Green synthesis of thiazol-2-ylthiazolidin-4-ones as potential antifungals

Article abstract of DOI:10.1134/S10704272150120253

MORE (Microwave oriented reaction enhancement) green methodology was utilized to synthesize benzothiazol/thiazol-2-ylthiazolidin-4-ones and relatively assayed for their antifungal activity w.r.t precursors against three agriculturally important phytopathogenic fungi viz. Colletotrichum falcatum, Pyricularia grisea and Ustilago hordei. Thiazol-2-ylthiazolidin-4-ones displayed better inhibition of growth of fungi than their precursor's thiazol-2-amines, with some compounds showing results comparable to their standard fungicides endorsing the effectiveness of chemical hybridization of thiazoles/benzothiazoles with thiazolidin-4-ones in a single molecule. In silico toxicity of all the compounds was found to be equivalent to the standard fungicides. Lipinski parameters were used to rationalize structure activity relation using statistical analysis software.

Full text of DOI:10.1134/S10704272150120253

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2015, Vol. 88, No. 12, pp. 2065−2073. © Pleiades Publishing, Ltd., 2015.
VARIOUS TECHNOLOGICAL
PROCESSES
Green Synthesis of Thiazol-2-ylthiazolidin-4-ones
as Potential Antifungals1
K. Gumbera*, A. Sidhua, and V. Kumarb
aDepartment of Chemistry, Punjab Agricultural University, Ludhiana, 141004 India
bDepartment of Plant Pathology, Punjab Agricultural University, Ludhiana, 141004 India
e-mail: khushbu.chem@yahoo.com
Received December 17, 2015
Abstract—MORE (Microwave oriented reaction enhancement) green methodology was utilized to synthesize
benzothiazol/thiazol-2-ylthiazolidin-4-ones and relatively assayed for their antifungal activity w.r.t precursors
against three agriculturally important phytopathogenic fungi viz. Colletotrichum falcatum, Pyricularia grisea and
Ustilago hordei. Thiazol-2-ylthiazolidin-4-ones displayed better inhibition of growth of fungi than their precursor’s
thiazol-2-amines, with some compounds showing results comparable to their standard fungicides endorsing the
effectiveness of chemical hybridization of thiazoles/benzothiazoles with thiazolidin-4-ones in a single molecule.
In silico toxicity of all the compounds was found to be equivalent to the standard fungicides. Lipinski parameters
were used to rationalize structure activity relation using statistical analysis software.
DOI: 10.1134/S10704272150120253
INTRODUCTION
position commonly resulted in the change of its bioactivity
[12]. Combination of thiazoles with other heterocyclics is
a well-known approach to design new drug like molecules
which allows achieving new pharmacological profile with
different mode of action and lowered toxicity [13].
Inspite of the introduction of a variety of pesticidal
agents, in multiple unrelated chemical classes, resistance
continues to emerge [1]. So, it is imperative to find
novel chemical solution to eradicate this fungal menace
especially at the time of emergency. Sulphur-nitrogen
heterocycles viz. thiazoles, benzothiazoles, isothiazole,
thiadiazoles groups are of special attention with the
view that they belong to the category of low or unknown
resistance behaviour and
Thiazolidin-4-one nucleus exhibits diverse pharma-
cological activities like antifungal [10], antituberculor
[14], anti-HIV [15], analgesic, anti-inflammatory [16],
ulcerogenic activity, etc. These observations served as
an impetus for the extension of investigation in the field
of synthesis of 4-thiazolidinone derivatives in the hope
of discovering compounds with good pharmacological
properties.
they are among the category of low risk pesticides
(FRAC code list [2]). 2-substituted-1,3-thiazoles among
them are an important scaffolds of biological interest and
have number of characteristic pharmacological features
which enhances bioactivity profile, such as, relative
stability, their ease to use as starting materials, built in
biocidal unit, enhanced lipid solubility with hydrophilicity
and easy metabolism [3]. They, exclusively, inflict many
biological activities like anti-inflammatory [4], anticancer
[5], analgesic [6], anti-HIV [7], antitumor [8] along
with anti-fungal [9], pesticidal [10], and antiprotozoal
[11]. Change of the structure of substituent group at C-2
In continuation with our work to find novel hybrid
molecules with higher antifungal potential [17], the
present study involves them microwave oriented synthesis
of thiazol/benzothiazol-2-ylthiazolidin-4-ones [18, 19]
and to evaluate in vitro antifungal potential against
various phytopathogenic fungi viz. C. falcatum, P. grisea
and U. hordei. The compounds were checked for their in
silico toxicity using Toxtree software programme. Drug
like indexes viz. Lipinski parameters [20] were evaluated
to establish structure-activity relationship (SAR) of the
synthesized compounds using SAS statistical analysis
programme.
