Synthesis and biological activity of some 3-[(4-Amino-5-thioxo-1,2,4- triazol-3-yl)methyl]benzothiazol-2(3H)-one Derivatives

Article abstract of DOI:10.14233/ajchem.2013.12903

Fourteen new 3-[(4-amino-5-thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol- 2(3H)-one derivatives have been synthesized. The structures of these compounds were confirmed by IR, 1H NMR, mass spectrum and elemental analysis. The synthesized compounds were evaluated for their antibacterial activity against various gram-positive and gram-negative strains of bacteria and their clinical isolates, for their antifungal activity against Candida albicans and C. krusei and for their antimycobacterial activity against M. tuberculosis H37Rv and its clinical isolate. Some of the compounds showed promising activity.

Full text of DOI:10.14233/ajchem.2013.12903

Asian Journal of Chemistry; Vol. 25, No. 1 (2013), 225-230
http://dx.doi.org/10.14233/ajchem.2013.12903
Synthesis and Biological Activity of Some 3-[(4-Amino-5-thioxo-
1,2,4-triazol-3-yl)methyl]benzothiazol-2(3H)-one Derivatives
1
2
1,*
YASEMIN DÜNDAR , FATMA KAYNAK ONURDAG and TIJEN ÖNKOL
1Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Gazi University, 06330 Etiler, Ankara, Turkey
2Department of Microbiology, Faculty of Pharmacy, Gazi University, 06330 Etiler, Ankara, Turkey
*Corresponding author: Fax: +90 312 223 5018; Tel: +90 312 202 3233; E-mail: tijen@gazi.edu.tr
(Received: 21 October 2011;
Accepted: 16 July 2012)
AJC-11852
Fourteen new 3-[(4-amino-5-thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol-2(3H)-one derivatives have been synthesized. The structures
of these compounds were confirmed by IR, 1H NMR, mass spectrum and elemental analysis. The synthesized compounds were evaluated
for their antibacterial activity against various gram-positive and gram-negative strains of bacteria and their clinical isolates, for their
antifungal activity against Candida albicans and C. krusei and for their antimycobacterial activity against M. tuberculosis H37Rv and its
clinical isolate. Some of the compounds showed promising activity.
Key Words: Benzothiazol-2(3H)-one, 4-Amino-5-thioxo-1,2,4-triazol, Antimicrobial, Antitubercular.
Recently, the use of microwave irradiation (MWI) in
accelerating organic reactions is rapidly increasing because it
induces short reaction times and improves economic as well
as environmental and operational aspects. In our studies, a
wide range of organic reactions have been achieved using
INTRODUCTION
The development of resistance to current antimicrobial
and antimycobacterial therapy endorses the search for more
effective agents. In addition, primary and opportunistic
microbial infections continue to increase rapidly because of
the increased number of immunocompromised patients (AIDS,
cancer and transplants). Several reviews have appeared, which
illustrate the problems encountered by today's infectious
disease clinicians1-3.
As known, the easily gained resistance is the main problem
encountered in developing safe and efficient antimicrobial and
antimycobacterial agents. Therefore, there is a need to develop
new, potent, fast-acting antimicrobial and antimycobacterial
drugs with low toxicity4,5. For this reason, it is critical to
discover new drugs acting with different mechanism from those
drugs which are used in current therapy6,7. There has been
considerable interest in the chemistry of benzothiazol-2(3H)-
one ring. This heterocyclic core shows a broad spectrum of
biological activity such as antibacterial8, antifungal8, antiviral8,
anticonvulsant9, antiinflammatory10,11 and analgesic12-15 activities.
In addition, the 1,2,4-triazole nucleus and their heterocyclic
derivatives represent an interesting class of compounds which
possess a wide range of biological activities, such as anthel-
mintic16, antitubercular17, antiviral18, antimicrobial18-21 and
anticancer21 properties. Furthermore, Schiff bases derived from
various heterocyclic were reported to possess some biological
microwave irradiation26,27
.
In the present study, a number of new Schiff bases (Fig. 1)
of 4-amino-5-thioxo-1,2,4-triazole derivatives were prepared
by using the biologically active benzothiazol-2(3H)-one
moiety as starting material utilizing microwave irradiation in
order to be able to develop more effective antimicrobial
derivatives.
R
N
S
N
NH
N
N
O
S
R: H, F, Cl, Br, CF3, C(CH3)3, CH3, OCH3
Fig. 1.
