Synthesis, antioxidant and antimicrobial activities of novel thiopyrano[2,3-d]thiazoles based on aroylacrylic acids

Article abstract of DOI:10.1007/s11030-017-9737-8

Abstract: Here it is described the synthesis, antioxidant and antimicrobial activity determination of novel rel-(5 R, 6 S, 7 R)-6-benzoyl-7-phenyl-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-carboxylic acids. The target compounds were obtained in good yields from 5-arylidene-4-thioxo-2-thiazolidinones and β -aroylacrylic acids via regio- and diastereoselective hetero-Diels–Alder reaction. The stereochemistry of the cycloaddition was confirmed by NMR spectra. The antioxidant and antimicrobial activity screening identified 7 compounds (3c, 3e, 3f, 3g, 3k, 3l, 3p) with a high level of free radical scavenging (43–77% DPPH assay), and compounds with significant influence on Staphylococcus aureus, Bacillus subtilis and Candida albicans (MIC 3.13–6.25 μ g/mL), but slight effect on Escherichia coli.

Full text of DOI:10.1007/s11030-017-9737-8

Mol Divers
DOI 10.1007/s11030-017-9737-8
ORIGINAL ARTICLE
Synthesis, antioxidant and antimicrobial activities of novel
thiopyrano[2,3-d]thiazoles based on aroylacrylic acids
Andrii Lozynskyi1 · Viktoria Zasidko2 · Dmytro Atamanyuk1 ·
Danylo Kaminskyy1 · Halyna Derkach3 · Olexandr Karpenko4 ·
Volodymyr Ogurtsov5 · Roman Kutsyk2 · Roman Lesyk1
Received: 29 September 2016 / Accepted: 4 April 2017
© Springer International Publishing Switzerland 2017
Abstract Here it is described the synthesis, antioxidant
and antimicrobial activity determination of novel rel-(5R,
6S, 7R)-6-benzoyl-7-phenyl-2-oxo-3,5,6,7-tetrahydro-2H-
thiopyrano[2,3-d]thiazole-5-carboxylic acids. The target
compounds were obtained in good yields from 5-arylidene-4-
thioxo-2-thiazolidinones and β-aroylacrylic acids via regio-
and diastereoselective hetero-Diels–Alder reaction. The
stereochemistry of the cycloaddition was confirmed by NMR
spectra. The antioxidant and antimicrobial activity screening
identified 7 compounds (3c, 3e, 3f, 3g, 3k, 3l, 3p) with a
high level of free radical scavenging (43–77% DPPH assay),
and compounds with significant influence on Staphylococcus
aureus, Bacillus subtilis and Candida albicans (MIC 3.13–
6.25 μg/mL), but slight effect on Escherichia coli.
Electronic supplementary material The online version of this
article (doi:10.1007/s11030-017-9737-8) contains supplementary
material, which is available to authorized users.
Roman Lesyk
dr_r_lesyk@org.lviv.net; roman.lesyk@gmail.com
B
1
Department of Pharmaceutical, Organic and Bioorganic
Chemistry, Danylo Halytsky Lviv National Medical
University, 69 Pekarska, Lviv 79010, Ukraine
2
Department of Microbiology, Virology and Immunology,
Ivano-Frankivsk National Medical University, 2 Halytska,
Ivano-Frankivsk 76018, Ukraine
3
Department of Chemistry, Ivano-Frankivsk National Medical
University, 2 Halytska, Ivano-Frankivsk 76018, Ukraine
4
Enamine Ltd., 23 Alexandra Matrosova, Kiev 01103, Ukraine
5
Department of General, Bioinorganic, Physical and Colloidal
Chemistry, Danylo Halytsky Lviv National Medical
University, 69 Pekarska, Lviv 79010, Ukraine
123

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Graphical abstract
Thiopyrano[2,3-d]thiazoles
COOH
Antioxidant activity
HOOC
O
H
N
S
DPPH assay, 43-77 % inhibition
S
O
O
NH
S
+
H
S
R2
O
Antimicrobial activity
R2
R1
R1
MIC = 3.13; 6.25 µg/mL
3a-r
stages of different domino and tandem processes in the syn-
thesis of complex heterocycles [20–22].
Keywords Hetero-Diels–Alder reaction · Thiopyrano[2,3-
d]thiazoles · Antioxidant activity · Antimicrobial activity
This work is an extension of our ongoing efforts toward
the synthesis of new substituted thiopyrano[2,3-d]thiazoles
via a hetero-Diels–Alder reaction using β-aroylacrylic acids
as dienophiles (Fig. 1). The reaction of β-aroylacrylic acids,
which are polyfunctional molecules [23–26], with nucle-
ophiles has been investigated [12,27,28]; however, their
utilization as dienophiles in the hetero-Diels–Alder reaction
has not been studied.
Introduction
Thiazolidinones, as privileged structures, are of special inter-
est in modern medicinal chemistry due to a wide range of
biological activities as well as synthetic features [1,2]. Anti-
cancer [3,4], antimicrobial [5,6], antiinflammatory [7,8],
and antioxidant agents [9,10] have been identified among
4-thiazolidinone derivatives. A majority of biologically
active 4-thiazolidinones belongs to a 5-ene-derivative sub-
type. Thus, the statement about the impact of the substituent
at the C5 position (namely 5-ene) of the 4-thiazolidinone
core on biological activity realization [3,11,12] was pro-
posed. The conjugation of a C5 exocyclic double bond to
the C4 carbonyl group of the thiazolidinone core makes
5-ene-4-thiazolidinones to be possible Michael acceptors.
Based on such Michael acceptor functionality, 5-ene-4-
thiazolidinones are assigned as frequent hitters or pan
assay interference compounds (PAINS) that are often dis-
carded in modern drug discovery [13]. The annulation of
5-ene-4-thiazolidinones into the thiopyrano[2,3-d]thiazole
system removes the unwanted Michael acceptor function-
ality and keeps pharmacological profiles similar to 5-ene-
4-thiazolidinones. Thus, thiopyrano[2,3-d]thiazoles could
be considered as cyclic isosteric mimetics of 5-ene-4-
thiazolidinones[14–19]. Thiopyrano[2,3-d]thiazolesarealso
a source of new anticancer [14–17], antimicrobial [18], anti-
inflammatory [19], and antitrypanosomal [20] agents.
