Design, Synthesis and Antibacterial Evaluation of 1-[(1R,2S)-2-Fluorocyclopropyl]ciprofloxacin-1,2,4-triazole-5(4H)-thione Hybrids

Article abstract of DOI:10.1002/cbdv.201800261

A new class of 1-[(1R,2S)-2-fluorocyclopropyl]ciprofloxacin (CPFX)-1,2,4-triazole-5(4H)-thione hybrids 6a?–?6o was designed, synthesized and evaluated for their in?vitro antibacterial activities against a panel of clinically important drug-sensitive and d

Full text of DOI:10.1002/cbdv.201800261

Article Type: Communication
Design, Synthesis and Antibacterial Evaluation of 1-[(1R,
2S)-2-Fluorocyclopropyl]ciprofloxacin-1,2,4-triazole-5(4H)-thione
Hybrids
by Yang Gaoa)1), Lu-Xin Nab)1), Zhi Xub)c), Shu Zhang*d), A-Peng Wangb), Kai Lvb),
Hui-Yuan Guob), and Ming-Liang Liu*b)
a)Xuanwu Hospital, Capital Medical University, Beijing 100053, P. R. China;
b)Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union
Medical College, Beijing 100050, P. R. China;
c)HuangHuai University, Zhumadian, P. R. China;
d)Pony Testing International Group Co. Ltd (Wuhan), Wuhan, P. R. China.
*)Corresponding author: zhangshufsy@126.com (S. Zhang); lmllyx@126.com (M. L. Liu)
1)These authors contributed equally to this work.
A new class of 1-[(1R, 2S)-2-fluorocyclopropyl]ciprofloxacin
(CPFX)-1,2,4-triazole-5(4H)-thione hybrids 6a-o was designed, synthesized and evaluated for their in
vitro antibacterial activities against a panel of clinically important drug-sensitive and drug-resistant
Gram-positive and Gram-negative pathogens. Our results revealed that all hybrids 6a-o have great
potency against the tested strains, especially Gram-negative pathogens. The synthesized hybrids were
more potent than the parent 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX 5, and were comparable to CPFX
and levofloxacin against the majority of the tested pathogens, worth to be further investigated.
Keywords: Quinolone; ciprofloxacin; 1,2,4-triazole-5(4H)-thione; Antibacterial; Structure-activity
relationship
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been through the copyediting, typesetting, pagination and proofreading process, which may
lead to differences between this version and the Version of Record. Please cite this article as
doi: 10.1002/cbdv.201800261
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Introduction
Bacterial infections are account for the majority of hospital-acquired infections, and place a
heavy burden on global healthcare systems[1]. The antibiotics are common weapons to treat
bacterial infections, but bacteria have already developed resistance towards almost all current
therapeutic options duo to long-term, broad and inappropriate usage[2]. Therefore, new
antibacterial agents are strongly sought and research on the agents has been carried out in the
recent decades.
Fluoroquinolones, which play a pivotal role in drug discovery as they exhibit a variety of
biological properties such as anti-tumor[3,4], anti-tubercular[5], anti-HIV[6], anti-malarial[7,8]
and anti-bacterial activities[2], are the second widest used antibiotics in clinical practice for
the treatment of various bacterial infections both in hospital and community settings[1].
Unfortunately, fluoroquinolone-resistant bacteria have already emerged and widely spread
globally[2]. Therefore, it’s imperative to develop new fluoroquinolone agents with great
potency against both drug-sensitive and drug-resistant Gram-positive and Gram-negative
pathogens.
Molecular hybridization is a useful tool for the development of new drug candidates, and
several fluoroquinolone hybrids which are exemplified by MCB3681 and CBR-2092 have
already under clinical trials for treatment of infections caused by fluoroquinolone-resistant,
multidrug-resistant and difficult to treat pathogens[9,10]. Obviously, fluoroquinolone hybrids
are promising candidates with unique mechanism of action different from those of the
currently used drugs.
The structure-activity relationship (SAR) demonstrated that the substituents at C-7 position of
fluoroquinolone motif have significantly influence on antibacterial potency, spectrum and
pharmacokinetic profiles, and the C-7 position is proven to be the most adaptable site for
chemical modification[11,12]. Furthermore, the research results revealed that introduction of
bulky substituent at C-7 position of fluoroquinolones is not a barrier to penetration, so various
biological pharmacophores have been incorporated into this position[11,12]
.