1 The text was submitted by the authors in English.
2065

2066
GUMBER et al.
1
MATERIAL AND METHODS
900; H NMR (DMSO, 400 MHz) δ, ppm: 5.7 (2H, s,
NH2), 7.2–8.1 (3H, m, Ar C–H). 13C NMR (DMSO,
400 MHz) δ, ppm: 166.3, 131.3, 159.3, 144.3, 119.1,
117.3, 121.3.
Chemistry
Melting points were determined on electrical melting
point apparatus and are uncorrected. The products were
splendidly purified and the purity of all the compounds
was checked on a silica gel-G plates and visualization was
done using iodine lamp. All solvents and reagents were
purchased from Sigma-Aldrich Company. Solvents used
were of analytical reagent grade and purified by simple
distillation. Elemental analyses were done on Vario
EL, CHNOS elemental analyzer. The IR spectra were
recorded on a Perkin Elmer FT-IR spectrometer using
KBr disc. 1H NMR and 13C NMR spectra were recorded
on a Bruker Avance II 400 MHz spectrometer in CDCl3
and DMSO-d6 using TMS as an internal standard. Mass
spectra were recorded on Perkin Elmer Clarus 500 Mass
Spectrometer. The microwave assisted procedures were
carried out in domestic microwave at 180 W.
General procedure forthe synthesis of 4-arylthiazol-
2-amines (4–6). Thiourea (0.2 mol) and iodine (0.2 mol)
were triturated and mixed with acetophenone/its
derivatives (0.1 mol). The mixture was heated on a water
bath, with constant shaking, for 8 h. The solid obtained
was triturated with diethyl ether to remove unreacted
acetophenone. Excess of ether was distilled off. The
crude product was dissolved in hot water and filtered to
remove sulphone formed during the course of reaction.
The product was precipitated by adding ammonia solution
to the filtrate. The precipitates were washed with water
and crystallized from methanol to obtain 4-phenylthiazol-
2-amine and its derivatives 4-6 [23, 24].
4-Phenylthiazol-2-amine (4). Off white crystals;
IR (KBr), cm–1: 3420, 3240, 1500, 1460, 715; 1H NMR
(DMSO, 400 MHz) δ, ppm: 6.74 (1H, s, NH2), 6.75 (1H,
s, thiazole C–H), 7.2–7.8 (5H, m, Ar C–H). 13C NMR
(DMSO, 400 MHz) δ, ppm: 168.8, 101.9, 150.2, 133.0,
127.5, 127.5, 129.2, 129.2, 128.7.
Generalmethodforthesynthesisof1,3-benzothiazol-
2-amines (1-3). Arylamine (0.1 mol) and potassium
thiocyanate (0.4 mol) were dissolved in glacial acetic
acid (40 mL) and cooled. Bromine (0.04 mol) mixed with
glacial acetic acid (24 mL) was added from dropping
funnel at such a rate that temperature does not rise beyond
5–6°C. After all bromine had been added, the solution
was stirred with glass rod for an additional 2 h at low
temperature. The mixture was allowed to stand overnight,
during which period orange-yellow precipitates get settled
at the bottom. Water was added and slurry formed was
heated at 850°C on steam bath for 20 min and filtered hot.
The filtrate was cooled and neutralised with ammonia
solution to pH 6. Yellow precipitates obtained were
collected, washed with water and recrystallized from
benzene to get crystals of 1,3-benzothiazol-2-amine and
its derivatives 1-3 [21, 22].
4-(4-Chlorophenyl)thiazol-2-amine (5). Off white
crystals; IR (KBr), cm–1: 3392, 3276, 1473, 1400, 731,
667; 1H NMR (DMSO, 400 MHz): δ 6.71 (1H, s, NH2),
δ 6.74 (1H, s, thiazole C–H), δ 7.4–7.9 (4H, m, Ar C–H).
13C NMR (DMSO, 400 MHz): 168.8, 101.9, 150.2, 134.3,
131.1, 129.3, 128.9, 129.3, 128.9.
