Synthesis of some novel 2-substituted-5-[isopropylthiazole] clubbed 1,2,4-triazole and 1,3,4-oxadiazoles as potential antimicrobial and antitubercular agents

Article abstract of DOI:10.1016/j.ejmech.2010.01.045

In the present study a series of 2-substituted-5-[isopropylthiazole] clubbed 1,2,4-triazole and 1,3,4-oxadiazole derivatives have been synthesized and characterized by IR, ¹H NMR, ¹³C NMR and mass spectral analysis. Synthesized compounds were evaluated for their preliminary cytotoxicity, antimicrobial and antitubercular activity against Mycobacterium tuberculosis H37Rv strain by broth dilution assay method. Antimycobacterial activity tested against M. tuberculosis indicated that compounds 4b and 6g exhibited twofold enhanced potency than parent compound 1 and the results indicate that some of them exhibited promising activities and they deserve more consideration as potential antitubercular agents. Compound 3c, 4b and 6c exhibited good or moderate antibacterial inhibition and compounds 3h and 7c showed excellent antifungal activity.

Full text of DOI:10.1016/j.ejmech.2010.01.045

European Journal of Medicinal Chemistry 45 (2010) 2063–2074
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
Synthesis of some novel 2-substituted-5-[isopropylthiazole] clubbed
1,2,4-triazole and 1,3,4-oxadiazoles as potential antimicrobial and
antitubercular agents
,
b
c
a
b
G.V. Suresh Kumar a , Y. Rajendraprasad , B.P. Mallikarjuna , S.M. Chandrashekar , C. Kistayya
*
a St. Johns Pharmacy College, Department of Medicinal Chemistry, 6, 2nd stage Vijaynagar, R.P.C. Layout, Bangalore 560040, Karnataka, India
b Department of Pharmaceutical Sciences, Andhra University, Visakhapatnam 530003, Andra Pradesh, India
c PES College of Pharmacy, Department of Medicinal Chemistry, 50 feet road, Hanumantha Nagar, B.S.K. Ist stage, Bangalore 560050, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study a series of 2-substituted-5-[isopropylthiazole] clubbed 1,2,4-triazole and 1,3,4-
oxadiazole derivatives have been synthesized and characterized by IR, 1H NMR, 13C NMR and mass
spectral analysis. Synthesized compounds were evaluated for their preliminary cytotoxicity, antimicro-
bial and antitubercular activity against Mycobacterium tuberculosis H37Rv strain by broth dilution assay
method.
Received 15 August 2009
Received in revised form
17 January 2010
Accepted 20 January 2010
Available online 28 January 2010
Antimycobacterial activity tested against M. tuberculosis indicated that compounds 4b and 6g
exhibited twofold enhanced potency than parent compound 1 and the results indicate that some of them
exhibited promising activities and they deserve more consideration as potential antitubercular agents.
Compound 3c, 4b and 6c exhibited good or moderate antibacterial inhibition and compounds 3h and
7c showed excellent antifungal activity.
Keywords:
4-Isopropylthiazole-2-carbohydrazide
analogs
Clubbed triazole-thiazole derivatives
Cytotoxicity
Antibacterial
Ó 2010 Elsevier Masson SAS. All rights reserved.
Antifungal
Antitubercular
Broth dilution assay
1. Introduction
a wide array of complex fatty acids, such as mycocerosic acid,
mycolic acid, arabinogalactans and peptidoglycans [4,5]. Earlier,
Despite the availability of effective treatments, tuberculosis (TB)
remains a major public health threat. Recent world health organi-
zation (WHO) reports show that TB is responsible for more than
three million deaths annually worldwide [1]. The raise can be
attributed to increase in emergence of drug-resistant strains of
Mycobacterium tuberculosis, multi drug-resistant (MDR) TB and
extensively drug-resistant (XDR) TB. For this reason it is critical to
discover new drugs acting with different mechanism from those
drugs used in current therapy [2,3].
several reports have appeared that azole class of compounds
posses key property (liphophilicity) that influence the ability of
drug to reach target by transmembrane diffusion and show
promising activity against resistant tuberculosis by blocking the
biosynthesis of lipids [6,7].
Clubbed 1,2,4-triazole and 1,3,4-oxadiazole are new classes of
azole anti-mycobacterials, which are proved to be highly active
both in vitro and in vivo [8,9]. In continuation of our research on
clubbed triazolyl-thiazoles [10–14] and clubbed triazolyl-iso-
propylthiazole, in previous communication it was proved iso-
propylthiazole moiety on coupling with other heterocyclic rings
provides novel biologically active compounds that could be
explored as potent antimicrobial and antitubercular agents [15].
The present study illustrates the details of further structural
modifications carried out on clubbed isopropylthiazole with 1,3,4-
oxadiazoles and 1,2,4-triazoles, studies its cytotoxicity, antimicro-
bial (bacterial and fungal) and antitubercular activity against H37Rv
strain. The synthetic route and the sequence of reactions are
depicted in Schemes 1 and 2.
One of the important strategies for the designing of effective
antitubercular agents is to develop inhibitors of mycobacterial
cell-wall biosynthesis. The cell-wall of mycobacteria consists of
* Corresponding author. Tel.: þ91 80 23190191; mobile: þ91 9886104039; fax:
þ91 80 23350035.
E-mail addresses: gvsureshkumar@yahoo.com (G.V. Suresh Kumar), dryrp@
rediffmail.com (Y. Rajendraprasad), mallibp@gmail.com (B.P. Mallikarjuna),
chandra_jan25@yahoo.co.in (S.M. Chandrashekar).
0223-5234/$ – see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.01.045

2064
G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
Technology, Chandigarh, India. The antibacterial activity of the
synthesized compounds was performed by broth dilution method
[16,17] against the following standard bacterial strains Staphylo-
coccus aureus (ATCC 11632), Streptococcus faecalis (ATCC 14506),
Bacillus subtilis (ATCC 60511), Klebsiella pneumoniae (ATCC 10031),
Escherichia coli and Pseudomonas aeruginosa (ATCC 10145) and
antifungal activity against yeasts: Saccharomyces cerevisiae (ATCC
9763, Sc) and Candida tropicalis (ATCC 1369, CT), mould: Aspergillus
niger (ATCC 6275). MIC of compounds was determined against
M. tuberculosis H37Rv strain by using broth dilution assay method.
The cytotoxicity of the synthesized compounds was evaluated for
their cytotoxic potential using A549 (lung adenocarcinoma) cell
lines in the presence of fetal bovine serum.
N
O
N
S
O
R
i
S
1
HN
NH2
HN
N
2a-h
iii
ii
N
COCH3
N
N
S
N
O
N
N
S
R
O
R
4a-f
3a-h
4. Results and discussion
Scheme 1. Reagent and conditions: (i) CH3OH/C2H5OH, RCOCH3, reflux, 4–6 h; (ii)
(CH3CO)2O, reflux, 4 h; (iii) POCl3, RCOOH, reflux 5 h.
The IR spectrum of compound 3d revealed broad stretching
band around 1713 cmꢀ1 accounting for C]O amide carbonyl group.
Lack of resonance’s of NH and NH2 and appearance of sharp singlet
2. Chemistry
at
accounted for oxadiazole ring formation and reconfirmed by the 13C
NMR peak at 67.58 due to C2 of oxadiazole. The molecular ion peak
d
1.84 of CH3 group in the 1H NMR spectrum of compound 3d
The reaction sequences employed for synthesis of target
compounds are shown in Schemes 1 and 2, and their physical
properties are depicted in Table 1.
The key intermediate in the present study 4-isopropylthiazole-
2-carbahydrazide 1, 2a–h and 5 were prepared as per the literature
[15]. Compounds 2a–h on reacting with acetic anhydride afforded
1,3,4-oxadiazole derivatives 3a–h in good yield. The 2-(4-iso-
propylthiazol-2-yl)-5-substituted-1,3,4-oxadiazoles 4a–f were
obtained on reacting compound 1 with appropriate aromatic acid
in presence of phosphorus oxychloride (Scheme 1).
The triazole 5 was condensed with various substituted benzal-
dehydes in the presence of catalytic amount of concentrated
sulphuric acid in refluxing ethanol to afford a series of 4-
substituted-5-(4-isopropylthiazol-2-yl)-4H-1,2,4-triazole-3-thiols
6a–l. Reaction of triazole 5 with appropriate heteroaromatic acids
in the presence of phosphorous oxychloride produced a series of
fused triazolo thiadiazoles 7a–f. Compound 1 on reaction with
phenylisothiocyanate in ethanol yielded compound 5-(4-iso-
propylthiazol-2-yl)-4-phenyl-4H-1,2,4-triazole-3-thiol 8. Further,
alkylation of compound 8 was performed by the reaction with
methyl iodide in basic media to obtain compound 9.
d
m/z at 374.10 in mass spectrum of compound 3d found to be in
conformity with its molecular formula of the assigned structure.
The structure of 4b was confirmed by lack of resonances cor-
responding to NH and NH2 in the 1H NMR spectrum and appear-
ance of peaks at 154.34 and 165.71 due to C2 and C5 of oxadiazole in
13C NMR spectra. The molecular ion base peak at m/z 305.04
confirmed structure of compound 4b.
The absence of NH2 stretch at 3248 cmꢀ1 and appearance of
C]N at 1674 cmꢀ1 in IR spectrum of compound 6b confirms the
formation of Schiff base. In the 1H NMR spectra of Schiff bases 6a–l,
a singlet corresponding to one proton characteristic of the N]CH
group was observed in between
3.82 ppm integrating for protons of
substituted at 3,4,5-position of phenyl and a peak at
d
9.18–9.91 ppm and a singlet at
methoxyl groups
164.23 ppm
9
3
d
due to HC]N in 13C NMR spectra of Schiff base 6b confirmed the
formation of compound 6b. Further, LC mass spectrum showed
molecular ion peak at m/z 419.52 (100%) which is in agreement
with the molecular formula C18H21N5O3S2 of compound 6b.
The absence of absorptions due to SH and NH2 and the presence
of a sharp absorption band at 1632 cmꢀ1 due to secondary amino
group in the IR spectrum of compounds 7a–f, established formation
of triazolo thiadiazoles. The 1H NMR, 13C NMR, mass spectra, and
elemental analysis supported the structure of various synthesized
triazolo thiadiazoles.
3. Biological activity
The standard strains were procured from the American Type
Culture Collection (ATCC) and Gene Bank, Institute of Microbial
N
N
N
SH
N
N
N
N
N
iii
N
N
S
O
N
i
iv
N
S
N
S
R
SH
S
S
N
HN
H2N
NH2
7a-f
8
5
1
ii
v
N
N
N
N
N
N
N
N
SH
S
SCH3
N
S
R
6a-l
9
Scheme 2. Reagent and conditions: (i) CS2, NH2NH2$H2O, C2H5OH, KOH, reflux, 16 h; (ii) R–CHO, H2SO4, reflux 4 h (iii) R–COOH, POCl3, reflux 5 h, (iv) PhNCS, C2H5OH, reflux 4 h (v)
CH3I, Na, C2H5OH, reflux 4 h.