Results and discussion
Chemistry
The synthesis of target thiopyrano[2,3-d]thiazoles was per-
formed according to the protocol outlined in Scheme 1.
5-Arylidene-4-thioxo-2-thiazolidinones (5-arylideneisorho-
danines) 1a–g were obtained from reacting 4-thioxo-2-
thiazolidinone and the appropriate aldehydes under Knoeve-
nagelcondensationconditions:usingglacialaceticacidinthe
presence of sodium acetate (method A) or using ethanol in
the presence of ethylenediamine diacetate (EDDA) (method
B) [16,21]. β-Aroylacrylic acids (2a–e) were obtained from
the Friedel–Crafts acylation of arenes and maleic anhy-
dride [29]. The thiopyrano[2,3-d]thiazoles synthesis was
carried out in boiling acetic acid in the presence of cat-
alytic amount of hydroquinone as a side polymerization
inhibitor and desired rel-(5R, 6S, 7R)-6-benzoyl-7-phenyl-
2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acids 3a–r were obtained with good yields.
The structure and stereochemistry of the synthesized
compounds were confirmed by spectral data. Thus, the
thiopyran protons in the 1H NMR spectra appear as a
triplet and two doublets at ∼3.73–5.87 ppm with appro-
priate coupling constants between 9.9 and 10.8 Hz that
prove an axial–axial interaction of the 5-H, 6-H and 6-H,
7-H proton pairs. The signals in the low field ∼11.40–
11.60 ppm were assigned to the amide protons. The 13C
The main synthetic protocol for thiopyrano[2,3-d]
thiazolesisbasedonthehetero-Diels–Alderreactionbetween
mentioned above 5-ene-4-thioxothiazolidines (as heterodi-
enes) and various dienophiles (e.g., acrylonitrile, acrylic acid
and its analogs, maleic and fumaric acids derivatives, aryli-
dene pyruvic and cinnamic acids derivatives, norbornene
derivatives). Such dienophiles can be considered as a tool
for the diversification of thiopyrano[2,3-d]thiazoles [14–20].
Moreover, this hetero-Diels–Alder reaction is one of the
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H
N
S
S
Structure of target compounds
HOOC
H
N
R1
R2
X
S
X
R2
R1
S
X=S,O
O
S
R2
NH
Active thiopyrano[2,3-d]thiazoles
Cl
H
S
H
O
Ph
S
S
H
H
N
O
H
N
O
R1
N
H
S
O
S
O
H
HOOC
S
H
O
NH
S
H
O
MeO
HO
Cl
Antiexudative activity [16]
Fig. 1 Background for target compounds synthesis
MeO
Antitrypanosomal activity [20]
Antitumor activity [14]
NMR spectra of compounds show signals at 170–200ppm
which are attributed to carbonyl groups. Similar signals were
observed for thiopyrano[2,3-d]thiazoles obtained from pyru-
vic, fumaric, and cinnamic acids [16,17,20,21]. For 3a, the
1H NMR signals of H-7 and H-6 appeared as a doublet at
4.10 ppm and a triplet at 4.42 ppm, respectively, and cor-
related with C-17 (200.0 ppm) and C-11 (133.7 ppm), C-12
(128.1ppm), C-2(114.7ppm)andC-6(107.4ppm)inHMBC
(Fig. 2).
pounds that possess higher EHOMO and ELUMO can be more
effective agents for stabilizing DPPH radicals [30].
Antimicrobial activity
The synthesized compounds were screened for their in vitro
antibacterial and antifungal activities using the agar diffusion
method. Screening was performed against Gram(+)Ve and
Gram(−)Ve bacterial strains: Staphylococcus aureus, Bacil-
lussubtilisandEscherichiacoli. Theobtaineddatarevealthat
some of the tested compounds possess good activity toward
tested microbial strains at a dose of 20 μg per well (Table 2).
Compound 3l shows the highest activity against S. aureus
and B. subtilis strains compared to streptomycin (stan-
dard). Compounds 3i and 3l, 3o–r show good antibacterial
activity against S. aureus methicillin-sensitive (MSSA) and
methicillin-resistant (MRSA) strains. Compounds 3h and
3j display moderate activity against MRSA. All the test
compounds exhibit slight inhibitory activity against E. coli.
Antifungal activity of the synthesized compounds was per-
formed against Candida albicans. Compounds 3h, 3b, 3n–q
show better antifungal activities than Amphotericin-B. The
minimum inhibitory concentrations for the most active com-
pounds 3b, 3h–j, 3l and 3n–r against the same microorgan-
isms were calculated using the microdilution susceptibility
method [31] (Table 3).
In vitro antioxidant assay
The 1,1-diphenyl-2-picryl-hydrazyl (DPPH) assay is a well-
known method for determination of the antioxidant activity
of various compounds. The radical scavenging activity of the
tested compounds (final concentration 12.5 μM) ranged from
good to moderate compared to L-ascorbic acid (Table 1).
