Synthesis and characterization of new thiazolidinones containing coumarin moieties and their antibacterial and antioxidant activities

Article abstract of DOI:10.3390/molecules17089321

New coumarin derivatives namely (2-(4-methyl-2-oxo-2H-chromen-7-yloxy)- N-(4-oxo-2-phenylthiazolidin-3-yl)acetamide, N-(2-(3-methoxyphenyl)-4- oxothiazolidin- 3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide, 2-(4-methyl-2-oxo-2H-chromen- 7-yloxy)-N-(

Full text of DOI:10.3390/molecules17089321

Molecules 2012, 17, 9321-9334; doi:10.3390/molecules17089321
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Characterization of New Thiazolidinones
Containing Coumarin Moieties and Their Antibacterial and
Antioxidant Activities
Naceur Hamdi 1,*, Abdullah Sulaiman Al-Ayed 1, Ridha Ben Said 1 and Alary Fabienne 2
1
College of Science and Arts at Ar-Rass, Qassim University, P.O. Box 53, Saudi Arabia
2
Laboratoire de chimie et physique quantiques, Université Paul Sabatier-Bât. 3R1b4,
118 route de Narbonne, 31062 Toulouse Cedex 09, France
* Author to whom correspondence should be addressed; E-Mail: naceur.hamdi@isste.rnu.tn;
Tel.: +966-505-142-736; Fax: +966-6333-9351.
Received: 18 June 2012; in revised form: 21 July 2012 / Accepted: 24 July 2012 /
Published: 3 August 2012
Abstract: New coumarin derivatives, namely (2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-
N-(4-oxo-2-phenylthiazolidin-3-yl)acetamide, N-(2-(3-methoxyphenyl)-4-oxothiazolidin-
3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide, 2-(4-methyl-2-oxo-2H-chromen-
7-yloxy)-N-(4-oxo-2-(2,3,4trimethoxyphenyl)thiazolidin-3-yl)acetamide and N-(2-(4-
bromophenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide)
were synthesized starting from 4-methyl-7-hydroxycoumarin. The structures of the
obtained compounds were confirmed by analytical IR and NMR spectra to elucidate the
different positions of protons and carbons and as well as theoretical studies (DFT/B3LYP).
The new compounds were screened for antibacterial activity. Most of them are more active
against E. coli S. aureus and B. subtilis than standard references.
Keywords: coumarin; ethyl bromoacetate; thiazolidinones; DFT studies; antibacterial
activities
1. Introduction
Small ring heterocycles containing nitrogen and sulfur have been under investigation for a long time
because of their important medicinal properties. Among the wide range of heterocycles explored to
develop pharmaceutically important molecules, thiazoles have played an important role in medicinal

