Synthesis and in vitro antibacterial activity of quinolone/naphthyridone derivatives containing 3-alkoxyimino-4-(methyl)aminopiperidine scaffolds

Article abstract of DOI:10.1016/j.bmcl.2013.01.048

We report herein the synthesis of a series of 7-[3-alkoxyimino-4-(methyl) aminopiperidin-1-yl]quinolone/naphthyridone derivatives. In vitro antibacterial activity of these derivatives was evaluated against representative strains, and compared with ciprofl

Full text of DOI:10.1016/j.bmcl.2013.01.048

Bioorganic & Medicinal Chemistry Letters 23 (2013) 1754–1759
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and in vitro antibacterial activity of quinolone/naphthyri-
done derivatives containing 3-alkoxyimino-4-(methyl)aminopiperi-
dine scaffolds
a
a
a
Kai Lv a, , Jinwei Wu b, , Jian Wang c, Mingliang Liu a, , Zengquan Wei , Jue Cao , Yexin Sun ,
⇑
Huiyuan Guo a
a Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, China
b Zhejiang Starry Pharmaceutical Co., Ltd, Xianju 317300, China
c The No. 5 Hospital of Harbin, Harbin 150040, China
a r t i c l e i n f o
a b s t r a c t
Article history:
We report herein the synthesis of a series of 7-[3-alkoxyimino-4-(methyl)aminopiperidin-1-yl]quino-
lone/naphthyridone derivatives. In vitro antibacterial activity of these derivatives was evaluated against
representative strains, and compared with ciprofloxacin (CPFX), levofloxacin (LVFX) and gemifloxacin
(GMFX). The results reveal that all of the target compounds 19a–c and 20 have considerable Gram-posi-
tive activity, although they are generally less active than the reference drugs against the Gram-negative
strains with some exceptions. Especially, novel compounds 19a2, 19a4 and 19a5 were found to show
Received 5 November 2012
Revised 3 January 2013
Accepted 15 January 2013
Available online 24 January 2013
Keywords:
Quinolone/naphthyridone
Synthesis
strong antibacterial activity (MICs: <0.008–0.5 lg/mL) against all of the tested 15 Gram-positive strains
including MRSA, LVFX- and GMFX-resistant MRSE, and CPFX-, LVFX- and GMFX-resistant MSSA.
Ó 2013 Elsevier Ltd. All rights reserved.
Antibacterial activity
Since the discovery of norfloxacin (NFLX) by Koga et al. in the
early 1980s,1 fluoroquinolones/naphthyridones, as important
weapons in our antibacterial arsenal,2 have been used mainly to
fight both community-acquired and serious hospital-acquired
infections.3 These antibiotics depict several properties such as
excellent bioavailability, good tissue penetrability, and a relatively
low incidence of adverse and toxic effects.4 During the past 30 years,
a great number of fluoroquinolone/naphthyridone derivatives have
been designed and synthesized, and a large body of structure–
activity relationship (SAR) has been accumulated. The C-4 carbonyl
and C-3 carboxylic groups are known to be essential for antibacte-
rial activity. Cyclopropyl and methoxyl (or hydrogen) groups are
generally accepted as the optimal substituents at the N-1 and C-8
positions of fluoroquinolones, respectively.5 And for fluor-
onaphthyri dones, the optimal substituent at the N-1 position can
be cyclopropyl [gemifloxacin (GMFX)] or 2,4-diflurophenyl group
(tosufloxacin, trovafloxacin). Moreover, 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, and the
presence of a five- or six-membered nitrogen heterocycle including
pyrrolidine, piperazine and piperidine at this position is particularly
structural feature of important fluoroquinolones/naphthyridones
on the market,6 such as ciprofloxacin (CPFX), levofloxacin (LVFX),
GMFX and moxifloxacin, and so on.
Recently, oxime-functionalized pyrrolidines as novel C-7 sub-
stituents have attracted great attention and led to the discovery
of some new fluoronaphthyridones, such as GMFX, zabofloxacin
(DW224a) and DW286. All of the three show excellent antibacte-
rial activity and pharmacokinetic profiles which emphasize the
importance of the oxime group with respect to biological
activity.7–9
As part of an ongoing program to develop novel fluoroquino-
lones/naphthyridones, we have focused our attention on introduc-
tion of an oxime functional group to azetidine or piperidine ring
containing an amino/aminomethyl moiety, as side chains at the
C-7 position.10–12 IMB-070593 (Fig. 1), a candidate discovered in
O
N
O
O
N
O
F
F
OH
OH
H2N
MeON
MeHN
N
X
N
N
MeON
IMB-070593 (X = C-OMe)
IMB-070595 (X = N)
DZH
⇑
Corresponding author. Tel.: +86 10 63036965; fax: +86 10 63036965.
E-mail address: lmllyx@yahoo.com.cn (M. Liu).
These authors contributed equally to the work.
Figure 1. Structures of some fluoroquinolones/fluoronaphthyridones.
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.01.048

K. Lv et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1754–1759
1755
O
O
HN
O
HN
O
.
iv
HCl
N
N
H
O
OEt
O
OEt
OH
O
NH2
Boc
O
OH
5
6
i
ii
iii
N
N
Boc
N
Boc
HN
HN
Boc
Boc
Boc
O
OH
v
1
3
2
N
N
Boc
Boc
7
4
vi
Boc
R2
Boc
R2
Boc
N
HN
NH
HN
N
NOR1
NOR1
NOR1
NOH
iv
viii
vii
.
2HCl
N
N
N
H
Boc
Boc
Boc
11a-c
10a,b
9a,b
8
iv
10a: R1 = Me, R2 = Me
10b: R1 = Et, R2 = Me
9a: R1 = Me
9b: R1 = Et
11a: R1 = Me, R2 = Me
11b: R1 = Et, R2 = Me
1
= Me, R2 = H
11c:
R
Scheme 1. Synthesis of piperidine derivatives 6 and 11a–c. Reagents and conditions: (i) KBH4, EtOH, rt, 2 h; (ii) NH3ÁH2O, DMF, H2O, rt, 36 h; (iii) NaBrO, (Boc)2O, H2O, EtOH,
4 h, 80 °C; (iv) HCl gas, CH2Cl2, rt, 3 h; (v) DPCP, Et3N, DMSO, CH2Cl2, À25 °C, 5 h; (vi) HONH2ÁHCl, pyridine, rt, 5 h; (vii) R1I, K2CO3, DMF, rt, 5 h; (viii) R2I, NaH, MeCN, rt, 4 h.
