Synthesis, urease inhibition, antioxidant and antibacterial studies of some 4-Amino-5-aryl-3H-1,2,4-triazole-3-thiones and their 3,6-Disubstituted 1,2,4-Triazolo[3,4-b]1,3,4-thiadiazole derivatives

Article abstract of DOI:10.1590/S0103-50532012000500010

A new series of 4-amino-5-aryl-3H-1,2,4-triazole-3-thiones, bearing various methoxybenzyl- and methoxyphenethyl groups, was synthesized by refluxing potassium hydrazinecarbodithioate salts in dilute aqueous solution of hydrazine hydrate. These salts were formed by the reaction of acid hydrazides and carbon disulfide in methanolic potassium hydroxide solution at 0-5 °C. 4-Amino-5-aryl-3H-1,2,4-triazole-3-thiones were condensed with different substituted aromatic acids to yield 3,6-disubstituted-1,2,4-triazolo[3,4-b]1,3, 4-thiadiazoles. The structures of the synthesized compounds were characterized by infrared (IR), ¹H and ¹³C nuclear magnetic resonance (NMR), elemental analysis and mass spectrometric (MS) studies. All the synthesized compounds were screened for their urease inhibition, antioxidant and antibacterial activities. Some compounds showed excellent urease inhibition activity, more than the standard drug. Others exhibited potent antioxidant activity. All the compounds showed significant antibacterial activities as compared to the standard drug.

Full text of DOI:10.1590/S0103-50532012000500010

J. Braz. Chem. Soc., Vol. 23, No. 5, 854-860, 2012.
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0103 - 5053 $6.00+0.00
Article
A
Synthesis, Urease Inhibition, Antioxidant and Antibacterial Studies of
Some 4-Amino-5-aryl-3H-1,2,4-triazole-3-thiones and
their 3,6-Disubstituted 1,2,4-Triazolo[3,4-b]1,3,4-thiadiazole Derivatives
Muhammad Hanif,a Muhammad Saleem,a Muhammad Tahir Hussain,b
Nasim Hasan Rama,*,a Sumera Zaib,c Muhammad Adil M. Aslam,c
Peter G. Jonesd and Jamshed Iqbal*,c
aDepartment of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
bDepartment of Applied Sciences, national textile university, Faisalabad 37610, Pakistan
cDepartment of Pharmaceutical Sciences, COMSATS Institute of Information Technology
Abbottabad 22060, Pakistan
dInstitute for Inorganic and Analytical Chemistry, Technical University of Braunschweig,
Hagenring 30, 38106 Braunschweig, Germany
Uma nova série de 4-amino-5-aril-3H-1,2,4-triazol-3-tionas, tendo vários grupos metoxibenzila
e metoxifenila, foi sintetizada através de refluxo de sais de hidrazina carboditioato de potássio
em solução aquosa diluída de hidrato de hidrazina. Estes sais foram formados pela reação de
hidrazinas ácidas e dissulfeto de carbono em solução de hidróxido de potássio metanólico a 0-5
°C. 4-Amino-5-aril-3H-1,2,4-triazol-3-tionas foram condensadas com diferentes ácidos aromáticos
substituídos para produzir 1,2,4-triazol[3,4-b]1,3,4-tiodiazols 3,6-disubstituídos. As estruturas
dos compostos sintetizados foram caracterizadas pelas espectroscopias no infravermelho (IR) e
ressonância magnética nuclear (NMR) de 1H e 13C, análise elementar e espectrometria de massa
(MS). Todos os compostos sintetizados foram examinados com relação as suas atividades de
inibição de urease, antioxidante e antibacteriana.Alguns compostos mostraram excelente atividade
de inibição de urease, mais do que a droga padrão. Outros compostos apresentaram potente
atividade antioxidante. Todos os compostos mostraram atividades antibacterianas significativas
em comparação com a droga padrão.
A new series of 4-amino-5-aryl-3H-1,2,4-triazole-3-thiones, bearing various methoxybenzyl- and
methoxyphenethyl groups, was synthesized by refluxing potassium hydrazinecarbodithioate salts
in dilute aqueous solution of hydrazine hydrate. These salts were formed by the reaction of acid
hydrazides and carbon disulfide in methanolic potassium hydroxide solution at 0-5 °C. 4-Amino-
5-aryl-3H-1,2,4-triazole-3-thiones were condensed with different substituted aromatic acids to
yield 3,6-disubstituted-1,2,4-triazolo[3,4-b]1,3,4-thiadiazoles. The structures of the synthesized
compounds were characterized by infrared (IR), 1H and 13C nuclear magnetic resonance (NMR),
elemental analysis and mass spectrometric (MS) studies. All the synthesized compounds were
screened for their urease inhibition, antioxidant and antibacterial activities. Some compounds
showed excellent urease inhibition activity, more than the standard drug. Others exhibited potent
antioxidant activity. All the compounds showed significant antibacterial activities as compared
to the standard drug.
