Antibacterial, antioxidant and binding studies of some novel diaryl sulphide derivatives

Article abstract of DOI:10.1080/10426507.2012.685996

A series of novel acyclic and cyclic diaryl sulphides was synthesized from 2,2-dithiobenzoic acid. The various diaryl sulphides were characterized by use of spectral (IR, ¹H and ¹³C NMR, ESI/MS) and elemental analyses. The antimicrobial activities of the compounds were evaluated in terms of their minimum inhibition concentration (MIC) against a panel of clinical isolates bacteria and were found to possess only moderate antimicrobial activities. N,N-Bis(2-hydroxyphenyl)-2,2-thiodibenzamide (13), exhibiting a hydroxy group at the phenyl ring, was the most active antimicrobial agent within the series, with MIC values of 0.05 mg mL^-1 and 10 mg mL ^-1 against Staphylococcus aureus and Bacillus cereus, respectively. The antioxidant efficiency of the diaryl sulphides was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity with 13 being the most active compound. The interaction of 2,2-thiodibenzanilide, N,N-bis(2- methylphenyl)-2,2-thiodibenzamide, and N,N-bis(2-hydroxyphenyl)-2,2- thiobenzamide with guanine, glutamic acid, and urea were studied quantitatively with binding constants ranging from 1 × 10³ M¹ to 2.7 × 10⁴ M¹.

Full text of DOI:10.1080/10426507.2012.685996

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Phosphorus, Sulfur, and Silicon and the
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Antibacterial, Antioxidant and Binding
Studies of Some Novel Diaryl Sulphide
Derivatives
Salma Moosun a , John A. Joule b , Minu G. Bhowon a & Sabina
Jhaumeer-Laulloo a
a Department of Chemistry, Faculty of Science , University of
Mauritius , Réduit , Mauritius
b The School of Chemistry , The University of Manchester ,
Manchester , M13 9PL , UK
Accepted author version posted online: 24 Apr 2012.Published
online: 06 Aug 2012.
To cite this article: Salma Moosun , John A. Joule , Minu G. Bhowon & Sabina Jhaumeer-
Laulloo (2012) Antibacterial, Antioxidant and Binding Studies of Some Novel Diaryl Sulphide
Derivatives, Phosphorus, Sulfur, and Silicon and the Related Elements, 187:11, 1383-1400, DOI:
10.1080/10426507.2012.685996
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Phosphorus, Sulfur, and Silicon, 187:1383–1400, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.685996
ANTIBACTERIAL, ANTIOXIDANT
AND BINDING STUDIES OF SOME NOVEL DIARYL
SULPHIDE DERIVATIVES
Salma Moosun,1 John A. Joule,2 Minu G. Bhowon,1
and Sabina Jhaumeer-Laulloo1
1Department of Chemistry, Faculty of Science, University of Mauritius, Re´duit,
Mauritius
2The School of Chemistry, The University of Manchester, Manchester M13 9PL, UK
GRAPHICAL ABSTRACT
Abstract A series of novel acyclic and cyclic diaryl sulphides was synthesized from 2,2ꢁ-
dithiobenzoic acid. The various diaryl sulphides were characterized by use of spectral (IR,
1H and 13C NMR, ESI/MS) and elemental analyses. The antimicrobial activities of the com-
pounds were evaluated in terms of their minimum inhibition concentration (MIC) against a
panel of clinical isolates bacteria and were found to possess only moderate antimicrobial
activities. N,Nꢁ-Bis(2-hydroxyphenyl)-2,2ꢁ-thiodibenzamide (13), exhibiting a hydroxy group
at the phenyl ring, was the most active antimicrobial agent within the series, with MIC val-
ues of 0.05 mg mL–1 and 10 mg mL–1 against Staphylococcus aureus and Bacillus cereus,
respectively. The antioxidant efficiency of the diaryl sulphides was determined by 2,2-diphenyl-
1-picrylhydrazyl (DPPH) scavenging activity with 13 being the most active compound.
Received 17 February 2012; accepted 13 April 2012.
The authors acknowledge the help of the Candos Hospital for providing the clinical isolates. One of the
authors is grateful to the Tertiary Education Commission of Mauritius for financial assistance.
Address correspondence to Sabina Jhaumeer-Laulloo, Department of Chemistry, Faculty of Science,
University of Mauritius, Re´duit, Mauritius. E-mail: sabina@uom.ac.mu
1383

1384
S. MOOSUN ET AL.
The interaction of 2,2ꢁ-thiodibenzanilide, N,Nꢁ-bis(2-methylphenyl)-2,2ꢁ-thiodibenzamide, and
N,Nꢁ-bis(2-hydroxyphenyl)-2,2ꢁ-thiobenzamide with guanine, glutamic acid, and urea were
studied quantitatively with binding constants ranging from 1 × 103 M−1 to 2.7 × 104 M−1
.
Keywords Diaryl sulphides; benzamides; antibacterial; antioxidant; binding constants
INTRODUCTION
Molecules containing a C S bond constitute a very important class of organic com-
pounds that have important biological, pharmaceutical, catalytic, and materials interest.1–5
The impetus for the advancement of C S bond forming reactions is the prevalence of
biaryl sulphides in natural and synthetic products and because of their broad application to
organic and medicinal chemistry.6
The various methods for the synthesis of aryl sulphides include nucleophilic attack on
disulphides,7 aromatic substitution reactions,8 and metal-mediated disulphide reductions.9
The development of practical and efficient methods to generate aryl sulphides has been
realized through transition metal catalysis.10 In this context, metal-catalyzed systems using
copper oxide have been used to synthesize the novel diaryl sulphides.
Compounds containing diaryl sulphide moieties have been reported to exhibit various
biological activities such as antioxidant,11,12 antileishmanial,13 inhibition of trypanothione
reductase,14–16 inhibition of BCR-ABL kinase,17 antitrypanosomal and antimalarial,18,19
anti-inflammatory,20 and antibacterial.21–23 It is also known that the biological activities
of the compounds are often related to the presence of additional groups such as aromatic
rings, the substituents linked to the rings,24–27 as well as the presence of amide functional
moieties.28,29
The study of the interaction of simple molecules with biomolecules such as proteins,
nucleic acids, or even byproducts such as urea generated through metabolic pathways, have
aroused great interest among chemists and biologists.30 A number of established spectro-
scopic methods are available for the quantitative study of these kinds of interactions. Among
all of these, ultraviolet-visible (UV) spectrophotometry represents one of the simplest ana-
lytical methods used for explaining the interactions of the receptors with the biomolecules
as well as for the determination of their binding constants.31
Keeping in view the biological importance of aryl sulphides and the few reports avail-
able on antibacterial and antioxidant activities of such types of compounds, we report here
the synthesis of a new class of diaryl sulphide derivatives 1–30 along with their biological
evaluations. The results of this study may be useful in search for new antimicrobials and
antioxidants.
RESULTS AND DISCUSSION
Chemistry
Synthesis of the key intermediates 2,2ꢁ-thiodibenzoic acid 1 and 4-nitro-2,2ꢁ-
thiodibenzoic acid 2 was carried out using a modified reported synthetic strategy.32
Thus, the reaction of 2-chlorobenzoic acid or 4-nitro-2-chlorobenzoic acid with 2-
mercaptobenzoic acid using copper(I) oxide as catalyst under nitrogen atmosphere was
utilized. The physical and spectroscopic data of 133 and 234 are corroborated by the data
reported in literature. The presence of a nitro group was found to enhance the yield of

