Synthesis and Antimicrobial Activity of a New Series of Thiazolidine-2,4-diones Carboxamide and Amino Acid Derivatives

Abstract

Novel thiazolidine-2,4-dione carboxamide and amino acid derivatives were synthesized in excellent yield using OxymaPure/N,N′-diisopropylcarbodimide coupling methodology and were characterized by chromatographic and spectrometric methods, and elemental analysis. The antimicrobial and antifungal activity of these derivatives was evaluated against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), two-Gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa), and one fungal isolate (Candida albicans). Interestingly, several samples demonstrated weak to moderate antibacterial activity against Gram-negative bacteria, as well as antifungal activity. However, only one compound namely, 2-(5-(3-methoxybenzylidene)-2,4-dioxothiazolidin-3-yl)acetic acid, showed antibacterial activity against Gram-positive bacteria, particularly S. aureus.

Full text

molecules
Article
Synthesis and Antimicrobial Activity of a New Series
of Thiazolidine-2,4-diones Carboxamide and Amino
Acid Derivatives
Rakia Abd Alhameed 1, Zainab Almarhoon 1, Sarah I. Bukhari 2, Ayman El-Faham 1,3,* ,
Beatriz G. de la Torre 4,5 and Fernando Albericio 1,5,6,*
1Department of Chemistry, College of Science, King Saud University, P.O. Box 2455,
Riyadh 11451, Saudi Arabia; Roki.ahmed@yahoo.com (R.A.A.); zalmarhoon@ksu.edu.sa (Z.A.)
2Department of Pharmaceutics, College of Pharmacy, King Saud University, P.O. Box 4584,
Riyadh 11451, Saudi Arabia; sbukhari@ksu.edu.sa
3Chemistry Department, Faculty of Science, Alexandria University, P.O. Box 426, Ibrahimia,
Alexandria 12321, Egypt
4
KwaZulu-Natal Research Innovation and Sequencing Platform (KRISP), School of Laboratory Medicine and
Medical Sciences, College of Health Sciences, University of KwaZulu-Natal, Durban 4041, South Africa;
garciadelatorreb@ukzn.ac.za
5Peptide Science Laboratory, School of Chemistry and Physics, University of KwaZulu-Natal,
Durban 4001, South Africa
6CIBER-BBN, Networking Centre on Bioengineering, Biomaterials and Nanomedicine, and Department of
Organic Chemistry, University of Barcelona, Martíi Franqués 1-11, 08028 Barcelona, Spain
*Correspondence: aelfaham@ksu.edu.sa or aymanel_faham@hotmail.com (A.E.-F.); albericio@ukzn.ac.za or
albericio@ub.edu (F.A.); Tel.: +966-114-673-195 (A.E.-F.); +27-614-009-144 (F.A.)
Received: 5 December 2019; Accepted: 25 December 2019; Published: 27 December 2019


Abstract:
Novel thiazolidine-2,4-dione carboxamide and amino acid derivatives were synthesized
in excellent yield using OxymaPure/N,N
0
-diisopropylcarbodimide coupling methodology and
were characterized by chromatographic and spectrometric methods, and elemental analysis.
The antimicrobial and antifungal activity of these derivatives was evaluated against two
Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), two-Gram negative bacteria
(Escherichia coli and Pseudomonas aeruginosa), and one fungal isolate (Candida albicans).
Interestingly, several samples demonstrated weak to moderate antibacterial activity against
Gram-negative bacteria, as well as antifungal activity. However, only one compound namely,
2-(5-(3-methoxybenzylidene)-2,4-dioxothiazolidin-3-yl)acetic acid, showed antibacterial activity
against Gram-positive bacteria, particularly S. aureus.
Keywords:
OxymaPure; thiazolidine-2,4-dione carboxamide; thiazolidine-2,4-dione amino acid ester;
antibacterial activity
1. Introduction
The underlying goal for research into medicinal chemistry is to discover new products with
greater biological activity, achieving a low number of by-products during the synthesis and low
toxicity of both the intermediates and the final products. Accordingly, considerable attention has
been devoted to thiazolidinedione derivatives (TZDs), both from a synthetic point of view and
biological applications [
1
–
6
]. In this regard, TZDs have been used as the following: antibacterial and
antifungal agents [
7
–
12
]; anti-inflammatory drugs [
13
–
16
]; aldose reductase inhibitors [
17
,
18
]; and
anticancer [
19
–
25
], antiplasmodial inhibitors [
26
], and antidiabetic agents [
27
–
32
]. Consequently, TZDs
Molecules 2020,25, 105; doi:10.3390/molecules25010105 www.mdpi.com/journal/molecules

Molecules 2020,25, 105 2 of 17
have become a pharmacologically important group of heterocyclic compounds and the object of great
interest as precursors of novel drugs.
A survey of the literature reveals that the inclusion of the substituted aromatic ring at the ortho
position, as well as substituents at the meta position, is required to enhance the biological activity of
compounds [
33
,
34
]. Regarding the thiazolidinedione ring, substitution at the third position confers
antimicrobial properties, especially when chloro, bromo, hydroxyl, and nitro groups are attached to the
aromatic moiety [
34
]. Here we prepared a new series of thiazolidine-2,4-dione carboxamide and amino
acid derivatives and characterized their antibacterial activity against Gram-positive, Gram-negative
bacteria and fungal as well.
2. Results and Discussion
2.1. Chemistry
2-(5-Arylidene-2,4-dioxothiazolidine-3-yl)acetic acids
3a
–
g
were synthesized as outlined in
Scheme 1, where TZD
1
was prepared following the reported strategy [
35
] with minor modifications.
TZD solution was treated with various appropriate aldehydes via refluxing in ethanol for 24 h in
the presence of piperidine as a catalyst to afford compounds
2a
–
g
. Furthermore, reaction of
2a
–
g
with ethyl 2-bromoacetate in acetone in the presence of potassium carbonate as a base, followed by
acidic hydrolysis using acetic acid-HCl, furnished target acid derivatives
3a
–
g
. Some spectral data are
reported in [7,13,15] and other spectra are given in the Supplementary Materials.
Molecules 2020, 25, x FOR PEER REVIEW 3 of 17
Scheme 1. Synthesis of 2,4-dioxothiazolidine-carboxamide and amino acid derivatives derivatives.
Reaction of 3a–g was performed with amino acid esters hydrochloride using OxymaPure/DIC
as a coupling agent in the presence of 1 equiv. DIEA as a base to afford 5a–o as shown in Scheme 1.
All the derivatives prepared were characterized by FT-IR, 1H-NMR, 13C-NMR techniques and
elemental analysis.
The 1H-NMR spectrum of 5g (Figure 2) as a prototype for the 5a–o series showed a singlet peak
at δ 0.84 ppm, which integrated six protons for 2CH3 (valine residue), and one broad singlet peak at
δ 2.00, which integrated one proton for CH(CH3)2 (valine residue), singlet at δ 3.61 represents 3H for
OCH3 and two singlet peaks appeared at δ 4.18 and 4.34, related to NHCHCO (valine residue) and
NCH2CO, Ha), respectively. Multiple peaks belonging to five aromatic protons appeared at δ 7.51–
7.60, while the CH=C-S (Hb) and NH protons appeared at δ 7.92 and 8.64 ppm, respectively.
Figure 2. Structure of compound 5g.
The 13C-NMR spectrum of 5g displayed six peaks at δ 121.4, 129.8, 130.6, 131.2, 133.3, and 133.8
related to the aromatic carbons, in addition to four peaks at δ 165.6, 165.8, 167.4, 172.1 corresponding
to four (CO), and also six peaks at δ 18.5, 19.3, 30.6, 43.6, 52.2 and 58.0, attributed to three carbons,
(CH(CH3)2), (NCH2CO), (COOCH3), and (CH CO), respectively.
Scheme 1. Synthesis of 2,4-dioxothiazolidine-carboxamide and amino acid derivatives derivatives.