AcO OAc
O
O
O
N
O
B
O
O
X
N
O
O
F
OH
OH
X
F
F
OH
11a-c, 6
O
Z
N
R3
or
N
N
or
x or xi
Cl
N
N
R3
R2
N
R3
N
HN
O
Y
H
NOR1
O
12-14
15-18
20
19a-c
15: Y = MeO, R3
=
3
12:
X = F, R
=
=
F
O
13: X = F, R3
14: X = H, R3
F
16: Y, R3
17: Y = F, R3
18: Y = F, R3 = Et
=
Me
=
=
Scheme 2. Synthesis of the target compounds 19a–c and 20 (See Table 1 for structures). Reagents and conditions: (x) Et3N, CH3CN, 50 °C, 5 h; (xi) (1) Et3N, CH3CN, 50 °C,
overnight. (2) 5% NaOH, 50 °C, 1 h.
our lab, was found to have better in vitro antibacterial activity than
LVFX and GMFX, and good in vivo activity comparable to GMFX
and MXFX against Gram-positive strains including methicillin-
resistant Staphylococcus aureus (MRSA) and methicillin-resistant
Staphylococcusepidermidis (MRSE).11 IMB-070593 in late pre-clinical
stage of development currently, was also observed to possess ex-
tremely low phototoxicity, hepatotoxicity and cardiac toxicity
(unpublished). Moreover, a preliminary SAR study shows that
oxime-containing fluoroquinolones have significantly increased
activity, when directly compared to the corresponding fluor-
onaphthyridones (IMB-070593 vs IMB-070595, Fig. 1).11
The most active compound DZH Figure 1 shows excellent in vitro
antibacterial activity against some important pathogens such as
methicillin-sensitive S. aureus (MSSA), Staphylococcus pneumoniae,
Enterococcus faecalis, and Pseudomonas aeruginosa, which is even
better than vancomycin and GMFX. However, it is a pity that 1-
cyclopropyl fluoronaphthyridone was chosen as the only nucleus
in this study.13
The above research results intensified our interest, and consid-
ering the fact small structural changes of quinolone/naphthyridone
nuclei usually cause dramatic improvement in antibacterial activ-
ity (such as NFLX vs CPFX and ofloxacin vs LVFX), it was decided to
synthesize a series of 3-alkoxyimino-4-(methyl)aminopiperidine-
containing derivatives in which the selected nuclei were common
Dang et al. reported a series of fluoronaphthyridone derivatives
containing 3-alkoxyimino-4-(methyl)aminopiperidine moieties.

1756
K. Lv et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1754–1759
Table 1
Structures and physical data of compounds 19a–c and 20
O
N
O
O
O
F
X
N
OH
OH
N
N
Z
N
R2
R3
N
HN
O
H
NOR1
O
19a-c
20
Compd R1
R2
X
R3
Z
Yield (%)
Mpa (°C)
19a1
19a2
Me Me
Me Me
F
F
Cyclopropyl
Cyclopropyl
N
18.6
23.4
201–203
179–180
C–OMe
19a3
Me Me
F
25.8
156–159
O
Me
19a4
19a5
Me Me
Me Me
F
F
Cyclopropyl
2,4-
C–F
N
33.4
25.2
134–135
151–153
Diflurophenyl
Cyclopropyl
Ethyl
Cyclopropyl
Cyclopropyl
19a6
19a7
19b1
19b2
Me Me
Me Me
H
F
F
N
C–F
N
22.0
17.5
27.4
20.6
203–204
135–137
200–202
130–131
Et
Et
Me
Me
F
C–OMe
19b3
Et
Me
F
22.5
140–142
O
Me
19b4
19c1
19c2
Et
Me
Me
Me
H
H
F
F
F
Cyclopropyl
Cyclopropyl
Cyclopropyl
C–F
N
C–OMe
25.0
31.4
29.3
159–161
172–174
109–110
19c3
20
Me
H
F
34.0
125–127
O
Me
47.5
296–299
a
Melting points are uncorrected.
quinolones and other naphthyridones instead of the 1-cyclopropyl
fluoronaphthyridone in Dang’s study. It could be anticipated that
some of these derivatives (such as 8-methoxylfluoroquinolone)
should have superior antibacterial activity to DZH. Our primary
objective was to optimize the potency of these compounds against
clinical familiar pathogens (especially Gram-positive ones). A
preliminary SAR study is also explored to facilitate the further
development of the quinolones/naphthyridones.
Dang et al. reported a synthetic route of piperidine derivatives
11a–c via a 12-step procedure with low total yield.13 To overcome
its disadvantages, a simpler route for synthesis of 11a–c was devel-
oped in this work.
Detailed synthetic pathways to 11a–c and quinolones/naph-
thyridones 19a–c are depicted in Schemes 1 and 2, respectively.
By the way, three known compounds 19a1 (DZH), 19b1 and
19c113 were also prepared in this work for the purpose of compar-
ing antibacterial activity and exploring SAR.
Reduction of readily available 1-tert-butyl 4-ethyl 3-oxopiperidine-
1,4-dicarboxylate 1 with KBH4 in ethanol gave hydroxyl ester 2,
which upon aminolysis in NH3ÁH2O–DMF (catalytic amount) solu-
tion yielded hydroxyl amide 3. However, Hoffmann degradation of
the amide 3 used commercially sodium hypochlorite met no
success.
Degradation of 3 was then conducted successfully by freshly
prepared sodium hypobromite instead of sodium hypochlorite,
and subsequent protection of the resulting primary amine by
treatment with di-tert-butyl dicarbonate (Boc2O) gave the desired
bis-Boc protected amino alcohol 4. Unexpectedly, a new compound
containing a lactam ester moiety was simultaneously separated and
its chemical structure (shown as 5) was established by 1H NMR and
MS. Compound 6 was prepared from 5 via deprotection of the Boc
group by pumping dry hydrogen chloride gas in dichloromethane

K. Lv et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1754–1759
1757
(Scheme 1). Given the oxazolidinone moiety of 5 is one of the key
constituents of linezolid, it was also decided to synthesized a naph-
thyridone derivative 20 containing lactam ester 6 (Scheme 2) so
that more SAR could be explored.
The oxime 8 was obtained using ‘one-pot’ method from the
alcohol 4 via Swern oxidation14 involving phenyl dichlorophos-
phate (DPCP) as the electrophilic activator, and subsequent con-
activity. Their MIC values against Gram-positive strains are gener-
ally smaller than those against Gram-negative ones. Although
19a–c and 20 are less active than GMFX, LVFX and CPFX against
the Gram-negative strains with some exceptions, all of them have
considerable activity against the Gram-positive ones. Novel com-
pounds 19a2, 19a4 and 19a5 exhibit strong activity (MICs:
<0.008–0.5 lg/mL) against all of the tested fifteen Gram-positive
densation of the resulting ketone
7
with hydroxylamine
strains including MSSA, MRSA, methicillin-susceptible S. epidermi-
dis (MSSE), MRSE, and S. pneumoniae. It is especially worth to note
that 19a2, 19a4 and 19a5 also display excellent activity (MICs:
hydrochloride in the presence of pyridine. Nucleophilic substitu-
tion of 8 with iodoalkanes in the presence of anhydrous K2CO3 gave
alkyloximes 9a–b, which upon methylation by reaction with iodo-
methane in the presence of NaH produced compounds 10a–b.