Triazoles, one of the most important classes of nitrogen-containing heterocycles, possess
diverse biological profiles including antibacterial activity which may due to their ability to
exert various noncovalent interactions (π-π, electrostatic interactions, hydrogen bonds, metal
coordination and van der Waals force etc.) with the various active sites in organisms[13]
.
Obviously, hybridization of triazoles with fluoroquinolones is a reasonable choice to develop
new antibacterial agents.
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Figure 1 Chemical structures of ciprofloxacin-1,2,4-triazole-5(4H)-thione hybrids and
1-[(1R, 2S)-2-fluorocyclopropyl]ciprofloxacin 1
In recent year, several series of ciprofloxacin(CPFX)-1,2,4-triazole-5(4H)-thione hybrids
(Figure 1) were assessed for their in vitro antibacterial activities against various clinically
relevant bacteria, and some of them were more potent than the parent CPFX[14-17]. The SAR
studies suggested that phenyl group at C-3 position of the 1,2,4-triazole moiety was crucial
for the high antibacterial activity, and the substituents on the phenyl ring were one of the key
factors.
Clinical data indicated that N1-cyclopropyl fluoroquinolones with outstanding antibacterial
activity could cause serious central nervous system (CNS) toxicity[18], while the
corresponding 2-fluorocyclopropyl counterparts could modulate the lipophilicity and reduce
the CNS toxicity[19]. Sitafloxacin, bearing a (1R, 2S)-2-fluorocyclopropyl group at the
N1-position, was approved in Japan for the treatment of a number of bacterial infections[20]
Moreover, many of 1-[(1R, 2S)-2-fluorocyclopropyl]fluoroquinolones with an oxime
functional moiety at C-7 position were found to have a broad spectrum of antibacterial
.
activity in our lab recently[21,22]
.
Inspired by the above research results and as a continuous program to develop new
fluoroquinolone antibacterial agents, we intended to introduce 1,2,4-triazole-5(4H)-thione
moieties to the piperazine ring of 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX 1. Thus, a series of
novel hybrids were designed, synthesized and screened for their in vitro antibacterial
activities against various clinically relevant pathogens in this study. A preliminary SAR study
is also explored to facilitate the further development of this kind of hybrids.
Results and Discussion
Chemistry
The desired 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX-1,2,4-triazole-5(4H)-thione hybrids 6a-o
were prepared according to the literature reported procedure [15], and the detailed synthetic
route was depicted in Scheme 1. Treatment of aromatic hydrazides 2 with substituted
phenyl/benzyl isothiocyanates 3 yielded the corresponding thiosemicarbazides 4, which were
cyclized in 2% NaOH solution provided the key intermediates 1,2,4-triazole-5(4H)-thiones 5.
Finally, Mannich reaction of 1,2,4-triazole-5(4H)-thiones 5, 1-[(1R,
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2S)-2-fluorocyclopropyl]CPFX 1 and formaldehyde was performed in ethanol for 10 h to
give the titled hybrids 6a-o. The chemical structures of hybrids 6a-o were presented in Table
1.
Scheme 1 Synthetic route for 1-[(1R,
2S)-2-fluorocyclopropyl]CPFX-1,2,4-triazole-5(4H)-thione hybrids 6a-o
a) EtOH, reflux, 10 min. b) 2% NaOH, reflux, 12 h. c) 1-[(1R,
2S)-2-fluorocyclopropyl]CPFX 1, (HCHO)n, EtOH, reflux, 10 h.
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Table 1. Chemical structures of hybrids 6a-o
Compd.