EXPERIMENTAL
Chemicals and all the solvents, used in this study, were
purchased locally fromAldrich, (Germany), Merck (Germany)
and Acros (Germany) Chemical. Synthesis of benzothiazol-
activities22-26
.

226 Dündar et al.
Asian J. Chem.
TABLE-1
PHYSICO-CHEMICAL DATA OF THE COMPOUNDS (5a-5m)
Comp.
5a
R
Cry. sol.
Yield (%)
74
m.p. (ºC)
223-224
m.f.
HR MS (ESI+)
368.0637
Elemental analysis (cal./found)
H
Acetone-water
C17H13N5OS2
C: 55.57 (55.53); H:3.57 (3.66);
N: 19.06 (19.15
5b
5c
5d
5e
5g
5h
5i
4-F
4-Cl
4-Br
Acetone-ethanol
Acetone-ethanol
Acetone-ethanol
Acetone-ethanol
Acetone-ethanol
Acetone-ethanol
Acetic acid
70
63
89
87
81
79
80
77
89
92
227-228
228-229
238-239
245-246
248-249
221-222
219-220
235-236
219-220
115-116
C17H12N5OS2F
C17H12N5OS2Cl
C17H12N5OS2Br
C18H12N5OS2F3
C21H21N5OS2
386.0546
402.0251
447.9742
436.0525
424.1279
398.0745
386.0540
402.0253
447.9743
398.0746
C: 52.97 (52.83); H: 3.14 (3.23);
N: 18.17 (18.55)
C:50.81 (51.00); H: 3.01 (3.06);
N: 17.43 (17.31)
C: 45.75 (46.00); H: 2.71 (2.66);
N: 15.69 (15.62)
C: 49.65 (49.83); H: 2.78 (2.80);
N: 16.08 (16.12)
C: 59.55 (59.85); H: 5.00 (4.94);
N: 16.53 (16.45)
C: 54.39 (54.74); H: 3.80 (3.89);
N: 17.62 (17.59)
C: 52.97 (53.05); H: 3.14 (3.01;
N: 18.17 (18.18)
C: 50.81 (50.85; H: 3.01 (2.97);
N: 17.43 (17.44)
4-CF3
4-C(CH3)3
4-OCH3
2-F
C18H15N5O2S2
C17H12N5OS2F
C17H12N5OS2Cl
C17H12N5OS2Br
C18H15N5O2S2
5j
2-Cl
Acetone
5k
5m
2-Br
Acetone
C: 45.75 (45.78); H: 2.71 (2.73);
N: 15.69 (15.60)
C: 54.39 (54.56); H: 3.80 (3.64);
N: 17.62 (17.51)
2- OCH3
Acetone-ethanol
2(3H)-one (1)28, ethyl(benzothiazol-2(3H)-one-3-yl)acetate
(2)29, (benzothiazol-2(3H)-one-3-yl)acetic acid (3)29 were
synthesized according to the published procedures.
the reaction (monitored by TLC using toluene: methanol, 9:1)
and kept overnight at room temperature. After precipitated by
filtration, washed with water, dried and crystallized from a
suitable solvent (Table-1).
Melting points of the compounds were recorded on
an Electrothermal-9200 digital melting points apparatus
and are uncorrected. Microwave reaction was carried out in
MicroSYNTH Microwave Labstation at 1600 W (2 magne-
Microbiological studies
Microdilution method: Standard strains of P. aeruginosa
ATCC 27853, E. coli ATCC 25922, E. coli ATCC 35218, S.
aureus ATCC 29213, E. faecalis ATCC 29212, clinical
isolates of these microorganisms and C. albicansATCC 10231,
C. krusei ATCC 6258 were included in the study. Resistance
in clinical isolates was determined by disc diffusion method
according to the guidelines of clinical and laboratory standards
institute (CLSI)30. Standard powders of ampicillin trihydrate,
gentamycin sulfate, amphotericin B and fluconazole were
obtained from the manufacturers. Stock solutions were dissolved
in pH 8 phosphate buffered saline (PBS) (ampicillin trihydrate)
and distilled water (gentamycin sulfate and amphotericin B).