Keywords: amino-1,2,4-triazoles, triazolothiadiazoles, urease inhibitors, antioxidants,
antibacterial activity
*e-mail: nhrama@qau.edu.pk, drjamshed@ciit.net.pk

Vol. 23, No. 5, 2012
Hanif et al.
855
Introduction
inhibition studies, antioxidant and antibacterial activities of
5-substituted-4-amino-1,2,4-triazole and 3,6-disubstituted-
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazoles.
Urease (urea amidohydrolase, E.C. 3.5.1.5) is
an enzyme that catalyzes the hydrolysis of urea to
ammonia and carbamate, which is the final step of nitrogen
metabolism in living organisms.1,2 Carbamate rapidly and
spontaneously decomposes, yielding a second molecule
of ammonia. These reactions may cause significant
increase in pH and are responsible for negative effects of
urease activity in human health and agriculture. Urease is
responsible for urinary tract and gastrointestinal infections,3
possibly causing severe diseases such as peptic ulcers and
stomach cancer as in the case of Helicobacter pylori.4
Ureases are also involved in the development of urolithiasis,
pyelonephritis, hepatic encephalopathy, hepatic coma and
urinary catheter encrustation.5
The efficiency of soil nitrogen fertilization with
urea (the most used fertilizer worldwide) decreases due
to ammonia volatilization and root damage caused by
increased soil pH.6 Control of the activity of urease through
the use of inhibitors could counteract these negative effects.
Reactive oxygen species (ROS), which are capable
of causing damage to DNA, have been associated with
carcinogenesis, coronary heart diseases and many other
health problems related to advancing age.7,8 In low
concentrations, synthetic antioxidants are also in use
for many industrial processes, e.g. inhibition of radical
formation for preventing premature polymerization during
processing, storage and transportation of unsaturated
monomers. They exert their effects by scavenging or
preventing the generation of ROS,9 protecting the formation
of free radicals and retarding the progress of many
chronic diseases,10 including cancer, neurodegenerative,
inflammation and cardiovascular diseases.11
Recently, 5-substituted-4-amino-1,2,4-triazole-
3-thiones and their fused triazolothiadiazole derivatives
have received considerable attention owing to their
synthetic and potent pharmacological importance.
Heterocyclic compounds bearing 1,2,4-triazole nuclei and
their triazolothiadiazole derivatives have been reported to
show a broad spectrum of pharmacological properties such
as antimicrobial,12 anti-inflammatory,13 anticonvulsant,14
anticancer,15 antitubercular16 and antitumor activities.17
Literature survey reveals that 5-substituted-4-amino-
1,2,4-triazoles and their 3,6-disubstituted-1,2,4-triazolo-
[3,4-b]-1,3,4-thiadiazole derivatives have not been paid
much attention for their enzymatic inhibition studies.
Hence, the present studies were undertaken to explore
the urease inhibition potential of 5-substituted-4-amino-
1,2,4-triazoles and their fused triazolothiadiazole
derivatives. In this work, we report the synthesis, urease
Experimental
All the common solvents and chemicals were of
analytical grade or purified by distillation. The purity
of the synthesized compounds was ascertained by thin
layer chromatography (TLC) and the Rf values were
determined by employing pre-coated silica gel aluminum
plates (Kieselgel 60 F254 from Merck (Germany)), using
petroleum ether:EtOAc (8:2) as an eluent. The spots
were visualized under an UV lamp. Melting points (mp)
were determined on a Stuart melting point apparatus
(SMP3) and are uncorrected. The infrared (IR) spectra were
recorded on a Bruker OpticsAlpha FTIR spectrophotometer.
Nuclear magnetic spectra (NMR) spectra were recorded
on a Bruker Avance 300 MHz spectrometer with TMS
(tetramethylsilane) as internal standard. The multiplicities
were expressed as s = singlet, d = doublet, t = triplet,
q = quartet, dt = doublet of triplets. Mass spectra (MS)
were recorded on Agilent Technologies 6890N gas
chromatograph and an inert mass selective detector 5973
mass spectrometer. The elemental analysis was performed
on Leco CHNS-932 ElementalAnalyzer, Leco Corporation
(USA).