Deprotection of the bis-Boc groups on the amines 10a–b and 9a
was carried out in a similar manner as for the preparation of 6 to
afford the piperidine derivative dihydrochlorides 11a–b and 11c,
respectively (Scheme 1).15
Finally, the target compounds 19a–c and 20 were obtained by
coupling piperidine derivatives 11a–c and 6 with various com-
pounds containing naphthyridone and quinolone cores according
to well-established literature procedures.16 In the case of quino-
lone/naphthyridone derivatives 19a1, 19a5, 19a6, 19b1, 19c1 and
20, condensations of 12–14 with 6 and 11a–c were performed in
the presence of triethylamine. However, for 19a2–4, 19a7, 19b2–
4, 19c2 and 19c3, boric chelates 15–18 were required to increase
reactivity (Scheme 2). Table 1 shows structures and physical data
of compounds 19a–c and 20.17
Because the oxime group is present in the E or Z configuration, it
was necessary to determine the geometries of all the oxime target
compounds 19a–c. Unfortunately, we were unable to prepare X-
ray-quality single crystals of any oxime intermediate or product.
Nonetheless, we can speculate that the oxime group of the target
compounds is present in a single configuration of E or Z isomer
due to signal singleness of the piperidine ring of the compounds
observed in the 1H NMR spectra.
The target compounds 19a–c and 20 were evaluated for their
in vitro antibacterial activity against representative strains using
standard techniques.18 Minimum inhibitory concentration (MIC)
is defined as the compound concentration required to give
complete inhibition of bacterial growth, and MIC values of 19a–c
and 20 against Gram-positive and Gram-negative strains, along
with those of the three standard drugs GMFX, LVFX and CPFX for
comparison, are listed in Tables 2 and 3, respectively.
<0.008–0.125
MSSA (MICs: 4–64
(MICs: 4–8 g/mL).
l
g/mL) against GMFX-, LVFX- and CPFX-resistant
l
g/mL), and GMFX- and LVFX-resistant MRSE
l
In the case of Gram-positive strains, the activity of the nuclei in
this study is in the order 2,4-difluorophenyl-1,8-naphthyri-
done ꢀ 1-cyclopropyl-6,8-difluoroquinolone > 1-cyclopropyl-8-me
thoxylfluoroquinolone > LVFX
nucleus > 1-ethyl-6,8-difluoroqu
inolone when 3-alkoxyimino-4-(methylamino)piperidines serve
as the C-7 side chains. Introduction of a methyl group on the amino
moiety of the piperidine ring seems to contribute to the antibacte-
rial activity (19a1 vs 19c1, 19a2 vs 19c2, 19a3 vs 19c3), while
replacement of the fluorine with hydrogen at C-6 position results
in decreased activity (19a1 vs 19a6). Moreover, fluoroquinolones
featuring methyloxime-incorporated piperidino-substitution at
C-7 position are more active than the corresponding analogs con-
taining ethyloxime (19a1 vs 19b1, 19a2 vs 19b2, 19a3 vs 19b3,
19a4 vs 19b4). It is interesting that 1-cyclopropylfluoronaphthyri-
dones do show significantly decreased activity when compared to
the corresponding 8-methoxylfluoroquinolones (19a1 vs 19a2,
19b1 vs 19b2, 19c1 vs 19c2), which is consistent with the SAR in
our previous study.11 Anyway, the validity of our strategy has been
supported by the data listed in Table 2, especially two quinolone
derivatives (19a2, 19a4) and one naphthyridone derivatives
(19a5) possessing better Gram-positive activity than the most
active compound DZH (19a1) reported in Dang’s study.13
Notably, the naphthyridone derivative containing a lactam ester
moiety at C-7 position (20) has also good activity with the MIC
values of 0.5–2 lg/mL against all of the Gram-positive strains
except MSSA 12-7. Furthermore, it was found to be comparable
to or slightly less active than the corresponding compounds with
the same naphthyridone nulei (19a1, 19b1, 19c1). This implies
the existence of a free amino group on the piperidine ring at C-7
position is not always essential for antibacterial activity of the
naphthyridones.
Our results indicate that the derivatives 19a–c and 20, like the
reference drugs, have potential broad-spectrum antibacterial
Table 3
In vitro antibacterial activity of compounds 19a–c and 20 against Gram-negative strains
Strains
Compd MIC (
lg/mL)
19a1
19a2
19a3 19a4 19a5
19a6 19a7 19b1 19b2 19b3 19b4 19c1
19c2 19c3 20
GMFX LVFX
CPFX
E. co. ATCC25922 0.125 0.125 0.25
0.03
2
>128 >128
>128 >128
>128 >128
0.125 0.5
64
0.5
8
4
32
16
8
16
4
16
8
32
2
4
2
8
4
1
16
0.015
0.125
0.015 0.008
E.co. 12-1
E.co. 12-4
E.co. 12-5
E. co.a12-1
4
4
8
8
0.5
8
0.125
8
>128
>128
>128
>128
16
>128
128
>128
>128
32
128
128
128
>128 >128 >128 >128 >128 >128 >128
>128 >128 >128 >128 >128 >128 >128
>128 >128 >128 >128 >128 >128 >128
128
64
64
64
16
2
>128 >128 16
128
128
>128 >128 16
16
8
>128 16
>128
8
2
8
16
16
0.5
0.06
0.06
0.25
1
32
16
2
0.03
0.125
0.125
2
a
E.co. 12-2
>128 >128 >128
16
1
128
64
2
>128 >128 >128 >128 >128 64
128
4
4
1
a
E.co. 12-4
128
0.5
0.5
0.5
8
8
0.5
4
32
1
32
4
4
2
64
32
4
4
2
32
64
2
1
1
8
16
2
1
1
16
16
32
0.25
0.25
0.125 0.5
8
8
64
2
2
32
128
>128
128
8
2
K. p. 12-1
0.5
1
0.03
0.06
0.06
2
2
2
1
8
16
K. p. 12-2
0.5
2
1
1
2
2
1
1
K. p. 12-4
0.125 0.5
0.5
16
16
0.5
4
1
2
K. p. a12-1
K. p. a12-2
K. p. a12-4
P. a. ATCC27853
P. a. 12-1
16
16
16
16
64
32
1
128
>128 32
2
16
8
0.5
16
128
32
16
16
>128 32
>128 >128 >128 >128 >128
4
128
128
32
16
64
4
16
16
8
4
0.125 0.5
1
8
8
8
4
4
2
8
8
8
16
16
16
32
16
8
16
16
16
32
8
8
1
4
16
0.5
0.125
16
16
16
16
16
8
8
8
8
4
8
16
8
16
16
P. a. 12-2
GMFX, gemifloxacin; LVFX, levofloxacin; CPFX, ciprofloxacin; E. co., Escherichia coli; K. p., Klebsiella pneumoniae; P. a., Pseudomonas aeruginosa.
a
Extended-spectrum b-lactamase-producing.

