Synthesis and in vitro antibacterial activity of 7-(3-alkoxyimino-4-methyl- 4-methylaminopiperidin-1-yl)-fluoroquinolone derivatives

Article abstract of DOI:10.1002/ardp.200900191

A series of novel 7-(3-alkoxyimino-4-methyl-4-methylaminopiperidin-1-yl) fluoroquinolone derivatives were designed, synthesized, and characterized by ¹H-NMR, MS, and HRMS. These fluoroquinolones were evaluated for their in-vitro antibacterial activity against representative Gram-positive and Gram-negative strains. Generally, all of the target compounds have considerable antibacterial activity against the tested forty strains, and exhibit exceptional potency in inhibiting the growth of methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) ATCC33591 (MICs: 0.06 to 2 μg/mL). In particular, compounds 14, 19, 28, and 29 are fourfold more potent than ciprofloxacin against MSSA 08-49. Compounds 23, 26, and 27 are twofold more potent than ciprofloxacin against MRSA ATCC33591 and MSSA ATCC29213. In addition, compound 14 exhibits excellent activity (MIC: 0.06 μg/mL) against Acinetobacter calcoaceticus, which is two- to 16-fold more potent than the reference drugs gemifloxacin, levofloxacin, and ciprofloxacin.

Full text of DOI:10.1002/ardp.200900191

Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
Y.-B. Zhang et al.
143
Full Paper
Synthesis and In Vitro Antibacterial Activity of
7-(3-Alkoxyimino-4-methyl-4-methylaminopiperidin-1-yl)-
fluoroquinolone Derivatives
Yi-Bin Zhang, Lian-Shun Feng, Xue-Fu You, Qiang Guo, Hui-Yuan Guo, and Ming-Liang Liu
Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical
College, Beijing, P.R. China
A series of novel 7-(3-alkoxyimino-4-methyl-4-methylaminopiperidin-1-yl)fluoroquinolone deriv-
atives were designed, synthesized, and characterized by 1H-NMR, MS, and HRMS. These fluoroqui-
nolones were evaluated for their in-vitro antibacterial activity against representative Gram-posi-
tive and Gram-negative strains. Generally, all of the target compounds have considerable anti-
bacterial activity against the tested forty strains, and exhibit exceptional potency in inhibiting
the growth of methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aur-
eus (MRSA) ATCC33591 (MICs: 0.06 to 2 lg/mL). In particular, compounds 14, 19, 28, and 29 are
fourfold more potent than ciprofloxacin against MSSA 08-49. Compounds 23, 26, and 27 are two-
fold more potent than ciprofloxacin against MRSA ATCC33591 and MSSA ATCC29213. In addi-
tion, compound 14 exhibits excellent activity (MIC: 0.06 lg/mL) against Acinetobacter calcoaceticus,
which is two- to 16-fold more potent than the reference drugs gemifloxacin, levofloxacin, and
ciprofloxacin.
Keywords: Antibacterial activity / Fluoroquinolone / Synthesis /
Received: August 10, 2009; Accepted: November 25, 2009
DOI 10.1002/ardp.200900191
Supporting information for this article is available from the author or on the WWW under
http://www.wiley-vch.de/contents/jc_2019/2010/2009-00191_s.pdf
Although most of the quinolones currently on the mar-
ket or under development are generally characterized by
a broad antimicrobial spectrum, their activity against
clinically important Gram-positive pathogens, including
Staphylococcus aureus, Streptococcus pyogenes, Streptococcus
pneumoniae, and Enterococcus, is relatively moderate,
which has not only limited their use in infections caused
by these organisms, but is also believed to be one of the
reasons for the rapidly developing quinolone resistance.
Thus, recent efforts have been directed toward the syn-
thesis of new quinolones that can provide improved
Gram-positive antibacterial activity, while retaining the
good Gram-negative activity of early fluoroquinolones,
such as ciprofloxacin (CPFX) and ofloxacin [5–8].
Introduction
Quinolone antibacterial agents are among the most
important drugs in the anti-infective chemotherapy
field. These antibiotics exert their antimicrobial effect by
inhibition of two type-II bacterial topoisomerase
enzymes, DNA gyrase and topoisomerase IV, which are
essential cellular enzymes that catalyze the double-
strand breakage of DNA to allow strand passage and,
thereby, control the topology and conformation of DNA
[1–4].
Correspondence: Dr. Ming-Liang Liu, Institute of Medicinal Biotechnol-
ogy, Chinese Academy of Medical Sciences and Peking Union Medical
College, Beijing 100050, P.R. China.
E-mail: lmllyx@yahoo.com.cn
Fax: +86 10 630 47865
Structure-activity relationship (SAR) studies of quino-
lone antibacterial agents showed that the basic group at
the C-7 position is the most adaptable site for chemical
change and an area that greatly influences their potency,
spectrum, and safety [9, 10]. In general, 5- and 6-mem-
Abbreviations: ciprofloxacin (CPFX); gemifloxacin (GMFX); levofloxacin
(LVFX); methicillin-resistant S. aureus (MRSA); methicillin-sensitive S.
aureus (MSSA)
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144
Y.-B. Zhang et al.
Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
Figure 1. Structures of Gemifloxacin, DW 286, and DZH.
bered nitrogen heterocycles including piperazinyl-, pyr-
rolidinyl-, and piperidinyl-type side chains have been pro-
ven to be the optimal substituents [11]. However, rela-
tively few quinolone antibacterial agents possessing
piperidine substitution have been reported in the litera-
ture, as compared to that of piperazinyl- and pyrroli-
dinyl-based derivatives [12].
As part of an ongoing program to find potent new qui-
nolones displaying strong Gram-positive antibacterial
activity, we have focused our attention on introducing
new functional groups to the piperidine ring [13, 14]. Pre-
vious work on pyrrolidine analogs suggested that intro-
duction of a methyl group in the 3-position of the pyrroli-
dine ring can increase Gram-positive activity [15]. For
example, an analog of gemifloxacin (GMFX), DW 286
(Fig. 1), possessing an additional methyl group at the 3-
position of the pyrrolidine ring, displays far more potent
antibacterial activity than GMFX against important
Gram-positive organisms, methicillin-resistant S. aureus
(MRSA), and ofloxacin-resistant organisms, while main-
taining an excellent pharmacokinetic profile [16]. We
applied this structural modification to DZH (Fig. 1), which
shows good in-vitro activity against Gram-positive and
Gram-negative organisms, including MRSA and Pseudomo-
nas aeruginosa [12]. A series of fluoroquinolone com-
pounds containing piperidinyl substitution at the C-7
position were designed and synthesized. These derivatives
are structurally novel, having both a methylamino and a
methyl group at the 4-position and an alkoxyimino group
at the 3-position of the piperidine ring. Our primary objec-
tive was to optimize the potency of these compounds
against Gram-positive and Gram-negative organisms.