Molecules 2020,25, 105 3 of 17
The acid derivatives
3a
–
g
were reacted with different amines in DMF and in the presence of ethyl
(hydroxyimino)cyanoacetate [OxymaPure] and N,N
0
-diisopropylcarbodiimide (DIC) as a coupling
cocktail [
36
,
37
] to give the carboxamide derivatives
4a
–
s
in >90% yield (Scheme 1). All the prepared
derivatives were characterized by FT-IR, 1H, 13C-NMR techniques and elemental analysis.
It could be envisaged a synthetic scheme based first on the alkylation of the NH of the thiazolidine,
followed by the amidation, and finally the condensation with the aldehyde as previously described
for different thiazolidine based derivatives [
38
]. However, the strategy chosen herein facilitates
excellent yields for all reactions due presumably to the solubility of all the intermediates in the
corresponding solvents.
The
1
H-NMR spectrum of
4b
as a prototype for the
4a
–
s
series (Figure 1) showed two singlet
peaks at
δ
3.80 and 4.49 integrated for the hydrogens of the methoxy group and the methylene
group H
a
, respectively. In addition, multiple peaks at
δ
7.07–7.53 represented nine aromatic protons,
while the better to numbering it in the figure CH=C=S (H
b
) and NH proton appeared at
δ
7.95 and
10.38 ppm, respectively.
Molecules 2020, 25, x FOR PEER REVIEW 2 of 17
A survey of the literature reveals that the inclusion of the substituted aromatic ring at the ortho
position, as well as substituents at the meta position, is required to enhance the biological activity of
compounds [33,34]. Regarding the thiazolidinedione ring, substitution at the third position confers
antimicrobial properties, especially when chloro, bromo, hydroxyl, and nitro groups are attached to
the aromatic moiety [34]. Here we prepared a new series of thiazolidine-2,4-dione carboxamide and
amino acid derivatives and characterized their antibacterial activity against Gram-positive, Gram-
negative bacteria and fungal as well.
2. Results and Discussion
2.1. Chemistry
2-(5-Arylidene-2,4-dioxothiazolidine-3-yl)acetic acids 3a–g were synthesized as outlined in
Scheme 1, where TZD 1 was prepared following the reported strategy [35] with minor modifications.
TZD solution was treated with various appropriate aldehydes via refluxing in ethanol for 24 h in the
presence of piperidine as a catalyst to afford compounds 2a–g. Furthermore, reaction of 2a–g with
ethyl 2-bromoacetate in acetone in the presence of potassium carbonate as a base, followed by acidic
hydrolysis using acetic acid-HCl, furnished target acid derivatives 3a–g. Some spectral data are
reported in [7,13,15] and other spectra are given in the Supplementary Materials.
The acid derivatives 3a–g were reacted with different amines in DMF and in the presence of
ethyl (hydroxyimino)cyanoacetate [OxymaPure] and N,N′-diisopropylcarbodiimide (DIC) as a
coupling cocktail [36,37] to give the carboxamide derivatives 4a–s in >90% yield (Scheme 1). All the
prepared derivatives were characterized by FT-IR, 1H, 13C-NMR techniques and elemental analysis.
It could be envisaged a synthetic scheme based first on the alkylation of the NH of the
thiazolidine, followed by the amidation, and finally the condensation with the aldehyde as
previously described for different thiazolidine based derivatives [38]. However, the strategy chosen
herein facilitates excellent yields for all reactions due presumably to the solubility of all the
intermediates in the corresponding solvents
The 1H-NMR spectrum of 4b as a prototype for the 4a–s series (Figure 1) showed two singlet
peaks at δ 3.80 and 4.49 integrated for the hydrogens of the methoxy group and the methylene group
Ha, respectively. In addition, multiple peaks at δ 7.07–7.53 represented nine aromatic protons, while
the better to numbering it in the figure CH=C=S (Hb) and NH proton appeared at δ 7.95 and 10.38
ppm, respectively.
Figure 1. Structure of compound 4b.
The 13C-NMR spectrum of 4b showed that two peaks at δ 44.5 and 55.8 belonged to the
methylene group (CH2-CO-N-) and (OCH3), respectively, twelve aromatic carbon peaks at δ 116.0,
117.2, 119.6, 121.8, 122.4, 124.2, 129.3, 131.0, 134.2, 134.6, 138.8, and 160.1. In addition, while three
peaks appear at δ 164.2, 165.7 and 167.5, were attributed to (CO).
Figure 1. Structure of compound 4b.
The
13
C-NMR spectrum of
4b
showed that two peaks at
δ
44.5 and 55.8 belonged to the methylene
group (CH
2
-CO-N-) and (OCH
3
), respectively, twelve aromatic carbon peaks at
δ
116.0, 117.2, 119.6,
121.8, 122.4, 124.2, 129.3, 131.0, 134.2, 134.6, 138.8, and 160.1. In addition, while three peaks appear at
δ
164.2, 165.7 and 167.5, were attributed to (CO).
Reaction of
3a
–
g
was performed with amino acid esters hydrochloride using OxymaPure/DIC as
a coupling agent in the presence of 1 equiv. DIEA as a base to afford 5a–oas shown in Scheme 1.
All the derivatives prepared were characterized by FT-IR,
1
H-NMR,
13
C-NMR techniques and
elemental analysis.
The
1
H-NMR spectrum of
5g
(Figure 2) as a prototype for the
5a
–
o
series showed a singlet peak at
δ
0.84 ppm, which integrated six protons for 2CH
3
(valine residue), and one broad singlet peak at
δ
2.00, which integrated one proton for
CH
(CH
3
)
2
(valine residue), singlet at
δ
3.61 represents 3H for
OCH
3
and two singlet peaks appeared at
δ
4.18 and 4.34, related to NH
CH
CO (valine residue) and
NCH
2
CO, H
a
), respectively. Multiple peaks belonging to five aromatic protons appeared at
δ
7.51–7.60,
while the CH=C-S (Hb) and NH protons appeared at δ7.92 and 8.64 ppm, respectively.
Molecules 2020, 25, x FOR PEER REVIEW 3 of 17
Scheme 1. Synthesis of 2,4-dioxothiazolidine-carboxamide and amino acid derivatives derivatives.
Reaction of 3a–g was performed with amino acid esters hydrochloride using OxymaPure/DIC
as a coupling agent in the presence of 1 equiv. DIEA as a base to afford 5a–o as shown in Scheme 1.
All the derivatives prepared were characterized by FT-IR, 1H-NMR, 13C-NMR techniques and
elemental analysis.
The 1H-NMR spectrum of 5g (Figure 2) as a prototype for the 5a–o series showed a singlet peak
at δ 0.84 ppm, which integrated six protons for 2CH3 (valine residue), and one broad singlet peak at
δ 2.00, which integrated one proton for CH(CH3)2 (valine residue), singlet at δ 3.61 represents 3H for
OCH3 and two singlet peaks appeared at δ 4.18 and 4.34, related to NHCHCO (valine residue) and
NCH2CO, Ha), respectively. Multiple peaks belonging to five aromatic protons appeared at δ 7.51–
7.60, while the CH=C-S (Hb) and NH protons appeared at δ 7.92 and 8.64 ppm, respectively.
Figure 2. Structure of compound 5g.
The 13C-NMR spectrum of 5g displayed six peaks at δ 121.4, 129.8, 130.6, 131.2, 133.3, and 133.8
related to the aromatic carbons, in addition to four peaks at δ 165.6, 165.8, 167.4, 172.1 corresponding
to four (CO), and also six peaks at δ 18.5, 19.3, 30.6, 43.6, 52.2 and 58.0, attributed to three carbons,
(CH(CH3)2), (NCH2CO), (COOCH3), and (CH CO), respectively.
Figure 2. Structure of compound 5g.
The
13
C-NMR spectrum of
5g
displayed six peaks at
δ
121.4, 129.8, 130.6, 131.2, 133.3, and 133.8
related to the aromatic carbons, in addition to four peaks at
δ
165.6, 165.8, 167.4, 172.1 corresponding
to four (CO), and also six peaks at
δ
18.5, 19.3, 30.6, 43.6, 52.2 and 58.0, attributed to three carbons,
(CH(CH3)2), (NCH2CO), (COOCH3), and (CH CO), respectively.

Molecules 2020,25, 105 4 of 17
2.2. Biology
Using the well diffusion technique, we examined the
in vitro
antibacterial activity of the synthesized
compounds against two Gram-positive bacteria, namely Staphylococcus aureus (ATCC 29213) and
Bacillus subtilis (ATCC 10400), two Gram-negative bacteria, namely Escherichia coli (ATCC 25922) and
Pseudomonas aeruginosa ATCC 27853, and one fungal strain of Candida albicans (ATCC 10231).
Antimicrobial activity was determined by measuring the inhibition zone around each well in
mm (Table 1). Inhibition zones above 8 mm indicated that the micro-organism was susceptible to the
specific chemical compound used. Data were compared to the positive control standard antibiotic discs
of an Impenem (10
µ
g), Sulfamethzole trioxamethoprim for the bacterial isolates, and Fluconazole
for the Candida isolate. Tests were repeated three times and the average of the inhibition zone was
recorded in Table 1.
Table 1.
Antimicrobial activity (zones of inhibition, mm) compared with several standard
antimicrobial drugs.
Average Inhibition Zone in mm
Chemical Compounds S. aureus Bacillus subtilis E. coli Ps. aeruginosa C. albicans
3a 12 - 11 16 15
3b 12 - 12 11 11
3c - - - 10 -
3d - - 10 15 15
3e - - 12 13 -
3f - - - 13 -
3g 20 - 7 14 7
4a - - - 12 14
4b - - - - 12
4c - - - - 12
4d - - - 14 -
4e - - - - 13
4f - - - 11 -
4g - - - 12 14
4h - - - 13 -
4i - - - 12 -
4k - - - - 15
4l - - - - 13
4m - - - 10 -
4n - - - 11 13
4o - - - 10 -
4p - - - 12 14
4q - - - 12 12
4r - - - 14 -
4s - - 11 12 12
5a - - - - -
5b - - - - 15
5c - - - - 13
5d - - - - -
5e - - - 12 -
5f - - - - -
5g - - 10 12 15
5h - - 11 11 13
5i - - 12 12 -
5j - - - - -
5k - - 7 13 18
5l - - - - 12
5m - - - - 12
5n - - 10 - -
5o - - 11 12 16
Impenem * 30 34 20 35
SXT ** 22 20 - 30
Fluconazole - - - - -
* 10 µg; ** 23.75/1.25 µg.

Molecules 2020,25, 105 5 of 17
Table 1showed that the tested micro-organisms had variable sensitivity and susceptibility to the
chemical compounds. Indeed, the antimicrobial assay revealed that most of compounds tested had
no or negligible activity against S. aureus and B. subtilis with the exception of some acid derivatives
(
3a
,
3b
, and
3g
)
.
This observation could be explained by the difference in the cell wall structure of
Gram-positive and Gram-negative bacteria or it may be due to the charges and the kinetics of the
chemical compounds, which can damaged the bacterial cell wall via electrostatic interactions, as
previously reported by Azevedo et al. [39].
Regarding the series
3a
–
g
, the presence of methoxy and chloro groups and their positions has a
great impact on the biological activity. Whereas the methoxy group at the meta position (compound
3g
)
enhanced the activity more than the same group at the para position (compound
3f
) also chloro at the
ortho position (compound 3d) showed more activity than the same group at the para position as in 3c.
The latter showed only minor activity against Gram-negative bacteria (Ps. aeruginosa), achieving an
inhibition zone of 10 mm. The unsubstituted derivative
3a
and the derivative with chloro at the ortho
position 3d showed moderate activity against C. albicans as shown in Table 1.
The two series of 2,4-dioxothiazolidine carboxamides
4a
–
s
and 2,4-dioxothiazolidine amino acid
ester derivatives
5a
–
o
showed no activity against Gram-positive bacteria. While some derivatives
showed weak activity against Gram-negative bacteria (E. coli), compounds
4s
from the series
4a
–
s
showed weak activity, while compounds
5g
,
5h
,
5i
,
5n
and
5o
from series
5a
–
o
showed moderate
activity. Most of the compounds from series
4a
–
s
, especially derivatives with the ethyl morpholine
moiety
4m
–
s
showed activities against Gram-negative bacteria (Ps. aeruginosa), with inhibition zones
ranging from 10–14 mm (Table 1). The presence and position of the bromo in the carboxamide series
4a
–
s
had a remarkable effect on the antifungal activity, as shown in
4c
,
4k
, and
4i
(Table 1). On the other
hand, the antifungal activity increased as the number of the bromo atom increased in the molecules as
shown in
4k
vs.
4c
(15 mm vs. 12 mm, respectively). In contrast, increasing the methoxy group as in
4h
had no effect on activity against C. albicans as shown in Table 1. However, the presence of bromo
beside the methoxy group 4g showed good antifungal activity (14 mm).
For the
5a
–
o
series, utilizing glycinate, alaninate, butanoate, and phenylalaninate without
any substitution on the benzene ring
5a
,
5j
, and
5d
did not lead to microbial activity, except
5m,
which showed activity against C. albicans (12 mm). However, valinate and its derivatives
5g
–
i
did
show inhibitory activity. Glycinate derivatives
5a
–
c
showed no activity against Gram-positive or
Gram-negative bacteria. However, they exerted antifungal activity when halogen present in the
molecule
5b
and
5c
(15 mm and 13 mm
,
respectively)
.
The alaninate derivatives with halogen
substituent
5k
–
l
demonstrated activity against C. albicans, and the derivative with chloro
5k
(18 mm)
was more active than the other derivatives. In addition,
5k
showed activity (7 mm and 13 mm) against
two-Gram negative bacteria (E. coli and Ps. aeruginosa, respectively).
Butanoate derivatives
5d
–
f
showed no antimicrobial activity, except the derivative with a chlorine
atom
5e,
which showed minor activity against Ps. aeruginosa (12 mm). All valinate derivatives
5g
–
i
recorded activity against gram-negative bacteria and antifungal activity, except
5i
with a bromine
substitution, which did not exert antifungal activity.
Compound
5o
showed antimicrobial activity against E. coli, Ps. Aeruginosa and C.albicans,
respectively (10 mm, 12 mm, and 16 mm). These promising new compounds lend themselves to minor
structural modifications to enhance their activity or may find applications in other pharmaceutical fields.
3. Materials and Methods
3.1. Materials and Methods
All the starting materials, chemicals, reagents and solvents were purchased from commercial
known reputable sources and were used without further purification. TLC (silica gel 60-F254
protected aluminum sheets) was used to monitor the reactions. All melting points were performed in
open capillary tubes using a Gallenkamp melting point apparatus (Sigma-Aldrich Chemie GmbH,

