5-Nitro-heteroarylidene analogs of 2-thiazolylimino-4-thiazolidinones as a novel series of antibacterial agents

Article abstract of DOI:10.1007/s00044-012-0224-6

In the pursuit of novel antibacterial agents with the 2-thiazolylimino-4- thiazolidinone as a core structure, a series of 5-nitro-heteroarylidene and 5-(2-oxoindolin-3-ylidene) analogs of 2-thiazolylimino-5-arylidene-4- thiazolidinone were synthesized and their antibacterial activities were evaluated against some strains of Gram-positive and Gram-negative bacteria, as well as Helicobacter pylori strains. Biological data indicated that 5-nitrofuran analog 5a and 5-nitroimidazole analog 7a containing no substitutions on the thiazole ring were the most potent compounds.

Full text of DOI:10.1007/s00044-012-0224-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:2293–2302
DOI 10.1007/s00044-012-0224-6
ORIGINAL RESEARCH
5-Nitro-heteroarylidene analogs of 2-thiazolylimino-4-
thiazolidinones as a novel series of antibacterial agents
•
Nouraddin Hosseinzadeh Mohammad Hasani Alireza Foroumadi
•
•
•
•
•
Hamid Nadri Saeed Emami Nasrin Samadi Mohammad Ali Faramarzi
•
•
Parastoo Saniee Farideh Siavoshi Neda Abadian Yasaman Mahmoudjanlou
•
•
•
•
Amirhossein Sakhteman Alireza Moradi Abbas Shafiee
•
Received: 14 March 2012 / Accepted: 1 September 2012 / Published online: 13 September 2012
Ó Springer Science+Business Media, LLC 2012
Abstract In the pursuit of novel antibacterial agents with
the 2-thiazolylimino-4-thiazolidinone as a core structure,
a series of 5-nitro-heteroarylidene and 5-(2-oxoindolin-3-
ylidene) analogs of 2-thiazolylimino-5-arylidene-4-thiazo-
lidinone were synthesized and their antibacterial activities
were evaluated against some strains of Gram-positive and
Gram-negative bacteria, as well as Helicobacter pylori
strains. Biological data indicated that 5-nitrofuran analog
5a and 5-nitroimidazole analog 7a containing no substitu-
tions on the thiazole ring were the most potent compounds.
resistant pathogens including both Gram-positive and
Gram-negative bacteria (Muroi et al., 2004; Pfeltz and
Wilkinson, 2004; Tenover and McDonald, 2005). The
synthesis and pharmacological evaluation of thiazole
derivatives have been frequently reported over the years
because of their various therapeutic effects (Hutchinson
et al., 2002). Among the synthesized structures, 2-aryli-
mino-4-thiazolidinone derivatives exhibited various phar-
macological effects such as antimicrobial, antifungal,
antituberculosis, anticonvulsant, anti-inflammatory, and
antineoplastic activity (Bell et al., 1995; Hargrave et al.,
1983; Patt et al., 1992; Tsubouchi et al., 1994). Moreover,
a new class of antimicrobial agents bearing 2-thiazolyli-
mino-5-arylidene-4-thiazolidinone scaffold have been
reported (Vicini et al., 2006; Vicini et al., 2008). It was
found that the 5-arylidene moiety plays an important role in
the antimicrobial activity of this class of compounds
(Vicini et al., 2008).
Keywords Antibacterial activity Á Helicobacter pylori Á
4-Thiazolidinones Á Thiazole Á 5-Nitroheterocycles
Introduction
The treatment of some infectious diseases still remains a
challenging problem due to the emergence of multi-drug
N. Hosseinzadeh Á A. Foroumadi Á A. Shafiee (&)
Department of Medicinal Chemistry, Faculty of Pharmacy
and Pharmaceutical Sciences Research Center,
Tehran University of Medical Sciences,
Tehran 14176, Iran
N. Samadi Á N. Abadian
Department of Drug and Food Control, Faculty of Pharmacy
and Drug Design and Development Research Center,
Tehran University of Medical Sciences, Tehran, Iran
e-mail: ashafiee@ams.ac.ir
M. A. Faramarzi Á Y. Mahmoudjanlou
Department of Pharmaceutical Biotechnology,
Faculty of Pharmacy and Drug Design and Development
Research Center, Tehran University of Medical Sciences,
Tehran, Iran
M. Hasani
School of Chemistry, College of Science,
University of Tehran, Tehran, Iran
H. Nadri Á A. Sakhteman Á A. Moradi
Faculty of Pharmacy, Shahid Sadoughi University
of Medical Sciences, Yazd, Iran
P. Saniee Á F. Siavoshi
Microbiology Department, Faculty of Sciences,
University of Tehran, Tehran, Iran
S. Emami
Department of Medicinal Chemistry and Pharmaceutical
Sciences Research Center, Faculty of Pharmacy,
Mazandaran University of Medical Sciences, Sari, Iran
123

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Med Chem Res (2013) 22:2293–2302
On the other hand, it should be noted that the antibac-
spectrometer (Bruker, Rheinstetten, Germany) and chemical
shifts are expressed as d with tetramethylsilane (TMS) as
internalstandard. The IRspectra were taken using NicoletFT-
IR Magna 550 spectrometer (Nicolet, Madison, WI, USA).
The mass spectra were run on a Finnigan MAT TSQ-70
spectrometer (Finnigan Mat, Bremen, Germany) at 70 eV.