Reagents and conditions: i) H2, Pd/C, EtOH; ii) Boc2O, NaHCO3, EtOH, H2O; iii)
MeI, K2CO3, Me2CO; iv) R1ONH2 . HCl, Et3N, EtOH, H2O; v) aq. NaOH, EtOH; vi)
HOAc, H2O; vii) ClCOOBu-i, Et3N, CH2Cl2; viii) NH3, CH2Cl2; ix) aq. NaBrO, MeCN; x)
Boc2O, MeOH; xi) MeI, NaH, MeCN; xii) HCl, CH2Cl2.
Scheme 1. Synthesis of new piperidine derivatives 12a, b.
Reagents and conditions: xiii) 12a, b, Et3N, MeCN; xiv) 2% NaOH; xv) aq. HCl.
Results and discussion
Scheme 2. Synthesis of novel fluoroquinolones 14–29.
Chemistry
3, which was methylated with methyl iodide to produce
methyl ketone 4. The ketone 4 was smoothly converted to
oximes 5a, b by reaction with alkoxylamines in ethanol
at 608C. However, direct ammonolysis of the ester moiety
in 5a, b was unsuccessful.
Therefore, the esters 5a, b were first converted to the
acids 6a, b by saponification and acidification. The acids
6a, b were subsequently reacted with isobutyl chlorofor-
The new piperidine derivatives 12a, b and novel fluoro-
quinolones 14–29 described herein were synthesized as
shown in Schemes 1 and 2, respectively. According to
published procedures [17–22], catalytic hydrogenation of
ethyl N-benzyl-3-oxopiperidine-4-carboxylate hydrochlo-
ride 1 gave the secondary amine 2. The amine 2 was sub-
sequently treated with di-tert-butyl dicarbonate in etha-
nol to form the tert-butoxycarbonyl-protected compound
i 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
New Piperidinylquinolone Derivatives
145
Table 1. Structures and physical data of novel fluoroquinolones 14–29.
Compound R1
R2
X
N
N
Yield (%)
48
M.p. (8C)§
170–171
199–201
ESI-MS[M+ + H]
14
15
Me
Et
418
432
47
16
17
18
19
Me
Et
Me
Et
2,4-F2-C6H3
2,4-F2-C6H3
Et
N
N
CF
CF
37
32
55
56
115–118
161–164
172–175
174–177
490
504
423
449
20
21
Me
Et
2-F-C2H4
2-F-C2H4
CF
CF
41
53
171–174
168–170
441
455
22
Me
CH
24
192–194
417
23
Et
CH
21
158–160
431
24
25
Me
Et
Et
Et
CH
CH
17
18
168–169
204–206
405
419
26
27
Me
Et
COMe
COMe
36
35
82–84
447
461
167–169
28
29
Me
Et
40
39
169–170
159–162
433
447
§ Melting points are uncorrected.
mate to give the activated esters 7a, b, which upon well-established literature procedures (Scheme 2; [23]). In
ammonolysis afforded amides 8a, b by pumping ammo- the case of quinolones 14–17, condensation of 12a, b
nia gas in methylene chloride. The three steps mentioned with 13a, b was carried out in the presence of triethyl-
above were performed by one-pot method in an overall amine. However, for 18–29, boric chelates 13c–i were
yield of 40%.
used to increase the reactivity. Table 1 shows the novel
Hoffmann degradation of the amides 8a, b used freshly fluoroquinolone analogs, yields of the final coupling
prepared sodium hypobromite instead of commercially step, and the melting points of the purified compounds.
available sodium hypochlorite to give amines 9a, b,
Since the oxime group can exist in the E- or Z-configu-
which were subsequently protected by a tert-butoxycar- ration, it was necessary to determine the geometries of
bonyl group to form compounds 10a, b. Methylation of all the oxime target compounds 14–29. It was a pity that
10a, b was performed by reaction with methyl iodide in we were not successful in preparing X-ray-quality single
the presence of sodium hydride to produce compounds crystals of compounds 14–29. In the NOE spectra of 14–
11a, b. Deprotection of the bis-tert-butoxycarbonyl 29, there was no correlation between the oxime group
groups on the amines 11a, b was carried out by pumping and its neighbor group (methylamino group or methyl
dry hydrogen chloride gas in methylene chloride to group). So it is quite probable that the geometry of the
afford the new piperidine derivative dihydrochlorides oxime group is the E-configuration. Finally, we were able
12a, b in a good yield.
to obtain X-ray data for compound 8a [24]. As expected,
The coupling reaction of the piperidine derivatives the geometry of the methyloxime group on the piperi-
12a, b with various compounds containing quinolone dine ring which adopts a boat conformation is the E-con-
and naphthyridine cores was performed according to figuration (Fig. 2).
i 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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146
Y.-B. Zhang et al.
Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
Table 2. In-vitro antibacterial activity of compounds 14–29.
Com-
MIC (lg/mL)§
pound
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
GMFX LVFX
CPFX
S.a. 1#
S.a. 2
S.a. 3
S.a. 4
S.a. 5
S.e. 1
S.e. 2
S.e. 3
S.p. 1
S.p. 2
S.p. 3
S.p. 4
S.py. 1
S.py. 2
S.py. 3
E.fa. 1
E.fa. 2
E.fa. 3
E.fa. 4
E.fm. 1
E.fm. 2
E.fm. 3
E.co. 1
E.co. 2
E.co. 3
K.p. 1
K.p. 2
P.a. 1
P.a. 2
P.a. 3
S.s.