Molecules 2012, 17
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chemistry. A survey of literature has shown that compounds having a thiazole nucleus possess a
broad range of biological activities such as anti-inflammatory [1], antibacterial [2] and antifungal
properties [3]. Among these type of molecules 4-thiazolidinones have shown to have various important
biological activities such as antibacterial, antifungal, antiviral, diuretic, antituberculostatic, anti-HIV,
antihistaminic, anticancer, anticonvulsant, anti-inflammatory and analgesic properties [4–11].
Recently, a study reported the synthesis, chemical and wide rang biological properties of a series
of 4-thiazolidinone molecules [12–18]. Some of these compounds showed moderate to good biological
properties. The observed interesting biological properties of this class of compounds impelled us to
synthesize new examples with possible improved biological properties with applicative possibilities.
In the current study we aimed to synthesize some new coumarins derived from umbelliferone
(7-hydroxycoumarin), with predictable biological activities. The chemical structures of the synthesized
compounds were proven by IR, NMR spectra and elemental analysis data.
2. Results and Discussion
The starting compound (7-hydroxy-2-oxo-2H-chromen-4-yl)-acetic acid methyl ester (2) was
prepared in 92% yield by esterification of 7-hydroxy-4-methylcoumarin (1). Hydrazinolysis of 2
with 86% hydrazine hydrate in ethanol at reflux for 4 h afforded hydrazide 3 in good yield. The FT-IR
spectra of carbohydrazide 3 showed absorption bands at 3317 cm−1, possibly due to the hydrazide
NH-NH2, 3269 cm−1 (aromatic CH), 1711 cm−1 (-C=O carbonyl stretching) and in the range
1
1621–1640 cm−1 (-CO-NH-NH2 groups). The H-NMR spectrum exhibited a singlet due to
the -CO-NH-NH2 proton at δ 4.34 ppm. Methylene protons (–OCH2) resonate as singlets at 4.94 ppm.
Refluxing 3 and aromatic aldehydes with a catalytic amount of glacial acetic acid in absolute
ethanol for 4 h afforded the new series of coumarin N′-benzylidene-2-(4-methyl-2-oxo-2H-chromen-7-
yloxy) acetohydrazide Schiff bases 4a–d. The structures of compounds 4a–d were inferred from their
analytical and spectroscopic properties. Thus the IR spectrum of compound 4a showed characteristic
bands in the range 1610 cm–1 (CONH), at 1681 cm–1 (C=O, lactone), and at 1258 cm–1 (-HC=N-
1
azomethine). The H-NMR spectrum did not only show the absence of NH2 protons at 3.38, but also
the presence of the N=CH proton at 8.24 ppm.
N-(2-aryl-4-oxo-thiazolidin-3-yl)-2-(4-(2-aryl-4-oxo-thiazolidin-3-ylcarbamoyl)-methyl)-2-oxo-2H-
chromen-7-yloxy)-acetamides 5a–d were obtained by reaction of the compounds 4a–d with
thioglycolic acid in refluxing 1,4-dioxane for 6–8 h in the presence of anhydrous ZnCl2 (Scheme 1).
The IR spectrum of 5b showed a characteristic band at 1728 cm−1 that supports the presence in the
1
molecule of a thiazolidinone C=O group. The H-NMR spectrum of 5b displayed signals between
7.30–7.60 δ ppm for aromatic protons and a doublet at 4.84 ppm ascribable to the thiazolidinones CH2
protons. The proposed 5a–d structures were evaluated by using a DFT/B3LYP approach implemented
in the Gaussian 09 series programs [19]. The B3LYP hybrid functional has been used in describing
potential energy surfaces (PES). The geometries of the compounds were fully optimized using analytic
gradients. The harmonic vibrational frequencies of the stationary points of the PES have been
calculated at the same level of theory in order to identify the local minima as well as to estimate the
corresponding zero point vibrational energy (ZPE) [20]. For each atom no pseudopotential are used. A

Molecules 2012, 17
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Def2-SVP EMSL Basis Set Exchange was employed for each atom [21]. Values of selected
geometrical parameters are listed in Table 1 and optimized geometry for 5a is depicted in Figure 1.
Scheme 1. Synthesis of 2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-arylthiazolidin-
3-yl) acetamide 5.
CH3
CH3
O
K2CO3,
O
+
Br
O
O
O
acetone
reflux 12h
HO
O
O
O
O
2
1
N2H2, Ethanol
reflux 4h
CH3
CH3
Ar
H
5
4
10
9
3
2
6
11
13
O
HN
N
12
O
HN
H2N
7
O
O
1
O
O
O
O
8
Ar
Ethanol
O
reflux 4h
3
4
thioglycolic acid
ZnCl2
1,4 Dioxane
reflux 4h
CH3
5
Ar
4
10
3
6
13
S
11
2
HN
N
12
O
15
7
9
O
O
1
O
14
8
O
5
Compounds 5
Ar
C6H5
p-OCH3 C6H4
2,3,4 OCH3 C6H2
p-Br C6H4
Yield
40
76
52
72
5a
5b
5c
5d

Molecules 2012, 17
Table 1. DFT/B3LYP optimized geometrical parameters a for 5a–d.
9324
Compounds
5a
5b
5c
5d
1-2
1-12
1-5
2-3
3-4
4-5
5-6
12-13
13-14
14-15
15-7′
1′-2′
1′-9′
2′-3′
3′-4′
4′-10′
1,385
1.374
1.463
1.520
1.829
1.863
1.510
1.394
1,530
1.401
1.352
1.396
1.354
1.457
1.362
1.454
1.105
1.020
1.107
111.1
107.8
92.9
1.384
1.374
1.465
1.521
1.829
1.864
1.506
1.393
1.530
1.401
1.352
1.396
1.354
1.457
1.362
1.454
1.106
1.020
1.108
111.0
107.8
92.8
1.383
1.372
1.462
1.520
1.826
1.866
1.509
1.389
1.531
1.402
1.352
1.396
1.354
1.457
1.362
1.454
1.101
1.020
1.108
110.7
107.6
93.0
1.386
1.374
1.462
1.520
1.829
1.863
1.510
1.394
1.529
1.401
1.353
1.397
1.354
1.457
1.362
1.454
1.105
1.020
1.108
111.1
107.8
92.9
5-H5
12-H12
14-H14
1-2-3
2-3-4
3-4-5
4-5-1
1-5-6
103.4
115.5
109.5
118.1
114.9
119,0
111.9
108.3
115.4
123.3
118.6
118.0
6.1
−15.4
19.9
−12.6
144.3
−136.1
1.0
103.2
115.6
109.5
118.2
114.9
118.9
111.9
108.3
115.4
123.3
118.6
118.0
7.5
−17.0
21.1
−11.8
145.8
−135.1
1.1
103.4
115.6
108.4
119.5
114.7
121.2
111.2
108.9
115.4
123.3
118.5
117.9
−13.9
18.6
−17.9
−0.7
109.4
−122.1
−0.9
109.1
−161.7
−177.7
103.5
115.5
109.6
118.1
114.8
119.0
112.0
108.4
115.4
123.3
118.5
118.0
6.5
1-5-H5
2-1-12
1-12-H12
1-12-13
12-13-14
13-14-15
1′-2′-3′
2′-3′-4′
3′-4′-10′
4′-10′-9′
1-2-3-4
2-3-4-5
3-4-5-1
H5-5-6-11
3-4-5-6
1-5-6-7
2-3-5-12
2-5-7′-6′
12-13-14-15
13-14-15-7′
−15.8
20.0
−12.8
144.5
−136.4
−11.6
118.2
−155.2
−174.9
113.0
−158.1
−175.5
114.1
−157.1
−174.8