G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
2065
Table 1
Analytical and physico-chemical data of synthesized compounds.
Compound
R
Molecular formula
M.Wa
M.p (ꢁC)b/crystallization solvent
126, Methanol
Yield (%)
81
% Analysis of C, H, N found (calc.)c
C
H
N
3a
3b
CH3
C12H17N3O2S
267.35
329.42
53.91 (54.01)
6.41 (6.23)
15.72 (15.65)
C17H19N3O2S
116, Methanol
76
61.98 (61.45)
56.12 (56.45)
54.53 (56.23)
50.01 (50.65)
62.95 (62.76)
59.11 (59.87)
60.15 (60.82)
61.97 (61.88)
54.99 (54.09)
53.16 (53.65)
63.13 (63.48)
58.52 (58.27)
5.81 (5.86)
4.99 (4.49)
4.85 (4.65)
4.44 (4.60)
6.16 (6.69)
5.54 (5.87)
5.89 (5.87)
4.83 (4.88)
3.96 (3.76)
3.82 (3.76)
5.30 (5.39)
4.56 (4.45)
12.76 (12.72)
Cl
NO2
Br
3c
3d
3e
3f
C17H18ClN3O2S
C17H18N4O4S
C17H18BrN3O2S
C18H21N3O2S
C17H19N3O3S
C18H21N3O3S
C14H13N3OS
363.86
374.41
408.31
343.44
345.42
359.44
271.34
305.78
316.34
285.36
287.34
121, Methanol
87
84
71
74
70
69
80
87
91
92
85
11.55 (11.09)
14.96 (14.09)
10.29 (10.21)
12.23 (12.62)
12.17 (12.65)
11.69 (11.65)
15.49 (15.09)
13.74 (13.87)
17.71 (17.38)
14.73 (14.38)
14.62 (14.65)
128, Methanol
136, Methanol
CH3
OH
116, Methanol
3g
3h
4a
4b
4c
4d
4e
124, Methanol
OCH3
123, Methanol
231, Ethylacetate:hexane (2:4)
223, Ethylacetate:hexane (2:4)
198, Ethylacetate:hexane (2:4)
196, Ethylacetate:hexane (2:4)
242, Ethylacetate:hexane (2:4)
Cl
C14H12ClN3OS
C14H12N4O3S
C15H15N3OS
NO2
CH3
OH
C14H13N3O2S
OCH3
4f
C15H15N3O2S
301.36
232, Ethylacetate:hexane (2:4)
88
59.78 (58.39)
5.02 (5.09)
13.95 (13.86)
(continued on next page)

2066
G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
Table 1 (continued)
% Analysis of C, H, N found (calc.)c
Compound
R
Molecular formula
C15H14BrN5S2
M.Wa
M.p (ꢁC)b/crystallization solvent
160, Ethanol
Yield (%)
69
C
H
N
Br
6a
408.34
44.12 (44.09)
3.46 (3.49)
17.15 (17.76)
OCH3
OCH3
6b
C18H21N5O3S2
419.52
190, Ethanol
86
51.53 (51.87)
5.05 (5.38)
16.69 (16.47)
OCH3
N
6c
6d
6e
6f
C17H20N6S2
372.51
389.5
198, Ethanol
206, Ethanol
214, Ethanol
240, Ethanol
80
75
82
81
54.81 (54.87)
52.42 (52.38)
53.46 (53.45)
52.15 (52.29)
5.41 (5.47)
4.92 (4.37)
4.77 (4.77)
4.38 (4.30)
22.56 (22.38)
17.98 (17.30)
19.48 (19.45)
20.27 (20.88)
OCH3
C17H19N5O2S2
C16H17N5OS2
C15H15N5OS2
OCH3
OC3
359.47
345.44
HO
Cl
6g
C15H14ClN5S2
363.89
170, Ethanol
86
49.51 (49.08)
3.88 (3.87)
19.25 (19.83)
6h
6i
C15H15N5S2
329.44
355.09
156, Ethanol
186, Ethanol
79
76
54.69 (54.39)
57.44 (57.38)
4.59 (4.39)
4.82 (4.30)
21.26 (21.39)
19.70 (19.03)
HC
HC
C17H17N5S2
CH3
6j
C16H17N5S2
343.47
318.42
240, Ethanol
232, Ethanol
88
83
55.95 (55.39)
49.04 (49.38)
4.99 (4.39)
4.43 (4.48)
20.39 (20.37)
26.39 (26.76)
6k
C13H14N6S2
N
OCH3
6l
C16H17N5O2S2
375.47
204, Ethanol
89
51.18 (51.16)
4.56 (4.38)
18.65 (18.23)
OH

G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
2067
Table 1 (continued)
% Analysis of C, H, N found (calc.)c
Compound
R
Molecular formula
C15H13N5S2
M.Wa
M.p (ꢁC)b/crystallization solvent
245, Ethanol:DMF (2:1)
Yield (%)
85
C
H
N
7a
327.43
55.02 (55.39)
4.00 (4.39)
21.39 (21.87)
19.35 (19.38)
22.57 (22.86)
20.51 (20.43)
20.39 (20.01)
19.59 (19.99)
Cl
NO2
CH3
OH
7b
7c
7d
7e
7f
C15H12ClN5S2
C15H12N6O2S2
C16H15N5S2
361.87
372.42
341.45
343.43
357.45
221, Ethanol:DMF (2:1)
235, Ethanol:DMF (2:1)
245, Ethanol:DMF (2:1)
219, Ethanol:DMF (2:1)
243, Ethanol:DMF (2:1)
77
69
71
73
58
49.79 (49.30)
48.38 (48.39)
56.28 (56.73)
52.46 (52.38)
53.76 (53.06)
3.34 (3.39)
3.25 (3.29)
4.43 (4.39)
3.82 (3.38)
4.23 (4.37)
C15H13N5OS2
OCH3
C16H15N5OS2
8
9
–
–
C14H14N4S2
C15H16N4S2
302.42
316.44
211, Ethanol/water (1:1)
234, Ethanol/water (1:1)
89
71
55.60 (55.11)
56.93 (56.01)
4.67 (4.98)
5.10 (5.62)
18.53 (18.38)
17.71 (17.72)
a
Molecular weight of the compound.
Melting point of the compound at their decomposition.
Elemental analysis of C, H, and N were within ꢂ0.4% of theoretical value.
b
c
The absence of signals due to NH and NH2 group of hydrazide in
Gram-positive bacteria at MIC 8 to 32.5
chloro substituted compound 4b exhibited excellent inhibition at
MIC 4–8 g/mL
against M. tuberculosis H37Rv. In contradiction compound 4f
comprising methoxy substitution showed moderate to good inhi-
bition against tested Gram ꢀve organisms.
mg/mL. Particularly, para-
1H NMR spectra of compound 8 and additional signals due to
phenyl ring in the 1H NMR and 13C NMR spectra evidenced
formation of triazole ring. The conversion of compound 8 to 3-(4-
isopropylthiazol-2-yl)-5-(methylthio)-4-phenyl-4H-1,2,4-triazole
compound 9 was confirmed by the appearance a singlet at
m
g/mL against tested gram þve bacteria and 4
m
d
2.86 ppm in 1H NMR spectra due to –SCH3 group.
The results of antimicrobial testing of synthesized compounds
Schiff bases derived from 1,2,4-triazoles are reported to possess
significant antimicrobial activity, particularly against M. tubercu-
losis H37Rv because of its increased ability to penetrate bacterial cell
[18]. The antimicrobial activity of the series 6a–l revealed that all
the tested compounds possessed moderate to good inhibition,
compounds 6g and 6i showed comparatively good activity against
all tested microbial strains and excellent inhibition towards
against selected Gram-positive, Gram-negative bacteria, yeasts,
moulds and M. tuberculosis H37Rv are illustrated in Tables 2 and 3
respectively.
The results of antimicrobial testing of synthesized compounds
against selected Gram-positive, Gram-negative bacteria, yeasts,
moulds and M. tuberculosis H37Rv are illustrated in Tables 2 and 3
respectively.
The antimicrobial activity of 1-(5-(4-isopropylthiazol-2-yl)-2,
methyl 2-substituted-1,3,4-oxadiazol-3(2H)-yl)ethanones 3a–h
divulged that compound 3c showed improved antimicrobial
activity against tested bacterial and fungal species and excellent
M. tuberculosis H37Rv at MIC 4
sessing mono methoxy and pyrole substitution exhibit moderate
activity at MIC 16–62.5 g/mL.
mg/mL. Compounds 6e and 6k pos-
m
The antimicrobial activity of the series 7a–f revealed
compound 7b comprising p-chloro substitution exhibited excel-
lent inhibition, whereas the compound 7c with higher electron
withdrawing NO2 showed increased antifungal inhibition, but loss
of activity against tested bacterial species. The antimicrobial
activity of compounds 8 and 9 exhibited good to moderate anti-
microbial activity.
Compounds 3c, 4c, 6g and 6i were evaluated for their cytotoxic
potential using A549 (lung adenocarcinoma) cell lines in the pres-
ence of fetal bovine serum. The compound 3c showed maximum
activity against M. tuberculosis H37Rv at MIC 8 mg/mL. Compounds
3f and 3g possessing p-CH3 and p-OH substitution on phenyl ring
exhibited moderate antimicrobial activity against gram þve species
and good activity against tested gram ꢀve species K. pneumoniae
and E. coli than P. aeruginosa. The compound 3h having p-methoxy
substitution showed excellent antifungal activity at MIC 4–16
than antibacterial action.
mg/mL
Evaluating the antimicrobial activity of the synthesized 2-(4-
isopropylthiazol-2-yl)-5-substituted-1,3,4-oxadiazole derivatives
4a–f, revealed compounds were more effective against the
cytotoxicity at a concentration of 250
other compounds showed appreciable cytotoxicity of about 50% of
the vehicle control at a concentration of 250 M.
mM as depicted in Fig. 1. The
m

