Synthesis of new 4-isopropylthiazole hydrazide analogs and some derived clubbed triazole, oxadiazole ring systems - A novel class of potential antibacterial, antifungal and antitubercular agents

Article abstract of DOI:10.1016/j.ejmech.2009.06.008

In the present study a series of 4-isopropylthiazole-2-carbohydrazide analogs, derived clubbed oxadiazole-thiazole and triazole-thiazole derivatives have been synthesized and characterized by IR, ¹H NMR, ¹³C NMR, elemental and mass s

Full text of DOI:10.1016/j.ejmech.2009.06.008

European Journal of Medicinal Chemistry 44 (2009) 4739–4746
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
Synthesis of new 4-isopropylthiazole hydrazide analogs and some derived
clubbed triazole, oxadiazole ring systems – A novel class of potential
antibacterial, antifungal and antitubercular agents
,
,
b,2
B.P. Mallikarjuna a 1, B.S. Sastry b, G.V. Suresh Kumar c , Y. Rajendraprasad
,
*
S.M. Chandrashekar c 3, K. Sathisha d
,
,4
a PES College of Pharmacy, Department of Medicinal Chemistry, 50 Feet Road, Hanumantha Nagar, B.S.K. Ist Stage, Bangalore-560050, Karnataka, India
b Department of Pharmaceutical Sciences, Andhra University, Visakhapatnam-530002, Andra Pradesh, India
c St Johns Pharmacy College, Department of Medicinal Chemistry, 6, 2nd stage Vijaynagar, R.P.C. Layout, Bangalore-560040, Karnataka, India
d Molecular Biophysics Unit, Indian Institute of Science, Bangalore-12, 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 4-isopropylthiazole-2-carbohydrazide analogs, derived clubbed oxadia-
zole–thiazole and triazole–thiazole derivatives have been synthesized and characterized by IR, 1H NMR,
13C NMR, elemental and mass spectral analyses. The synthesized compounds were evaluated for their
preliminary in vitro antibacterial, antifungal and antitubercular activity against Mycobacterium tuber-
culosis H37Rv strain by broth dilution assay method.
Received 3 February 2009
Received in revised form
29 May 2009
Accepted 8 June 2009
Available online 17 June 2009
The synthesized compounds 7a, 7b, 7d and 4 showed an antitubercular efficacy considerably greater
than that of the parent 4-isopropyl-1,3-thiazole-2-carbohydrazide 1, suggesting that the substituted
4-isopropylthiazole-2-carbohydrazide moiety plays an important role in enhancing the antitubercular
properties of this class of compounds. Compounds 2c, 3, 4, 6d, 7a and 7b exhibited good or moderate
Keywords:
4-Isopropylthiazole-2-carbohydrazide
analogs
antibacterial and antifungal activity. Compounds
a concentration of 250 M.
4 and 7b showed appreciable cytotoxicity at
Clubbed triazole–thiazole derivatives
Antibacterial
m
Antifungal
Cytotoxicity
Ó 2009 Elsevier Masson SAS. All rights reserved.
Antitubercular
Broth dilution assay
1. Introduction
In addition, primary and opportunistic microbial infections have
increased rapidly because of immunocompromised patients (AIDS,
cancer and transplants). The deadly synergy between tuberculosis
(TB) and human immunodeficiency virus (HIV) had led to the
containment of tubercle bacilli (macrophages and CD4-receptor-
bearing lymphocytes) and promotes the progression of recently or
remotely acquired TB infection to active disease. Therefore, the
development of new drugs with activity against multi drug-resis-
tant (MDR) TB, extensively drug-resistant (XDR) TB and latent TB is
a priority task, which will shorten the chemotherapy [2].
Tuberculosis (TB) is a worldwide problem: about 2 million
people die each year, particularly in developing countries. It is
estimated that about one-third of the world population is currently
infected with Mycobacterium tuberculosis in its latent form and
addition of nine million new cases per year threatens efforts to
control the disease [1].
Lipophilicity is a key property that influences the ability of
a drug to reach the target by transmembrane diffusion and to have
a major effect on the biological activity [3]. The azole antituber-
culars are regarded as emerging class and thiazoles known as
lipophilic analogs of imidazoles are expected to increase log P. And
further, isopropyl group containing thiazoles has emerged as new
class of potent antibacterial and antifungals, which are reported to
inhibit bacteria by blocking the biosynthesis of certain bacterial
lipids and/or by additional mechanisms [4,5].