All bacterial isolates were subcultured in Mueller HintonAgar
(MHA; Merck) plates and incubated overnight at 37 ºC. The
solutions of the newly synthesized compounds and standard
drugs were prepared and diluted at 2048, 1024, 512,… 0.0625
µg/mL concentrations in the wells of microplates within the
liquid media. Bacterial susceptibility testing was performed
according to the guidelines of CLSI M100-S1831. The bacterial
suspensions used for inoculation were prepared at 105 CFU/
mL by diluting fresh cultures at MacFarland 0.5 density (107
CFU/mL). Suspensions of the bacteria at 105 CFU/mL concen-
trations were inoculated to the two-fold diluted solution of
the compounds. There were 104 CFU/mL bacteria in the wells
after inoculations. Mueller Hinton Broth (MHB; Merck) was
used for diluting the bacterial suspension and for two-fold
dilution of the compound. Dimethyl sulphoxide (DMSO),
phosphate buffered saline, pure microorganisms and pure
media were used as control wells. A 10 µL bacteria inoculum
was added to each well of the microdilution trays. The trays
1
trons 800W × 2). (Milestone S.R.L. Italy). The H NMR
spectra was recorded in DMSO-d6 on Bruker 400 MHz NMR
spectrometer. Chemical shifts are reported in parts per
million relative to internal standard tetramethylsilane. FTIR
spectra of the surface layer of grafted membranes were
measured with a Perkin-Elmer 400 (USA) ATR attachment
(32 scans, wavenumber 4000-650 cm-1) and analyzed using
the Spectrum v2.0 software. The mass spectra were obtained
on a waters ZQ micromass TOF-MS spectrometer (Waters
Corporation, Milford, MA, USA) using the ESI(+) method.
Synthesis of 3-[(4-Amino-5-thioxo-1,2,4-triazol-3-yl)-
methyl]benzothiazol-2(3H)-one (4): [2(3H)-benzo-thiazolon-
3-yl]acetic acid (0.01 mol) and thiocarbohydrazide (0.01 mol)
fused at 160-170 ºC in an oil bath for 10 min. The fused mass
thus obtained was recrystallized from N,N-dimethyl
1
formamide-water. Yield 80 %, m.p. 222-223 ºC, H-NMR
(DMSO-d6) δ; 13,64 (1H, s, NH), 7.69 (1H, m, H7), 7.33 (1H,
m, H4), 7.28 (1H, m, H6), 7.22 (1H, m, H5), 5,66 (2H, s,
NH2), 5.24 (2H, s, CH2); IR (νmax, cm-1): 3291, 3109, 1633,
1592, 1309;Anal. calcd. (found) (%) for: C10H9N5OS2: C: 43.00
(43.06), H: 3.25 (3.24), N: 25.07 (24.89).
3-[(4-{[Substituted phenylmethylidene]amino}-5-
thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol-2(3H)-one
(5a-5m): To a suspension of o/p-substituted benzaldehyde
(0.0015 mol) in glasial acetic acid (3 mL) was added 0.0015
mol of the [(4-amino-5-thioxo-1,2,4-triazol-3-yl)methyl]-
benzothiazol-2(3H)-one. The reaction mixture was taken in
round bottom flask placed in a microwave reactor and irradi-
ated for 15 or 25 min at 125 ºC (400 W). After completion of

Vol. 25, No. 1 (2013)
NH
Studies of Some 3-[(4-Amino-5-thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol-2(3H)-one Derivatives 227
S
2
S
NH
2
a
b
O
O
H N
2
+
N
N
H
O
SH
COOC H
2
1
2
5
S
S
S
e
d
c
O
O
O
N
N
N
O
N
HO
N
HN
HN
N
N
N
NH
2
3
S
S
4
5a-5m
R: H, F, Cl, Br, CF , C(CH ) , CH , OCH
3
R
3
3 3
3
a: fusion, MW; b: BrCH COOC2H5, K2CO3, acetone, MW; c: HCl, reflux; d: CS(NHNH2)2, fusion;
2
e: o/p-substitued benzaldehyde, CH3COOH, MW
Scheme-I: Synthesis of 3-[(o/p-substituted phenylmethylidene]amino-5-thioxo-1,2,4-triazol-3-yl)methyl]-benzothiazol-2(3H)-one (5a-m)
were incubated at 37 ºC and minimum inhibitory concentra-
tion (MIC) endpoints were read after 24 h of incubation. All
organisms were tested in triplicate in each run of the experi-
ments. The lowest concentration of the compound that
completely inhibits macroscopic growth was determined and
minimum inhibitory concentrations were reported. Candida
were subcultured in sabouraud dextrose agar (SDA; Merck)
plates and incubated at 35 ºC for 24-48 h. Susceptibility testing
was performed in RPMI-1640 medium with L-glutamine
(Sigma) buffered with MOPS (pH 7) (Sigma) and culture
suspensions were prepared through the guideline of CLSI M27-
A332.Yeast suspensions were prepared according to McFarland
0.5 density and a working suspension was made by a 1:100
dilution followed by a 1:20 dilution of the stock suspension
(2.5 × 103 CFU/mL). A 10 µL yeast inoculum was added to
each well of the microdilution trays. The trays were incubated
at 35 ºC and minimum inhibitory concentration endpoints were
read after 48 h of incubation. All organisms were tested in
triplicate in each run of the experiments. The lowest concen-
tration of the compound that completely inhibits macroscopic
growth was determined and minimum inhibitory concentrations
were reported.