Molecules 2020,25, 105 6 of 17
Taufkirchen, Germany) and are uncorrected. FTIR spectra were recorded on a Shimadzu 8201 PC FTIR
spectrophotometer (Shimadzu, Ltd., Chiyoda-ku, Tokyo, Japan). Elemental analyses were performed
on a Perkin-Elmer 2400 elemental analyzer (PerkinElmer, Inc., Waltham, MA, USA), and the values
found were within
±
0.3% of the theoretical values.
1
H- and
13
C-NMR spectra were recorded on a
Varian-Agilent-NMR 600 MHz spectrometer (Varian, Inc., Palo Altro, CA, USA).
UPLC-MS conditions were as follows: instrument: Waters Acquity UPLC system (Waters Corp.,
Milford, MA, USA) and a triple quadrupole (TQD) mass spectrometer equipped with a Z-electrospray
interface. Parameters of the electrospray ionization source were as follows: capillary voltage: 3.0 kV;
cone voltage: 28 V; desolvation gas: nitrogen with flow 800 L/h; cone gas: nitrogen with flow 70 L/h;
source temperature: 120
◦
C; and desolvation temperature: 300
◦
C. Analysis was done in full scan mode
with positive ionization in the mass range of 50–850 Da. The sample solutions were directly infused to
the ion source at a flow rate of 10
µ
L/min. Data acquisition and processing were done using Waters
MassLynx software.
3.2. General Procedure for the Synthesis of 2,4-Dioxothiazolidine Acid Derivatives
2,4-Dioxothiazolidine acid derivatives were prepared in three steps following the reported
method [
35
,
40
]. A solution of previously prepared TZD
1
was treated with various appropriate
aldehydes via refluxing in ethanol for 24 h in the presence of piperidine as a catalyst. The reaction
mixture was poured into water, followed by acidification with acetic acid to afford compounds
2a
–
g
.
Then a mixture of
2a
–
g
(1 mmol) and ethyl 2-bromoacetate (2 mmol) was refluxed for 24 h in acetone
in the presence of potassium carbonate (2 mmol) to furnish the target product as a white solid after
evaporation of the solvent. The crude product was used directly in the next step for the preparation of
the free carboxylic acid derivatives
3a
–
g
, where the solid product was refluxed with glacial acetic acid
and HCl at a ratio of 4:1 for 2 h to afford the pure (2,4-dioxothiazolidine-3-yl)-acetic acid derivatives
3a
–
g
after evaporation of the solvents and crystallization with ethanol. The spectral data for
3a
,
3f
, and
3g
are in good agreement with previously reported ones [
7
,
13
,
15
] and other spectra in the
Supplementary Materials.
3.2.1. 2-(5-(4-Methylbenzylidene)-2,4-dioxothiazolidin-3-yl)acetic Acid (3b)
The product was obtained as light-yellow crystals in 96% yield, mp: 226–228
◦
C. IR (KBr, cm
−1
):
2950 (CH-aliphatic); 1733, 1685, 1600 (CO); 1H-NMR (DMSO-d6,δppm): 2.34 (3H, s, CH), 4.36 (2H, s,
CH
2
COOH); 7.33 (2H, d, J=6.6 Hz, H
30
& H
50
); 7.51 (2H, d, J=7.2 Hz, H
20
& H
60
), 7.92 (1H, s, CH=C).
13
C-NMR (DMSO-d
6
,
δ
ppm): 21.6 (CH
3
); 42.7 (CH
2
-COOH); 119.8, 130.5, 130.7, 134.4, 141.7; 165.5,
167.4, 168.4 (CO). Anal. Calc. for C
13
H
11
NO
4
S (277.3): C, 56.31; H, 4.00; N, 5.05; Found C, 56.44; H,
4.12; N, 5.26. LC/MS (ESI): 278.32 [M +H]+.
3.2.2. 2-(5-(4-Chlorobenzylidene)-2,4-dioxothiazolidin-3-yl)acetic Acid (3c)
The product was obtained as light-yellow crystals in yield 92%, mp: 250–252
◦
C. IR (KBr, cm
−1
):
3008 (CH-aromatic); 1738, 1690 & 1607 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 4.42 (2H, s, CH
2
-COOH);
7.59–8.00 (4H, m, aromatic protons), 8.03 (1H, s, CH=C);
13
C-NMR (DMSO-d
6
,
δ
ppm): 42.2
(CH
2
-COOH); 121.3, 129.3, 131.5, 131.7, 132.4, 35.3; 164.8, 166.5, 167.8 (CO). Anal. Cal. For C
12
H
8
ClNO
4
S
(297.7): C, 48.40; H, 2.70; N, 4.70; Found C, 48.61; H, 2.83; N, 4.81. LC/MS (ESI): 298.72 [M +H]+.
3.2.3. 2-(5-(2-Chlorobenzylidene)-2,4-dioxothiazolidin-3-yl)acetic Acid (3d)
The product was obtained as white crystals in 90% yield, mp: 243–245
◦
C. IR (KBr, cm
−1
): 3064
(CH-aromatic); (2940) CH-aliphatic; 1490 (C=C); 1722, 1691, 1608 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
3.78 (3H, s, OCH
3
); 4.43 (2H, s, CH
2
COOH); 7.55–7.69 (4H, m, aromatic protons); 8.09 (1H, s, CH=C);
13
C-NMR (DMSO-d
6
,
δ
ppm): 42.0 (CH
2
COOH); 124.1, 128.0, 128.8, 130.8, 130.6, 132.0; 134.4 (CH=C);
164.3, 166.3, 167.6 (CO). Anal. Cal. for C
12
H
8
ClNO
4
S (297.7): C, 48.41; H, 2.71; N, 4.70; Found: C, 48.65;
H, 2.84; N, 4.95.

Molecules 2020,25, 105 7 of 17
3.2.4. 2-(5-(4-Bromobenzylidene)-2,4-dioxothiazolidin-3-yl)acetic Acid (3e)
The product was obtained as yellowish white crystals in 94% yield, mp: 260–262
◦
C. IR (KBr, cm
−1
):
2948 (CH-aliphatic); 1696, 1606 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 4.37 (2H, s, CH
2
COOH); 7.56, (2H,
d, J=6.6 Hz, H
20
& H
60
); 7.73 (2H, d, J=6 Hz, H
30
& H
50
); 7.95 (1H, s, CH=C);
13
C-NMR (DMSO-d
6
,
δ
ppm): 42.8 (CH
2
-COOH); 121.9, 124.9, 132.4, 132.8, 133.1; 165.3, 167.08, 168.4 (CO). Anal. Calc. for
C12H8BrNO4S (342.16): C, 42.12; H, 2.36; N, 4.09; Found C, 42.45; H, 2.59; N, 4.25.
3.3. General Procedure for the Synthesis of 2,4-Dioxothiazolidine Carboxamide Derivatives 4a–s
A mixture of an acid
3a
–
g
(1 mmol), and OxymaPure (1 mmol) was dissolved in 5 mL DMF at
0
◦
C, followed by dropwise addition of DIC (1.1 mmol) at 0
◦
C. The reaction mixture was preactivated
for 5 min and then 1 mmol of an amine (aniline, p-OMe aniline, p-Br aniline and 4-(2-aminoethyl)
morpholine) was added dropwise at the same temperature. After that, the mixture was stirred at
0
◦
C for 1 h and then left overnight under stirring at rt. The progress of the reaction was followed by
TLC (ethyl acetate-hexane; 4:6 or MeOH-CHCl
3
; 1:9). Excess water was added, and the mixture was
extracted with ethyl acetate three times (3
×
20 mL), followed by washing with 1 N HCl (2
×
10 mL), a
saturated solution of Na
2
CO
3
(2
×
10 mL), and a saturated solution of NaCl (10 mL). It was then dried
over anhydrous MgSO
4
for 20 min (when there was precipitation after pouring into water, the final
product was isolated by normal filtration and 3 washings with water).
3.3.1. 2-(5-Benzylidene-2,4-dioxothiazolidine-3-yl)-N-phenylacetamide (4a)
The product was obtained as a white powder from ethanol in 97% yield, mp: 256–258
◦
C. IR
(KBr, cm
−1
): 3278 (N-H); 1748, 1694 & 1662 (C=O);
1
H-NMR (DMSO-d
6
,
δ
ppm): 4.50 (2H, s, CH
2
CO);
7.06–7.64 (10H, m, 2-Ph); 7.98 (1H, s, C
H
=C); 10.38 (s, 1H, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 44.5
(
CH2
CONH), 119.6, 121.4, 124.2, 129.3, 129.9, 130.6, 131.3, 133.3, 134.1, 138.8; 164.2, 165.7, 167.6 (CO).
Anal.Calc for C
18
H
14
N
2
O
3
S (338.38): C, 63.89; H, 4.17; N, 8.28; Found: C, 64.02; H, 4.31; N, 8.42. LC/MS
(ESI): 339.61 [M +H]+.
3.3.2. 2-(5-(3-Methoxybenzylidene)-2,4-dioxothiazolidine-3-yl)-N-phenylacetamide (4b)
The product was obtained as a white powder from ethanol in 96% yield, mp: 227–229
◦
C. IR
(KBr, cm
−1
): 3271 (NH); 1745, 1667 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.80 (3H, s, OCH
3
); 4.50 (2H, s,
CH
2
); 7.07–7.53 (9H, m, aromatic protons); 7.95 (1H, s, CH=C); 10.38 (1 H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 44.5 (CH
2
CONH); 55.8 (OCH
3
); 116.0, 117.2, 119.6, 121.8, 122.4, 124.2, 129.3, 131.0, 134.0, 134.6,
138.8, 160.1; 164.2, 165.7, 167.5 (CO). Anal. Calc for C
19
H
16
N
2
O
4
S (368.41): C, 61.94; H, 4.38; N, 7.60;
Found: C, 61.82; H, 4.44; N, 7.82. LC/MS (ESI): 369.54 [M +H]+.
3.3.3. 2-(5-(4-Bromobenzylidene)-2,4-dioxothiazolidine-3-yl)-N-phenylacetamide (4c)
The product was obtained as a white powder from ethanol in 96% yield, mp: 273–275
◦
C. IR
(KBr, cm−1):
3296 (NH); 1748, 1694, 1668 (CO); 1605 (C=C aromatic);
1
H-NMR (DMSO-d
6
,
δ
ppm): 4.51
(2H, s, CH
2
-CO); 7.05 (1H, s, H
4”
); 7.29 (2H, d, J=3.6 Hz, H
3”
& H
5”
); 7.55 (4H, t, J=7.2 Hz, H
20
, H
60
,
H
30
& H
50
); 7.71 (2H, s, H
2”
& H
6”
); 7.93 (1H, s, CH=C); 10.4 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm):
44.5 (CH
2
CONH); 119.6, 122.2, 124.2, 124.8, 129.3, 132.4, 132.5, 132.8, 138.8; 164.1, 165.6, 167.3 (3CO).
Anal. Calc for C
18
H
13
BrN
2
O
3
S (417.28): C, 51. 81; H, 3.14; N, 6.71; Found: C, 51.98; H, 3.33; N, 6.91.
LC/MS (ESI): 418.41 [M +H]+.
3.3.4. 2-(5-(4-Methoxybenzylidene)-2,4-dioxothiazolidine-3-yl)-N-phenylacetamide (4d)
The product was obtained as a white powder from ethanol in 98% yield, mp: 249–251
◦
C. IR
(KBr, cm
−1
): 3297 (NH); 1742, 1679 and 1594 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.81 (3H, s, OCH
3
);
4.49 (2H, s, CH
2
); 7.08 (3H, dd, J=6.6 Hz,3.6 Hz H
4”
, H
30
& H
50
); 7.30 (2H, d, J=4.2 Hz, H
3”
& H
5”
); 7.53
(2H, s, H
2”
& H
6”
); 7.60 (2H, s, H
20
& H
60
); 7.92 (1H, s, CH=C); 10.38 (1H, s, NH);
13
C-NMR (DMSO-d
6
,