Compounds 3c, 3e–h, 3k, 3l and 3p stabilize DPPH in the
range of 43–77% except of 3a, b, 3d and 3o. Our SAR anal-
ysis suggests that the presence of substituents (especially
methoxy group) in phenyl and benzoyl fragments (position
6 and 7 of thiopyrano[2,3-d]thiazole core) is favorable for
antioxidant potency. The antioxidant activity of the com-
pounds is probably related to their electron or hydrogen
radical releasing ability to DPPH so that they become sta-
ble diamagnetic molecules. The antioxidant activity of the
compounds can be explained by EHOMO and ELUMO. Com-
Our SAR study revealed that compounds with electron-
withdrawing groups (Cl > Br > F > OCH3) exhibit
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Mol Divers
O
H
N
O
O
S
2a R2 = F
O
R2
2b R2 = H
2c R2 = MeO
2d R2 = Br
2e R2 = Cl
OH
dioxane
P2S5
S
O
O
AlCl3
R2
O
2a-e
H
N
O
S
CHO
A: AcOH, AcONa
or
B: EtOH, EDDA
O
R1
O
OH
O
S
OH
R2
S
R1
NH
O
R2
2a-e
AcOH, hydroquinone
S
NH
O
O
S
R1
3j R1 = 4-Br, R2 = Me, 64%
3k R1 = 3,4-diMeO, R2 = MeO, 57%
3l R1 = 4-MeO, R2 = Br, 56%
3m R1 = H, R2 = H, 59%
3a R1 = 4-Cl, R2 = F, 65%
1a R1 = 4-Cl
3b R1 = 4-MeO, R2 = F, 72%
1b R1 = 4-MeO
1c R1 = 4-COOMe
1d R1 = 4-Me
1e R1 = 3,4-diMeO
1f R1 = 4-Br
3c R1 = 4-COOMe, R2 = F, 67%
3d R1 = 4-Me, R2 = F, 65%
3n R1 = 4-Cl, R2 = H, 76%
3o R1 = 4-Br, R2 = Cl, 51%
3p R1 = 4-Cl, R2 = MeO, 54%
3q R1 = 4-Cl, R2 = Cl, 63%
3r R1 = 4-Cl, R2 = Br, 50%
3e R1 = 4-MeO, R2 = H, 62%
3f R1 = 3,4-diMeO, R2 = H, 56%
3g R1 = 4-Br, R2 = MeO, 60%
3h R1 = 3,4-diMeO, R2 = Br, 88%
3i R1 = 4-Br, R2 = Br, 52%
1g R1 = H
Scheme 1 Synthesis of rel-(5R, 6S, 7R)-6-benzoyl-7-phenyl-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-carboxylic acids
1Н NMR
signal,
δ, ppm
11.60
The cross peaks in13С NMR
HMBC
11.60
H
HMQC
-
482
HOOC
S
7.71
114.7; 107.4; 170.3
165.7; 130.6;
114.7
N
S
O
169.3
170.3
47.1
49.2
7.07
114.4
7.71
130.6
O
200.0; 114.4
130.6
45.1
7.21
7.15
7.07
4.82
128.1
118.7
114.4
47.1
45.1; 131.6; 128.1
133.7; 118.7
200.0
132.1
107.4
4,10
4.42
165.7; 132.1; 114.4;
169.3; 49.2; 45.1
F
165.7
133.7
7.21
128.1
118.7
200.0; 169.3; 133.7; 128.1;
114.7; 107.4; 47.1; 45.1
200.0; 133.7; 128.1;
114.7; 107.4; 49.2; 47.1
4.42
49.2
4.10
45.1
7.15
130.6
Cl
Fig. 2 Heteronuclear 1H-13C correlations for compound 3a
higher antimicrobial activity. The data suggest that Cl
is a favorable substituent in the phenyl ring at posi-
tion 7 of the thiopyrano[2,3-d]thiazole core. The similar
trend was observed for antiviral thiopyrano[2,3-d]thiazole-
6-carbaldehydes [32].
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Table 1 Antioxidant activity of thiopyrano[2,3-d]thiazoles
Conclusions
Compound
Absorbance of a sample, As
% Inhibition
Thenewrel-(5R, 6S, 7R)-6-benzoyl-7-phenyl-2-oxo-3,5,6,7-
tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-carboxylicacids
were synthesized via a regio- and stereoselective hetero-
Diels–Alder reaction from appropriate β-aroylacrylic acids
and5-arylideneisorhodanines. TheantioxidantactivityDDPH
assay identified thiopyrano[2,3-d]thiazole derivatives with
radical scavenging activity in the range of 43–77%. An
antimicrobial screening led to the identification of active
compounds against Staphylococcus aureus, Bacillus subtils,
and Candida albicans (MIC 3.13–6.25 μg/mL). The results
obtained in this work could be used as the basis to explore
more thiopyrano[2,3-d]thiazole analogs with better antioxi-
dant and antimicrobial properties.
3a
0.710 0.013
0.726 0.015
0.399 0.009
0.715 0.015
0.304 0.005
0.349 0.007
0.305 0.007
0.440 0.009
0.597 0.011
0.543 0.009
0.174 0.004
0.389 0.009
0.733 0.014
0.699 0.013
0.775 0.016
0.230 0.005
0.646 0.012
0.585 0.011
0.533 0.012
9.00
6.88
3b
3c
48.81
8.39
3d
3e
61.00
55.29
60.96
43.57
23.49
30.40
77.71
50.07
6.00
3f
3g
3h
3i
3j
3k
3l
3m
3n
10.36
0.61
Experimental
Chemistry
3o
3p
70.49
17.18
25.02
31.70
3q
3r
Materials and methods
Ascorbic acid
All materials were purchased from commercial sources and
used as received. Melting points were measured in open cap-
Data are given as mean SD
Table 2 Antimicrobial activity of thiopyrano[2,3-d]thiazole-5-carboxylic acids
Compound
Zone of growth inhibition (mm)
S. aureus
S. aureus
E. coli
B. subtils
C. albicans
MSSA
MRSA
Fungistatic
Fungicidal
3a
5.29 0.35
5.52 0.48
5.11 0.37
4.42 0.41
4.45 0.30
4.12 0.30
5.70 0.21
10.24 1.15
6.78 0.36
4.03 0.26
7.78 0.47
4.74 0.27
7.48 0.34
10.16 0.13
11.56 0.73
13.00 0.42
–
6.19 0.31
6.81 0.19
6.42 0.48
–
5.26 0.28
5.14 0.28
4.99 0.48
4.22 0.41
4.90 0.27
4.32 0.59
4.93 0.08
4.59 0.47
4.90 0.14
4.92 0.21
5.69 0.36
4.23 0.36
5.96 1.01
5.16 0.36
5.31 0.34
10.00 0.36
–
5.83 0.53
5.27 0.14
10.38 0.58
7.58 0.89
9.04 0.69
5.08 0.14
7.88 0.59
13.21 0.46
6.73 0.57
6.91 0.52
5.93 0.57
7.71 0.38
8.94 0.53
11.92 0.24
9.76 0.52
7.46 0.54
–
4.29 0.09
7.46 0.22
6.79 0.63
5.76 0.33
4.73 0.21
5.99 0.20
10.89 0.22
5.25 0.38
5.49 0.42
4.61 0.28
5.46 0.61
7.02 0.36
10.45 0.37
8.25 0.67
5.63 0.65
–
3b
4.73 0.3
3c
5.37 0.16
3d
–
3f
6.35 0.15
5.60 0.29
10.20 0.82
11.42 1.31
10.02 0.42
–
–
3g
5.47 0.36
3h
–
3i
5.24 0.73
3j
–
3k
–
3l
18.15 1.11
5.93 0.14
13.25 0.99
9.67 0.35
9.50 0.58
–
10.55 0.15
5.13 0.21
6.83 0.98
–
3n
3o
3q
3r
5.34 0.27
10.00 0.38
–
Streptomycin
Amphotericin–B
–
9.00 0.65
–
Data are given as mean SD
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Table 3 Minimum inhibitory
concentration of tested
compounds, μg/mL
Microorganism
MIC (μg/mL)
3b
3h
3i
3j
3l
3n
3o
3q
3r
S. aureus/MSSA
S. aureus/MRSA
E. coli
>50
>50
>50
50
>50
25
25
>50
25
50
>50
>50
>50
>50
50
25
25
25
25
12.5
>50
>50
6.25
>50
>50
12,5
>50
12.5
>50
3.13
>50
>50
>50
>50
>50
C. albicans
25
illary tubes on a BÜCHI B-545 melting point apparatus and
are uncorrected. Elemental analyses (C, H, N) were per-
formed using a PerkinElmer 2400 CHN analyzer and were
washed with methanol (5–10 mL), and the product recrystal-
lized from acetic acid (10–15 mL).
