Synthesis and evaluation of the antimicrobial activities of 3-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)-2-thioxothiazolidin-4-one derivatives

Article abstract of DOI:10.1016/j.ejmech.2013.12.054

Two novel series of 3-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)-2- thioxothiazolidin-4-one derivatives were designed and synthesized, and their anti-bacterial activities evaluated. These compounds showed broad-spectrum inhibitory activities against both Gram-positive and Gram-negative bacteria with minimum inhibitory concentration (MIC) values in the range of 1-64 μg/mL. The activity of compound 6c was the more potent with MIC values of 1 μg/mL against the MRSA (3167 and 3506) strains than those of gatifloxacin, oxacillin, and norfloxacin. Compared to the previously reported rhodanine derivatives, 2-thioxothiazolidin-4-one derivatives exhibited an inhibition against Gram-negative strains due to the introduction of a 1,3,4-oxadiazole moiety, among which compounds 3 showed moderate activities against the Gram-negative bacteria (Escherichiacoli 1924) with MIC values of 16 μg/mL.

Full text of DOI:10.1016/j.ejmech.2013.12.054

European Journal of Medicinal Chemistry 74 (2014) 405e410
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and evaluation of the antimicrobial activities of 3-((5-phenyl-
1,3,4-oxadiazol-2-yl)methyl)-2-thioxothiazolidin-4-one derivatives
Jia-Chun Liu 1, Chang-Ji Zheng 1, Meng-Xiao Wang, Ya-Ru Li, Long-xu Ma, Shao-Pu Hou,
*
Hu-Ri Piao
Key Laboratory of Natural Resources and Functional Molecules of the Changbai Mountain, Affiliated Ministry of Education, Yanbian University,
College of Pharmacy, Yanji, Jilin Province 133002, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel series of 3-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)-2-thioxothiazolidin-4-one derivatives
were designed and synthesized, and their anti-bacterial activities evaluated. These compounds showed
broad-spectrum inhibitory activities against both Gram-positive and Gram-negative bacteria with
Received 3 August 2013
Received in revised form
15 November 2013
Accepted 24 December 2013
Available online 8 January 2014
minimum inhibitory concentration (MIC) values in the range of 1e64
mg/mL. The activity of compound 6c
was the more potent with MIC values of 1 g/mL against the MRSA (3167 and 3506) strains than those of
m
gatifloxacin, oxacillin, and norfloxacin. Compared to the previously reported rhodanine derivatives, 2-
thioxothiazolidin-4-one derivatives exhibited an inhibition against Gram-negative strains due to the
introduction of a 1,3,4-oxadiazole moiety, among which compounds 3 showed moderate activities
Keywords:
2-Thioxothiazolidin-4-one
1,3,4-Oxadiazole
against the Gram-negative bacteria (Escherichiacoli 1924) with MIC values of 16 mg/mL.
Ó 2014 Elsevier Masson SAS. All rights reserved.
Antibacterial activity
1. Introduction
the number of infections progressing into deadly diseases and
previously incogitable losses growing in number [4e8]. There is
therefore an urgent need for the development of novel antimicro-
bial agents.
2-Thioxothiazolidin-4-one heterocyclic ring derivatives have a
broad spectrum of biological activities, including their application
as JSP-1 inhibitors [9], antidiabetic drugs [10], and antitubercular
agents [11]. 1,3,4-Oxadiazole represents a key structural motif in
heterocyclic chemistry and occupies a prominent position in anti-
microbial agents, with some of its derivatives showing good activity
There has been a significant increase in the development of
multidrug resistance (MDR) in bacteria in recent years, which has
been linked to the overuse of antibiotics and antibacterial chem-
icals. According to worldwide studies, MDR is becoming increas-
ingly prevalent, especially in Gram-positive pathogens such as
Staphylococcus aureus (S. aureus), Streptococcus pneumoniae and
Enterococcus [1]. For instance, the emergence of vancomycin
resistance in the last decade, first in Enterococcus [2] and more
recently in S. aureus [3], has caused considerable concern, because
vancomycin is currently the drug of last-resort for the treatment of
methicillin-resistant S. aureus (MRSA) infections. Furthermore,
Gram-negative bacteria such as Pseudomonas aeruginosa, Acineto-
against Gram-negative bacteria (Escherichia coli, MIC ¼ 3
mg/mL)
[12,13]. In our previous work [14e19], we reported the identifica-
tion of a series of 2-(4-oxo-2-thioxothiazolidin-3-yl)acetic acid
derivatives, with all of the compounds belonging to this series
showing outstanding bacteriostatic activity against Gram-positive
bacter spp. and the b-lactamase-producing Enterobacteriaceae can
be more difficult to treat with standard therapies. Taken together,
these developments effectively highlight the fact that antibiotic
resistance is becoming increasingly serious as the spectrum of
bacteria that are sensitive to drugs becomes ever narrower, and the
effect of combined medications becomes worse and worse. Bacte-
rial infections are becoming increasingly difficult to treat as a result
of the emergence of multidrug resistant pathogenic bacteria, with
bacteria, such as compound A (MIC ¼ 2
mg/mL). Unfortunately,
however, compounds belonging to this series did not show any
bacteriostatic activity against Gram-negative bacteria. In contrast,
compound B exhibited strong anti-bacterial activities against
S. aureus, Bacillus subtilis and E. coli (MIC ¼ 4
mg/mL) [20]. With
these results in mind, we designed and synthesized twenty-one
novel compounds using a structure-based design strategy with
compounds A and B being used as the lead compounds. These
compounds were subsequently evaluated for their antibacterial
activities with the aim of finding a broader spectrum antimicrobial
agent. Detailed designs are shown in Fig. 1.