DIARYL DISULFIDE DERIVATIVES
1385
the diacid and to reduce the reaction time. The syntheses of the compounds 1–30 were
performed by reacting suitable commercially available amines/diamines with bis-acid
chlorides of 1 and 2 (Scheme 1). The structures of the compounds were fully characterized
by spectroscopic methods and elemental analyses. Out of these amides only compounds 7
and 9 are known but no spectral data were given.35 The structures of 11, 21, and 25 were
confirmed by single crystal X-ray analyses, the details of which will be reported elsewhere.
Compounds 3–5 are cyclic anilides, 7–10 are anilides with no substituents, while 13–26
are substituted anilides. The compounds 27–30 are derivatives of urea and thiourea.
The IR spectra of the synthesized compounds showed two characteristic bands near
3200–3400 cm−1 and 1635–1680 cm−1 corresponding to νNH and νC = O, respectively. The
nitro derivatives showed νNH at slightly higher frequencies. In the compounds 13–20, the
broad band in the region of 3000–3200 cm−1 was due to νOH. In the 1H NMR spectra, the
amide protons appeared in the range of δ 8.00–10.50. The OH protons in 13–20 appeared
at δ 8.00–9.00.
The reaction of compound 1 with urea and thiourea led to the formation of cyclic
compounds 27 and 29 while in the case of their nitro derivatives, a mixture of cyclic and
acyclic compounds were formed with the cyclic compounds 28 and 30 obtained as major
products.
Biological Activity
Antibacterial Activity. All the compounds exhibited poor activities against the
fungi tested (Candida albicans, Aspergillus niger) at 200 mg mL–1 (data not shown).
Compounds 1–20, 28, and 30 were screened for antibacterial activity against two
Gram-positive (Staphylococcus aureus, Bacillus cereus) and three Gram-negative bacte-
ria (Shigella flexneri, Klebsiella pneumonia, Pseudomonas aeruginosa) and two fungi
(C. albicans, A. niger) of clinical isolates using the conventional agar dilution method.36
Preloaded erythromycin disc (30 µg mL–1) was used as positive control (PC). The data
showed that all strains were more sensitive against the Gram-positive bacteria compared
to the Gram-negative bacteria. Table 1 shows the minimum inhibition concentration (MIC;
mg mL–1) values of the compounds on all the bacteria tested.
The deduced patterns of antibacterial activity of the diaryl sulphide derivatives are in
the following order: S .aureus > B. cereus > K. pneumonia > P. aeruginosa ≈ S. flexneri.
Carboxylic acids and amides generally showed good antimicrobial activity.37–39 The
diaryl sulphide amides displayed better antibacterial activities compared to the diacids 1
and 2, thus highlighting the importance of the CONH moiety in antimicrobial activity.
The antimicrobial activity of the compounds depends a lot on physicochemical pa-
rameters such as lipophilicity and hydrosolubility of the compounds.40 By comparing the
activities of the compounds, it was found that they globally showed higher sensitivity to-
wards Gram-positive bacteria than Gram-negative bacteria. This may be due to the presence
of the hydrophilic lipopolysaccharide molecules surrounding the Gram-negative bacteria,
which provide protection against hydrophobic molecules.41
Compounds bearing nitro groups on the phenyl ring showed lower activity compared
to the corresponding compounds having no nitro groups. This may be attributed to the
electron-withdrawing inductive effect of NO2. It decreases the ability of the compound to
interact with the hydrophobic part of the bacterial membrane.42 Reports on the effect of NO2
on antibacterial activity are often contradictory since in some cases it has been reported to
enhance the antibacterial activity43,44 while in others reduced activity was observed.45

1386
S. MOOSUN ET AL.
Scheme 1 Synthesis of substituted diaryl sulphide amides 1–30.

DIARYL DISULFIDE DERIVATIVES
1387
Table 1 Antibacterial assay. Minimum inhibitory concentration of compounds 1–20, 28 and 30[a], and log P[b]
values
Minimum inhibitory concentration in mg mL–1
Compound
S. aureus
B. cereus
K. pneumonia
S. flexneri
P. aeruginosa
log P
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
28
30
25
75
50
75
5
50
15
50
10
25
1
25
75
25
50
5
50
5
75
5
15
0.5
10
10
50
100
100
>100
100
100
100
50
75
100
100
100
100
100
100
100
100
100
100
>100
10
25
50
50
50
75
75
100
100
25
75
100
>100
>100
100
>100
>100
>100
>100
>100
100
>100
25
50
75
50
75
100
3.251
2.856
2.177
1.586
2.496
1.907
5.886
4.886
5.748
5.552
6.722
6.382
4.969
4.774
4.969
4.774
4.969
4.774
6.936
7.014
2.503
3.01
>100
>100
>100
>100
100
>100
>100
>100
100
>100
15
25
50
50
75
100
75
75
100
100
25
0.05
1
25
75
10
25
50
50
75
50
50
100
50
100
100
100
10
[a]Compounds 21–26, 27, and 29 showed no activities. Erythromycin (30 µg mL–1) = positive control
(S. aureus = 32 mm, B. cereus = 18 mm, K. pneumonia = 10 mm, S. flexneri = 10 mm). DMSO = nega-
tive control. [b]Calculated using ChemDraw.
Compound 5 having a methyl group in the aliphatic chain, exhibited the highest
activity in this cyclic series against both Gram-positive bacteria (MIC = 5 mg mL–1) used
in this study. Compound 13 with a hydroxy substituent at the ortho-position, showed highest
activity against S. aureus with MIC = 0.05 mg mL–1 and was very effective against all the
clinical isolates as well. Compound 19 with a 2-hydroxynaphth-1-yl unit was expected to
show higher activity due to the presence of the OH group and an increase in aromaticity.
However, it was found to be less potent compared to 13 (Table 1). This is may be due to
the steric factor that overcomes the lipophilic character and contributed to poor diffusion
of the compound making it less accessible for cell permeation.
Among the heterocyclic urea derivatives, which are known to be good antimicrobial
agents,46 compound 30 was found to exhibit better activity than 28 perhaps due to the
presence of the thiocarbonyl group.
The arrangement of hydroxy groups as substituents is known to be important in
antimicrobial activity.47,48 The diaryl sulphides 13 and 14 with a hydroxy group in the
ortho-positions exhibited the most powerful inhibitory activity compared to meta-positions
or para-positions. Usually, it has been found that para-substituted groups gave better
antimicrobial activities compared to the ortho- or meta-isomers49,50 but for a hydroxy
group, an ortho-position is preferred.51 The diaryl sulphides 13–18 were also found to be
effective against the Gram-negative bacteria. The broad spectrum activity of the phenolic