1758
K. Lv et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1754–1759
filtered. The filtrate was concentrated under reduced pressure. The residue was
In summary,
a new synthetic route of 3-alkoxyimino-4-
purified by chromatography eluted with petroleum ether and ethyl acetate
(V:V = 3:1) to afford 5 as a white solid, mp: 169–171 °C. 1H NMR (600 MHz,
DMSO-d6) dppm: 7.50 (1H, s), 4.70–4.62 (1H, m), 3.96–3.94 (1H, m), 3.78–3.76
(1H, m), 3.25–3.13 (3H, m), 1.87–1.81 (1H, m), 1.59–1.56 (1H, m), 1.38 (9H, s).
13C NMR (100 MHz, DMSO-d6) dppm: 158.62, 155.22, 79.29, 73.47, 47.81, 42.30,
37.68, 28.54, 25.59. MS-ESI (m/z): 260 (M+NH4)+. To a stirring solution of 5
(2.42 g, 10 mmol) in dichloromethane (80 mL) was pumped dried
hydrochloride gas at room temperature for 30 min. The reaction mixture was
stirred for 3 h at the same temperature, and then filtered. The precipitate was
washed with dichloromethane, and dried in vacuo to yield 6 (1.01 g, 47.0%) as a
white solid, mp: 232–234 °C. 1H NMR (500 MHz, DMSO-d6) dppm: 9.55 (1H, br
s), 8.87 (1H, br s), 7.89 (1H, s), 4.74–4.71 (1H, m), 3.93–3.89 (1H, m), 3.40–3.37
(1H, m), 3.25–3.28 (1H, m), 3.03–2.95 (2H, m), 2.05–1.98 (1H, m), 1.64–1.57
(1H, m). MS-ESI (m/z): 143 (M+H)+. To a stirring solution of DMSO (23.40 g,
300 mmol) in anhydrous dichloromethane (150 mL) was added dropwise
phenyl dichlorophosphate (38.00 g, 180 mmol) at À25 °C over a period of
30 min. The mixture was stirred for 1 h at the same temperature.
Triethylamine (30.30 g, 300 mmol) was added dropwise to the reaction
mixture at À20 to À25 °C over a period of 2 h, and then the mixture was
stirred for 3 h at the same temperature. A solution of 4 (19.01 g, 60 mmol) in
dichloromethane (400 mL) was added dropwise to the reaction mixture over a
period of 3 h at À20 to À25 °C, and then was stirred at room temperature for
10 h to produce a mixture containing 7. To the above mixture were added
hydroxylamine hydrochloride (5.56, 80 mmol) and pyridine (12.66 g,
160 mmol) at room temperature. The reaction mixture was stirred for 5 h at
the same temperature, and concentrated under reduced pressure. The residue
was treated with ethyl acetate, washed successively with water and saturated
saline solution, dried over anhydrous MgSO4, and filtered. The filtrate was
concentrated under reduced pressure. The residue was treated with petroleum
ether to afford 8 (8.49 g, 43.8%) as a white solid, mp: 124–126 °C. 1H NMR
(400 MHz, CDCl3) dppm: 7.26 (1H, br s), 5.35 (1H, br s), 5.20 (1H, d, J = 16 Hz),
4.33 (1H, br s), 3.98 (1H, br s), 3.59–3.57 (1H, m), 3.20 (1H, br s), 2.44-2.42 (1H,
br s), 1.60–1.51 (19H, m). MS-ESI (m/z): 330 (M+H)+. To a stirring solution of 8
(9.87 g, 30 mmol) in DMF was added potassium carbonate (16.58 g, 120 mmol)
and methyl iodide (12.77 g, 90 mmol) at room temperature. The reaction
mixture was stirred at the same temperature for 5 h, and concentrated under
reduced pressure. The residue was purified by column chromatography (silica
gel) eluted with petro ether and ethyl acetate (V:V = 2:1) to give 9a as a light
yellow oil (75.4%). 1H NMR (400 MHz, CDCl3) dppm: 5.39 (1H, br s), 5.01 (1H, d,
J = 16 Hz), 4.20 (1H, m), 3.85 (4H, m), 3.49 (1H, d, J = 16 Hz), 3.15–3.09 (1H, m),
2.38 (1H, d, J = 12 Hz), 1.58–1.47 (18H, m). MS-ESI (m/z): 366 (M+Na)+. The
compound 9b was obtained from ethyl iodide as a colorless oil (70.0%) in a
similar manner as for the preparation of 9a. Compound 9b, 1H NMR (500 MHz,
CDCl3) dppm: 5.40 (1H, br s), 5.04 (1H, br s), 4.22 (1H, br s), 4.13 (2H, q, J = 7 Hz),
3.98 (1H, br s), 3.53 (1H, br s), 3.17 (1H, br s), 2.48 (1H, br s), 1.60 (1H, br s),
1.48 (18H, s), 1.33 (3H, t, J = 7 Hz). MS-ESI (m/z): 358 (M+H)+. To a solution of
9a (5.49 g, 16 mmol) in acetonitrile (50 mL) was added 60% sodium hydride
(1.92 g, 48 mmol) and methyl iodide (6.81 g, 48 mmol) at room temperature.
The reaction mixture was stirred for 4 h at the same temperature, quenched
with distilled water (3 mL), and concentrated under reduced pressure. The
residue was treated with ethyl acetate, washed successively with water and
saturated saline solution, dried over anhydrous MgSO4, and filtered. The filtrate
was concentrated under reduced pressure. The residue was treated with
petroleum ether at À20 °C. The precipitate was filtered, and washed with
petroleum ether to afford 10a as a light yellow solid (47.5%), mp: 108–110 °C.
1H NMR (400 MHz, CDCl3) dppm: 4.99 (1H, d, J = 16 Hz), 4.82 (1H, br s), 4.01 (1H,
m), 3.82 (3H, s), 3.56 (1H, d, J = 16 Hz), 3.09–3.04 (1H, m), 2.75 (3H, s), 2.00–
1.80 (2H, m), 1.45 (18H, s). 13C NMR (100 MHz, CDCl3) dppm: 156.15, 154.58,
149.93, 80.24, 79.80, 62.06, 54.50, 42.07, 37.58, 28.44, 22.66. MS-ESI (m/z): 375
(M+NH4)+, 380 (M+Na)+ . The compound 10b was obtained from 9b as a light
(methyl)aminopiperidine derivatives 11a–c was developed in this
study. A series of quinolone/naphthyridone derivatives containing
these heterocyclic amines were synthesized and evaluated for their
in vitro antibacterial activity, and a preliminary SAR was also ex-
plored. All of the target compounds 19a–c and 20 have consider-
able Gram-positive activity, although they are generally less
active than the reference drugs against the Gram-negative strains
with some exceptions. In especial, compounds 19a2, 19a4 and
19a5 were found to have strong activity (MICs: <0.008–0.5 lg/
mL) against all of the fifteen Gram-positive strains including MRSA,
GMFX- and LVFX-resistant MRSE, and GMFX-, LVFX- and CPFX-
resistant MSSA.