Table 2
Antimicrobial activity expressed as MIC (mg/mL).
Compounds
Gram-positive organismsa
Gram-negative organismsb
Fungic
Sc
Sa
62.5
Sf
Bs
Kp
Ec
Pa
Ct
62.5
An
62.5
3a
3b
3c
3d
3e
3f
3g
3h
4a
4b
4c
4d
4e
4f
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
7a
7b
7c
7d
7e
7f
125
125
62.5
31.25
62.5
31.25
16
31.25
31.25
62.5
125
125
125
31.25
62.5
125
62.5
31.25
31.25
16
31.25
4
62.5
62.5
16
62.5
62.5
31.25
125
62.5
31.25
125
62.5
125
31.25
125
31.25
31.25
31.25
250
125
31.25
8
31.25
16
31.25
16
31.25
62.5
62.5
31.25
31.25
62.5
31.25
31.25
31.25
8
62.5
62.5
31.25
31.25
31.25
62.5
62.5
16
8
8
8
62.5
16
31.25
16
16
62.5
16
31.25
16
125
16
31.25
31.25
8
125
31.25
125
16
8
125
62.5
125
62.5
125
31.25
125
62.5
16
62.5
125
16
250
31.25
250
16
31.25
16
31.25
62.5
125
31.25
8
31.25
62.5
125
31.25
31.25
16
,5
,5
16
125
8
125
125
250
125
125
125
125
62.5
62.5
16
62.5
62.5
16
125
125
4
125
16
125
125
62.5
31.25
31.25
16
31.25
16
62.5
31.25
125
62.5
125
125
31.25
31.25
31.25
31.25
31.25
125
125
31.25
125
31.25
62.5
125
62.5
31.25
125
31.25
62.5
31.25
62.5
125
16
125
31.25
62.5
125
125
125
62.5
125
31.25
31.25
62.5
62.5
16
250
62.5
125
62.5
16
125
125
125
31.25
250
62.5
62.5
4
31.25
250
31.25
16
250
8
31.25
4
250
8
250
4
31.25
16
250
8
31.25
31.25
250
31.25
31.25
125
31.25
125
62.5
62.5
8
31.25
31.25
62.5
125
16
16
31.25
62.5
125
16
8
16
62.5
125
125
16
125
31.25
125
125
16
125
62.5
125
125
16
125
125
31.25
8
125
125
16
16
16
–
125
31.25
125
16
125
125
31.25
16
31.25
125
8
16
16
125
125
250
125
125
125
16
16
250
125
125
125
125
125
16
250
250
16
8
16
–
–
ꢃ1
31.25
31.25
8
9
16
16
125
16
31.25
31.25
ꢃ1
31.25
62.5
Ciprofloxacin
Norfloxacin
Flucanozole
ꢃ5
,5
–
ꢃ5
,5
–
ꢃ1
ꢃ1
–
–
ꢃ1
ꢃ1
ꢃ1
–
–
–
–
–
ꢃ1
ꢃ1
a
The screening organisms. Gram-positive bacteria: Staphylococcus aureus (ATCC 11632, Sa), Streptococus faecalis (ATCC 14506, Sf), and Bacillus subtilis (ATCC 60511, Bs).
the screening organisms. Gram-negative bacteria: Klebsiella penumoniae (ATCC 10031, Kp), Escherichia coli (ATCC 10536, Ec), and Pseudomonas aeruginosa (ATCC 10145, Pa).
The screening organisms. Yeasts: Saccharomyces cerevisiae (ATCC 9763, Sc) and Candida tropicalis (ATCC 1369, Ct), mould: Aspergillus niger (ATCC 6275, An).
b
c

G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
2069
Table 3
(s, 1H, thiazole-C5), 3.26 (m, 1H, isopropyl), 2.21 (s, 3H of acetyl
CH3), 1.51 (s, 6H, 2CH3 of C2 oxadiazole), 1.23 (d, 6H, terminal
CH3) ppm.
Primary antitubercular activity.
Compound
MIC values (mg/mL) of M. tuberculosis H37Rv
13C NMR (DMSO-d6, 300 MHz)
d: 170.11 (acetyl C]O), 162.98
3a
3b
3c
3d
3e
3f
3g
3h
4a
4b
4c
4d
4e
4f
6a
6b
6c
6d
6e
6f
6g
6h
6i
125
62.5
16
125
125
31.25
62.5
62.5
31.25
4
62.5
16
125
16
125
125
125
31.25
31.25
62.5
4
(thiazole C4), 154.29 (thiazole-C2), 144.76 (oxadiazole C5), 121.09
(thiazole-C5), 67.43 (oxadiazole C2), 33.12 (tertiary-1C-isopropyl),
27.24(2CH3 of C2 oxadiazole), 24.16 (acetyl CH3), 22.36 (terminal
2CH3-isopropyl) ppm.
MS (%) 267.43 (Mþ 100.0%), 268.11 (M þ 1, 13.6%), 269.10 (4.2%),
268.10 (1.1%), 269.11 (1.5%).
5.1.1.2. 1-(5-(4-Isopropylthiazol-2-yl)-2-methyl-2-phenyl-1,3,4-oxa-
diazol-3(2H)-yl)ethanone (3b). IR (KBr)
n
max, cmꢀ1: 3056 (Ar C–H),
1632 (amide C]O). 1H NMR (DMSO-d6, 300 MHz)
d: 7.6–7.8 (m, 5H,
Ar–H), 7.21 (s, 1H, thiazole-C5), 3.25 (m, 1H, isopropyl), 1.82
(s, oxadiazole-C2-CH3), 2.51 (s, 3H, acetyl CH3), 1.25 (d, 6H, terminal
CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 166.11 (acetyl C]O), 163.98
(thiazole C4), 153.29 (thiazole-C2), 142.76 (oxadiazole C5), 136.76
(phenyl-C1), 124.98 (phenyl-C3 and C5), 123.11 (phenyl-C2 and C6),
123.09 (thiazole-C5), 122.11 (phenyl-C4), 67.21 (oxadiazole C2),
33.12 (tertiary-1C-isopropyl), 28.24 (CH3 at oxadiazole C2), 23.24
(acetyl CH3), 21.24 (terminal 2CH3-isopropyl) ppm.
62.5
4
6j
6k
6l
7a
7b
7c
7d
7e
7f
32.5
31.25
62.5
62.5
8
31.25
31.25
62.5
31.25
31.25
62.5
0.25
MS (%) 329.12 (Mþ 100.0%), 330.12 (M þ 1, 20.4%), 331.12 (5.3%),
331.13 (1.6%).
5.1.1.3. 1-(2-(4-Chlorophenyl)-5-(4-isopropylthiazol-2-yl)-2-methyl-
1,3,4-oxadiazol-3(2H)-yl)ethanone (3c). IR (KBr)
n
max, cmꢀ1: 3046
(Ar C–H),1642 (amide C]O). 1H NMR (DMSO-d6, 300 MHz)
d: 7.43–
7.86 (m, 4H, Ar–H), 7.32 (s, 1H, thiazole-C5), 3.36 (m, 1H, isopropyl),
2.23 (s, 3H of acetyl CH3), 1.81 (s, oxadiazole-C2-CH3), 1.24 (d, 6H,
terminal CH3) ppm.
8
9
Isoniazid
13C NMR (DMSO-d6, 300 MHz)
d: 167.11 (acetyl C]O), 162.98
(thiazole C4), 152.29 (thiazole-C2), 142.14 (oxadiazole C5), 140.11
(phenyl-C1), 132.11 (phenyl-C4), 128.11 (phenyl-C2 and C6), 124.98
(phenyl-C3 and C5), 123.09 (thiazole-C5), 65.11 (oxadiazole C2),
33.43 (tertiary-1C-isopropyl), 28.53 (CH3 at oxadiazole C2), 23.81
(acetyl CH3), 21.17 (terminal 2CH3-isopropyl) ppm.
MS (%) 363.08 (Mþ 100.0%), 365.43 (36.4%), 365.09 (2.1%), 367.07
(1.1%).
5. Experimental
5.1. Chemical protocols
Melting points were determined in open capillary tubes in
a Thomas Hoover melting point apparatus and are uncorrected.
Infrared spectra were recorded on Shimadzu FT-IR 157, 1H NMR and
13C NMR spectra were recorded (in CDCl3/DMSO-d6) on a Bruker
spectrometer at 300/400 MHz using TMS as an internal standard.
Mass spectra (EI) on (AMD-604) mass spectrometer operating at
70 eV. Elemental analysis was performed on Thermo Finnigan Flash
(EA 1112 CHNS Analyzer).
Thin layer chromatography (TLC) was performed through out
the reaction on Merck silica gel GF254 aluminium sheets using
mixture of different polar and nonpolar solvents in varying
proportions and spots were observed using iodine as visualizing
agent.
4
250µM
100µM
50µM
200µM
150µM
3
2
1
0
5.1.1. General procedure for the synthesis of 3-acetyl-5-(4-
isopropylthiazole-4-yl)-2-methyl-21 substituted-2,3-dihydro-1,3,4-
oxadiazoles (3a–h)
A mixture of compound (2a–h) (0.003 mol) and acetic anhy-
dride (10 mL) was heated under reflux for 4 h. After the reaction
mixture attained room temperature, excess acetic anhydride was
decomposed by water and the mixture was stirred for further
30 min. The separated product was filtered, washed with water,
dried and recrystallised.
6i
3c
4c
6g
cells
dmso
Treatment
Fig. 1. Cytotoxic activity of compounds 3c, 4c, 6g and 6i tested in A549 cells by MTT
assay. The bars reflect the viable cells in each treatment. Cells alone without any
treatment, DMSO denote the vehicle control. The experiment was done in duplicate
with triplicate readings of each experiment.
5.1.1.1. 1-(5-(4-Isopropylthiazol-2-yl)-2,2-dimethyl-1,3,4-oxadiazol-
3(2H)-yl)ethanone (3a). IR (KBr)
n
max, cmꢀ1: 2987 (C–H of
CH3),1669 (amide C]O). 1H NMR (DMSO-d6, 300 MHz)
d: 7.32