General procedure for synthesis of substituted aromatic
esters (2a-e) and aromatic acid hydrazides (3a-e)
Substituted aromatic acids (1a-e) were esterified (2a-e)
by refluxing in methanol and in the presence of catalytic
amount of sulfuric acid. Substituted aromatic esters (2a-e)
were converted into their corresponding acid hydrazides
3 by refluxing in hydrazine hydrate in methanol through
literature procedure.18-20
General procedure for synthesis of 3-substituted 4-amino-
5-aryl-3H-1,2,4-triazole-3-thiones (5a-e)
Aryl hydrazide 3 (0.125 mol) was added to a solution
of potassium hydroxide (0.125 mol) in dry methanol
(50 mL) and cooled in ice. Carbon disulfide (0.125 mol)
was then added in small portions with constant stirring.
The solid product of potassium dithiocarbazinate 4 formed
was filtered, washed with chilled diethyl ether and dried.
It was directly used for next step without purification. The
above potassium dithiocarbazinate 4 was taken in water
(20 mL), and hydrazine hydrate (0.250 mol) was added
followed by reflux for 4-5 h. The reaction mixture turned

856
Synthesis, Urease Inhibition, Antioxidant and Antibacterial Studies of Some 4-Amino-5-aryl-3H-1,2,4-triazole-3-thiones
J. Braz. Chem. Soc.
green with evolution of hydrogen sulphide and finally
it became homogeneous. It was then poured in ice and
acidified with concentrated hydrochloric acid. The white
precipitate was filtered, washed with cold water and
recrystallized from aqueous methanol.
method described by Weatherburn.21 The assay mixture,
containing 10 µL of enzyme (5 U mL-1) and 10 µL of test
compound in 40 µL buffer (100 mmol L-1 urea, 0.01 mol L-1
K2HPO4, 1 mmol L-1 EDTA and 0.01 mol L-1 LiCl2, pH 8.2),
o
were incubated for 30 min at 37 C in 96-well plates.
Briefly, 40 µL each of phenol reagents (1%, m/v phenol and
0.005%, m/v sodium nitroprusside) and 40 µL of alkali
reagent (0.5%, m/v NaOH and 0.1% active chloride NaOCl)
were added to each well. The absorbance at 625 nm was
measured after 30 min, using a microplate reader (Bio-Tek
ELX 800TM, Instruments, Inc. USA). All the reactions
were performed in triplicate. Percentage inhibition was
calculated by using the following equation.
General procedure for synthesis of 3,6-disubstituted [1,2,4]
triazolo[3,4- b][1,3,4]thiadiazoles (6a-o)
A mixture 3-substituted 4-amino-1,2,4-triazole 5
(1 mmol) and substituted benzoic acid (1.1 mmol) in
phosphorous oxychloride (10 mL) was refluxed for 6-7 h.
The reaction mixture was slowly poured into crushed ice
with stirring and neutralized with solid sodium bicarbonate.
The solid material was filtered, washed with cold water,
dried and recrystallized from chloroform.
(1)
Pharmacological assays
Thiourea was used as the standard inhibitor of urease.
The Cheng-Prusoff equation was used to calculate the Ki
values from the IC50 values, determined by the non-linear
curve fitting program PRISM 4.0 (GraphPad, San Diego,
California, USA). At 37 °C, 1 µmol of ammonia being
produced per min by enzyme is known as one unit of
enzyme at pH 8.2.
Urease inhibition bioassay
The synthesized compounds were screened for their
urease inhibition activity, which is shown in Table 1. The
compounds were found inhibiting the urease in variable
concentrations. Thiourea was used as reference compound.
The urease activity was determined by measuring the
amount of ammonia being produced using the indophenol
Antioxidant activity (DPPH scavenging assay)
The synthesized compounds were screened for
antioxidant activity, which is shown in the Table 2. The
compounds have shown hydrogen-donating ability on
reaction with DPPH (1,1-diphenyl-2-picrylhydrazyl)
radical. Propyl gallate was used as standard drug.