Acknowledgments
This work was supported by the National S&T Major Special
Project on Major New Drug Innovation (Number 2012ZX093010
02-001-017).
References and notes
1. Koga, H.; Itoh, A.; Murayama, S.; Suzue, S.; Irikura, T. J. Med. Chem. 1980, 23,
1358.
2. Feng, L. S.; Liu, M. L.; Wang, S.; Chai, Y.; Lv, K.; Shan, G. Z.; Cao, J.; Li, S. J.; Guo, H.
Y. Tetrahedron 2011, 67, 8264.
3. Wang, J. X.; Guo, Q.; Chai, Y.; Feng, L. S.; Guo, H. Y.; Liu, M. L. Chin. Chem. Lett.
2010, 21, 55.
4. Sharma, P. C.; Jain, A.; Jain, S.; Pahwa, R.; Yar, M. S. J. Enzyme Inhib. Med. Chem.
2010, 25, 577.
5. Liu, M. L.; Guo, H. Y. World Notes Antibiot. 2006, 2, 69.
6. Chai, Y.; Liu, M. L.; Lv, K.; Feng, L. S.; Li, S. J.; Sun, L. Y.; Wang, S.; Guo, H. Y. Eur. J.
Med. Chem. 2011, 46, 4267.
7. Hong, C. Y.; Kim, Y. K.; Chang, J. H.; Kim, S. H.; Choi, H.; Nam, D. H.; Kim, Y. Z.;
Kwak, J. H. J. Med. Chem. 1997, 40, 3584.
8. Kwon, A. R.; Min, Y. H.; Ryu, J. M.; Choi, D. R.; Shim, M. J.; Choi, E. C. J.
Antimicrob. Chemother. 2006, 58, 684.
9. Choi, D. R.; Shin, J. H.; Yang, J.; Yoon, S. H.; Jung, Y. H. Bioorg. Med. Chem. Lett.
2004, 14, 1273.
10. Lv, K.; Sun, Y. X.; Sun, L. Y.; Wei, Z. Q.; Guo, H. Y.; Wu, J. W.; Liu, M. L.
ChemMedChem 2012, 7, 1230.
11. Wang, X. Y.; Guo, Q.; Wang, Y. C.; Liu, B. Q.; Liu, M. L.; Sun, L. Y.; Guo, H. Y. Acta
Pharm. Sin. 2008, 43, 819.
12. Wang, J. X.; Zhang, Y. B.; Liu, M. L.; Wang, B.; Chai, Y.; Li, S. J.; Guo, H. Y. Eur. J.
Med. Chem. 2011, 46, 2421.
13. Dang, Z.; Yang, Y.; Ji, R.; Zhang, S. Bioorg. Med. Chem. Lett. 2007, 17, 4523.
14. Bisai, A.; Chandrasekhar, M.; Singh, V. K. Tetrahedron Lett. 2002, 43, 8355.
15. To a stirring solution of 1 (13.55 g, 50 mmol) in ethanol (50 mL) was added
potassium borohydride (1.10 g, 20 mmol) at room temperature. The reaction
mixture was stirred for 2 h at the same temperature, quenched with distilled
water (100 mL), and extracted with ethyl acetate. The combined extracts were
washed successively with water and saturated saline solution, dried over
anhydrous MgSO4, and filtered. The filtrate was concentrated under reduced
pressure. The residue was purified by column chromatography eluted with
petroleum ether and ethyl acetate (V:V = 2:1) to afford 2 (12.28 g, 90.2%) as a
colorless oil. 1H NMR (400 MHz, CDCl3) dppm: 4.21–4.00 (5H, m), 2.97 (1H, d,
J = 13 Hz), 2.88–2.81 (1H, m), 2.53 (1H, d, J = 11 Hz), 2.06–2.03 (1H, m), 1.73
(1H, dd, J1 = 13 Hz, J2 = 2 Hz), 1.45 (9H, s) ,1.27 (3H, t, J = 7 Hz). MS-ESI (m/z):
274 (M+H)+, 296 (M+Na)+. To a stirring solution of 2 (81.90 g, 300 mmol) in 25%
ammonia solution (250 mL) was added dimethyl formamide (25 mL) at room
temperature. The reaction mixture was stirred for 36 h at the same
temperature, then cooled to 0 °C. The precipitate was filtered, washed with
distilled water, and dried in vacuo to afford 3 (23.42 g, 32.5%) as a white solid,
mp:133–135 °C. 1H NMR (400 MHz, CDCl3) dppm: 5.63 (2H, s), 4.16–4.09 (3H,
m), 2.94–2.81 (2H, m), 2.41 (1H, d, J = 11 Hz), 2.07 (1H, qd, J1 = 12 Hz, J2 = 3 Hz),
1.75–1.72 (1H, m), 1.46 (9H, s). MS-ESI (m/z): 245 (M+H)+, 267 (M+Na)+. To a
stirring suspension of 3 (29.28 g, 120 mmol) in distilled water (300 mL) was
added dropwise 10% sodium hypobromite solution (300 mL) at 5 °C for 1 h. The
reaction mixture was stirred for 3 h at room temperature, and then 4 h at 80 °C.
A solution of (Boc)2O (30.52 g, 140 mmol) in ethanol (50 mL) was added to the
reaction mixture over a period of 30 min at 50 °C. The reaction mixture was
stirred for 3 h at the same temperature. The precipitate was filtered, washed
with distilled water, and dried in vacuo to afford 4 (9.5 g, 30.8%) as a white
solid, mp: 133–136 °C. 1H NMR (400 MHz, CDCl3) dppm: 4.96 (1H, s), 4.16 (1H,
d, J = 14 Hz), 4.01 (1H, d, J = 14 Hz), 3.88 (1H, br s), 3.65 (1H, br s), 2.97 (1H, d,
J = 14 Hz), 2.86–2.79 (1H, m), 1.97 (1H, br s), 1.72–1.65 (2H, m) ,1.45 (18H, s).
13C NMR (100 MHz, CDCl3) dppm: 155.86, 155.43, 80.06, 79.47, 67.09, 50.61,
42.97, 28.33, 26.53. MS-ESI (m/z): 339 (M+Na)+. The filtrate was extracted with
ethyl acetate. The combined extracts were dried over anhydrous MgSO4 and
yellow solid (58.3%) in
a similar manner as for the preparation of 10a.
Compound 10b, mp: 95–97 °C. 1H NMR (600 MHz, CDCl3) dppm: 5.02 (1H, d,
J = 16 Hz), 4.95 (1H, br s), 4.06 (2H, 7 Hz), 4.02 (1H, br s), 3.54 (1H, br s), 3.07
(1H, br s), 2.75 (3H, s), 2.00–1.82 (2H, m), 1.45 (18H, s), 1.23 (3H, t, J = 7 Hz).