* Corresponding author. Tel.: þ91 80 23190191; fax: þ91 80 23350035; mobile:
þ91 9886104039.
E-mail addresses: mallibp@gmail.com (B.P. Mallikarjuna), bssastryau@yahoo.
com (B.S. Sastry), gvsureshkumar@yahoo.com (G.V. Suresh Kumar), dryrp@rediff
mail.com (Y. Rajendraprasad), Chandra_jan25@yahoo.co.in (S.M. Chandrashekar),
satishkmb@gmail.com (K. Sathisha).
1
Mobile: þ91 9341254261.
2
Mobile: þ91 9440132537.
3
Mobile: þ91 9986019452.
4
Mobile: þ91 9964782885.
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.06.008

4740
B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
Thiazole derivatives were reported to possess antitubercular
reacting compound 1 with carbon disulfide under strong basic
conditions followed by acidification with dilute hydrochloric acid.
Compound 1 was converted into the corresponding potassium
dithiocarbazinate, which on cyclizationwithhydrazine hydrateyields
4-amino-5-(4-isopropyl-1,3-thiazol-2-yl)-4H-1,2,4-triazole-3-thiol
4. Compound 5, N-acetyl-4-isopropylthiazole-2-carbohydrazide, was
synthesized by heating compound 1 with acetic anhydride. The
reaction of compound 1 with different aldehydes in alcohol gave
Schiff bases 6a–6f, which on further heating with acetic anhydride
afforded 1,3,4-oxadiazole derivatives 7a–7f.
activity and their coupling with other heterocyclic rings furnishes
novel biologically active compounds [6]. So after extensive litera-
ture search [7–11] and in continuation of our research work on
thiazoles [12–15] it was contemplated to synthesize some novel 4-
isopropylthiazoles, clubbed with 1,3,4-oxadiazole and 1,2,4-tri-
azoles and study their antimicrobial (bacterial and fungal) activity
followed by antitubercular activity.
2. Chemistry
The reaction sequences employed for synthesis of the target
compounds are shown in Scheme 1, and their physical properties are
depicted in Table 1. The key intermediate in the present study
4-isopropylthiazole-2-carbahydrazide 1, was prepared by hydrazi-
nolysis of the ethyl ester of 4-isopropylthiazole-2-carboxylate with
hydrazine hydrate [16]. Reacting the starting compound 1 with
acetone and appropriate substituted acetophenones resulted in the
formation of corresponding hydrazone derivatives 2a–2g. The prep-
aration of 5-(4-isopropylthiazol-2-yl)-1,3,4-oxadiazole-2-thiol 3, [17]
was achieved by adopting simple one pot procedure that involves
3. Biological activity
The standard strains were procured from the American Type
Culture Collection (ATCC) and Gene Bank, Institute of Microbial
Technology, Chandigarh, India. The antibacterial activities of the
synthesized compounds were determined by broth dilution
method [18,19] against the following standard bacterial strains
Staphylococcus aureus (ATCC 11632), Streptococcus faecalis (ATCC
14506), Bacillus subtilis (ATCC 60511), Klebsiella pneumoniae (ATCC
10031), Escherichia and Pseudomonas aeruginosa (ATCC 10145) and
CH3
2a
2b
H
N
N
CH3COR
N
C6H5
R
O
S
4-Cl -C6H4
2c
2a-g
2d 4-NO2 - C6H4
C2H5OH
N
N
4-Br - C 6H4
2e
N
CS 2 / KOH
SH
O
4-CH3 - C6H4
2f
S
3
2g
4-OH - C 6H4
N
N
NH2NH2.H2O
N
N
C2H5OH
CS 2 / KOH
SH
N
CONHNH2
S
S
NH2
1
4
O
N
(CH3CO)2O
N
H
S
H
N
COCH3
5
N
N
O
N
R-CHO
N
H
H
S
C
R
6a-f
(CH3CO)2O
COCH3
N
N
R
O
7a
7b
7c
7d
C6H5
S
6a
C6H5
3,4,5 -(OCH 3 )3-C6H2
4-N(CH3)2-C6H4
4-OH-C 6H4
7a-f
3,4,5 -(OCH 3 )3-C6H2
4-N(CH3)2-C6H4
4-OH-C 6H4
6b
6c
6d
7e 4-NO2-C6H4
2,3 -(Cl) 2 - C6H3
7f
4-NO2-C6H4
6e
6f
2,3 -(Cl) 2 - C6H3
Scheme 1.