6a
R1
R2
4-pyridinyl
3-pyridinyl
2-pyridinyl
2-naphthyl
3,5-diOMePh
4-pyridinyl
3-pyridinyl
2-pyridinyl
3-OHPh
-Bn
-Bn
-Bn
-Bn
-Bn
-Ph
-Ph
-Ph
-Ph
-Ph
-Ph
-Ph
-Ph
-Ph
-Ph
6b
6c
6d
6e
6f
6g
6h
6i
2-OHPh
6j
3-OMePh
6k
6l
2-OMePh
3,4-diOMePh
3,5-diOMePh
3,4,5-triOMePh
6m
6n
6o
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Antibacterial Activity
The 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX-1,2,4-triazole-5(4H)-thione hybrids 6a-o were
evaluated for their in vitro antibacterial activity against a panel of clinically important
drug-sensitive and drug-resistant Gram-positive and Gram-negative strains using standard
techniques[22]. The minimum inhibitory concentration (MIC) defined as the concentration of
the compound required to give complete inhibition of bacterial growth, and the MIC values
of 6a-o against Gram-positive and Gram-negative strains, along with those of the references
vancomycin (VAN), CPFX, levofloxacin (LVFX) and 8-methoxy CPFX (8-OMe CPFX) and
the parent 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX 1 for comparison, are listed in Table 2 and
Table 3, respectively.
The in vitro antibacterial data suggested that all of the target hybrids 6a-o have a similar
antibacterial spectrum with the references VAN, CPFX, LVFX and 8-OMe CPFX. Further
analysis indicated that all hybrids exhibited considerable potency in inhibiting the growth of
some tested Gram-positive strains including methicillin-sensitive Staphylococcus epidermidis
(MSSE), methicillin-sensitive S. aureus (MSSA), methicillin-resistant S. aureus (MRSA) and
Enterococcus faecalis (two strains) as well as Gram-negative strains, and the MICs for these
hybrids against Gram-positive and Gram-negative pathogens were 0.44~>208.06 μM and
≤0.04~92.99 μM, respectively. The antibacterial activity of hybrids 6a-o was found to be
more potent than the parent 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX 1 (MIC: ≤0.09~>366.64
μM), and was comparable to CPFX (MIC: ≤0.08~>348.67 μM) and LVFX (MIC:
≤0.08~>177.22 μM) against the majority of the tested pathogens. Moreover, the
anti-Gram-negative bacteria activity of hybrids 6a-o was far more potent than VAN (MIC:
>88.32 μM).
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Table 2. In vitro antibacterial activity of hybrids 6a-o against Gram-positive strains.
Compd.
MIC (μM)
MRSA
MSSE
0.79
0.79
0.44
0.74
0.76
1.63
3.25
1.63
0.79
0.79
0.78
1.55
1.48
1.48
1.42
0.35
0.34
2.86
0.35
0.69
MRSE
6.36
6.36
6.36
5.9
MSSA
0.79
1.59
1.59
1.47
0.73
3.25
3.25
1.63
3.17
1.59
3.1
E.fa.1
6.36
3.18
3.18
11.8
5.81
6.5
E.fa.2
6.36
3.18
1.59
5.9
E.fm.1
>203.43
>203.43
>203.43
>188.73
>185.98
>208.06
>104.03
>208.06
>203.11
>203.11
>99.35
E.fm.2
50.86
25.43
50.86
47.18
46.50
104.03
26.11
26.01
25.39
50.78
24.84
24.84
23.73
94.93
45.44
44.3
6a
6b
6c
6d
6e
0.79
1.59
1.59
1.47
1.45
6.5
11.62
26.01
13
2.91
13
6f
3.25
1.63
3.17
1.59
3.10
1.55
2.97
2.97
1.42
0.35
0.68
5.73
0.69
0.69
3.25
3.25
6.35
3.17
6.21
3.1
6.5
6g
6.5
3.25
6.35
3.17
6.21
6.21
11.87
5.93
2.84
1.38
1.36
5.73
1.38
0.69
6h
12.69
12.69
24.84
6.21
8.00
11.87
11.36
5.54
10.9
22.88
5.54
0.69
6i
6j
6k
1.55
2.97
2.97
1.42
0.35
0.68
2.86
0.35
0.35
>198.69
>189.85
>94.93
6l
5.93
2.97
2.84
2.77
1.36
5.73
2.77
2.76
6m
6n
>181.76
177.22
6o
LVFX
CPFX
1
348.67
21.79
91.66
22.15
0.69
>366.64
88.61
8-OMeCPFX
VAN
>88.32
Abbreviations: MSSE, methicillin-sensitive Staphylococcus epidermidis ATCC 12228; MRSE, methicillin- resistant
Staphylococcus epidermidis 16-3; MSSA, methicillin-sensitive Staphylococcus aureus ATCC 29213; MRSA,
methicillin-resistant Staphylococcus aureus ATCC 33591; E.fa.1, Enterococcus faecalis ATCC 29212; E.fa.2, Enterococcus
faecalis ATCC 51575; E.fm.1, Enterococcus faecium ATCC 700221; E.fm.2, Enterococcus faecium 16-4; LVFX,
levofloxacin; CPFX, ciprofloxacin; 8-OMeCPFX, 8-methoxy ciprofloxacin; VAN, vancomycin.
