2-hydroxyiminoethyl]pipera-
zin-1-yl]-4-oxo-3- quinolone carboxylic acid (6a). Yield
69%; mp 249–250 ꢁC (dec); mmax (KBr) 1710 and 1725
4.5. General procedure for the synthesis of N-[2-[5-
(methylthio)thiophen-2-yl]-2-oxoethyl]piperazinylquinol-
ones 5a–c
(C@O) cmÀ1 1H NMR (CDCl3) 1.15–1.40 (m, 4H,
;
cyclopropyl), 2.49 (s, 3H, S-CH3), 2.61 (br s, 4H, piper-
azine), 3.36 (br s, 4H, piperazine), 3.50 (s, 2H, CH2N),
3.61–3.92 (m, 1H, cyclopropyl), 7.10 (d, 1H,
A mixture of compound 11 (83 mg, 0.33 mmol), piper-
azinylquinolone 1–3 (0.3 mmol), and NaHCO3 (26 mg,

3426
A. Foroumadi et al. / Bioorg. Med. Chem. 14 (2006) 3421–3427
J = 4.4 Hz, thiophene), 7.60 (d,1H, H8, JH,F = 7.0 Hz),
7.75 (d, 1H, J = 4.4 Hz, thiophene), 7.90 (d, 1H, H5-
quinoline, JH,F = 12.6 Hz), 8.65 (s, 1H, H2-quinoline),
12.00 (s, 1H, OH).
zine), 3.25 (br s, 4H, piperazine), 3.55 (s, 2H, CH2N),
3.90 (s, 3H, OCH3), 4.25 (q, 2H, J = 7.0 Hz, -CH2- eth-
yl), 6.85 (d,1H, H8, JH,F = 7.0 Hz), 6.90 (d, 1H,
J = 4.4 Hz, thiophene), 7.30 (d, 1H, J = 4.4 Hz, thio-
phene), 8.00 (d, 1H, H5-quinoline, JH,F = 12.6 Hz),
8.60 (s, 1 H, H2-quinoline).
4.6.2.
1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methyl-
thio)thiophen-2-yl]-2- hydroxyiminoethyl]piperazin-1-yl]-
4-oxo-3-quinolone carboxylic acid (6b). Yield 81%; mp
240–241 ꢁC (dec); mmax (KBr) 1715 and 1725 (C@O)
4.7.3. 1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methylthio)
thiophen-2-yl]-2-methoxyiminoethyl]piperazin-1-yl]-4-oxo-
1,8-naphthyridine-3-carboxylic acid (7c). Yield 64%; mp
177–178 ꢁC (dec); mmax (KBr) 1710 and 1725 (C@O)
cmÀ1 1H NMR (DMSO-d6) 1.40 (t, 3H, J = 7.0 Hz,
;
-CH3 ethyl), 2.56 (s, 3H, S-CH3), 2.65 (br s, 4H, pipera-
zine), 3.30 (br s, 4H, piperazine), 3.55 (s, 2H, CH2N),
4.59 (q, 2H, J = 7.0 Hz, -CH2- ethyl), 7.05 (d, 1H,
J = 4.4 Hz, thiophene), 7.20 (d,1H, H8, JH,F = 7.0 Hz),
7.75 (d, 1H, J = 4.4 Hz, thiophene), 7.90 (d, 1H, H5-
quinoline, JH,F = 12.6 Hz), 8.89 (s, 1H, H2-quinoline),
11.91 (s, 1H, OH).
1
cmÀ1; H NMR (CDCl3) 1.50 (t, 3H, J = 7.0 Hz, -CH3
ethyl), 2.49 (s, 3H, S-CH3), 2.64 (br s, 4H, piperazine),
3.55 (s, 2H, CH2N), 3.89 (br s, 4H, piperazine), 3.90 (s,
3H, OCH3), 4.30 (q, 2H, J = 7.0 Hz, -CH2- ethyl), 6.90
(d, 1H, J = 4.3 Hz, thiophene), 7.30 (d, 1H, J = 4.3 Hz,
thiophene), 8.05 (d, 1H, H5-quinoline, JH,F = 12.8 Hz),
8.70 (s, 1H, H2-quinoline).