* Corresponding author. Tel.: þ86 433 2435003; fax: þ86 433 2435004.
E-mail address: piaohuri@yahoo.com.cn (H.-R. Piao).
1
These authors contributed equally to this work.
0223-5234/$ e see front matter Ó 2014 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2013.12.054

406
J.-C. Liu et al. / European Journal of Medicinal Chemistry 74 (2014) 405e410
were weaker than gatifloxacin (MIC ¼ 0.25
floxacin (MIC ¼ 0.25 g/mL) against S. aureus RN 4220. Compounds
3aek and 4aec exhibited weak anti-bacterial activities with MIC
values in the range of 16e64 g/mL, whereas compounds 5aec, 5k
and 6aec did not exhibit any activity (MIC > 64 g/mL) at all
mg/mL) and moxi-
m
m
m
against S. aureus KCTC 209 or S. aureus KCTC 503. Some compounds
were sensitive towards S. mutans 3065 with MIC values in the range
of 1e8 mg/mL. The inhibitory effects of compounds 5aec were 2e8-
fold greater than those of 3aec and that the antibacterial effects of
compounds 6aec were 4e16-fold greater than those of 4aec
against S. mutans 3065. Compound 6c showed the strongest activity
of all of the compounds tested with an MIC value of 1
although the activity of this compounds was slightly weaker than
gatifloxacin (MIC ¼ 0.5 g/mL) and moxifloxacin (MIC ¼ 0.25 g/
mL) against the S. mutans 3065 strains.
mg/mL,
m
m
Fig. 1. Structure of the leading compounds and design of the target compounds.
As shown in Table 1, the antibacterial activities of all the com-
pounds were evaluated against several different strains of Gram-
negative bacteria (E. coli, Salmonella typhimurium and P. aerugi-
nosa). Compounds 3aek exhibited good inhibitory activities
2. Chemistry
The synthetic route to the amino acid-derived 2-
thioxothiazolidin-4-one derivatives 3aek, 4aec, 5aec, 5k, 6aec
is depicted in Scheme 1. Compound 1 had already been reported in
a previous paper [21]. Compound 2 was synthesized through an
esterification reaction followed by a hydrazinolysis reaction. Com-
pounds 3aek and 5aec were synthesized by refluxing an equi-
molar mixture of 2 with 1 in phosphorous oxychloride (105e110 ꢀC)
for 6 h. Compounds 3aek and 5aec were subjected to a Knoeve-
nagel condensation reaction with 4-formylbenzoic acid to give the
target compounds 4aec and 6aec, respectively. The structures of
the desired compounds were confirmed by FTIR, 1H and 13C NMR,
and mass spectral analysis.
against E. coli 1924 with MIC values in the range of 16e64
well as weak levels of activity against S. typhimurium (1926 and
2421) with MIC values in the range of 32e128 g/mL. Compounds
3aec, 3e, 3gei showed good levels of activity against E. coli 1924
strains with MIC values of 16 g/mL, although these compounds
were weaker inhibitors than the standard drugs gatifloxacin
(MIC ¼ 2 g/mL) and moxifloxacin (MIC ¼ 2 g/mL). Disappoint-
ingly, compounds 4aec, 5aec, 5k and 6aec did not show any ac-
tivity (MIC > 128 g/mL) against E. coli 1924 or S. typhimurium
(1926 and 2421). Furthermore, none of the compounds synthesized
in the current study exhibited activity (MIC > 128 g/mL) against E.
mg/mL, as
m
m
m
m
m
m
coli 1356 or the P. aeruginosa (2742 and 2004) strains.
3. Results and discussion
The inhibitory activities of the title compounds against Candida
albicans 7535 are shown in Table 1. Compounds 3aek were only
weakly active against C. albicans 7535 with MIC values in the range
All of the synthesized compounds were evaluated in vitro using
a 96-well microtiter plate and a serial dilution method to obtain
their minimum inhibitory concentration (MIC) values against a
variety of different strains, including multidrug-resistant clinical
isolates. The MIC is defined as the lowest concentration of anti-
bacterial agent required to visibly inhibit the growth of the bacteria.
Gatifloxacin, moxifloxacin, norfloxacin and oxacillin were used as
positive controls.
of 32e64
these inhibitors with MIC values of 32
not as potent as the standard drugs gatifloxacin (MIC ¼ 0.5
and moxifloxacin (MIC ¼ 0.5 g/mL). Compounds 5aec, 5k, and
m
g/mL. Compounds 3b, 3c and 3e were the most potent of
g/mL, although they were
g/mL)
m
m
m
6aec did not exhibit any activity against the C. albicans 7535 strain.
The MIC values against the clinical isolates of multidrug-
resistant Gram-positive bacterial strains are reported in Table 2.