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Table 3. In vitro antibacterial activity of hybrids 6a-o against Gram-negative strains.
Compd.
MIC (μM)
E.co.1
E.co.2
K.p.1
1.59
K.p.2
P.a.
A.c.
E.c.
E.a.
0.1
S.m.1
0.2
M.m.
P.r.
P.v.
P.m.
S.m.2
50.86
C.f.
6a
6b
6c
6d
≤0.05
≤0.05
≤0.05
0.79
12.71
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.04
≤0.05
≤0.05
≤0.04
0.4
≤0.05
≤0.05
0.09
1.59
0.79
1.47
6.36
6.36
11.8
≤0.05
≤0.05
≤0.04
0.1
0.1
0.2
0.2
≤0.05
≤0.05
≤0.04
≤0.05
≤0.05
≤0.04
≤0.05
≤0.05
≤0.04
≤0.05
≤0.05
≤0.04
25.43
12.71
47.18
≤0.05
≤0.05
≤0.04
0.79
1.47
0.18
0.37
6e
6f
≤0.04
0.1
≤0.04
0.1
1.45
3.25
1.63
1.63
1.59
1.59
1.55
0.78
2.97
1.48
1.42
0.09
0.2
1.45
3.25
1.63
1.63
1.59
1.59
6.21
3.1
5.81
13
≤0.04
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.04
≤0.04
≤0.04
0.18
0.2
0.36
0.41
0.2
0.09
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
0.09
≤0.04
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.04
≤0.04
≤0.04
≤0.04
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.04
≤0.04
≤0.04
0.09
0.10
92.99
52.02
26.01
26.01
25.39
25.39
24.84
24.84
23.73
23.73
22.72
≤0.04
0.10
6g
6h
6i
≤0.05
≤0.05
≤0.05
0.10
≤0.05
≤0.05
≤0.05
0.1
0.10
13
0.1
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
≤0.05
0.09
≤0.05
≤0.05
0.1
≤0.05
≤0.05
0.10
6.5
0.1
0.2
6.35
12.69
12.42
6.21
23.73
5.93
5.68
0.1
0.2
6j
0.2
0.2
≤0.05
0.09
6k
6l
≤0.05
≤0.05
≤0.04
≤0.04
≤0.04
≤0.05
≤0.05
≤0.04
≤0.04
≤0.04
≤0.05
≤0.05
0.19
0.19
0.09
0.19
0.09
≤0.04
0.19
0.19
0.37
0.19
0.18
≤0.05
0.09
6m
6n
6o
1.48
1.48
0.71
0.09
≤0.04
≤0.04
≤0.04
≤0.04
0.09
0.09
0.09
LVFX
CPFX
1
88.61
≤0.08
1.38
0.17
5.54
0.35
1.36
≤0.08
≤0.08
≤0.09
0.17
≤0.08
0.17
0.35
0.16
0.36
≤0.08
≤0.08
≤0.09
≤0.08
≤0.08
≤0.09
≤0.08
≤0.08
≤0.09
≤0.08
≤0.08
≤0.09
1.38
5.45
≤0.08
1.38
≤0.08
≤0.09
≤0.08
≤0.09
1.36
2.86
≤0.08
≤0.09
0.68
2.86
11.46
45.83
5.54
≤0.09
8-OMeCPFX
VAN
≤0.08
≤0.08
2.77
0.17
5.54
1.38
≤0.08
0.35
0.69
≤0.08
≤0.08
≤0.08
0.35
0.17
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
>88.3
Abbreviations: E.co.1, Escherichia coli ATCC 25922 ESBLs(-); E.co.2, Escherichia coli ATCC 35218
ESBLs(+);
K.p.1, Klebsiella pneumoniae ATCC 700603 ESBLs(+); K.p.2, Klebsiella pneumonia 7 ESBLs(-); P.a., Pseudomonas
aeruginosa ATCC 27853; A.c., Acinetobactercal coacetious ATCC 19606; E.c., Enterobacter cloacae ATCC 43560; E.a.,
Enterobacter aerogenes ATCC 13048; S.m.1, Serratia marcescens ATCC 21074; M.m., Morganella morganii ATCC 25830;
P.r., Providentia rettgeri ATCC 31052; P.v., Proteus vulgaris ATCC 29905; P.m., Proteus mirabilis ATCC 49565; S.m.2,
Stenotrophomonas maltophilia ATCC 13636; C.f., Citrobacter freundii ATCC 43864. ESBLs(+): Extended spectrum
beta-lactamases (ESBLs)-producing; LVFX, levofloxacin; CPFX, ciprofloxacin; 8-OMeCPFX, 8-methoxy ciprofloxacin;
VAN, vancomycin.