Elemental analyses were carried out on a CHN–O rapid ele-
mental analyzer (GmbH-Germany) for C, H, and N, and the
results are within 0.4 % of the theoretical values. Merck
silica gel 60 F254 plates were used for analytical TLC. Yields
are based on the purified products and were not optimized.
Column chromatography was performed on Merck silica gel
(70-230 mesh).
terial activity of nitroimidazoles, nitrofurans, and nitrothi-
ophenes have been established (Apt, 2010; Graham and
Fischbach, 2010; Lienhardt et al., 2010). Also, antimicro-
bial agents containing nitroimidazole or nitrofuran scaf-
folds have been used to treat Helicobacter pylori and the
other microbial infections with varying degrees of success
(Foroumadi et al., 2009).
Based on these findings and in pursuit of the previous
studies todevelop new antimicrobial agents(Foroumadietal.,
2009; Jazayeri et al., 2009; Khalaj et al., 2011; Mirzaei et al.,
2008), we have designed novel structures with the 2-thiazo-
lylimino-4-thiazolidinoneasa corestructure, inwhichvarious
5-nitro-heteroarylidene scaffolds have been attached at the
5-position instead of bezylidene moiety (Fig. 1). Thus, we
describe here, the synthesis of 5-nitrofuran, 5-nitrothiophene,
and 5-nitroimidazole analogs of 2-thiazolylimino-5-aryli-
dene-4-thiazolidinone (compounds 5–7, respectively) and
their antibacterial activity against some strains of Gram-
positive and Gram-negative bacteria as well as H. pylori.
Beside of the 5-nitro-heteroarylidene analogs 5–7, 5-(2-oxo-
indolin-3-ylidene) derivatives 8 were considered as new type
of 5-arylidene-4-thiazolidinones containing fused 5-bezylid-
ene moiety (Fig. 1).
Experimental
General procedure for the synthesis of
2-thiazolylimino-5-arylidene-4-thiazolidinones (5–8)
To a well-stirred solution of thiazolidin-4-one 4a–d
(4 mmol) in acetic acid (35 mL), buffered with sodium
acetate (8 mmol) was added appropriate aldehyde or isatin
(6 mmol). The mixture was irradiated in the microwave
oven at 450 W for 15 min (5 9 3 min). The precipitated
product was filtered off and washed with cold water. The
crude product was recrystallized from dioxane to give pure
compounds 5–8.
Materials and methods
Chemistry
(5Z)-5-((5-Nitrofuran-2-yl)methylene)-2-(thiazol-2-ylimino)
thiazolidin-4-one (5a) Yield: 85 %; mp: 293–295 °C; IR
(KBr, cm-1): 3419 (N–H), 1716 (C=O), 1615 (N=C), 1541,
All chemicals and solvents used in this study were purchased
from Merck AG and Aldrich. Melting points were determined
on a Kofler hot stage apparatus (C. Reihert, Vienna, Austria).
1H-NMR spectra were recorded using a Bruker 500
1
and 1347 (NO2); H NMR (DMSO-d6) d: 7.32 (d, 1H,
J = 3.4 Hz), 7.54 (d, 1H, J = 4.0 Hz), 7.61 (s, 1H), 7.72
(d, 1H, J = 4.0 Hz), 7.83 (d, 1H, J = 3.4 Hz), 12.83
Fig. 1 Designed
5-heteroarylidene-4-
O
H
HN
thiazolidinone derivatives
5–8 as antibacterial agents
Het
N
S
R
5-Arylidene-4-thiazolidinones
O
O
O
H
H
HN
Het
HN
HN
Het
N
N
S
X
Het
N
S
N
S
NH
N
NO2
Me
O
NO2
7a-d
5a-d: X = O
6a-d: X = S
8a-d
Het: thiazol-2-yl, 4-phenylthiazol-2-yl, 4-(4-Methoxyphenyl)thiazol-2-yl,
benzothiazol-2-yl
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Med Chem Res (2013) 22:2293–2302
2295
(s, 1H, NH). MS (m/z, %): 322 (M?, 42), 276 (87), 184
(29), 126 (41). Anal. Calcd. For C11H6N4O4S2: C, 40.99;
H, 1.88; N, 17.38. Found: C, 40.58; H, 1.81; N, 17.43.
J = 7.25 Hz), 8.25 (d, 1H, J = 3.8 Hz), 12.81 (s, 1H, NH).
MS (m/z, %): 414 (M?, 75), 368 (58), 261 (27), 202 (49).
Anal. Calcd. For C17H10N4O3S3 : C, 49.26; H, 2.43; N,
13.52. Found: C, 49.41; H, 2.40; N, 13.42.
(5Z)-5-((5-Nitrofuran-2-yl)methylene)-2-(4-phenylthiazol-2-
ylimino)thiazolidin-4-one (5b) Yield: 80 %; mp: [300 °C;
IR (KBr, cm-1): 3430 (N–H), 1696 (C=O), 1588 (N=C),
(5Z)-2-(4-(4-Methoxyphenyl)thiazol-2-ylimino)-5-((5-nitrothio-
phen-2-yl)methylene)thiazolidin-4-one (6c) Yield: 74 %;
mp: [300 °C; IR (KBr, cm-1): 3429 (N–H), 1714 (C=O),
1
1555, and 1348 (NO2); H NMR (DMSO-d6) d: 7.37–7.42
1
(m, 2H), 7.56 (t, 2H, J = 7.10 Hz), 7.67 (s, 1H), 7.86 (d,
1H, J = 3.4 Hz), 7.97 (s, 1H), 8.14 (d, 2H, J = 7.25 Hz),
12.87 (s, 1H, NH). MS (m/z, %): 398 (M?, 31), 352 (64),
261 (45), 201 (29). Anal. Calcd. For C17H10N4O4S2 : C,
51.25; H, 2.53; N, 14.06. Found: C, 51.28; H, 2.59; N, 14.01.
