Synthesis and antimicrobial activity evaluation of new 1,2,4-triazoles and 1,3,4-thiadiazoles bearing imidazo[2,1-b]thiazole moiety

Article abstract of DOI:10.1016/j.ejmech.2009.09.024

A series of 4-alkyl/aryl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thiones (3a-i) and 2-alkyl/arylamino-5-((6-(4-bromophenyl)imidazo[2,1-b]thiazol-3-yl)methyl)-1,3,4-thiadiazoles (4a-c) were synthesized starting from 6-(4-bromophenyl)imidazo[2,1-b]thiazole-3-acetic acid hydrazide. The newly synthesized compounds were characterized by IR, ¹H NMR, mass and elemental analysis. All compounds were tested for antibacterial and antifungal activities. The antimicrobial activities of the compounds were assessed by the microbroth dilution technique. The compounds were also evaluated for antituberculosis activity against Mycobacterium tuberculosis H₃₇Rv (ATCC 27294). The preliminary results revealed that some of the compounds exhibited promising antimicrobial activities.

Full text of DOI:10.1016/j.ejmech.2009.09.024

European Journal of Medicinal Chemistry 45 (2010) 63–68
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis and antimicrobial activity evaluation of new 1,2,4-triazoles and
1,3,4-thiadiazoles bearing imidazo[2,1-b]thiazole moiety
,
b
Nuray Ulusoy Gu¨zeldemirci a , Omer Ku¨çu¨kbasmacı
*
¨
a
_
_
Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Istanbul University, Istanbul, Turkey
Department of Microbiology, Cerrahpas¸a Faculty of Medicine, Istanbul University, Istanbul, Turkey
b
_
_
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 4-alkyl/aryl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-b]thiazol-3-yl)methyl)-3H-1,2,4-
triazole-3-thiones (3a–i) and 2-alkyl/arylamino-5-((6-(4-bromophenyl)imidazo[2,1-b]thiazol-3-yl)
methyl)-1,3,4-thiadiazoles (4a–c) were synthesized starting from 6-(4-bromophenyl)imidazo
[2,1-b]thiazole-3-acetic acid hydrazide. The newly synthesized compounds were characterized by IR, 1H
NMR, mass and elemental analysis. All compounds were tested for antibacterial and antifungal activities.
The antimicrobial activities of the compounds were assessed by the microbroth dilution technique. The
compounds were also evaluated for antituberculosis activity against Mycobacterium tuberculosis H37Rv
(ATCC 27294). The preliminary results revealed that some of the compounds exhibited promising anti-
microbial activities.
Received 16 March 2009
Accepted 10 September 2009
Available online 16 September 2009
Keywords:
Imidazo[2,1-b]thiazole
1,2,4-Triazole
1,3,4-Thiadiazole
Antibacterial activity
Antifungal activity
Antimycobacterial activity
Ó 2009 Elsevier Masson SAS. All rights reserved.
1. Introduction
Moreover, the development of drug-resistant strains of myco-
bacterium species, has contributed to the inefficiency of the
Since resistance of pathogenic bacteria towards available anti-
biotics is rapidly becoming a major worldwide problem, the design
of new compounds to deal with resistant bacteria has become one
of the most important areas of antibacterial research today. In
addition, primary and opportunistic fungal infections continue to
increase rapidly because of the increased number of immuno-
compromised patients. As known, not only biochemical similarity
of the human cell and fungi forms a handicap for selective activity,
but also the easily gained resistance is the main problem encoun-
tered in developing safe and efficient antifungals. On the other
hand, Mycobacterium tuberculosis remains a leading infectious
cause of death in the world today. The incidence of tuberculosis is
increasing worldwide, partly due to poverty and inequity and partly
to the HIV/AIDS pandemic, which greatly increase the risk of
infection proceeding to overt disease [1]. In particular, the
appearance of multi-drug-resistant (MDR) strains of M. tuberculosis,
which exhibit in vitro resistance to at least two major antituber-
culosis drugs (usually Isoniazide and Rifampicin) and cause
intractable tuberculosis, has greatly contributed to the increased
incidence of tuberculosis [2,3].
conventional antituberculosis therapy, thus, it is still necessary to
search for new antimycobacterial agents.