0.5
0.125 0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
2
1
2
0.5
0.25
0.5
2
1
2
0.25
>128
2
8
1
2
1
2
0.5
0.25
1
0.5
1
2
1
2
0.25
0.25
1
0.5
0.5
0.5
0.06
64
0.5
2
0.5
2
4
128
2
4
8
128
2
f0.03 0.125 0.5
0.125 0.25
0.5 0.25
0.125 0.125 0.25
128
1
2
0.5
0.5
4
64
0.5
2
4
128
2
0.125 0.125 0.5
0.25
f0.03 0.06
0.125
0.5
0.06
64
0.5
2
0.5
2
4
128
1
8
8
128
1
0.5
0.25
1
f0.03 0.125 0.5
0.125 0.125 0.5
0.125 0.06
>128
4
16
2
16
16
>128
16
16
16
>128
8
4
8
8
>128
>128
>128
1
0.25
>128
2
16
2
16
32
>128
16
16
32
>128
4
4
8
8
128
>128
>128
2
0.125 0.125 0.25
64
4
32
4
64
64
64
16
64
64
64
8
16
16
32
0.06
128
1
2
0.5
2
2
128
2
2
4
128
2
2
2
2
128
128
>128
0.5
0.5
>128
16
>128
>128
2
f0.03 0.06
0.25
4
64
0.5
2
0.5
1
4
128
1
4
4
128
1
1
>128
2
4
1
1
2
>128
1
2
4
>128
4
2
4
8
>128
1
8
1
2
8
>128
2
4
8
>128
16
4
4
16
>128
>128
>128
8
64
1
2
0.5
1
2
64
1
2
64
0.5
2
0.25
2
4
128
2
4
8
128
1
1
>128
2
16
1
32
0.5
1
0.25
0.5
1
128
0.5
1
2
128
1
1
1
64
0.5
1
0.5
1
2
128
1
2
2
128
1
1
2
2
64
>128
64
1
0.5
1
0.06
0.06
0.125 0.25
1
2
f0.03 0.125 0.25
8
8
f0.03 0.5
1
1
64
1
1
16
>128
16
16
32
>128
4
4
8
8
16
128
8
16
16
128
4
2
4
4
0.5
32
2
32
f0.03 0.5
0.125
1
4
1
4
2
32
1
128
0.5
0.5
1
32
0.5
0.5
1
f0.03 0.5
1
1
2
2
2
2
2
2
4
0.06
0.06
0.5
32
32
32
0.25
0.5
2
64
64
64
1
4
1
2
2
1
1
128
128
>128
0.25
0.25
>128
8
>128
>128
1
>128
0.06
0.06
0.125
0.06
0.125
1
64
64
64
0.25
0.5
>128
16
>128
>128
2
>128
0.5
0.25
2
0.5
2
>128
>128
>128
4
64
128
64
0.25
0.25
>128
16
>128
128
2
>128
0.25
0.125 0.5
1
0.25
>128
>128
>128
2
64
64
128
0.5
0.5
>128
16
>128
>128
4
>128
0.5
0.25
1
1
1
64
64
64
0.5
1
>128
32
>128
>128
8
>128
1
1
4
1
128
128
>128
2
64
128
128
64
0.25
0.25
>128
16
>128
32
2
128
0.25
0.125 0.5
1
0.25
1
128
128
128
0.5
1
>128
32
>128
128
8
>128
2
0.5
4
8
4
>128
64
>128
128
128
16
f0.03 f0.03 f0.03
f0.03 f0.03 f0.03
4
16
2
2
2
2
32
1
>128
64
>128
>128
8
>128
4
2
8
2
8
8
>128
128
>128
>128
32
>128
8
16
64
8
64
64
>128
32
>128
>128
8
>128
2
0.5
4
2
4
4
2
>128
32
>128
>128
8
>128
64
>128
>128
8
>128
2
1
8
4
4
4
>128
64
>128
>128
16
>128
2
1
8
4
4
>128
>128
>128
>128
64
>128
4
4
32
16
16
16
>128
32
>128
>128
2
32
0.5
32
1
32
0.5
32
1
128
0.5
64
1
0.125 0.25
32
0.25
16
>128
4
>128
1
>128
0.5
0.06
2
2
2
2
1
2
2
8
f0.03 f0.03 f0.03
f0.03 f0.03 f0.03
B.t.
E.cl.
A.c.
E.a.
S.m.
M.m.
P.r.
P.v.
P.m.
4
4
4
4
2
4
4
>128
4
1
4
8
2
4
4
>128
f0.03 0.06
0.125 0.25
f0.03
1
2
2
1
2
2
>128
2
4
4
4
4
>128
f0.03 f0.03 f0.03
0.125 0.25 0.25
f0.03 f0.03
0.25 f0.03
4
2
4
4
2
1
2
1
4
2
8
4
8
1
2
1
4
2
8
2
0.5
1
1
16
8
8
32
32
32
>128
2
8
8
>128
16
32
16
>128
0.06
0.06
8
4
>128
f0.03 f0.03 f0.03
>128
>128
>128
>128
>128
64
128
128
8
1
2
§ The values were reproduced in three experiments; # Abbreviations: S.a. 1: Staphylococcus aureus ATCC29213; S.a. 2: Staphylococcus aureus ATCC13709; S.a. 3: Staphylococcus aureus
ATCC33591; S.a. 4: methicillin-sensitive Staphylococcus aureus 08-49; S.a. 5: methicillin-resistant Staphylococcus aureus 08-52; S.e. 1: Staphylococcus epidermidis ATCC12228; S.e. 2: me-
thicillin-sensitive Staphylococcus epidermidis 08-17; S.e. 3: methicillin-resistant Staphylococcus epidermidis 08-18; S.p. 1: Streptococcus pneumoniae ATCC49619; S.p. 2: Streptococcus
pneumoniae ATCC6301; S.p. 3: Streptococcus pneumoniae ATCC10813; S.p. 4: penicillin-resistant Streptococcus pneumoniae 08-2; S.py. 1: Streptococcus pyogenes 556; S.py. 2: Streptococcus
pyogenes 08-12; S.py. 3: Streptococcus pyogenes 08-13; E.fa. 1: Enterococcus faecalis ATCC29212; E.fa. 2: Enterococcus faecalis ATCC51299; E.fa. 3: Enterococcus faecalis HH22; E.fa. 4: vanco-
mycin-resistant Enterococcus faecalis EFL1004; E.fm. 1: Enterococcus faecium ATCC700221; E.fm. 2: Enterococcus faecium 06-7; E.fm. 3: vancomycin-resistant Enterococcus faecium 05-7;
E.co. 1: Escherichia coli ATCC25922; E.co. 2: Escherichia coli ATCC35218; E.co. 3: Escherichia coli 08-5 (ESBLs); K.p. 1: Klebsiella pneumoniae ATCC700603; K.p. 2: Klebsiella pneumoniae 08-
2 (ESBLs); P.a. 1: Pseudomonas aeruginosa ATCC27853; P.a. 2: Pseudomonas aeruginosa 17; P.a. 3: Pseudomonas aeruginosa PA01; S.s.: Shigella sonnei 51592; B.t.: Bacillus typhi 50035; E.cl.:
Enterobacter cloacae 45301; A.c.: Acinetobacter calcoaceticus 25001; E.a.: Enterobacter aerogenes 45102; S.m.: Serratia marcescens 41002; M.m.: Morganella morganii 49086; P.r.: Proteus re-
ttgeri 49006; P.v.: Proteus vuigaris 56; P.m.: Proteus mirabilis 08-19.
Antibacterial activity
The novel fluoroquinolones 14–29 were evaluated for
their in-vitro antibacterial activity against 22 Gram-posi-
tive and 18 Gram-negative strains using standard tech-
niques [25]. Minimum inhibitory concentration (MIC) is
defined as the concentration of the compound required
to give complete inhibition of bacterial growth and MICs
of the synthesized compounds along with that of the
standard drugs GMFX, CPFX, and levofloxacin (LVFX) for
comparison are reported in Table 2.
All of the target compounds 14–29 generally have a
potent antibacterial activity against the tested 40 strains.