1595 (N=C), 1560, and 1384 (NO2); H NMR (DMSO-d6)
d: 3.83 (s, 3H), 7.08 (d, 2H, J = 8.25 Hz), 7.73 (d, 1H,
J = 3.8 Hz), 7.76 (s, 1H), 7.98 (s, 1H), 8.01 (d, 2H,
J = 8.25 Hz), 8.23 (d, 1H, J = 3.8 Hz), 12.91 (s, 1H, NH).
MS (m/z, %): 444 (M?, 56), 398 (35), 291 (28), 231 (42).
Anal. Calcd. For C18H12N4O4S3 : C, 48.64; H, 2.72; N,
12.60. Found: C, 48.71; H, 2.75; N, 12.69.
(5Z)-2-(4-(4-Methoxyphenyl)thiazol-2-ylimino)-5-((5-nitro-
furan-2-yl)methylene)thiazolidin-4-one (5c) Yield: 91 %;
mp: [300 °C; IR (KBr, cm-1): 3138 (N–H), 1712 (C=O),
(5Z)-2-(Benzodthiazol-2-ylimino)-5-((5-nitrothiophen-2-yl)meth-
ylene)thiazolidin-4-one (6d) Yield: 82 %; mp: 283–287 °C;
IR (KBr, cm-1): 3444 (N–H), 1720 (C=O), 1596, (N=C),
1550, and 1328 (NO2); 1H NMR (DMSO-d6) d: 7.40 (t, 1H,
J = 7.2 Hz), 7.52 (t, 1H, J = 7.1 Hz), 7.72 (d, 1H,
J = 3.8 Hz), 7.91 (d, 1H, J = 8.0 Hz), 8.1–8.2 (m, 2H),
7.91–8.05 (m, 3H), 8.23 (d, 1H, J = 3.8 Hz), 13.05 (s, 1H,
NH). MS (m/z, %): 388 (M?, 53), 341 (65), 236 (41), 175
(59). Anal. Calcd. For C15H8N4O3S3 : C, 46.38; H, 2.08; N,
14.42. Found: C, 46.28; H, 2.03; N, 14.49.
1
1584 (N=C), 1553, and 1359 (NO2); H NMR (DMSO-d6)
d: 3.81 (s, 3H), 7.09 (d, 2H, J = 8.25 Hz), 7.35 (d, 1H,
J = 3.4 Hz), 7.65 (s, 1H), 7.79 (s, 1H), 7.85 (d, 1H,
J = 3.4 Hz), 8.06 (d, 2H, J = 8.25 Hz), 12.85 (s, 1H). MS
(m/z, %): 428 (M?,43), 382 (24), 291 (33), 231 (58). Anal.
Calcd. For C18H12N4O5S2 : C, 50.46; H, 2.82; N, 13.08.
Found: C, 50.61; H, 2.90; N, 13.11.
(5Z)-2-(Benzodthiazol-2-ylimino)-5-((5-nitrofuran-2-yl)meth-
ylene)thiazolidin-4-one (5d) Yield: 73 %; mp: 299–303 °C;
IR (KBr, cm-1): 3436 (N–H), 1723 (C=O), 1596 (C=N),
(5Z)-5-((1-Methyl-5-nitro-1H-imidazol-2-yl)methylene)-2-
(thiazol-2-ylimino)thiazolidin-4-one (7a) Yield: 63 %;
mp: [300 °C; IR (KBr, cm-1): 3440 (N–H), 1724 (C=O),
1
1544, and 1350 (NO2); H NMR (DMSO-d6) d: 7.35-7.41
(m, 2H), 7.55 (t, 1H, J = 7.2 Hz), 7.67 (s, 1H), 7.83–7.85
(m, 2H), 8.03 (d, 1H, J = 7.6 Hz), 13.05 (s, 1H). MS (m/z,
%): 372 (M?, 78), 326 (71), 176 (100), 95 (60). Anal.
Calcd. For C15H8N4O4S2 : C, 48.38; H, 2.17; N, 15.05.
Found: C, 48.29; H, 2.21; N, 15.11.
1
1615, and 1689 (N=C), 1548, and 1351 (NO2); H NMR
(DMSO-d6) d: 4.06 (s, 3H), 7.50 (d, 1H, J = 4.0 Hz), 7.59
(s, 1H), 7.74 (d, 1H, J = 4.0 Hz), 8.43 (s, 1H), 12.76 (s,
1H, NH). MS (m/z, %): 336 (M?, 86), 211 (57), 183 (100),
96 (53). Anal. Calcd. For C11H8N6O3S2 : C, 39.28; H, 2.40;
N, 24.99. Found: C, 39.39; H, 2.43; N, 25.11.
(5Z)-5-((5-Nitrothiophen-2-yl)methylene)-2-(thiazol-2-ylimi-
no)thiazolidin-4-one (6a) Yield: 72 %; mp: 269–272 °C;
IR (KBr, cm-1): 3425 (N–H), 1716 (C=O), 1600 (N=C),
1559, and 1363 (NO2); 1H NMR (DMSO-d6) d: 7.55 (d, 1H,
J = 4.0 Hz), 7.70 (d, 1H, J = 3.8 Hz), 7.81 (d, 1H,
J = 4.0 Hz), 8.01 (s, 1H), 8.24 (d, 1H, J = 3.8 Hz), 12.95 (s,
1H, NH). MS (m/z, %): 338 (M?, 46), 292 (24), 185 (52), 126
(61), 95 (61), 73 (91), 43 (100). Anal. Calcd. For
C11H6N4O3S3 : C, 39.04; H, 1.79; N, 16.56. Found: C, 39.21;
H, 1.82; N, 16.66.