All of the compounds synthesized in the current study exhibited
inhibitory activities towards the multidrug-resistant Gram-positive
bacterial strains (MRSA CCARM 3167 and 3506, QRSA CCARM 3505
The MIC values of the synthesized compounds against S. aureus
and Streptococcus mutans are shown in Table 1. The majority of the
compounds exhibited good MIC values in the range of 2e64 mg/mL
against S. aureus RN 4220. By comparison, the MIC values of com-
pounds 5aec were 2e8-fold more potent than those of 3aec, and
the antibacterial activities of compounds 6aec were 4e8-fold more
potent than those of 4aec against S. aureus RN 4220. Among these
compounds, compounds 6aec showed the strongest activity with
and 3519) with MIC values in the range of 1e64
mg/mL. The
inhibitory activities of compounds 5aec were 4e8-fold greater
than those of 3aec, whereas the inhibitory activities of compounds
6aec were 4e16-fold greater than that of 4aec against the different
MRSA (CCARM 3167 and 3506) and QRSA (CCARM 3505 and 3519)
strains. Compound 6c, in particular, showed the greatest inhibitory
MIC values of 2 mg/mL, although the activities of these compounds
effect with MIC values of 1
Furthermore, the activities of compound 6c were found to be
equivalent to those of the standard drug moxifloxacin (MIC ¼ 1 g/
mL), and greater than those of gatifloxacin (MIC ¼ 2 g/mL),
oxacillin (MIC > 64 g/mL, 4 g/
mg/mL against two of these strains.
m
m
m
g/mL) and norfloxacin (MIC ¼ 8
m
m
mL) against the MRSA (3167 and 3506) strains. The activities of
compound 6c were slightly weaker than those of the standard drug
oxacillin (MIC ¼ 1
they were stronger than those of moxifloxacin (MIC ¼ 4
norfloxacin (MIC > 64 m
m
g/mL) with MIC values of 2
m
g/mL, although
g/mL),
g/mL,
m
mg/mL) and gatifloxacin (MIC ¼ 8
4
m
g/mL) against the QRSA (3505 and 3519) strains, respectively.
Consideration of the results revealed several structureeactivity
relationships. First, compounds 3aek showed that the antibacte-
rial activities were not significantly influenced by the substituent
group or the position of the substituent on the phenyl ring.
Scheme 1. Synthetic scheme for the synthesis of compounds 3e6. Reagents and
conditions: (a) POCl3, 105e110ꢀ C reflux, 5e7 h (b) Piperidine, AcOH, EtOH, 50-60 ꢀC,
4e6 h.

J.-C. Liu et al. / European Journal of Medicinal Chemistry 74 (2014) 405e410
407
Table 1
Inhibitory activity of compounds 3e6 expressed as MIC (
(Escherichia coli, Salmonela typhinurium and Pseudomonas aeruginosa) bacteria and Candida albicans 7535.
mg/mL) again strains of Gram-positive (Staphylococcus aureus and Streptococcus mutans) bacteria and Gram-negative
Compound
Substituent
Gram-positive strains
Gram-negative strains
Fungus
S. aureus
Streptococcus
mutans
Escherichia coli
Pseudomonas
aeruginosa
Salmonela
typhinurium
Candida
albicans
R
R1
4220a
209b
503c
3065d
1924e
1356f
2742g
2004h
2421i
1926j
7535
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
4a
4b
4c
5a
5b
3-CH3
3-Cl
3-Br
4-CH3
4-Cl
4-Br
2-CH3
2-Cl
2-Br
2-F
H
H
H
H
H
H
H
H
H
H
H
H
H
H
32
16
32
64
32
64
32
32
32
64
64
16
8
16
8
8
4
16
2
16
16
16
64
32
64
16
16
16
16
32
32
16
32
32
32
64
64
64
64
32
64
64
64
32
16
8
16
16
64
16
16
16
16
16
32
64
16
16
16
4
4
2
8
4
2
1
0.5
0.25
16
16
16
64
16
64
16
16
16
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
16
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
1
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
1
128
64
128
128
128
128
128
64
128
64
32
32
64
32
64
32
32
64
64
32
32
64
32
64
64
64
64
32
64
64
128
64
64
64
64
H
3-CH3
3-Cl
3-Br
3-CH3
3-Cl
3-Br
H
3-CH3
3-Cl
3-Br
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
2
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
0.5
>128
>128
>128
>128
>128
>128
>128
>128
>128
>128
2
>64
>64
>64
>64
>64
>64
>64
>64
>64
>64
0.5
16
16
Benzyl
Benzyl
Benzyl
Benzyl
Benzyl
Benzyl
Benzyl
>64
>64
>64
>64
>64
>64
>64
2
>64
>64
>64
>64
>64
>64
>64
4
5c
5k
6a
6b
2
2
0.25
0.25
6c
Gatifloxacin
Moxifloxacin
2
2
2
128
1
2
0.5
1
0.5
a
Staphylococcus aureus RN 4220.
Staphylococcus aureus 209.
Staphylococcus aureus 503.
Streptococcus mutans 3065.
Escherichia coli KCTC 1924.
Escherichia coli CCARM 1356.
Pseudomonas aeruginosa 2742.
Pseudomonas aeruginosa 2004.
Salmonella typhimurium 2421.