MS-ESI (m/z): 372 (M+H)+, 389 (M+NH4)+, 394 (M+Na)+ . To a stirring solution
of 10a (0.50 g, 1.4 mmol) in dichloromethane (10 mL) was pumped dried
hydrochloride gas at 0–5 °C for 30 min. The reaction mixture was stirred for
another 1 h at room temperature, and concentrated under reduced pressure.
The residue was treated with ethyl acetate. The precipitate was collected by
suction, and dried in vacuo to give 11a as a white solid (0.15 g, 66.5%), mp: 76–
78 °C. 1H NMR (500 MHz, DMSO-d6) dppm: 9.60 (4H, br s), 4.35 (1H, d, J = 15 Hz),
4.10–4.08 (1H, m), 3.92 (3H, s), 3.82 (1H, d, J = 15 Hz), 3.51–3.47 (1H, m), 3.20–
3.15 (1H, m), 2.55 (3H, s), 2.42–2.38 (1H, m), 2.13–2.11 (1H, m). 13C NMR
(100 MHz, DMSO-d6) dppm: 145.06, 62.57, 53.79, 46.58, 37.35, 30.50, 24.17. MS-
ESI (m/z): 158 (M+H)+. The compounds 11b and 11c were obtained in a similar
manner as for the preparation of 11a. Compound 11b, yield: 47.0% (from 10b),
white solid. mp: 80–82 °C. 1H NMR (400 MHz, DMSO-d6) dppm: 9.75 (4H, br s),
4.46 (1H, d, J = 15 Hz), 4.17 (2H, q, J = 7 Hz), 4.15–4.05 (1H, m), 3.85 (1H, d,
J = 15 Hz), 3.40–3.10 (2H, m), 2.53 (3H, s), 2.49–2.48 (1H, m), 2.22–2.12 (1H,
m), 1.24 (3H, t, J = 7 Hz). MS-ESI (m/z): 172 (M+H)+. Compound 11c, yield:
39.7% (from 9a), off-white solid easily absorbing moisture.
16. Wan, Z. L.; Chai, Y.; Liu, M. L.; Guo, H. Y.; Sun, L. Y. Acta Pharm. Sin. 2010, 45,
860.
17. To a solution of 11a (0.23 g, 1 mmol) and triethylamine (0.42 mL, 3 mmol) in
anhydrous acetonitrile (10 mL) was added 12 (0.23 g, 0.8 mmol) at room

K. Lv et al. / Bioorg. Med. Chem. Lett. 23 (2013) 1754–1759
1759
temperature. The reaction mixture was stirred for 5 h at 50 °C, and
concentrated under reduced pressure. The residue was dissolved in 20%
acetic acid (10 mL), stirred for 0.5 h at 50 °C, and filtered. The filtrate was
adjusted to pH 6.5–7.5 by 15% sodium hydroxide and extracted by
dichloromethane. The combined extracts were dried over anhydrous MgSO4
and concentrated under reduced pressure. The crude product was purified by
column chromatography (silica gel), eluting with dichloromethane and
methanol (V:V = 10:1) to afford the target compound 19a1 as a off-white
solid. 1H NMR (500 MHz, DMSO-d6) dppm: 8.63 (1H, s), 8.13 (1H, d, J = 13 Hz),
5.12 (1H, d, J = 14 Hz), 4.57 (1H, d, J = 16 Hz), 4.25–4.22 (1H, m), 4.07 (1H, br s),
3.87 (3H, s), 3.82-3.79 (1H, m), 3.70 (1H, m), 2.49 (3H, s), 1.12 (1H, br s), 1.99–
1.97 (1H, m), 1.20–1.19 (2H, m), 1.13–1.11 (2H, m). MS-ESI (m/z): 404 (M+H)+.
HRMS-ESI (m/z): Calcd for C19H23O4N5F (M+H)+: 404.1728; Found 404.1732.
The other target compounds 19a5, 19a6, 19b1, 19c1 and 20 were obtained as
off-white or light yellow solids in a similar manner as for the preparation of
19a1. Compound 19a5 (from 11a and 13), 1H NMR (600 MHz, CDCl3) dppm: 8.67
(1H, s), 8.11 (1H, d, J = 13 Hz), 7.43–7.37 (1H, m), 7.11–7.06 (2H, m), 4.41 (1H,
d, J = 14 Hz), 4.12–4.08 (1H, m), 3.97 (1H, d, J = 14 Hz), 3.86 (1H, br s), 3.81 (3H,
s), 3.62–3.55 (1H, m), 2.36 (3H, s), 1.90–1.86 (1H, m), 1.78-1.70 (1H, m). 13C
NMR (150 MHz, CDCl3) dppm: 177.65, 166.32, 157.09 (d, J = 250 Hz), 153.72,
149.99, 147.19 (d, J = 258 Hz), 147.09, 145.85, 129.96, 123.98, 119.05 (d,
J = 22 Hz), 112.92, 112.27, 110.11, 105.36 (d, J = 21 Hz), 61.85, 50.29, 46.64,
42.67, 33.98, 29.14. MS-ESI (m/z): 476 (M+H)+. HRMS-ESI (m/z): Calcd for
(d, J = 250 Hz), 149.96, 138.68, 133.70, 122.53, 108.10, 107.83, 62.17, 61.89,
57.80, 47.90, 45.62, 40.61, 33.77, 31.99, 9.53, 9.47. MS-ESI (m/z): 433 (M+H)+.
HRMS-ESI (m/z): Calcd for C21H26O5N4F (M+H)+: 433.1881; Found 433.1892.