(5Z)-5-((1-Methyl-5-nitro-1H-imidazol-2-yl)methylene)-2-
(4-phenylthiazol-2-ylimino)thiazolidin-4-one (7b) Yield:
73 %; mp: [300 °C; IR (KBr, cm-1): 3443 (N–H), 1712
(C=O), 1596 (N=C), 1558, and 1342 (NO2); 1H NMR
(DMSO-d6) d: 4.06 (s, 3H), 7.38 (t, 1H, J = 7.25 Hz), 7.56
(t, 2H, J = 7.10 Hz), 7.63 (s, 1H), 7.93 (s, 1H), 8.03 (d,
2H, J = 7.25 Hz), 8.47 (s, 1H), 12.79 (s, 1H). MS (m/z,
%): 412 (M?, 39), 366 (32), 261 (42), 201 (65). Anal.
Calcd. For C17H12N6O3S2: C, 49.51; H, 2.93; N, 20.38.
Found: C, 49.07; H, 2.85; N, 20.21.
(5Z)-5-((5-Nitrothiophen-2-yl)methylene)-2-(4-phenylthiazol-2-
ylimino)thiazolidin-4-one (6b) Yield: 68 %; mp: [300 °C;
IR (KBr, cm-1): 3417 (N–H), 1704 (C=O), 1572 (N=C),
1544, and 1332 (NO2); 1H NMR (DMSO-d6) d: 7.43 (t, 1H,
J = 7.25 Hz), 7.54 (t, 2H, J = 7.10 Hz), 7.75 (d, 1H,
J = 3.8 Hz), 7.95 (s, 1H), 8.03 (s, 1H), 8.1 (d, 2H,
(5Z)-2-(4-(4-Methoxyphenyl)thiazol-2-ylimino)-5-((1-methyl-
5-nitro-1H-imidazol-2-yl) methylene)thiazolidin-4-one (7c)
Yield: 78 %; mp: [300 °C; IR (KBr, cm-1): 3428 (N–H),
1712 (C=O), 1596 (N=C), 1561, and 1369 (NO2); 1H NMR
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Med Chem Res (2013) 22:2293–2302
(DMSO-d6) d: 3.85 (s, 3H), 4.07 (s, 3H), 7.13 (d, 2H,
J = 8.25 Hz), 7.63 (s, 1H), 7.76 (s, 1H), 7.97 (d, 2H,
J = 8.25 Hz), 8.53 (s, 1H), 12.77 (s, 1H, NH). MS (m/z, %):
442 (M?, 69), 396 (71), 291 (25), 260 (38), 231 (49). Anal.
Calcd. For C18H14N6O4S2: C, 48.86; H, 3.19; N, 18.99.
Found: C, 48.65; H, 3.27; N, 19.09.
(KBr, cm-1): 3184 (N–H), 1717 (C=O), 1687 (C = O),
1562 (N=C); 1H NMR (DMSO-d6) d: 6.93 (d, 1H,
J = 7.65), 7.06 (t, 1H, J = 7.5 Hz),7.35–7.39 (m, 2H), 7.50
(t, 1H, J = 7.2 Hz), 7.90 (d, 1H, J = 8.4 Hz), 8.00 (d, 1H,
J = 7.6 Hz), 8.84 (d, 1H, J = 7.65 Hz), 11.21 (s, 1H, NH),
13.10 (s, 1H, NH). MS (m/z, %): 378 (M?, 84), 275 (38),
247 (21), 235 (22). Anal. Calcd. For C18H10N4O2S2 : C,
57.13; H, 2.66; N, 14.81. Found: C, 57.35; H, 2.51; N, 14.72.
(5Z)-2-(Benzodthiazol-2-ylimino)-5-((1-methyl-5-nitro-1H-
imidazol-2-yl)methylene)thiazolidin-4-one
(7d) Yield:
81 %; mp: [300 °C; IR (KBr, cm-1): 3405 (N–H), 1720
(C=O), 1562, and 1370 (NO2); 1H NMR (DMSO-d6) d: 4.08 (s,
3H), 7.39 (t, 1H, J = 7.2 Hz), 7.52 (t, 1H, J = 7.2 Hz), 7.67 (s,
1H), 7.90 (d, 1H, J = 8.3 Hz), 8.02 (d, 1H, J = 7.6 Hz), 8.42
(s, 1H), 12.98 (s, 1H, NH). MS (m/z, %): 386 (M?, 34), 340
(81), 235 (32), 175 (28). Anal. Calcd. For C15H10N6O3S2 : C,
46.62; H, 2.61; N, 21.75. Found: C, 46.78; H, 2.65; N, 21.85.