They exhibit good potency in inhibiting the growth of
Figure 2. X-ray structure of compound 8a.
i 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
New Piperidinylquinolone Derivatives
147
methicillin-sensitive S. aureus (MSSA) and MRSA ATCC fold more potent than CPFX against MSSA 08-49. Com-
33591 (MICs: 0.06–2 lg/mL). In particular, compounds 14, pounds 23, 26, and 27 are twofold more potent than CPFX
19, 28, and 29 are comparable to LVFX, and fourfold more against MRSA ATCC33591 and MSSA ATCC29213. In addi-
potent than CPFX against MSSA 08-49. Compounds 23, 26, tion, compound 14 exhibits excellent activity (MIC: 0.06
and 27 are twofold more potent than CPFX against MRSA lg/mL) against A. calcoaceticus, which is 2- to 16-fold more
ATCC33591 and MSSA ATCC29213. In addition, com- potent than GMFX, LVFX, and CPFX.
pound 14 exhibits excellent activity (MIC: 0.06 lg/mL)
against Acinetobacter calcoaceticus, which is 2- to 16-fold
more potent than GMFX, LVFX, and CPFX (MICs: 0.125 to 1
lg/mL). However, overall the piperidinyl analogs exhibit
Experimental
Chemistry
less activity than the reference drugs against Gram-posi-
tive and Gram-negative strains, except against MSSA.
Compound 14, bearing the same quinolone nucleus as
DZH, is much less active than GMFX against the tested
strains, except against A. calcoaceticus. These results sug-
gest that introduction of another methyl group into the
4-position of the piperidine ring causes reduced antibac-
terial activity, which is in contrary to the activity profiles
of pyrrolidine-containing fluoroquinolones.
The activity of the quinolone nuclei in this study are in
the order: 1-cyclopropyl-8-fluoroquinolone L 1-cyclo-
propyl-8-methoxylquinolone > 1-cyclopropyl-8-hydrogen-
quinolone L 1-cyclopropyl-1,8-naphthyridine > levofloxa-
cin nuclei > 1-(2,4-difluorophenyl)-1,8-naphthyridine > 1-
ethyl-8-hydrogen-quinolone L 1-(2-fluoroethyl)-8-fluoro-
quinolone > 1-ethyl-8-fluoroquinolone against Gram-posi-
tive strains. In the case of Gram-negative strains, the
activity is in the order: 1-cyclopropyl-8-fluoroquinolone >
1-cyclopropyl-1,8-naphthyridine > 1-cyclopropyl-8-meth-
oxyl-quinolone L 1-cyclopropyl-8-hydrogenquinolone L
levofloxacin nuclei > 1-ethyl-8-fluoroquinolone L 1-(2-flu-
oroethyl)-8-fluoroquinolone > 1-ethyl-8-hydrogenquino-
lone > 1-(2,4-difluorophenyl)-1,8-naphthyridine. Gener-
ally, in both Gram-positive and Gram-negative strains,
better results are obtained with a cyclopropyl group at
the N-1 position, while analogs bearing an ethyl or 2-fluo-
roethyl group show relatively low potency. In addition,
fluoroquinolones featuring methyloxime-incorporated
piperidino-substitution at the C-7 position are at least as
potent as the analogs containing ethyloxime.
All chemical reagents and solvents used in this study were pur-
chased from Beihua Fine Chemicals Company (Beijing, China).
The starting material 1 was purchased from Bayoupharm Com-
pany (Chengdu, China). Melting points were determined in open
glass capillaries and are uncorrected. 1H-NMR spectra were
recorded on a Varian Mercury-400 or an INOVA-500 spectrome-
ter 400 (both: Varian Inc., Palo Alto, CA, USA) using tetramethyl-
silane as internal standard. Electron spray ionization (ESI) mass
spectra and high resolution mass spectra (HRMS) were recorded
on a MDSSCIEX Q-Tap mass spectrometer (Applied Biosystems,
USA). Merck silica gel ART5554 60F254 plates (Merck, Germany)
were used for analytical TLC. Column chromatography was car-
ried out on silica gel HG/T2354-92 made in Haiyang Chemical
Company (Qingdao, China).
Ethyl 3-oxopiperidine-4-carboxylate hydrochloride 2
A mixture of 1 (18.0 g, 60.4 mmol), ethanol (200 mL) and 5% Pd/C
(2.5 g) was stirred for 4 h at 0.5 MPa hydrogen pressure and room
temperature and filtered. The filtrate was concentrated under
reduced pressure. The resulting solid residue was recrystallized
from methanol/ethyl acetate to afford compound 2 (11.8 g, 95%)
as a white solid. M. p.: 200–2028C; 1H-NMR (CDCl3, 500 MHz) dH:
1.29 (t, 3H, J = 6.5 Hz, OCH2CH3), 1.66–1.67 (m, 1H), 2.69–2.71 (m,
2H), 3.30–3.35 (m, 2H), 3.80–3.81 (m, 2H), 4.26 (q, 2H, J = 6.5 Hz,
OCH2CH3), 10.24 (br, 2H, NH2 ); ESI-MS m/z: 172 [M+ + H].
+
Ethyl N-tert-butoxycarbonyl-3-oxopiperidine-4-
carboxylate 3
To a stirred solution of 2 (2.1 g, 10.1 mmol) in ethanol (12 mL)
were added sodium bicarbonate (1.0 g, 10.1 mmol) dissolved in
water (12 mL) and di-tert-butyl dicarbonate (2.2 g, 10.1 mmol),
respectively. The reaction mixture was stirred for 1 h at the
room temperature and concentrated under reduced pressure.
The residue was diluted with water (20 mL) and extracted with
methylene chloride (3615 mL). The combined extracts were
washed with saturated brine, dried over anhydrous sodium sul-
fate, and concentrated under reduced pressure. The crude prod-
uct was purified by column chromatography (silica gel, petro-
leum ether/ethyl acetate) to afford compound 3 (2.7 g, 100%) as a
colorless liquid. 1H-NMR (CDCl3, 500 MHz) dH: 1.32 (t, 3H, J = 7.0
Hz, OCH2CH3), 1.47 (s, 9H, Boc-9H), 1.52–1.53 (m, 1H), 2.32–2.34
(m, 2H), 3.47–3.49 (m, 2H), 4.02–4.03 (m, 2H), 4.23 (q, 2H, J = 7.0
Hz, OCH2CH3); ESI-MS m/z: 272 [M+ + H].
Conclusion
In summary, a series of novel 7-(3-alkoxyimino-4-methyl-
4-methylaminopiperidin-1-yl)fluoroquinolone derivati-
ves were designed, synthesized, and evaluated for their
in-vitro antibacterial activity against 40 Gram-positive
and Gram-negative strains. Generally, all of the target
compounds 14–29 demonstrate potent antibacterial
activity, and they exhibit good potency in inhibiting the
growth of MSSA and MRSA ATCC33591 (MICs: 0.06–2 lg/
mL). In particular, compounds 14, 19, 28, and 29 are four-
Ethyl N-tert-butoxycarbonyl-4-methyl-3-oxopiperidine-4-
carboxylate 4
A solution of methyl iodide (20.0 mL, 0.32 mol) in dry acetone
(90 mL) was added to a suspension of 3 (43.6 g, 0.16 mol) and
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anhydrous potassium carbonate (88.8 g, 0.32 mol) in dry acetone
(300 mL) while stirring at 508C under an atmosphere of nitro-
gen. The reaction mixture was stirred for 1.5 h at the same tem-
perature, and then cooled to room temperature and filtered.