Molecules 2020,25, 105 8 of 17
δ
ppm): 44.4 (CH
2
CO NH); 56.0 (OCH
3
); 115.5, 118.1, 119.6, 124.1, 125.7, 129.3, 132.8, 134.0, 138.8, 161.7;
164.3, 165.9, 167.7 (CO). Anal. Calc for C
19
H
16
N
2
O
4
S (368.41): C, 61.94; H, 4.38; N, 7.60; Found: C,
61.77; H, 4.29; N, 7.81. LC/MS (ESI): 369.30 [M +H]+.
3.3.5. 2-(5-Benzylidene-2,4-dioxothiazolidine-3-yl)-N-(4-methoxyphenyl)acetamide (4e)
The product was obtained as a white powder from ethanol in 97% yield, mp: 258–260
◦
C. IR
(KBr, cm−1):
3280 (NH), 1745, 1694, 1658 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.70 (3H, s, OCH
3
); 4.46
(2H, s, CH
2
CO); 6.87 (2H, d, J=7.2 Hz, H
3”
& H
5”
); 7.44 (2H, s, H
2”
& H
6”
); 7.52 (3H, dd, J=7.8, 6 Hz,
H
30
, H
50
& H
40
); 7.64 (2H, s, H
20
& H
60
); 7.97 (1H, s, CH=C); 10.24 (H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 44.4 (CH
2
CONH); 55.6 (OCH
3
); 114.4, 121.2, 121.5, 129.9, 130.6, 131.3, 131.9, 133.3, 134.0, 155.9;
163.7, 165.8, 167.6 (3CO). Anal. Calc for C
19
H
16
N
2
O
4
S (368.41): C, 61.94; H, 4.38; N, 7.60; Found: C,
62.12; H, 4.55; N, 7.87. LC/MS (ESI): 369.41[M +H]+.
3.3.6. 2-(5-(3-Methoxybenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(4-methoxyphenyl)acetamide (4f)
The product was obtained as a white powder from ethanol in 97% yield, mp: 225–227
◦
C. IR
(KBr, cm
−1
): 3339 (NH), 1749, 1694 & 1612 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.70 (3H, s, OCH
3
); 3.80
(3H, s, OCH
3
); 4.46 (2H, s, CH
2
CO); 6.87 (2H, s, H
3”
& H
5”
); 7.08 (1H, s, H
20
); 7.20 (2H, s, H
60
& H
40
),
7.44 (3H, t, J=8.4 Hz, 12 Hz, H
2”
, H
50
, H
6”
); 7.95 (1H, d, J=1.2 Hz, CH=C); 10.23 (1H, s, NH);
13
C-NMR
(DMSO-d
6
,
δ
ppm): 44.3 (CH
2
CONH); 55.6, 55.7 (2OCH
3
); 114.4, 115.9, 117.1, 121.1, 121.8, 122.4, 130.9,
131.9, 133.9, 134.6, 155.9, 160.1; 163.6, 165.7, 167.5 (CO).Anal. Calc for C
20
H
18
N
2
OS (398.43): C, 60.29;
H, 4.55; N, 7.03; Found: C, 60.55; H, 4.67; N, 7.27. LC/MS (ESI): 399.21 [M +H]+.
3.3.7. 2-(5-(4-Bromobenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(4-methoxyphenyl)acetamide (4g)
The product was obtained as a white powder from ethanol in 96% yield, mp: 270–272
◦
C. IR
(KBr, cm
−1
): 3280 (NH), 1746, 1693, 1662 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.69 (3H, s, OCH
3
); 4.46
(2H, s, CH
2
CO); 6.86 (2H, s, H
3”
& H
5”
); 7.43 (2H, s, H
2”
& H
6”
), 7.57 (2H, s, H
20
& H
60
), 7.72 (2H, s, H
30
& H
50
); 7.93 (1H, s, CH=C); 10.24 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm); 44.4 (CH
2
CONH); 55.6
(OCH
3
); 114.4, 121.2, 122.3, 124.8, 131.9, 132.4, 132.5, 132.8, 132.8, 155.9; 163.6, 165.6, 167.3 (CO). Anal.
Calc for C
19
H
15
BrN
2
O
4
S (447.3): C, 51.02; H, 3.38; N, 6.26; Found: C, 51.39; H, 3.54; N, 6.43. LC/MS
(ESI): 448.32 [M +H]+.
3.3.8. 2-(5-(4-Methoxybenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(4-methoxyphenyl)acetamide (4h)
The product was obtained as an off-white powder from ethanol in 98% yield, mp: 257–259
◦
C.
IR (KBr, cm
−1
): 3270 (NH), 1740, 1687, 1668 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.69 (3H, s, OCH
3
);
3.81 (3H, s, OCH
3
); 4.45 (2H, s, CH
2
); 6.87 (2H, s, H
30
& H
50
); 7.09 (2H, s, H
20
& H
60
); 7.44 (2H, s, H
30
&
H
50
); 7.60 (2H, s, H
20
& H
60
); 7.91 (1H, s, CH=C); 10.23 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm); 44.3
(CH
2
CONH); 55.6, 56.0 (2OCH
3
); 114.4, 115.5, 118.1, 121.1, 125.8, 132.0, 132.8, 134.0, 155.9, 161.7; 163.8,
165.9, 167.7 (CO). Anal. Calc for C20H18N2O5S (398.43): C, 60.29; H, 4.55; N, 7.03. Found: C, 60.54; H,
4.66; N, 7.29. LC/MS (ESI): 399.62 [M +H]+.
3.3.9. 2-(5-Benzylidene-2,4-dioxothiazolidine-3-yl)-N-(4-bromophenyl)acetamide (4i)
The product was obtained as a white powder from ethyl acetate-ethanol (2:1) in 95% yield, mp:
252–254
◦
C. IR (KBr, cm
−1
): 3278 (N-H); 1750, 1693, 1660 (C=O);
1
H-NMR (DMSO-d
6
,
δ
ppm): 4.51 (2H,
s, CH
2
); 7.50 (5H, s, -Ph proton); 7.54 (2H, d, J=6 Hz, H
2”
& H
6”
); 7.65 (2H, d, J=7.2 Hz, H
20
& H
60
); 7.98
(1H, s, CH=C); 10.52 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm); 44.5 (CH
2
CONH); 115.8, 121.4, 121.6,
129.9, 130.7, 131.3, 132.2, 133.3, 134.1, 138.2; 164.5, 165.7, 167.5 (CO). Anal. Calc for C
18
H
13
BrN
2
O
3
S
(417.28): C, 51.81; H, 3.14; N, 6.71; Found: C, 51.98; H, 3.23; N, 6.92. LC/MS (ESI): 418.51 [M +H]+.

Molecules 2020,25, 105 9 of 17
3.3.10. N-(4-Bromophenyl)-2-(5-(3-methoxybenzylidene)-2,4-dioxothiazolidine-3-yl) acetamide (4j)
The product was obtained as a white powder from ethyl acetate-ethanol (2:1) in yield, mp:
253–255
◦
C. IR (KBr, cm
−1
): 3330 (N-H); 1748, 1688, 1609 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.79 (3H,
s, OCH
3
); 4.50 (2H, s, CH
2
); 7.07–7.49 (8H, m, aromatic proton); 7.94 (1H, s, CH=C); 10.54 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 44.5 (CH
2
CONH); 55.7 (OCH
3
); 115.8, 116.0, 117.2, 121.6, 121.7, 122.4,
132.0, 132.2, 134.1, 134.6, 138.1, 160.1; 164.4, 165.64, 167.5 (CO). Anal. Calc for for C
19
H
15
BrN
2
O
4
S
(447.30): C, 51.02; H, 3.38; N, 6.26; Found: C, 51.33; H, 3.51; N, 6.43. LC/MS (ESI): 448.21 [M +H]+.
3.3.11. 2-(5-(4-Bromobenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(4-bromophenyl)acetamide (4k)
The product was obtained as a white powder from ethyl acetate-ethanol (2:1) in 96% yield, mp:
286–288
◦
C. IR (KBr, cm
−1
): 3259 (NH); 1748 & 1691 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 4.50 (2H, s,
CH
2
CO); 7.49 (4H, s, H
2”
, H
3”
, H
5”
& H
6”
); 7.57 (2H, s, H
20
& H
60
), 7.73 (2H, s, H
30
& H
50
), 7.94 (1H, s,
CH=C); 10.53 (1 H, s, NH);
13
C-NMR (DMSO-d
6
;
δ
ppm): 44.5 (CH
2
CO NH); 115.8, 121.6, 122.2, 124.8,
132.2, 132.4, 132.5, 132.8, 132.9, 138.1 (C-sp
2
); 164.4, 165.6, 167.3 (CO). Anal. Calc for C
18
H
12
Br
2
N
2
O
3
S
(496.17): C, 43.57; H, 2.44; N, 5.65; Found: C, 43.71; H, 2.61; N, 5.80. LC/MS (ESI): 497.21 [M +H]+.
3.3.12. N-(4-Bromophenyl)-2-(5-(4-methoxybenzylidene)-2,4-dioxothiazolidine-3-yl)acetamide (4l)
The product was obtained as a yellowish white powder from ethyl acetate-ethanol (2:1) in 98%
yield, mp: 260–262
◦
C. IR (KBr, cm
−1
): 3267 (NH); 1740 & 1689 (C=O);
1
H-NMR (DMSO-d
6
,
δ
ppm):
3.81 (3H, s, OCH
3
); 4.49 (2H, s, CH
2
CO); 7.09 (2H, d, J=6.6 Hz, H
30
& H
50
); 7.48 (4H, d, J=7.8 Hz, H
2”
,
H
3”
, H
5”
, H
6”
), 7.60 (2H, s, H
20
& H
60
); 7.92 (1H, s, CH=C); 10.52 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 44.4 (CH
2
CONH); 56.0 (OCH
3
); 115.5, 115.8, 118.0, 121.5, 125.7, 132.1, 132.8, 134.1, 138.2, 161.8;
164.5, 165.8, 167.6 (CO). Anal. Calc for C
19
H
15
BrN
2
O
4
S (447.30): C, 51.02; H, 3.38; N, 6.26; Found: C,
51.22; H, 3.47; N, 6.50. LC/MS (ESI): 448.51 [M +H]+.
3.3.13. 2-(5-Benzylidene-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (4m)
The product was obtained as a white powder from ethanol in 89% yield, mp: 180–182
◦
C. IR
(KBr, cm
−1
): 3308 (NH); 2941 (CH-aliphatic); 1748, 1691, 1658 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 2.33
(6H, d, J=6 Hz), (CH
2
NCH
2
& CH
2
CH
2
N); 3.18 (2H, s, NHCH
2
CH
2
); 3.54 (4H, s, CH
2
OCH
2
); 4.25
(2H, s, NCH
2
CO); 7.49 (5H, m, -Ph proton); 7.93 (1H, s, CH=C); 8.21 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 36.6 (NHCH
2
); 43.9 (CH
2
CO); 53.7 (CH
2
NCH
2
); 57.6 (CH
2
CH
2
N); 66.6 (CH
2
OCH
2
); 121.6,
129.9, 130.6, 131.2, 133.3, 133.7; 165.4, 165.7, 167.5 (CO). Anal. Calc for C
18
H
21
N
3
O
4
S (375.44): C, 57.58;
H, 5.64; N, 11.19; Found: C, 57.69; H, 5.74; N, 11.33. LC/MS (ESI): 376.62 [M +H]+.
3.3.14. 2-(5-(2-Chlorobenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (4n)
The product was obtained as a white powder from ethanol in 95% yield, mp: 177–179
◦
C. IR
(KBr, cm
−1
): 3307 (NH); 2958 (CH-aliphatic); 1751, 1703 and 1657 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
2.33 (6H, s, CH
2
NCH
2
& CH
2
CH
2
N); 3.18 (2H, s, NHCH
2
CH
2
); 3.54 (4H, s, CH
2
OCH
2
; 4.26 (2H, s,
NCH
2
C=O); 7.51 (2H, s, H
40
& H
50
);7.59 (1H, d, J=9 Hz, H
60
);7.63 (1H, s, H
30
); 8.03 (1H, s, CH=C);
8.24 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 36.6 (NH CH
2
); 44.0 (CH
2
-CO); 53.7 (CH
2
NCH
2
); 57.6
(CH
2
CH
2
N); 66.6 (CH
2
OCH
2
); 125.3, 128.6, 128.8, 129.4, 130.8, 131.3, 132.6, 134.9; 165.3, 165.3, 167.3
(CO). Anal. Calc for C
18
H
20
ClN
3
O
4
S (409.9): C, 52.75; H, 4.92; N, 10.25; Found: C, 52.93; H, 5.01; N,
10.41. LC/MS (ESI): 411.21 [M +H]+.
3.3.15. 2-(5-(4-Bromobenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (4o)
The product was obtained as a white powder from ethanol in 95% yield, mp: 224–226
◦
C. IR
(KBr, cm
−1
): 3298 (NH); 2931 (CH-aliphatic); 1751, 1693, 1664 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
2.34 (6H, s, CH
2
NCH
2
and CH
2
CH
2
N); 3.18 (2H, s, NHCH
2
CH
2
); 3.54 (4H, s, CH
2
OCH
2
); 4.25 (2H,
s, NCH
2
CO); 7.56 (2H, s, H
30
& H
50
); 7.73 (2H, s, H
20
& H
60
); 7.91 (1H, s, CH=C); 8.21 (1H, s, NH);