1,2,4-Triazoles and their heterocyclic derivatives represent an
interesting class of compounds possessing a wide spectrum of
biological activities. A large number of 1,2,4-triazole containing ring
systems exhibits antibacterial [4–10], antifungal [7–11], antituber-
cular [12–14], analgesic [15,16], antiinflammatory [16–18], anti-
cancer [19,20], anticonvulsant [21,22], antiviral [23,24], insecticide
[25], antidepressant [26], central nervous system (CNS) [27] activ-
ities. In addition, 1,3,4-thiadiazole nucleus constitutes the active
part of several biologically active compounds, including antibac-
terial [27–30], antifungal [29,30], antitubercular [31–33], analgesic
[34], antiinflammatory [29,30,34], antidepressant [26], leishmani-
cidal [35] agents. In view of these facts and as a continuation of our
research on the biological properties of 1,2,4-triazole and 1,3,4-
thiadiazole containing derivatives [36–41], we have designed and
synthesized a number of imidazo[2,1-b]thiazole substituted fused
1,2,4-triazole and 1,3,4-thiadiazole systems, as potential antibac-
terial, antifungal and antitubercular agents.
2. Chemistry
The key intermediate 1 was prepared from ethyl 6-(4-bromo-
phenyl)imidazo[2,1-b]thiazole-3-acetate and hydrazine hydrate
following the literature method [42]. The synthetic route of the
* Corresponding author.
E-mail address: nulusoy@istanbul.edu.tr (N.U. Gu¨zeldemirci).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.09.024

¨
N.U. Gu¨zeldemirci, O. Ku¨çu¨kbasmacı / European Journal of Medicinal Chemistry 45 (2010) 63–68
64
compounds is outlined in Scheme 1. 4-Alkyl/aryl-1-((6-(4-bromo-
phenyl)imidazo[2,1-b]thiazol-3-yl)acetyl)-3-thiosemicarbazides (2)
were obtained by the reactions of alkyl/arylisothiocyanates with
6-(4-bromophenyl)imidazo[2,1-b]thiazole-3-acetatic acid hydra-
zide (1) whose synthesis was previously described [43]. Alkaline
cyclisation of the compounds 2 using sodium hydroxide affor-
ded the corresponding 4-alkyl/aryl-2,4-dihydro-5-((6-(4-bromo-
phenyl)imidazo[2,1-b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thi
ones (3a–i). Reacting thiosemicarbazides (2) with concentrated
sulfuric acid at room temperature resulted in the formation of
the corresponding 2-alkyl/arylamino-5-((6-(4-bromophenyl)imi-
dazo[2,1-b]thiazol-3-yl)methyl)-1,3,4-thiadiazoles (4a–c).
compounds 3a, 3b, 3f, 4a, 4b and 4c displayed molecular ions
which confirmed their molecular weights. Fragmentation followed
the route in accordance with literature [45].
4. Biological activity
All compounds to be tested were dissolved in DMSO at a stock
concentration of 3200 m
g cmꢀ3 .The final desired concentration
were prepared with RPMI 1640 medium for Candida species and
dermatophytes and with Mueller–Hinton broth of bacteria. The
final DMSO concentration was reduced to 1%.
4.1. Antibacterial activity
3. Results and discussion
MICs were determined by the microbroth dilution method using
the National Committee for Clinical Laboratory Standards (NCCLS)
recommendations [46]. Mueller–Hinton broth (Oxoid, Hemakim,
Turkey) was used as the test medium. An inoculum of approxi-
mately 5 ꢁ105 CFU cmꢀ3 was delivered per well. Serial twofold
The structures of the synthesized compounds were confirmed
by analytical (Table 1) and spectral data (IR, 1H NMR, EIMS). The IR
spectra of 3a–i and 4a–c exhibited N–H bands in the 3440–3389
and 3428–3347 cmꢀ1, respectively. The absorption bands at 1616–
1414 and 1600–1417 cmꢀ1 are due to the presence of –C]N–
stretch of the triazole and thiadiazole ring system, respectively.