4-p-Tolylthiazol-2-amine (6). Light yellow crystals;
IR (KBr), cm–1: 3405, 3245, 1500, 1460, 717; 1H NMR
(DMSO, 400 MHz) δ, ppm: 6.74 (1H, s, NH2), 6.75 (1H,
s, thiazole C–H), 7.2–7.6 (4H, m, Ar C–H), 2.34 (3H,
s, –CH3). 13C NMR (DMSO, 400 MHz) δ, ppm: 168.8,
101.9, 150.2, 130.0, 131.7, 125.7, 129.5, 125.7, 129.5, 21.3.
General procedure for the microwave oriented
synthesis of thiazol-2-ylthiazolidinones (1a-6a).
Benzothiazol/thiazol-2-amines (1–6) (0.01 mol) and
vanillin (0.01 mol) were dissolved in minimum amount
of ethanol. The reaction mixture was subjected to
microwave irradiation at 180 W for 5 min. The formation
of Schiff base as intermediate was checked by TLC at
regular intervals. The mercaptoacetic acid (0.02 mol)
was added in same beaker after the formation of Schiff
base. The reaction mixture was again irradiated at
180 W for 5 min. Completion of reaction was checked
by using TLC with hexane:ethyl acetate (1 : 1) solvent
system. After completion, the solvent was evaporated
1,3-Benzothiazol-2-amine (1). Orange red crystals;
IR (KBr): 3430, 3100, 3010, 1350, 900 cm–1; 1H NMR
(DMSO, 400 MHz) δ, ppm: 5.3 (2H, s, NH2), 6.6–7.3 (4H,
m,Ar C–H). 13C NMR (DMSO, 400 MHz) δ, ppm: 166.3,
130.8, 153.2, 121.8, 118.3, 124.5, 125.3.
6-Fluoro-1,3-benzothiazol-2-amine (2). Off white
crystals; IR (KBr), cm–1: 3452, 3080, 3010, 1350, 1215,
900; 1H NMR (DMSO, 400 MHz) δ, ppm: 5.4 (2H, s, NH2),
6.5–7.4 (3H, m, Ar C–H). 13C NMR (DMSO, 400 MHz)
δ, ppm: 166.3, 131.6, 148.8, 158.5, 108.0, 117.8, 113.9.
6-Nitro-1,3-benzothiazol-2-amine 3. Yellow
crystals; IR (KBr), cm–1: 3460, 3100, 3010, 1558, 1350,
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GREEN SYNTHESIS OF THIAZOL-2-YLTHIAZOLIDIN-4-ONES
2067
and the crude product was digested with sodium
bicarbonate solution. The product was crystallised using
methanol to afford pure 3-(benzo[d]thiazol-2-yl)-2-(3-
hydroxy-4-methoxyphenyl)thiazolidin-4-ones 1a–3a and
2-(3-hydroxy-4-methoxyphenyl)-3-(4-phenylthiazol-2-
yl)thiazolidines 4a–6a.
6.7–7.9 (8H, m, Ar C–H), 9.0 (1H, s, –OH). 13C NMR
(DMSO, 400 MHz) δ, ppm: 160.3, 65.6, 105.0, 33.5,
171.2, 150.2, 134.3, 148.5, 147.0, 132.9, 131.1, 129.3,
115.4, 112.7, 122.3, 128.9, 129.3, 128.9, 56.1.
2-(3-Hydroxy-4-methoxyphenyl)-3-(4-p-tolyl-
thiazol-2-yl)thiazolidin-4-one (6a). Light yellow
crystals; IR (KBr), cm–1: 3437, 1719, 1575, 1500, 1460,
3-(Benzo[d]thiazol-2-yl)-2-(3-hydroxy-4-methoxy-
phenyl)thiazolidin-4-one (1a). Off white crystals; IR
(KBr), cm–1: 3446, 2815, 1650, 1575, 1500, 1460, 1026.
1H NMR (DMSO, 400 MHz) δ, ppm: 5.0 (1H, s, Ar–
CH), 3.1 (2H, d.d, S-CH2), 3.4 (3H, s, –OCH3), 6.3–7.9
(7H, m, Ar C–H), 9.0 (1H, s, –OH).13C NMR (DMSO,
400 MHz) δ, ppm: 164.6, 65.6, 130.8, 33.5, 171.2, 149.2,
148.5, 147.0, 121.8, 118.3, 132.9, 115.4, 112.7, 122.3,
124.5, 125.3, 56.1.