1388
S. MOOSUN ET AL.
amides may be due to the presence of the OH groups which easily bind to the hydrophilic
area of the bacteria and facilitate their entry across the membrane.
Further, antimicrobial studies on 11, 13, 21–27, and 29 were carried out using coded
bacteria S. aureus (25923, 29123), B. cereus (11778), Escherichia coli (25922), and Proteus
mirabilis (12453). Except 11 and 13, the compounds tested did not possess any activities
against the coded bacteria. Compound 11 displayed moderate activity against B. cereus with
only 14.7 mm zone of inhibition. Compound 13 was found to be active against S. aureus
and B. cereus with 18 (25923), 7.3 (29123), and 12.7 (11778) mm as zones of inhibition
while it showed no activity against the Gram-negative strains. The standard erythromycin
drug showed a zone of inhibition of 20 mm (25923) and 14 mm (29123).
The importance of lipophilicity for antibacterial activity has been emphasized in
many reports.52–55 As a result of their lipophilic character, the compounds will preferentially
partition from an aqueous phase into membrane structures and that will cause an expansion
of the membrane, resulting in increased membrane fluidity and permeability, and their
disruption.56 The lipophilicities of the compounds 1–20, 28, and 30 were measured in
terms of log P where log P is defined as the 1-octanol/water coefficient.57 This coefficient
can be determined by HPLC58 or calculated using ChemDraw (Table 1). We have attempted
to establish a relationship between log P and MIC of the compounds.
The log P values were in the range 1.586–7.014 showing variable MIC values against
the evaluated strains. In the aliphatic system 3–6, we found that compound 5, having the
highest log P value, showed a better activity with an MIC value (5 mg mL–1) which is in
accordance to work reported in the literature, where it has been argued that compounds with
higher lipophilicity are better antibacterial agents.59,60 It is also interesting to note that the
presence of the polar nitro groups decreases the lipophilicity and these compounds showed
lower activity with higher MIC values in each case. Comparing the aromatic compounds 9
and 11, it was observed that compound 11 with a methyl group, displayed a higher log P
(6.722) and a better activity with MIC = 0.5 mg mL–1. The introduction of polar groups like
hydroxy onto the benzene ring causes a decrease in lipophilic character (log P = 4.969) but
highest activity was obtained (MIC = 0.05 mg mL–1). Compounds 13, 15, and 16 having
hydroxy groups in the ortho-, meta-, and para-positions have the same log P value but
exhibited different MIC values against the strains tested. Compound 19 having the highest
log P value exhibited moderate activity. The results obtained in the present work indicate
that lipophilicity is not the main factor influencing antibacterial properties as suggested by
other authors.61,62
2,2-diphenyl-1-picrylhydrazyl (DPPH) Radical-Scavenging Activity
The power of an antioxidant to transfer one electron to reduce any compound may be
a significant indicator of the potential antioxidant activity of a compound.63 The ability to
scavenge stable DPPH radical is a widely used and accurate method to evaluate antioxidant
activity.64 It has been reported that antioxidant activity depends on the number of hydrogen-
donating hydroxy groups65–67 and on the structural features which stabilize the radical
formed. But there are very few reports on potential antioxidants that do not possess a
phenolic group. The radical-scavenging activity of the acyclic aryl sulphides 9, 11–13, and
23–28 bearing hydroxy, alkyl, or halide groups, and of the cyclic aryl sulphides 3, 27, and
29 were evaluated by monitoring the reduction of light absorption at 492 nm by DPPH
radicals upon reaction with aryl sulphides in methanol solution (Table 2 and Figure 1). These

DIARYL DISULFIDE DERIVATIVES
1389
Table 2 IC50 (mg mL–1) values for the DPPH free radical scavenging activities of compounds 9, 11, 13, 21, and
22[a]
Entry
Compound
IC50 (mg mL–1
)
1
2
3
4
5
6
9
11
13
21
22
1.37 0.042
16.7 0.807
3.10 × 10−3 0.001
12.6 2.59
4.48 0.496
4.88 × 10−3 0.108
Ascorbic acid
[a]The IC50 of compounds 23–26 could not be determined.
particular compounds were chosen to investigate the structural effect on the antioxidant
activity.
It was found that the compounds tested exhibited moderate to good activity except
for the halide-substituted aryl sulphides. As shown in Figure 1, increasing the concentration
of the compounds (0.05–100 mg mL–1) led to increased inhibitory activities. The radical-
scavenging activity is expressed as the 50% scavenging concentration (IC50) based on the
amount of compound required to decrease the initial DPPH radical concentration to half
of its initial value. The aryl sulphides containing halogen substituents 23–26 with log P =
6.064, 6.864, 7.406, and 8.643 showed negligible inhibition except the iodo derivative
(45.1% at 100 mg mL–1). This is in agreement with what has been reported in the literature
that compounds with substituents having the highest lipophilicity (log P), the lowest electron
withdrawing power, and the highest polarizability lead to the highest antioxidant activity68
(Table 1).
Compound 3 displayed a very poor scavenging activity. Compound 27 containing a
urea moiety did not possess any antioxidant properties whereas the thiourea derivative 29
showed some inhibition at 3.125 mg mL–1. However, the IC50 of compound 29 could not
be calculated due to its insolubility and precipitation upon addition of DPPH. This suggests
that cyclic diaryl sulphides show poor scavenging activity compared to acyclic compounds.
120
100
80
60
40
20
0
9
11
13
21
22
ascorbic
-2
-1
0
1
2
3
log C
Figure 1 Free radical scavenging activity of compounds (9, 11, 13, 21, 22) and ascorbic acid with concentration
ranging from 0.05–100 mg mL–1 where log C is the logarithm of the concentration of the compounds.

1390
S. MOOSUN ET AL.
Comparing the IC50 values of the aryl sulphides 11, 21, and 22 with different alkyl
substituents at the aromatic ring revealed a slight to moderate increase in the radical-
scavenging activity with increasing length of the alkyl chain. The activity could be correlated
with an increase in lipophilicity character as the alkyl chain length increases (log P values:
6.722, 7.557, 8.391). However 9, with no alkyl substituent group and the lowest log P value,
exhibited a significantly higher activity compared to the other three compounds mentioned
above. Compound 13 possessing a hydroxy proton showed the highest activity in the series
and this is concordant with the reported fact that the main structural-scavenging unit is
a phenolic hydroxyl group.69,70 At the same time, it is important to note that 13 showed
comparable activities compared to the control antioxidant, ascorbic acid.
Binding Studies
Noncovalent interactions play a leading role in controlling the secondary and tertiary
structures of natural macromolecules such as polypeptides or polynucleotides.71 Glutamic
acid is a key molecule in cellular metabolism and guanine is the preferred site in the DNA
helix whereby anticancer agents bind covalently.72,73 In addition, these interactions are also
important for metabolites such as urea which is a chief nitrogenous end product of the
metabolic breakdown of proteins.74 Therefore, the interactions of the host molecules 9, 11,
and 13 were investigated by means of electronic absorption in order to evaluate their binding
affinities with guest molecules such as guanine, glutamic acid, and urea. In the UV visible
spectrum of the selected diaryl sulphides, the intense absorption bands with maxima at
257 nm for 9, 249 nm for 11, and 247 and 290 nm for 13 were attributed to the intra-ligand
π-π∗ transition. The UV absorption peak was obtained by titration of the diaryl sulphides
with increasing concentrations of the guest molecules. The absorption spectra of the three
compounds being investigated in the absence and presence of the guest molecules are given
in Figure 2. The binding of small molecules to biomolecules is classically characterized
through absorption titrations. Generally, a red shift or blue shift and hypochromic (lower
absorbance) or hyperchromic (enhanced absorbance) effects are observed in the absorption
spectra of small molecules if they intercalate with the biomolecules.75
The binding constant was calculated using the double-reciprocal equation given
below:
1/(A0 − A) = 1/A0 + 1/(K × A0 × C)
where A0 and A are the absorbances of the host molecules in the absence and presence of
guest molecules respectively. K is the binding constant between host and guest molecule
and C is the concentration of the host molecules. The values for binding constant at 40 ◦C
are given in Table 3.
With increasing concentration of guanine, a hyperchromic shift was observed for 9,
11, and 13 accompanied by a blue (2–5 nm) or red shift (2–9 nm) which is consistent
with groove binding, and this may be attributed to external contact (surface binding) with
the guanine. In the case of glutamic acid, hyperchromism was observed with no change
in wavelength. For 13, an increase in urea concentration resulted in a hypochromism with
slight red shift at 247 nm, and a hyperchromic effect with blue shift at 290 nm was
observed. Compounds 9 and 11 displayed hypochromism with no change in wavelength.
The dissimilar effects observed for 13 could be due to a different mode of interaction. The

DIARYL DISULFIDE DERIVATIVES
1391
Figure 2 Absorption spectra of diaryl sulphides (0.1–0.05 mM) in phosphate buffer (pH 7.4) in the absence and
presence of increasing amounts (0.01 M to 1 mM) of guest molecules.