Absence of the C]O absorptions in 3a–i and 4a–c provided
definitive proof for the formation of new products. The 1H NMR of
3a, 3b and 3f chosen as prototypes showed single NH resonances in
the 13.74–13.52 ppm regions. In the 1H NMR spectra of 4a, 4b and
4c, the NH proton at 2-position of 1,3,4-thiadiazole ring appeared at
7.59–7.55, 7.62–7.55 ppm together with Ar–H as a multiplet and
10.31 ppm as a singlet, respectively. The exocyclic S–CH2 protons of
3 and 4 resonated at 4.44–4.13 and 4.64–4.48 ppm, respectively.
The protons of the imidazo[2,1-b]thiazole nucleus and the other
protons resonated at the expected regions [44]. The EIMS of
dilutions of the test compounds (64–0.25
dilutions (0.12–0.015 ) for antibiotic standards were
g cmꢀ3
m
g cmꢀ3) and extra
m
prepared. Plates were incubated for 16–20 h at 35 ꢂC in an ambient
air incubator. The lowest concentration of the test compounds
inhibiting visible growth was taken as the MIC value.
4.2. Antifungal activity
4.2.1. Antifungal activity for Candida species
MICs were determined by the microbroth dilution method using
the NCCLS recommendations [47]. RPMI broth was prepared from
RPMI 1640 medium (Sigma, St. Louis, Mo, USA) supplemented with
O
O
C2H5
C2H5
Br
N
O
N
O
Br
Br
+
H2N
S
N
S
O
H2NNH2.H2O
NH
NH2
N
O
Br
S
N
1
RNCS
S
S
NH
R
NH
NH
N
O
Br
N
2
NaOH
H2SO4
H
N
N
N
N
NH
R
S
S
N
R
N
N
Br
Br
S
4a-c
N
S
N
3a-i
Scheme 1.

¨
N.U. Gu¨zeldemirci, O. Ku¨çu¨kbasmacı / European Journal of Medicinal Chemistry 45 (2010) 63–68
65
Table 1
Some physical and analytical data of compounds 3a–i and 4a–c.
Compd.
R
Formula (Mw
)
M.p. (ꢂC)
Yield (%)
Analysis (%) (calc./found)
C
H
N
3a
3b
3c
3d
3e
3f
CH3
C15H12BrN5S2 (406.34)
C16H14BrN5S2 (420.36)
C17H16BrN5S2.H2O (452.41)
C18H18BrN5S2.H2O (466.43)
C17H14BrN5S2.H2O (450.39)
C20H14BrN5S2 (468.40)
C20H13Br2N5S2 (547.30)
C20H13BrClN5S2 (502.84)
C21H16BrN5S2 (482.43)
C15H12BrN5S2 (406.34)
C16H14BrN5S2 (420.36)
C20H14BrN5S2 (468.40)s
>300
98
98
94
98
99
98
98
98
98
97
98
98
44.33
44.15
45.71
45.16
45.13
44.78
46.35
45.76
45.33
44.80
51.28
51.69
43.89
43.66
47.77
47.96
52.28
52.70
44.33
44.34
45.71
46.09
51.28
50.70
2.97
2.81
3.35
3.40
4.00
3.80
4.49
4.29
3.58
3.36
3.01
3.19
2.39
2.29
2.60
2.82
3.34
3.55
2.97
2.94
3.35
3.47
3.01
2.69
17.23
16.65
16.66
16.01
15.48
14.85
15.01
14.68
15.55
14.95
14.95
15.17
12.79
12.20
13.92
13.95
14.51
14.53
17.23
16.80
16.66
16.74
14.95
14.65
C2H5
273–274
259–260
244–245
223–224
>300
C3H7
C4H9
CH2CH]CH2
C6H5
3g
3h
3i
C6H4Br(4-)
C6H4Cl(4-)
C6H4CH3(4-)
CH3
287–288
294–295
289
4a
4b
4c
246–247
184–185
>300
C2H5
C6H5
0.3 g of glutamine per dm3, bufferred with 3-(N-morpholino)-
propanesulfonic acid (MOPS), and adjusted to pH 7.0. A working
suspension of the inoculum was prepared by a 1:100 dilution of the
0.5 McFarland standards yeast suspension in 0.85% saline followed
by a 1:20 dilution in RPMI broth.
to an inverted reading mirror after 7 days for dermatophytes. For all
drugs, the MIC was defined as the lowest concentration showing
100% inhibition of growth.