Molecules 2020,25, 105 10 of 17
13
C-NMR (DMSO-d
6
,
δ
ppm): 36.6 (NHCH
2
); 43.9 (CH
2
CO); 53.7 (CH
2
NCH
2
); 57.6 (CH
2
CH
2
N); 66.6
(CH
2
OCH
2
); 122.5, 124.7, 132.4, 132.5, 132.9; 165.3, 165.6, 167.3 (CO). Anal. Calc for C
18
H
20
BrN
3
O
4
S
(454.3): C, 47.59; H, 4.44; N, 9.25; Found: C, 47.77; H, 4.52; N, 9.49. LC/MS (ESI): 454.3 [M +H]+.
3.3.16. 2-(5-(4-Methylbenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (
4p
)
The product was obtained as a white powder from ethanol in 95% yield, mp: 212–214
◦
C. IR
(KBr, cm
−1
): 3291 (NH); 2933 (CH-aliphatic); 1747, 1696, 1657 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
2.34 (9H, s, CH
2
NCH
2
, CH
2
CH
2
N & CH
3
); 3.18 (2H, s, NHCH
2
CH
2
); 3.54 (4H, s, CH
2
OCH
2
); 4.24
(2H, s, NCH
2
CO); 7.34 (2H, s, H
30
& H
50
);7.51 (2H, s, H
20
& H
60
); 7.89 (1H, s, CH=C); 8.20 (1H, s,
NH);
13
C-NMR (DMSO-d
6
,
δ
ppm); 21.5 (CH
3
); 36.6 (NHCH
2
); 43.9 (CH
2
CO); 53.7 (CH
2
NCH
2
); 57.6
(CH
2
CH
2
N); 66.6 (CH
2
OCH
2
); 120.4, 130.5, 130.6, 130.7, 133.8 & 141.6; 165.4, 165.8, 167.6 (CO). Anal.
Calc for C
19
H
23
N
3
O
4
S (389.5): C, 58.59; H, 5.95; N, 10.79. Found: 58.71; H, 6.09; N, 10.98. LC/MS (ESI):
390.12 [M +H]+.
3.3.17. 2-(5-(4-Methoxylbenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (
4q
)
The product was obtained as a white powder from ethanol in 95% yield, mp: 231–233
◦
C. IR
(KBr, cm
−1
): 3290 (NH); 2933 (CH-aliphatic); 1739, 1691 & 1660 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
2.33 (6H, d, CH
2
-N-CH
2
& CH
2
CH
2
N-); 3.17 (2H, d, J=4.8 Hz, NHCH
2
CH
2
); 3.53 (4H, s, CH
2
OCH
2
);
3.81 (3H, t, J=1.2 Hz, OCH
3
); 4.24 (2H, s, NCH
2
CO); 7.09 (1H, s, H
30
& H
50
); 7.58 (2H, s, H
20
& H
60
);
7.87 (1H, s, CH=CS); 8.20 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 36.6 (NH CH
2
); 43.8 (CH
2
CO);
53.7 (CH
2
NCH
2
; 56.0 (OCH
3
); 57.6 (CH
2
CH
2
N); 66.6 (CH
2
OCH
2
; 115.4, 118.3, 125.8, 132.7, 133.7; 161.7,
165.5, 165.9 & 167.6 (CO). Anal. Calc for C
19
H
23
N
3
O
5
S (405.47): C, 56.28; H, 5.72; N, 10.36; Found: C,
56.44; H, 5.91; N, 10.55. LC/MS (ESI): 406.81[M +H]+.
3.3.18. 2-(5-(4-Chlorobenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (4r)
The product was obtained as a white powder from ethanol in 94% yield, mp: 222–224
◦
C. IR
(KBr, cm
−1
): 3294 (NH); 2930 (CH-aliphatic); 1751, 1693, 1662 (CO).
1
H-NMR (DMSO-d
6
,
δ
ppm):
2.33 (6H, s, CH
2
NCH
2
& CH
2
CH
2
N); 3.17 (2H, s, NHCH
2
CH
2
); 3.53 (4H, s, CH
2
OCH
2
); 4.25 (2H,
s, NCH
2
CO); 7.59 (2H, d, J=1.2 Hz, H
30
& H
50
); 7.63 (2H, s, H
20
& H
60
); 7.92 (1H, s, CH=C); 8.21
(1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 36.59 (NH CH
2
); 43.9 (CH
2
CO); 53.7 (CH
2
N-CH
2
); 57.6
(NHCH
2
CH
2
); 66.5 (CH
2
OCH
2
); 122.4, 129.9, 132.2, 132.4, 135.8; 165.3; 165.6, 167.3 (CO). Anal. Calc for
C
18
H
20
ClN
3
O
4
S (409.9): C, 52.75; H, 4.92; N, 10.25; Found: C, 52.99; H, 5.10; N, 10.47. LC/MS (ESI):
411.51 [M +H]+.
3.3.19. 2-(5-(3-Methoxybenzylidene)-2,4-dioxothiazolidine-3-yl)-N-(2-morpholinoethyl)acetamide (
4s
)
The product was obtained as a white powder from ethanol in 95% yield, mp: 164–166
◦
C. IR (KBr,
cm
−1
): 3296 (NH); 2943 (CH-aliphatic); 1748, 1693, 1659 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 2.33 (6H, d,
J=6 Hz, (CH
2
NCH
2
& CH
2
CH
2
N); 3.18 (2H, s, NHCH
2
CH
2
); 3.53 (4H, s, CH
2
OCH
2
); 3.79 (3H, s,
OCH
3
); 4.25 (2H, s, NCH
2
CO); 7.06 (1H, s, H
40
); 7.18 (2H, s, H
20
& H
60
); 7.45 (1H, d, J=6.6 Hz, H
50
);
7.91 (1H, s, CH=C); 8.21 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 36.6 (NHCH
2
); 43.9 (CH
2
CO); 53.7
(CH
2
NCH
2
); 55.8 (OCH
3
); 57.6 (CH
2
CH
2
N); 66.6 (CH
2
OCH
2
); 115.9, 117.1, 122.0 122.4, 131.0, 133.7,
134.7 & 160.1; 165. 4, 165.7, 167.5 (CO). Anal. Calc for C
19
H
23
N
3
O
5
S (405.47): C, 56.28; H, 5.72; N, 10.36;
Found: C, 56.45; H, 5.91; N, 10.53. LC/MS (ESI): 406.12 [M +H]+.
3.4. General Procedure for the Synthesis of Amino Acid Ester Derivatives 5a–o
Compounds
5a–o
were prepared using the method mentioned above for the preparation of
4a
–
s,
employing OxymaPure/DIC as a coupling reagent in the presence of diisopropylamine (DIEA) as a
base to neutralize the amino acid ester hydrochloride salt.