Salmonella typhimurium 1926.
b
c
d
e
f
g
h
i
j
Second, compounds 3aec, 3e, 3gei exhibited moderate levels of
activity against E. coli 1924 with MIC values of 16 g/mL.
current study, compounds 3aek showed moderate to significant
levels of antibacterial activity and a broader antimicrobial spec-
trum than two of the leading compounds. Moreover, compound 6c
m
Compared with the previously reported rhodanine derivatives that
were prepared in our laboratory [14e19], the introduction of a
1,3,4-oxadiazole moiety as well as the lack of a carboxylic acid
group appeared to be critical to the inhibition of both Gram-
negative and Gram-positive strains. Third, the introduction of a
benzyl group to the methylene moiety in compounds 3aek
resulted in a significant improvement in the activities against S.
aureus RN 4220 and S. mutans 3065, as well as the MRSA CCARM
(3167 and 3506) and QRSA CCARM (3505 and 3519) strains. Un-
fortunately, however, this change also resulted in a complete loss
of activity against S. aureus KCTC 209, S. aureus KCTC 503, E. coli
1924, S. typhimurium (1926 and 2421) and C. albicans 7535. Of all
of the compounds tested, compound 6c showed the strongest
antibacterial activity against S. mutans 3065 and MRSA (3167 and
was found to be the most potent inhibitor with MIC values of 1 mg/
mL against the MRSA (3167 and 3506) strains, which were greater
than those of gatifloxacin, oxacillin, and norfloxacin. Compound 6c
was also more potent than moxifloxacin, norfloxacin, and gati-
floxacin against the QRSA (3505 and 3519) strains with MIC values
of 2
mg/mL. These results have demonstrated that compounds
containing
the 3-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one core structure could be used to develop
new inhibitors against fungi as well as Gram-negative and Gram-
positive bacteria (including multidrug-resistant clinical isolates).
5. Experimental protocols
3506) with MIC values of 1
high levels of activity against S. aureus RN 4220 and QRSA (3505
mg/mL. This compound also showed
5.1. Chemistry
and 3519), with MIC values of 2 mg/mL.
Melting points were determined in open glass capillaries in an
electrical melting point apparatus and are uncorrected. Reaction
courses were monitored by TLC on silica gel-precoated F254 Merck
plates. Developed plates were examined with UV lamps (254 nm).
IR spectra were recorded (in KBr) on a FTIR1730. 1H NMR and 13C
NMR spectra were recorded in pure DMSO-d6 on Bruker NMR
spectrometers at 300 MHz and 75 MHz respectively using tetra-
methylsilane (TMS) as internal standard. Chemical shifts were
4. Conclusion
Based on our previous work, we designed and synthesized two
novel series of 3-((5-phenyl-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one derivatives (3aek, 4aec, 5aec, 5k, 6ae
c), and evaluated their antimicrobial activities against a fungus (C.
albicans), as well as several Gram-negative and Gram-positive
bacteria (including multidrug-resistant clinical isolates). In the
expressed in
d, ppm. High resolution mass spectroscopy were
measured on a Bruker ultrafleXtreme MALDI-TOF/TOF.

408
J.-C. Liu et al. / European Journal of Medicinal Chemistry 74 (2014) 405e410
7.69e7.64 (m, 1H), 5.42 (s, 2H), 4.45 (s, 2H). 13C NMR (75 MHz,
DMSO): 203.08, 174.08, 163.75, 161.63, 134.55, 132.51, 132.03,
126.51, 125.77, 125.37, 38.78, 36.71. HRMS (MALDI) calcd for
12H8ClN3S2O2: 325.9819, found: 325.9829 (M þ 1).
Table 2
Inhibitory activity (MIC,
multidrug-resistant Gram-positive strains.
mg/mL) of compounds 3e6 against clinical isolates of
d
Compound
Substituent
Gram-positive strains
C
MRSA
QRSA
R
R1
3167a
3506b
3505c
3519d
5.3.3. 3-((5-(3-Bromophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3c)
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
4a
4b
4c
5a
5b
3-CH3
3-Cl
3-Br
4-CH3
4-Cl
4-Br
2-CH3
2-Cl
2-Br
2-F
H
H
H
H
H
H
H
H
H
H
H
H
H
H
32
32
16
64
32
64
32
32
16
64
64
32
8
8
8
4
2
16
2
2
1
2
32
32
32
64
32
64
64
32
32
64
64
32
32
16
8
32
32
32
64
64
64
32
32
32
64
64
32
16
16
8
32
32
32
64
64
64
64
32
32
64
64
32
16
16
8
Yield 65.2%; m.p.118e120 ꢀC. IR (KBr) cmꢁ1: 1745 (C]O). 1H
NMR (300 MHz, DMSO-d6):
7.96 (m, 1H), 7.88e7.85 (m, 1H), 7.61e7.55 (m, 1H), 5.40 (s, 2H), 4.43
(s, 2H). 13C NMR (75 MHz, DMSO):
203.05, 174.07, 163.63, 161.61,
d
8.09e8.07 (t, J ¼ 3.0 Hz, 1H), 7.99e
d
135.38, 132.18, 129.31, 126.11, 125.56, 122.88, 38.78, 36.71. HRMS
(MALDI) calcd for C12H8BrN3S2O2: 369.9314, found: 369.9318
(M þ 1).