4.3. Antimycobacterial activity
Twofold dilutions of test compounds from 64 to 0.25 m
g cmꢀ3
were prepared with the working suspension of the inoculum. Extra
dilutions (0.12–0.015 mg cmꢀ3) were added for itraconazole. The
plates were incubated at 35 ꢂC for 48 h in ambient air. The MIC is
the lowest concentration of a compound that inhibits growth of the
organism as detected visually.
A primary screening was conducted at 6.25 mg/ml (or molar
equivalent of highest molecular weight compound in a series of
congeners) against M. tuberculosis H37Rv (ATCC 27294) in BACTEC
12B medium using a broth microdilution assay, the Microplate
Alamar Blue Assay (MABA) [50]. Compounds exhibiting fluores-
cence were tested in the BACTEC 460 radiometric system.
Compounds effecting <90% inhibition in the primary screen
4.2.2. Antifungal activity for dermatophytes
Microdilution method was used according to
a standard
(MIC > 6.25 mg/ml) were not generally evaluated further.
protocol by NCCLS [46]. RPMI 1640 broth with -glutamine wihtout
L
Compounds demonstrating at least 90% inhibition in the primary
screen were retested at lower concentrations against M. tubercu-
losis H37Rv to determine the actual minimum inhibitory concen-
tration (MIC) using MABA. The MIC was defined as the lowest
concentration effecting a reduction in fluorescence of 90% relative
to controls.
sodium bicarbonate was and 0.165 M MOPS buffer (34.54 g/lt) and
used. The medium was adjusted to pH 7.0 at 25 ꢂC. Preparation of
inoculum suspensions of dermatophytes were based according to
the NCCLS quidelines [48] and previously described procedure [49].
The isolates were subcultured on to potato dextrose agar (PDA)
plates at 28 ꢂC, during 7–14 days. The fungal colonies were covered
with 1 ml of sterile 0.85% saline, and suspensions were made by
gently probing the surface with the tip of Pasteur pipette. The
resulting mixture of conidia and hyphal fragments was withdrawn
and transferred to a sterile tube. Heavy particles were allowed to
settle for 15–20 min at room temperature; the upper suspension
was mixed with a vortex for 15 s. The turbidity of supernatants was
measured spectrophotometrically at a wavelength of 530 nm, and
transmission was adjusted to 65–75%. These stock suspensions
were diluted 1:50 in RPMI medium to obtain the final inoculum
sizes, which range from 0,4 ꢁ104 to 5 ꢁ104 CFU/ml. Microdilution
plates were prepared and frozen at ꢀ70 ꢂC until needed. Rows from
4.3.1. Radiometric susceptibility test
A total of 0.1 cm3 of BACTEC 12B-passaged inoculum was
delivered without prior dilution into 4 cm3 of test medium.
Subsequent determination of bacterial titers yielded average titers
(three experiments) of 1 ꢁ105, 2.5 ꢁ105, and 3.25 ꢁ104 CFU cmꢀ3
of BACTEC 12B medium for M. tuberculosis H37Rv. Frozen inocula
were initially diluted 1:20 in BACTEC 12B medium, and then
0.1 cm3 was delivered to test medium. This yielded 5.0 ꢁ 105 and
1.25 ꢁ105 CFU per BACTEC vial for H37Rv. Twofold drug dilutions
were prepared in either DMSO (Sigma) or distilled deionized H2O
and delivered via a 0.5-cm3 insulin syringe in a 50-mm3 volume.