Molecules 2020,25, 105 11 of 17
3.4.1. 2-(5-Benzylidene-2,4-dioxothiazolidine-3-yl) acetyl)glycinate (5a)
The product was obtained as a white powder from ethanol in 97% yield, mp: 177–179
◦
C. IR
(KBr, cm
−1
): 3312 (NH); 1745, 1662, 1698, 1609 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.61 (3H, s, CH3);
3.87 (2H, s, NHCH
2
CO); 4.31 (2H, s, CH
2
CONH); 7.47–7.61 (5H, m, aromatic); 7.93 (1H, s, CH=C); 8.74
(1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 41.1 (NHCH
2
COO); 43.7 (NCH
2
CO); 52.2 (COOCH
3
); 121.5,
129.8, 130.6, 131.2, 133.3, 133.8; 165.6, 166.1, 167.5, 170.4 (CO). Anal. Calc for C
15
H
14
N
2
O
5
S (334.35): C,
53.89; H, 4.22; N, 8.38; Found: C, 53.11; H, 4.40; N, 8.54. LC/MS (ESI): 335.67 [M +H]+.
3.4.2. Methyl-(2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidine-3-yl)acetyl)glycinate (5b)
The product was obtained as a white powder from ethanol in 96% yield, mp: 236–238
◦
C. IR
(KBr, cm
−1
): 3294 (NH); 1751, 1694, 1663, 1610 (CO).
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.61 (3H, s, OCH
3
);
3.87 (2H, s, NHCH
2
COO); 4.31 (2H, s, NCH
2
CONH); 7.58 (2H, s, H
20
& H
60
); 7.63 (2H, s, H
30
& H
50
); 7.93
(1H, s, CH=CS); 8.74 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 41.1 (NHCH
2
COO); 43.7 (CH
2
CONH);
52.2 (COOCH
3
); 122.3, 129.9, 132.2, 132.5, 135.8; 165.5, 166.1, 167.2, 170.3 (CO). Anal. Calc for C
15
H
13
Cl
N
2
O
5
S (368.79): C, 48.85; H, 3.55; N, 7.60; Found: C, 48.01; H, 3.56; N, 7.82. LC/MS (ESI): 370.12
[M +H]+.
3.4.3. Methyl-(2-(5-(4-bromobenzylidene)-2,4-dioxothiazolidine-3-yl) acetyl)glycinate (5c)
The product was obtained as a white powder from ethanol in 96% yield, mp: 239–241
◦
C. IR
(KBr, cm
−1
): 3294 (NH); 1751, 1693, 1664, 1607 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 3.60 (3H, s, OCH
3
);
3.87 (2H, s, NHCH
2
COO); 4.31 (2H, s, CH
2
CONH); 7.56 (2H, s, H
20
& H
50
); 7.72 (2H, s, H
30
& H
50
); 7.91
(1H, s, CH=CS); 8.74 (1H, s, NH).
13
C-NMR (DMSO-d
6
,
δ
ppm): 41.2 (NHCH
2
COO); 43.7 (CH
2
CONH);
52.2 (COOCH
3
); 122.4, 124.7, 132.4, 132.5, 132.6, 132.8; 165.5, 166.1, 167.2, 170.3 (CO). Anal. Calc for
C
15
H
13
BrN
2
O
5
S (413.24): C, 43.60; H, 3.17; N, 6.78. Found: C, 43.81; H, 3.31; N, 6.91. LC/MS (ESI):
415.41 [M +H]+.
3.4.4. Methyl-4-(2-(5-benzylidene-2,4-dioxothiazolidine-3-yl)acetamido)butanoate (5d)
The product was obtained as a white powder from ethanol in 98% yield, mp: 169–171
◦
C.
IR (KBr, cm
−1
): 3306 (NH); 1734, 1692, 1660 & 1607 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 1.62 (2H,
m, CH
2
CH
2
CH
2
); 2.28 (2H, s, CH
2
CH
2
CO); 3.05 (2H, s, NHCH
2
); 3.55 (3H, s, OCH
3
); 4.22 (2H, s,
NCH
2
CO); 7.48–7.49 (3H, m, H
30
, H
40
& H
50
); 7.61 (2H, s, H
20
& H
60
);7.93 (1H, s, CH=CS); 8.26 (1H, s,
NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 24.8 (CH
2
CH
2
CH
2
); 31.0 (CH
2
CH
2
CO); 38.5 (NHCH
2
CH
2
); 43.9
(NCH
2
CO); 51.7 (COOCH
3
); 121.6, 129.8, 130.6, 131.2, 133.3, 133.7; 165.4, 165.7, 167.5, 173.5 (CO). Anal.
Calc for C
17
H
18
N
2
O
5
S (362.40): C, 56.34; H, 5.01; N, 7.73; Found: C, 56.56; H, 5.19; N, 7.98. LC/MS
(ESI): 363.41 [M +H]+.
3.4.5. Methyl-4-(2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidine-3-yl)acetamide)butanoate (5e)
The product was obtained as a white powder from ethanol in 97% yield, mp: 192–194
◦
C.
IR (KBr, cm
−1
): 3304 (NH); 1743, 1692, 1662, 1609 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 1.62 (2H, s,
CH
2CH2
CH
2
); 2.28 (2H, s, CH
2CH2
CO); 3.05 (2H, s, NH
CH2
CH
2
); 3.56 (3H, s, OCH
3
); 4.22 (2H,
s, N
CH2
CO); 7.59 (2H, s, H
30
& H
50
); 7.64 (2H, s, H
20
& H
60
); 7.93 (1H, s,
CH
=CS); 8.25 (1H, s,
NH);
13
C-NMR (DMSO-d
6
,
δ
ppm):
δ
24.8 (CH
2CH2
CH
2
); 31.0 (CH
2CH2
CO); 38.5 (NH
CH2
CO); 44.0
(N
CH2
CO); 51.7 (COO
CH3
); 122.4, 129.9, 132.2, 132.4, 135.8; 165.3, 165.6, 167.3, 173.5 (CO). Anal. Calc
for C17H17 ClN2O5S (396.84): C, 51.45; H, 4.32; N, 7.06; Found: C, 51.61; H, 4.44; N, 7.28. LC/MS (ESI):
398.12 [M +H]+.
3.4.6. Methyl-4-(2-(5-(4-bromobenzylidene)-2,4-dioxothiazolidine-3-yl)acetamido)butanoate (5f)
The product was obtained as a white powder from ethanol in 95% yield, mp: 191–193
◦
C.
IR (KBr, cm
−1
): 3293 (NH); 1744, 1690, 1659, 1608 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 1.63 (2H, s,

Molecules 2020,25, 105 12 of 17
CH
2
CH
2
CH
2
); 2.28 (2H, s, CH
2
CH
2
CO); 3.06 (2H, s, NHCH
2
CH
2
); 3.55 (3H, s, OCH
3
); 4.22 (2H, s,
NCH
2
CO); 7.54 (2H, d, J=2.4 Hz, H
20
& H
60
); 7.70 (2H, s, H
30
& H
50
); 7.89 (1H, s, CH=CS); 8.27 (1H, s,
NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 24.8 (CH
2
CH
2
CH
2
); 31.0 (CH
2
CH
2
CO); 38.5 (NHCH
2
CO); 43.9
(NCH
2
CO); 51.7 (COOCH
3
); 122.4, 124.7, 132.3, 132.5, 132.8; 165.3, 165.6, 167.3, 173.4 (CO). Anal. Calc
for C
17
H
17
BrN
2
O
5
S (441.30): C, 46.27; H, 3.88; N, 6.35. Found: C, 46.44; H, 4.05; N, 6.58. LC/MS (ESI):
442.52 [M +H]+.
3.4.7. Methyl-2-(5-benzylidene-2,4-dioxothiazolidine-3-yl)acetyl)valinate (5g)
The product was obtained as a white powder from ethanol in 98% yield, mp: 186–188
◦
C. IR
(KBr, cm
−1
): 3300 (NH); 1749, 1697, 1662 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
δ
0.84 (6H, s, 2 CH
3
); 2.00
(1H, s,
CH(
CH
3
)
2
); 3.61 (3H, s, OCH
3
); 4.18 (1H, s, NH
CH
CO); 4.34 (2H, s, N
CH2
CO); 7.51–7.60 (5H, m,
-Ph proton); 7.92 (1H, s,
CH
=CS); 8.64 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm):
δ
18.5, 19.3 (2CH
3
);
30.6 (
CH
(CH
3
)
2
); 43.6 (N
CH2
CO); 52.2 (COOCH
3
); 58.0 (
CH
CO); 121.4, 129.8,130.6, 131.2, 133.3, 133.8;
165.6, 165.8, 167.4, 172.1 (CO). Anal. Calc for C18H20N2O5S (376.43): C, 57.43; H, 5.36; N, 7.44; Found:
C, 57.66; H, 5.51; N, 7.61. LC/MS (ESI): 377.92 [M +H]+.
3.4.8. Methyl-(2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidine-3-yl)acetyl)valinate (5h)
The product was obtained as a yellowish white powder from ethanol in 97% yield, mp: 193–195
◦
C.
IR (KBr, cm
−1
): 3278 (NH), 1745, 1688, 1658, 1606 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 0.84 (6H, s, 2CH
3
);
2.00 (1H, s, CH(CH
3
)
2
); 3.62 (3H, s, OCH
3
); 4.19 (1H, s, NHCHCO); 4.35 (2H, s, NCH
2
CO); 7.55 (2H,
d, J=9.6 Hz, H
20
& H
60
); 7.61 (2H, s, H
30
& H
50
); 7.91 (1H, s, CH=CS); 8.65 (1H, s, NH);
13
C-NMR
(DMSO-d
6
,
δ
ppm): 18.5, 19.3 (2CH
3
); 30.6 (CH (CH
3
)
2
); 43.6 (NCH
2
CO); 52.2 (COOCH
3
); 57.9 (CH
CO); 121.2, 129.9, 132.2, 132.5, 135.8; 165.5, 165.8, 167.1, 172.1 (CO). Anal. Calc for C
18
H
19
ClN
2
O
5
S
(410.87): C, 52.62; H, 4.66; N, 6.82; Found: C, 52.81; H, 4.72; N, 6.63. LC/MS (ESI): 412.33 [M +H]+.
3.4.9. Methyl-2-(5-(4-bromobenzylidene)-2,4-dioxothiazolidine-3-yl)acetyl)valinate (5i)
The product was obtained as a yellowish white powder from ethylacetate-ethanol (2:1) in 96%
yield, mp: 222–224
◦
C. IR (KBr, cm
−1
): 3280 (NH), 1744, 1688, 1658, 1606 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 0.84 (6H, d, 2CH
3
); 2.01 (1H, d, CH(CH
3
)
2
); 3.62 (3H, s, OCH
3
); 4.19 (1H, s, CHCO); 4.35 (2H,
s, NCH
2
CO); 7.53 (2H, s, H
20
& H
60
); 7.70 (2H, s, H
30
& H
50
); 7.89 (1H, s, CH=CS); 8.65 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 18.5, 19.3 (2CH
3
); 30.6 (CH (CH
3
)
2
); 43.6 (-NCH
2
CO); 52.2 (COOCH
3
);
57.9 (CHCO); 122.3, 124.7, 132.3, 132.5, 132.6, 132.8; 165.5, 165.8, 167.1, 172.2 (CO). Anal. Calc for
C
18
H
19
BrN
2
O
5
S (455.32): C, 47.48; H, 4.21; N, 6.15; Found: C, 47.67; H, 4.39; N, 6.31. LC/MS (ESI):
456.43 [M +H]+.
3.4.10. Methyl-2-(5-benzylidene-2,4-dioxothiazolidine-3-yl)acetyl)alaninate (5j)
The product was obtained as a white powder from ethanol and 2 drops dimethylformamide in
97% yield, mp: 202–204
◦
C. IR (KBr, cm
−1
): 3304 (NH); 1743, 1691, 1663, 1607 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 1.26 (3H, s, CH
3
); 3.59 (3H, s, OCH
3
); 4.27, 4.28 (3H, d, NCH
2
COCHCOO); 7.47–7.61 (5H, m,
-Ph proton); 7.93 (1H, s, CH=CS); 8.74 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm):
δ
17.5 (CH
3
); 43.6
(NCH
2
CO); 48.2 (NHCHCO); 52.4 (COOCH
3
); 121.5, 129.8, 130.6, 131.2, 133.3, 133.8; 165.4, 165.6, 167.4,
173.1 (CO). Anal. Calc for C
16
H
16
N
2
O
5
S (348.37): C, 55.16; H, 4.63; N, 8.04; Found: C, 55.33; H, 4.78; N,
8.24. LC/MS (ESI): 349.56 [M +H]+.
3.4.11. Methyl-2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidine-3-yl)acetyl)alaninate (5k)
The product was obtained as a yellowish white powder from ethylacetate-ethanol (2:1) in 95%
yield, mp: 233–235
◦
C. IR (KBr, cm
−1
): 3295 (NH); 1748, 1693, 1660, 1608 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm):
δ
1.25 (3H, s, CH
3
); 3.59 (3H, s, OCH
3
); 4.27, 4.28 (3H, d, NCH
2
COCHCOO); 7.58 (2H, s, H
20
&
H
60
); 7.62 (2H, s, H
30
& H
50
); 7.92 (1H, s, CH=CS); 8.74 (1H, s, NH);
13
C-NMR DMSO-d
6
,
δ
ppm):
δ
17.5