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The SAR revealed that 1) hybrids were more active against Gram-negative pathogens than
against Gram-positive bacteria; 2) the substituents on the N’-4 position of
1,2,4-triazole-5(4H)-thione have great influence on the antibacterial activity, and hybrids
with substituted phenyl groups were more potent than the corresponding benzyl substituted
analogs; 3) for the substituents at C’-3 position, -OMe on the phenyl ring was more favorable
than -OH; 4) in general, introduction of the second and the third -OMe was detrimental to the
activity; 5) hybrids with pyridine-2-yl at C’-3 position were more active than the
pyridine-3-yl and pyridine-4-yl analogs. It is worth noting that hybrid 6a exhibited promising
activity against all tested pathogens, could act as a starting point for further optimization.
Experimental Section
1 mmol of the 1,2,4-triazole-5(4H)-thiones 5 was dissolved in 40 mL of anhydrous ethanol
and then 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX 1 (1 mmol) and formaldehyde solution (aq.
37%, 1 mmol) were added. The mixture was stirred at refluxing for 10 h, and then cooled to
room temperature. The precipitate was filtered off, dried, and crystallized by ethanol (10 mL)
to give desired hybrids 6a-o.
7-(4-((4-benzyl-3-(pyridin-4-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-
1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid
(6a)
Yield: 52%. M.p.: 167-169 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.77-1.98 (2H, m,
cyclopropyl-H, CH2), 3.04 (4H, s, piperazine-4H), 3.40-3.46 (5H, m, piperazine-4H and
cyclopropyl-H), 3.89-3.90 (1H, m, cyclopropyl-H), 5.31-5.38 (2H, m, CH2), 5.51-5.58 (2H,
m, CH2), 7.08-7.09 (2H, m, Ar-H), 7.28-7.29 (3H, m, Ar-H), 7.51-7.52 (1H, m, Ar-H),
7.61-7.62 (2H, m, Ar-H), 7.92-7.95 (1H, s, Ar-H), 8.71-8.77 (3H, m, Ar-H).
7-(4-((4-benzyl-3-(pyridin-3-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-
1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid
(6b)
Yield: 56%. M.p.: 239-240 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.78-2.04 (2H, m,
cyclopropyl-H, CH2), 3.05 (4H, s, piperazine-4H), 3.40-3.50 (5H, m, piperazine-4H and
cyclopropyl-H), 3.88-3.90 (1H, m, cyclopropyl-H), 5.34 (2H, s, CH2), 5.48 (2H, s, CH2),
7.05-7.06 (2H, m, Ar-H), 7.27-7.28 (3H, m, Ar-H), 7.53-7.54 (2H, m, Ar-H), 7.92-7.95 (1H,
m, Ar-H), 8.00-8.02 (1H, m, Ar-H), 8.74-8.77 (3H, m, Ar-H).
7-(4-((4-benzyl-3-(pyridin-2-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-
1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic acid
(6c)
Yield: 53%. M.p.: 165-167 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.77-2.00 (2H, m,
cyclopropyl-H, CH2), 3.03 (4H, s, piperazine-4H), 3.40-3.45 (5H, m, piperazine-4H and
cyclopropyl-H), 3.89-3.90 (1H, m, cyclopropyl-H), 5.35 (2H, s, CH2), 5.93 (2H, s, CH2),
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7.19-7.25 (5H, m, Ar-H), 7.50-7.51 (2H, m, Ar-H), 7.90 (1H, s, Ar-H), 7.93-8.01 (2H, m,
Ar-H), 8.71-8.80 (2H, m, Ar-H).