Drug-free control vials consisted of solvent with bacterial inoculum
and solvent with a 1:100 dilution of bacterial inoculum (1:100
controls). Vials were incubated at 37 ꢂC, and the GI was determined
in a BACTEC 460 instrument (Becton Dickinson) until the GI of the
1:100 controls reached at least 30. All vials were read the following
2 to 12 contained the series of drug dilutions in 100
first row contained 100 l of drug-free medium, which served as
the growth control. Each well was inoculated on the day of the test
with 100 l of the corresponding inoculum. This step brought the
ml volumes and
m
m
drug dilutions and inoculum size to the final test concentrations
given above. The microplates of dermatophytes were incubated at
28 ꢂC during 7 days. The microplates were read visually with the aid
day, and the GI and daily change in GI (
DGI) were recorded for each
drug dilution. The MIC was defined as the lowest concentration for

¨
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N.U. Gu¨zeldemirci, O. Ku¨çu¨kbasmacı / European Journal of Medicinal Chemistry 45 (2010) 63–68
Table 2
which the DGI was less than the DGI of the 1:100 control. If the GI of
Antibacterial activity of compounds 3a–i and 4a–c (MIC mg/mL).
the test sample was greater than 100, the sample was scored as
resistant even if the GI was less than the GI of the 1:100 control.
Microorganismsa
A
D
D
Comp.
B
C
4.3.2. Alamar blue susceptibility test (MABA)
3a
3b
3c
3d
3e
3f
3g
3h
3i
4a
4b
4c
>64
64
64
32
>64
64
>64
>64
64
>64
64
>64
>64
>64
64
>64
>64
>64
>64
64
>64
64
Antimicrobial susceptibility testing was performed in black,
clear-bottomed, 96-well microplates (black view plates; Packard
Instrument Company, Meriden, Conn.) in order to minimize back-
ground fluorescence. Outer perimeter wells were filled with sterile
H2O to prevent dehydration in experimental wells. Initial drug
dilutions were prepared in either DMSO or distilled deionized H2O,
and subsequent twofold dilutions were performed in 0.1 cm3 of
7H9GC (no Tween 80) in the microplates. BACTEC 12B-passaged
inocula were initially diluted 1:2 in 7H9GC, and 0.1 cm3 was added
to wells. Subsequent determination of bacterial titers yielded
1 ꢁ106, 2.5 ꢁ106, and 3.25 ꢁ105 CFU cmꢀ3 in plate wells for M.
tuberculosis H37Rv. Frozen inocula were initially diluted 1:20 in
BACTEC 12B medium followed by a 1:50 dilution in 7H9GC. Addi-
tion of 0.1 cm3 to wells resulted in final bacterial titers of 2.0 ꢁ 105
and 5 ꢁ104 CFU cmꢀ3 for H37Rv. Wells containing drug only were
used to detect autofluorescence of compounds. Additional control
wells consisted of bacteria only (B) and medium only (M). Plates
were incubated at 37 ꢂC. Starting at day 4 of incubation, 20 mm3 of
10ꢁ alamar Blue solution (Alamar Biosciences/Accumed, Westlake,
Ohio) and 12.5 mm3 of 20% Tween 80 were added to one B well and
one M well, and plates were reincubated at 37 ꢂC. Wells were
observed at 12 and 24 h for a color change from blue to pink and for
a reading of ꢃ50,000 fluorescence units (FU). Fluorescence was
measured in a Cytofluor II microplate fluorometer (PerSeptive
Biosystems, Framingham, Mass.) in bottom-reading mode with
excitation at 530 nm and emission at 590 nm. If the B wells became
pink by 24 h, reagent was added to the entire plate. If the well
remained blue or ꢄ50,000 FU was measured, additional M and B
wells were tested daily until a color change occured, at which time
reagents were added to all remaining wells. Plates were then
incubated at 37 ꢂC, and results were recorded at 24 h post-reagent
addition. Visual MICs were defined as the lowest concentration of
drug that prevented a color change. For fluorometric MICs, a back-
ground subtraction was performed on all wells with a mean of
triplicate M wells. Percent inhibition was defined as 1 ꢀ (test well
FU/mean FU of triplicate B wells) ꢁ 100. The lowest drug concen-
tration effecting an inhibition of ꢃ90% was considered the MIC.