1
1045; H NMR (DMSO, 400 MHz) δ, ppm: 5.3 (1H,
s, Ar–CH), 3.0 (2H, d.d, S-CH2), 3.2 (3H, s, –OCH3),
6.7–7.4 (8H, m,Ar C–H), δ 8.8 (1H, s, –OH), δ 2.35 (3H,
s, –CH3). 13C NMR (DMSO, 400 MHz): 160.3, 65.6,
105.0, 33.5, 171.2, 150.2, 148.5, 147.0, 132.9, 130.0,
131.7, 115.4, 112.7, 122.3, 125.7, 129.5, 125.7, 129.5,
56.1, 21.3.
Antifungal Evaluation
3-(5-Fluorobenzo[d]thiazol-2-yl)-2-(3-hydroxy-
4-methoxyphenyl)thiazolidin-4-one (2a) Off white
crystals; IR (KBr), cm–1: 3450, 2817, 1649, 1575, 1500,
1460, 1262, 1026; 1H NMR (DMSO, 400 MHz) δ, ppm:
5.2 (1H, s, Ar–CH), 3.2 (2H, d.d, S-CH2), 3.36 (3H,
s, –OCH3), 6.7–8.0 (6H, m, Ar C–H), 9.1 (1H, s, –OH).
13C NMR (DMSO, 400 MHz) δ, ppm: 164.6, 65.6, 26.4,
33.5, 171.2, 150.6, 157.8, 148.5, 147.0, 123.4, 109.1,
132.9, 114.6, 115.4, 112.7, 122.3, 56.1.
The in vitro antifungal activity of the compounds
were performed by Poisoned food technique [25, 26]
against two phytopathogenic fungi viz C. falcatum and
P. grisea and by Spore germination inhibition technique
[27] against U. hordei in comparison with the standard
fungicides Bavistin 50 WP (methyl benzimidazol-
2-ylcarbamate), Raxil [(RS)-1-(4-Chlorophenyl)-
4,4-dimethyl-3-(1H,1,2,4-triazol-1-ylmethyl)pentan-
3-ol] and Tilt{1-[[2-(2,4-dichlorophenyl)-4-propyl-
1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole}. The
isolates of phytopathogenic fungi were provided by the
Plant Pathology Department of the Punjab Agricultural
University and the standards Bavistin, Tilt, and Raxil
which served as the positive control were obtained from
their respective manufacturers.
2-(3-Hydroxy-4-methoxyphenyl)-3-(5-nitrobenzo-
[d]thiazol-2-yl)thiazolidin-4-one (3a). Yellow crystals;
IR, cm–1 (KBr): 3460, 3026, 1745, 1575, 1565, 1500,
1
1460, 1027; H NMR (DMSO, 400 MHz) δ, ppm:
5.7 (1H, s, Ar-CH), 3.3 (2H, d.d, S-CH2), 3.45 (3H,
s, –OCH3), 7.3–8.7 (6H, m, Ar C–H), 9.1 (s, –OH).
13C NMR (DMSO, 400 MHz): 164.6, 65.6, 136.9, 33.5,
171.1, 149.9, 148.5, 147.0, 146.2, 122.7, 117.3, 132.9,
115.4, 112.7, 119.2, 122.3, 56.1.
Stock solutions. Stock solution of the test com-
pounds and standard fungicide were prepared by
dissolving each chemical (20 mg) in 1 mL of Tween
20 (Polyoxyethylenesorbitan) volume was made to
10 mL with sterilized distilled water. Stock solutions of
2000 μg mL–1, were kept in refrigerator till further use.
Serial dilutions were done to 1000, 500, 250, 100, 50, 25,
and 10 μg mL–1, respectively.
2-(3-Hydroxy-4-methoxyphenyl)-3-(4-phenyl-
thiazol-2-yl)thiazolidin-4-one (4a). Light yellow
crystals; IR (KBr), cm–1: 3430, 1717, 1575, 1500, 1460,
1045; 1H NMR (DMSO, 400 MHz) δ, ppm: 5.5 (1H, s,
Ar–CH), 3.0 (2H, d.d, S-CH2), 3.25 (3H, s, –OCH3),
6.7–7.8 (9H, m, Ar C–H), 9.04 (1H, s, –OH). 13C NMR
(DMSO, 400 MHz) δ, ppm: 160.3, 65.6, 105.0, 33.5,
171.2, 150.2, 148.5, 147.0, 132.9, 133.0, 115.4, 112.7,
122.3, 127.5, 127.5, 129.2, 129.2, 128.7, 56.1.