7-(4-((4-benzyl-3-(naphthalen-2-yl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)piper
azin-1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carboxylic
acid (6d)
Yield: 63%. M.p.: 194-196 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.80-1.86 (2H, m,
cyclopropyl-H, CH2), 3.07 (4H, s, piperazine-4H), 3.45-3.49 (5H, m, piperazine-4H and
cyclopropyl-H), 3.83-3.85 (1H, m, cyclopropyl-H), 5.18-5.20 (2H, m, CH2), 5.38-5.44 (2H,
m, CH2), 6.80-6.81 (2H, m, Ar-H), 7.06-7.08 (3H, m, Ar-H), 7.47-7.65 (6H, m, Ar-H),
7.88-7.90 (1H, m, Ar-H), 8.04-8.05 (1H, m, Ar-H), 8.17-8.19 (1H, m, Ar-H), 8.70 (1H, s,
Ar-H).
7-(4-((4-benzyl-3-(3,5-dimethoxyphenyl)-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)p
iperazin-1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carbo
xylic acid (6e)
Yield: 66%. M.p.: 164-166 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.86-2.09 (2H, m,
cyclopropyl-H, CH2), 2.95-3.09 (4H, s, piperazine-4H), 3.35-3.45 (4H, m, piperazine-4H),
3.61-3.63 (1H, m, cyclopropyl-H), 3.75 (6H, s, 2×OCH3), 3.83-3.85 (1H, m, cyclopropyl-H),
5.25-5.35 (2H, m, CH2), 5.36-5.52 (2H, m, CH2), 6.61-6.71 (1H, m, Ar-H), 7.05-7.15 (3H, m,
Ar-H), 7.25-7.41 (4H, m, Ar-H), 7.48-7.62 (1H, m, Ar-H), 7.85-8.01 (1H, m, Ar-H),
8.71-8.78 (1H, m, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-7-(4-((4-phenyl-3-(pyridin-4-yl)-5-thioxo-4,5
-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic
acid (6f)
Yield: 66%. M.p.: 274-276 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.79-1.93 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.42-3.62 (5H, m, piperazine-4H and
cyclopropyl-H), 3.90-3.91 (1H, s, cyclopropyl-H), 5.35 (2H, s, CH2), 7.30 (2H, s, Ar-H),
7.50-7.57 (6H, m, Ar-H), 7.94 (1H, d, Ar-H), 8.62 (2H, d, Ar-H), 8.77 (1H, s, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-7-(4-((4-phenyl-3-(pyridin-3-yl)-5-thioxo-4,5
-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic
acid (6g)
Yield: 63%. M.p.: 256-258 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.71-2.01 (2H, m,
cyclopropyl-H, CH2), 3.05-3.21 (4H, m, piperazine-4H), 3.41-3.50 (5H, m, piperazine-4H
and cyclopropyl-H), 3.85-3.87 (1H, m, cyclopropyl-H), 5.28 (2H, s, CH2), 7.41-7.61 (7H, m,
Ar-H), 7.71-7.79 (1H, m, Ar-H), 7.91-8.01 (1H, m, Ar-H), 8.55 (1H, s, Ar-H), 8.62 (1H, s,
Ar-H), 8.77 (1H, s, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-7-(4-((4-phenyl-3-(pyridin-2-yl)-5-thioxo-4,5
-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic
acid (6h)
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Yield: 66%. M.p.: 272-273 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.78-1.99 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.42 (5H, s, piperazine-4H and
cyclopropyl-H), 3.89-3.91 (1H, m, cyclopropyl-H), 5.35 (2H, s, CH2), 7.37-7.38 (2H, m,
Ar-H), 7.42-7.47 (4H, m, Ar-H), 7.53-7.54 (1H, m, Ar-H), 7.82-7.84 (1H, m, Ar-H),
7.92-7.94 (2H, m, Ar-H), 8.40 (1H, s, Ar-H), 8.78 (1H, s, Ar-H). 13C NMR (100 MHz,
DMSO-d6) δ 13.29, 13.40, 37.25, 37.33, 49.99, 50.07, 69.41, 69.74, 71.94, 111.37, 111.61,
124.77, 125.69, 128.90, 129.29, 129.46, 136.05, 137.82, 139.73, 145.26, 148.67, 149.53,
149.77, 152.22, 166.17, 170.56, 176.89.