Table 1. Urease inhibition activities (IC50 and Ki) of compounds (5a-e) and
(6a-o)
Compound
IC50 / µM
26
Ki
21
Thiourea
5a
5
5
The free radical scavenging capacity of the compounds
was measured by modified 1,1-diphenyl-2-picrylhydrazyl
methods described by Choudhary et al.22 Test compounds
were allowed to react with stable free radical, 1,1-diphenyl-
2-picrylhydrazyl radical, for 30 min at 37 °C. The
concentration of DPPH was kept as 100 mmol L-1. The test
samples were dissolved in DMSO (dimethyl sulfoxide) while
the DPPH solution was prepared in ethanol.After incubation,
the decrease in absorption was measured at 515 nm using
multiplate reader (Spectra MAX-384). Percent radical
scavenging activity (RSA) of samples was determined in
comparison with a DMSO treated control group23,24 using
the following formula (Table 2):
2.25 0.023
0.85 0.03
2.08 0.03
1.93 0.02
9.1 1.7
NSa
1.30 0.01
5b
5c
0.49 0.05
1.20 0.01
5d
5e
1.11 0.02
5.3 1.1
6a
–
6c
NSa
–
6e
NSa
–
6f
5.5 1.2
NSa
3.18 0.67
6g
–
6h
6i
15
10
4
3
–
–
6j
5.0 0.7
10
NSa
–
6k
6l
3
–
(2)
–
6m
6n
6o
NSa
NSa
–
–
Antibacterial activity
1.55 0.16
8.96 1.30
The synthesized compounds were screened for
antibacterial activity, which is shown in the Table 3. The
aNS: not soluble; bND: not determined.

Vol. 23, No. 5, 2012
Hanif et al.
857
Table 2. DPPH radical scavenging activities of the synthesized compounds
(5a-e) and (6a-o)
sterilized nutrient broth aseptically in a laminar air flow
cabinet. It was then incubated for a period of 24 h at 37 °C in
a B.O.D. incubator. Bacterial stain suspension was prepared
(after 24 h incubation) by aseptically inoculating 0.2 mL of
revived bacterial colony into 100 mL of 0.9% m/v saline. The
study involved a series of 5 assay tubes for each compound
against each strain. A stock solution of each test compound
at concentration 5 µg mL-1 was serially diluted in series of
5 assay test tubes (containing 1 mL nutrient broth) to give
concentration of 2.5, 1.25, 0.625, 0.313 and 0.156 µg mL-1.
Then, 0.1 mL of normal saline suspension of revived bacteria
was added to each test tube. The inoculated tubes were
incubated at 37 °C for 24 h. The MIC (minimum inhibitory
concentration) values were determined by subsequently
checking for the absence of visual turbidity.25
Concentration /
Compound
RSA / % IC50 / µM
(µg mL-1)
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
5a
60.6
54.4
58.5
52.3
59.8
44.9
56.3
56.7
63.1
15.2
33.1
59.8
51.4
–
108.6
57.2
155.6
51.8
113.0
36.8
223.1
390.6
785.4
9.04
35.3
501.5
69.2
–
5b
5c
5d
5e
6a
6b
6c
6d
6e
6f
6g
Results and Discussion
6h
6i
Chemistry
6j
–
–
6k
58.2
–
423.1
–
The synthesis of the target compounds,
1,2,4-triazolo[3,4-b]1,3,4-thiadiazoles (6a-o), is illustrated
in Scheme 1. Substituted aromatic esters (2a-e) were
synthesized by the reaction of the corresponding substituted
aromatic acids (1a-e) with methanol in the presence of
catalytic amount of sulfuric acid. These esters (2a-e)
were converted to the corresponding aromatic acid
hydrazides (3a-e) by refluxing with hydrazine hydrate
(80%) in methanol. Syntheses of hydrazides (3a-e) were
confirmed by IR and NMR spectroscopies. In the IR
spectrum, the typical doublet absorption in the range of
3296-3338 cm-1 and a peak in the range of 3204-3214 cm–1
for primary and secondary amines, respectively, were
observed. The 1H NMR exhibited a singlet in the range of
9.16-9.96 ppm for NH proton, next to the carbonyl group.
A broad singlet for two protons for NH2 group in the
range of d 4.16-4.46 indicated the formation of hydrazides
(3a-e). The reaction of acid hydrazides (3a-e) with carbon
disulfide in alcoholic potassium hydroxide solution yielded
potassium hydrazinecarbodithioate salts (4a-e), which were
used for the next step without purification. 5-Substituted-
4-amino-1,2,4-triazoles (5a-e) were synthesized by
refluxing potassium hydrazinecarbodithioate salts (4a-e) in
dilute solution of hydrazine hydrate. Structures of amino
1,2,4-triazoles (5a-e) were characterized by IR, NMR and
mass spectrometry. In IR spectra, a relatively strong peak
in the range of 3327-3249 cm-1 for NH2 stretching and a
peak in the range of 3105-3202 cm-1 for NH stretching
6l
6m
62.2
29.5
59.9
92.5
431.7
34.7
264.4
40.8
6n
6o
Standard (n-propyl gallate)
RSA: radical scavenging activity; –: not determined.
compounds were found active against bacterial strains in
variable concentration. Ciprofloxacin was used as standard
drug.