4.6.3.
1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methyl-
thio)thiophen-2-yl]-2- hydroxyiminoethyl]piperazin-1-yl]-
4-oxo-1,8-naphthyridine-3-carboxylic acid (6c). Yield
73%; mp 248–249 ꢁC (dec); mmax (KBr) 1710 and 1725
4.8. General procedure for the synthesis of N-[2-[5-
(methylthio)thiophen-2-yl]-2-(benzyloxyimino)ethyl]piper-
azinylquinolones 8a–c
(C@O) cmÀ1
;
1H NMR (DMSO-d6) 1.40 (t, 3H,
J = 7.0 Hz, -CH3 ethyl), 2.49 (s, 3H, S-CH3), 2.62 (br
s, 4H, piperazine), 3.50 (s, 2H, CH2N), 3.85 (br s, 4H,
piperazine), 4.48 (q, 2H, J = 7.0 Hz, -CH2- ethyl), 7.11
(d, 1H, J = 4.4 Hz, thiophene), 7.70 (d, 1H, J = 4.4 Hz,
thiophene), 8.10 (d, 1H, H5-quinoline, JH,F = 12.6 Hz),
8.95 (s, 1H, H2-quinoline), 11.95 (s, 1H, OH).
A mixture of compound 12c (100 mg, 0.28 mmol), piper-
azinylquinolone 1–3 (0.25 mmol), and NaHCO3 (21 mg,
0.25 mmol) in DMF (8 mL) was stirred at room temper-
ature for 12 h. After consumption of piperazinylquino-
lone (monitored by TLC), H2O (25 mL) was added
and extracted with CHCl3. The organic layer was
washed (H2O), dried (Na2SO4), and evaporated in vac-
uo. The residue was crystallized from ethanol to give
compounds 8a–c.
4.7. General procedure for the synthesis of N -[2-[5-
(methylthio)thiophen-2-yl]-2-methoxyiminoethyl] piper-
azinylquinolones 7a–c
4.8.1. 1-Cyclopropyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(meth-
ylthio)thiophen-2-yl]-2-(benzyloxyimino)ethyl]piperazin-1-
yl]-4-oxo-3-quinolone carboxylic acid (8a). Yield 50%;
mp 164–165 ꢁC; mmax (KBr) 1710 and 1725 (C@O)
A mixture of compound 12b (92 mg, 0.33 mmol), piper-
azinylquinolone 1–3 (0.3 mmol), and NaHCO3 (26 mg,
0.3 mmol) in DMF (10 mL) was stirred at room temper-
ature for 6–10 h. After consumption of piperazinylqui-
nolone (monitored by TLC), H2O (25 mL) was added
and extracted with CHCl3. The organic layer was
washed (H2O), dried (Na2SO4), and evaporated in vac-
uo. The residue was crystallized from EtOH–DMF to
give compounds 7a–c.
1
cmÀ1; H NMR (CDCl3) 1.21–1.50 (m, 4H, cyclopro-
pyl), 2.55 (s, 3H, S-CH3), 2.75 (br s, 4H, piperazine),
3.40 (br s, 4H, piperazine), 3.50 (m, 1H, cyclopropyl),
3.70 (s, 2H, CH2N), 5.22 (s, 2H, OCH2), 6.95 (d, 1H,
J = 4.4 Hz, thiophene), 7.00 (d, 1H, H8, JH,F = 7.0 Hz),
7.25–7.50 (m, 5H, phenyl), 7.70 (d, 1H, J = 4.4 Hz, thi-
ophene), 8.00 (d, 1H, H5-quinoline, JH,F = 12.6 Hz),
8.75 (s, 1H, H2-quinoline).
4.7.1.