2070
G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
5.1.1.4. 1-(5-(4-Isopropylthiazol-2-yl)-2-methyl-2-(4-nitrophenyl)-
1,3,4-oxadiazol-3(2H)-yl)ethanone (3d). IR (KBr)
max, cmꢀ1: 3083
(Ar C–H), 1713 (amide C]O). 1H NMR (DMSO-d6, 300 MHz)
: 7.53–
(s, 3H, OCH3), 3.26 (m, 1H, isopropyl), 2.13 (s, 3H, CH3), 1.82 (s,
oxadiazole-C2-CH3), 1.33 (d, 6H, terminal CH3) ppm.
n
d
13C NMR (DMSO-d6, 300 MHz)
d: 170.11 (acetyl C]O), 163.65
7.80 (m, 4H, Ar–H), 7.32 (s, 1H, thiazole-C5), 3.26 (m, 1H, isopropyl),
2.82 (s, 3H, acetyl CH3), 1.84 (s, oxadiazole-C2-CH3), 1.21 (d, 6H,
terminal CH3) ppm.
(thiazole C4), 157.54 (phenyl-C4), 154.76 (thiazole-C2), 143.76 (oxa-
diazole C5), 139.82 (phenyl-C1), 126.11 (phenyl-C2 and C6), 113.65
(phenyl-C3 and C5), 112.87 (thiazole-C5), 68.65 (oxadiazole C2),
53.24 (OCH3), 36.12 (tertiary-1C-isopropyl), 29.11 (oxadiazole-C2-
CH3), 24.54 (acetyl CH3), 21.24 (terminal 2CH3-isopropyl) ppm.
MS (%) 359.13 (Mþ 100.0%), 360.13 (M þ 1, 21.5%), 361.13 (5.5%),
361.14 (1.9%).
13C NMR (DMSO-d6, 300 MHz)
d: 170.11 (acetyl C]O), 160.98
(thiazole C4), 151.29 (thiazole-C2), 144.76 (oxadiazole C5), 140.87
(phenyl-C1), 128.11 (phenyl-C4), 125.98 (phenyl-C3 and C5), 123.11
(phenyl-C2 and C6), 111.09 (thiazole-C5), 67.58 (oxadiazole C2), 38.12
(tertiary-1C-isopropyl), 28.65 (oxadiazole-C2-CH3), 23.87 (terminal
2CH3-isopropyl), 23.41 (acetyl CH3) ppm.
5.1.2. General procedure for synthesis of 2-(4-isopropylthiazol-2-
yl)-5-substituted-1,3,4-oxadiazoles (4a–f)
MS (%) 374.10 (Mþ 100.0%), 375.11 (M þ 1, 18.7%), 376.10 (4.5%),
376.11 (2.9%), 375.10 (2.3%).
A mixture of compound 1 (0.001 M) and the appropriate
aromatic acid (0.001 M) in phosphorus oxychloride (10 ml) was
refluxed for 5 h. The reaction mixture was slowly poured over
crushed ice and kept overnight. The solid thus separated out was
filtered, treated with dilute NaOH, washed with water and
recrystallised.
5.1.1.5. 1-(2-(4-Bromophenyl)-5-(4-isopropylthiazol-2-yl)-2-methyl-
1,3,4-oxadiazol-3(2H)-yl)ethanone (3e). IR (KBr)
n
max, cmꢀ1: 3036
(Ar C–H), 1640 (amide C]O). 1H NMR (DMSO-d6, 300 MHz)
d
: 7.5–
7.8 (m, 4H, Ar–H), 7.35 (s, 1H, thiazole-C5), 3.26 (m, 1H, isopropyl),
2.41 (s, 3H of acetyl CH3), 1.83 (s, oxadiazole-C2-CH3), 1.23 (d, 6H,
terminal CH3) ppm.
5.1.2.1. 2-(4-Isopropylthiazol-2-yl)-5-phenyl-1,3,4-oxadiazole
13C NMR (DMSO-d6, 300 MHz)
d: 169.11 (acetyl C]O), 161.21
(4a). IR (KBr)
(DMSO-d6, 300 MHz) d: 8.01 (d, 2H, C2 and C6 phenyl), 7.74 (s, 1H,
n
max, cmꢀ1: 3057 (Ar C–H), 1651 (C]N). 1H NMR
(thiazole-C4), 152.15 (thiazole-C2), 144.21 (oxadiazole-C5), 140.11
(phenyl-C1), 129.11 (phenyl-C2, C6), 125.98 (phenyl-C3 and C5),
128.11 (phenyl-C4), 113.21 (thiazole-C5), 68.21 (oxadiazole C2),
38.12 (tertiary-1C-isopropyl), 28.24 (oxadiazole-C2-CH3), 21.84
(terminal 2CH3-isopropyl), 23.11 (acetyl CH3) ppm.
thiazole-C5), 7.64 (d, 2H, C3 and C5 phenyl), 7.24 (m, 1H, C4 phenyl),
3.21 (m, 1H, isopropyl), 1.24 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 165.71 (oxadiazole-C2), 161.95
(thiazole C4), 154.54 (oxadiazole-C5), 153.21 (thiazole-C2), 131.76
(phenyl C3 and C5), 129.32 (C4-phenyl), 127.51 (phenyl C2 and C6),
125.43 (C1-phenyl), 115.32 (thiazole-C5), 32.07 (tertiary-1C-iso-
propyl), 22.41 (terminal 2CH3-isopropyl) ppm.
MS (%) 409.03 (Mþ 100.0%), 407.03 (97.5%), 410.03 (20.4%),
408.03 (19.9%), 411.02 (4.3%), 411.03 (2.4%), 409.04 (1.6%).
5.1.1.6. 1-(5-(4-Isopropylthiazol-2-yl)-2-methyl-2-p-tolyl-1,3,4-oxa-
MS (%) 271.43 (Mþ 100.0%), 272.43 (M þ 1, 16.1%), 273.81 (4.5%),
273.08 (1.6%), 272.07 (1.1%).
diazol-3(2H)-yl)ethanone (3f). IR (KBr)
n
max, cmꢀ1: 3096 (Ar C–H),