Molecules 2012, 17
9325
Table 1. Cont.
Compounds
5a
5b
5c
5d
14-15-7′-6′
7′-8′-9′-10′
10′-9′-1′-2′
1′-2′-3′-4′
178.5
0.0
0.0
178.2
0.0
0.1
176.8
0.4
0.0
179.2
0.1
0.0
0.1
0.2
0.6
0.1
a Distances are in A˚ and angles in degrees.
Optimized geometry for
.
5a
Figure 1.
Some conclusions can be extracted from the results obtained. The calculated values for length and
angles are similar for compounds 5a–d. This fact suggests that the R group has no influence on
interatomic distances and angles. Additionally the dihedral angles 1-2-3-4, 2-3-4-5 and 3-4-5-1
indicate that the thiazolidinone ring in the compounds is not in a plane and that fact is not dependent
on the R group. The plane constituted by the thia-ring is perpendicular to that of the coumarin group
(for exemple the angle 2-5-6′-7′ = 113.0 in 5a). It is important to point out that the 5c thia-ring displays
a different orientation that those for the other calculated compounds. Important information on the
chemical groups present in compounds 5a–d can be obtained from their calculated vibrational spectra.
As example, intensities and their harmonic wave numbers calculated with the method DFT/B3LYP
and the corresponding experimental values of the compound 5c are grouped in Table 2.
Table 2. Theoretical and experimental vibrational frequencies (cm−1) and theoretical
infrared intensities (km mol−1) of 5c.
Experimental
Theoretical
Functional group
CO thiaz.
Frequencies
Intensities
strong
strong very
mean
Frequencies
Intensities
328
1666
1682
1712
3313
1831
1862
1871
3513
CO lactone
CO amide
NH
652
130
23
weak
The values of the theoretical IR frequencies are in agreement with the experimental ones. The
largest shifting is less than 10% that could be due to the approximations used in the DFT/B3LYP
method; consequently the proposed structures were supported by theoretical calculations.

Molecules 2012, 17
9326
The NBO analysis allows the determination of the atomic natural charges. Table 3 reports the
natural charges of the acid protons in compound 5c calculated at DFT/B3LYP level of theory. We find
that proton H12 carried by the nitrogen was the most acidic.
NBO charge of the acidic protons of the compound
calculated at the
5c
Table 3.
DFT/B3LYP level of theory.
Hi
H3
Charge
0.25
H5
0.22
H12
H14
0.39
0.22
2.1. Antioxidant Activities
The imbalance between reactive oxygen species (ROS) and antioxidant defence mechanisms leads
to oxidative modification in cellular membrane or intracellular molecules. Phytochemicals like
phenolics, commonly found in plants, could constitute strong natural antioxidants and could play an
important role in health care system.
The effect of the different synthetic compounds on DPPH radical scavenging was compared to
those of Trolox, using as positive control, and appreciated by the determination of the IC50 values. The
results are shown in Figure 2 and listed in Table 4.
Figure 2. Scavenging effect on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical of compound 5.
Table 4. Values of IC50 exhibited by coumarinic derivatives 5a–d.
Compounds 5
IC50 (10−9 mol/L)
5a
5b
5c
92.60
82.00
8.62
5d
9.43
Trolox
7.35