The other target compounds 19a3, 19a4, 19a7, 19b2–4, 19c2 and 19c3 were
obtained as light yellow solids in a similar manner as for the preparation of
19a2. Compound 19a3 (from 11a and 16), 1H NMR (600 MHz, CDCl3) dppm: 8.61
(1H, s), 7.74 (1H, d, J = 12 Hz), 4.47–4.33 (2H, m), 4.36–4.27 (2H, m), 4.07 (1H,
d, J = 16 Hz), 3.87 (3H, s), 3.60-3.53 (1H, m), 3.37–3.30 (2H, m), 2.47 (3H, s),
2.23–2.20 (1H, m), 1.90–1.88 (1H, m), 1.61 (3H, s). 13C NMR (100 MHz, CDCl3)
dppm: 177.05, 167.14, 156.24 (d, J = 246 Hz), 153.79, 144.80, 140.07, 132.11,
124.59, 121.16, 107.99, 105.12 (d, J = 24 Hz), 68.24, 61.81, 57.41, 55.44, 47.74,
46.34, 33.80, 31.21, 18.31. MS-ESI (m/z): 419 (M+H)+. HRMS-ESI (m/z): Calcd
for C20H24O5N4F (M+H)+: 419.1725; Found 419.1734. Compound 19a4 (from
11a and 17), 1H NMR (600 MHz, C5D5N) dppm: 8.91 (1H, s), 8.04 (1H, d,
J = 12 Hz), 4.82 (1H, d, J = 15 Hz), 4.25 (1H, d, J = 15 Hz), 4.18–4.16 (1H, m), 3.89
(3H, s), 3.87 (1H, br s), 3.82–3.79 (1H, m), 3.42–3.39 (1H, m), 2.82 (3H, s), 2.77–
2.73 (1H, m), 2.35–2.30 (1H, m), 1.10–1.07 (2H, m), 1.03–1.01 (2H, m). 13C NMR
(100 MHz, DMSO-d6) dppm: 175.82, 165.30, 153.28 (d, J = 253 Hz), 150.24,
149.53, 146.33 (d, J = 248 Hz), 132.54, 126.33, 121.08, 107.45, 106.78, 62.08,
55.37, 47.78, 45.91, 30.78, 28.27, 8.43. MS-ESI (m/z): 421 (M+H)+. HRMS-ESI
(m/z): Calcd for C19H23O4N4F2 (M+H)+: 421.1681; Found 421.1690. Compound
19a7 (from 11a and 18), 1H NMR (600 MHz, CDCl3) dppm: 8.61 (1H, s), 7.98 (1H,
d, J = 12 Hz), 4.49–4.45 (2H, m), 4.36 (1H, d, J = 15 Hz), 4.16 (1H, d, J = 15 Hz),
3.89 (3H, s), 3.67–3.64 (1H, m), 3.45–3.43 (1H, m), 3.38–3.34 (1H, m), 2.52 (3H,
s), 2.32 (1H, m), 1.98–1.94 (1H, m), 1.57 (3H, t, J = 7 Hz). 13C NMR (100 MHz,
CDCl3) dppm: 176.20, 166.57, 154.25 (d, J = 251 Hz), 152.47, 150.06, 146.25 (d,
J = 254 Hz), 133.88, 127.05, 121.98, 108.34 (d, J = 24 Hz), 108.16, 61.93, 57.30,
54.68, 47.86, 45.99, 33.56, 31.36, 16.33. MS-ESI (m/z): 409 (M+H)+. HRMS-ESI
(m/z): Calcd for C19H23O4N4F2 (M+H)+: 409.1681; Found 409.1690. Compound
19b2 (from 11b and 15), 1H NMR (400 MHz, CDCl3) dppm: 8.81 (1H, s), 7.87 (1H,
d, J = 12 Hz), 4.45 (1H, d, J = 15 Hz), 4.17–4.11 (3H, m), 4.06–4.02 (1H, m), 3.77
(3H, s), 3.72 (1H, br s), 3.50 (1H, br s), 3.45–3.40 (1H, m), 2.57 (2H, s), 2.35–2.32
(1H, m), 2.05–2.03 (1H, m), 1.27–1.21 (5H, m), 1.07–0.99 (2H, m). 13C NMR
(100 MHz, CDCl3) dppm: 177.00, 166.66, 156.42 (d, J = 251 Hz), 149.99, 146.50,
138.42, 133.70, 122.49, 108.10 (d, J = 23 Hz), 107.84, 69.86, 62.23, 57.73, 47.76,
45.83, 40.60, 33.25, 31.47, 14.54, 9.56, 9.48. MS-ESI (m/z): 447 (M+H)+. HRMS-
C
22H21O4N5F3 (M+H)+: 476.1540; Found 476.1552. Compound 19a6 (from 11a
and 14), 1H NMR (400 MHz, CDCl3) dppm: 8.66 (1H, s), 8.38 (1H, d, J = 9 Hz), 6.86
(1H, d, J = 9 Hz), 4.80–4.67 (2H, m), 3.98–3.86 (5H, m), 3.62 (1H, br s), 3.46 (1H,
br s), 2.50 (3H, s), 2.21 (1H, br s), 2.04 (1H, br s), 1.28–1.25 (2H, m), 1.08–1.03
(2H, m). 13C NMR (150 MHz, CDCl3) dppm: 177.36, 167.25, 158.76, 152.43,
151.31, 146.87, 136.38, 111.82, 108.78, 106.97, 62.18, 56.82, 41.19, 40.27,
34.41, 33.71, 29.03, 7.43, 7.35. MS-ESI (m/z): 386 (M+H)+. HRMS-ESI (m/z):
Calcd for C19H24O4N5 (M+H)+: 386.1723; Found 386.1771. Compound 19b1
(from 11b and 12), 1H NMR (600 MHz, CDCl3) dppm: 8.73 (1H, s), 8.08 (1H, d,
J = 13 Hz), 4.90 (1H, d, J = 16 Hz), 4.75 (1H, d, J = 16 Hz), 4.16–4.14 (3H, m),
3.96–3.93 (1H, m), 3.64–3.60 (1H, m), 3.49–3.46 (1H, m), 2.48 (3H, s), 2.28–
2.26 (1H, m), 1.98–1.97 (1H, m), 1.34–1.26 (5H, m), 1.18–1.14 (2H, m). 13C
NMR (100 MHz, CDCl3) dppm: 177.05, 166.83, 151.97, 150.06, 149.97, 147.35 (d,
J = 258 Hz), 146.65, 119.89, 113.40, 108.86, 69.88, 57.20, 43.63, 42.31, 34.74,
33.70, 30.26, 14.51, 7.42. MS-ESI (m/z): 418 (M+H)+. HRMS-ESI (m/z): Calcd for
ESI (m/z): Calcd for
C
22H28O5N4F (M+H)+: 447.2038; Found 447.2046.
Compound 19b3 (from 11b and 16), 1H NMR (400 MHz, CDCl3) dppm: 8.64
(1H, s), 7.71 (1H, d, J = 12 Hz), 4.52–4.30 (4H, m), 4.18–4.10 (3H, m), 3.62–3.57
(1H, m), 3.43–3.32 (2H, m), 2.52 (3H, s), 2.28–2.24 (1H, m), 2.01–1.98 (1H, m),
C
20H25O4N5F (M+H)+: 418.1885; Found 418.1893. Compound 19c1 (from 11c
and 12), 1H NMR (500 MHz, DMSO-d6) dppm: 8.74 (1H, s), 8.09 (1H, d, J = 13 Hz),
5.24 (1H, d, J = 16 Hz), 4.33 (1H, d, J = 16 Hz), 4.32–4.30 (1H, m), 3.88 (3H, s),
3.78–3.72 (2H, m), 3.66–3.63 (1H, m), 2.28–2.25 (1H, m), 1.83–1.78 (1H, m),
1.61 (3H, d, J = 6 Hz), 1.25 (3H, t, J = 7 Hz). 13C NMR (100 MHz, CDCl3) dppm
:
177.13, 167.04, 157.61, 153.83 (d, J = 259 Hz), 144.65, 140.11, 132.19 (d,
J = 14 Hz), 124.60, 121.24, 108.01, 105.23 (d, J = 24 Hz), 69.70, 68.28, 57.55,
55.47, 47.62, 46.40, 33.52, 30.98, 18.30, 14.57. MS-ESI (m/z): 433 (M+H)+.