H
3-CH3
3-Cl
3-Br
3-CH3
3-Cl
3-Br
H
3-CH3
3-Cl
3-Br
5.3.4. 2-Thioxo-3-((5-(p-tolyl)-1,3,4-oxadiazol-2-yl)methyl)
thiazolidin-4-one (3d)
Yield 63.3%; m.p.176e178 ꢀC. IR (KBr) cmꢁ1: 1740 (C]O). 1H
Benzyl
Benzyl
Benzyl
Benzyl
Benzyl
Benzyl
Benzyl
8
4
16
4
4
8
2
16
2
2
8
4
16
4
4
NMR (300 MHz, DMSO-d6):
d
7.87e7.84 (d, J ¼ 9.0 Hz, 2H), 7.43e
5c
5k
6a
6b
7.41 (d, J ¼ 6.0 Hz, 2H), 5.39 (s, 2H), 4.43 (s, 2H), 2.40 (s, 3H). 13
C
NMR (75 MHz, DMSO):
d 203.08, 174.09, 164.92, 160.98, 142.87,
130.49, 126.99, 120.72, 38.80, 36.63, 21.61. HRMS (MALDI) calcd for
13H11N3S2O2: 306.0365, found: 306.0367 (M þ 1).
6c
1
2
2
8
2
4
C
Gatifloxacin
Moxifloxacin
Norfloxacin
Oxacillin
1
8
>64
1
4
>64
4
>64
1
4
>64
1
5.3.5. 3-((5-(4-Chlorophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3e)
a
Methicillin-resistant S. aureus CCARM 3167.
Methicillin-resistant S. aureus CCARM 3506.
Quinolone-resistant S. aureus CCARM 3505.
Quinolone-resistant S. aureus CCARM 3519.
Yield 68.5%; m.p.178e180 ꢀC. IR (KBr) cmꢁ1: 1740 (C]O). 1H
b
c
NMR (300 MHz, DMSO-d6):
d
7.97e7.94 (d, J ¼ 9.0 Hz, 2H), 7.69e
7.66 (d, J ¼ 9.0 Hz, 2H), 5.39 (s, 2H), 4.41 (s, 2H). 13C NMR (75 MHz,
d
DMSO):
d 203.07, 174.07, 164.13, 161.45, 137.40, 130.16, 128.86,
122.34, 38.77, 36.69. HRMS (MALDI) calcd for C12H8ClN3S2O2:
325.9819, found: 325.9826 (M þ 1).
5.2. General synthetic procedure for the key intermediates 1 and 2
Intermediates 1 were synthesized according to the literature
[22,23]. Intermediates 2 were synthesized using the reported pro-
cedure [24].
5.3.6. 3-((5-(4-Bromophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3f)
Yield; 70.4%; m.p.198e200 ꢀC. IR (KBr) cmꢁ1: 1741 (C]O). 1H
5.3. General procedure for the target compounds 3aek, 5aec and
5k
NMR (300 MHz, DMSO-d6):
d
7.89e7.87 (d, J ¼ 6.0 Hz, 2H), 7.82e
7.80 (d, J ¼ 6.0 Hz, 2H), 5.38 (s, 2H), 4.41 (s, 2H). 13C NMR (75 MHz,
DMSO):
d 203.05, 174.07, 164.25, 161.45, 133.06, 128.95, 126.31,
An
equimolar
mixture
of
N-carboxyl-2-(4-oxo-2-
122.67, 38.77, 36.69. HRMS (MALDI) calcd for C12H8BrN3S2O2:
thioxothiazolidin-3-yl) 1 with the appropriate benzohydrazide 2
was refluxed with phosphorous oxychloride (105e110 ꢀC) for 5e
7 h. Reaction mixture was quenched with ice water and the solid
separated was filtered off, washed with water and further purified
by silica gel column chromatography (dichloromethane/petroleum
ether, 80:1) to afford yellow or reddish brown compounds 3aek
and 5aec. The yield, melting point and spectral data of each com-
pound are given below.
369.9314 found: 369.9324 (M þ 1).
5.3.7. 2-Thioxo-3-((5-(o-tolyl)-1,3,4-oxadiazol-2-yl)methyl)
thiazolidin-4-one (3g)
Yield 58.6%; m.p.140e142 ꢀC. IR (KBr) cmꢁ1: 1741 (C]O). 1H
NMR (300 MHz, DMSO-d6):
7.49 (m, 1H), 7.45e7.39 (m, 2H), 5.42 (s, 2H), 4.43 (s, 2H), 2.58 (s,
3H). 13C NMR (75 MHz, DMSO):
203.09, 174.10, 165.06, 160.80,
d
7.86e7.84 (d, J ¼ 6.0 Hz, 1H), 7.54e
d
138.10, 132.23, 132.11, 129.25, 126.97, 122.64, 38.74, 36.68, 21.77.
HRMS (MALDI) calcd for C13H11N3S2O2: 306.0365, found: 306.0370
(M þ 1).