rel-(5R,6S,7R)-7-(4-Chlorophenyl)-6-(4-fluorobenzoyl)-
2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3a). Yield 65%, mp 228–230 ◦C. 1H NMR
(400 MHz, DMSO-d ): 4.10 (d, 1H, J = 10.2 Hz, 7-H),
1
within 0.4% of theoretical values. The H- and 13C-NMR
spectra were recorded on Varian Gemini 400 MHz in DMSO-
d6 using tetramethylsilane as an internal standard (chemical
shift values are reported in ppm units, coupling constants
(J) are in Hz). Abbreviations are as follows: s—singlet;
d—doublet; t—triplet; m—multiplet; br—broad. Chemical
δ
6
4.42 (t, 1H, J = 10.2 Hz, 6-H), 4.82 (d, 1H, J = 10.2 Hz,
5-H), 7.07 (d, 2H, J = 8.4 Hz, arom.), 7.15 (d, 2H, J = 8.4
Hz, arom.), 7.21 (d, 2H, J = 8.4 Hz, arom.), 7.71 (dd, 2H,
J = 4.1, 3.2 Hz, arom.), 11.60 (s, 1H, NH), 13.41 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 45.1, 47.1, 49.2,
shifts are reported in ppm units with use of scale. Mass
δ
spectra were obtained using electrospray ionization (ESI)
techniques on an Agilent 1100 Series LCMS. The purity of
all obtained compounds was checked by TLC (silica gel 60
F254 coated plates (Merck), eluent Benzene : EtOAc 2:1).
δ
6
107.4, 114.7, 118.7 (d, JCF = 3.0 Hz), 128.1, 130.6, 131.6
(d, JCF = 30.0 Hz, CH, arom.), 132.1, 133.7, 137.9, 165.7
(d, JCF = 200.0 Hz, C, arom.), 169.3 (C=O), 170.3 (C=O),
200.0 (C=O). ESI-MS m/z 450/452 (M+H)+. Anal. Calcd
for C20H13ClFNO4S2: C, 53.39; H, 2.91; N, 3.11. Found: C,
53.37; H, 2.93; N, 3.10.
rel-(5R,6S,7R)-6-(4-Fluorobenzoyl)-7-(4-methoxyphenyl)
-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3b). Yield 72%, mp 215–217 ◦C. 1H NMR
General procedure for 5-arylidene-4-thioxo-
2-thiazolidinones 1a–g synthesis
The starting 4-thioxo-2-thiazolidinone was obtained accord-
ing to the literature [33]. 5-Arylidene-4-thioxo-2-thiazolidin-
ones (1a–g) were prepared under Knoevenagel reaction
conditions:
Method A A mixture of 4-thioxo-2-thiazolidinone (10
mmol), an appropriate aldehyde (10 mmol) and sodium
acetate (10 mmol) in 10 mL of glacial acetic acid was stirred
for 20 min using a water bath (100 ◦C). The resulting solid
was collected by filtration, washed with water, dried and used
without further purification.
Method B A mixture of 4-thioxo-2-thiazolidinone (10
mmol), an appropriate aldehyde (10 mmol) and catalytic
amount of EDDA in the ethanol (10 mL) was heated under
reflux for 10 min. The resulting solid was collected by filtra-
tion, washed with ethanol and diethyl ether, dried and used
without further purification.
(400 MHz, DMSO-d ): 3.55 (s, 3H, OCH ), 3.95 (d, 2H,
δ
6
3
J = 10.2 Hz, 7-H), 4.36 (t, 1H, J = 10.2 Hz, 6-H), 4.79 (d,
1H, J = 10.2 Hz, 5-H), 6.58 (d, 2H, J = 8.4 Hz, arom.),
6.99 (d, 2H, J = 8.4 Hz, arom.), 7.04 (d, 2H, J = 8.4 Hz,
arom.), 7.65 (d, 2H, J = 8.4 Hz, arom.), 11.52 (s, 1H, NH),
13.55 (br.s, 1H, COOH). 13C NMR (100 MHz, DMSO-d ):
δ
6
45.1, 47.2, 49.4, 54.9, 108.6, 114.8, 118.1 (d, JCF = 3.0 Hz),
129.8, 130.9, 131.1 (d, JCF = 30.0 Hz), 133.8, 133.9, 158.4,
165.5 (d, JCF = 200.0 Hz), 169.4 (C=O), 170.5 (C=O),
200.5 (C=O). ESI-MS m/z 446 (M+H)+. Anal. Calcd for
C21H16FNO5S2: C, 56.62; H, 3.62; N, 3.14. Found: C, 56.63;
H, 3.64; N, 3.12.
rel-(5R,6S,7R)-6-(4-Fluorobenzoyl)-7-(4-methoxycarbon-
ylphenyl)-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d◦]th-
iazole-5-carboxylic acid (3c). Yield 67%, mp 188–190 C.