Microplate alamar blue assay: Mycobacterium tuber-
culosis H37RVATCC 27294 were subcultured on Middlebrook
7H11 agar (Becton Dickinson). Culture suspensions were
prepared in 0.04 % (v/v) tween 80-0.2 % bovine serum albumin
(Sigma) at MacFarland 1 density. Suspensions were then
diluted 1:25 in 7H9GC broth 4.7 g of Middlebrook 7H9 broth
base (Difco), 20 mL of 10 % (vol/vol) glycerol, 1 g of Bacto
Casitone (Difco), 880 mL of distilled water, 100 mL of oleic
acid, albumin, dextrose and catalase (Sigma). Compounds were
dissolved in dimethylsulphoxide (DMSO; Merck) at a final
concentration of 4096 µg/mL and sterilized by filtration using
0.22 µm syringe filters (millipore) and used as the stock
solutions. The stock solutions of the agents were diluted within
liquid media. Stock solutions of EMB (Sigma) were prepared
in deionized water. The solution of the newly synthesized
compounds and standard drugs were prepared and diluted at
2048, 1024, 512,… 0.0625 µg/mL concentrations in the wells
of microplates within the liquid media.
The plates were sealed with parafilm and were incubated
at 37 ºC for 5 days. Fifty microliters of a freshly prepared 1:1
mixture of 10X alamar blue (AbD Serotec) reagent and 10 %
tween 80 was added to the control well. The plates were
incubated at 37 ºC for 24 h. Control well turned pink and the
reagent mixture was added to all wells in the microplate. The
microplates were resealed with parafilm and were incubated
for 24 h at 37 ºC and the colours of all wells were recorded. A
blue colour in the well was recorded as no growth and a pink
colour was scored as growth. The minimum inhibitory concen-
tration was defined as the lowest drug concentration which
prevented a colour change from blue to pink33.
RESULTS AND DISCUSSION
In this present work, we reported the preparation of 15
new series of 3-[(4-substituted phenylmethylidene]amino-5-
thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol-2(3H)-one by
using a microwave technique. Scheme-I illustrates the way
used for the preparation of target compounds. We report that,
the condensation of 2-aminothiophenol with urea results in
the rapid formation of benzothiazol-2(3H)-one in high yield
and enhanced reaction rate when subjected to microwave
irradiation under solvent-free condition28. This reaction needs
a long reaction time and a solvent under conventional heating.
Benzothiazol-2(3H)-one (1) was reacted with ethyl
bromoacetate to obtain ethyl(benzothiazol-2(3H)-one-3-yl)

228 Dündar et al.
Asian J. Chem.
TABLE-2
IR AND 1H NMR SPECTRAL DATA OF THE COMPOUNDS 4, 5a-5m
IR νmax (cm-1)
3291, 3109,
1633, 1592, 1309 (2H, s, CH2)
1H NMR δ (DMSO-d6)
Comp.