1636 (amide C]O). 1H NMR (DMSO-d6, 300 MHz)
d
: 7.34 (s, 1H,
thiazole-C5), 7.3–7.8 (m, 4H, Ar–H), 3.24 (m, 1H, isopropyl), 2.10 (s,
3H, p-CH3), 2.94 (s, 3H of acetyl CH3), 1.87 (s, oxadiazole, C2-CH3),
1.23 (d, 6H, terminal CH3) ppm.
5.1.2.2. 2-(4-Chlorophenyl)-5-(4-isopropylthiazol-2-yl)-1,3,4-oxadi-
azole (4b). IR (KBr)
NMR (DMSO-d6, 300 MHz)
n
max, cmꢀ1: 3091 (Ar C–H), 1636 (C]N). 1H
d
: 8.26 (d, 2H, C3 and C5 phenyl), 7.85
13C NMR (DMSO-d6, 300 MHz)
d: 170.11 (acetyl C]O), 164.98
(s, 1H, thiazole-C5), 7.68 (d, 2H, C2 and C6 phenyl), 3.24 (m, 1H,
(thiazole C4), 155.29 (thiazole-C2), 145.32 (oxadiazole C5), 139.14
(phenyl-C1), 138.11 (phenyl-C4), 127.98 (phenyl-C3 and C5), 126.11
(phenyl-C2 and C6), 113.09 (thiazole-C5), 68.34 (oxadiazole C2),
36.12 (tertiary-1C-isopropyl), 28.24 (oxadiazole-C2-CH3 CH3), 23.24
(acetyl CH3), 21.24 (terminal 2CH3-isopropyl), 20.60 (p-CH3) ppm.
MS (%) 343.14 (Mþ 100.0%), 344.14 (M þ 1, 19.8%), 345.13 (4.5%),
345.14 (2.6%), 344.13 (1.9%).
isopropyl), 1.29 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 165.71 (oxadiazole-C2), 162.21
(thiazole-C2), 160.35 (thiazole C4), 154.34 (oxadiazole-C5), 139.32
(C4-phenyl), 134.81 (C3 and C5), 127.51 (C2 and C6), 125.43 (C1-
phenyl), 114.11 (thiazole-C5), 32.65 (tertiary-1C-isopropyl), 21.41
(terminal 2CH3-isopropyl) ppm.
MS (%) 305.2 (Mþ 100.0%), 307.04 (M þ 1, 32.5%), 306.04 (17.1%),
308.04 (5.9%), 307.03 (4.5%), 309.03 (1.5%), 307.05 (1.1%).
5.1.1.7. 1-(2-(4-Hydroxyphenyl)-5-(4-isopropylthiazol-2-yl)-2-
methyl-1,3,4-oxadiazol-3(2H)-yl)ethanone (3g). IR (KBr)
cmꢀ1: 3530 (OH), 3066 (Ar C–H), 1643 (amide C]O). 1H NMR
(DMSO-d6, 300 MHz) : 7.45 (s, 1H, thiazole-C5), 7.5–7.8 (m, 4H, Ar–
n
max,
5.1.2.3. 2-(4-Isopropylthiazol-2-yl)-5-(4-nitrophenyl)-1,3,4-oxadi-
azole (4c). IR (KBr)
NMR (DMSO-d6, 300 MHz) d: 8.06 (d, 2H, C3 and C5 phenyl), 7.88 (d,
n
max, cmꢀ1: 3061 (Ar C–H), 1646 (C]N). 1H
d
H), 5.22 (s, 1H, OH), 3.24 (m, 1H, isopropyl), 2.31 (s, 3H of acetyl
CH3), 1.87 (s, oxadiazole-C2-CH3), 1.23 (d, 6H, terminal CH3) ppm.
2H, C2 and C6 phenyl), 7.75 (s, 1H, thiazole-C5), 3.26 (m, 1H, iso-
propyl), 1.27 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 169.61 (acetyl C]O), 166.43
13C NMR (DMSO-d6, 300 MHz)
d: 165.21 (oxadiazole-C2), 162.20
(thiazole C4), 158.11 (phenyl-C4), 154.43 (thiazole-C2), 144.09
(oxadiazole C5), 139.65 (phenyl-C1), 127.09 (phenyl-C3 and C5),
126.44 (phenyl-C2 and C6), 112.54 (thiazole-C5), 68.09 (oxadiazole
C2), 36.18 (tertiary-1C-isopropyl), 28.24 (oxadiazole-C2-CH3), 23.09
(acetyl CH3), 21.54 (terminal 2CH3-isopropyl) ppm.
(thiazole-C2), 159.48 (thiazole C4), 154.43 (oxadiazole-C5), 143.65
(C4-phenyl), 135.76 (C1-phenyl), 127.87 (phenyl C2 and C6), 118.48
(phenyl C3 and C5), 115.24 (thiazole-C5), 32.49 (tertiary-1C-iso-
propyl), 21.34 (terminal 2CH3-isopropyl) ppm.
MS (%) 316.06 (Mþ 100.0%), 317.07 (M þ 1, 15.4%), 318.06 (4.8%),
317.06 (2.3%), 318.07 (1.8%).
MS (%) 345.11 (Mþ 100.0%), 346.12 (M þ 1, 18.7%), 347.11 (4.5%),
347.12 (2.6%), 346.11 (1.9%).
5.1.2.4. 2-(4-Isopropylthiazol-2-yl)-5-p-tolyl-1,3,4-oxadiazole
5.1.1.8. 1-(5-(4-Isopropylthiazol-2-yl)-2-(4-methoxyphenyl)-2-
(4d). IR (KBr)
(DMSO-d6, 300 MHz) d: 7.87 (d, 2H, C2 and C6 phenyl), 7.61 (d, 2H,
n
max, cmꢀ1: 3077 (Ar C–H), 1642 (C]N). 1H NMR
methyl-1,3,4-oxadiazol-3(2H)-yl)ethanone (3h). IR (KBr)
cmꢀ1: 3056 (Ar C–H), 1673 (amide C]O). 1H NMR (DMSO-d6,
300 MHz) : 7.32 (s, 1H, thiazole-C5), 7.6–7.9 (m, 4H, Ar–H), 3.74
n
max,
C3 and C5 phenyl), 7.45 (s, 1H, thiazole-C5), 1.27 (d, J ¼ 8.5 Hz, 6H,
d
CH3), 3.15 (m, 1H, isopropyl), 2.43 (s, 3H, CH3 at C4 phenyl) ppm.