1H NMR (400 MHz, DMSO-d6): 3.80 (s, 3H, OCH3),
δ
General procedure for hetero-Diels–Alder products 3a–r
synthesis
4.14 (d, 1H, J = 10.2 Hz, 7-H), 4.48 (t, 1H, J = 10.2
Hz, 6-H), 4.82 (d, 1H, J = 10.2 Hz, 5-H), 6.88 (d, 2H,
J = 8.7 Hz, arom.), 7.06 (d, 2H, J = 8.7 Hz, arom.),
7.79 (d, 2H, J = 8.1 Hz, arom.), 8.16 (dd, 2H, J = 4.2,
8,7 Hz, arom.), 11.68 (s, 1H, NH), 13.80 (br.s, 1H, COOH).
13C NMR (100 MHz, DMSO-d ): 45.6, 47.5, 49.0, 52.1,
Amixtureofanappropriate5-arylidene-4-thioxo-2-thiazolid-
inone 1(10 mmol), β-aroylacrylic acid 2(11 mmol) and a
catalytic amount of hydroquinone (2–3 mg) in glacial acetic
acid (10 mL) was heated under reflux for 1 h and then left
overnight at room temperature. The precipitate was filtered,
δ
6
104.7, 107.1, 116.3, 118.9 (d, JCF = 3.0 Hz), 128.7, 129.2,
123

Mol Divers
131.7 (d, JCF = 30.0 Hz), 132.3, 133.6, 144.5, 165.7 (d,
JCF = 120.0 Hz), 169.8 (C=O), 170.6 (C=O), 199.8 (C=O).
ESI-MS m/z 474 (M+H)+. Anal. Calcd for C22H16FNO6S2:
C, 55.81; H, 3.41; N, 2.96. Found: C, 55.82; H, 3.42; N, 2.98.
rel-(5R,6S,7R)-6-(4-Fluorobenzoyl)-2-oxo-7-(4-methylph-
enyl)-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3d). Yield 65%, mp 230–232 ◦C. 1H NMR
1H, J = 10.2 Hz, 5-H), 6.94 (d, 2H, J = 8.7 Hz, arom.),
7.09 (d, 2H, J = 8.7 Hz, arom.), 7.21 (d, 2H, J = 8.4 Hz,
arom.), 7.33 (d, 2H, J = 8.4 Hz, arom.), 11.41 (s, 1H, NH),
13.35 (br.s, 1H, COOH). 13C NMR (100 MHz, DMSO-d6):
40.8, 46.7, 50.2, 55.6, 107.7, 113.8, 118.3, 120.4, 127.1,
δ
130.7, 131.5, 139.6, 142.1, 163.1, 170.7(C=O), 172.6(C=O),
192.6 (C=O). ESI-MS m/z 506/508 (M+H)+. Anal. Calcd
for C21H16BrNO5S2: C, 49.81; H, 3.18; N, 2.77. Found: C,
49.82; H, 3.16; N, 2.75.
(400 MHz, DMSO-d ): 2.09 (s, 3H, CH ), 4.00 (d, 1H,
δ
6
3
J = 10.2 Hz, 7-H), 4.38 (t, 1H, J = 10.2 Hz, 6-H), 4.81 (d,
1H, J = 10.2 Hz, 5-H), 6.87 (d, 2H, J = 7.8 Hz, arom.),
7.02 (d, 2H, J = 7.8 Hz, arom.), 7.07 (d, 2H, J = 8.1 Hz,
arom.), 7.68 (d, 2H, J = 8.1 Hz, arom.), 11.52 (s, 1H, NH),
13.52 (br.s, 1H, COOH). 13C NMR (100 MHz, DMSO-d ):
rel-(5R,6S,7R)-6-(4-Bromobenzoyl)-7-(3,4-dimethoxyphe-
nyl)-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-
5-carboxylic acid (3h). Yield 88%, mp 112–114 ◦C. 1H
NMR (400 MHz, DMSO-d ): 3.74 (s, 3H, OCH ), 3.75
δ
δ
6
6
3
20.5, 45.5, 47.3, 49.5, 108.4, 114.8, 118.2 (d, JCF = 3.0 Hz),
128.5, 131.0, 133.8, 133.9 (d, JCF = 30.0 Hz, CH, arom.),
135.8, 136.7, 165.6 (d, JCF = 200.0 Hz), 169.4 (C=O), 170.5
(C=O), 200.3 (C=O). ESI-MS m/z 430 (M+H)+. Anal. Calcd
for C21H16FNO4S2: C, 58.73; H, 3.75; N, 3.26. Found: C,
58.72; H, 3.75; N, 3.24.
(s, 3H, OCH3), 3.76 (t, 1H, J = 10.2 Hz, 6-H), 3.94 (d, 1H,
J = 10.2 Hz, 7-H), 4.80 (d, 1H, J =10.2 Hz, 5-H), 6.55
(d, 1H, J =8.1 Hz, arom.), 6.75 (s, 1H, arom.), 6.98 (d, 1H,
J =8.1 Hz, arom.), 7.59 (d, 2H, J=8.4 Hz, arom.), 7.97 (d,
2H, J =8.4 Hz, arom.), 11.50 (s, 1H, NH), 13.40 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 45.5, 47.0, 48.8,
δ
6
rel-(5R,6S,7R)-6-Benzoyl-7-(4-methoxyphenyl)-2-oxo-
(4-methylphenyl)-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]
thiazole-5-carboxylic acid (3e). Yield 62%, mp 206–208 ◦C.
1H NMR (400 MHz, DMSO-d ): 3.78 (s, 3H, OCH ), 3.81
50.6, 55.1, 111.6, 118.0, 120.3, 125.1, 128. 8, 130.0, 131.5,
132.3, 133.5, 134.3, 136.0, 148.2, 169.5(C=O), 170.6(C=O),
201.3 (C=O). ESI-MS m/z 536/538 (M+H)+. Anal. Calcd
for C22H18BrNO6S2: C, 49.26; H, 3.38; N, 2.61. Found: C,
49.27; H, 3.35; N, 2.60.