Poisoned food technique. Antifungal activity of test
compounds against Phytopathogenic fungi C. falcatum
and P. grisea was tested by means of poison food
technique. PDA (Potato dextrose agar) media (99 mL)
was taken in the round bottom flasks, each compound
(1 mL, different concentrations) was added to different
flasks and the contents were mixed thoroughly. The
3-(4-(4-Chlorophenyl)thiazol-2-yl)-2-(3-hydroxy-4-
methoxyphenyl)thiazolidin-4-one (5a). White crystals;
IR (KBr), cm–1 : 3435, 1720, 1560, 1445, 1405, 1045,
1
670; H NMR (DMSO, 400 MHz) δ, ppm: 5.7 (1H, s,
Ar–CH), 3.15 (2H, d.d, S-CH2), 3.3 (3H, s, –OCH3),
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2068
GUMBER et al.
contents of the flask were poured aseptically into the
petriplates. Test compound was, however, replaced by an
equal amount of tween 20 only in the control set. After
the media solidified, one inoculum disc of mycelium
of the test fungus was aseptically placed/inoculated to
each petriplate and incubated at 24 ± 1°C. The average
diameter of fungal colonies was measured on the 7th day
after inoculation. EC50 values were calculated by using
PDO software programme.
with an interest in the application of computer-based
estimation methods in the assessment of chemical
toxicity. The new module with the revised list of SAS
includes also structure–activity relationships (SAR)
models that enable the toxicity evaluations for a number
of chemical classes to be fine-tuned.
In order to find out the toxic hazards of all the
synthesized compounds, two dimensional models of
the compounds were first converted into its simplified
molecular-input line-entry system
For P. grisea CDA media was taken instead of PDA
and same procedure was followed [28].
(SMILES format). Then simply putting the SMILES
code into the Chemical identifier row available in the
Toxtree software we can easily get the toxic characters.
Spore germination inhibition method. Antifungal
activity of test compounds against phytopathogenic
fungus, U. hordei was tested by means of Spore
germination inhibition technique. The spores of U. hordei
were taken and used as such without culturing for testing.
The spore suspension was made by addition of sterilized
distilled water in the infected smuts of barley. The
suspension was filtered through three layers of sterilized
cheese cloth under aseptic conditions in order to remove
agar bits and mycelium. Haemocytometer was used to
get spore suspension (1 × 106 spore mL–1). Screening of
the test compounds against U. hordei involved floating
of fungal spores on the surface of test solution in cavity
slides. Small droplets (0.02 mL) of the test solution and
spore suspension in equal amount were seeded in the
cavity slides. These slides were kept in petriplates lined
with moist filter paper and incubated for 72 h at 25 ±
1°C. The slides were checked for germination and per
cent spore germination inhibition was determined from
which EC50 values were calculated [29].
Lipinski parameter. Molinspiration, a web based
software, was used to obtain parameters of Lipinski’s
parameters. These parameters were formulated by
Christopher A. Lipinski in 1997 [30]. This analysis
involved two computer assisted steps: (a) To draw
geometrically optimized structure of the molecule
followed by its conversion into SMILES (Simplified
Molecular-Input Line-Entry System), (b) calculation of
molecular descriptors. The structures of the molecules
were drawn by ChemOffice 2006 and saved as .mol file
formats. The .mol file formats were then converted into
SMILES format using Online SMILES Translator and
Structure File Generator.
The various drugs like descriptors chosen are log P,
where P is the partition coefficient in n-octanol/water
system. It reflects the overall lipophilicity of a molecule, a
property of major importance in biochemical applications.
The molecular weight, that defines the effect of size of the
molecule on its biological activity, the topological polar
surface area (TPSA), another physiochemical property
describing the polarity of the molecules that gives the
correlation with passive molecular transport through
membranes [31]. The number of hydrogen donors and
hydrogen acceptors helps in determines the upper limits
for the biomolecules to be able to penetrate through
biomembranes.
In Silico Analysis
In silico molecular modification was the most
important preliminary step in the molecular designing
of novel biomolecules. In the present study different
proposed derivatives were screened for different
biological and physicochemical properties by using
different software.
Toxicity analysis. Toxtree v2.6.6 is an open-source
software application that places chemicals into categories
and predicts various kinds of toxic effect by applying
various decision tree approaches. Toxtree was developed
by IdeaConsult Ltd. (Sofia, Bulgaria) under the terms of
an ECB contract. The software is made freely available
by ECB as a service to scientific researchers and anyone
Statistical Analysis
The SAS 9.3.1 statistical software was used for
analysis of the results recorded for antifungal evaluation.