1392
S. MOOSUN ET AL.
Table 3 Binding constants, K (M−1) for compounds 9, 11, and 13
Compounds
9
11
13
Guanine
Urea
Glutamic acid
2.5 × 103
2 × 104
1 × 103
1.3 × 104
4 × 103
3 × 103
7.5 × 103
2.7 × 104
1.3 × 104
low hyperchromic and hypochromic effects observed indicate weak interaction with the
host molecules.
It is evident from the binding constants (Table 3) that the three compounds 9, 11, and
13 exhibit almost similar binding affinities with the same guest molecules with 13 > 9 >
11. The binding constants obtained for the compounds studied are lower compared to the
standard intercalator ethidium bromide (K = 1.4 × 106 M−1).74 Compound 13 having the
highest binding constant also showed higher radical scavenging activity.76
CONCLUSION
In the present investigation, it has been observed that an increase in lipophilicity gen-
erally leads to an increase in antibacterial and antioxidant properties. However, compound
13 with a 2-hydroxy substituent at the phenyl ring having a lower log P value showed a
good biological profile with MIC = 0.05 mg mL–1 against S. aureus and SC50 = 3.10 ×
10−3 0.0009 in the DPPH-free radical assay. This clearly indicates that lipophilicity is
not the only criterion determining biological activities. Steric and electronic factors must
also have an influence, as well as the position of substituents at the aromatic ring. The
results of binding studies indicate that the compounds 9, 11, and 13 have similar binding
affinities with the biomolecules used. The present findings lead to the basis for the synthesis
of compounds to be potential template molecules for pharmaceutical applications.
EXPERIMENTAL
All reagents and solvents were purchased from Aldrich (Germany), Sigma-Aldrich
(France), Alpha Chemica (India), Alfa Aesar (UK), BDH (UK) without any further purifi-
cation. The coded bacteria were purchased from Microbiologics (St. Cloud, MN). They
were used without further purification except for thionyl chloride (98%) which was distilled
◦
prior to use and the fraction boiling at 78 C was collected under anhydrous conditions.
Thin layer chromatography (TLC) was carried out on plates precoated with Merck silica
gel. Melting points of the samples were determined using a Stuart Scientific Electric melt-
ing point apparatus and are uncorrected. Infrared spectra were recorded as KBr pellets on
1
an Avatar 320 FTIR spectrometer in the range 400–4000 cm−1. H NMR and 13C NMR
spectra were recorded at 250 MHz and 75 MHz on a Bruker Electro Spin spectrometer
using DMSO-d6. Carbon, hydrogen, nitrogen, and sulfur contents were determined with a
LECO CHNS-932 analyzer. Centrifugation was performed using a Hermlt Z320 appara-
tus. Mass spectra were recorded as electron spray on a Micromass Trio 2000 instrument.
The absorbance of the compounds for antioxidant activity was recorded using Labsystems
Multiskan Ms EIA Reader and the electronic spectra of the samples were measured with
an UV spectrophotometer Biochrom Libra S22.

DIARYL DISULFIDE DERIVATIVES
1393
General Procedure for Synthesis of Diacids (1, 2)
To a suspension of NaH (0.23 g, 9.58 mmol) in DMF (10–15 mL), 2-mercaptobenzoic
acid (0.500 g, 3.25 mmol) was added and the reaction mixture was stirred at room tem-
perature until the evolution of hydrogen gas stopped. 2-Chlorobenzoic acid or 2-chloro-
4-nitrobenzoic acid (3.25 mmol) and Cu2O (0.0715 g, 0.50 mmol) were then added and
the resulting mixture was refluxed under a nitrogen atmosphere for 5 h with continuous
stirring. The residue was cooled, poured onto ice, and filtered. The solid obtained was
extracted with diethyl ether (30 mL) and the filtrate and washings were combined and then
concentrated to give a solid that was recrystallized from ethyl acetate and petroleum ether
(1:5, 60–80 ◦C) to give a pale yellow solid.
2,2ꢁ-Thiodibenzoic acid (1): Yield 94%, m.p. 223 ◦C (lit.: 227–230 ◦C). IR:
2510–3527, 1689, 746. 1H NMR: 7.25 (d, 2H, J = 7 Hz, ArH), 7.56 (t, 2H, J = 8 Hz, ArH),
7.96 (d, 2H, J = 7 Hz, ArH), 8.18 (d, 2H, J = 8 Hz, ArH). 13C NMR: 125.4, 126.6, 128.5,
132.1, 133.7, 140.2, 168.4. Anal. Calcd. for C14H10O4S: C, 61.3; H, 3.67; S, 11.7. Found:
C, 61.0; H, 3.68; S, 12.1.
◦
◦
4-Nitro-2,2ꢁ-thiodibenzoic acid (2): Yield 97%, m.p. 293 C (lit.: 290 C). IR:
2505–3567, 1682, 1688, 1524, 1346, 763. 1H NMR: 6.76 (d, 1H, J = 8 Hz, ArH), 7.19 (d,
1H, J = 8 Hz, ArH), 7.28 (t, 1H, J = 8 Hz, ArH), 7.54 (dd, 1H, J = 8 Hz, ArH), 7.71 (d,
1H, J = 7 Hz, ArH), 7.94 (d, 1H, J = 8 Hz, ArH), 8.02 (s, 1H, ArH). 13C NMR: 124.1,
127.1, 128.4, 129.6, 132.5, 133.7, 135.2, 136.7, 137.9, 144.6, 152.5, 166.1, 171.3. Anal.
Calcd. for C14H9NO6S: C, 52.7; H, 2.84; N, 4.39; S, 10.0. Found: C, 52.9; H, 2.42; N, 3.73;
S, 10.0. MS m/z: 319 (M+, 15), 318 (100).
General Procedures for the Synthesis of the Amides
Thionyl chloride (1–2 mL) was added to the substituted dithiobenzoic acid (1.8 mM)
dissolved in DCM (20 mL). After the addition, the mixture was heated at reflux for 2 h.
The excess thionyl chloride was removed by distillation. To the substituted dithiobenzoyl
dichloride, amine was added (1.8 mM/3.6 mM). The mixture was heated at reflux or stirred
at room temperature for the required time and allowed to cool. The resultant precipitate
was filtered and washed with water and ethanol.
N,Nꢁ-Ethylene-2,2ꢁ-thiodibenzamide (3): Yield 37%, m.p. 273 ◦C. IR: 3267, 1627,
734. 1H NMR: 3.06 (s, 2H, CH2CH2), 3.31 (s, 2H, CH2CH2), 7.08–7.10 (d, 2H, J = 7 Hz,
ArH), 7.19–7.32 (m, 4H, ArH), 7.45–7.47 (d, 2H, J = 6 Hz, ArH), 8.33 (s, 1H, NH), 8.44
(s, 1H, NH). 13C NMR: 36.5, 126.9, 127.9, 130.1, 132.3, 134.0, 134.3, 138.2, 138.8, 167.8.
Anal. Calcd. for C16H14N2O2S: C, 64.4; H, 4.73; N, 9.39; S, 10.8. Found: C, 64.0; H, 4.10;
N, 8.95; S, 10.5.
N,Nꢁ-Ethylene-4-nitro-2,2ꢁ-thiodibenzamide (4): Yield 71%, m.p. 205 ◦C. IR: 3435,
1713, 1648, 1537, 1354, 732. 1H NMR: 3.35 (s, 4H, CH2CH2, merging with DMSO), 7.22
(t, 2H, J = 7 Hz, ArH), 7.58 (d, 2H, J = 6 Hz, ArH), 7.67 (d, 2H, J = 8 Hz, ArH), 7.85 (s,
1H, ArH), 8.11 (s, 1H, NH), 8.28 (s, 1H, NH). Anal. Calcd. for C16H13N3O4S: C, 56.0; H,
3.82; N, 12.2; S, 9.34. Found: C, 56.4; H, 4.19; N, 12.8; S, 9.10. MS m/z: 344 (M+, 16),
287 (25), 286 (35), 284 (100).
◦
N,Nꢁ-(Methylethylene)-2,2ꢁ-thiodibenzamide (5): Yield 47%, m.p. 293 C. IR:
3270, 1714, 1631, 734. 1H NMR: 1.12–1.23 (d, 3H, J = 8 Hz, CH3), 3.05 (m, 2H, CH2),
3.54 (1H, CH, merging with DMSO), 7.42–8.42 (m, 8H, ArH), 8.74 (s, 1H, NH), 8.97 (s,
1H, NH). 13C NMR: 16.8, 46.3, 47.2, 127.5, 128.3, 129.2, 133.9, 138.4, 147.4, 179.5. Anal.