The filtrate was concentrated under reduced pressure. The resi-
due was diluted with ethyl acetate (100 mL) and washed with
water and saturated saline, dried over anhydrous sodium sul-
fate, and concentrated under reduced pressure. The crude prod-
uct was purified by column chromatography (silica gel, petro-
leum ether/ethyl acetate) to afford compound 4 (32.0 g, 70%) as a
colorless liquid. 1H-NMR (CDCl3, 400 MHz) dH: 1.23 (t, 3H, J = 7.2
Hz, OCH2CH3), 1.32 (s, 3H, CH3), 1.44 (s, 9H, Boc-9H), 1.66–1.71 (m,
1H), 2.52–2.57 (m, 1H), 3.60–3.61 (m, 3H), 4.13–4.19 (m, 3H); ESI-
MS m/z: 284 [M+ + H].
tic acid solution, water, and saturated brine, dried over anhy-
drous sodium sulfate and concentrated under reduced pressure.
The residue was purified by column chromatography (silica gel,
petroleum ether/ethyl acetate) to afford compound 8a (22.6 g,
40%) as a white solid. M. p.: 140–1428C;1H-NMR (CDCl3, 400 MHz)
dH: 1.37–1.46 (m, 12H), 1.50–1.57 (m, 1H), 2.43–2.49 (m, 1H),
3.38–3.53 (m, 2H), 3.89 (s, 3H, OCH3), 4.17–4.45 (m, 2H), 5.57 (br,
1H), 6.00 (br, 1H); ESI-MS m/z: 286 [M+ + H].
N-tert-Butoxycarbonyl-4-carbamyl-3-ethoxyimino-4-
methylpiperidine 8b
The title compound was obtained in a similar manner as for the
preparation of 8a (41%) as a white solid. M.p.: 88–908C; 1H-NMR
(CDCl3, 400 MHz) dH: 1.27 (t, 3H, J = 6.8 Hz, OCH2CH3), 1.42–1.45
(m, 12H), 1.50–1.58 (m, 2H), 2.45–2.51 (m, 1H), 3.32–3.51 (m, 2H),
3.88 (q, 2H, J = 6.8 Hz, OCH2CH3), 4.20–4.33 (m, 1H), 5.23 (br, 1H),
6.01 (br, 1H); ESI-MS m/z: 300 [M+ + H].
Ethyl N-tert-butoxycarbonyl-3-methoxyimino-4-
methylpiperidine-4-carboxylate 5a
A solution of methoxylamine hydrochloride (21.0 g, 0.25 mol)
and triethylamine (35.0 mL, 0.25 mol) in 80% ethanol (85 mL)
was added dropwise to a solution of 4 (65.5 g, 0.23 mol) in etha-
nol (250 mL) while stirring at 608C. The reaction mixture was
stirred for 2 h at the same temperature and concentrated under
reduced pressure. The residue was diluted with water (100 mL)
and extracted with methylene chloride (3650 mL). The com-
bined extracts were washed with saturated brine, dried over
anhydrous sodium sulfate, and concentrated under reduced
pressure. The crude product was purified by column chromatog-
raphy (silica gel, petroleum ether/ethyl acetate) to afford com-
pound 5a (64.2 g, 89%) as a colorless liquid. 1H-NMR (CDCl3, 400
MHz) dH: 1.22–1.25 (m, 3H), 1.39 (s, 3H, CH3), 1.45 (s, 9H, Boc-9H),
1.55–1.62 (m, 1H), 2.38–2.44 (m, 1H), 3.36–3.49 (m, 2H), 3.88 (s,
3H, OCH3), 4.03–4.06 (m, 1H), 4.17–4.20 (m, 2H), 4.53–4.57 (m,
1H); ESI-MS m/z: 315 [M+ + H].
N-tert-Butoxycarbonyl-4-(N-tert-butoxycarbonyl)amino-3-
methoxyimino-4-methylpiperidine 10a
To a solution of 8a (11.5 g, 40.4 mmol) in acetonitrile (300 mL) a
freshly prepared sodium hypobromite solution (95 mL) was
added dropwise at 58C. The reaction mixture was stirred for 10 h
at the same temperature and then concentrated under reduced
pressure. The residue containing 9a was dissolved in methanol
(150 mL), and to this solution di-tert-butyl dicarbonate (4.4 g,
20.2 mmol) was added portionwise and stirred for 2 h at room
temperature. After removal of the methanol under reduced pres-
sure, the residue was diluted with water (200 mL) and extracted
with methylene chloride (36100 mL). The combined extracts
were washed with saturated brine, dried over anhydrous sodium
sulfate, and concentrated under reduced pressure. The crude
product was purified by column chromatography (silica gel,
petroleum ether / ethyl acetate) to afford compound 10a (6.4 g,
44%) as a colorless liquid. 1H-NMR (CDCl3, 400 MHz) dH: 1.41–1.47
(m, 18H, 2 Boc-9H), 1.54 (s, 3H, CH3), 1.97–2.04 (m, 1H), 2.44–2.45
(m, 1H), 3.22–3.29 (m, 1H), 3.68–3.74 (m, 1H), 3.85–3.95 (m, 4H),
4.72–4.73 (m, 1H), 5.64 (br, 1H); ESI-MS m/z: 358 [M+ + H].
Ethyl N-tert-butoxycarbonyl-3-ethoxyimino-4-
methylpiperidine-4-carboxylate 5b
The title compound was obtained in a similar manner as for the
preparation of 5a (80%) as a colorless liquid. 1H-NMR (CDCl3, 500
MHz) dH: 1.23–1.26 (m, 6H), 1.40 (s, 3H, CH3), 1.45 (s, 9H, Boc-9H),
1.52–1.62 (m, 1H), 2.38–2.42 (m, 1H), 3.41–3.51 (m, 2H), 4.07–4.20
(m, 5H), 4.57–4.63 (m, 1H); ESI-MS m/z: 329 [M+ + H].
N-tert-Butoxycarbonyl-4-(N-tert-butoxycarbonyl)amino-3-
ethoxyimino-4-methylpiperidine 10b
The title compound was obtained in a similar manner as for the
preparation of 10a (50%) as a colorless liquid.1H-NMR (CDCl3, 400
MHz) dH: 1.26 (t, 3H, J = 6.8 Hz, OCH2CH3), 1.42–1.47 (m, 18H, 2
Boc-9H), 1.54 (s, 3H, CH3), 1.99–2.05 (m, 1H), 2.44–2.45 (m, 1H),
3.22–3.29 (m, 1H), 3.70–3.73 (m, 1H), 3.94–3.95 (m, 1H), 4.13 (q,
2H, J = 6.8 Hz, OCH2CH3), 4.75–4.76 (m, 1H), 5.66 (br, 1H); ESI-MS
m/z: 372 [M+ + H].