G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
2071
13C NMR (DMSO-d6, 300 MHz)
d
: 168.43 (thiazole-C2), 165.87
13C NMR (DMSO-d6, 300 MHz)
d
: 168.31 (C]S), 164.23 (HC]N),
(oxadiazole-C2), 154.36 (oxadiazole-C5), 144.43 (C4-phenyl), 135.43
(C1-phenyl), 127.34 (phenyl C2 and C6), 121.65 (thiazole C4), 119.81
(phenyl C3 and C5), 115.24 (thiazole-C5), 32.34 (tertiary-1C-iso-
propyl), 24.9 (CH3 at C4 phenyl), 21.47 (terminal 2CH3-
isopropyl) ppm.
162.21 (thiazole C4), 152.15 (thiazole-C2), 150.43 (Ar C3–C5), 143.53
(triazole-C5), 142.27 (Ar C6), 139.21 (Ar C4), 132.27 (Ar C1), 107 (Ar
C2–C6), 116.19 (thiazole-C5), 53.82 (3OCH3), 30.123 (tertiary-1C-
isopropyl), 23.12 (terminal 2CH3-isopropyl) ppm.
MS (%) 419.11 (Mþ 100.0%), 420.11 (M þ 1, 23.3%), 421.10 (9.1%),
422.11 (1.9%), 421.12 (1.9%), 421.11 (1.3%).
MS (%) 285.09 (Mþ 100.0%), 286.10 (M þ 1, 16.4%), 287.09 (4.7%),
286.09 (1.9%), 287.10 (1.6%).
5.1.3.3. 4-(4-Dimethylaminebenzylideneamino)-5-(4-iso-
5.1.2.5. 2-(4-Isopropylthiazol-2-yl)-5-phenol-1,3,4-oxadiazole
propylthiazol-2-yl)-4H-1,2,4-triazole-3-thiol (6c). IR (KBr)
n max,
(4e). IR (KBr)
n
max, cmꢀ1: 3509 (OH), 3068 (Ar C–H), 1636 (C]N).
cmꢀ1: 3356 (NH), 1654 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d:
1H NMR (DMSO-d6, 300 MHz)
d: 7.64 (d, 2H, C2 and C6 phenyl), 7.48
13.29 (s, 1H, N]C-SH, disappeared on D2O exchange), 9.81 (s, 1H,
N]CH), 7.8–8.0 (4H, ArH), 7.11 (s, 1H, thiazole-C5), 3.15 (m, 1H,
isopropyl), 3.0 (s, 6H, N-2CH3), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
(d, 2H, C3 and C5 phenyl), 7.03 (s,1H, thiazole-C5), 5.08 (s,1H, OH at C4
phenyl), 3.21 (m, 1H, isopropyl), 1.43 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 165.87 (oxadiazole-C2), 163.19
13C NMR (DMSO-d6, 300 MHz)
d: 164.24 (C]S), 164.49 (HC]N),
(thiazole-C2), 154.87 (oxadiazole-C5), 151.21 (C4-phenyl), 135.11
(C1-phenyl), 125.11 (phenyl C2 and C6), 121.32 (thiazole C4), 118.32
(phenyl C3 and C5), 115.15 (thiazole-C5), 32.34 (tertiary-1C-iso-
propyl), 21.47 (terminal 2CH3-isopropyl) ppm.
162.21 (thiazole C4), 152.27 (Ar C4–), 150.15 (thiazole-C2), 142.5
(triazole-C5), 131.54 (Ar C1), 129.76 (Ar C3 C5), 116.19 (thiazole-C5),
115.09 (Ar C2–C6), 41.04 (N-2CH3), 30.123 (tertiary-1C-isopropyl),
23.12 (terminal 2CH3-isopropyl) ppm.
MS (%) 287.07 (Mþ 100.0%), 288.08 (M þ 1, 15.4%), 289.43 (4.7%),
288.09 (1.9%), 289.08 (1.6%).
MS (%) 372.12 (Mþ 100.0%), 373.12 (M þ 1, 22.2%), 374.11 (9.1%),
375.12 (1.7%), 374.13 (1.6%).
5.1.2.6. 2-(4-Isopropylthiazol-2-yl)-5-(4-methoxyphenyl)-1,3,4-oxa-
5.1.3.4. 4-(3,4-Dimethoxybenzylideneamino)-5-(4-isopropylthiazol-
diazole (4f). IR (KBr)
n
max, cmꢀ1: 3086 (Ar C-H), 1638 (C]N). 1H
2-yl)-4H-1,2,4-triazole-3-thiol (6d). IR (KBr)
n
max, cmꢀ1: 3266
NMR (DMSO-d6, 300 MHz)
d
: 7.52 (d, 2H, C2 and C6 phenyl), 7.32
(NH), 1655 (amide C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 13.59 (s,
(s, 1H, thiazole-C5), 7.16 (d, 2H, C3 and C5 phenyl), 3.75 (s, 3H, OCH3
at C4 phenyl), 3.45 (m, 1H, isopropyl), 1.22 (d, J ¼ 8.5 Hz, 6H,
CH3) ppm.
1H, N]C–SH, disappeared on D2O exchange), 9.91 (s, 1H, N]CH),
7.6–8.0 (3H, ArH), 7.51 (s, 1H, thiazole-C5), 3.82 (s, 6H, OCH3), 3.65
(m, 1H, isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d
: 165.81 (thiazole-C2), 162.41
13C NMR (DMSO-d6, 300 MHz)
d: 163.09 (HC]N), 161.87 (C]S),
(oxadiazole-C2), 154.54 (oxadiazole-C5), 144.43 (C4-phenyl), 135.01
(C1-phenyl), 127.92 (phenyl C2 and C6), 121.04 (thiazole C4), 119.83
(phenyl C3 and C5), 115.73 (thiazole-C5), 55.87 (OCH3 at C4 phenyl),
32.32 (tertiary-1C-isopropyl), 21.54 (terminal 2CH3-isopropyl)
ppm.
160.98 (thiazole C4), 151.29 (thiazole-C2), 148.11 (phenyl-C4), 146.11
(phenyl-C5), 145.29 (triazole-C5), 128.11 (phenyl-C1), 125.98
(phenyl-C3), 123.11 (phenyl-C2, C6), 111.09 (thiazole-C5), 57.21
(2OCH3), 33.12 (tertiary-1C-isopropyl), 22.24 (terminal 2CH3-
isopropyl) ppm.
MS (%) 301.43 (Mþ 100.0%), 302.09 (M þ 1, 18.4%), 303.72 (4.5%),
303.34 (1.3%).
MS (%) 389.10 (Mþ 100.0%), 390.10 (M þ 1, 22.1%), 391.09 (9.1%),
391.10 (2.7%), 392.10 (1.8%).
5.1.3. General method for synthesis of 4-substituted- 5-(4-
isopropylthiazol-2-yl)-4H-1,2,4-triazole-3-thiols (6a–l)
5.1.3.5. 4-(4-Methoxybenzylideneamino)-5-(4-isopropylthiazol-2-
yl)-4H-1,2,4-triazole-3-thiol (6e). IR (KBr)
n
max, cmꢀ1: 3276 (NH),
A mixture of compound 5 (10 mmol), substituted benzaldehydes
(10 mmol) and 4–5 drops of concentrated sulphuric acid in ethanol
washeatedtorefluxfor 4 h. Theresultingsolutionwascooledtoroom
temperature and the precipitated solid was filtered under suction,
washed with cold ethanol and recrystallized from hot ethanol.
1632 (amide C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 14.09 (s, 1H,
N]C–SH, disappeared on D2O exchange), 9.19 (s, 1H, N]CH), 7.11
(s, 1H, thiazole-C5), 7.6–8.0(4H, ArH), 3.62 (3H OCH3), 3.15 (m, 1H,
isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 165.89 (HC]N), 163.98
(thiazole C4), 160.43 (C]S), 158.11 (phenyl-C4), 151.29 (thiazole-
C2), 147.29 (triazole-C5), 128.54 (phenyl-C1), 125.98 (phenyl-C3
and C5), 118.11 (phenyl-C2, C6), 111.09 (thiazole-C5), 53.09 (OCH3),
31.12 (tertiary-1C-isopropyl), 23.24 (terminal 2CH3-isopropyl)
ppm.
5.1.3.1. 4-(4-Bromobenzylideneamino)-5-(4-isopropylthiazol-2-yl)-
4H-1,2,4-triazole-3-thiol (6a). IR (KBr)
n
max, cmꢀ1: 3357 (NH),
1654 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 14.49 (s,1H, N]C-SH,
disappeared on D2O exchange), 10.63 (s, 1H, N]CH), 7.6–7.9 (4H,
phenyl), 7.61 (s, 1H, thiazole-C5), 3.15 (m, 1H, isopropyl), 1.23
(d, J ¼ 8.5 Hz, 6H, CH3) ppm.
MS (%) 359.09 (Mþ 100.0%), 360.09 (M þ 1, 19.1%), 361.08 (9.1%),
361.09 (2.2%), 360.08 (1.8%), 362.09 (1.6%).
13C NMR (DMSO-d6, 300 MHz)
d: 168.31 (C]S), 164.44 (HC]N),
162.21 (thiazole C4), 153.14 (thiazole C2), 142.51 (triazole-C5), 125–
132 (Ar C1–C6), 116.19 (thiazole-C5), 30.123 (tertiary-1C-isopropyl),
23.12 (terminal 2CH3-isopropyl) ppm.
5.1.3.6. 4-(2-Hydroxybenzylideneamino)-5-(4-isopropylthiazol-2-
yl)-4H-1,2,4-triazole-3-thiol (6f). IR (KBr)
n
max, cmꢀ1: 3550 (OH),
1643 (C]N), 3327 (NH). 1H NMR (DMSO-d6, 300 MHz)
d
: 14.19 (s,
MS (%) 407.99 (Mþ 100.0%), 408.99 (M þ 1, 99.1%), 409.99
(17.5%), 410.98 (9.1%), 408.98 (9.1%), 409.98 (3.6%), 410.99 (1.9%),
407.98 (1.8%), 411.98 (1.7%).
1H, N]C-SH), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3), 9.44 (s, 1H, N]CH),
7.8–8.0 (4H,ArH), 7.11 (s, 1H, thiazole-C5), 3.15 (m, 1H, isopropyl),
5.49 (s, 1H OH) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 167.54 (HC]N), 162.98 (thia-
5.1.3.2. 4-(3,4,5-Trimethoxybenzylideneamino)-5-(4-iso-
zole C4), 160.87 (C]S), 158.11 (phenyl-C2), 151.29 (thiazole-C2),
147.29 (triazole-C5), 125.98 (phenyl-C4 and C5), 123.11 (phenyl-C3,
C6), 118.11 (phenyl-C1), 111.09 (thiazole-C5), 31.12 (tertiary-1C-iso-
propyl), 23.24 (terminal 2CH3-isopropyl) ppm.
propylthiazol-2-yl)-4H-1,2,4-triazole-3-thiol (6b). IR (KBr)
n max,
cmꢀ1: 3257 (NH), 1674 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d:
14.29 (s, 1H, N]C–SH, disappeared on D2O exchange), 9.73 (s, 1H,
N]CH), 7.11 (s, 1H, thiazole-C5), 7.8–8.0 (2H, Ar H), 4.21 (s, 9H
OCH3), 3.15 (m, 1H, isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
MS (%) 345.07 (Mþ 100.0%), 346.08 (M þ 1, 16.4%), 347.07 (9.6%),
346.07 (3.4%), 348.07 (1.6%), 347.08 (1.5%).