HRMS-ESI (m/z): Calcd for C21H26O5N4F (M+H)+: 433.1881; Found 433.1889.
Compound 19b4 (from 11b and 17), 1H NMR (400 MHz, CDCl3) dppm: 8.79 (1H,
s), 7.93 (1H, d, J = 12 Hz), 4.35 (1H, d, J = 15 Hz), 4.19 (1H, d, J = 15 Hz), 4.13 (2H,
q, J = 7 Hz), 4.00–3.98 (1H, m), 3.67–3.62 (1H, m), 3.47–3.41 (2H, m), 2.49 (3H,
s), 2.29–2.24 (1H, m), 1.95–1.88 (1H, m), 1.33–1.24 (5H, m), 1.22–1.18 (2H, m).
13C NMR (100 MHz, CDCl3) dppm: 176.82, 165.29, 153.10 (d, J = 250 Hz), 150.18,
149.33, 145.33 (d, J = 247 Hz), 132.44, 126.30, 121.08, 107.45, 106.78, 68.40,
61.83, 43.63, 42.31, 34.74, 33.70, 30.26, 14.51, 7.42. MS-ESI (m/z): 435 (M+H)+.
HRMS-ESI (m/z): Calcd for C21H25O4N4F2 (M+H)+: 435.1838; Found 435.1846.
Compound 19c2 (from 11c and 15), 1H NMR (400 MHz, CDCl3) dppm: 8.82 (1H,
s), 7.88 (1H, d, J = 12 Hz), 4.68 (1H, d, J = 15 Hz), 4.04–3.98 (1H, m), 3.89 (3H, s),
3.88–3.79 (1H, m), 3.74 (3H, m), 3.70–3.61 (1H, m),3.52–3.41 (2H, m), 2.39–
2.34 (1H, m), 1.99–1.90 (1H, m), 1.24–1.19 (2H, m), 1.06–1.01 (2H, m). 13C NMR
(100 MHz, CDCl3) dppm: 177.07, 166.58, 158.37, 155.91 (d, J = 250 Hz), 150.08,
146.38, 138.39, 133.66, 121.65, 108.13 (d, J = 23 Hz), 107.90, 62.35, 62.19,
50.22, 46.49, 40.58, 33.29, 32.53, 9.46, 9.40. MS-ESI (m/z): 419 (M+H)+. HRMS-
1.31–1.29 (2H, m), 1.10–1.07 (2H, m). 13C NMR (100 MHz, DMSO-d6) dppm
:
176.41, 165.64, 154.84, 149.46, 147.22, 146.62 (d, J = 254 Hz), 146.49, 119.50
(d, J = 22 Hz), 112.50, 107.66, 61.49, 48.83, 43.67, 41.81, 34.95, 31.87, 6.88. MS-
ESI (m/z): 390 (M+H)+. HRMS-ESI (m/z): Calcd for C18H21O4N5F (M+H)+:
390.1572; Found 390.1563. Compound 20 (from
6
and 12), 1H NMR
(400 MHz, DMSO-d6) dppm: 15.24 (1H, s), 8.58 (1H, s), 8.04 (1H, d, J = 16 Hz),
7.72 (1H, s), 4.94 (1H, d, J = 9 Hz), 4.46 (1H, d, J = 15 Hz), 4.16–4.12 (2H, m),
3.82–3.67 (2H, m), 2.15–2.06 (1H, m), 1.82–1.77 (1H, m), 1.22–1.07 (4H, m).
13C NMR (100 MHz, DMSO-d6) dppm: 176.84, 166.23, 158.53, 150.74, 147.49,
147.15, 146.80 (d, J = 250 Hz), 119.40 (d, J = 22 Hz), 73.50, 47.74, 44.18, 41.47,
35.93, 25.93, 7.34, 7.25. MS-ESI (m/z): 387 (MÀH)À. HRMS-ESI (m/z): Calcd for
C
18H16O5N4F (MÀH)À: 387.1099; Found 387.1100. To a solution of 11a (0.23 g,
1 mmol) and triethylamine (0.42 mL, 3 mmol) in acetonitrile (10 mL) was
added 15 (0.34 g, 0.8 mmol) at room temperature. The reaction mixture was
stirred overnight at 50 °C, and concentrated under reduced pressure. The
residue was dissolved in a solution of 5% sodium hydroxide solution (8 mL) and
stirred for 1 h at 50 °C. After cooling to room temperature, the mixture was
adjusted to pH 7.0–7.5 with 5% acetic acid, and extracted with
dichloromethane. The combined extracts were concentrated under reduced
pressure. The residue was dissolved in 20% acetic acid (10 mL), stirred for 0.5 h
at 50 °C, and filtered. The filtrate was adjusted to pH 6.5–7.5 by 15% sodium
hydroxide and extracted by dichloromethane. The combined extracts were
dried over anhydrous MgSO4 and concentrated under reduced pressure. The
crude product was purified by column chromatography (silica gel), eluting
with dichloromethane and methanol (V:V = 10:1) to afford the target
compound 19a2 as a light yellow solid. 1H NMR (600 MHz, CDCl3) dppm: 8.82
(1H, s), 7.88 (1H, d, J = 13 Hz), 4.37 (1H, d, J = 15 Hz), 4.10 (1H, d, J = 15 Hz),
4.05–4.02 (1H, m), 3.87 (3H, s), 3.76 (3H, s), 3.70–3.63 (1H, m), 3.40–3.37 (2H,
m), 2.50 (3H, s), 2.33–2.27 (1H, m), 1.90–1.86 (1H, m), 1.24–1.19 (2H, m), 1.03–
1.00 (2H, m). 13C NMR (100 MHz, CDCl3) dppm: 177.03, 166.69, 164.93, 156.60
ESI (m/z): Calcd for
C
20H24O5N4F (M+H)+: 419.1725; Found 419.1732.
Compound 19c3 (from 11c and 16), 1H NMR (400 MHz, CDCl3) dppm: 8.63
(1H, s), 7.77 (1H, d, J = 12 Hz), 4.53–4.40 (4H, m), 3.87 (3H, s), 3.80–2.93 (4H,
m), 2.40–2.01 (2H, m), 1.62 (3H, d, J = 6 Hz). 13C NMR (100 MHz, CDCl3) dppm
:
176.48, 166.35, 155.48 (d, J = 248 Hz), 152.68, 144.20, 139.47, 134.09, 128.64,
121.29, 108.15, 107.90, 69.58, 57.48, 47.87, 46.01, 40.14, 33.92, 31.77, 14.54.
MS-ESI (m/z): 404 (M+H)+. HRMS-ESI (m/z): Calcd for C19H22O5N4F (M+H)+:
405.1574; Found 405.1576.
18. Performance standards for antimicrobial susceptibility testing: 17th
informational supplement, Clinical and Laboratory Standards Institute,
Wayne, PA, 2007, M100eS17.