5.3.1. 2-Thioxo-3-((5-(m-tolyl)-1,3,4-oxadiazol-2-yl)methyl)
thiazolidin-4-one (3a)
Yield 61.7%; m.p.136e138 ꢀC. IR (KBr) cmꢁ1: 1742 (C]O). 1H
NMR (300 MHz, DMSO-d6):
5.39 (s, 2H), 4.44 (s, 2H), 2.41 (s, 3H). 13C NMR (75 MHz, DMSO-d6):
202.57, 173.61, 164.47, 160.71, 138.97, 132.83, 129.36, 126.80,
123.76, 122.91, 38.34, 36.21, 20.81. HRMS (MALDI) calcd for
13H11N3S2O2: 306.0365, found: 306.0368 (M þ 1).
d 7.79e7.75 (m, 2H), 7.54e7.44 (m, 2H),
5.3.8. 3-((5-(2-Chlorophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3h)
d
Yield 59.8%; m.p.138e140 ꢀC. IR (KBr) cmꢁ1: 1741 (C]O). 1H
C
NMR (300 MHz, DMSO-d6):
7.66 (dd, J ¼ 15.0, 9.0 Hz, 2H), 7.64e7.55 (m,1H), 5.43 (s, 2H), 4.44 (s,
2H). 13C NMR (75 MHz, DMSO):
202.93, 174.05, 162.98, 161.63,
d
7.95e7.92 (d, J ¼ 9.0 Hz, 1H), 7.74e
5.3.2. 3-((5-(3-Chlorophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3b)
d
133.84, 132.33, 131.75, 131.60, 128.34, 122.66, 38.78, 36.68. HRMS
(MALDI) calcd for C12H8ClN3S2O2: 325.9819, found: 325.9814
(M þ 1).
Yield 62.4%; m.p.130e132 ꢀC. IR (KBr) cmꢁ1: 1742 (C]O). 1H
NMR (300 MHz, DMSO-d6): d 7.97e7.94 (m, 2H), 7.77e7.73 (m, 1H),

J.-C. Liu et al. / European Journal of Medicinal Chemistry 74 (2014) 405e410
409
5.3.9. 3-((5-(2-Bromophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3i)
d6): d 203.17, 174.41, 164.40, 163.50, 135.96, 132.64, 129.92, 129.80,
128.92, 127.60, 127.09, 123.49, 52.62, 35.46, 33.73. HRMS (MALDI)
calcd for C19H15N3S2O2: 382.0678, found: 382.0684 (M þ 1).
Yield 60.5%; m.p.134e136 ꢀC. IR (KBr) cmꢁ1: 1741 (C]O). 1H
NMR (300 MHz, DMSO-d6):
d
7.91e7.87 (m, 2H), 7.65e7.55 (m, 2H),
202.85,174.04,
5.44 (s, 2H), 4.46 (s, 2H) 13C NMR (75 MHz, DMSO):
d
5.4. General procedure for the target compounds 4aec and 6aec
163.64, 161.63, 134.81, 133.90, 132.18, 128.73, 124.78, 121.36, 38.80,
38.70. HRMS (MALDI) calcd for C12H8BrN3S2O2: 369.9314, found:
369.9323 (M þ 1).
To a solution of compounds 3aec or 5aec (1.0 mmoL) and 4-
formylbenzoic acid (1.5 mmol) in absolute ethanol (10.0 mL) were
added 5 drops glacial acetic acid and 5 drops piperidine. The re-
action mixture was stirred at 50e60 ꢀC for 4e6 h, until the
completion of the reaction as evidenced by TLC. The resulting re-
action mixture was concentrated to dryness, recrystallized with
water to give yellow solid 4aec and purified by silica gel column
chromatography (dichloromethane/methanol, 150:1) to afford pure
yellow products 6aec. The yield, melting point and spectral data of
each compound are given below.
5.3.10. 3-((5-(2-Fluorophenyl)-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3j)
Yield 59.8%; m.p.114e116 ꢀC. IR (KBr) cmꢁ1: 1745 (C]O). 1H
NMR (300 MHz, DMSO-d6):
7.55e7.42 (m, 2H), 5.43 (s, 2H), 4.44 (s, 2H). 13C NMR (75 MHz,
DMSO): 203.02, 174.06, 161.50, 161.43, 134.97, 134.86, 130.11,
125.83, 117.75, 117.48, 38.76, 36.66. HRMS (MALDI) calcd for
12H8FN3S2O2: 310.0115, found: 310.0112 (M þ 1).
d 8.01e7.95 (m, 1H), 7.75e7.68 (m, 1H),
d
C
5.4.1. (Z)-4-((4-Oxo-2-thioxo-3-((5-(m-tolyl)-1,3,4-oxadiazol-2-yl)
methyl)thiazolidin-5-ylidene)methyl)benzoic acid (4a)
5.3.11. 3-((5-Phenyl-1,3,4-oxadiazol-2-yl)methyl)-2-
thioxothiazolidin-4-one (3k)
Yield 88.7%; m.p.246e248 ꢀC. IR (KBr) cmꢁ1: 3500 (OH), 1724
Yield 71.2%; m.p.144e146 ꢀC. IR (KBr) cmꢁ1: 1740 (C]O). 1H
(C]O), 1608 (C]O). 1H NMR: 1H NMR (300 MHz, DMSO-d6):
NMR (300 MHz, DMSO-d6):
d
7.98e7.95 (m, 2H), 7.65e7.59 (m, 3H),
203.12, 174.09,
5.41 (s, 2H), 4.44 (s, 2H). 13C NMR (75 MHz, DMSO):
d
d
13.31 (s, 1H), 8.10e8.08 (d, J ¼ 6.0 Hz, 2H), 7.98 (s, 1H), 7.82e7.76
(m, 4H), 7.52e7.44 (m, 2H), 5.59 (s, 2H), 2.40 (s, 3H). 13C NMR
(75 MHz, DMSO-d6): 192.81, 166.53, 166.15, 164.61, 160.58, 138.97,
164.85, 161.27, 132.67, 129.96, 127.03, 123.45, 38.81, 36.69. HRMS
(MALDI) calcd for C12H9N3S2O2: 292.0209, found: 292.0211 (M þ 1).
d
136.62, 132.86, 132.50, 132.32, 130.74, 130.17, 129.37, 126.83, 124.18,
123.80,122.91, 38.69, 20.80. HRMS (MALDI) calcd for C21H15N3O4S2:
438.0577, found: 438.0570 (M þ 1).