Molecules 2012, 17
9327
As shown in Figure 2, DPPH test revealed that increase in compounds concentration resulted in
increase in free radical-scavenging activity in a dose dependent manner. Based on the IC50 values, the
most active compound is 5c.
2.2. ABTS Radical Cation Decolourization Assay
As shown for DPPH scavenging, the obtained results indicate the higher capacity of 5a–d to quench
ABTS as compared to the synthetic antioxidant Trolox (Figure 3 and Table 5).
Scavenging ability on ABTS radical of compounds .
Figure 3.
5
Table 5. Values of IC50 exhibited by coumarinic derivatives 5a–d.
Compounds 5
IC50 (10−9 mol/L)
5a
5b
5c
92.60
82.00
8.62
5d
9.43
Trolox
7.35
2.3. Antibacterial Activity
The antibacterial activity of the tested compounds against a series of bacteria and fungi is shown in
Table 6.
Table 6. Antibacterial activity against bacteria of 5a–d, inhibition zone expressed in mm.
Compounds
Standard-drug
Organism
ampicillin
5a
19
20
17
18
5b
19
20
17
18
5c
19
20
17
18
5d
19
20
17
18
E. coli ATCC1225
P. vulgaris
B. megaterium
16
22
23
25
S. aureus ATCC2353

Molecules 2012, 17
9328
All the compounds 5 displayed maximum activity against P. vulgaris. The compound 5b is highly
active against E. coli. The compounds 5b and 5d also showed very good activity against
B. megaterium, while compounds 5a and 5c showed good activity against S. aureus.
Our results also showed that the purified compounds had great potential for antibacterial activity
against a panel of microorganisms. There is evidence in the literature that Gram-positive bacteria are
more sensitive to plant extracts and essential oil than Gram-negative bacteria [22]. On the basis of
inhibition zone diameters values P. vulgaris was more sensitive to the purified compounds than the
other Gram positive bacteria. The observed differences in the inhibition zones within pathogenic
bacteria could be probably due to cell membrane permeability or other genetic factors.
3. Experimental
3.1. General
All reagents were obtained from commercial sources. Solvents were either commercially obtained
as analytical grade or freshly distilled prior to use. Analytical thin layer chromatography was carried
out on precoated silica gel 60F254 plates using either UV absorption or iodine staining for visualization.
Column chromatography was carried out using 100–200 mesh silica gel. 1H-NMR and 13C{1H}-NMR
spectra were recorded on a Bruker DRX 300 MHz instrument (300/75 MHz); chemical shift values are
reported relative to tetramethylsilane as internal standard. The IR spectra were recorded on a Thermo
Mattson IR300 and Nicolet 510 PET spectrometers. Elemental microanalysis was carried out using a
model 5500-Carlo Erba C.H.N.S.O elemental analyzer instrument.
General procedure for the preparation of ethyl 2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetate (2).
A mixture of 7-hydroxy-4-methylcoumarin (5.6 mmol), anhydrous potassium carbonate (5.6 mmol)
and ethyl bromoacetate (5.6 mmol) in dry acetone (10 mL) was refluxed with continuous stirring for
12 h. After filtration, the solution was concentrated under reduced pressure, vacuum dried and the
solid product was recrystallized from ethanol. m.p. 185–186 °C, yield 92%; IR: νmax CO lactone:
1,714 cm−1, NH: 3,435 cm−1, CO (ketone): 1,606 cm−1; 1H-NMR: δ 7.76 (d, JH5.6 = 14.6 Hz, 1H, H-5),
7.04 (d, JH5.6 = 14.6 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 4.92 (s, 2H, -OCH2), 4.19 (q,
JH2-H3 = 10.6 Hz, 2H, CH2, -CH2CH3), 4.02 (s, 2H, CH2), 1.22 (t, JH2-H3 = 10.6 Hz, 3H, CH3,
13
-CH2CH3); C{1H}- NMR: δ 14.2 (CH2CH3), 34.8 (CH2CO), 61.3 (CH2CH3), 65.5 (COCH2O), 109.6
(C-8), 112.8 (C-6), 113.8 (C-3), 114.8 (C-10), 128.3 (C-5), 151.2 (C-9), 155.2 (C-4), 160.3 (C-7), 160.9
(C-2), 168.9 (CO-O), 169.3 (C-CO-C). Found, %: C, 64.12; H, 5.2; O, 30.40. C14H14O5. Calculated, %: C,
64.12; H, 5.38; O, 30.50.
2-(4-Methyl-2-oxo-2H-chromen-7-yloxy)acetohydrazide (3). To a solution of ethanol (15 mL) and
hydrazine hydrate (10 mmol), ethyl 2-(4-methyl-2-oxo-2H-chromen-7-yloxy) acetate (2, 10 mmol)
was added, and the mixture was refluxed for 4 h. The product precipitated and was collected by suction
filtration, washed with methanol and recrystallized from dil. Acetic acid. m.p. = 300 °C, yield 70%; IR:
1
νmax CO lactone: 1,681 cm−1, CONH (amide): 1,612 cm−1, CN: 1,271 cm−1; H-NMR: δ 9.41 (s, 1H,
NH), 7.76 (d, JH5.6 = 14.6 Hz, 1H, H-5), 7.04 (d, JH5.6 = 14.6 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s,
13
1H, H-3), 4.94 (s, 2H, -OCH2), 4.34 (s, 2H, NH2). C{1H}-NMR: δ 45.8 (CH2), 68.9 (CH2O-), 108.0