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S. MOOSUN ET AL.
Calcd. for C17H16N2O2S: C, 65.4; H, 5.16; N, 8.97; S, 10.3. Found: C, 65.1; H, 5.80; N,
8.54; S, 10.5.
N,Nꢁ-(Methylethylene)-4-nitro-2,2ꢁ-thiodibenzamide (6): Yield 63%, m.p. 214 ◦C.
1
IR: 3416, 1731, 1637, 1523, 1349, 1349, 731. H NMR: 1.74 (s, 3H, CH3), 2.02 (d, 2H,
J = 14 Hz, CH2), 2.57 (s, 1H, CH), 7.52–7.58 (t, 2H, J = 8 Hz, ArH), 8.09 (d, 2H, J =
8 Hz, ArH), 8.31–8.33 (dd, 3H, J = 9 Hz/7 Hz, ArH), 8.57 (s, 2H, NH). 13C NMR: 31.2,
40.9 (merging with DMSO), 121.3, 123.3, 127.0, 131.1, 134.7, 137.0, 171.1, 189.3. Anal.
Calcd. for C17H15N3O4S: C, 57.1; H, 4.23; N, 11.8; S, 8.97. Found: C, 57.8; H, 4.20; N,
11.3; S, 9.10.
◦
N,Nꢁ-Dibenzyl-2,2ꢁ-thiodibenzamide (7): Yield 24%, m.p. 180 C (lit.: 160–161
◦C). IR: 3279, 1646, 1520, 1323, 743. 1H NMR: 4.53 (d, 4H, J = 7 Hz, CH2), 7.56–7.84
(m, 15H, ArH), 8.06 (d, 1H, J = 7 Hz, ArH), 8.41 (d, 1H, J = 8 Hz, ArH), 8.62 (d, 1H, J =
8 Hz, ArH), 9.38 (s, 2H, NH). 13C NMR: 43.2, 126.3, 127.8, 128.3, 129.1, 130.1, 131.9,
132.7, 133.7, 136.8, 138.5, 138.8, 139.6, 167. Anal. Calcd. for C28H24N2O2S: C, 74.3; H,
5.35; N, 6.19; S, 7.09. Found: C, 73.9; H, 4.97; N, 5.89; S, 7.65.
N,Nꢁ-Dibenzyl-4-nitro-2,2ꢁ-thiodibenzamide (8): Yield 62%, m.p. 210 ◦C. IR: 3408,
1732, 1637, 1524, 1349, 730. 1H NMR: 4.53 (s, 4H, CH2, merging with DMSO), 7.42–6.89
(t, 2H, J = 6 Hz, ArH), 7.48–7.45 (t, 3H, J = 9 Hz, ArH), 8.21–7.96 (dd, 3H, J = 2 Hz/5 Hz,
ArH), 8.32–8.24 (m, 6H, ArH), 8.46 (s, 1H, NH), 8.48 (s, 1H, NH), 8.51–8.49 (m, 3H,
ArH). 13C NMR: 46.2 (merging with DMSO), 124.3, 126.3, 130.0, 130.1, 133.4, 134.1,
134.7, 137.7, 140.0, 142.5, 143.3, 153.0, 170.4, 181.7. Anal. Calcd. for C28H23N3O4S: C,
67.6; H, 4.66; N, 8.45; S, 6.44. Found: C, 67.2; H, 4.12; N, 8.52; S, 6.52.
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◦
2,2ꢁ-Thiodibenzanilide (9): Yield 77%, m.p. 224 C (lit.: 223–224 C). IR: 3304,
1663, 750. 1H NMR: 7.21–7.27 (t, 2H, J = 7 Hz, ArH), 7.35–7.49(m, 6H, ArH), 7.53–7.58
(t, 4H, J = 7 Hz, ArH), 7.67–7.76 (m, 6H, ArH), 10.5 (s, 2H, NH). 13C NMR: 123.4,
127.6, 130.9, 131.3, 132.2, 134.1, 135.9, 137.1, 141.9, 142.2, 170.1. Anal. Calcd. for
C26H20N2O2S: C, 73.6; H, 4.75; N, 6.60; S, 7.55. Found: C, 73.8; H, 4.42; N, 6.62; S, 7.34.
MS m/z: 424 (M+, 22), 422 (50), 308 (100).
4-Nitro-2,2ꢁ-thiodibenzanilide (10): Yield 32%, m.p. 186 ◦C. IR: 3279, 1646, 1520,
1323, 743. 1H NMR: 7.02–7.16 (m, 4H, ArH), 7.28–7.41 (m, 5H, ArH), 7.45–7.56 (m, 2H,
ArH), 7.64–7.79 (m, 4H, ArH), 7.89–7.91 (m, 1H, ArH), 8.15–8.19 (dd, 1H, J = 7 Hz/5 Hz
Hz, ArH), 10.53 (s, 1H, NH), 10.70 (s, 1H, NH). 13C NMR: 119.7, 120.8, 124.7, 127.0,
128.9, 129.3, 129.4, 129.8, 132.0, 135.2, 136.8, 138.6, 141.3, 148.8, 165.2, 166.8. Anal.
Calcd. for C26H19N3O4S: C, 66.5; H, 4.08; N, 8.95; S, 6.83. Found: C, 65.7; H, 4.48; N,
9.21; S, 6.81.
N,Nꢁ-Bis(2-methylphenyl)-2,2ꢁ-thiodibenzamide (11): Yield 55%, m.p. 164 ◦C. IR:
3249, 1716, 1642, 740. 1H NMR: 2.22 (s, 6H, CH3), 7.09–7.25 (m, 9H, ArH), 7.35–7.40 (m,
6H, ArH), 7.62–7.65 (t, 2H, J = 5 Hz, ArH), 9.89 (s, 2H, NH). 13C NMR: 18.5, 126.4, 127.7,
128.6, 130.9, 131.0, 134.1, 134.6, 136.6, 139.6, 167.0. Anal. Calcd. for C28H24N2O2S: C,
74.3; H, 5.35; N, 6.19; S, 7.09. Found: C, 73.8; H, 5.40; N, 5.85; S, 7.82.
◦ N,Nꢁ-Bis(2-methylphenyl)-4-nitro-2,2ꢁ-thiodibenzamide (12): Yield 69%, m.p.
1
211 C. IR: 3254, 1651, 1643, 1530, 1351, 740. H NMR: 1.62 (t, 6H, J = 7 Hz, CH3),
7.16–7.19 (d, 4H, J = 7 Hz, ArH), 7.48–7.51 (m, 3H, ArH), 7.59 (s, 1H, ArH), 7.63–7.68
(t, 3H, J = 13 Hz, ArH), 7.78 (d, 4H, J = 7 Hz, ArH), 8.04 (s, 1H, NH), 8.07 (s, 1H, ArH),
9.89 (s, 1H, NH). 13C NMR: 17.9, 122.5, 123.5, 126.5, 126.6, 129.0, 130.7, 131.7, 134.9,
135.5, 135.7, 137.7, 142.6, 148.7, 164.7, 166.1. Anal. Calcd. for C28H23N3O4S: C, 67.6;
H, 4.66; N, 8.45; S, 6.44. Found: C, 67.3; H, 4.36; N, 8.15; S, 6.95. MS m/z: 497 (M+, 40),
496 (100).