The results recorded in triplicates were subjected to one
way analysis of variance (ANOVA) followed by post
hoc Duncan’s test to confirm its effective demarcation
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 12 2015

GREEN SYNTHESIS OF THIAZOL-2-YLTHIAZOLIDIN-4-ONES
2069
from control set. The paired student’s test was applied to
Scheme 1.
compare the parent compounds with their thiazolidinone
derivatives. The correlation analysis was performed to
confirm a relationship between the calculated Lipinski
parameters and the resultant EC50 values.
The relationship between EC50 values and Lipinski
parameters was assessed using a dynamic regression
model. Multiple regression analysis involving finding
the best fit of a dependent variable (antifungal activity,
EC50) to a linear combination of independent variables
(molecular descriptors) by the least square method was
used. This is formally expressed as follows:
Y = a0 + a1x1 + a2x2 + a2x2 + a4x4 … + anxn,
where, Y is related to antifungal activity of a compound,
x1, x2, x3 …, xn are the molecular descriptor values
related to the compounds and a0, a1, a2, a3, …, an are the
regression coefficients determined by the least square
analysis. This equation is developed for each compound
in the QSAR study. P < 0.05, i.e., statistical significance
at 5% level of significance was chosen as criterion for
compilation of all the results.
Compd. no.
–R
–H
1
2
3
1a
2a
3a
–F
–NO2
–H
–F
–NO2
RESULTS AND DISCUSSION
Scheme 2.
Chemistry
The compounds described in this paper were synthe-
sized by the multistep reaction protocol. The synthetic
strategies adopted for the synthesis of 2-substituted benzo
fused thiazoles viz. 1,3-benzothiazol-2-amines (1–3) and
3-(benzo[d]thiazol-2-yl)-2-phenylthiazolidin-4-ones
(1a–3a) are given in Scheme 1 and the synthetic route
followed for the synthesis of 2- arylthiazoles viz. 4-ar-
ylthiazol-2-amines (4–6) and 2-phenyl-3-(4-arylthiazol-
2-yl)thiazolidin-4-ones (4a–6a) are given in Scheme 2.
The Microwave procedure adopted for the synthesis of
thiazol-2yl thiazolidin-4-ones reduced the long reaction
hours taken in conventional refluxing methods to just few
minutes [13].
Purity of the compounds was checked by TLC and
melting points were determined. The structural assign-
ments of the synthesized compounds were based on their
elemental analysis and spectral studies viz. IR, NMR and
Mass spectrometry. The physical characteristics, mass
spectrometric peaks and elemental analysis of synthesized
thiazol-2-amines (1–6) and thiazol-2-ylthiazolidin-4-ones
(1a–6a) are outlined in Table 1.
Compd. no.
–R
–H
4
5
–Cl
6
–CH3
–H
4a
5a
6a
–Cl
–CH3
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 12 2015

2070
GUMBER et al.
Table 1. Physical characteristics, elemental analysis, and molecular formula of thiazoles 1–6 and thiazolidinones 1a–6a
Elemental analysis calculated (found), %
Yield,
Compd. no.
mpa, °C
Molecular formula
%
C
H
N
1
2
130
185
165
147
169
134
150
170
160
145
175
160
55
84
74
88
58
52
72
60
75
66
55
70
55.97 (55.89)
49.99 (49.95)
43.07 (43.01)
61.34 (61.42)
51.31 (51.35)
63.13 (63.03)
56.96 (56.94)
54.24 (54.22)
50.61 (50.63)
59.35 (59.19)
54.47 (54.26)
60.28 (60.14)
4.03 (4.02)
3.00 (3.04)
2.58 (2.64)
4.58 (4.55)
3.35 (3.30)
5.30 (5.34)
3.94 (3.98)
3.48 (3.46)
3.25 (3.20)
4.19 (4.25)
3.61 (3.54)
4.55 (4.63)
18.65 (18.74)
16.66 (16.61)
21.53 (21.55)
15.90 (15.93)
13.30 (13.34)
14.72 (14.78)
7.82 (7.81)
C7H6N2S
C7H5FN2S
3
C7H5N3O2S
C9H8N2S
4
5
C9H7N2SCl
6
C10H10N2S
1a
2a
3a
4a
5a
6a
C17H14N2O3S2
C17H13FN2O3S2
C17H13N3O5S2
C19H16N2O3S2
C19H15FN2O3S2
C20H18N2O3S2
7.44 (7.40)
10.42 (10.35)
7.29 (7.18)
6.69 (6.63)
7.03 (7.12)
a
The mp were determined on electric melting point apparatus and are uncorrected.
Table 2. Antifungal potential of 2-substituted thiazoles
EC50 values, μmol mL–1
Compd.
no.