Molecules 2012, 17
9329
(C-8), 111.8 (C-6), 112.9 (C-3), 114.1 (C-10), 128.3 (C-5), 152.2 (C-9), 155.2 (C-4), 160.4 (C-7),
160.9 (C-2), 166.8 (COCH2O), 169.6 (COCH2). Found, %: C, 58.1; H, 4.82; N, 11.1; O, 25.70
C12H12O4N2. Calculated, %: C, 58.06; H, 4.87; N, 11.29; O, 25.78.
General procedure for the preparation of N′-benzylidene-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)
acetohydrazide (4). A mixture of 2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetohydrazide (3, 3.06 g,
0.01 mol) and appropriate aromatic aldehyde (Ar/a-d, 0.01 mol) was refluxed in absolute ethanol (30
mL) in the presence of a catalytic amount of glacial acetic for 4 h. The reaction mixture was cooled;
the solid separated was filtered and recrystallized from methanol to give compounds 4a–d.
N'-Benzylidene-2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide (4a). m.p. 268–269 °C; yield
1
74%; IR: νmax CO lactone: 1681 cm−1, CONH (amide): 1610 cm−1, C=N: 1258 cm−1; H-NMR: δ 8.30
(s, 1H, HC=N-), 8.02 (s, 1H, NH), 7.76 (d, JH5.6 = 15.6 Hz, 1H, H-5), 7.72–7.31 (m, 10H, arom.), 7.04
13
(d, JH5.6 = 15.6 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 4.83 (s, 2H, -OCH2), C{1H}-
NMR: δ 45.7 (CH2), 69.2 (CH2O-), 108.1 (C-8), 111.6 (C-6), 112.5 (C-3), 114.4 (C-10), 127.9 (C-5),
128.4 (C-3,5, Ar-), 129.0 (C-2,6, Ar-), 131.4 (C-4, Ar-), 133.9 (C-1, Ar-), 143.6 (N=CH-), 151.8 (C-9),
155.2 (C-4), 160.4 (C-7), 160.9 (C-2), 166.9 (COCH2O), 170.0 (CONH-). Found, %: C, 67.75; H, 4.8;
N, 8.2; O, 19.1. C19H16O4N2. Calculated, %: C, 67.85; H, 4.79; N, 8.33; O, 19.03.
N′-(3-Methoxybenzylidene)-2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide
(4b).
m.p.
225–226 °C, yield (76%); IR: νmax CO lactone:1,681 cm−1,CONH (amide): 1,614 cm−1, C=N:
1
1,255 cm−1; H-NMR: δ 8.73 (s, 1H, -HC=N-), 8.45 (s, 1H, NH), 7.72 (d, JH5.6 = 15.5 Hz, 1H, H-5),
7.60–7.30 (m, 8H, arom.), 3.65 (s, 3H,OCH3) ,7.04 (d, JH5.6 = 15.4 Hz ,1H, H-6), 7.02 (s, 1H, H-8),
13
6.34 (s, 1H, H-3), 4.84 (s, 2H, -OCH2), C{1H} NMR: δ 45.6 (CH2), 68.9 (CH2O-), 107.8 (C-8),
111.5(C-6), 112.7 (C-3), 113.9 (C-10), 127.8 (C-5), 129.4 (C-3, Ar-), 130.6 (C-6, Ar-), 132.7 (C-4,
Ar-),133.8 (C-1, Ar-), 134.3 (C-2, Ar-), 143.5 (N=CH-), 151.7 (C-9), 155.0 (C-4), 160.3 (C-7), 160.9
(C-2),166.4 (COCH2O), 169.9 (CONH-). Found, %: C, 65.5; H, 4.80; N, 7.6; O, 21.8. C20H18O5N2.
Calculated, %: C, 65.57; H, 4.95; N, 7.65; O, 21.84.
N′-(2.3.4-Trimethoxybenzylidene)-2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide (4c). m.p.
259–261 °C, yield 72%; IR: νmax CO lactone: 1,681 cm−1, CONH (amide): ,1618 cm−1, C=N: 1,281 cm−1.
1H-NMR: δ 8.31 (s, 1H, -HC=N-), 7.76 (d, JH5.6 = 15.5Hz, 1H, H-5), 7.67–7.30 (m, 8H, arom.), 7.04
(d, JH5.6 = 15.6 Hz ,1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 3.78 (s, 9H, 2,3,4 OCH3), 4.84
13
(s,2H, -OCH2), C{1H}-NMR: δ 45.5 (CH2), 69.1 (CH2O-), 107.9 (C-8), 111.4 (C-6),112.5 (C-3),
113.4 (C-10), 127.3 (C-6, Ar-), 127.9 (C-5), 129.3 (C-2, Ar-), 130.3 (C-5, Ar-), 131.2 (C- 4, Ar-),
135.2 (C-1, Ar-), 134.4 (C-3, Ar-), 143.4 (N=CH-), 151.6 (C-9), 155.2 (C-4), 160.6 (C-7), 160.9 (C-2),
166.7 (COCH2O), 169.8 (CONH-). Found, %: C, 61.9; H, 5.1; N, 6.5; O, 26.3. C22H22O7N2.
Calculated, %: C, 61.97; H, 5.20; N, 6.57; O, 26.26.
N′-(4-Bromobenzylidene)-2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide
(4d).
m.p.
273–275 °C, yield 52%; IR: νmax CO lactone: 1,681 cm−1, CONH (amide): 1,612 cm−1, 1H-NMR: 8.30
(s, 1H, -HC=N-), 8.23 (s, 1H, NH), 7.76 (d, JH5.6 = 15.5 Hz, 1H, H-5), 7.61–7.30 (m, 6H, arom.), 7.04
13
(d, JH5.6 = 15.5 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 4.82 (s, 2H, -OCH2), C{1H}-