Molecules 2020,25, 105 13 of 17
(CH
3
); 43.6 (NCH
2
CO); 48.2 (NHCHCOO); 52.4 (COOCH
3
); 122.2, 129.9, 132.2, 132.5, 135.8 (C-sp
2
);
165.3, 165.5, 167.2, 173.1 (CO). Anal. Calc for C
16
H
15
ClN
2
O
5
S (382.82): C, 50.20; H, 3.95; N, 7.32; Found:
C, 50.41; H, 4.12; N, 7.51. LC/MS (ESI): 384.22[M +H]+.
3.4.12. Methyl-2-(5-(4-bromobenzylidene)-2,4-dioxothiazolidine-3-yl) acetyl)alaninate (5l)
The product was obtained as a white powder from ethylacetate-ethanol (2:1) in 94% yield, mp:
220–222
◦
C. IR (KBr, cm
−1
): 3300 (NH); 1745, 1692, 1661, 1606 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 1.26
(3H, s, CH
3
); 3.60 (3H, s, OCH
3
); 4.28 (3H, s, NCH
2
COCHCOO); 7.55 (2H, s, H
20
& H
60
); 7.71 (2H, s,
H
30
& H
50
); 7.90 (1H, s, CH=CS); 8.74 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm):
δ
17.5 (CH
3
); 43.6
(-NCH
2
CO); 48.2 (NHCH-CO); 52.4 (COOCH
3
); 122.3, 124.7, 132.4, 132.5, 132.6, 132.8 (C-sp
2
); 165.3,
165.5, 167.1, 173.1 (CO). Anal. Calc for C
16
H
15
BrN
2
O
5
S (427.27): C, 44.98; H, 3.54; N, 6.56. Found: C,
45.12; H, 3.66; N, 6.73. LC/MS (ESI): 42,854 [M +H]+.
3.4.13. Methyl-(2-(5-benzylidene-2,4-dioxothiazolidine-3-yl) acetyl)phenylalaninate (5m)
The product was obtained as a white powder from ethanol in 96% yield, mp: 164–166
◦
C. IR
(KBr, cm−1)
: 3329 (NH); 1740, 1693, 1662 & 1609 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 2.92 (2H, t, CH
2
ph);
3.31 (3H, s, COOCH
3
); 4.26 (2H, s, NCH
2
CONH); 4.32 (1H, s, NHCHCOO), 7.19–7.61 (10H, m, 2 -Ph
proton); 7.93 (1H, s, CH=CS); 8.68 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm):
δ
37.3 (CH
2
ph); 43.6
(CH
2
CONH); 54.9 (COOCH
3
); 81.4 (CHCOOCH
3
), 121.5, 127.0, 128.6, 129.7, 129.8, 130.6, 131.2, 133.3,
133.8, 137.3; 165.4, 165.6, 167.4, 170.5 (CO). Anal. Calc for C
22
H
20
N
2
O
5
S (424.47): C, 62.25; H, 4.75; N,
6.60; Found: C, 62.41; H, 4.87; N, 6.80. LC/MS (ESI): 425.82 [M +H]+.
3.4.14. Methyl-2-(5-(4-chlorobenzylidene)-2,4-dioxothiazolidine-3yl)acetyl)phenylalaninate (5n)
The product was obtained as a white powder from ethanol and 2 drops dimethylformamide
94% yield, mp: 164–166
◦
C. IR (KBr, cm
−1
): 3341 (NH); 1741, 1685, 1607 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 2.91 (2H, t, -CH
2
ph); 3.32 (3H, s, COOCH
3
); 4.26 (2H, s, CH
2
CONH), 4.32 (1H, d, J=4.2 Hz,
NHCHCOOCH
3
), 7.19–7.25 (5H, m, -Ph proton); 7.58 (2H, s, H
20
& H
60
); 7.63 (2H, s, H
30
& H
50
); 7.93
(1H, s, CH=CS); 8.68 (1H, s, NH);
13
C-NMR (DMSO-d
6
,
δ
ppm): 37.3 (CH
2
ph); 43.7 (CH
2
CONH); 54.9
(COOCH
3
); 81.4 (CHCOOCH
3
); 122.3, 127.0, 128.6, 129.7, 129.9, 132.2, 132.5, 135.8, 137.3; 165.4, 165.5,
167.1, 170.5 (CO). Anal. Calc for C
22
H
19
ClN
2
O
5
S (458.91): C, 57.58; H, 4.17; N, 6.10; Found: C, 57.77; H,
4.32; N, 6.29. LC/MS (ESI): 410.10 [M +H]+.
3.4.15. Methyl-(2-(5-(4-bromobenzylidene)-2,4-dioxothiazolidine-3-yl)acetyl)phenylalaninate (5o)
The product was obtained as a white powder from ethanol in 94% yield, mp: 161–163
◦
C. IR
(KBr, cm−1):
3341 (NH); 1741, 1683, 1606 (CO);
1
H-NMR (DMSO-d
6
,
δ
ppm): 2.91 (2 H, t, CH
2
ph); 3.31
(3H, s, COOCH
3
); 4.26 (2H, s, CH
2
CONH); 4.32 (1H, d, J=4.2 Hz, NHCHCOOCH
3
), 7.19–7.25 (5H,
m, -Ph proton); 7.55 (2H, s, H
20
& H
60
); 7.71 (2H, s, H
30
& H
50
); 7.91 (1H, s, CH=CS); 8.69 (1H, s, NH).
13
C-NMR (DMSO-d
6
,
δ
ppm): 37.3 (CH
2
ph); 43.7 (CH
2
CONH); 54.9 (COOCH
3
); 81.3 (CHCOOCH
3
),
122.4, 124.7, 127.0, 128.6, 129.7, 132.2, 132.4, 132.5, 132.6, 132.8, 137.3; 165.4, 165.5, 167.1, 170.5 (CO).
Anal. Calc for C
22
H
19
BrN
2
O
5
S (503.37): C, 52.49; H, 3.80; N, 5.57; Found: C, 52.64; H, 4.01; N, 5.71.
LC/MS (ESI): 503.54 [M +H]+.
3.5. Antimicrobial Activity
3.5.1. Microbial Preparation
All tested organisms were pre-cultured on Nutrient agar plates (Oxoid, Lenexa, KS, USA)
incubated at 37
◦
C for 18–24 h, and microbial suspensions of each of the pure isolates, following pre
culture, were prepared in nutrient broth tubes with 0.5 McFarland turbidity needed for the
in vivo
antimicrobial test. We tested two gram-positive bacteria, namely Staphylococcus aureus ATCC 29213

Molecules 2020,25, 105 14 of 17
and Bacillus subtilis ATCC 10400, two-gram negative bacteria, namely Escherichia coli ATCC 25922 and
Pseudomonas aeruginosa ATCC 27853, and one fungal isolate, Candida albicans ATCC 10231.
3.5.2. Well Diffusion Technique
Before applying the in vivo antimicrobial test, 20 mg of each chemical compound was dissolved
in 1 mL DMSO and mixed thoroughly to form a solution. Mueller Hinton plates were prepared for
the sensitivity test. Next, each microbial suspension was spread on the surface of the plates using a
sterile cotton swab. Equidistant holes with a diameter of 6 mm were then made using a sterile cork
borer. One hundred
µ
L of each chemical compound was added to the corresponding well. Plates were
incubated at 37
◦
C for 18–24 h. Antimicrobial activity was determined by measuring the inhibition
zone around each well in mm. Inhibition zones above 8 mm in diameter indicated susceptibility
of the micro-organism to the specific compound used. Data were compared to the positive control
standard impenem 10
µ
g antibiotic discs, sulfamethoxazole trimethoprim for the bacterial isolates, and
fluconazole for the Candida isolate. Tests were repeated three times and the average of the inhibition
zone was recorded (Table 1).
4. Conclusions
Novel thiazolidine-2,4-diones carboxamide and amino acid derivatives were synthesized in
excellent yield and purity using OxymaPure/DIC coupling methodology and were characterized by
IR, NMR (
1
H and
13
C), elemental analysis, and LC-MS. The presence of the OxymaPure as additive
during the coupling facilitates this reaction, which is not straightforward due to the poor reactivity of
the carboxylic moiety.
Interestingly, some compounds from the three series showed weak activity against E. coli, while
most of the prepared compounds showed weak to moderate activity against gram-negative bacteria
P. aeruginosa and antifungal activity against C. albicans. On the other hand, none of the prepared
compounds showed any any antimicrobial activity against Gram-positive bacteria (S. aureus and
B. subtilis) except compound
3g
that gave good activity against S. aureus. These results are of special
relevance because to the lack of new antibiotic drugs against Gram-negative resistant strains.
Finally, the type of substituent at the thiazolidine ring and at carboxylic moiety (carboxamide or
amino acid ester derivatives) has a great impact on the antimicrobial activity of the compound. Based
on these results, the preparation of a new series of compounds with different thiazolidine derivatives
are currently carrying out in our laboratories with the objective of finding compounds with better
antimicrobial activity against Gram-negative bacteria.
Supplementary Materials:
The following are available online, Figures S1–S37 represent the NMR (
1
H and
13
C)
spectra for the prepared compounds.
Author Contributions:
Chemistry part was carried out by R.A.A. and the series were designed and supervised
by A.E.-F., Z.A., B.G.d.l.T., and F.A. the antimicrobial part was carried by S.I.B. all authors were contributed in the
explanation of the results. The first draft of the manuscript was prepared by R.A.A., Z.A., and S.I.B. and all authors
were contributed in the final version. All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Acknowledgments:
This work was funded in part by the following: the International Scientific Partnership
Program ISPP at King Saud University (ISPP# 0061) (Saudi Arabia); National Research Foundation (NRF) and the
University of KwaZulu-Natal (South Africa); MINECO, (RTI2018-093831-B-100), and the Generalitat de Catalunya
(2017 SGR 1439) (Spain).
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Asati, V.; Mahapatra, D.K.; Bharti, S.K. Thiazolidine-2,4-diones as multi-targeted scaffold in medicinal
chemistry: Potential anticancer agents. Eur. J. Med. Chem. 2014,87, 814–833. [CrossRef] [PubMed]