δ
6
3
(t, 1H, J = 10.8 Hz, 6-H), 4.14 (d, 1H, J = 10.8 Hz, 7-H),
5.87 (d, 1H, J = 10.8 Hz, 5-H), 6.90 (d, 2H, J = 9.3 Hz,
arom.), 7.15 (d, 2H, J = 9.3 Hz, arom.), 7.59 (t, 1H,
J = 7.5 Hz, arom.), 7.71 (t, 2H, J = 7.5 Hz, arom.), 8.12 (d,
2H, J = 7.5 Hz, arom.), 11.51 (s,1H, NH), 13.52 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 43.6, 47.2, 51.2,
rel-(5R,6S,7R)-6-(4-Bromobenzoyl)-7-(4-bromophenyl)-2
-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3i). Yield 52%, mp 174–176 ◦C. 1H NMR
(400 MHz, DMSO-d ): 4.06 (d, 1H, J = 10.2 Hz, 7-H),
δ
6
4.36 (t, 1H, J = 10.2 Hz, 6-H), 4.85 (d, 1H, J = 10.2
Hz, 5-H), 7.09 (d, 2H, J = 8.4 Hz, arom.), 7.26 (d, 2H, J
= 8.4 Hz, arom.), 7.48 (d, 2H, J = 8.7 Hz, arom.), 8.01 (d,
2H, J = 8.7 Hz, arom.), 11.59 (s, 1H, NH), 13.39 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 45.0, 47.0, 49.2,
δ
6
54.9, 109.0, 113.8, 115.1, 117.4, 128.9, 129.5, 132.8, 134.5,
136.2, 158.6, 170.4 (C=O), 172.7 (C=O), 194.4 (C=O). ESI-
MS m/z 428 (M+H)+. Anal. Calcd for C21H17NO5S2: C,
59.00; H, 4.01; N, 3.28. Found: C, 58.99; H, 4.03; N, 3.29.
rel-(5R,6S,7R)-6-Benzoyl-7-(3,4-dimethoxyphenyl)-2-
oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3f). Yield 56%, mp 188–190 ◦C. 1H NMR
δ
6
107.3, 118.8, 126.8, 130.0, 130.9, 131.1, 131.5, 132.0, 135.9,
138.3, 169.3 (C=O), 170.3 (C=O), 200.7 (C=O). ESI-MS m/z
554/556/558 (M+H)+. Anal. Calcd for C20H13Br2NO4S2:
C, 43.26; H, 2.36; N, 2.52. Found: C, 43.24; H, 2.35; N,
2.50.
(400 MHz, DMSO-d6): 3.73 (t, 1H, J = 9, 9 Hz, 6-
δ
H), 3.75 (s, 3H, OCH3), 3.78 (s, 3H, OCH3), 4.10 (d, 1H,
J = 9.9 Hz, 7-H), 5.84 (d, 1H, J = 9.9 Hz, 5-H,), 6.71 (d,
1H, J = 9.9 Hz, arom.), 6.78 (s, 1H, arom.), 6.84 (d, 1H,
J = 8.7 Hz, arom.), 7.00 (t, 1H, J = 7.8 Hz, arom.), 7.73
(t, 2H, J = 7.8 Hz, arom.), 8.07 (d, 2H, J = 7.8 Hz, arom.),
11.42 (s, 1H, NH), 13.58 (br.s, 1H, COOH). 13C NMR (100
rel-(5R,6S,7R)-7-(4-Bromophenyl)-6-(4-methylbenzoyl)-2
-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3j). Yield 64%, mp 162–164 ◦C. 1H NMR
(400 MHz, DMSO-d ): 2.51 (s, 3H, CH ), 4.08 (d, 1H, J =
δ
6
3
10.5 Hz, 7-H), 4.37 (t, 1H, J = 10.5 Hz, 6-H,), 4.75 (d, 1H, J
= 10.5 Hz, 5-H), 7.10 (d, 2H, J = 8.4 Hz, arom.), 7.26 (d, 2H,
J = 8.4 Hz, arom.), 7.52 (d, 2H, J = 8.1 Hz, arom.), 7.99 (d,
2H, J = 8.1 Hz, arom.), 11.57 (s, 1H, NH), 13.58 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 21.0, 45.0, 47.4,
MHz, DMSO-d ): 40.5, 43.9, 47.2, 50.9, 55.5, 108.7, 111.6,
δ
6
117.5, 120.4, 128.1, 128.5, 128.9, 133.2, 134.2, 134.4, 147.9,
148.9, 170.5 (C=O), 170.8 (C=O), 194.7 (C=O). ESI-MS m/z
458 (M+H)+. Anal. Calcd for C22H19NO6S2: C, 57.75; H,
4.19; N, 3.06. Found: C, 57.73; H, 4.18; N, 3.04.
δ
6
49.1, 107.5, 118.7, 120.7, 128.2, 128.5, 130.8, 131.0, 134.4,
rel-(5R,6S,7R)-7-(4-Bromophenyl)-6-(4-methoxybenzoyl)- 138.6, 143.1, 169.2 (C=O), 170.3 (C=O), 200.4 (C=O). ESI-
2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
MS m/z 490/492 (M+H)+. Anal. Calcd for C21H16BrNO4S2:
C, 51.43; H, 3.29; N, 2.86. Found: C, 51.42; H, 3.27; N, 2.85.