N-tert-Butoxycarbonyl-4-carbamyl-3-methoxyimino-4-
methylpiperidine 8a
To a stirring solution of 5a (64.2 g, 0.20 mol) in ethanol (60 mL)
was added dropwise a solution of sodium hydroxide (13.9 g, 0.35
mol) dissolved in water (30 mL) at room temperature. The reac-
tion mixture was stirred for 5 h at the same temperature. After
removal of the ethanol under reduced pressure, the reaction
mixture was diluted with water (30 mL), adjusted to pH = 6–6.5
with acetic acid (24.0 mL, 0.42 mol), and then extracted with
methylene chloride (3650 mL). The combined extracts were
washed with saturated brine, dried over anhydrous sodium sul-
fate, and filtered. To the filtrate containing 6a was added tri-
ethylamine (70 mL, 0.50 mol). The reaction mixture was cooled
to –15 to –208C using an ice-salt bath, isobutyl chloroformate (65
mL, 0.50 mol) was added dropwise and stirred for 2 h at the same
temperature to give the activated ester 7a. To the reaction mix-
ture containing 7a ammonia gas was cautiously pumped at 0–
58C for 1 h. The reaction mixture was then washed with 10% ace-
N-tert-Butoxycarbonyl-3-methoxyimino-4-methyl-4-(N-
tert-butoxycarbonyl)methylaminopiperidine 11a
To a stirring solution of 10a (5.0 g, 14.4 mmol) in dry acetonitrile
(80 mL) 60% sodium hydride (1.7 g, 42.5 mmol) was added at 58C
under an atmosphere of nitrogen and then stirred for 0.5 h at
the same temperature. A solution of methyl iodide (2.6 mL, 42.0
mmol) in dry acetonitrile (20 mL) was added to the suspension
and stirred for 3 h at 58C. To this mixture enough water was
added dropwise to consume the excess sodium hydride, and
then concentrated under reduced pressure. The residue was
diluted with water (100 mL) and extracted with methylene chlor-
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Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
New Piperidinylquinolone Derivatives
149
ide (3650 mL). The combined extracts were washed with satur-
ated brine, dried over anhydrous sodium sulfate, and concen-
trated under reduced pressure. The crude product was purified
by column chromatography (silica gel, petroleum ether/ethyl
acetate) to afford compound 11a (4.2 g, 81%) as a colorless liquid.
1H-NMR (CDCl3, 400 MHz) dH: 1.42–1.46 (m, 18H, 2 Boc-9H), 1.58
(s, 3H, CH3), 2.80–2.86 (m, 4H), 3.41–3.52 (m, 2H), 3.78–3.88 (m,
4H), 4.24–4.66 (m, 2H); ESI-MS m/z: 394 [M+ + Na].
1-Cyclopropyl-6-fluoro-7-(3-ethoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-1,8-
naphthyridin-3-carboxylic acid 15
1H-NMR (CDCl3, 400 MHz) dH: 1.06–1.10 (m, 2H), 1.23–1.32 (m,
5H), 1.35 (s, 3H, CH3), 1.90–2.02 (m, 3H), 2.32 (s, 3H, NCH3), 3.62–
3.66 (m, 1H), 3.97–4.02 (m, 1H), 4.06–4.16 (m, 3H), 4.40 (d, 1H, J =
16.4 Hz, C29-H), 5.24 (d, 1H, J = 16.4 Hz, C29-H), 8.07 (d, 1H, J = 13.2
Hz, C5-H), 8.73 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C21H27FN5O4
[M+ + H]: 432.20471. Found: 432.20362.
N-tert-Butoxycarbonyl-3-ethoxyimino-4-methyl-4-(N-tert-
butoxycarbonyl)methylaminopiperidine 11b
1-(2,4-Difluorophenyl)-6-fluoro-7-(3-methoxyimino-4-
methyl-4-methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-
The title compound was obtained in a similar manner as for the
preparation of 11a (92%) as a colorless liquid.1H-NMR (CDCl3, 400
MHz) dH: 1.24 (t, 3H, J = 6.8 Hz, OCH2CH3), 1.43–1.49 (m, 18H, 2
Boc-9H), 1.55 (s, 3H, CH3), 2.79–2.88 (m, 4H), 3.35–3.56 (m, 2H),
3.87–3.88 (m, 1H), 4.10 (q, 2H, J = 6.8 Hz, OCH2CH3), 4.33–4.70 (m,
2H); ESI-MS m/z: 386 [M+ + H].
1,8-naphthyridine-3-carboxylic acid 16
1H-NMR (CDCl3, 400 MHz) dH: 1.27 (s, 1H, CH3), 1.72–1.88 (m, 3H),
2.22–2.25 (m, 3H), 3.78–3.85 (m, 5H), 4.05–4.12 (m, 1H), 4.65–4.76
(m, 1H), 7.05–7.11 (m, 2H, ph-2H), 7.36–7.39 (m, 1H, ph-1H), 8.11
(d, 1H, J = 13.2 Hz, C5-H), 8.68 (s, 1H, C2-H). HRMS-ESI m/z calcd. for
C23H23F3N5O4 [M+ + H]: 490.17021. Found: 490.17115.
3-Methoxyimino-4-methyl-4-methylaminopiperidine
dihydrochloride 12a
1-(2,4-Difluorophenyl)-6-fluoro-7-(3-ethoxyimino-4-
methyl-4-methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-
To a stirring solution of 11a (5.1 g, 13.6 mmol) dissolved in
methylene chloride (100 mL) dry hydrogen chloride gas was
pumped at room temperature for 0.5 h. The reaction mixture
was allowed to stir for another 0.5 h at the same temperature.
The resulting solid was collected by suction and dried in vacuo to
give the title compound 12a (3.1 g, 94%) as a white solid. 1H-NMR
(D2O, 400 MHz) dH: 1.72 (s, 3H, CH3), 2.27–2.28 (m, 1H), 2.44–2.45
(m, 1H), 2.79 (s, 3H, NCH3), 3.48–3.50 (m, 1H), 3.70–3.71 (m, 1H),
3.83–3.85 (m, 1H), 4.02 (s, 3H, OCH3), 4.80–4.83 (m, 1H); ESI-MS
m/z: 172 [M+ + H].
1,8-naphthyridine-3-carboxylic acid 17
1H-NMR (CDCl3, 400 MHz) dH: 1.20–1.28 (m, 6H, OCH2CH3, CH3),
1.56 (br, 1H, NH), 1.73–1.80 (m, 1H), 1.83–1.87 (m, 1H), 2.23–2.26
(m, 3H), 3.76–3.77 (m, 2H), 4.06–4.13 (m, 3H), 4.67–4.78 (m, 1H),
7.05–7.11 (m, 2H, ph-2H), 7.36–7.42 (m, 1H, ph-1H), 8.11 (d, 1H, J
= 13.2 Hz, C5-H), 8.68 (s, 1H, C2-H). HRMS-ESI m/z calcd. for
C24H25F3N5O4 [M+ + H]: 504.18586. Found: 504.18675.