The antibacterial activities of all the synthesized
derivatives were evaluated in vitro by serial tube dilution
method. For antibacterial activity, two gram positive
bacterias namely Staphylococcus aureus and Bacillus
subtilis, and two gram negative bacteria namely Escherichia
coli and Shigella flexneri were used.
The compounds and standard drug ciprofloxacin were
dissolved in N,N-dimethylformamide (DMF) to give a
concentration of 5 µg mL-1 (stock solution). A set of test
tubes of capacity 5 mL was washed, cleaned and dried
completely. Double strength nutrient broth was used as a
growth/culture media for all bacteria. The culture media was
made by dissolving 15 g of nutrient broth No. 2 in 1 L of
distilled water. Approximately 1 mL of culture media was
prepared and transferred to each test tube by micropipette and
capped with non-adsorbent cotton plugs. A set of test tubes
containing 1 mL culture media was sterilized in an autoclave
at 15 psi pressure at 121 °C for 20 min. Sub-culturing of
bacteria was done by transferring a loopful of particular
bacterial strain from standard bacterial agar slant to 10 mL
1
were observed. In the H NMR, NH proton in the range
of 13.71-13.44 ppm was observed. This proton exists
as thione-thiol tautomeric form. The dominant form is

858
Synthesis, Urease Inhibition, Antioxidant and Antibacterial Studies of Some 4-Amino-5-aryl-3H-1,2,4-triazole-3-thiones
J. Braz. Chem. Soc.
Table 3. In vitro antibacterial activity of (5a-e) and (6a-o)
MIC / (µg mL-1)
Compound
Escherichia coli
Bacillus subtilis
Staphylococcus aureus
0.313
Shigella flexneri
0.156
0.313
0.313
0.156
0.156
0.156
0.313
0.625
0.313
0.313
0.313
0.156
0.313
0.156
0.313
0.156
0.313
0.313
0.313
5a
0.313
0.625
0.313
0.313
0.625
0.313
0.313
0.313
0.313
0.313
0.156
0.625
0.156
0.156
0.313
0.156
0.313
0.156
0.156
0.313
0.313
0.625
0.313
0.313
0.625
0.313
0.313
0.156
0.156
0.313
0.313
0.313
0.313
0.313
0.313
0.156
0.156
0.625
5b
0.313
5c
0.313
5d
0.313
5e
0.625
6a
0.313
6b
0.313
6c
0.313
6d
0.156
6e
0.156
6f
0.313
6g
0.156
6h
0.313
6i
0.156
6k
0.313
6m
0.156
6n
0.156
6o
0.156
Ciprofloxacin
0.156
thione as there was no peak for the SH group in the IR
spectrum, and this is further confirmed by single crystal.
Two NH protons appeared in the range of 5.54-5.59 ppm.
got precipitated in our standard urease assay media. These
compounds are under investigation.
Antioxidant activity
Pharmacology
Compounds 5b, 5d, 6a, 6f and 6n with the IC50 values
57.2, 51.8, 36.8, 35.3 and 34.7 µM, respectively, have
shown hydrogen donating ability on reaction with DPPH
radical. It is clear from the results that the antioxidant
potential of the compounds is associated with the position
of the substituents on the ring Y. In compounds 5b and
5d, chloro group is present at position 2 and 4 in X ring.
