Antioxidant activity of thio-schiff bases

Article abstract of DOI:10.2174/1570180811310070002

This study evaluated and compares the antioxidant activity of six resveratrol analogues. The analogues 4'- Hydroxyphenyl-benzo[d]thiazole (A), p-(N,N-dimethyl)aminobenzylidene-2-aminothiophenol (B) and p-Nitrobenzylidene- 2-aminothiophenol (C) were synthe

Full text of DOI:10.2174/1570180811310070002

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Letters in Drug Design & Discovery, 2013, 10, 557-560 557
Antioxidant Activity of Thio-Schiff Bases
Juliana Alves dos Santos1, Rebeca Mól Lima2, Thamiris Vilela Pereira2, Antônio Márcio Resende
do Carmo3, Nádia Rezende Barbosa Raposo2,* and Adilson David da Silva1,*
1Departamento de Química, I.C.E., Universidade Federal de Juiz de Fora, Campus Universitário, Juiz de Fora, Minas
Gerais 36036-900, Brasil
2Faculdade de Farmácia, NUPICS, Campus Universitário, Juiz de Fora, Minas Gerais 36036-900, Brasil
3Faculdade de Odontologia, Campus Universitário, Juiz de Fora, Minas Gerais 36036-900, Brasil
Abstract: This study evaluated and compares the antioxidant activity of six resveratrol analogues. The analogues 4’-
Hydroxyphenyl-benzo[d]thiazole (A), p-(N,N-dimethyl)aminobenzylidene-2-aminothiophenol (B) and p-Nitrobenzylidene-
2-aminothiophenol (C) were synthesized and the antioxidant activity was evaluated using the DPPH method. A descrip-
tive statistical analysis and ANOVA followed by the Tukey test, with the aid of software. The best antioxidant activity
was demonstrated by compound C (half maximal inhibitory concentration (IC50) = 18.45µM), this compound is two times
more active than resveratrol (IC50= 37.28µM). Taken together, the data presented herein suggest that these molecules
might serve as potential antioxidant considering that molecular modification is an effective strategy. As such, the com-
pounds described herein can serve as prototypes for further research and the development of novel antioxidant agents.
Keywords: Antioxidants, Chemical synthesis, Resveratrol, Statistical analysis, Structure-activity relationship, Thio-Schiff bases.
INTRODUCTION
without the presence of sulfide group (Table 1). The antioxi-
dant activity of compounds D, E and F, has been previously
described by our group [2].
Schiff bases derived from aromatic amines and aldehydes
are the important compound owing to their wide range of
biological activities and industrial application [1]. In relation
to their potential therapeutic and pharmacological properties,
Schiff bases are known to have biological activities such as
antioxidant [2], antibacterial [3, 4], antitumor [5], antimicro-
bial [6] and antifungal [7]. Particularly, thio-Schiff bases
have received considerable attention in the field of coordina-
tion chemistry as ligands for the formation metal complexes
[8], without, however, have explored their biological activi-
ties alone. Among the few existing reports on the biological
activity of thio-Schiff bases, the majority refers to its anti-
fungal properties [9]. No information on the antioxidant ac-
tivity of this class of molecules was found in the literature.
MATERIALS AND METHODS
Chemistry
Melting points were recorded in a Mel-Temp apparatus
and are uncorrected. Infrared spectra were recorded on a
1
Schimadzu 8400 series FTIR instrument. H NMR spectra
were recorded on a Bruker AC-300 spectrometer at 300.13
MHz and 13C NMR spectra were recorded on a Bruker AC-
300 at 75 MHz. The chemical shifts are given in parts per
million relative to tetramethylsilane. Chromatography were
performed with Merck grade 60 silica gel (0.04–0.063 mm).
All chemical reagents were of analytical reagent grade.
Reactive oxygen species (ROS) are chemically-reactive
molecules and act as second messengers in energy produc-
tion, including phagocytosis, intracellular communication
signaling of living organisms, gap junctional [10]. Lower
levels of ROS can promote proliferation and differentiation,
while high levels of ROS can induce oxidation of lipids, pro-
teins and DNA, leading to cellular damage [11, 12].
General procedure for the synthesis of thio-Schiff bases
A, B and C:
The thio-Schiff bases were prepared by condensation of
o-aminothiophenol with the equimolar amount of aromatic
aldehydes in ethanol at room temperature (Scheme 1). The
structures of the compounds obtained A, B and C and their
antioxidant activities are show in the Table 1, as well as data
for compounds previously synthesized D, E and F.
Thus, in this paper we evaluated and compare the anti-
oxidant activity of six resveratrol analogues. The compounds
A, B and C were synthesized and their biological activities
were compared to their analogues, compounds D, E and F,
1
All compounds were characterized by H and 13C NMR
spectroscopy, IR spectroscopy and melting point and were in
accord with data in the literature [13-16]. The Table 2 shows
a characteristic singlet for the imine proton and imine carbon
to thio-Schiff bases and Schiff bases and Melting point (ºC).
The data of the compounds A, B and C are shown: 4’-
Hydroxyphenyl-benzo[d]thiazole (A). Pale yellowish solid;
reaction time: 24 h; yield 35%; melting point, 227.0-228.5
*Address correspondence to this author at the Departamento de Química,
I.C.E., Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais,
36036900, Brasil; Tel +55 32 2102 3310; Fax +55 32 2102 3314;
E-mail: david.silva@ufjf.edu.br
1875-628X/13 $58.00+.00
©2013 Bentham Science Publishers