64
32
>64
>64
>64
>64
64
>64
32
>64
>64
64
>64
64
0.12
Levofloxacin
0.5
0.015
a
A ¼ S. aureus ATCC 29213, B ¼ P. aeruginosa ATCC 27853, C ¼ E. coli ATCC 25922.
were generally more active than the triazole derivatives 3a–i.
However, the most active compound was compound 4c (16%
inhibition) which had phenylamino group at the 2-position of the
thiadiazole ring. The antimicrobial activity results indicated that
some of the tested compounds showed the most promising anti-
bacterial, antifungal and antimycobacterial activities.
6. Experimental
Melting points were determined by using a Bu¨chi 530 melting
point apparatus in open capillary tubes and are uncorrected.
Elemental analyses were performed on a Carlo Erba 1106 elemental
analyzer. IR spectra were recorded on KBr discs, using a Perkin
Elmer 1600 FT-IR spectrophotometer. 1H NMR (DMSO-d6/TMS)
spectra were measured on a Bruker AC 200 (200 MHz) spectrom-
eter. EI mass spectra were recorded on a VG Zab Spec (70 eV)
instrument. The starting materials were either commercially
available or synthesized according to the references cited.
6.1. General procedure for the synthesis of 4-alkyl/aryl-2,4-dihydro-
5-((6-(4-bromophenyl)imidazo[2,1-b]thiazol-3-yl)methyl)-3H-
1,2,4-triazole-3-thiones (3a–i)
6.1.1. 4-Methyl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-
b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thione (3a)
5. Conclusion
IR (KBr, n
, cmꢀ1): 3420 (N–H), 1581, 1539, 1505, 1467 (C]N,
C]C); 1H NMR (200 MHz,
d, ppm, DMSO-d6): 3.50 (s, 3H, N–CH3),
Compounds 3a–i and 4a–c were evaluated for in vitro antibac-
terial activity against Staphylococcus aureus ATCC 29213, Pseudo-
monas aeruginosa ATCC 27853 and Escherichia coli ATCC 25922 as
well as for antifungal activity against Candida albicans ATCC 10231,
Candida parapsilosis ATCC 22019, Candida krusei ATCC 6258, Tri-
chophyton mentagrophytes var. erinacei NCPF 375, Microsporum
gypseum NCPF 580 and Trichophyton tonsurans NCPF 245 using the
microbroth dilution method [46]. As can be seen in Table 2, 3d
(R ¼ C4H9) showed the highest activity against S. aureus ATCC 29213
Table 3
Antifungal activity of compounds 3a–i and 4a–c (MIC
m
g/mL).
Comp.
Microorganismsa
A
B
C
D
E
F
3a
3b
3c
3d
3e
3f
3g
3h
3i
4a
4b
4c
32
32
32
32
64
32
64
64
16
32
64
64
0.12
n.t.
32
32
64
64
64
32
32
>64
16
16
64
64
0.06
n.t.
32
32
64
64
64
32
64
64
16
16
32
32
0.12
n.t.
8
16
16
16
32
64
32
64
32
16
16
16
64
n.t.
0.5
16
8
8
32
32
16
32
32
16
8
16
16
32
64
32
64
32
16
16
16
64
n.t.
0.5
and E. coli ATCC 25922 (MIC ¼ 32
m
g cmꢀ3). 4b (R ¼ C2H5) showed
the highest activity against E. coli ATCC 25922 (MIC ¼ 32
m
g cmꢀ3).
Derivatives 3b (R ¼ C2H5), 3c (R ¼ C3H7), 4a (R ¼ CH3) and 4b
(R ¼ C2H5) were most active against T. tonsurans NCPF 245
(MIC ¼ 8
m
g cmꢀ3, Table 3). Compound 3a (R ¼ CH3) also showed
8
the highest activity against T. mentagrophytes var. erinacei NCPF 375
32
n.t.