Biological activities
Microdilution method (minimum inhibitory concentration
determination)
The minimum inhibitory concentrations (MICs) of synthetic
compounds against microorganisms including Gram-positive
bacteria (Staphylococcus aureus ATCC 6538p, Staphylo-
coccusepidermidisATCC 12228, and Bacillussubtilis ATCC
6633) and Gram-negative bacteria (Escherichia coli ATCC
8739, Klebsiella pneumoniae ATCC 10031, and Pseudomo-
nas aeruginosa ATCC 9027) were determined by microdi-
lution method by using 96 U-shaped wells plates (Jazayeri
et al., 2009). A stock solution of compounds (200 lg/ml) was
prepared in Mueller–Hinton broth (MHB) by 10 % v/v
DMSO. Then twofold serial dilution of the stock solution of
each compound (100 ll) was prepared by using MHB
(100 ll) in 12 wells. The stock microbial suspension with
twofold test inoculum(1 9 106 CFU/ml)was preparedfroma
24 h-old culture. Then aliquot of 100 ll of twofold test strain
inoculum was added to each well to reach the final inoculum
size of 5 9 105 CFU/ml. After 24 h incubation at 35–37 °C,
the microdilution plates were tested for the absence or pres-
enceofvisiblegrowthincomparisonwith that ofthegrowthin
drug-free control well. The endpoint MIC is the lowest con-
centration of the compound at which the test strain does not
demonstrate visible growth.
(5Z)-5-(2-Oxoindolin-3-ylidene)-2-(thiazol-2-ylimino)thiaz-
olidin-4-one (8a) Yield: 79 %; mp: [300 °C; IR (KBr,
cm-1): 3374 (N–H), 1708 (C=O), 1693 (C=O), 1580
(N=C); 1H NMR (DMSO-d6) d: 6.91 (d, 1H, J = 7.65 Hz),
7.05 (t, 1H, J = 7.5 Hz), 7.35 (t, 1H, J = 7.3 Hz), 7.51 (d,
1H, J = 4.0 Hz), 7.73 (d, 1H, J = 4.0 Hz), 8.83 (d, 1H,
J = 7.65 Hz), 11.18 (s, 1H, NH), 12.86 (s, 1H, NH). MS
(m/z, %): 328 (M?, 27), 197 (45), 185 (62), 132 (24), 125
(52). Anal. Calcd. For C14H8N4O2S2: C, 51.21; H, 2.46; N,
17.06. Found: C, 51.45; H, 2.38; N, 17.19.
(5Z)-5-(2-Oxoindolin-3-ylidene)-2-(4-phenylthiazol-2-ylimino)
thiazolidin-4-one (8b) Yield: 82 %; mp: [300 °C; IR
(KBr, cm-1): 3207 (N–H), 1715 (C=O), 1697 (C=O), 1583
1
(N=C); H NMR (DMSO-d6) d: 6.95 (d, 2H, J = 7.5 Hz),
7.07 (t, 1H, J = 7.5 Hz), 7.38 (m, 2H), 7.49 (t, 2H,
J = 7.10 Hz), 7.94 (s, 1H), 8.04 (d, 2H, J = 7.3 Hz), 8.85
(d, 1H, J = 7.6 Hz), 11.12 (s, 1H, NH), 12.93 (s, 1H, NH).
MS (m/z, %): 404 (M?, 83), 273 (34), 201 (41), 144 (65),
88 (29). Anal. Calcd. For C20H12N4O2S2: C, 59.39; H,
2.99; N, 13.85. Found: C, 59.54; H, 3.11; N, 13.64.
H. pylori growth inhibition assay (disk diffusion method)
Growth inhibition assay was done using the filter paper
disk diffusion method on Mueller–Hinton agar with 7 % of
defibrinated horse blood under microaerophilic conditions
at 37 °C (Foroumadi et al., 2009; Mirzaei et al., 2008).
Different doses of compounds were tested. The compounds
were dissolved in methanol and then dropped on the paper
disks (6 mm diameter) using a microsyringe. After drying
the paper disks in the fume hood, they were placed on the
agar surface that was inoculated with H. pylori. Following
incubation for 3–5 days at 37 °C, the inhibition zone
around each disk (average diameter) was recorded. All tests
were performed in triplicate and the antibacterial activity
was expressed as the mean of inhibition diameters (mm)
produced by title compounds.
(5Z)-2-(4-(4-Methoxyphenyl)thiazol-2-ylimino)-5-(2-oxoin-
dolin-3-ylidene)thiazolidin-4-one (8c) Yield: 84 %; mp:
[300 °C; IR (KBr, cm-1): 3426 (N–H), 1721, 1693
1
(C=O), 1581 (N=C); H NMR (DMSO-d6) d: 3.82 (s, 3H),
6.95 (d, 1H, J = 7.5 Hz), 7.02–7.06 (m, 3H), 7.37 (t, 1H,
J = 7.4 Hz), 7.76 (s, 1H), 7.97 (d, 2H, J = 8.25 Hz), 8.85
(d, 1H, J = 7.65 Hz), 11.09 (s, 1H, NH), 12.89 (s, 1H,
NH). MS (m/z, %): 434 (M?, 73), 302 (37), 291 (54), 263
(28), 89 (22). Anal. Calcd. For C21H14N4O3S2 : C, 58.05;
H, 3.25; N, 12.89. Found: C, 58.42; H, 3.08; N, 12.62.
(5Z)-2-(Benzothiazol-2-ylimino)-5-(2-oxoindolin-3-ylidene)
thiazolidin-4-one (8d) Yield: 85 %; mp: [300 °C; IR
123

Med Chem Res (2013) 22:2293–2302
Results and discussion
Chemistry
2297
The proposed mechanism for the formation of the
2-(heteroarylimino) thiazolidin-4-ones has been previously
described (Vicini et al., 2006, 2008). The new synthesized
1
compounds 5–8 were characterized by H NMR, IR, and
The target compounds were synthesized according to the multi-
step reaction protocol reported earlier (Vicini et al., 2006). The
general synthetic pathway was depicted in Scheme 1.