DIARYL DISULFIDE DERIVATIVES
1395
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N,Nꢁ-Bis(2-hydroxyphenyl)-2,2ꢁ-thiodibenzamide (13): Yield 67%, m.p. 180 C.
IR: 2800–3352, 3303, 1645, 747. 1H NMR: 6.74–6.80 (t, 2H, J = 7 Hz, ArH), 6.88 (d, 2H,
J = 7 Hz, ArH), 6.96–7.01 (t, 2H, J = 7 Hz, ArH), 7.24–7.27 (d, 2H, J = 8 Hz, ArH),
7.34–7.43 (t, 4H, J = 12 Hz, ArH), 7.63–7.72 (dd, 4H, J = 7 Hz/12 Hz, ArH), 9.54 (s, 2H,
OH), 9.73 (s, 2H, NH). 13C NMR: 116.4, 119.5, 125.9, 126.3, 127.7, 129.2, 133.1, 134.9,
138.9, 140.9, 149.0, 166.8. Anal. Calcd. for C26H20N2O4S: C, 68.4; H, 4.42; N, 6.14; S,
7.02. Found: C, 68.0; H, 4.05; N, 6.11; S, 7.09. MS m/z: 456 (M+, 28), 455 (100).
N,Nꢁ-Bis(2-hydroxyphenyl)-4-nitro-2,2ꢁ-thiodibenzamide (14): Yield 81%, m.p.
281 ◦C. IR: 2870–3400, 3309, 1644, 1532, 1378, 747. 1H NMR: 6.73–7.03 (m, 6H, ArH),
7.39–7.47 (m, 3H, ArH), 7.67–7.72 (m,3H, ArH), 7.75–7.91 (t, 2H, J = 10 Hz, ArH), 8.11
(d, 1H, J = 6 Hz, ArH), 9.54 (s, 1H OH), 9.70 (s, 1H, NH), 9.81 (s, 1H, NH), 9.85 (s,
1H, OH). 13C NMR: 119.7, 123.7, 126.4, 126.5, 128.8, 129.2, 129.8, 131.6, 132.1, 134.4,
138.6, 140.4, 143.1, 149.1, 149.4, 165.4. Anal. Calcd. for C26H19N2O6S: C, 62.3; H, 3.82;
N, 8.38; S, 6.39. Found: C, 61.6; H, 3.93; N, 8.27; S, 6.71.
◦
N,Nꢁ-Bis(3-hydroxyphenyl)-2,2ꢁ-thiodibenzamide (15): Yield 68%, m.p. 190 C.
1
IR: 2984–3229, 3340, 1649, 766. H NMR: 6.45–6.48 (m, 2H, ArH), 7.29 (s, 2H, ArH),
7.05–7.20 (m, 4H, ArH), 7.21–7.24 (m, 2H, ArH), 7.36–7.41 (m, 4H, ArH), 7.53–7.57 (m,
2H, ArH), 9.41 (s, 2H, OH), 10.3 (s, 2H, s, NH). 13C NMR: 107.4, 111.5, 128.0, 128.3,
129.8, 131.6, 133.0, 134.6, 139.5, 140.5, 158.0, 166.7. Anal. Calcd. for C26H20N2O4S: C,
68.4; H, 4.42; N, 6.14; S, 7.02. Found: C, 67.9; H, 4.30; N, 5.85; S, 6.64.
◦ N,Nꢁ-Bis(3-hydroxyphenyl)-4-nitro-2,2ꢁ-thiodibenzamide (16): Yield 76%, m.p.
1
283 C. IR: 2943–3246, 3309, 1645, 1504, 1347, 775. H NMR: 6.46–6.53 (t, 3H, J =
9 Hz, ArH), 7.04 (d, 3H, J = 8 Hz, ArH), 7.11 (s, 1H, ArH), 7.14 (s, 1H, ArH), 7.25 (d, 2H,
J = 8 Hz, ArH), 7.36–7.43 (t, 1H, J = 9 Hz, ArH), 7.52 (d, 1H, J = 5 Hz, ArH), 7.62 (d,
1H, J = 7 Hz, ArH), 7.81 (d, 1H, J = 9 Hz, ArH), 7.86 (s, 1H, ArH), 8.13 (d, 2H, J = 8 Hz,
OH), 10.4 (s, 1H, NH), 10.6 (s, 1H, NH). 13C NMR: 107.4, 111.2, 121.9, 128.7, 131.5,
134.3, 138.4, 139.9, 140.2, 141.3, 148.7, 158.0, 166.6. Anal. Calcd. for C26H19N3O6S: C,
62.3; H, 3.82; N, 8.38; S, 6.39. Found: C, 62.8; H, 4.24; N, 8.39; S, 5.96.
◦
N,Nꢁ-Bis(4-hydroxyphenyl)-2,2ꢁ-thiodibenzamide (17): Yield 38%, m.p. 183 C.
1
IR: 3055–3200, 3447, 1630, 753. H NMR: 6.83 (d, 5H, J = 9 Hz, ArH), 6.86–7.02 (m,
3H, ArH), 7.12–7.34 (t, 4H, J = 5 Hz, ArH), 7.49 (s, 4H, ArH), 8.09 (s, 2H, OH), 9.15
(s, 2H, NH). Anal. Calcd. for C26H20N2O2S: C, 68.4; H, 4.42; N, 6.14; S, 7.02. Found: C,
68.5; H, 3.95; N, 5.93; S, 6.58.
N,Nꢁ-Bis(4-hydroxyphenyl)-4-nitro-2,2ꢁ-thiodibenzamide (18): Yield 35%, m.p.
280 ◦C. IR: 2915–3374, 3400, 1647, 739. 1H NMR: 6.43 (d, 1H, J = 3 Hz, ArH), 6.68–6.75
(t, 1H, J = 16 Hz, ArH), 6.89 (d, 2H, J = 7 Hz, ArH), 6.96–7.02 (t, 2H, J = 9 Hz, ArH),
7.27 (d, 2H, J = 9 Hz, ArH), 7.38–7.49 (m, 4H, ArH), 7.62–7.72 (dd, 3H, J = 8 Hz/11 Hz,
ArH), 9.52 (s, 2H, OH), 10.3 (s, 1H, NH), 10.5 (s, 1H, NH). Anal. Calcd. for C26H19N3O6S:
C, 62.3; H, 3.82; N, 8.38; S, 6.39. Found: C, 61.6; H, 3.73; N, 8.01; S, 6.00.
N,Nꢁ-Bis(2-hydroxynaphth-1-yl)-2,2ꢁ-thiodibenzamide (19): Yield 75%, m.p. 190
1
◦C. IR: 2943–3304, 3882, 1651, 737. H NMR: 7.21–7.41 (m, 8H, ArH), 7.61–7.68 (m,
8H, ArH), 8.49 (s, 4H, ArH), 9.5 (s, 2H, OH), 10.5 (s, 2H, NH). 13C NMR: 109.4, 123.8,
125.7, 125.9, 126.0, 127.7, 127.8, 128.1, 128.8, 129.9, 131.6, 131.8, 138.5, 140.2, 148.1,
148.8, 167.0. Anal. Calcd. for C34H24N2O4S: C, 73.4; H, 4.35; N, 5.03; S, 5.76. Found: C,
72.9; H, 4.75; N, 5.23; S, 5.94.
N,Nꢁ-Bis(2-hydroxynaphth-1-yl)-4-nitro-2,2ꢁ-thiodibenzamide (20): Yield 75%,
1
m.p. 280 ◦C. IR: 3101–3399, 3610, 1653, 1543, 1347, 754. H NMR: 7.21–7.36 (m, 6H,
ArH), 7.41–7.51 (s, 2H, ArH), 7.63–7.77 (m, 5H, ArH), 7.90 (m, 1H, J = 9 Hz, ArH), 8.00