0.25
(MIC ¼ 8
m
g cmꢀ3). The synthesized compounds (3a–i and 4a–c)
Itraconazole
Amphotericin B
were evaluated for in vitro antimycobacterial activity against M.
tuberculosis H37Rv (ATCC 27294) in BACTEC 12B medium using
a broth microdilution assay (Microplate Alamar Blue Assay (MABA)
[50]). As can be seen from Table 4, thiadiazole derivatives 4a–c
a
A ¼ C. albicans ATCC 10231, B ¼ C. parapsilosis ATCC 22019, C ¼ C. krusei ATCC
6258, D ¼ T. mentagrophytes var. erinacei NCPF 375, E ¼ M. gypseum NCPF 580, F ¼ T.
tonsurans NCPF 245, n.t. ¼ not tested.

¨
N.U. Gu¨zeldemirci, O. Ku¨çu¨kbasmacı / European Journal of Medicinal Chemistry 45 (2010) 63–68
67
Table 4
Antimycobacterial activity of compounds 3a–i and 4a–c.
6.1.9. 4-Methylphenyl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo
[2,1-b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thione (3i)
g/mL)a
Inhibition %
IR (KBr,
n
, cmꢀ1): 3393 (N–H), 1609, 1570, 1515, 1467 (C]N,
Compd.
R
Assay
MIC (
m
C]C) cmꢀ1
.
3a
3b
3c
3d
3e
3f
3g
3h
3i
CH3
C2H5
C3H7
C4H9
CH2CH]CH2
C6H5
C6H4Br(4-)
C6H4Cl(4-)
C6H4CH3(4-)
CH3
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
Alamar
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
>6.25
n.a.
n.a.
n.a.
n.a.
1
6.2. General procedure for the synthesis of 2-alkyl/arylamino-5-((6-
(4-bromophenyl)imidazo[2,1-b]thiazol-3-yl)methyl)-1,3,4-
thiadiazoles (4a–c)
3
n.a.
n.a.
4
n.a.
2
6.2.1. 2-Methylamino-5-((6-(4-bromophenyl)imidazo[2,1-
b]thiazol-3-yl)methyl)-1,3,4- thiadiazole (4a)
4a
4b
4c
IR (KBr,
n
, cmꢀ1): 3347 (N–H), 1583, 1536, 1490, 1466 (C]N,
C2H5
C6H5
C]C); 1H NMR (200 MHz,
d
, ppm, DMSO-d6): 2.84 (d, 3H, J ¼ 4.7 Hz,
16
NH–CH3), 4.48 (s, 2H, CH2), 7.12 (s, 1H, C2–H), 7.55–7.59 (m, 3H, ar
and NH), 7.76 (d, 2H, J ¼ 8.5 Hz, ar), 8.18 (s, 1H, C5–H); EIMS (70 eV)
m/z (%): 407 ((M þ 2)þ, 100), 405 (Mþ, 94), 319 (22), 317 (21), 293
(19), 291 (20), 211 (32), 179 (15), 153 (35).
a
MIC RMP ¼ 0.25 g/mL, 97–99% inhibition vs. M. tuberculosis H37Rv, n.a. ¼ not
m
active.
4.40 (s, 2H, CH2), 7.16 (s, 1H, C2–H), 7.56 (d, 2H, J ¼ 8.5 Hz, ar), 7.75
(d, 2H, J ¼ 8.5 Hz, ar), 8.22 (s, 1H, C5–H), 13.52 (s, 1H, NH); EIMS
(70 eV) m/z (%): 407 ((M þ 2)þ, 100), 405 (Mþ, 94), 374 (12), 372
(11), 338 (11), 336 (10), 319 (12), 317 (11), 293 (17), 291 (16), 211
(30), 163 (12).