2-Bromo-1-phenylethanone (1a, R = H) or 2-bromo-1-(4-
methoxyphenyl)ethanone (1b, R = MeO) was reacted with
thiourea in refluxing ethanol to yield 4-phenylthiazol-2-amine
(2b) or 4-(4-methoxyphenyl)thiazol-2-amine (2c), respec-
tively. 2-Aminothiazole (2a) and 2-aminobenzothiazole (2d)
were commercially available. Reaction of appropriate amine
2a–d with chloroacetyl chloride in DMF at room temperature
for 2 h, furnished compound 3a–d in good yield (Geronikaki
et al., 2003; Vicini et al., 1990). 2-Chloroacetamides 3a–d
efficiently reacted with ammonium thiocyanate in refluxing
ethanol to give 2-(heteroarylimino) thiazolidin-4-ones 4a–d.
To obtain the final compounds 5–8, intermediate 4 and
appropriate 5-nitroheteroaryl-2-carboxaldehyde or isatin were
mixed in acetic acid buffered with sodium acetate and irradi-
ated in a microwave oven at 450 W for 15 min (5 9 3 min).
By using microwave-assisted synthesis method, it was possible
to decrease the reaction time up to 15 min respect to 2–4 h in
conventional heating method. The yields of the reactions were
also improved in several cases comparing to the previously
described method (Vicini et al., 2006, 2008).
mass spectroscopy. Theoretically, all final compounds 5–8
exist as potential E and Z geometrical isomers. Configu-
ration of the exocyclic C=C double bond in compounds
1
5–7 was assigned as (Z)-geometry according to H NMR
spectroscopy data (Fig. 2). The vinylic hydrogen in com-
pounds 5–7 was detected at 7.59–8.01 ppm as a sharp
singlet peak which was deshielded by an adjacent carbonyl
group. In 5-(2-oxoindolin-3-ylidene) derivatives 8, the H-4
proton of indoline ring was appeared at downfield
(d 8.83–8.85 ppm) due to the proximity of carbonyl group
(Fig. 2). These findings were in agreement with spectroscopic
data of 4-thiazolidinones and 2,4-thiazolidinediones analogs
(Bruno et al., 2002; Ottana et al., 2005). The proton emerging
at 12.76–13.10 ppm in the 1H NMR spectra was attributed to
Deshielding
Effect
Deshielding
Effect
= 8.83-8.85
H
O
O
= 7.59-8.01
H
HN
HN
Het
Het
N
S
N
S
R
NH
O
5-7
8
Fig. 2 The geometry assignment of the exocyclic C=C double bond
1
in compounds 5–8 according to H NMR spectroscopy data
Scheme 1 Synthesis of the
compounds 5–8. Reagents and
conditions: (a) EtOH, reflux,
1.5 h; (b) ClCOCH2Cl, DMF, rt,
2 h; (c) NH4SCN, EtOH, reflux,
2 h; (d) 5-nitrofurfural or
5-nitrothiophene-2-
carboxaldehyde, CH3COOH,
CH3COONa, MW;
(e) 1-methyl-5-nitro-1H-
imidazole-2-carbaldehyde,
CH3COOH, CH3COONa, MW;
(f) isatin, CH3COOH,
O
S
Br
NH2
N
R
R= H, MeO
2a
1a, b
b
a
O
S
b
b
S
Het
Cl
O
NH2
N
H
N
R
NH2
N
2b , 2c
3a-d
2d
c
CH3COONa, MW
HN
Het
N
S
f
d
O
H
4a-d
HN
O
Het
HN
X
N
S
Het
e
NO2
N
S
NH
O
5a-d: X = O
6a-d: X = S
8a-d
O
H
HN
Het
N
N
S
N
Me
NO2
7a-d
123

2298
Med Chem Res (2013) 22:2293–2302
Antibacterial activity
the NH of thiazolidinone ring. The feature of a thiazolidi-
none ring in the solid state is also supported by the IR
spectral data (NH group band at *3,400 cm-1 and a strong
C=O band at 1,690–1,714 cm-1) for the majority of the
compounds.