General procedure for the synthesis of 7-(3-alkoxyimino-
4-methyl-4-methylaminopiperidin-1-yl)fluoroquinolone
3-Ethoxyimino-4-methyl-4-methylaminopiperidine
dihydrochloride 12b
derivatives 18–29
The title compound was obtained in a similar manner as for the
preparation of 12a (99%) as a white solid. 1H-NMR (DMSO-d6, 400
MHz) dH: 1.24 (t, 3H, J = 6.8 Hz, OCH2CH3), 1.55 (s, 3H, CH3), 2.11–
2.17 (m, 1H), 2.24–2.33 (m, 1H), 2.51 (s, 3H, NCH3), 3.20–3.26 (m,
1H), 3.44–3.50 (m, 1H), 3.90–3.91 (m, 1H), 4.17 (q, 2H, J = 6.8 Hz,
A mixture of 13c–i (1.0 mmol), 12a, b (1.2 mmol), dry triethyl-
amine (8.0 mmol), and dry acetonitrile (20 mL) was stirred for 6–
10 h at room temperature under an atmosphere of nitrogen.
After completion of the condensation, the reaction mixture was
concentrated under reduced pressure. The residue was dissolved
in 2% sodium hydroxide solution (20 mL) and stirred for 1–4 h at
room temperature. The reaction mixture was adjusted to pH = 7
with 6 N hydrochloric acid. The resulting solid was collected by
suction, and dried in vacuo to give 18–29 as a yellow solid.
+
OCH2CH3), 4.35–4.55 (m, 1H), 9.75–9.94 (m, 4H, 2 NH2 ); ESI-MS
m/z: 186 [M+ + H].
General procedure for the synthesis of 7-(3-alkoxyimino-
4-methyl-4-methylaminopiperidin-1-yl)fluoroquinolone
derivatives 14–17
A mixture of 13a, b (1.0 mmol), 12a, b (1.2 mmol), dry triethyl-
amine (8.0 mmol), and dry acetonitrile (20 mL) was stirred at
room temperature under an atmosphere of nitrogen for 3–8 h.
The resulting solid was collected by suction, and dried in vacuo
to give 14–17 as a yellow solid.
1-Ethyl 6,8-difluoro-7-(3-methoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-quinoline-
3-carboxylic acid 18
1H-NMR (CDCl3, 400 MHz) dH: 1.36 (s, 3H, CH3), 1.57 (t, 3H, J = 7.2
Hz, NCH2CH3), 1.93–1.96 (m, 2H), 2.33 (s, 3H, NCH3), 3.32–3.35 (m,
1H), 3.63–3.66 (m, 1H), 3.87 (s, 3H, OCH3), 4.11–4.12 (m, 1H),
4.40–4.42 (m, 1H), 4.44–4.49 (m, 2H), 7.98 (d, 1H, J = 11.6 Hz, C5-
H), 8.61 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C20H25F2N4O4 [M+ +
H]: 423.18439. Found: 423.18571.
1-Cyclopropyl-6-fluoro-7-(3-methoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-1,8-
naphthyridine-3-carboxylic acid 14
1-Cyclopropyl-6,8-difluoro-7-(3-ethoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-quinoline-
1H-NMR (CDCl3, 400 MHz) dH: 1.05–1.10 (m, 2H), 1.25–1.27 (m,
2H), 1.37 (s, 3H, CH3), 1.94–2.01 (m, 2H), 2.34 (s, 3H, NCH3), 3.63–
3.66 (m, 1H), 3.89 (s, 3H, OCH3), 4.00–4.04 (m, 1H), 4.06–4.11 (m,
1H), 4.40–4.41 (m, 1H), 5.24–5.25 (m, 1H), 8.07 (d, 1H, J = 13.2 Hz,
C5-H), 8.73 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C20H25FN5O4 [M+ +
H]: 418.18905. Found: 418.18978.
3-carboxylic acid 19
1H-NMR (CDCl3, 400 MHz) dH: 1.18–1.35 (m, 10H), 1.93–1.97 (m,
2H), 2.33 (s, 3H, NCH3), 3.35–3.39 (m, 1H), 3.62–3.67 (m, 1H),
3.99–4.02 (m, 1H), 4.09–4.15 (m, 3H), 4.42–4.43 (m, 1H), 7.91–7.93
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(d, 1H, J = 11.6 Hz, C5-H), 8.79 (s, 1H, C2-H). HRMS-ESI m/z calcd. for
1-Ethyl-6-fluoro-7-(3-ethoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-quinoline-
C22H27F2N4O4 [M+ + H]: 449.20004. Found: 449.20110.
3-carboxylic acid 25
1H-NMR (CDCl3, 400 MHz) dH: 1.30–1.34 (m, 6H), 1.56 (t, 3H, J = 7.2
Hz, NCH2CH3), 1.82 (br, 3H), 2.32 (s, 3H, NCH3), 3.65–3.68 (m, 1H),
3.76–3.81 (m, 1H), 4.05–4.06 (m, 1H), 4.18–4.26 (m, 2H), 4.30 (q,
2H, J = 7.2 Hz, NCH2CH3), 4.52–4.54 (m, 1H), 7.00 (d, 1H, J = 6.8 Hz,
C8-H), 8.05 (d, 1H, J = 13.2 Hz, C5-H), 8.66 (s, 1H, C2-H). HRMS-ESI
m/z calcd. for C21H28FN4O4 [M+ + H]: 419.20946. Found: 419.20961.
1-(2-Fluoroethyl)-6,8-difluoro-7-(3-methoxyimino-4-
methyl-4-methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-
quinoline-3-carboxylic acid 20
1H-NMR (CDCl3, 400 MHz) dH: 1.35 (s, 3H, CH3), 1.92–1.95 (m, 2H),
2.32 (s, 3H, NCH3), 3.31–3.34 (m, 1H), 3.63–3.66 (m, 1H), 3.87 (s,
3H, OCH3), 4.09–4.11 (m, 1H), 4.39–4.40 (m, 1H), 4.68–4.88 (m,
4H), 8.00 (d, 1H, J = 11.6 Hz, C5-H), 8.59 (s, 1H, C2-H). HRMS-ESI: m/z
calcd. for C20H24F3N4O4 [M+ + H]: 441.17497. Found: 441.17585.
1-Cyclopropyl-6-fluoro-7-(3-methoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-8-methoxyl-1,4-dihydro-4-
oxo-quinoline-3-carboxylic acid 26
1H-NMR (CDCl3, 400 MHz) dH: 1.00–1.06 (m, 2H), 1.21–1.26 (m,
2H), 1.39 (s, 3H, CH3), 1.59 (br, 1H, NH), 1.96–1.99 (m, 2H), 2.37 (s,
3H, NCH3), 3.38–3.41 (m, 1H), 3.65–3.67 (m, 1H), 3.76 (s, 3H,
OCH3), 3.87 (s, 3H, NOCH3), 4.02–4.06 (m, 1H), 4.13–4.14 (m, 1H),
4.40–4.42 (m, 1H), 7.89 (d, 1H, J = 12.0 Hz, C5-H), 8.82 (s, 1H, C2-H).
HRMS-ESI m/z calcd. for C22H28FN4O5 [M+ + H]: 447.20437. Found:
447.20548.