4
13,64 (1H, s, NH), 7.69 (1H, m, H7), 7.33 (1H, m, H4), 7.28 (1H, m, H6), 7.22 (1H, m, H5), 5,66 (2H, s, NH2), 5.24
5a
5b
5c
5d
5e
5g
5h
5i
3058,1685,
1591, 1275
3042,1657,
1596, 1263
3050, 1666,
1591, 1263
3040, 1666,
1586, 1254
3070, 1651,
1592, 1267
3070, 1653,
1595, 1269
3060, 1673,
1601, 1255
3040, 1657,
1590, 1256
3040, 1702,
1589, 1275
3064, 1667,
1583, 1249
3052, 1668,
1591, 1249
14.04 (1H, s, NH), 9.99 (1H, s, =CH), 7.86 (2H, d, phenyl-H2,6), 7.68 (1H, d, H7), 7.62 (1H, t, phenyl-H4), 7.54
(2H, t, phenyl-H3,5), 7.38 (1H, d, H4), 7.34 (1H, t, H6), 7.21 (1H, t, H5), 5.39 (2H, s, CH2)
14.04 (1H, s, NH), 9.96 (1H, s, =CH), 7.90 (2H, m, phenyl-H2,6), 7.68 (1H, d, H7), 7.42-7.32 (mH, m, phenyl-
H3,5, H4, H6), 7.23 (1H, t, H5), 5.39 (2H, s, CH2)
13.70 (1H, s, NH), 9.99 (1H, s, =CH), 7.90 (2H, d, phenyl-H2, 6), 7.68 (1H, d, H7), 7.62 (2H, d, phenyl-H3,5),
7.37-7.34 (2H, m, H4, H6), 7.23 (1H, t, H5), 5.40 (2H, s, CH2)
14.06 (1H, s, NH), 10.04 (1H, s, =CH), 7.82 (2H, d, phenyl-H2,6), 7.75 (2H, d, phenyl-H3, 5), 7.68 (1H, d, H7),
7.39-7.32 (2H, m, H4, H6), 7.23 (1H, t, H5), 5.04 (2H, s, CH2)
14.11 (1H, s, NH), 10.26 (1H, s, =CH), 8.11 (2H, d, phenyl-H2, 6), 7.91 (2H, d, phenyl-H3, 5), 7.68 (1H, d, H7),
7.38 (1H, d, H4), 7.34 (1H, t, H6), 7.22 (1H, t, H5), 5.43 (2H, s, CH2)
14.01 (1H, s, NH), 9.89 (1H, s, =CH), 7.81 (2H, d, H7, H4), 7.68 (1H, d, H6), 7.55 (2H, d, phenyl-H3, 5), 7.37-7.35
(2H, m, phenyl-H2, 6), 7.21 (1H, t, H5), 5.37 (2H, s, CH2), 1.33 (9H, s, CH3)
13.65 (1H, s, NH), 9.68 (1H, s, =CH), 7.82 (2H, d, phenyl-H2, 6), 7.67 (1H, d, H7), 7.38-7.32 (2H, m, H4, H6), 7.23
(1H, t, H5), 7.09 (2H, d, phenyl-H3, 5), 5.37 (2H, s, CH2), 3.86 (3H, s, OCH3)
14.01 (1H, s, NH), 10.42 (1H, s, =CH), 7.96 (1H, t, phenyl-4, 7.59 (2H, d, H7, H4), 7.30-7.23 (4H, m, phenyl-H3, 5,
6, H6), 7.12 (1H, t, H5), 5.32 (2H, s, CH2)
5j
14.11 (1H, s, NH), 10.81 (1H, s, =CH), 8.13 (1H, d, H7), 7.70 (1H, d, H4), 7.68-7.62 (2H, m, H6, phenyl-H6), 7.52-
7.48 (1H, m, H5), 7.39 (1H, d, phenyl-H3), 7.35 (1H, t, phenyl-H5), 7.22 (1H, t, phenyl-H4), 5.43 (2H, s, CH2)
14.01 (1H, s, NH), 10.70 (1H, s, =CH), 8.05-8.03 (1H, m, phenyl-H3), 7.73-7.70 (1H, m, phenyl-H5), 7.60 (1H, d,
H7), 7.45-7.43 (2H, m, phenyl-H4, 6), 7.31 (1H, d, H4), 7.27 (1H, t, H6), 7.13 (1H, t, H5), 5.34 (2H, s, CH2)
14.39 (1H, s, NH), 10.31 (1H, s, =CH), 7.94 (1H, dd, H7), 7.67(1H, d, H4), 7.60 (1H, t, H6), 7.39-7.32 (2H, m,
phenyl-H4, 6), 7.23-7.18 (2H, m, phenyl-H3, 5), 7.07 (1H, t, H5), 5.37 (2H, s, CH2), 3.89 (3H, s, OCH3)
5k
5m
acetate (2) catalyzed by potassium carbonate on exposure to
microwave irradiation in the presence. Benzothiazol-2(3H)-
one (1), ethyl(benzothiazol-2(3H)-one-3-yl) acetate (2) and
(benzothiazol-2(3H)-one-3-yl)acetic acid (3) were accomp-
lished according to the previously reported procedures29. 3-
[(4-Amino-5-thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol-
2(3H)-one (4) was easily prepared from the reaction between
(benzothiazol-2(3H)-one-3-yl) acetic acid and thiocarbo-
hydrazide in an oil-bath. 3-[(o/p-substitutedphenylmethy-
lidene] amino-5-thioxo-1,2,4-triazol-3-yl)methyl]-benzo-
thiazol-2(3H)-one (5) derivatives thus obtained was reacted
with o/p-substituebenzaldehyde derivatives in acetic acid under
microwave irradiation. Most preparations of Schiff bases were
reacted in the ethanol solvent, using an acid as the catalyst.