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G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
5.1.3.7. 4-(2-Chlorobenzylideneamino)-5-(4-isopropylthiazol-2-yl)-
4H-1,2,4-triazole-3-thiol (6g). IR (KBr)
max, cmꢀ1: 3347 (NH),
1654 (C]N). 1H NMR (DMSO-d6, 300 MHz)
: 13.59 (s,1H, N]C-SH,
13C NMR (DMSO-d6, 300 MHz)
d: 167.12 (HC]N), 162.98 (thia-
n
zole C4), 160.76 (C]S), 151.29 (thiazole-C2), 145.09 (triazole-C5),
128.98–118.11 (pyrroll-C5C2C3C4), 111.09 (thiazole-C5), 30.12
(tertiary-1C-isopropyl), 23.24 (terminal 2CH3-isopropyl) ppm.
MS (%) 318.07 (Mþ 100.0%), 319.08 (M þ 1, 14.2%), 320.07 (9.6%),
319.07 (3.8%), 321.07 (1.4%).
d
disappeared on D2O exchange), 9.76 (s, 1H, N]CH), 7.11 (s, 1H,
thiazole-C5), 7.6–8.0(4H, ArH), 3.15 (m, 1H, isopropyl), 1.23 (d,
J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 167.09 (HC]N), 160.98 (thia-
zole C4), 158.33 (C]S), 151.29 (thiazole-C2), 147.29 (triazole-C5),
128.11 (phenyl-C4), 125.98 (phenyl-C3 and C5), 123.11 (phenyl-C2,
C6), 111.09 (thiazole-C5), 119.11 (phenyl-C1), 38.12 (tertiary-1C-iso-
propyl), 21.24 (terminal 2CH3-isopropyl) ppm.
5.1.3.12. 4-(2-Hydroxy,4-methoxy benzylideneamino)-5-(4-isopropyl
thiazol-2-yl)-4H-1,2,4-triazole-3-thiol (6l). IR (KBr)
n :
max, cmꢀ1
3540 (OH), 3256 (NH), 1652 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d
: 13.59 (s, 1H, N]C–SH), 9.78 (s, 1H, N]CH), 1.23 (d, J ¼ 8.5 Hz, 6H,
MS (%) 363.04 (Mþ 100.0%), 365.03 (M þ 1, 41.0%), 364.04
(18.0%), 366.04 (6.8%), 367.03 (3.2%), 364.03 (1.8%), 365.04 (1.8%),
366.03 (1.3%).
CH3), 4.59 (s, 1H, OH), 3.59 (s, 1H, CH3), 3.15 (m, 1H, isopropyl), 7.51
(s, 1H, thiazole-C5), 7.6–7.75 (3H, ArH) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 167.94 (HC]N), 162.98 (thia-
zole C4), 160.21 (C]S), 158.11 (phenyl-C5), 151.29 (thiazole-C2),
148.11 (phenyl-C4), 145.18 (triazole-C5), 124.21 (phenyl-C1), 123.76
(phenyl-C2, C6), 119.43 (phenyl-C3), 111.09 (thiazole-C5), 48.11
(phenyl-OCH3), 31.12 (tertiary-1C-isopropyl), 21.24 (terminal 2CH3-
isopropyl) ppm.
5.1.3.8. 4-(Benzylideneamino)-5-(4-isopropylthiazol-2-yl)-4H-1,2,4-
triazole-3-thiol (6h). IR (KBr)
n
max, cmꢀ1: 3383 (NH), 1641 (C]N).
1H NMR (DMSO-d6, 300 MHz)
d
: 13.19 (s, 1H, N]C–SH, disappeared
on D2O exchange), 9.38 (s, 1H, N]CH), 7.11 (s, 1H, thiazole-C5),
7.8–8.0 (5H, ArH), 3.15 (m, 1H, isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H,
CH3) ppm.
MS (%) 375.08 (Mþ 100.0%), 376.09 (M þ 1, 17.6%), 377.08 (9.4%),
376.08 (3.4%), 377.09 (2.1%), 378.08 (1.8%).
13C NMR (DMSO-d6, 300 MHz)
d: 167.09 (HC]N), 162.65 (C]S),
160.98 (thiazole C4), 151.29 (thiazole-C2), 147.29 (triazole-C5),
128.43 (phenyl-C3, C5), 127.29 (phenyl-C4), 123.47 (phenyl-C1),
121.34 (phenyl-C2, C6), 111.09 (thiazole-C5), 38.12 (tertiary-1C-iso-
propyl), 23.24 (terminal 2CH3-isopropyl) ppm.
5.1.4. General method for the synthesis of 3-(4-isopropylthiazol-2-
yl)-6-substituted-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles (7a–f)
An equimolar mixture (0.1 M) of compound 5 and appropriate
aromatic acids in phosphorus oxychloride (10 mL) was refluxed for
5 h. The reaction mixture was cooled to room temperature and then
gradually poured on to crushed ice with stirring. The mixture was
allowed to stand overnight and the solid separated out was filtered,
treated with dilute sodium hydroxide solution and washed thor-
oughly with cold water. The compound so obtained was dried and
recrystallized.
MS (%) 329.08 (Mþ 100.0%), 330.08 (M þ 1, 18.0%), 331.07 (9.1%),
330.07 (1.8%), 331.08 (1.8%), 332.08 (1.5%).
5.1.3.9. 4-((E)-3-phenylallylideneamino)-5-(4-isopropylthiazol-2-
yl)-4H-1,2,4-triazole-3-thiol (6i). IR (KBr)
n
max, cmꢀ1: 3216 (NH),
1634 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 14.09 (s, 1H,
N]C–SH, disappeared on D2O exchange), 9.18 (s, 1H, N]CH), 7.11
(s, 1H, thiazole-C5), 7.6–7.8(5H,ArH), 5.73–6.5 (2H, CH]CH,), 3.15
(m, 1H, isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
5.1.4.1. 3-(4-Isopropylthiazol-2-yl)-6-phenyl-[1,2,4]triazolo[3,4-b]-
[1,3,4]thiadiazole (7a). IR (KBr)
n
max, cmꢀ1: 3091 (Ar C–H), 1636
13C NMR (DMSO-d6, 300 MHz)
d: 167.12 (HC]N), 162.98 (thia-
(C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 8.02 (d, 2H, C3 and C5
zole C4), 160.32 (C]S), 151.29 (thiazole-C2), 145.29 (triazole-C5),
139 (C]CH), 121.54 (phenyl-C2, C6), 127.09 (phenyl-C4), 123.65
(phenyl-C1), 124.76 (phenyl-C3 and C5), 119.73 (CH]CH),
111.09 (thiazole-C5), 38.12 (tertiary-1C-isopropyl), 23.24 (terminal
2CH3-isopropyl) ppm.
phenyl), 7.74 (s, 1H, thiazole-C5), 7.71 (t, 2H, C2 and C6 phenyl), 7.64
(m, 1H, C4 phenyl), 3.21 (m, 1H, isopropyl), 1.24 (d, J ¼ 8.5 Hz, 6H,
CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 168.21 (thiadiazole-C2), 161.95
(thiazole C4), 154.58 (thiazole-C2), 149.87 (triazole-C2), 147.11 (tri-
azole-C5), 134.43 (C1-phenyl), 131.32 (C4-phenyl), 129.34 (C2 and
C6), 124.76 (C3 and C5), 112.69 (thiazole-C5), 33.38 (tertiary-1C-
isopropyl), 23.71 (terminal 2CH3-isopropyl) ppm.
MS (%) 355.09 (Mþ 100.0%), 356.10 (M þ 1, 18.6%), 357.09 (9.4%),
356.09 (3.4%), 358.09 (1.9%), 357.10 (1.9%).
5.1.3.10. 4-(4-Methylbenzylideneamino)-5-(4-isopropylthiazol-2-yl)-
MS (%) 327.43 (Mþ 100.0%), 328.09 (M þ 1, 19.7%), 329.36 (9.7%),
330.00 (1.6%), 329.81 (1.3%).
4H-1,2,4-triazole-3-thiol (6j). IR (KBr)
n
max, cmꢀ1: 3266 (NH),1652
(C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 14.29 (s, 1H, N]C–SH,
disappeared on D2O exchange), 9.65 (s, 1H, N]CH), 7.8–8.0(4H,
ArH), 7.11 (s, 1H, thiazole-C5), 3.15 (m, 1H, isopropyl), 2.15 (S, 1H,
CH3), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
5.1.4.2. 3-(4-Isopropylthiazol-2-yl)-6-(4-chlorophenyl)-[1,2,4]tri-
azolo[3,4-b][1,3,4]thiadiazole (7b). IR (KBr)
n
max, cmꢀ1: 3081 (Ar
C–H), 1629 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d
: 8.12 (d, 2H, C3
13C NMR (DMSO-d6, 300 MHz)
d
: 167.87 (HC]N), 163.43 (thia-
and C5 phenyl), 7.61 (t, 2H, C2 and C6 phenyl), 7.45 (s, 1H, thiazole-
zole C4), 160.09 (C]S), 151.29 (thiazole-C2), 145.29 (triazole-C5),
138.11 (phenyl-C4), 126.98 (phenyl-C2, C6), 127.98 (phenyl-C1),
124.32 (phenyl-C3 and C5), 111.09 (thiazole-C5), 38.12 (tertiary-1C-
isopropyl), 24.15 (CH3), 23.24 (terminal 2CH3-isopropyl) ppm.
MS (%) 343.09 (Mþ 100.0%), 344.10 (M þ 1, 17.5%), 345.09 (9.4%),
344.09 (3.4%), 346.09 (1.8%), 345.10 (1.7%).
C5), 3.32 (m, 1H, isopropyl), 1.31 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 166.01 (thiadiazole-C2), 163.29
(triazole-C5), 162.59 (thiazole C4), 154.87 (thiazole-C2), 150.54 (tri-
azole-C2),131.11 (C1-phenyl),130.38 (C4-phenyl),128.37 (C2 and C6),
124.18 (C3 and C5), 112.6 (thiazole-C5), 33.43 (tertiary-1C-iso-
propyl), 23.58 (terminal 2CH3-isopropyl) ppm.
MS (%) 361.34 (Mþ 100.0%), 363.54 (M þ 1, 41.3%), 362.36
(16.4%), 364.98 (8.0%), 362.02 (3.4%), 365.02 (3.3%), 363.03 (1.5%).
5.1.3.11. 4-((2H-Pyrrol-2-yl)methyleneamino)-5-(4-isopropylthiazol-
2-yl)-4H-1,2,4-triazole-3-thiol (6k). IR (KBr)
(NH), 1654 (C]N).
n
max, cmꢀ1: 3288
5.1.4.3. 3-(4-Isopropylthiazol-2-yl)-6-(4-nitrophenyl)-[1,2,4]tri-
1H NMR1H NMR (DMSO-d6, 300 MHz)
d
: 14.29 (s, 1H, N]C–SH,
azolo[3,4-b][1,3,4]thiadiazole (7c). IR (KBr)
n
max, cmꢀ1: 3086 (Ar
disappeared on D2O exchange), 12.29 (s, 1H, py NH), 9.23 (s, 1H,
N]CH), 7.11 (s, 1H, thiazole-C5), 6.1–7.25 (s 3H,py), 3.15 (m, 1H,
isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
C–H), 1626 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 7.61 (d, 2H, C3
and C5 phenyl), 7.49 (t, 2H, C2 and C6 phenyl), 7.26 (s, 1H, thiazole-
C5), 3.38 (m, 1H, isopropyl), 1.54 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.