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-7-(4-((3-(3-hydroxyphenyl)-4-phenyl-5-thioxo-4,5-d
ihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-4-oxo-1,4-dihydroquinoline-3-carboxylic
acid (6i)
Yield: 65%. M.p.: 227-229 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.77-1.94 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.40 (5H, s, piperazine-4H and
cyclopropyl-H), 3.88-3.89 (1H, m, cyclopropyl-H), 5.31 (2H, s, CH2), 6.69 (1H, d, Ar-H),
6.84-6.85 (2H, m, Ar-H), 7.12-7.15 (1H, m, Ar-H), 7.42-7.43 (2H, m, Ar-H), 7.53 (4H, m,
Ar-H), 7.91 (1H, d, Ar-H), 8.74 (1H, s, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-7-(4-((3-(2-hydroxyphenyl)-4-phenyl-5-thioxo-4,5-d
ihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-4-oxo-1,4-dihydroquinoline-3-carboxylic
acid (6j)
Yield: 60%. M.p.: 251-252 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.71-2.01 (2H, m,
cyclopropyl-H, CH2), 3.11 (4H, s, piperazine-4H), 3.25-3.38 (5H, m, piperazine-4H and
cyclopropyl-H), 3.87-3.89 (1H, m, cyclopropyl-H), 5.25 (2H, s, CH2), 6.80 (1H, d, Ar-H),
6.84-6.90 (1H, m, Ar-H), 7.17-7.28 (1H, m, Ar-H), 7.29-7.48 (7H, m, Ar-H), 7.58 (1H, d,
Ar-H), 7.88 (1H, d, Ar-H), 8.75 (1H, s, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-7-(4-((3-(3-methoxyphenyl)-4-phenyl-5-thioxo-4,5-
dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-4-oxo-1,4-dihydroquinoline-3-carboxyli
c acid (6k)
Yield: 61%. M.p.: 250-251 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.77-2.04 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.34-3.35 (1H, m, cyclopropyl-H), 3.42
(4H, s, piperazine-4H), 3.60 (3H, s, OCH3), 3.89-3.90 (1H, m, cyclopropyl-H), 5.32 (2H, s,
CH2), 6.83 (1H, s, Ar-H), 7.02 (2H, s, Ar-H), 7.30-7.33 (1H, m, Ar-H), 7.44-7.45 (2H, m,
Ar-H), 7.54 (4H, m, Ar-H), 7.93 (1H, d, Ar-H), 8.77 (1H, s, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-7-(4-((3-(2-methoxyphenyl)-4-phenyl-5-thioxo-4,5-
dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-4-oxo-1,4-dihydroquinoline-3-carboxyli
c acid (6l)
Yield: 67%. M.p.: 257-259 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.79-1.98 (2H, m,
cyclopropyl-H, CH2), 3.07 (4H, s, piperazine-4H), 3.34-3.42 (5H, m, piperazine-4H and
cyclopropyl-H), 3.60 (3H, s, OCH3), 3.89-3.90 (1H, m, cyclopropyl-H), 5.32 (2H, s, CH2),
6.82 (1H, s, Ar-H), 7.02 (1H, s, Ar-H), 7.30-7.33 (1H, m, Ar-H), 7.43-7.53 (6H, m, Ar-H),
7.93 (1H, d, Ar-H), 8.77 (1H, s, Ar-H).
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7-(4-((3-(3,4-dimethoxyphenyl)-4-phenyl-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)p
iperazin-1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carbo
xylic acid (6m)
Yield: 57%. M.p.: 235-237 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.78-1.93 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.38-3.42 (5H, m, piperazine-4H and
cyclopropyl-H), 3.50 (3H, s, OCH3), 3.77 (3H, s, OCH3), 3.87-3.88 (1H, m, cyclopropyl-H),
5.31 (2H, s, CH2), 6.79 (1H, s, Ar-H), 6.97-7.02 (2H, m, Ar-H), 7.43-7.44 (2H, m, Ar-H),
7.52-7.55 (4H, m, Ar-H), 7.91 (1H, d, Ar-H), 8.73 (1H, s, Ar-H).