But in this experiment, 3-[(4-amino-5-thioxo-1,2,4-triazol-3-
yl)methyl] benzothiazol-2(3H)-one was only slightly dissolved
in ethanol. Here in, the acetic acid played a role not only as a
solvent but also as a catalyst34. The significant advantages of
these procedures are operational simplicity, short reaction time,
pure products and good yields.
was seen as singlet at about 14.11-13.95 ppm. The signal due
to benzothiazol-2(3H)-one-CH2- methylene protons, present
in all compounds, appeared at 5.37-5.43 ppm, as singlet. The
-N=CH proton of compounds 5a-m appeared at 9.74-10.26
ppm as singlet. All the other aromatic and aliphatic protons
were observed at the expected regions. Mass spectra (MS
(TOF-MS)) of compounds showed M+1 peaks, in agreement
with their molecular formula.
The synthesized compounds were tested for their in vitro
antibacterial activity against some gram positive bacteria; S.
aureus ATCC 29213, methicillin-resistant S. aureus (MRSA,
clinical isolate), E. faecalisATCC 29212, E. faecalis (resistant
to vancomycin, clinical isolate), some gram negative bacteria;
E. coliATCC 25922, E. coliATCC 35218, E. coli isolate, which
has an extended spectrum beta lactamase enzyme (ESβL), P.
aeruginosa ATCC 27853, P. aeruginosa (resistant to gentamycin,
clinical isolate) and yeast-like fungi; C. albicans ATCC 10231
and C. kruseiATCC 6258 by using broth microdilution method.
Ampicillin and gentamycin were used as standard antimicrobial
agents and amphotericin B and fluconazole were used as standard
antifungal agents (Table-3). The synthesized compounds were
also tested in vitro for antimycobacterial activity against M.
tuberculosis H37RV ATCC 27294, M. tuberculosis (clinical
isolate) by using microplate alamar blue assay method.
Ethambuthol was used as standard antimycobacterial agent.
The biological activity results of the compounds were shown
in Table-3. Minimum inhibitory concentrations were recorded
as the minimum concentration of compound, which inhibits
the growth of tested microorganisms.
The structure of the compounds was elucidated by IR, 1H
NMR, mass spectral data and elemental analysis (Tables 1
and 2).
In the IR spectra of all the compounds C=N and C=C
bands were observed at ca. 1601-1430 cm-1 region and benzo-
thiazol-2(3H)-ones have C=O stretching bands at 1702-653
cm-1 region. According to the IR spectroscopic data of the
compounds 5a-m which have 3-[(4-substitued phenylmethy-
lidene]amino-5-thioxo-1,2,4-triazol-3-yl)methyl]- benzothiazol-
2(3H)-one structure, the observation of C=S stretching bands
at 1275-1249 cm-1 and the absence of an absorption at about
2600-2550 cm-1 region cited for SH group, have proved that
these compounds were in the thionic form.
As shown in Table-3, the synthesized compounds exhibited
a broad spectrum of activity with minimum inhibitory concen-
tration values 64-256 µg/mL against both gram-positive and
gram-negative bacteria. Generally, synthesized compounds
were more active against gram-positive bacteria rather than
gram-negative bacteria. Among the gram-positive bacteria
1
In the H NMR spectra of compounds (5a-m) that are
taken in DMSO-d6 (Table-2), NH proton of the Schiff base

Vol. 25, No. 1 (2013)
Studies of Some 3-[(4-Amino-5-thioxo-1,2,4-triazol-3-yl)methyl]benzothiazol-2(3H)-one Derivatives 229
TABLE-3
ANTIMICROBIAL AND ANTIMYCOBACTERIAL ACTIVITY RESULTS (MICs, µg/mL)
OF THE SYNTHESIZED COMPOUNDS WITH THE STANDARD DRUGS
Comp.