Molecular
weight
log P
TPSA
H donors no.
H acceptors no.
C. falcatum
P. grisea
U. hordei
1
1.33
0.54
1.69
0.99
0.95
1.34
0.50
0.48
0.99
0.39
0.61
0.65
0.392
–
1.16
1.96
1.28
1.13
1.52
1.57
0.45
0.95
0.74
0.46
0.52
0.63
–
1.06
1.25
1.28
0.97
1.21
1.47
0.56
0.67
0.78
0.47
0.54
0.64
–
1.98
2.12
1.91
2.15
2.83
2.60
3.21
3.35
3.15
3.38
4.06
3.83
1.46
3.59
150.03
168.02
195.01
176.04
210.00
190.06
358.04
376.04
403.03
384.06
418.02
398.08
191.19
307.82
38.91
38.91
84.74
38.91
38.91
38.91
62.66
62.66
108.49
62.66
62.66
62.66
67.02
50.95
2
2
5
2
2
2
5
5
8
5
5
5
5
4
2
2
2
2
2
2
1
1
1
1
1
1
2
1
2
3
4
5
6
1a
2a
3a
4a
5a
6a
Bavistina
Raxila
–
0.08
Tilta
–
0.146
–
3.64
342.43
49.19
5
0
a
Standard fungicide against C. falcatum, P. griseaand U. hordei
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 12 2015

GREEN SYNTHESIS OF THIAZOL-2-YLTHIAZOLIDIN-4-ONES
2071
the significant p-values i.e. less tham 0.05, for pooled test
calculated using statistical analysis programme. Thus,
the synergistic effect of thiazolidin-4-one and thiazole
moieties in a single molecule had proved.
Antifungal Assays
All the synthesized compounds 1–6 and 1a–6a were
screened for their in vitro antifungal potential against
various phytopathogenic fungi and EC50 values were
calculated (Table 2). These data are the mean of three
replicate tests performed with each antifungal compound.
The results of antifungal evaluation of the synthesized
compounds along with standard fungicides used viz.
Bavistin, Raxil and Tilt against various phytopathogenic
fungi, are reported in Table 2.
In Silico Analysis
Toxtree Analysis. Estimation of toxic hazards by
Cramer rules was carried out using Toxtree v.2.6.6
software [32], showed that compounds belong to class III
level of toxicity, which was same as that of the toxicity
level of standards fungicides used.
For the sake of comparison of fungitoxicity of the
molecules with standard fungicides, it was appropriate
to express the results in terms of mM. Investigation of
antifungal screening revealed that most of the synthesized
compounds showed promising inhibition of germination
against all the test fungi.
SAR Analysis. Table 2 shows all the synthesized
compounds had followed the rules of Lipinski filtration.
The molecular weights of all the compounds along with
the standards were below 500 and log P values lower
than 5. The number of hydrogen bond acceptors and
donors were also less than 5 and at par with the standard
compounds except for the nitro substituted derivatives.
All the synthesized compounds had shown EC50 values
of less than 1.96 mM against all the test fungi. Against
C. falcatum, the EC50 value of all the test compounds
were found to be less than 1.69 M. Thiazol-2-amines 1–6
were found to be less potent than thiazol-2-ylthiazolidin-
4-ones 1a–6a. 2-(3-hydroxy-4-methoxyphenyl)-3-
(4-phenylthiazol-2-yl)thiazolidin-4-one (4a) inflicted
appreciable fungitoxicity with EC50 of 0.39 mM which
is comparable to standard fungicide Bavistin (EC50 value
0.23 mM). This was followed by compounds 2a and 1a
showing moderate potential with EC50 values of 0.48 mM
and 0.50 mM, respectively.
Regression Analysis
The best fit multiple regression equation and cross
validation were carried out to analyze the structure
activity relationship of the Lipinski parameters with
observed fungitoxicity and the results are given below.
For C. falcatum,
EC50 = 5.607 – 1.495log P – 0.022MW
+ 0.108TPSA – 1.138Hdon + 0.03Hacc
,
Against P. grisea, similar trend of greater potential of
thiazol-2ylthiazolidin-4-one derivatives was observed.
The unsubstituted thiazol-2-amines and thiazol-2-
ylthiazolidin-4-ones1a and 4a were found to be more
effective than their substituted derivatives. The most
potent among the series was 3-(benzo[d]thiazol-2-yl)-2-
(3-hydroxy-4-methoxyphenyl)thiazolidin-4-one (1a) with
the EC50 value of 0.45 mM followed by 2-(3-hydroxy-
4-methoxyphenyl)-3-(4-phenylthiazol-2-yl)thiazolidin-
4-one (4a) with EC50 value of 0.46 mM.