The antibacterial activity of compounds 5–8 in comparison
with the reference drug ciprofloxacin was reported in
Table 1. The MIC values of test compounds revealed that
Table 1 Minimum inhibitory concentrations (MICs, lg/ml) of compounds 5–8
O
R2
R1
HN
Het
N
S
Compounds
R1
R2
H
Het
S. a.a
0.97
50
S. e.
0.006
25
B. s.
0.19
50
E. c.
1.56
K. p.
1.56
P. a.
0.39
S
N
5a
5b
NO2
NO2
O
O
S
H
[100
[100
[100
N
S
5c
5d
6a
6b
6c
6d
H
H
H
H
H
H
25
12.5
0.39
12.5
0.39
[100
3.125
[100
[100
100
[100
6.25
100
NO2
NO2
NO2
NO2
NO2
NO2
NO2
N
O
O
S
S
S
S
MeO
S
0.97
1.56
[100
[100
0.39
[100
[100
[100
[100
[100
N
S
N
0.39
0.78
[100
[100
[100
[100
S
[100
[100
0.19
[100
[100
0.78
N
S
N
MeO
S
[100
N
N
S
N
7a
7b
7c
7d
8a
8b
8c
8d
H
H
H
H
0.78
[100
[100
25
0.19
50
0.19
50
12.5
0.39
[100
100
[100
[100
[100
[100
[100
50
N
Me
N
S
NO2
NO2
NO2
[100
[100
[100
[100
[100
100
N
N
Me
N
S
25
50
N
N
MeO
Me
N
S
25
12.5
6.25
[100
[100
[100
0.19
25
N
N
Me
S
N
25
12.5
[100
100
[100
[100
[100
[100
0.006
NH
NH
NH
NH
O
O
O
O
S
[100
[100
[100
0.19
N
S
[100
[100
0.39
N
MeO
S
[100
0.097
[100
0.012
N
Ciprofloxacin
a
Staphylococcus aureus ATCC 6538p, Staphylococcus epidermidis ATCC 12228, Bacillus subtilis ATCC 6633, Escherichia coli ATCC 8739,
Klebsiella pneumoniae ATCC 10031, Pseudomonas aeruginosa ATCC 9027
123

Med Chem Res (2013) 22:2293–2302
2299
Anti-H. pylori activity
unsubstituted thiazole analogs 5a, 6a, 7a, and benzothia-
zole derivatives 5d and 6d exhibited good antibacterial
activity against Gram-positive bacteria including S. aureus,
S. epidermidis, and B. subtilis (MICs = 0.006–1.56 lg/
ml). Also, compounds 5b, 5c, 7d, and 8a showed moderate
growth inhibitory activity at concentrations less than
50 lg/ml against all tested Gram-positive strains.
Generally, most of the tested compounds exhibited
higher activity against Gram-positive bacteria rather than
Gram-negatives. Among them, compounds 5a, 5d, and 7a
displayed moderate to good activity against E. coli and K.
pneumoniae (MICs = 0.39–12.5 lg/ml). The rest of
remaining compounds showed no significant activity
against Gram-negative organisms. Notably, compound 5a
showed high activity against P. aeruginosa with MIC value
of 0.39 lg/ml.
The antibacterial data demonstrated that compounds bearing
5-nitroheterocycles including furan, thiophene and N-methyl-
imidazole had anti-Gram positive potential. In contrast, com-
pounds 8b–d with an attached 2-oxoindoline group did not
show any antibacterial activity. It could be concluded that the
introduction of a 2-oxoindoline moiety on position 5 of thia-
zolidinone significantly diminishes the antibacterial activity.
By comparing the MIC values of thiazolylimino-deri-
vatives in each 5-nitroheterocycle series, it obviously
revealed that the introduction of phenyl or 4-methoxy-
phenyl on thiazole ring have largely decreased the anti-
bacterial activity, and compounds with no substitution on
thiazole ring were the most active compounds in each
series. Moreover, compounds with benzothiazole moiety
instead of thiazole ring showed to be slightly less active.
The anti-H. pylori activity of the target compounds along
with commercially available antibiotic metronidazole was
evaluated using paper disc diffusion bioassay method. The
synthesized compounds were evaluated against three
strains of H. pylori at four doses (8, 16, 32, and 64 lg/
disk). The antibacterial activity of compounds was con-
sidered as follow: strong response, zone diameter[20 mm;
moderate response, zone diameter 16–20 mm; weak
response, zone diameter 11–15 mm; and little or no
response, zone diameter \10 mm. The anti-H. pylori
activity of tested compounds was depicted in Table 2.
The inhibitory activity of test compounds against
H. pylori strains revealed that compounds 5a and 7a had
complete growth inhibition at the doses of 8, 16, 32, and
64 lg/disk (inhibition zone diameter [50 mm), while
compounds 7b, 7c, and 8c have shown no inhibitory
activity even at the high dose of 64 lg/disk. Also, com-
pounds 5d, 6a, 6c, and 7d showed a strong activity at all
tested concentrations (inhibition zone diameter [20 mm).
From the bioassay data, it is evident that nitrohetero-
cycle analogs which have no substitution on thiazole ring
exhibited higher anti-H. pylori activity (compounds 5a, 6a,
and 7a). This pattern was also observed in 2-oxoindoline
series. Compound 8a was the most effective compound in
this series. Thus, it is worthwhile to note that the intro-
duction of a phenyl or 4-methoxyphenyl as a substituent on
the 4-position of thiazole ring decreases the anti-H. pylori
activity. However, the potency is relatively dependent
on the type of attached group at the 5 position of
Table 2 Inhibition zone diameters (mm) of test compounds at different doses against H. pylori strains
Compoundsa
Strain 1
Strain 2
Strain 3
8 lg
16 lg
32 lg
64 lg
8 lg
16 lg
32 lg
64 lg
8 lg
16 lg
32 lg
64 lg
5a
5b
5c
5d
6a
6c
7a
7b
7c
7d
8a
8b
8c
8d
a
[50b
10
B6
20
36
22
[50
6
[50
13
10
24
40
25
[50
6
[50
15
12
28
42
27
[50
6
[50
20
14
33
45
30
[50
6
[50
10
15
22
25
30
[50
6
[50
12
17
24
28
32
[50
6
[50
18
19
26
30
35
[50
6
[50
23
20
30
34
39
[50
6
[50
13
12
25
33
22
[50
6
[50
15
16
28
35
25
[50
6
[50
18
19
30
40
30
[50
6
[50
20
26
34
45
35
[50
6
6
6
6
6
6
6
6
6
6
6
6
6
23
10
6
26
12
6
29
13
6
32
15
6
27
12
6
29
14
6
33
18
6
35
20
6
22
10
6
24
10
6
26
14
6
30
15
14
6
6
6
6
6
6
6
6
6
6
6
6
6
6
10
13
11
13
16
18
6
6
6
10
Metronidazole was used as standard drug. The inhibition zone diameters of metronidazole at the dose of 16 lg/disk were 14–27 mm
b
The values represent the mean. P \ 0.05 was considered statistically significant
123

2300
Med Chem Res (2013) 22:2293–2302
Table 3 The two top models of MLR analysis in QSAR study
MLR models
R
Rcv
PRESS
Y = [93.99 (X5v
)
13.51] - [1.57 9 103 (R8P?) 497.16] - [120.69 28.27]
17.87] - [2.23 9 103 (R8P?) 512.73] - [1.08 9 104 (GATS7m) 4.58 9 103]
0.88
0.92
0.81
0.85
9.57 9 103
8.17 9 103
Y = [125.92 (X5v
)
- [74.02 31.4]
thiazolidinone nucleus. Generally, the pattern of anti-
H. pylori activity for test compounds was in accordance
with the pattern of antibacterial activity against Gram-
positive bacteria.