Molecules 2012, 17
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NMR: δ 45.6 (CH2), 69.2 (CH2O-), 103.8 (C-3, Ar-), 107.6 (C-8), 108.7 (C-5, Ar-),111.3 (C-6), 112.7
(C-3), 113.4 (C-10), 127.2 (C-6, Ar-), 127.9 (C-5), 135.2 (C-1, Ar-), 143.0 (N=CH-), 151.2 (C-9),
155.1 (C-4), 160.5 (C-7), 160.9 (C-2), 162.4 (C-2, Ar-), 162.6 (C-4, Ar-), 166.5 (COCH2O), 169.4
(CONH-). Found, %: C, 54.8; H, 3.6; Br, 19.1; N, 6.7; O, 15.4. C19H15O4N2. Calculated, %: C, 54.96;
H, 3.64; Br, 19.24; N, 6.75; O, 15.41.
General procedure for the preparation of 2-(4-methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2
arylthiazolidin-3-yl) acetamide (5). A mixture of N′-benzylidene-2-(4-methyl-2-oxo-2H-chromen-7-
yloxy) acetohydrazide (4, 0.01 mol) and mercaptoacetic acid (1.82 g, 0.02 mol) in 1,4-dioxane (30 mL)
containing a pinch of anhydrous ZnCl2 was refluxed for 6–8 h. The reaction mixture was cooled and
poured onto crushed ice. The solid thus obtained was filtered, washed with water and recrystallized
from DMF yielding 5a–d.
2-(4-Methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-phenylthiazolidin-3-yl)acetamide (5a). m.p.
202–204 °C, yield 40%; IR: νmax CO lactone: 1,681 cm−1, CONH (amide): 1,615 cm−1; 1H-NMR: 2.15
(s, 3H), 8.12 (s, 1H, -NH), 7.76 (d, JH5.6 = 10.6 Hz, 1H, H-5), 7.71–7.23 (m, 10H, arom.), 7.04 (d,
JH5.6 = 10.6 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 5.92 (s, 1H, -SCHN-), 4.83 (s,
13
2H, -OCH2), 3.38 (s, 2H, COCH2S-); C{1H}-NMR: δ 35.8 (COCH2S), 45.5 (CH2), 57.4 (NCHS),
69.1 (CH2O-) 107.6 (C-8), 111.0 (C-6), 112.5 (C-3), 113.4 (C-10), 127.2 (C-4, Ar-), 127.8 (C-5), 128.7
(C-3,5, Ar-),128.8 (C-2,6 Ar-), 139.2 (C-1, Ar-), 151.2 (C-9), 155.0 (C-4), 160.3 (C-7), 160.9 (C-2),
166.4 (COCH2O), 168.8 (SCH2CO-N), 173.3 (CONH-). Found, %: C, 61.3; H, 4.4; N, 6.8; O, 19.5; S,
7.7. C21H18O5N2S. Calculated, %: C, 61.45; H, 4.42; N, 6.83; O, 19.49; S, 7.81.
N-(2-(3-Methoxyphenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide
(5b).
m.p. 184 °C, yield 76%; IR: νmax CO lactone: 1,681 cm−1, CONH (amide): 1,614 cm−1; 1H-NMR: 8.62
(s, 1H, NH-), 2.20 (s, 3H), 7.76 (d, JH5.6 = 10.5 Hz, 1H, H-5), 7.60–7.30 (m, 8H, arom.), 3.67 (s, 3H,
OCH3), 7.04 (d, JH5.6 = 10.5 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 5.92 (s, 1H, NCHS),
13
4.84 (s, 2H, -OCH2), 3.38 (s, 2H, COCH2S); C{1H}-NMR: δ 35.7 (COCH2S), 45.5 (CH2), 57.4
(NCHS), 69.10 (CH2O-), 107.6 (C-8), 111.0 (C-6), 112.5 (C-3), 113.4 (C-10), 127.0 (C-5), 129.0 (C-3,
Ar-), 130.6 (C-6, Ar-), 132.5 (C-4, Ar-), 133.4 (C-1, Ar-), 134.0 (C-2, Ar-), 143.0 (N=CH-), 151.2
(C-9), 155.0 (C-4), 160.3 (C-7), 160.9 (C-2), 166.4 (COCH2O), 173.0 (CONH-). Found, %: C, 59.9; H,
4.5; N, 6.4; O, 21.8; S, 7.2. C22H20O6N2S. Calculated, %: C, 59.99; H, 4.58; N, 6.36; O, 21.79; S, 7.28.
2-(4-Methyl-2-oxo-2H-chromen-7-yloxy)-N-(4-oxo-2-(2,3,4-trimethoxyphenyl)thiazolidin-3-yl)acetamide
(5c). m.p. 239–241 °C, yield 52%; IR: νmax 1,712 (C=O, lactone), 1,624 (C=O, amide) cm−1; 1H-NMR:
2.12 (s, 3H), 8.30 (s, 1H, NH-), 7.76 (d, JH5.6 = 10.4 Hz, 1H, H-5), 7.61–7.30 (m, 6H, arom.), 7.04
(d, JH5.6 = 10.4 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 5.92 (s, 1H, NCHS), 4.82
(s, 2H, -OCH2), 3.75 (s, 9H, 2,3,4 OCH3), 4.28 (s, 2H, CH2), 3.38 (s, 2H,COCH2S); 13C{1H}-NMR: δ
35.7 (COCH2S), 45.5 (CH2), 47.4 (NCHS), 69.10 (CH2O-), 103.7 (C-3, Ar-), 107.6 (C-8), 108.4 (C-5,
Ar-), 110.1 (C-1, Ar-), 111.0 (C-6), 112.5 (C-3), 113.4 (C-10), 127.8 (C-5),131.3 (C-6, Ar-), 151.2
(C-9), 157.2 (C-2, Ar-), 158.2 (C-4), 160.3 (C-7), 160.9 (C-2), 166.4 (CONH),168.8 (NCOCH2), 173.3
(CH2CONH). Found, %: C, 57.4; H, 4.75; N, 5.7; O, 25.6; S, 6.5. C24H24O8N2S. Calculated, %: C,
57.59; H, 4.83; N, 5.60; O, 25.57; S, 6.41.