558 Letters in Drug Design & Discovery, 2013, Vol. 10, No. 7
Santos et al.
Table 1. Concentration of Synthetic Schiff Bases Analogues and of the Standards that Inhibits 50% of DPPH Radicals.
Sample
Chemical Structure
IC50 (µM)*
S
HO
A
247.53
N
HS
N
B
C
76.22
18.45
N
HS
O2N
HO
N
N
N
N
N
D
E
F
403.87
2721.87
1577.80
O2N
HO
Resveratrol
37.28
OH
HO
p< 0.05 for comparison between average values of IC50 of Schiff bases analogues.
O
A. R = S; R1 = OH
R
N
R
R1
NH2
R
R1
B. R = SH; R1 = N(CH3)2
C. R = SH; R1 = NO2
D. R = H; R1 = OH
EtOH, r.t.
N
E. R = H; R1 = N(CH3)2
F. R = H; R1 = NO2
R1
Scheme 1. Synthetic pathway for thio-Schiff bases and Schiff bases.
°C. IR (KBr): υmax 3481, 2987, 1606, 1523, 1483 cm-1. RMN
1H (300 MHz, DMSO-d6), δ (ppm), J (Hz): 10.25 (s, 1H);
8.06 (d, 1H, J= 6.0); 7.97 (d, 1H, J= 9.0); 7.93 (d, 2H, J=
9.0); 7.49 (td, 1H, J= 1.2, J= 7.5); 7.39 (td, 1H, J= 1.2, J=
7.5); 6.94 (d, 2H, J= 9.0). RMN 13C (75 MHz, DMSO-d6), δ
(ppm): 167.4; 160.5; 153.7; 134.1; 129.0; 126.4; 124.0;
125.5; 122.4; 121.6; 121.5; 113.0; 112.4; 40.6; p-
Nitrobenzylidene-2-aminothiophenol (C). Yellow solid; reac-
tion time: 10 h; yield 85%; melting point, 120.8-121.9 °C. IR
(KBr): υmax 3479, 3332, 2968, 1598, 1515, 1471 cm-1. RMN
1H (300 MHz, DMSO-d6), δ (ppm), J (Hz): 8.19 (d, 2H, J =
6.0); 7.68 (d, 2H, J = 9.0); 7.06 (d, 1H, J = 6.0); 7.00 (t, 1H,
J = 6.0); 6.83 (d, 1H, J = 6.0), 6.77 (t, 1H, J = 6.0, J = 9.0);
6.44 (s, 1H). RMN 13C (75MHz, DMSO-d6), δ (ppm): 149.4;
148.1; 145.9; 128.0; 127.4; 126.1; 124.2; 121.7; 110.7.
122.1;
116.1;
p-(N,N-dimethyl)aminobenzylidene-2-
aminothiophenol (B). Yellow solid; reaction time: 5 h; yield
68%; melting point, 162.9-165.0 °C. IR (KBr): υmax 3479,
1
2920, 1610, 1527, 1487 cm-1. RMN H (300 MHz, DMSO-
d6), δ (ppm), J (Hz): 7.98 (m, 1H); 7.42 (d, 2H, J= 9.0); 7.02
(d, 1H, J= 9.0); 6.92 (t, 1H, J= 9.0); 6.73 (m, 2H); 6.61 (d,
1H, J= 9.0); 6.34 (s, 1H); 2.95 (s, 6H). RMN 13C (75MHz,
DMSO-d6), δ (ppm): 154.6; 152.4; 149.5; 129.0; 128.4;
Antioxidant Activity
Studies have shown that resveratrol is rapidly absorbed
but quickly metabolized, usually in the first hour following
oral administration in humans [17]. Some alternatives to