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(s, 2H, ArH), 8.12 (d, 1H, J = 15 Hz, ArH), 8.54 (d, 2H, J = 10 Hz, ArH), 9.65 (s, 2H,
OH), 10.1 (s, 1H, NH),10.5 (d, 1H, J = 15 Hz, NH). 13C NMR: 109.4, 109.5, 123.8, 125.7,
125.9, 126.0, 127.7, 127.8, 128.1, 128.8, 129.9, 131.6, 131.8, 138.5, 140.2, 148.1, 148.8,
166.0. Anal. Calcd. for C34H23N3O6S: C, 67.9; H, 3.85; N, 6.98; S, 5.33. Found: C, 67.5;
H, 3.83; N, 6.83; S, 4.92.
N,Nꢁ-Bis(2-ethylphenyl)-2,2ꢁ-thiodibenzamide (21): Yield 70%, m.p. 163.5 ◦C. IR:
3363, 1664, 1650, 1529, 1305, 1252, 734, 730. 1H NMR: 1.03–1.09 (t, 6H, J = 8 Hz, CH3),
2.55–2.64 (q, 4H, J = 11 Hz, CH2), 7.14–7.17 (m, 4H, ArH), 7.20–7.24 (m, 6H, ArH),
7.37–7.40 (t, 4H, J = 4 Hz, ArH), 7.57–7.61 (t, 2H, J = 5 Hz, ArH), 9.90 (s, 2H, NH).
13C NMR: 14.1, 23.8, 125.9, 126.4, 127.0, 127.2, 127.9, 128.7, 130.5, 132.6, 134.0, 135.2,
139.1, 139.3, 166.7. Anal. Calcd. for C30H34N2O2S: C, 75.0; H, 5.87; N, 5.83; S, 6.67.
Found: C, 75.0; H, 5.87; N, 6.26; S, 6.67.
◦
N,Nꢁ-Bis(2-propylphenyl)-2,2ꢁ-thiodibenzamide (22): Yield 55%, m.p. 164.3 C.
IR: 3255, 1642, 1523, 1307, 1259, 734, 730. 1H NMR: 0.74–0.81 (t, 6H, J = 8 Hz, CH3),
2.46–1.53 (q, 4H, J = 11 Hz, CH2), 2.59–2.69 (m, 4H, CH2), 7.14–7.26 (m, 10H, ArH),
7.36–7.40 (t, 4H, J = 4 Hz, ArH), 7.55–7.58 (t, 2H, J = 4 Hz ArH), 9.92 (s, 1H, NH).
13C NMR: 13.8, 23.3, 32.8, 126.0, 126.3, 127.1, 127.3, 127.8, 129.5, 130.5, 132.7, 134.1,
135.4, 137.9, 139.2, 167.0. Anal. Calcd. for C32H38N2O2S: C, 75.6; H, 6.34; N, 5.51; S,
6.30. Found: C, 74.9; H, 7.14; N, 5.29; S, 6.35.
N,Nꢁ-Bis(2-fluorophenyl)-2,2ꢁ-thiodibenzamide (23): Yield 68%, m.p. 192 ◦C. IR:
3309, 1668, 1634, 1519, 1319, 1259, 734, 730. 1H NMR: 7.14–7.22 (m, 9H, ArH), 7.36–7.39
(t, 4H, J = 4 Hz, ArH), 7.56–7.68 (m, 4H, ArH), 10.2 (s, 2H, NH). 13C NMR: 126.1, 126.8,
127.2, 127.7, 128.5, 128.9, 130.0, 131.9, 132.8, 133.4, 134.2, 136.3, 137.5, 165.6. Anal.
Calcd. for C26H18F2N2O2S: C, 67.8; H, 3.84; N, 6.08; S, 6.96. Found: C, 70.1; H, 3.14; N,
5.89; S, 6.55.
N,Nꢁ-Bis(2-chlorophenyl)-2,2ꢁ-thiodibenzamide (24): Yield 45%, m.p. 223.2–
224.7 ◦C. IR: 3250, 1639, 1521, 1306, 1258, 734, 730. 1H NMR: 7.29–7.44 (m, 3H, ArH),
7.54–7.64 (m, 4H, J = 12 Hz, ArH), 7.68–7.83 (m, 5H, ArH), 8.18–8.21 (d, 1H, J =
4 Hz, ArH), 8.39–8.42 (d, 1H, J = 5 Hz, ArH), 8.63–8.67 (d, 2H, J = 5 Hz, ArH), 10.5 (s,
2H, NH). 13C NMR: 119.0, 127.3, 127.9, 128.0, 130.8, 132.6, 132.8, 134.4, 135.9, 137.8,
166.5. Anal. Calcd. for C26H18N2O2SCl2: C, 63.3; H, 3.68; N, 5.68; S, 6.50. Found: C,
64.4; H, 3.05; N, 5.10; S, 7.00.
◦
N,Nꢁ-Bis(2-bromophenyl)-2,2ꢁ-thiodibenzamide (25): Yield 30%, m.p.147.8 C.
1
IR: 3376, 1662, 1651, 1520, 1301, 1248, 734, 730. H NMR: 7.13–7.24 (m, 4H, ArH),
7.31–7.45 (m, 8H, ArH), 7.32–7.65 (d, 4H, J = 5 Hz, ArH), 10.0 (s, 2H, NH). 13C NMR:
119.5, 127.3, 127.9, 128.0, 130.8, 132.6, 132.8, 134.4, 135.9, 137.8, 166.6. Anal. Calcd.
for C26H18N2O2SBr2: C, 53.6; H, 3.12; N, 4.81; S, 5.51. Found: C, 53.6; H, 3.12; N, 4.18;
S, 5.51.
N,Nꢁ-Bis(2-iodophenyl)-2,2ꢁ-thiodibenzamide (26): Yield 65%, m.p. 167.4–167.7
◦C. IR: 3357, 1666, 1518, 1307, 1268, 734, 730. H NMR: 6.98–7.03 (t, 2H, J = 7Hz,
1
ArH), 7.22–7.24 (m, 2H, ArH), 7.35–7.38 (d, 8H, J = 4 Hz, ArH), 7.69 (s, 2H, ArH),
7.86–7.89 (d, 2H, J = 4 Hz, ArH), 10.1 (s, 2H, NH). 13C NMR: 127.1, 127.9, 128.0, 128.3,
128.8, 130.8, 132.6, 134.6, 138.0, 139.0, 139.2, 166.6. Anal. Calcd. for C26H18N2O2SI2:
C, 46.2; H, 2.68; N, 4.14; S, 4.74. Found: C, 45.1; H, 2.68; N, 4.61; S, 4.40.◦
N,Nꢁ-Carbonyl-2,2ꢁ-thiodibenzamide (27): Yield 47%, m.p. 259.6 C. IR: 3419,
1669, 1622, 1584, 1402, 733. 1H NMR: 7.13–7.16 (d, 1H, J = 7 Hz, ArH), 7.32–7.38 (d,
5H, J = 8 Hz, ArH), 7.52–7.55 (d, 1H, J = 8 Hz, ArH), 7.76 (s, 1H, ArH), 10.6 (s, 2H,
NH). 13C NMR: 127.2, 128.1, 131.2, 132.4, 134.1, 137.1, 153.6, 169.2.