4
512
512
256
512
512
512
512
512
512
512
512
512
128
512
2
512
512
256
512
512
512
512
512
512
512
512
512
256
512
-
512
512
256
512
512
512
512
512
512
512
512
512
256
512
>1024
512
-
256
256
256
256
256
128
256
128
256
256
256
256
128
256
-
256
256
256
256
256
256
256
256
256
256
256
256
256
256
-
512
64
256
256
256
256
256
128
256
128
256
256
256
256
256
256
-
512
256
128
512
256
128
512
128
128
256
256
256
256
512
0.5
8
512
256
128
512
512
256
512
512
512
512
512
512
128
512
0.5
8
128
64
128
64
128
128
64
128
64
256
256
256
64
256
-
256
256
128
256
128
256
256
256
256
256
256
256
256
128
-
256
128
128
256
128
256
128
256
128
128
256
256
256
256
-
256
256
256
256
256
128
256
128
256
256
256
256
128
128
-
5a
5b
256
512
512
256
512
64
512
512
512
512
128
512
0.5
0.5
-
5c
5d
5e
5f
5g
5h
5i
5j
5k
5l
5m
Ampicillin
Gentamycin
Amphotericin B
Fluconazole
Ethambutol
0.25
-
-
-
-
-
-
1
-
-
-
64
-
-
-
128
-
-
-
-
0.5
32
-
-
-
4
-
-
-
1
-
-
-
-
-
-
<0.03
0.0625
-
-
-
-
-
-
-
-
tested, S. aureus showed relative high sensitivity towards the
title compounds. Compounds 5a and 5g gave the best inhibi-
tory activity against S. aureus ATCC 29213 with a minimum
inhibitory concentration value of 64 µg/mL, but having less
activity than the tested control drugs. Compound 5b, 5e, 5g
and 5h showed more potent inhibitory effect against E. faecalis
ATCC 29212 with minimum inhibitory concentration value
of 128 µg/mL than the other tested compounds.
minimum inhibitory concentration value of 256 µg/mL than
the other compounds, even they were more potent than the
standard drug, gentamycin.
As a result, when their antimicrobial activity is compared;
the p-substituted schiff base derivatives are more active than
the o-substituted Schiff base derivatives. The minimum
inhibitory concentration values are generally within the range
of 64-256 µg/mL, most often between 128-512 µg/mL against
all evaluated strains.
With respect to antifungal activity of the synthesized
compounds, all compounds displayed antifungal activity
against both C. albicans and C. krusei with a minimum
inhibitory concentration value of 64-128 µg/mL. In contrast,
all the synthesized compounds did not show significant
activity against gram negative bacteria (minimum inhibitory
concentrations > 256 µg/mL). Although compounds 5a, 5c,
5f, 5h and 5l showed minimum inhibitory concentration value
64 µg/mL against C. albicans other compounds possess better
activity but they were less active than reference drug and
compound 4. On the otherhand, compounds 5b, 5d, 5e and 5g
were as effective as compound 4 but were less active than
reference drug. The compound (5c) substituted with a chloro
atom has a higher biological activity than those with other
halogen atoms. Compounds 5b, 5d and 5m gave slightly
inhibitory activity against C. krusei with a minimum inhibi-
tory concentration value of 128 µg/mL. Compounds 5l was
found to be effective against both gram positive (S. aureus)
and gram negative (P. aeruginosa) bacteria with a minimum
inhibitory concentration value of 128 µg/mL. In the same way,
compounds 5e and 5g were showed minimum inhibitory
concentration value 128 µg/mL against both types of bacteria
P. aeruginosa and E. faecalis. Moreover, compounds 5b and
5l were found to be more active against E. coli isolate with
The antimycobacterial assessment revealed that the Schiff
base derivatives possess only a moderate or slight activity.
However, compounds 5a, 5b, 5d, 5f and 5i were more effective
than compound 4.
These compounds are characterized by the presence of a
substituent in the para or ortho position of the phenyl ring but
their activity does not depend from electronic effects, since
electron-donating and electron-withdrawing substituents
produce the same level of activity. However, a few para sub-
stituted derivatives were active against C. albicans.
ACKNOWLEDGEMENTS
This study was supported by Gazi University BAP. Project
Number 02/2009-06. The authors are grateful to Dr. M. Sukuroglu
for providing mass spectral data.
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