Whereas in 6a, 6f and 6n halogenated substituents are
present in ringY.Among 4-amino-5-aryl-3H-1,2,4-triazole-
3-thiones (5a-e), compound 5d with IC50 51.8 µM was
most active and all other compounds of this series showed
activities with IC50 ranging from 57.2 to 155.6 µM. The
triazolothiadiazole class of compounds was found to be
significantly active against superoxide anion radical. The
compound 6e with an IC50 value 9.04 µM was found to
be most active at such a low concentration, even low than
standard. The activity of 6e is enhanced in this class due to
the presence of methoxy group at position 3 in ring X while
chloro group at position 4 in ring Y. The compounds 5a,
5c, 5e, 6b and 6o showed comparable antioxidant potential
with the standard, whereas the compound 6c, 6d, 6g, 6k and
6m showed a moderate superoxide anion scavenging
activity. In 4-amino-5-aryl-3H-1,2,4-triazole-3-thiones,
Urease inhibition bioassay
Almost all the compounds showed excellent urease
inhibition more than the standard inhibitor determined
through the standard urease assay.21 4-Amino-5-aryl-
3H-1,2,4-triazole-3-thiones (5a-e) were more active
than their 3,6-disubstituted 1,2,4-triazolo-[3,4-b]-
1,3,4-thiadiazole (6a-o) derivatives. Among 4-amino-
5-aryl-3H-1,2,4-triazole-3-thiones (5a-e), compound 5b
with IC50 0.85 0.02 µM was the most active and all other
compounds of this series showed activities with IC50 ranging
from 1.93 0.01 to 9.11 1.70 µM. Compound 6o, of
3,6-disubstituted- 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole
series, was the most active with IC50 1.55 0.16 µM. The
rest of the compounds showed inhibition with IC50 ranging
from 5 1 to 15 4 µM. The most active compound of 5
series, 5b has ortho-methoxybenzyl group attached with
amino-1,2,4-triazole moiety. The most active compound
of 6 series has 2,5-dimethoxy group in X part and ortho-
methyl group in Y part.
Despite identifying compounds with excellent
inhibitory activities, it was observed that some compounds

Vol. 23, No. 5, 2012
Hanif et al.
859
series were the most active for almost all bacterial strains.
The rest of the compounds showed moderate activities
compared to standard drug. Compounds 6i and 6m
contain fluorine and chlorine group, respectively, whereas
6o contains methyl group in ring Y. Overall most of the
compounds in both the series exhibit excellent antibacterial
activity as compared to standard drug ciprofloxacin.
Conclusion
A new series of triazole-3-thione (5a-e) and thiadiazole
(6a-o) was synthesized. The urease inhibition ability of
these compounds was evaluated. Some of the compounds
were found to be excellent inhibitors. The compounds
5a-e, 6f, 6h-k and 6o showed remarkable urease inhibition
activity, more than the standard drug. The most active
inhibitors were 5b and 6o. Therefore, the discovered
inhibitors should be further investigated for the control
of diseases whose tangible and beneficial alternatives are
still insufficient.
The synthesized compounds were also evaluated for
their antioxidant ability. The radical scavenging activity of
the compounds 5b, 5d, 6a, 6f and 6n was significant, being
very close to the standard drug. All the newly synthesized
compounds were further screened for antibacterial
activities, demonstrating that some compounds in the
series are most promising. The identified compounds can
be utilized for further optimization of bioactivity using
structural variations in the parent skeleton.
Scheme 1. Reagents and conditions: (i) MeOH, H2SO4 (2-3 drops), reflux,
(ii) H2N-NH2 H2O, reflux, (iii) KOH, CS2, 0-5 °C, (iv) H2N-NH2 H2O, H2O,
reflux, and (v) POCl3, substituted benzoic acids, reflux.
.
.
Supplementary Information
Supplementary information with characterization
data for all compounds and the corresponding spectra of
representative compound of each series is available free of
charge at http://jbcs.sbq.org.br, as PDF file.
5b and 5d along with 6a, 6f and 6n in 3,6-disubstituted
1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazoles (6a-o) derivatives
showed IC50 near to the standard and this represents that
they are less active.
Acknowledgments
Antibacterial activity
Almost all the compounds showed excellent
antibacterial activity more than or equal to the standard
drug ciprofloxacin, determined through the serial tube
dilution method. 3,6-Disubstituted 1,2,4-triazolo-[3,4-b]-
1,3,4-thiadiazoles (6a-o) derivatives were more active
than 4-amino-5-aryl-3H-1,2,4-triazole-3-thiones (5a-e).
Among 4-amino-5-aryl-3H-1,2,4-triazole-3-thiones (5a-e),
compounds 5a and 5d were more active against all bacterial
strains, especially against Shigella flexneri, and all other
compounds of this series showed significant activities for
all bacterial strains used. Compounds 6i, 6m and 6o of
3,6-disubstituted- 1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazole
This work was financially supported by COMSTECH–
TWAS and German-Pakistani Research Collaboration
Programme.
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Submitted: September 16, 2011
Published online: April 10, 2012
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