Molecules 2020,25, 105 15 of 17
2.
Chadha, N.; Bahia, M.S.; Kaur, M.; Silakari, O. Thiazolidine-2,4-dione derivatives: Programmed chemical
weapons for key protein targets of various pathological conditions. Bioorg. Med. Chem.
2015
,23, 2953–2974.
[CrossRef] [PubMed]
3.
Jain, V.S.; Vora, D.K.; Ramaa, C.S. Thiazolidine-2,4-diones: Progress towards multifarious applications.
Bioorg. Med. Chem. 2013,21, 1599–1620. [CrossRef] [PubMed]
4.
Ayhan-Kilcigil, G.; Altanlar, N. Synthesis of 3-substituted phenacyl-5-[2-phenyl-4H-4-oxo-1-benzopyran-6-yl)
methylenyl]-thiazolidine-2,4-diones and evaluation of their antimicrobial activity. Arzneim. Forsch. Drug Res.
2000,50, 154. [CrossRef]
5.
Tuncbilek, M.; Altanlar, N. Synthesis of new 3-(pubstituted phenacyl)-5-[3
0
-(4H-4-oxo-1-benzopyran-2-yl)-
benzylidene]-2,4-thiazolidinediones and their antimicrobial activity. Arch. Pharm. Chem. Life Sci.
2006
,339,
213–216. [CrossRef] [PubMed]
6.
Bozda˘g-Dundar, O.; Ozen, O.; Arzu, M.; Nurten, A.; Onur, A.; Engin, K.; Rahmiye, E. Synthesis and
antimicrobial activity of some new thiazolyl thiazolidine-2,4-dione derivatives. Bioorg. Med. Chem.
2007
,15,
6012–6017. [CrossRef] [PubMed]
7.
Alegaon, S.G.; Alagawadi, K.R.; Pawar, S.M.; Vinod, D.; Rajput, U. Synthesis, characterization, and biological
evaluation of thiazolidine-2,4-dione derivatives. Med. Chem. Res. 2014,23, 987–994. [CrossRef]
8.
Khan, F.A.K.; Patil, R.H.; Shinde, D.B.; Sangshett, J.N. Design and synthesis of
4
0
-((5-benzylidene-2,4-dioxothiazolidin-3-yl)methyl)biphenyl-2-carbonitrile analogs as bacterial Peptide
deformylase inhibitors. Chem. Biol. Drug. Des. 2016,88, 938–944. [CrossRef]
9.
Trotsko, N.; Kosikowska, U.; Paneth, A.; Plech, T.; Malm, A.; Wujec, M. Synthesis and antibacterial activity
of New Thiazolidine-2,4-dione-based chlorophenylthiosemi carbazone hybrids. Molecules
2018
,23, 1023.
[CrossRef]
10.
Moorthy, P.; Ekambaram, S.P.; Perumal, S.S. Synthesis, characterization and antimicrobial evaluation of
imidazolylthiazolidinedione derivatives. Arabian J. Chem. 2014,8, 1–7.
11.
Alagawadi, K.R.; Alegaon, S.G. Synthesis, characterization and antimicrobial activity evaluation of new
2,4-Thiazolidinediones bearing Imidazo [2, 1-b] [1, 3, 4] thiadiazole moiety. Arabian J. Chem.
2011
,4, 465–472.
[CrossRef]
12.
Aneja, D.K.; Lohan, P.; Arora, S.; Sharma, C.; Aneja, K.R.; Prakash, O. Synthesis of new
pyrazolyl-2,4-thiazolidinediones as antibacterial and antifungal agents. Org. Med. Chem. Lett.
2011
,
1, 1–15. [CrossRef] [PubMed]
13.
Mori, M.; Takagi, M.; Noritake, C.; Kagabu, S. 2,4-Dioxo-1,3-thiazolidine derivatives as a lead for new
fungicides. J. Pestic. Sci. 2008,33, 357–363. [CrossRef]
14.
Barros, C.D.; Amato, A.A.; de Oliveira, T.B.; Iannini, K.B.R.; da Silva, A.L.; da Silva, T.G.; Leite, E.S.;
Hernandes, M.Z.; de Lima, M.D.A.; Galdino, S.L.; et al. Synthesis and anti-inflammatory activity of new
arylidene-thiazolidine-2,4-diones as PPARγligands. Bioorg. Med. Chem. 2010,18, 3805–3811. [CrossRef]
15.
Maccari, R.; Vitale, R.M.; Ottan
à
, R.; Rocchiccioli, M.; Marrazzo, A.; Cardile, V.; Graziano, A.C.E.;
Amodeo, P.; Mura, U.; Corso, A.D. Structure-activity relationships and molecular modelling of new
5-arylidene-4-thiazolidinone derivatives as aldose reductase inhibitors and potential anti-inflammatory
agents. Eur. J. Med. Chem. 2014,81, 1–14. [CrossRef]
16.
Youssef, M.; White, M.S.; Villanueva, E.B.; El-Ashmawy, I.M.; Klegeris, A. Synthesis and biological
evaluation of novel pyrazolyl-2,4-thiazolidinediones as anti-inflammatory and neuroprotective agents.
Bioorg. Med. Chem. 2010,18, 2019–2028. [CrossRef]
17.
Ottan
à
, R.; Maccari, R.; Giglio, M.; Del Corso, A.; Cappiello, M.; Mura, U.; Cosconati, S.; Marinelli, L.;
Novellino, E.; Sartini, S.; et al. Identification of 5-arylidene-4-thiazolidinone derivatives endowed with dual
activity as aldose reductase inhibitors and antioxidant agents for the treatment of diabetic complications.
Eur. J. Med. Chem. 2011,46, 2797–2806. [CrossRef]
18.
Pandey, J.; Ali, A.; Gupta, A.K. Synthesis and evaluation of some new 2-(5-(4-benzamidobenzylidene)-
2,4-dioxothiazolidin-3-yl) acetic acid analogs as aldose reductase inhibitors. Asian J. Pharm. Clin. Res.
2017
,
10, 62–66.
19. Kumar, K.S.; Reddy, B.M.; Babu, V.H. Synthesis of some novel 2,4-thiazolidinedione incorporated pyrazole
derivatives as anti-cancer agent. Int. J. Pharm. Pharm. Sci. 2014,6, 831–834.

Molecules 2020,25, 105 16 of 17
20.
Trotsko, N.; Przekora, A.; Zalewska, J.; Ginalska, G.; Paneth, A.; Wujec, M. Synthesis and
in vitro
antiproliferative and antibacterial activity of new thiazolidine-2,4-dione derivatives. J. Enzyme. Inhib.
Med. Chem. 2017,33, 17–24. [CrossRef]
21.
Ozen, C.; C-Unlusoy, M.; Aliary, N.; Ozturk, M.; B-Dundar, O. Thiazolidinedione or Rhodanine: A study on
synthesis and anti-cancer activity comparison of novel thiazole derivatives. J. Pharm. Sci.
2017
,20, 415–427.
[CrossRef] [PubMed]
22.
Asati, V.; Bharti, S.K. Design, synthesis and molecular modeling studies of novel thiazolidine-2,4-dione
derivatives as potential anti-cancer agents. J. Mol. Structure. 2018,1154, 406–417. [CrossRef]
23.
Pavase1, L.S.; Mane, D.V. Synthesis and anticancer studies of 1-4-(2,4-Dioxo-thiazolidin-5-ylidenemethyl)-
benzenesulfonyl]-pyrrolidine-2-carboxylic acid derivatives. Chem. Biol. Inter. 2017,7, 183–194.
24.
Liu, K.; Rao, W.; Parikh, H.; Li, Q.; Guo, T.; Grant, S.; Kellogg, G.; Zhang, S.
3,5-Disubstituted-thiazolidine-2,4-dione analogs as anticancer agents: Design, synthesis and biological
characterization. Eur. J. Med. Chem. 2012,47, 125–137. [CrossRef] [PubMed]
25.
Sharma, P.; Reddy, T.S.; Kumar, N.P.; Senwar, K.R.; Bhargava, S.K.; Shankaraiah, N. Conventional and
microwave-assisted synthesis of new 1H-benzimidazole-thiazolidinedione derivatives: A potential anticancer
scaffold. Eur. J. Med. Chem. 2017,138, 234–245. [CrossRef]
26.
Sharma, R.K.; Younis, Y.; Mugumbate, G.; Njoroge, M.; Gut, J.; Rosenthal, P.J.; Chibale, K. Synthesis and
structure reactivity-relationship studies of thiazolidinediones as antiplasmodial inhibitors of the Plasmodium
falciparum cysteine protease falcipain-2. Eur. J. Med. Chem. 2015,90, 507–518. [CrossRef]
27.
Datar, P.A.; Aher, S.B. Design and synthesis of novel thiazolidine-2,4-diones as hypoglycemic agents. J. Saudi
Chem. Soc. 2016,20, 196–201. [CrossRef]
28.
Shrivastava, S.K.; Batham, A.; Sinha, S.K.; Parida, T.K.; Garabadu, D.; Choubey, P.K. Design, synthesis and
evaluation of novel thiazolidinedione derivatives as anti-hyperglycemic and anti-hyperlipidemic agents.
Med. Chem. Res. 2016,25, 2258–2266. [CrossRef]
29.
Naim, M.J.; Alam, M.J.; Nawaz, F.; Naidu, V.G.M.; Aaghaz, S.; Sahu, M.; Siddiqui, N.; Alam, O.
Synthesis, molecular docking and anti-diabetic evaluation of 2,4-thiazolidinedione based amide derivatives.
Bioorg. Chem. 2017,73, 24–36. [CrossRef]
30.
Bhat, B.A.; Ponnala, S.; Sahu, D.P.; Tiwari, P.; Tripathi, B.K.; Srivastava, A.K. Synthesis and anti-hyperglycemic
activity profiles of novel thiazolidinedione derivatives. Bioorg. Med. Chem. 2004,12, 5857–5864. [CrossRef]
31.
Mahapatra, M.K.; Kumar, R.; Kumar, M. Exploring sulfonate esters of 5-arylidene thiazolidine-2,4-diones as
PTP1B inhibitors with anti-hyperglycemic activity. Med. Chem. Res. 2018,27, 476–487. [CrossRef]
32.
Yoshioka, T.; Fujita, T.; Kanai, T.; Aizava, Y.; Kurumada, T.; Hasegava, K.; Horikoshi, H. Studies on hindered
phenols and analogues. 1. Hypolipidemic and hypoglycemic agents with ability to inhibit lipid peroxidation.
J. Med. Chem. 1989,32, 421–428. [CrossRef] [PubMed]
33.
Rakowitz, D.; Maccari, R.; Ottan
á
, R.; Vigorita, M.G.
In vitro
aldose reductase inhibitory activity of
5-benzyl-2,4-thiazolidinediones. Bioorg. Med. Chem. 2006,14, 567–574. [CrossRef] [PubMed]
34.
Momose, Y.; Maekawa, T.; Odaka, H.; Ikeda, H.; Sohdad, T. Novel 5-Substituted-1H-tetrazole derivatives as
potent glucose and lipid lowering agents. Chem. Pharm. Bull. 2002,50, 100–111. [CrossRef] [PubMed]
35.
Kumar, B.R.P.; Karvekar, M.D.; Adhikary, L.; Nanjan, N.J.; Suresh, B. Microwave induced
synthesis of the thiazolidine-2,4-dione motif and the efficient solvent free-solid phase parallel
syntheses of 5-Benzylidene-thiazolidine-2,4-dione and 5-benzylidene-2-thioxo-thiazolidine-4-one compounds.
J. Hetero. Chem. 2006,43, 897–903. [CrossRef]
36.
S-Funosas, R.; Prohens, R.; Barbas, R.; El-Faham, A.; Albericio, F. Oxyma: An Efficient additive for peptide
synthesis to replace the benzotriazole-based HOBt and HOAt with a lower risk of explosion. Chem. Eur. J.
2009,15, 9394–9403. [CrossRef]
37.
El-Faham, A.; Almarhoon, Z.; Ab-Megeed, A.; Albericio, F. OxymaPure/DIC: An efficient reagent for the
synthesis of a novel series of 4-[2-(2-Acetylaminophenyl)-2-oxo-acetylamino] benzoyl amino acid ester
derivatives. Molecules 2013,18, 14747–14759. [CrossRef]
38.
Romagnoli, R.; Baraldi, P.G.; Kimatrai Salvador, M.; Camacho, M.E.; Balzarini, J.; Bermejo, J.; Est
é
vez, F.
Anticancer activity of novel hybrid molecules containing 5-benzylidene thiazolidine-2,4-dione. Eur. J.
Med. Chem. 2013,63, 544–557. [CrossRef]

Molecules 2020,25, 105 17 of 17
39.
Azevedo, M.M.; Ramalho, P.; Silva, A.P.; T.-Santos, R.; P.-Vaz, C.; Rodrigues, A.G. Polyethyleneimine (PEI)
and PEI-based nanoparticles: Novel bacterial and yeast biofilm inhibitors. J. Med. Microbiol.
2014
,63,
1167–1173. [CrossRef]
40.
Maccari, R.; Ottana, R.; Curinga, C.; Vigorita, M.G.; Rakowitz, D.; Steindl, T.; Langer, T. Structure–activity
relationships and molecular modelling of 5-arylidene-2,4-thiazolidinediones active as aldose reductase
inhibitors. Bioorg. Med. Chem. 2005,13, 2809–2823. [CrossRef]
Sample Availability: Samples of the compounds 4a–sand 5a–oare available from the authors.
©
2019 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
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).