B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
4741
Table 1
Physical properties and elemental analysis data.
Compound
Molecular formula
Molecular weight
Elemental analysis (%)
Anal Calcd
Found
1
C7H11N3OS
185.25
225.09
287.11
321.07
332.09
365.02
301.12
303.1
227.02
241.05
227.07
273.09
363.13
316.14
289.09
318.08
341.02
315.1
C – 45.39; H – 5.99; N – 22.68; S – 17.31
C – 53.31; H – 6.71; N – 18.65; S – 14.23
C – 62.69; H – 5.96; N – 14.62; S – 11.16
C – 55.98; H – 5.01; N – 13.06; S – 9.96
C – 54.20; H – 4.85; N – 16.86; S – 9.65
C – 49.19; H – 4.40; N – 11.47; S – 8.75
C – 63.76; H – 6.35; N – 13.94; S – 10.64
C – 59.38; H – 5.65; N – 13.85; S – 10.57
C – 42.27; H – 3.99; N – 18.49; S – 28.21
C – 39.81; H – 4.59; N – 29.02; S – 26.57
C – 47.56; H – 5.77; N – 18.49; S – 14.11
C – 61.51; H – 5.53; N – 15.37; S – 11.73
C – 56.18; H – 5.82; N – 11.56; S – 8.82
C – 60.73; H – 6.37; N – 17.71; S – 10.13
C – 58.11; H – 5.23; N – 14.52; S – 11.08
C – 52.82; H – 4.43; N – 17.60; S – 10.07
C – 49.13; H – 3.83; N – 12.28; S – 9.37
C – 60.93; H – 5.43; N – 13.32; S – 10.17
C – 56.28; H – 5.72; N – 10.36; S – 7.91
C – 60.31; H – 6.19; N – 15.63; S – 8.95
C – 57.99; H – 5.17; N – 12.68; S – 9.68
C – 53.32; H – 4.47; N – 15.55; S – 8.90
C – 50.01; H – 3.93; N – 10.93; S – 8.34
C – 45.78; H – 6.09; N – 22.37; S – 17.14
C – 54.87; H – 6.07; N – 18.23; S – 14.99
C – 63.85; H – 5.88; N – 14.00; S – 11.56
C – 55.32; H – 5.91; N – 13.76; S – 9.01
C – 53.65; H – 4.59; N – 16.12; S – 9.05
C – 49.06; H – 4.65; N – 11.14; S – 8.09
C – 63.18; H – 6.11; N – 12.76; S – 10.69
C – 59.09; H – 5.98; N – 13.09; S – 10.28
C – 42.87; H – 3.23; N – 18.43; S – 28.56
C – 40.87; H – 4.03; N – 29.87; S – 26.11
C – 47.04; H – 5.05; N – 18.69; S – 14.09
C – 61.19; H – 5.69; N – 15.30; S – 11.98
C – 56.18; H – 5.82; N – 11.56; S – 8.17
C – 60.47; H – 6.60; N – 17.02; S – 10.17
C – 58.01; H – 4.87; N – 14.03; S – 11.02
C – 52.56; H – 4.02; N – 17.03; S – 10.10
C – 49.59; H – 3.34; N – 12.58; S – 10.48
C – 60.56; H – 5.54; N – 12.89; S – 10.19
C – 56.49; H – 5.68; N – 10.11; S – 7.32
C – 60.98; H – 6.68; N – 14.09; S – 7.87
C – 57.07; H – 4.98; N – 12.11; S – 9.23
C – 53.43; H – 4.18; N – 15.87; S – 7.87
C – 51.87; H – 3.43; N – 10.65; S – 8.54
2a
2b
2c
2d
2e
2f
2g
3
C10H15N3OS
C15H17N3OS
C15H16ClN3OS
C15H16N4O3S
C15H16BrN3OS
C16H19N3OS
C15H17N3O2S
C8H9N3OS2
4
5
C8H11N5S2
C9H13N3O2S
C14H15N3OS
C17H21N3O4S
C16H20N4OS
C14H15N3O2S
6a
6b
6c
6d
6e
6f
7a
7b
7c
7d
7e
7f
C
14H14N4O3S
C14H13ClN3OS
C16H17N3O2S
C19H23N3O5S
C18H22N4O2S
C16H17N3O3S
C16H16N4O4S
C16H15ClN3O2S
405.1
358.15
331.1
360.09
383.03
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.
spectrum shows peaks at d 25.3, d 167.54 and d 111.34 due to CH3,
C]O and thiazole CH respectively and molecular ion peak at m/z
227.07 confirmed the structure.