DIARYL DISULFIDE DERIVATIVES
1397
◦
N,Nꢁ-Carbonyl-4-nitro-2,2ꢁ-thiodibenzamide (28): Yield 57%, m.p. 206 C. IR:
1
3432, 1731, 1637, 1603, 1523, 1396, 731. H NMR: 7.52–7.58 (t, 2H, J = 7 Hz, ArH),
8.07–8.10 (d, 1H, J = 6 Hz, ArH), 8.31–8.33 (d, 1H, J = 6 Hz, ArH), 8.39–8.42 (d, 2H,
J = 9 Hz, ArH), 8.56 (s, 1H, ArH, merge with NH), 8.57 (s, 2H, NH). 13C NMR: 124.3,
126.2, 129.9, 130.0, 133.3, 134.0, 134.7, 137.7, 140.0, 142.4, 143.2, 153.0, 170.4, 181.7.
Anal. Calcd. for C15H9N3O5S: C, 52.5; H, 2.64; N, 12.2; S, 9.34. Found: C, 52.8; H, 1.47;
N, 11.3; S, 10.3. MS m/z: 343 (M+, 10), 341 (95), 329 (100).
N,Nꢁ-Thiocarbonyl-2,2ꢁ-thiodibenzamide (29): Yield 43%, m.p. 268.0 ◦C. IR: 3404,
1717, 1673, 1547, 1245, 742, 722. 1H NMR: 7.29–7.32(d, 2H, J = 8 Hz, ArH), 7.37–7.52
(m, 4H, ArH), 7.57–7.60 (d, 2H, J = 9 Hz, NH), 12.8 (s, 2H, NH).
4-Nitro-N,Nꢁ-thiocarbonyl-2,2ꢁ-thiodibenzamide (30): Yield 63%, m.p. 210 C.
◦
IR: 3273, 1703, 1639, 1524, 1346, 1228, 734, 730. 1H NMR 7.78 (t, 3H, J = 8 Hz, ArH),
8.30 (d, 2H, J = 9 Hz, ArH), 8.54 d, (1d, 1H, J = 8 Hz, ArH), 8.62 (d, 1H, J = 9 Hz, ArH),
8.76 (s, 1H, NH), 8.81 (d, 1H, J = 6 Hz, NH). 13C NMR: 124.3, 126.3, 130.0, 133.3, 134.1,
134.7, 137.7, 140.0, 143.3, 153.0, 170.4, 181.7. Anal. Calcd. for C15H9N3O4S2: C, 50.1;
H, 2.52; N, 11.7; S, 17.8. Found: C, 50.5; H, 1.97; N, 11.8; S, 18.4. MS m/z: 359 (M+, 10),
280 (100).
Biological
Antibacterial. The compounds were screened against positive Grams S. aureus,
B. cereus and negative Grams K. pneumonia, S. flexneri, and Pseudomonas aeruginosa of
clinical isolates using the disc diffusion method. Note that 10 µL of the test compounds
prepared in DMSO (100 mg mL–1 −0.1 mg mL–1) were transferred to the filter papers that
were placed in the middle of the base agar plate containing the bacteria. The tests were
carried out in duplicate. To ensure the validity of the test, DMSO was used as negative
control and erythromycin was used as PC. The plates were incubated for 24 h in sterile
◦
conditions at 40 C. The diameter of the growth inhibition zones were then measured to
the nearest millimeter.
Antioxidant Activity
The hydrogen atom or electron-donating abilities of the diaryl sulphides were mea-
sured from the bleaching of the purple-colored methanol solution of DPPH. The tested
compounds and ascorbic acid solutions were prepared of various concentrations ranging
from 0.04 to 100 mg mL–1. DPPH solution (100 µM, 200 µL) was added to the compounds
and 100 µL of the solution was placed in each well of an ELISA 96 well plate. After 30 min
◦
of incubation at 40 C, the absorbance of the compounds was recorded. The absorbance
of DPPH (blank) was measured at wavelength 492 nm. The experiment was performed in
duplicate. Ascorbic acid was used as the PC.
The percentage radical scavenging activity of the tested compounds, expressed as
percentage inhibition DPPH, was calculated according to the formula:
% Inhibition = [(A0 − At)/A0] × 100
where At is the absorbance value of the tested sample and A0 is the absorbance of the blank
sample. For each diaryl sulphide, the 50% scavenging concentration (IC50) based on the
amount of compound required to decrease the initial DPPH radical concentration by 50%

1398
S. MOOSUN ET AL.
was calculated using Growth formula in Microsoft Excel. All data were expressed as mean
standard deviation (SD) for the experiments.
Binding Studies
Absorption titration experiments were performed by maintaining the concentration of
the compounds tested (prepared in DMSO) constant (1 × 10−4 M, 1 × 10−2 M) while vary-
ing the concentration of the guest molecules (guanine, urea, glutamic acid) (0.01–0.001 M).
The stock solution of host molecules was prepared in the phosphate buffer solution (pH =
7.4). Samples were incubated at 40 ◦C for 24 h before recording each spectrum. Appropriate
blanks corresponding to buffer and DMSO were used as reference. The intrinsic binding
constant (K) was determined from a plot of [DNA]/(εa–εf) versus [DNA] using absorption
spectral titration data and the following equation:
[Guest]/(εa − εf) = [Guest]/(εb − εf) + 1/K((εb − εf)
where [Guest] is the concentration of the guest molecules, the apparent absorption coef-
ficients εa, εf, εb correspond to Aobsd/[Host], the extinction coefficient for the free host
molecule and the extinction coefficient for the host molecule in the fully bound form,
respectively. The K value is given by the ratio of the slope of the intercept.
Lipophilicity Factor
The log P values were calculated using the software ChemDraw Ultra Version 5.0.
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