1-Cyclopropyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-
(methylthio)thiophen-2-yl]-2-methoxyiminoethyl]piperazin-
1-yl]-4-oxo-3- quinolone carboxylic acid (7a). Yield 54%;
mp 175–176 ꢁC (dec.); mmax (KBr) 1710 and 1720 (C@O)
4.8.2. 1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methyl-
thio)thiophen-2-yl]-2-(benzyloxyimino)ethyl]piperazin-1-yl]-
4-oxo- 3-quinolone carboxylic acid (8b). Yield 62%; mp
1
cmÀ1; H NMR (CDCl3) 1.22–1.46 (m, 4H, cyclopro-
pyl), 2.61 (s, 3H, S-CH3), 2.75 (br s, 4H, piperazine),
3.36 (br s, 4H, piperazine), 3.55 (s, 2H, CH2N), 3.40–
3.70 (m, 1H, cyclopropyl), 4.11 (s, 3H, OCH3), 6.95
(d, 1H, J = 4.4 Hz, thiophene), 7.35 (d, 1H, H8,
JH,F = 7.0 Hz), 7.75 (d, 1H, J = 4.4 Hz, thiophene),
8.05 (d, 1H, H5-quinoline, JH,F = 12.6 Hz), 8.75 (s, 1H,
H2-quinoline).
166–167 ꢁC; mmax (KBr) 1710 and 1720 (C@O) cmÀ1
;
1H NMR (CDCl3) 1.55 (t, 3H, J = 7.0 Hz, -CH3 ethyl),
2.49 (s, 3H, S-CH3), 2.65 (br s, 4H, piperazine), 3.35 (br
s, 4H, piperazine), 3.71 (s, 2H, CH2N), 4.30 (q, 2H,
J = 7.0 Hz, -CH2- ethyl), 5.21 (s, 2H, OCH2), 6.85
(d,1H, H8, JH,F = 7.0 Hz), 6.95 (d, 1H, J = 4.2 Hz, thio-
phene), 7.20–7.50 (m, 5H, phenyl),7.70 (d, 1H,
J = 4.2 Hz, thiophene), 8.05 (d, 1H, H5-quinoline,
JH,F = 12.6 Hz), 8.66 (s, 1H, H2-quinoline).
4.7.2. 1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methyl-
thio)thiophen-2-yl]-2-methoxyiminoethyl]piperazin-1-yl]-4-
oxo-3-quinolone carboxylic acid (7b). Yield 72%; mp
;
4.8.3. 1-Ethyl-6-fluoro-1,4-dihydro-7-[4-[2-[5-(methyl-
thio)thiophen-2-yl]-2-(benzyloxyimino)ethyl]piperazin-1-yl]-
4-oxo-1,8-naphthyridine-3- carboxylic acid (8c). Yield
60%; mp 116–117 ꢁC; mmax (KBr) 1710 and 1725
180–181 ꢁC; mmax (KBr) 1710 and 1725 (C@O) cmÀ1
1H NMR (CDCl3 + DMSO-d6) 1.50 (t, 3H, J = 7.0 Hz,
-CH3 ethyl), 2.45 (s, 3H, S-CH3), 2.70 (br s, 4H, pipera-

A. Foroumadi et al. / Bioorg. Med. Chem. 14 (2006) 3421–3427
3427
(C@O) cmÀ1; 1H NMR (CDCl3) 1.50 (t, 3H, J = 7.0 Hz,
-CH3 ethyl), 2.45 (s, 3H, S-CH3), 2.50 (br s, 4H, pipera-
zine), 3.65 (s, 2H, CH2N), 3.70 (br s, 4H, piperazine),
4.35 (q, 2H, J = 7.0 Hz, -CH2- ethyl), 5.15 (s, 2H,
OCH2), 6.90 (d, 1H, J = 4.4 Hz, thiophene), 7.16–7.44
(m, 5H, phenyl), 7.70 (d, 1H, J = 4.4 Hz, thiophene),
8.00 (d, 1H, H5-quinoline, JH,F = 12.6 Hz), 8.60 (s, 1H,
H2-quinoline).
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double dilution with melted Muller–Hinton agar was
performed to obtain the required concentrations of 64,
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37 ꢁC for 18 h. The minimum inhibitory concentration
(MIC) was the lowest concentration of the test com-
pound, which resulted in no visible growth on the plate.
To ensure that the solvent had no effect on bacterial
growth, a control test was performed with test medium
supplemented with DMSO at the same dilutions as used
in the experiment.
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Acknowledgment
This work was partially supported by a grant from Iran
National Science Fundation (INSF).
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