Molecules 2012, 17
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N-(2-(4-Bromophenyl)-4-oxothiazolidin-3-yl)-2-(4-methyl-2-oxo-2H-chromen-7-yloxy)acetamide (5d).
1
m.p. 240–241 °C, yield 72%; IR: νmax 1,727 (CO, lactone), 1,616 (C=O, amide) cm−1; H-NMR: 2.14
(s, 3H), 8.22 (s, 1H, NH-), 7.76 (d, JH5.6 = 10.5 Hz, 1H, H-5), 7.67–7.30 (m, 8H, arom.), 7.04 (d,
JH5.6 = 10.5 Hz, 1H, H-6), 7.02 (s, 1H, H-8), 6.34 (s, 1H, H-3), 5.92 (s, 1H, NCHS), 4.84 (s, 2H,
13
-OCH2), 3.38 (s, 2H, COCH2S); C{1H}-NMR: δ 35.7 (COCH2S), 45.5 (CH2), 57.4 (NCHS), 69.10
(CH2O-), 107.6 (C-8), 111.0 (C-6), 112.5 (C-3), 113.4 (C-10), 127.3 (C-6, Ar-), 127.8 (C-5), 129.3
(C-2, Ar-), 130.3 (C-5, Ar-), 131.2 (C-4, Ar-), 135.2 (C-1, Ar-), 134.4 (C-3, Ar-), 143.0 (N=CH-),
151.2 (C-9), 155.0 (C-4), 160.3 (C-7), 160.9 (C-2), 173.0 (COCH2O), 173.0 (CONH-). Found, %: C,
51.6; H, 3.4; Br, 16.4; N, 5.75; O, 16.4; S, 6.7. C21H17O5N2BrS. Calculated, %: C, 51.54; H, 3.50; Br,
16.33; N, 5.72; O, 16.35; S, 6.55.
3.2. DPPH Test
The DPPH test aims to measure the capacity of the compounds for scavenging the stable free
radical 2,2-diphenyl-1-picrylhydrazyl (DPPH.) by donation of hydrogen atom or an electron[23] If
the compounds have the capacity to scavenge the DPPH free radical, the initial blue/purple solution
will change to a yellow colour due to the formation of diphenylpicrylhydrazine. Scavenging capacity
was read spectrophotometrically by monitoring the decrease of the absorbance at 517 nm. Lower
absorbance of the reaction mixture indicates higher free radical scavenging activity.
The percent DPPH scavenging effect was calculated using the following equation:
DPPH scavenging effect (%) = (Acontrol − Asample/Acontrol) × 100
where Acontrol is the absorbance of the control reaction were the sample is replaced by 500 µL ethanol.
Tests were carried out in triplicate.
3.3. ABTS Radical Cation Decolourization Assay
The potential of N-(2-aryl-4-oxo-thiazolidin-3-yl)-2-(4-(2-aryl-4-oxo-thiazolidin-3-ylcarbamoyl)-
methyl)-2-oxo-2H-chromen-7-yloxy)-acetamides 5a–d to scavenge free radicals was also assessed by
checking their ability to quench ABTS. depicted by the concentration-dependent decolourization of
ABTS.. ABTS radical-scavenging activity of 5a–d was determined according to Güven et al. [24]. The
ABTS. cation radical was produced by the reaction between 5 mL of 14 mM ABTS solution and 5 mL
of 4.9 mM potassium persulfate (K2S2O8) solution, stored in the dark at room temperature for 16 h.
Before use, this solution was diluted with ethanol to get an absorbance of 0.700 ± 0.020 at 734 nm. In
a final volume of 1 mL, the reaction mixture comprised 950 µL of ABTS. solution and 50 µL of 5a–d
at various concentrations. The reaction mixture was homogenized and its absorbance was recorded at
734 nm. Ethanol blanks were run in each assay, and all measurements were done after at least 6 min.
Similarly, the reaction mixture of standard group was obtained by mixing 950 µL of ABTS. solution
and 50 µL of Trolox. As for the antiradical activity, ABTS scavenging ability was expressed as
IC50 (µg/mL). The inhibition percentage of ABTS radical was calculated using the following formula:
ABTS scavenging effect % = {[(A0 − A1)]/A0} × 100%