G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
2073
13C NMR (DMSO-d6, 300 MHz)
d: 168.01 (thiadiazole-C2), 161.43
13C NMR (DMSO-d6, 300 MHz)
d
: 184.82 (C]S), 161.21 (thiazole
(thiazole C4), 154.17 (thiazole-C2), 149.17 (triazole-C2), 147.17 (tri-
azole-C5), 134.36 (C1-phenyl), 131.11 (C4-phenyl), 129.31 (phenyl C2
and C6), 124.32 (phenyl C3 and C5), 112.01 (thiazole-C5), 33.16
(tertiary-1C-isopropyl), 23.98 (terminal 2CH3-isopropyl) ppm.
MS (%) 372.05 (Mþ 100.0%), 373.05 (M þ 1, 18.0%), 374.04 (9.1%),
374.05 (2.3%), 373.04 (2.2%), 375.05 (1.6%).
C4), 153.84 (thiazole C2), 125–132 (ArC1–C6), 38.54 (tertiary-1C-
isopropyl), 116.10 (thiazole-C5), 23.43 (terminal 2CH3-
isopropyl) ppm.
MS (%) 302.07 (Mþ 100.0%), 303.43 (M þ 1, 16.1%), 304.06 (9.4%),
304.07 (1.9%), 305.07 (1.4%).
5.1.6. Synthesis of 3-(4-isopropylthiazol-2-yl)-5-methyl-4-phenyl-
4H-1,2,4-triazole (9)
5.1.4.4. 3-(4-Isopropylthiazol-2-yl)-6-p-tolyl-[1,2,4]triazolo[3,4-b]-
[1,3,4]thiadiazole (7d). IR (KBr)
n
max, cmꢀ1: 3078 (Ar C–H), 1642
To a solution of compound 8 (10 mmol) in absolute ethanol,
1 equiv of sodium was added and the mixture was stirred at room
temperature for 30 min. Then, methyl iodide (20 mmol) was added
and refluxed for 4 h. After evaporating the solvent under reduced
pressure a solid appeared. The solid was recyrstallized from
ethanol/water (1:1) to obtain target compound.
(C]N). 1H NMR (DMSO-d6, 300 MHz)
d
: 7.83 (d, 2H, C3 and C5
phenyl), 7.61 (t, 2H, C2 and C6 phenyl), 7.10 (s, 1H, thiazole-C5), 3.18
(m, 1H, isopropyl), 2.33 (s, 3H, CH3 at C4 phenyl), 1.57 (d, J ¼ 8.5 Hz,
6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 168.01 (thiadiazole-C2), 161.36
(thiazole C4), 154.87 (thiazole-C2), 149.17 (triazole-C2), 147.11 (tri-
azole-C5), 134.15 (C4-phenyl), 131.34 (C1-phenyl), 129.10 (phenyl C2
and C6), 124.21 (C3 and C5), 112.01 (thiazole-C5), 33.98 (tertiary-1C-
isopropyl), 25.23 (CH3 at C4 phenyl), 23.43 (terminal 2CH3-
isopropyl) ppm.
IR (KBr)
n
max, cmꢀ1: 3086 (NH), 2754 (SCH3).
: 7.6–7.9 (m, 5H, phenyl), 7.32 (s,
1H NMR (DMSO-d6, 300 MHz)
d
1H, thiazole-C5), 3.26 (m, 1H, isopropyl), 2.86 (s, triazole-C5, S-CH3
of triazole), 1.23 (d, 6H, terminal CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 160.33 (thiazole C4), 156.41
MS (%) 341.08 (Mþ 100.0%), 342.08 (M þ 1, 19.1%), 343.07 (9.1%),
343.08 (2.0%), 342.07 (1.8%), 344.08 (1.6%).
(triazole-C5), 153.43 (thiazole C2), 125–132 (ArC1–C6), 116.82
(thiazole-C5), 39.11 (tertiary-1C-isopropyl), 24.13 (terminal 2CH3-
isopropyl), 14.36 (triazole-C5 S–CH3) ppm.
5.1.4.5. 4-(3-(4-Isopropylthiazol-2-yl)-[1,2,4]triazolo[3,4-b]-
MS (%) 316.08 (Mþ 100.0%), 317.08 (M þ 1, 19.3%), 318.08 (9.6%),
319.08 (1.6%), 318.09 (1.3%).
[1,3,4]thiadiazol-6-yl)phenol (7e). IR (KBr)
n
max, cmꢀ1: 3501 (OH),
3094 (Ar C–H), 1638 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 7.91
(t, 2H, C2 and C6 phenyl), 7.81 (d, 2H, C3 and C5 phenyl), 7.10 (s, 1H,
thiazole-C5), 5.03 (s, 1H, OH at C4 phenyl), 3.17 (m, 1H, isopropyl),
1.23 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
5.2. Biological protocol
5.2.1. Antimicrobial activity
13C NMR (DMSO-d6, 300 MHz)
d
: 168.30 (thiadiazole-C2), 161.34
The antimicrobial susceptibility testing was performed in vitro
by broth microdilution method [19–21]. The MIC determination of
the synthesized compounds was carried out in side-by-side
comparison with ciprofloxacin and norfloxacin against Gram-
positive bacteria (S. aureus, S. faecalis, B. subtilis) and Gram-negative
(K. penumoniae, E. coli, P. aeruginosa). The antifungal activity was
assayed against yeasts (C. tropicalis, S. cerevisiae) and moulds (A.
(thiazole C4), 154.65 (thiazole-C2), 149.50 (triazole-C2), 147.41 (tri-
azole-C5), 134.21 (C1-phenyl), 134.94 (C4-phenyl), 129.14 (phenyl C2
and C6), 124.16 (phenyl C3 and C5), 112.01 (thiazole-C5), 33.02
(tertiary-1C-isopropyl), 23.54 (terminal 2CH3-isopropyl) ppm.
MS (%) 343.06 (Mþ 100.0%), 344.06 (M þ 1, 18.0%), 345.05 (9.1%),
345.06 (2.0%), 344.05 (1.8%), 346.06 (1.6%).
niger). The minimal inhibitory concentrations (MIC, mg/mL) were
5.1.4.6. 3-(4-Isopropylthiazol-2-yl)-6-(4-methoxyphenyl)-[1,2,4]tri-
defined as the lowest concentrations of compound that completely
inhibited the growth of each strain. Test compounds (10 mg) were
dissolved in dimethylsulfoxide (DMSO, 1 mL) then diluted in
culture medium (Mueller–Hinton Broth for bacteria and Sabouraud
Liquid Medium for fungi), further progressive dilutions to obtain
azolo[3,4-b][1,3,4]thiadiazole (7f). IR (KBr)
n
max, cmꢀ1: 3098 (Ar C–H),
1627 (C]N). 1H NMR (DMSO-d6, 300 MHz)
d: 7.81 (t, 2H, C2 and C6
phenyl), 7.34 (d, 2H, C3 and C5 phenyl), 7.00 (s, 1H, thiazole-C5), 3.89
(s, 1H, OCH3 at C4 phenyl), 3.23 (m, 1H, isopropyl), 1.43 (d, J ¼ 8.5 Hz,
6H, CH3) ppm.
final concentrations of 1, 2, 4, 8, 16, 31.25, 62.5, 125, 250 and 500 mg/mL.
13C NMR (DMSO-d6, 300 MHz)
d
: 168.19 (thiadiazole-C2), 161.21
DMSO never exceeded 1% v/v. The tubes were inoculated with
105 cfu mLꢀ1 (colony forming unit/mL) and incubated at 37 ꢁC for
24 h. The growth control consisting of media and media with
DMSO at the same dilutions as used in the experiments was
employed.
(thiazole C4), 154.43 (thiazole-C2), 149.34 (triazole-C2), 147.41 (tri-
azole-C5), 134.13 (C1-phenyl), 132.18 (C4-phenyl), 129.91 (phenyl C2
and C6), 124.16 (phenyl C3 and C5), 112.98 (thiazole-C5), 55.89 (s, 1H,
OCH3 at C4 phenyl), 33.87 (tertiary-1C-isopropyl), 23.43 (terminal
2CH3-isopropyl) ppm.
MS (%) 357.07 (Mþ 100.0%), 358.08 (M þ 1, 17.5%), 359.07 (9.7%),
358.07 (3.4%), 360.07 (1.7%), 359.08 (1.7%).
5.2.2. Antitubercular activity
The preliminary antitubercular screening for test compounds
was obtained for M. tuberculosis H37Rv, the MIC of each drug was
determined by broth dilution assay [22,23] and is defined as the
lowest concentration of drug, which inhibits ꢃ99% of bacterial
population present at the beginning of the assay. A frozen culture in
Middlebrook 7H9 broth supplemented with 10% albumin-dextrose-
catalase and 0.2% glycerol was thawed and diluted in broth to
105 cfu mLꢀ1 (colony forming unit/mL) dilutions. Each test
compound was dissolved in DMSO and then diluted in broth twice
at the desired concentration. The final concentration of DMSO in
the assay medium was 1.3%. Each U-tube was then inoculated with
0.05 mL of standardized culture and then incubated at 37 ꢁC for 21
days. The growth in the U-tubes was compared with visibility
against positive control (without drug), negative control (without
drug and inoculum) and with standard isoniazid.
5.1.5. Synthesis of 5-(4-isopropylthiazol-2-yl)-4-phenyl-4H-1,2,4-
triazole-3-thiol (8)
A mixture of compound 1 (10 mmol) and phenylisothiocyanate
(15 mmol) was refluxed in ethanol for 4 h to give a white solid.
The resulting solid (10 mmol) was dissolved in 2 N NaOH and
refluxed for 3 h. The resulting solution was cooled to room
temperature and acidified to pH 3–4 with 37% HCl to give a white
solid. The solid formed was filtered, washed with water and
recrystallized.
IR (KBr)
n
max, cmꢀ1: 3096 (C–H of aromatic), 2766 (SH).
: 14.49 (s, 1H, N]C-SH, dis-
1H NMR (DMSO-d6, 300 MHz)
d
appeared on D2O exchange), 7.32 (s,1H, thiazole-C5), 7.1–7.9 (m, 5H,
phenyl), 3.26 (m, 1H, isopropyl), 1.23 (d, 6H, terminal CH3) ppm.

2074
G.V. Suresh Kumar et al. / European Journal of Medicinal Chemistry 45 (2010) 2063–2074
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3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide re-
duction assay [24,25]. The compounds were dissolved in DMSO at
10 mM concentration and stored at ꢀ20 ꢁC. The dilutions were
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Acknowledgements
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We thank management of St. Johns Pharmacy College, Banga-
lore, for providing necessary facilities. We are grateful to Dr. K.G.
Bhat, Maratha Mandal’s Dental College, Hospital and Research
Centre, Belgaum, India, for providing the facilities to determine the
antibacterial and antitubercular activities. We also wish to thank
IISC, Bangalore, India for providing IR, NMR, mass spectra and
elemental analysis data.
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