data in Table 3, the first selected descriptor in both models
was X5v (valence connectivity index chi-5) which is among
the topological descriptors. The second descriptor was
R8p? (R maximal of lag 8/weighted by atomic polariz-
ability) which is among the Getaway descriptors. The next
descriptor in the second model was GATAS7M (Geary
autocorrelation -lag 7/weighted by atomic mass) and is
among the Getaway descriptors. The value for this
descriptor is highly related to the number of atoms in a
molecule. In the final equation, the activity of compounds
is also related to this descriptor with a minus coefficient. It
could be concluded that the compounds with less number
of atoms or less number of substituents are more likely to
be active than their larger counterparts.
QSAR study
In an attempt to investigate the role of structural properties
on the activity of the synthesized compounds, two common
methods of QSAR analysis including multiple linear
regression (MLR) and Kohonen maps were conducted
(Ballabio et al., 2009). Based on antibacterial data, among
the tested organisms, Gram-positive bacteria S. epidermi-
dis was more sensitive to designed compounds. Thus, the
most discriminative index of antibacterial activity for the
compounds (S. epidermidis) was used as the activity vector
(Y) to obtain its correlation with the structural features
(Y = b0 ? b1X1 ? b2X2 ? b3X3 ? ÁÁÁ ? bnXn). For this
purpose, the structures were drawn in ChemOffice10 and
saved as cdx format. Primary 3D generation and optimi-
zation of the structures was done using Openbabel 2.5 in
Linux operating system. Afterwards, final geometry opti-
mization of the compounds was performed by AM1
semiempirical method in HyperChem 8 (Hypercube) (Miri
et al., 2004; Khalafi-Nezhad et al., 2005). For doing the
optimization procedure in an automatic mode, our appli-
cation implemented in vb.Net was used in order to perform
dynamic data exchange (DDE) with HyperChem. Dragon
software was subsequently taken to calculate 1171
descriptors of the optimized structures (Todeschini et al.,
2002). The resulted matrix of descriptors together with
their corresponding activity vector was entered into Matlab
for further analysis. QSAR analysis was preceded by a
pretreatment process during which correlation of each
descriptor vector with the others in the data matrix has been
calculated and the ones with higher autocorrelations
(r C 0.85) were eliminated. The resulted matrix contained
127 descriptors. The stepwise feature selection method in
combination with MLR was used for primary model gen-
eration. Afterwards, the two top models according to the
rule of five were selected for the leave one out cross val-
idation (LOO-CV) test (Table 3). Among the two models
the second one with three descriptors had a more Rcv (0.85)
than the model with two descriptors (Rcv = 0.81). The
predicted residual error sum of squares (PRESS) in the
second model was also less than the first one. According to
To verify that the selected descriptors are predictive
enough and able to make an acceptable classification in the
synthesized compounds, a supervised self organizing
Kohonen map was used (Ballabio et al., 2009). This
method is similar to the action of human neural system in
such a way that each neuron accepts different signals from
neighboring neuron and is capable of processing them. The
Kohonen map is characterized by a squared toroidal space,
which include a grid of N2 neurons, where N is the number
of neurons for each side of the squared space. Each neuron
contains as many elements (weights) as the number of
input variables. The matrix of the three selected descriptors
Fig. 3 Visualization of the Kohonen map for the input data. The
compounds were clustered based on the similarities of the descriptors
in the second MLR model
123

Med Chem Res (2013) 22:2293–2302
2301
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visualized for clustering of the compounds. The result of
neural network clustering is depicted in Fig. 3. It reveals
that the three descriptor model is able to cluster the com-
pounds space in a reasonable way. According to this
classification, two active compounds 5a, 7a were placed in
one cluster and the compounds with the moderate to good
activity such as 5c, 6a, and 8a were clustered in the
neighboring neuron.
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In summary, we have described the synthesis of some novel
antibacterial agents with the 2-thiazolylimino-4-thiazolidi-
none as a core structure. Structurally, two distinct series of
compounds including 5-nitro-heteroarylidene and 5-(2-oxo-
indolin-3-ylidene) analogs of 2-thiazolylimino-5-arylidene-
4-thiazolidinone were synthesized and characterized as
(Z)-isomers. The antibacterial activity of title compounds was
evaluated against some strains of Gram-positive and Gram-
negative bacteria as well as H. pylori strains. Biological data
indicated that 5-nitrofuran analog 5a and 5-nitroimidazole
analog7a containingnosubstitutionsonthe thiazoleringwere
the most potent compounds. The result of QSAR study
revealed that the compounds with less number of atoms or less
number of substituents are more likely to be more active than
their counterparts with higher molecular weight.
Acknowledgments This work was supported by Grants from Teh-
ran University of Medical Sciences and INSF (Iran National Science
Foundation).
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