Hydrazones 6a–6f obtained from compound 1 show carbonyl
amide stretching at around 1600–1650 cmꢀ1 and N–H bands in
3180–3250 cmꢀ1 region. 1H NMR of compound 6a shows sharp
4. Results and discussion
singlets at
d
8.32 and
d
11.97 of N]CH and NH protons. N]CH peak
147.64.
The IR spectrum of compound 1 illustrates broad stretching
band around 3517 cmꢀ1 and 3335 cmꢀ1 due to NH and NH2 and
strong stretching band at 1673 cmꢀ1 accounting for amide carbonyl
in 13C NMR spectrum appears at
d
In IR spectra of 7a–7f, there is vanishing of NH stretching and
presence of C]O bands at around 1650 cmꢀ1 designated for acetyl
groups. 1H NMR of 1-(5-(4-isopropylthiazol-2-yl)-1,3,4-oxadiazole
derivatives shows singlets of O–CHR–N in oxadiazoline ring at
group. 1H NMR of compound 1 shows sharp singlets at
d
9.8 and
4.5, accountable for NH and NH2 which were absent on D2O
exchange. The 6 protons of terminal isopropyl group appeared as
doublet at 1.5 and multiplet at 3.2 for other isopropyl proton.
Thiazole proton appeared as singlet at
7.4. 13C NMR shows a peak
d
d
6.6 and acetyl CH3 at
d
2.21. Further same O–CHR–N in 13C NMR
118.1 and N–C]O of oxadiazole at
d
d
spectrum shows peak at
d
d
d
144.76. Compound 7a was confirmed by molecular ion peak
at m/z 315.
The results of antimicrobial testing of the synthesized compounds
against selected Gram-positive, Gram-negative bacteria, yeasts,
moulds and M. tuberculosis H37Rv are illustrated in Tables 2 and 3
respectively. Compounds 3 and 4 were found to be more active than
at 22.01 because of 2C of terminal isopropyl group and peak of C]O
at 164.10, further molecular ion peak at m/z 185.06 confirms its
molecular weight.
1H NMR of compound 2d showed a singlet at
d
2.1 due to methyl
8.32 accountable for aromatic
benzyl group. 13C NMR of the compound 2d confirms resonance of
CH3 and C]N at 14.9 and 165.25 respectively. Further, mass
group and doublet at
d 8.1 and d
other compounds at MIC 8 and 31.25 mg/mL against all tested
microorganisms except a moderate potency with S. aureus.
d
d
spectrum of compound 2d showed a molecular ion peak m/z 332.09
which confirmed its molecular weight.
Compounds 7a–7d which have 2,3-dihydro-1,3,4-oxadiazole ring
were more active than the starting compounds 6a–6f against most of
the test organisms. Interestingly 6a–6f exhibited significant inhibi-
Lack of 1H NMR resonances of NH and NH2 in the spectrum of
compound 3, further 13C NMR data of compound 3 showed a peak
tory (MIC 16 and 125 mg/mL) properties against Gram-negative
at
d
177.5 and
d
148.32 due to C2 and C5 of oxadiazole and the
bacteria, moulds and yeasts than Gram-positive bacteria. This
implies that compounds having inductively electron withdrawing
but mesomerically electron donating substituents on phenyl group
were found to be the most active compounds against the test
microorganisms, particularly dichloro benzene ring on compounds
6f and 7f had improved antimicrobial activity than other derivatives.
The synthesized compounds showed antimicrobial activity with
molecular ion base peak at m/z 227.02 confirmed the structure of
compound 3.
The IR spectrum of compound 4 displayed symmetric and
asymmetric stretching bands at 3353 cmꢀ1 and 3248 cmꢀ1 of NH/
NH2. 1H NMR spectra show a singlet at
d 6.01 of NH2 and a singlet at
d
14.09 (SH or HNCS) reflecting the thiol–thione tautomeric forms
[18]. 13C NMR spectrum of compound 4 showed signals at 185.24 and
153.15 due to C]S of triazole and C5 of triazole respectively. The mass
spectrum of compound 4 exhibited the molecular ion peak at m/z
241.05 which confirmed the molecular weight.