For P. grisea,
EC50 = 2.668 – 0.174log P – 0.005MW
+ 0.104TPSA – 1.55Hdon + 1.235Hacc
,
For U. hordei,
EC50 = 0.739 – 0.745log P – 0.01MW
+ 0.0045TPSA – 0.136Hdon + 0.001Hacc
,
The calculated p-values for all the three equations
were significant having R-square values 98.23, 96.83,
and 90.3%, respectively. The plot of the observed and
calculated values of the effective concentration of
compounds against all the test fungi using the best fit
equation is shown in the figure.
Against U. hordei, synthesized compounds were found
to be moderately effective with EC50 values of less than
1.47 mM. Compound 4a was found to be most potent with
the EC50 value of 0.47 mM followed by compounds 5a
and 1a with EC50 value of 0.52 and 0.56 mM.
The log P values were found to be negatively correlated
with the EC50 values, revealing that the fungitoxicity of
the compounds increases with increase in log P values
The overall results indicated that most of the hybrids
revealed fungitoxicity better than their parent analogues
against all the test fungi and this fact was supported by
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 12 2015

2072
GUMBER et al.
(b)
(a)
(c)
1.5
1.5
1.4
1.2
1.0
0.5
1.0
0.5
0.0
1.0
0.8
0.6
0.0
0.0
0.5
1.0
1.5
0.0
0.5
1.0
1.5
0.6 0.8 1.0 1.2 1.4
Predicted value
Predicted value
Predicted value
Plot of the observed and predicted values of the EC50 values against (a) C. falcatum, (b) P. grisea, and (c) U. hordei.
4. Ottana, R., Carotti, Maccari, S., Landini, R.I., Chiricosta, G.,
Caciagli, B., Vigoritaa, M.G., and Mini, E., Bioorg.& Med.
Chem., 2005, vol. 15, pp. 3930–3933.
i.e. the higher lipophilicity is required for the compounds
to be more effective. The TPSA values had not found to
be following any pattern but their intermediate values
were considered to be much supportive. The molecular
weight also follows the negative correlation, with high
value supporting the high fungitoxicity of the synthesized
compounds. Cross validation method applied to the data
set also proved the consonance of theoretical and actual
fungitoxicity results.
5. Ottana, R,, Maccari, R., Barreca, M.L., Bruno, G.,
Rotondo, A., Rossi, A., Giuseppa, C., Paola, R.D.,
Sautebin, L., Cuzzocrea, S., and Vigorita, M.G., Bioorg.&
Med. Chem., 2005, vol. 13, pp. 4243–4252.
6. Harish, K., Sadique,A.J., Suroor,A.K., and Mohammad,A.,
Eur. J. Med. Chem., 2008, vol. 43, pp. 2688–2698.
7. Balzarini, J., Orzeszko, B., Maurin, J.K., and Orzeszko,A.,
Eur. J. Med. Chem., 2007, vol. 42, pp. 993–1003.
CONCLUSIONS
8. Ghodgaonkar, S., Kulkarni, V.V., Wghulde, S.O.,
Laddha, S.S., and Shah, J., Int. E-conference on Syn. Org.
Chem., 14, p. 1.
The outstanding results for synthesized hybrid
compounds against phytopathogenic fungi viz. C.
falcatum, P. grisea, and U. hordei which are at par with the
standard fungicides, deserve further investigation of the
concept of lead hybridization to clarify the mode of action
at molecular level, responsible for the activity observed.
And the milder reaction conditions, simple workup, and
good yields are the other significant advantages of this
procedure in synthesis of these potential biologically
active compounds further compliment the results.
9. Suresh, S.H., Venkateshwara, R.J., and Jayaveera, K.N.,
Res. J. Pharm., Bio. Chem. Sci., 2010, vol. 1, no. 4,
pp. 635–640.
10. Rahman, V.P. M., Mukhtar, S., Ansari, W.H., and
Lemiere, G., Eur. J. Med. Chem., 2005, vol. 40, pp. 173–
184.
11. Warhurst, D.C.,Agadu, I.S., Nolder, D., and Rossignol, J.,
J. Antimicrob.Chemoth., 2002, vol. 49, no. 1, pp. 103–111.
12. Maru, M. and Shah, M.K., Int. J. Pharm. Sci., 2012, vol. 4,
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