1-(2-Fluoroethyl)-6,8-difluoro-7-(3-ethoxyimino-4-methyl-
4-methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-
quinoline-3-carboxylic acid 21
1H-NMR (CDCl3, 400 MHz) dH: 1.24 (t, 3H, J = 7.2 Hz, OCH2CH3),
1.35 (s, 3H, CH3), 1.63 (br, 1H, NH), 1.92–1.94 (m, 2H), 2.33 (s, 3H,
NCH3), 3.32–3.35 (m, 1H), 3.62–3.68 (m, 1H), 4.08–4.15 (m, 3H),
4.40–4.41 (m, 1H), 4.68–4.88 (m, 4H), 8.00 (d, 1H, J = 11.2 Hz, C5-
H), 8.60 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C21H26F3N4O4 [M+ +
H]: 455.19061. Found: 455.19287.
1-Cyclopropyl-6-fluoro-7-(3-ethoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-8-methoxyl-1,4-dihydro-4-
oxo-quinoline-3-carboxylic acid 27
1H-NMR (CDCl3, 400 MHz) dH: 0.99–1.05 (m, 2H), 1.19–1.27 (m,
5H), 1.40 (s, 3H, CH3), 1.96–2.01 (m, 2H), 2.38 (s, 3H, NCH3), 3.39–
3.42 (m, 1H), 3.67–3.72 (m, 1H), 3.77 (s, 3H, OCH3), 4.02–4.06 (m,
1H), 4.10–4.17 (m, 3H), 4.42–4.43 (m, 1H), 7.88 (d, 1H, J = 12.0 Hz,
C5-H), 8.82 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C23H30FN4O5 [M+ +
H]: 461.22002. Found: 461.21986.
1-Cyclopropyl-6-fluoro-7-(3-methoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-quinoline-
3-carboxylic acid 22
1H-NMR (CDCl3, 400 MHz) dH: 1.18–1.19 (m, 2H), 1.38–1.54 (m,
6H), 1.90–1.94 (m, 2H), 2.36 (s, 3H, NCH3), 3.54–3.61 (m, 2H),
3.72–3.74 (m, 1H), 3.91 (s, 3H, OCH3), 4.07–4.09 (m, 1H), 4.51–4.52
(m, 1H), 7.42 (d, 1H, J = 7.2 Hz, C8-H), 8.02 (d, 1H, J = 13.2 Hz, C5-H),
8.76 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C21H26FN4O4 [M+ + H]:
455.19380. Found: 417.19537.
9-Fluoro-3(S)-methyl-10-(3-methoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-7-oxo-2,3-dihydro-7H-
pyrrido[1,2,3-d,e][1,4]benzoxazine-6-carboxylic acid 28
1H-NMR (CDCl3, 400 MHz) dH: 1.36 (s, 3H, C49-CH3), 1.62 (d, 3H, J =
6.4 Hz, C3-CH3), 1.90–2.04 (m, 3H), 2.35 (s, 3H, NCH3), 3.31–3.35
(m, 1H), 3.55–3.58 (m, 1H), 3.87 (s, 3H, OCH3), 4.06–4.14 (m, 1H),
4.29–4.38 (m, 2H), 4.44–4.49 (m, 2H), 7.75 (d, 1H, J = 12.0 Hz, C8-
H), 8.62 (s, 1H, C5-H). HRMS-ESI m/z calcd. for C21H26FN4O5 [M+ + H]:
433.18872. Found: 433.19204.
1-Cyclopropyl-6-fluoro-7-(3-ethoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-quinoline-
3-carboxylic acid 23
1H-NMR (CDCl3, 400 MHz) dH: 1.16–1.18 (m, 2H), 1.28 (t, 3H, J = 7.2
Hz, OCH2CH3), 1.37–1.40 (m, 5H), 1.94–1.96 (m, 3H), 2.34 (s, 3H,
NCH3), 3.56–3.60 (m, 2H), 3.70–3.72 (m, 1H), 4.03–4.18 (m, 3H),
4.54–4.55 (m, 1H), 7.42 (d, 1H, J = 6.4 Hz, C8-H), 8.01 (d, 1H, J = 13.2
Hz, C5-H), 8.76 (s, 1H, C2-H). HRMS-ESI m/z calcd. for C22H28FN4O4
[M+ + H]: 431.20946. Found: 431.20919.
9-Fluoro-3(S)-methyl-10-(3-ethoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-7-oxo-2,3-dihydro-7H-
pyrrido[1,2,3-d,e][1,4]benzoxazine-6-carboxylic acid 29
1H-NMR (CDCl3, 400 MHz) dH: 1.24 (t, 3H, J = 7.2 Hz, OCH2CH3),
1.34 (s, 3H, C49-CH3), 1.62 (d, 3H, J = 6.8 Hz, C3-CH3), 1.88–2.04 (m,
2H), 2.34 (s, 3H, NCH3), 3.31–3.36 (m, 1H), 3.54–3.59 (m, 1H),
4.07–4.14 (m, 3H), 4.31–4.52 (m, 4H), 7.73 (d, 1H, J = 12.0 Hz, C8-
H), 8.63 (s, 1H, C5-H). HRMS-ESI m/z calcd. for C22H28FN4O5 [M+ + H]:
447.20437. Found: 447.20392.
1-Ethyl-6-fluoro-7-(3-methoxyimino-4-methyl-4-
methylaminopiperidin-1-yl)-1,4-dihydro-4-oxo-quinoline-
3-carboxylic acid 24
1H-NMR (CDCl3, 400 MHz) dH: 1.31 (s, 3H, CH3), 1.57 (t, 3H, J = 7.2
Hz, NCH2CH3), 1.76–1.79 (m, 2H), 2.31 (s, 3H, NCH3), 3.67–3.71 (m,
1H), 3.77–3.82 (m, 1H), 3.80 (s, 3H, OCH3), 4.05–4.06 (m, 1H), 4.31
(q, 2H, J = 7.2 Hz, NCH2CH3), 4.50–4.52 (m, 1H), 7.03 (d, 1H, J = 7.2
Hz, C8-H), 8.05 (d, 1H, J = 13.2 Hz, C5-H), 8.67 (s, 1H, C2-H). HRMS-
ESI m/z calcd. for C20H26FN4O4 [M+ + H]: 405.19381. Found:
405.19377.
Antibacterial activity
Compounds 14–29 were evaluated for their in-vitro antibacterial
activity using conventional agar-dilution method in comparison
to the reference drugs. Drugs (10.0 mg) were dissolved in 0.1 N
sodium hydroxide solution and water (10 mL). Further progres-
sive twofold serial dilution with melted Mueller–Hinton agar
was performed to obtain the required concentrations of 128, 64,
i 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.archpharm.com

Arch. Pharm. Chem. Life Sci. 2010, 343, 143–151
New Piperidinylquinolone Derivatives
151
32, 16, 8, 4, 2, 1, 0.5, 0.25, 0.125, 0.06, and 0.03 lg/mL. Petri
dishes were incubated with 104 colony forming units (cfu) and
incubated at 358C for 18 h. The minimum inhibitory concentra-
tion (MIC) was the lowest concentration of the test compound,
which resulted in no visible growth on the plate.
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This work was supported by the IMB Research Foundation.
The authors have declared no conflict of interest.
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