MIC between 16 and 250 mg/mL against S. faecalis and had less
potency against S. aureus. The majority of compounds exhibited
good inhibitory activity against Gram-negative bacteria, moulds
and yeasts than Gram-positive bacteria.
The experimental compounds showed activity against myco-
bacteria with MIC values ranging from 8 to 250 mg/mL. The results
1H NMR of compound 5 shows a singlet at
d
2.1,
d
10.21 and
d
7.23 due to methyl, NH and thiazole CH respectively. 13C NMR

4742
B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
Table 2
Antimicrobial activity expressed as MIC (mg/mL).
Compound
Gram-positive organismsa
Gram-negative organismsa
Fungia
Sc
Sa
Sf
Bs
Kp
Ec
Pa
Ct
An
1
2a
2b
2c
2d
2e
2f
2g
3
4
5
6a
6b
6c
6d
6e
6f
7a
7b
7c
7d
7e
7f
250
250
250
125
250
250
250
125
125
125
500
500
500
250
125
125
250
125
125
125
250
125
250
250
125
125
31.25
31.25
125
125
250
125
125
250
250
125
250
250
125
125
125
250
125
125
250
16
125
125
125
125
250
250
250
125
31.25
31.25
250
31.25
125
31.25
31.25
31.25
16
62.5
31.25
16
125
125
250
125
250
125
250
125
250
500
500
125
500
31.25
125
31.25
31.25
16
500
62.5
125
250
31.25
125
16
31.25
31.25
31.25
31.25
500
16
–
–
ꢁ1
500
125
500
125
125
125
250
31.25
16
8
125
500
250
125
125
125
500
125
31.25
8
500
31.25
31.25
62.5
31.25
31.25
125
16
16
31.25
16
31.25
31.25
31.25
250
125
250
250
16
31.25
8
31.25
16
125
16
31.25
31.25
16
125
31.25
16
16
16
250
125
125
125
125
125
31.25
31.25
16
125
125
125
125
31.25
125
31.25
125
62.5
62.5
125
16
62.5
31.25
16
16
31.25
16
125
16
–
–
31.25
62.5
16
125
31.25
125
62.5
62.5
31.25
31.25
31.25
125
125
125
125
ꢁ5
ꢁ5
–
31.25
16
250
16
250
125
ꢁ1
ꢁ1
–
31.25
125
125
16
ꢁ5
ꢁ5
16
ꢁ1
ꢁ1
125
ꢁ1
ꢁ1
–
31.25
ꢁ5
Ciprofloxacin
Norfloxacin
Flucanozole
–
–
ꢁ1
ꢁ5
–
–
–
ꢁ1
a
The screening organisms. Gram-positive bacteria: Staphylococcus aureus (ATCC 11632, Sa), Streptococus faecalis (ATCC 14506, Sf), and Bacillus subtilis (ATCC 60511, Bs).
Gram-negative bacteria: Klebsiella penumoniae (ATCC 10031, Kp), Escherichia coli (ATCC 10536, Ec), and Pseudomonas aeruginosa (ATCC 10145, Pa). Yeasts: Saccharomyces
cerevisiae (ATCC 9763, Sc) and Candida tropicalis (ATCC 1369, Ct), mould: Aspergillus niger (ATCC 6275, An).
(Table 3) imply that compounds 3, 4, and 7a–7d show better
activity against M. tuberculosis H37Rv, predominantly 3, 4 showed
5. Experimental
highest activity (8
mg/mL) against mycobacteria.
5.1. Chemical protocols
Compounds 4, 7b, and 7d were evaluated for their cytotoxic
potential using A549 (lung adenocarcinoma) cell lines in the pres-
ence of fetal bovine serum. Compound 7d showed maximum
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) were recorded on (AMD-604) mass
spectrometer operating at 70 eV. Elemental analysis was performed
on Thermo Finnigan Flash (EA 1112 CHNS Analyzer).
cytotoxicity at a concentration of 250
mM as depicted in Fig. 1. The
other compounds 4 and 7b showed appreciable cytotoxicity of
about 50% of the vehicle control at a concentration of 250 mM.
Table 3
Primary antitubercular activity.