rel-(5R,6S,7R)-7-(3,4-Dimethoxyphenyl)-6-(4-methoxylb-
enzoyl)-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thia-
carboxylic acid (3g). Yield 60%, mp 182–184 ◦C. 1H NMR
(400 MHz, DMSO-d ): 3.83 (s, 3H, OCH ), 4.16 (d, 1H,
δ
6
3
J = 10.2 Hz, 7-H), 5.48 (t, 1H, J = 10.2 Hz, 6-H), 5.79 (d,
123

Mol Divers
zole-5-carboxylic acid (3k). Yield 57%, mp 184–186 ◦C. 1H
NMR (400 MHz, DMSO-d ): 3.72 (s, 3H, OCH ), 3.74
rel-(5R,6S,7R)-7-(4-Bromophenyl)-6-(4-chlorobenzoyl)-2
-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3o). Yield 51%, mp 226–228 ◦C. 1H NMR
δ
6
3
(s, 3H, OCH3), 3.81 (t, 1H, J = 10.5 Hz, 6-H), 3.87 (s,
3H, OCH3), 4.08 (d, 1H, J = 10.5 Hz, 7-H), 5.77 (d, 1H,
J=10.5 Hz, 5-H), 6.72 (d, 1H, J =8.1 Hz, arom.), 6.77 (s,
1H, arom.), 6.87 (d, 1H, J = 8.1 Hz, arom.), 7.09 (d, 2H,
J = 8.7 Hz, arom.), 8.09 (d, 2H, J = 8.7 Hz, arom.), 11.47
(s, 1H, NH), 12.88 (br.s, 1H, COOH). 13C NMR (100 MHz,
DMSO-d ): 44.2, 46.9, 51.0, 55.3, 55.5, 55.7, 108.8, 111.3,
(400 MHz, DMSO-d ): 4.08 (d, 1H, J = 10.5 Hz, 7-H),
δ
6
4.42 (t, 1H, J = 10.5 Hz, 6-H), 4.86 (d, 1H, J = 10.5 Hz,
5-H), 7.10 (d, 2H, J = 8.1 Hz, arom.), 7.27 (d, 2H, J = 8.1
Hz, arom.), 7.35 (d, 2H, J = 8.4 Hz, arom.), 7.64 (d, 2H, J =
8.4 Hz, arom.), 11.60 (s, 1H, NH), 13.63 (br.s, 1H, COOH).
13C NMR (100 MHz, DMSO-d ): 45.1, 47.1, 49.2, 107.3,
δ
δ
6
6
111.7, 114.2, 117.6, 120.8, 126.8, 131.5, 132.0, 148.2, 148.5,
164.1, 170.5 (C=O), 172.9 (C=O), 192.5 (C=O). ESI-MS m/z
488 (M+H)+. Anal. Calcd for C23H21NO7S2: C, 56.66; H,
4.34; N, 2.87. Found: C, 56.64; H, 4.35; N, 2.88.
rel-(5R,6S,7R)-6-(4-Bromobenzoyl)-7-(4-methoxyphenyl)
-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3l). Yield 56%, mp 118–120 ◦C. 1H NMR
118.8, 120.8, 127.9, 129.9, 130.9, 131.1, 135.6, 137.6, 138.3,
169.3 (C=O), 170.33 (C=O), 200.5 (C=O). ESI-MS m/z
510/512/514 (M+H)+. Anal. Calcd for C20H13BrClNO4S2:
C, 47.03; H, 2.57; N, 2.74. Found: C, 47.02; H, 2.55; N, 2.73.
rel-(5R,6S,7R)-7-(4-Chlorophenyl)-6-(4-methoxybenzoyl)
-2-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3p). Yield 54%, mp 200–202 ◦C. 1H NMR
(400 MHz, DMSO-d ): 3.79 (s, 3H, OCH ), 4.01 (d, 1H,
(400 MHz, DMSO-d ): 3.83 (t, 1H, J = 10.5 Hz, 6-H), 3.89
δ
6
δ
6
3
J = 10.2 Hz, 7-H), 4.44 (t, 1H, J = 10.2 Hz, 6-H), 4.83
(d, 1H, J = 10.2 Hz, 5-H), 7.19 (d, 2H, J = 8.4 Hz, arom.),
7.27 (d, 2H, J = 8.4 Hz, arom.), 7.64 (d, 2H, J = 8.1 Hz,
arom.), 7.82 (d, 2H, J = 8.1 Hz, arom.), 11.40 (s, 1H, NH),
13.20 (br.s, 1H, COOH). 13C NMR (100 MHz, DMSO-d6):
(s, 3H, OCH3), 4.19 (d, 1H, J = 10.5 Hz, 7-H), 5.80 (d, 1H,
J = 10.5 Hz, 5-H), 6.95 (d, 2H, J = 8.7 Hz, arom.), 7.10 (d,
2H, J = 8.7 Hz, arom.), 7.28 (d, 2H, J = 8.4 Hz, arom.), 7.41
(d, 2H, J = 8.4 Hz, arom.), 11.56 (s, 1H, NH), 13.36 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 43.8, 46.7, 51.1,
δ
6
45.1, 47.2, 50.6, 54.9, 113.8, 125.2, 128.1, 128.8, 129.3,
55.7, 107.8, 114.2, 118.2, 128.5, 130.3, 130.5, 131.6, 139.2,
141.6, 164.1, 170.6 (C=O), 172.6 (C=O), 192.4 (C=O). ESI-
MS m/z 462/464 (M+H)+. Anal. Calcd for C21H16ClNO5S2:
C, 54.60; H, 3.49; N, 3.03. Found: C, 54.62; H, 3.47; N,
3.04.
δ
130.0, 130.5, 131.6, 133.5, 158.3, 170.6(C=O), 170.7(C=O),
193.7 (C=O). ESI-MS m/z 506/508 (M+H)+. Anal. Calcd
for C21H16BrNO5S2: C, 49.81; H, 3.18; N, 2.77. Found: C,
49.82; H, 3.17; N, 2.78.
rel-(5R,6S,7R)-6-Benzoyl-7-phenyl-2-oxo-3,5,6,7-tetra-
rel-(5R,6S,7R)-6-(4-Chlorobenzoyl)-7-(4-chlorophenyl)-2
hydro-2H-thiopyrano[2,3-d]thiazole-5-carboxylicacid(3m). -oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