Molecules 2012, 17
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where A0 is the absorbance of the control at 30 min, and A1 is the absorbance of the sample at 30 min.
All samples were analyzed in triplicate.
3.4. Antibacterial Activity
Antimicrobial activity of the purified compounds was evaluated by means of agar-well diffusion
assay according to Güven et al. [25] with some modifications. The nutrient agar broth prepared by the
usual method, was inoculated aseptically with 0.5 mL of 24 h old subculture of S. aureus ATCC 2353,
B. megaterium, P. vulgaris, and E. coli ATCC1225 in separate conical flasks at 40–50 °C and mixed
well by gentle shaking. About 25 mL of the contents of the flask were poured and evenly spread in
petridish (90 mm in diameter) and allowed to set for two h. The cups (10 mm in diameter) were
formed by the help of borer in agar medium and filled with 0.04 mL (40 μg/mL) solution of sample in
DMF. The plates were incubated at 37 °C for 24 h and the control was also maintained with 0.04 mL
of DMF in similar manner and the zones of inhibition of the bacterial growth were measured
in millimetre
4. Conclusions
A series of new coumarin-based thiazolidinone compounds were successfully synthesized,
characterized and tested for their antibacterial and antioxidant activities. Most of the synthesized
compounds are more active against E. coli and S. aureus than standard references. Some of the
compounds were found equipotent to ampicillin, but less active than other used standard drugs
Acknowledgements
This work was carried out with financial aid of the Qassim University in KSA through project
No. 1303.
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Sample Availability: Samples of the compounds 2–5 are available from the authors.
© 2012 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article
distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).