Da Silva AD.Antioxidant Activity of thio-Schiff bases
Letters in Drug Design & Discovery, 2013, Vol. 10, No. 7 559
Table 2. Spectral Data of thio and Schiff Bases.
Compounds
δ H imine (ppm)
δC=Nimine(ppm)
Melting point (ºC)
A
B
C
D
E
F
-
167.4
152.3
149.5
160.0
159.9
158.8
227.0-228.5
162.9-165.0
120.8-121.9
89.2-90.7
6.34
6.44
8.44
8.39
8.80
96.8-97.3
89.6-90.7
The NMR experiments were performed at 300 MHz for 1H and 75 MHz for 13C in DMSO-d6 (ppm).
improve resveratrol bioavailability were blocking its metabo-
lism, the discovery of more potent compounds that mimic its
effects or developing analogues with improved bioavailabil-
ity [18]. Resveratrol metabolites have a very short half-life
and are subjected to rapid urinary elimination [19]. Based on
this information valuated functional groups were inserted in
the phenyl ring. Based on the concept of bioisosterism [20]
the basic skeleton of trans-stilbene was modified by re-
placement of the central C=C linkage with a C=N double
bond [21]. In an attempt to preserve the resveratrol antioxi-
dant activity, the five analog molecules in this compound
kept the two aromatic rings and double bonds; they can form
relatively stable intermediates due to resonance of the ring
[22].
modifications. This method is based on the DPPH reduction
in the presence of an antioxidant (AH) a proton donor (H+)
for a non-radical (DPPH-H) [24]. A 150 µL of a DPPH etha-
nolic solution of 0.05 mM were added to 50 µL of ethanol
solution of thio-Schiff bases and Schiff bases at concentra-
tions from 0.97 to 250 µg /mL in 96-well plates. Resveratrol
(trans-resveratrol 99.0%, AttivosMagistrais, Brazil) was used
as a standard at the same concentrations. Reactions elapsed
at room temperature for 30 minutes in the dark and then the
absorbance was read in a spectrophotometer (λ= 510 nm).
Inhibition of DPPH radical was calculated using the equa-
tion:
% of inhibition = 100 x (A0 – As) / Ao
Being: Ao absorbance as the negative control and As a
The best antioxidant activity was demonstrated by com-
pound C (half maximal inhibitory concentration (IC50)=
18.45 µM). IC50 value is the concentration of the sample
required to inhibit 50% of the radical. This compound is two
times more active than resveratrol (IC50= 37.28 µM) and
85.5 times more active than compound F (IC50= 1577.80
µM). The difference structural between the compound C and
the compound F is a sulfide group linked to aromatic ring.
Taken together, the data presented herein suggest that these
molecules might serve as potential antioxidant considering
that molecular modification is an effective strategy. As such,
the compounds described herein can serve as prototypes for
further research and the development of novel antioxidant
agents.
absorbance of test samples.
The IC50 value was calculated from the line in the equa-
tion of the linear dispersion graph. All tests were performed
in triplicate.
Statistical Analysis
We performed a descriptive statistical analysis and
ANOVA followed by the Tukey test, with the aid of Statisti-
cal Package for Social Sciences (SPSS) v.14.0 for Windows
software, to compare the average values of IC50 calculated
between the thio-Schiff bases and Schiff bases versus the
standard. The level of significance was 5%.
CONCLUSIONS
Similarly, the compound B (IC50 = 76.22µM) is 36 times
more active than compound E (IC50 =2721.87 µM). The ana-
logues A had no significant results on the antioxidant activ-
ity test, which can be explained by the fact of not presenting
the sulfide groups, in this case the reaction of addition of
sulfide group provides the cyclized benzothiazole derivative
A.
The compounds B and C showed significant antioxidant
activity than compounds D, E and F. The compound C dem-
onstrated the best antioxidant activity (IC50 = 18.45µM)
which was two times more active than resveratrol (IC50
=
37.28µM). The difference structural between the compounds
B and C to compounds D, E and F is a sulfide group linked
to aromatic ring. The compound A show a cyclized form, as
expected, the antioxidant activity is comparably to com-
pounds without a sulfide group.
Resveratrol analogues may have an important antioxidant
activity, with one with higher IC50 presented by the natural
compound. Studies arising from the relationship between the
properties of the analogues chemical structure and coupled
with new molecular changes may contribute to the develop-
ment of more effective bioactive molecules.
CONFLICT OF INTEREST
None of the authors of the above manuscript has declared
any conflict of interest.
Antioxidant Activity
ACKNOWLEDGEMENTS
The antioxidant activity was evaluated using the 2,2-
diphenyl-1-picrylhydrazyl (DPPH; Sigma-Aldrich, USA)
assay, described by Sreejayan and Rao[23], with minor
The authors gratefully acknowledge FAPEMIG, CNPq,
CAPES and PROPESQ/UFJF for financial support.

560 Letters in Drug Design & Discovery, 2013, Vol. 10, No. 7
Santos et al.
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Accepted: March 17, 2013