◦
1
Yield 59%, mp 158–160 C. H NMR (400 MHz, DMSO-
carboxylic acid (3q). Yield 63%, mp 222–224 ◦C. 1H NMR
(400 MHz, DMSO-d ): 4.10 (d, 1H, J = 10.2 Hz, 7-H),
d ): 4.06 (d, 1H, J = 10.2 Hz, 7-H), 4.41 (t, 1H, J = 10.2
δ
δ
6
6
Hz, 6-H), 4.82 (d, 1H, J = 10.2 Hz, 5-H), 7.03-7.13 (m,
7H, arom.), 7.39 (t, 1H, J = 7.5 Hz, arom.), 7.58 (d, 2H, J =
7.5 Hz, arom.), 11.54 (s, 1H, NH), 12.74 (br.s, 1H, COOH).
13C NMR (100 MHz, DMSO-d ): 45.9, 47.5, 49.4, 108.3,
4.43 (t, 1H, J = 10.2 Hz, 6-H), 4.87 (d, 1H, J = 10.2 Hz, 5-
H), 7.14 (d, 2H, J = 8.7 Hz, arom.), 7.18 (d, 2H, J = 8.7 Hz,
arom.), 7.35 (d, 2H, J = 8.4 Hz, arom.), 7.65 (d, 2H, J = 8.4
Hz, arom.), 11.60 (s, 1H, NH), 13.30 (br.s, 1H, COOH). 13C
δ
6
118.4, 127.5, 127.8, 127.9, 128.1, 128.6, 132.5, 136.9, 138.9,
169.3 (C=O), 170.4 (C=O), 201.5 (C=O). ESI-MS m/z 398
(M+H)+. Anal. Calcd for C20H15NO4S2: C, 60.44; H, 3.80;
N, 3.52. Found: C, 60.42; H, 3.81; N, 3.53.
NMR(100MHz, DMSO-d ): 45.1, 47.1, 49.3, 107.4, 118.8,
δ
6
127.9, 128.2, 129.9, 130.6, 132.2, 135.6, 137.6, 137.9, 169.3
(C=O), 170.4 (C=O), 200.5 (C=O). ESI-MS m/z 466/468
(M+H)+. Anal. Calcd for C20H13Cl2NO4S2: C, 51.51; H,
2.81; N, 3.00. Found: C, 51.52; H, 2.83; N, 3.02.
rel-(5R,6S,7R)-6-Benzoyl-7-(4-chlorophenyl)-2-oxo-3,5,
6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-carboxylic
acid (3n). Yield 76%, mp 180–182 ◦C. 1H NMR (400 MHz,
DMSO-d ): 4.08 (d, 1H, J = 10.2 Hz, 7-H), 4.41 (t, 1H,
rel-(5R,6S,7R)-6-(4-Bromobenzoyl)-7-(4-chlorophenyl)-2
-oxo-3,5,6,7-tetrahydro-2H-thiopyrano[2,3-d]thiazole-5-
carboxylic acid (3r). Yield 50%, mp 214–216 ◦C. 1H NMR
(400 MHz, DMSO-d ): 4.08 (d, 1H, J = 10.2 Hz, 7-H),
δ
6
J = 10.2 Hz, 6-H), 4.85 (d, 1H, J = 10.2 Hz, 5-H), 7.12 (d,
2H, J = 8.7 Hz, arom.), 7.16 (d, 2H, J = 8.7 Hz, arom.), 7.38
(t, 1H, J =8.1Hz, arom.), 7.49(t, 2H, J =8.1Hz, arom.), 7.56
(d, 2H, J = 8.1 Hz, arom.), 11.58 (s, 1H, NH), 13.14 (br.s,
1H, COOH). 13C NMR (100 MHz, DMSO-d ): 45.9, 48.1,
δ
6
4.41 (t, 1H, J = 10.2 Hz, 6-H), 4.85 (d, 1H, J = 10.2
Hz, 5-H), 7.14 (d, 2H, J = 8.7 Hz, arom.), 7.38 (d, 2H,
J = 8.7 Hz, arom.), 7.48 (d, 2H, J = 8.4 Hz, arom.), 7.56 (d,
2H, J = 8.4 Hz, arom.), 11.53 (s, 1H, NH), 13.58 (br.s, 1H,
COOH). 13C NMR (100 MHz, DMSO-d ): 45.0, 47.1, 49.2,
δ
6
50.1, 108.4, 119.6, 128.7, 128.9, 131.4, 132.9, 133.5, 137.4,
138.9, 140.6, 170.1 (C=O), 171.2 (C=O), 202.2 (C=O). ESI-
MS m/z 433/434 (M+H)+. Anal. Calcd for C20H14ClNO4S2:
C, 55.62; H, 3.27; N, 3.24. Found: C, 55.64; H, 3.29; N, 3.22.
δ
6
107.4, 118.7, 128.2, 130.0, 130.6, 130.9, 131.7, 132.2, 135.9,
137.9, 169.3 (C=O), 170.3 (C=O), 200.7 (C=O). ESI-MS m/z
510/512/514 (M+H)+. Anal. Calcd for C20H13BrClNO4S2:
123

Mol Divers
C, 47.03; H, 2.57; N, 2.74. Found: C, 47.02; H, 2.55; N,
2.73.
References
1. Lesyk R, Zimenkovsky B (2004) 4-Thiazolidones: centenarian
history, current status and perspectives for modern organic and
medicinal chemistry. Curr Org Chem 8:1547–1577. doi:10.2174/
1385272043369773
Pharmacology
Free radical scavenging assay
2. Tripathi AC, Gupta SJ, Fatima GN, Sonar PK, Verma A, Saraf SK
(2014) 4-Thiazolidinones: the advances continue. Eur J Med Chem
72:52–77. doi:10.1016/j.ejmech.2013.11.017
The effect of the studied compounds on DPPH radicals was
estimated according to the Blois method [34]. A solution of
DPPH in ethanol (150 μM, 4 mL) was mixed with a solution
ofatestcompoundinethanol(250 μM, 0.2mL). Thereaction
mixture was vortex mixed thoroughly and incubated at room
temperature in the dark for 60 min. Simultaneously, a con-
trol was prepared: An solution of ascorbic acid in ethanol
(0.2 mL) was mixed with a solution of DPPH in ethanol
(4 mL). Reduction of absorbance at 540 nm was recorded
using ethanol as blank. Free radical scavenging activity was
expressed as percent of inhibition and was calculated as fol-
low:
3. Lesyk RB, Zimenkovsky BS, Kaminskyy DV, Kryshchyshyn AP,
Havrylyuk DYa, Atamanyuk DV, Subtel’na IYu, Khyluk DV (2011)
Thiazolidinone motif in anticancer drug discovery. Experience of
DH LNMU medicinal chemistry scientific group. Biopolym Cell
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