7-(4-((3-(3,5-dimethoxyphenyl)-4-phenyl-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)p
iperazin-1-yl)-6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-1,4-dihydroquinoline-3-carbo
xylic acid (6n)
Yield: 56%. M.p.: 232-234 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.75-1.78 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.51-3.52 (1H, m, cyclopropyl-H),
3.60-3.65 (10H, m, piperazine-4H and 2×OCH3), 3.77-3.79 (1H, m, cyclopropyl-H), 5.31
(2H, s, CH2), 6.49 (2H, s, Ar-H), 6.58 (1H, s, Ar-H), 7.42-7.45 (3H, m, Ar-H), 7.54-7.56 (3H,
m, Ar-H), 7.85 (1H, d, Ar-H), 8.66 (1H, s, Ar-H).
6-fluoro-1-((1R,2S)-2-fluorocyclopropyl)-4-oxo-7-(4-((4-phenyl-5-thioxo-3-(3,4,5-trimethoxy
phenyl)-4,5-dihydro-1H-1,2,4-triazol-1-yl)methyl)piperazin-1-yl)-1,4-dihydroquinoline-3-car
boxylic acid (6o)
Yield: 57%. M.p.: 213-214 °C. 1H NMR (500 MHz, DMSO-d6) δH 1.78-1.94 (2H, m,
cyclopropyl-H, CH2), 3.10 (4H, s, piperazine-4H), 3.51-3.58 (7H, m, cyclopropyl-H and
2×OCH3), 3.68 (3H, s, OCH3), 3.88-3.89 (1H, m, cyclopropyl-H), 5.32 (2H, s, CH2), 6.67
(2H, d, Ar-H), 7.46 (2H, d, Ar-H), 7.51-7.52 (4H, m, Ar-H), 7.91 (1H, d, Ar-H), 8.74 (1H, s,
Ar-H).
Conclusions
In summary, a series of novel 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX
-1,2,4-triazole-5(4H)-thione hybrids were designed, synthesized, and evaluated for their in
vitro antibacterial activity against representative pathogens. The results showed that all of the
hybrids were more potent than the parent 1-[(1R, 2S)-2-fluorocyclopropyl]CPFX 1, and were
comparable to CPFX and LVFX against the majority of the tested pathogens. Moreover, the
anti-Gram-negative bacteria activity of hybrids was far more potent than VAN.
Acknowledgments:
We gratefully acknowledge the financial support by NSFC (Nos. 21502237).
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Author Contribution Statement
S. Zhang, M. L. Liu and H. Y. Guo designed the study, analyzed the data, and revised the
manuscript. Y. Gao, L. X. Na, Z. Xu, A. P. Wang and K. Lv conducted all experiments,
collected the data and drafted the manuscript
Conflicts of Interest:
The authors declare no conflict of interest.
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Graphical Illustration
Design, Synthesis and Antibacterial Evaluation of 1-[(1R,
2S)-2-Fluorocyclopropyl]ciprofloxacin-1,2,4-triazole-5(4H)-thione
Hybrids
by Yang Gaoa)1), Lu-Xin Nab)1), Zhi Xub)c), Shu Zhang*d), A-Peng Wangb), Kai Lvb),
Hui-Yuan Guob), and Ming-Liang Liu*b)
a)Xuanwu Hospital, Capital Medical University, Beijing 100053, P. R. China;
b)Institute of Medicinal Biotechnology, Chinese Academy of Medical Sciences and Peking Union
Medical College, Beijing 100050, P. R. China;
c)HuangHuai University, Zhumadian, P. R. China;
d)Pony Testing International Group Co. Ltd (Wuhan), Wuhan, P. R. China.
*)Corresponding author: zhangshufsy@126.com (S. Zhang); lmllyx@126.com (M. L. Liu)
1)These authors contributed equally to this work.
A series of 1-[(1R, 2S)-2-fluorocyclopropyl]ciprofloxacin-1,2,4-triazole-5(4H)-thione hybrids 6a-o
were designed, synthesized and screened for their in vitro antibacterial activities against
Gram-positive and Gram-negative bacteria. All hybrids 6a-o have great potency against the tested
strains, and were comparable to ciprofloxacin and levofloxacin against the majority of the tested
pathogens, worth to be further investigated.
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