5.3.12. (S,Z)-3-(2-Phenyl-1-(5-(m-tolyl)-1,3,4-oxadiazol-2-yl)
ethyl)-2-thioxothiazolidin-4-one (5a)
Yield 74.4%; m.p.72e74 ꢀC. IR (KBr) cmꢁ1: 1738 (C]O). 1H NMR
(300 MHz, DMSO-d6):
d
7.80e7.77 (d, J ¼ 9.0 Hz, 2H), 7.52e7.45 (q,
5.4.2. (Z)-4-((3-((5-(3-Chlorophenyl)-1,3,4-oxadiazol-2-yl)
methyl)-4-oxo-2-thioxothiazolidin-5-ylidene)methyl)benzoic acid
(4b)
2H), 7.31e7.25 (m, 5H), 6.61e6.55 (t, J ¼ 9.0, 1H), 4.39e4.20 (dd,
J ¼ 36.0 Hz, J ¼ 18.0 Hz, 2H), 3.85e3.68 (m, 2H), 2.41 (s, 3H). 13C
Yield 85.9%; m.p.254e256 ꢀC. IR (KBr) cmꢁ1: 3500 (OH), 1725
NMR (75 MHz, DMSO-d6):
d 202.86, 173.96, 164.26, 162.97, 139.02,
(C]O), 1608 (C]O). 1H NMR (300 MHz, DMSO-d6):
d 13.32 (s, 1H),
135.65, 135.49, 132.87, 129.38, 128.44, 127.13, 126.83, 123.84, 122.94,
52.12, 34.98, 33.21, 20.81. HRMS (MALDI) calcd for C20H17N3S2O2:
396.0835, found: 396.0836 (M þ 1).
8.10e8.08 (d, J ¼ 6.0 Hz, 2H), 7.98e7.93 (m, 3H), 7.82e7.79 (d,
J ¼ 9.0 Hz, 2H), 7.74e7.72 (d, J ¼ 6.0 Hz, 1H), 7.67e7.62 (m, 1H), 5.59
(s, 2H). 13C NMR (75 MHz, DMSO):
d 193.33, 167.02, 166.63, 163.91,
5.3.13. (S,Z)-3-(1-(5-(3-Chlorophenyl)-1,3,4-oxadiazol-2-yl)-2-
phenylethyl)-2-thioxothiazolidin-4-one (5b)
161.49, 137.10, 134.53, 132.93, 132.84, 132.53, 132.04, 131.21, 130.66,
126.55, 125.83, 125.38, 124.72, 39.02. HRMS (MALDI) calcd for
Yield 73.6%; m.p.108e110 ꢀC. IR (KBr) cmꢁ1: 1737 (C]O). 1H
C20H12ClN3O4S2: 458.0031, found: 458.0032 (M þ 1).
NMR (300 MHz, DMSO-d6): d 8.00e7.95 (m, 2H), 7.75e7.72 (m, 1H),
7.67e7.62 (m, 1H), 7.31e7.25 (m, 5H), 6.60e6.55 (t, J ¼ 7.5 Hz, 1H),
5.4.3. (Z)-4-((3-((5-(3-Bromophenyl)-1,3,4-oxadiazol-2-yl)
methyl)-4-oxo-2-thioxothiazolidin-5-ylidene)methyl)benzoic acid
(4c)
4.38e4.19 (dd, J ¼ 39.0, 18.0 Hz, 2H), 3.85e3.67 (m, 2H). 13C NMR
(75 MHz, DMSO-d6): d 203.17, 174.39, 163.90, 163.56, 135.92, 134.59,
132.51, 132.00, 129.80, 128.91, 127.61, 126.54, 125.83, 125.38, 52.57,
35.51, 33.73. HRMS (MALDI) calcd for C19H14ClN3S2O2: 416.0289,
found: 416.0296 (M þ 1).
Yield 87.3%; m.p.262e264 ꢀC. IR (KBr) cmꢁ1: 3500 (OH), 1724
(C]O), 1605 (C]O). 1H NMR (300 MHz, DMSO-d6):
d 13.32 (s, 1H),
8.10e8.07 (m, 3H), 7.99e7.97 (m, 2H), 7.87e7.79 (dd, J ¼ 15.0,
6.0 Hz, 3H), 7.60e7.55 (m, 1H), 5.58 (s, 2H). 13C NMR (75 MHz,
5.3.14. (S,Z)-3-(1-(5-(3-Bromophenyl)-1,3,4-oxadiazol-2-yl)-2-
phenylethyl)-2-thioxothiazolidin-4-one (5c)
DMSO):
d 193.32, 167.02, 166.63, 163.76, 161.48, 137.10, 135.40,
132.92, 132.80, 132.21, 131.21, 130.66, 129.34, 126.16, 125.59, 124.71,
122.86, 39.00. HRMS (MALDI) calcd for C20H12BrN3O4S2: 501.9525,
found: 501.9526 (M þ 1).