6.2.2. 2-Ethylamino-5-((6-(4-bromophenyl)imidazo[2,1-b]thiazol-
3-yl)methyl)-1,3,4- thiadiazole (4b)
IR (KBr,
n
, cmꢀ1): 3410 (N–H), 1580, 1536, 1467, 1417 (C]N,
C]C); 1H NMR (200 MHz,
d
, ppm, DMSO-d6): 1.14 (t, 3H, J ¼ 7.2 Hz,
CH3), 3.18–3.31 (m, NH–CH2 and solv. H2O), 4.48 (s, 2H, CH2), 7.12 (s,
1H, C2–H), 7.55–7.62 (m, 3H, ar and NH), 7.76 (d, 2H, J ¼ 8.6 Hz, ar),
8.19 (s, 1H, C5–H); EIMS (70 eV) m/z (%): 421 ((M þ 2)þ, 100), 419
(Mþ, 96), 319 (18), 317 (17), 293 (13), 291 (14), 211 (22), 167 (25).
6.1.2. 4-Ethyl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-
b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thione (3b)
IR (KBr,
n
, cmꢀ1): 3404 (N–H), 1616, 1570, 1465, 1414 (C]N,
C]C); 1H NMR (200 MHz,
d, ppm, DMSO-d6): 1.22 (t, 3H, J ¼ 7.0 Hz,
CH3), 4.06 (q, 2H, J ¼ 7.0 Hz, N–CH2), 4.44 (s, 2H, CH2), 7.20 (s, 1H,
C2–H), 7.57 (d, 2H, J ¼ 8.4 Hz, ar), 7.76 (d, 2H, J ¼ 8.4 Hz, ar), 8.22 (s,
1H, C5–H), 13.54 (s, 1H, NH); EIMS (70 eV) m/z (%): 421 ((M þ 2)þ,
100), 419 (Mþ, 89), 406 (37), 404 (34), 307 (15), 305 (14), 211 (17),
170 (13).
6.2.3. 2-Phenylamino-5-((6-(4-bromophenyl)imidazo[2,1-
b]thiazol-3-yl)methyl)-1,3,4-thiadiazole (4c)
IR (KBr,
n
, cmꢀ1): 3428 (N–H), 1600, 1565, 1503, 1429 (C]N,
C]C); 1H NMR (200 MHz,
d
, ppm, DMSO-d6): 4.64 (s, 2H, CH2), 7.31
(s, 1H, C2–H), 7.48–7.64 (m, 7H, ar), 7.77 (d, 2H, J ¼ 8.5 Hz, ar), 8.40
(s, 1H, C5–H), 10.31 (s, 1H, NH); EIMS (70 eV) m/z (%): 469 ((M þ 2)þ,
7), 467 (Mþ, 6), 319 (48), 317 (45), 294 (10), 292 (10), 256 (7), 254
(7), 224 (4), 222 (4), 207 (100), 191 (11), 80 (47).
6.1.3. 4-Propyl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-
b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thione (3c)
IR (KBr,
(C]N, C]C).
n
, cmꢀ1): 3520, 3396 (O–H, N–H), 1612, 1569, 1465
Acknowledgements
6.1.4. 4-Butyl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-
We thank Dr. J. A. Maddry from the Tuberculosis Antimicrobial
Acquisition and Coordinating Facility (TAACF), National Institute of
Allergy and Infectious Diseases Southern Research Institute, GWL
Hansen’s Disease Center, Colorado State University, Birmingham,
Alabama, USA, for the in vitro evaluation of antimycobacterial
activity. This work was supported by the Research Fund of Istanbul
University (Project Numbers: BYP-57/03092002, BYP-179/
14032003 and BYP-478/22092004).
b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thione (3d)
IR (KBr,
C]C).
n
, cmꢀ1): 3520, 3433 (O–H, N–H), 1611, 1567, 1466 (C]N,
6.1.5. 4-Allyl-2,4-dihydro-5-((6-(4-bromophenyl)imidazo[2,1-
b]thiazol-3-yl)methyl)-3H-1,2,4-triazole-3-thione (3e)
IR (KBr, n
, cmꢀ1): 3520, 3440 (O–H, N–H), 1610, 1569, 1516, 1468
(C]N, C]C).
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