Yield 74.8%; m.p.82e84 ꢀC. IR (KBr) cmꢁ1: 1740 (C]O). 1H NMR
(300 MHz, DMSO-d6):
d 8.12 (s, 1H), 8.03e7.99 (m, 1H), 7.87e7.83
(m, 1H), 7.60e7.54 (t, J ¼ 9.0 Hz, 1H), 7.32e7.25 (m, 5H), 6.61e6.56
(t, J ¼ 6.0 Hz, 1H), 4.39e4.20 (dd, J ¼ 39.0, 18.0 Hz, 2H), 3.89e3.71
(m, 2H). 13C NMR (75 MHz, DMSO-d6):
d
202.77, 173.93, 163.43,
5.4.4. (S,Z)-4-((4-Oxo-3-(2-phenyl-1-(5-(m-tolyl)-1,3,4-oxadiazol-
2-yl)ethyl)-2-thioxothiazolidin-5-ylidene)methyl)benzoic acid (6a)
Yield 88.3%; m.p.110e112 ꢀC. IR (KBr) cmꢁ1: 3500 (OH), 1718
162.96, 135.44, 134.96, 131.73, 129.33, 128.84, 128.44, 127.13, 125.72,
125.09, 122.46, 52.08, 35.04, 33.21. HRMS (MALDI) calcd for
C
19H14BrN3S2O2: 459.9784, found: 459.9777 (M þ 1).
(C]O), 1604 (C]O). 1H NMR (300 MHz, DMSO-d6):
d 13.27 (s, 1H),
8.07 (s, 1H), 8.04 (s, 1H), 7.84e7.79 (m, 3H), 7.74 (s, 1H), 7.72 (s, 1H),
7.51e7.46 (m, 2H), 7.30e7.21 (m, 5H), 6.81e6.76 (t, J ¼ 7.5 Hz, 1H),
3.90e3.86 (m, 2H), 2.40 (s, 3H). 13C NMR (75 MHz, DMSO-d6):
5.3.15. (S,Z)-3-(2-Phenyl-1-(5-phenyl-1,3,4-oxadiazol-2-yl)ethyl)-
2-thioxothiazolidin-4-one (5k)
Yield 77.5%; m.p.90e92 ꢀC. IR (KBr) cmꢁ1: 1742 (C]O). 1H NMR
d 193.08, 166.97, 166.71, 164.88, 163.25, 139.46, 136.88, 135.77,
(300 MHz, DMSO-d6):
d
8.00e7.98 (d, J ¼ 6.0 Hz, 2H), 7.65e7.61 (m,
133.34, 133.21, 132.84, 131.30, 130.61, 129.83, 129.74, 128.95, 127.70,
127.32, 124.34, 123.38, 123.27, 52.78, 33.84, 21.27. HRMS (MALDI)
calcd for C28H21N3O4S2: 528.1046, found: 528.1047 (M þ 1).
3H), 7.31e7.26 (m, 5H), 6.61e6.56 (t, J ¼ 7.5 Hz, 1H), 4.38e4.20 (dd,
J ¼ 18.0, 9.0 Hz, 2H), 3.85e3.68 (m, 2H). 13C NMR (75 MHz, DMSO-

410
J.-C. Liu et al. / European Journal of Medicinal Chemistry 74 (2014) 405e410
5.4.5. (S,Z)-4-((3-(1-(5-(3-Chlorophenyl)-1,3,4-oxadiazol-2-yl)-2-
phenylethyl)-4-oxo-2-thioxothiazolidin-5-ylidene)methyl)benzoic
acid (6b)
inhibited growth of the micro-organism was recorded as the MIC
(expressed in g/mL). Gatifloxacin, moxifloxacin, norfloxacin and
oxacillin were used as the standard drugs. All experiments were
carried out three times.
m
Yield 89.2%; m.p.120e122 ꢀC. IR (KBr) cmꢁ1: 3500 (OH), 1725
(C]O), 1605 (C]O). 1H NMR (300 MHz, DMSO-d6):
d 13.33 (s, 1H),
8.08e8.05 (d, J ¼ 9.0 Hz, 3H), 8.02e8.00 (d, J ¼ 6.0 Hz, 1H), 7.85 (s,
1H), 7.76e7.73 (d, J ¼ 9.0 Hz, 3H), 7.67e7.62 (m, 1H), 7.31e7.25 (m,
5H), 6.81e6.76 (t, J ¼ 7.5 Hz, 1H), 3.93e3.82 (m, 2H). 13C NMR
Acknowledgments
This work was supported by the National Science Foundation of
China (81260468).
(75 MHz, DMSO-d6): d 192.67, 168.24, 166.52, 166.24, 163.26, 136.41,
135.27, 134.12, 132.67, 132.09, 131.56, 130.83, 130.15, 129.27, 128.50,
127.25, 126.12, 126.05, 125.43, 124.85, 122.88, 52.24, 33.32. HRMS
(MALDI) calcd for C27H18ClN3O4S2: 548.0500, found: 548.0513
(M þ 1).
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The micro-organisms used in the present study were S. aureus
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The lowest concentration of the test substance that completely