Compound
MIC values (mg/mL) of Mycobacterium tuberculosis H37Rv
4
1
125
125
125
62.5
125
31.25
125
125
8
250µM
2a
2b
2c
2d
2e
2f
2g
3
4
200µM
150µM
3
2
1
0
200µM
50µM
8
5
125
250
125
125
125
125
125
31.25
31.25
62.5
31.25
62.5
62.5
0.25
6a
6b
6c
6d
6e
6f
7a
7b
7c
7d
7e
7f
cells
DMSO
7d
7b
4
Treatment
Fig. 1. Cytotoxic activity of compounds 4, 7b and 7d 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.
Isoniazid

B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
4743
Thin layer chromatography (TLC) was performed through out
1H NMR (DMSO-d6, 300 MHz)
d
: 10.21 (s, 1H, NH, disappeared
the reaction to optimize the reaction for purity and completion of
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.
on D2O exchange), 7.61 (d, J ¼ 8.5 Hz, 2H, phenyl), 7.34 (s, 1H,
thiazole C5), 7.24 (d, J ¼ 8.5 Hz, 2H, phenyl), 3.25 (m, 1H, isopropyl),
1.23 (d, J ¼ 8.5 Hz, 6H, CH3), 0.9 (s, 3H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 174.13 (amide C]O), 162.86
(thiazole C4), 154.43 (thiazole C2), 137.84 (C4 – phenyl), 134.53
(C2 and C6), 130.71 (C3 and C5), 130.35 (C1 – phenyl), 111.36 (thiazole
C5), 37.12 (tertiary-1C-isopropyl), 23.65 (terminal 2CH3 – iso-
propyl), 19.54 (CH3) ppm.
5.1.1. Synthesis of 4-isopropyl-1,3-thiazole-2-carbohydrazide (1)
Compound 1 was synthesized by refluxing a mixture of ethyl
4-isopropylthiazole-2-carboxylate (0.015 mol) with hydrazine
hydrate (1.6 mL) in absolute ethanol (20 mL) for 5 h. The reaction
mixture was cooled and the crystalline mass obtained was recrys-
tallised from ethanol and obtained as yellow crystals in 84% yield.
M.p. 130–132 ꢂC.
MS (%) 321.07 (Mþ 100.0), 323.07 (37.0), 322.07 (18.2), 324.07
(6.3), 325.06 (1.4), 323.08 (1.3).
5.1.2.4. Synthesis
of
4-isopropyl-N-(1-(4-nitrophenyl)ethy-
IR (KBr)
n
max, cmꢀ1: 3517/3335 (NH/NH2), 1673 (amide C]O).
: 9.8 (s, 1H, NH, disappeared on
lidene)thiazole-2-carbohydrazide (2d). Recrystallised from ethanol
as yellow crystals in 81% yield.
1H NMR (DMSO-d6, 300 MHz)
d
D2O exchange), 7.4 (s, 1H, thiazole C5), 4.5 (s, 2H, NH2, disappeared
on D2O exchange), 3.2 (m, 1H, isopropyl), 1.5 (d, J ¼ 8.5 Hz, 6H, CH3)
ppm.
M.p. 194–198 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3322 (NH), 1598 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 10.91 (s, 1H, NH, disappeared
13C NMR (DMSO-d6, 300 MHz)
d: 168.46 (thiazole C4), 164.10
on D2O exchange), 8.32 (d, 2H, phenyl), 8.12 (d, 2H, phenyl), 7.49
(s, 1H, thiazole C5), 3.18 (m, 1H, isopropyl), 2.1 (s, 3H, CH3), 1.35
(d, J ¼ 8.5 Hz, 6H, CH3) ppm.
(amide C]O), 155.21 (thiazole C2), 119.21 (thiazole C5), 36.11
(tertiary-1C-isopropyl), 22.01 (terminal 2CH3 – isopropyl) ppm.
MS (%) 185.06 (Mþ 100.0), 186.07 (7.7), 187.06 (4.6), 186.06 (1.9).
13C NMR (DMSO-d6, 300 MHz)
d: 165.25 (amide C]N), 160.95
(thiazole C4), 155.23 (thiazole C2), 154.32 (C4 – phenyl), 145.53 (C1 –
phenyl), 127.5 (C2 and C6), 119.32 (thiazole C5), 116.76 (C3 and C5),
31.07 (tertiary-1C-isopropyl), 22.32 (terminal 2CH3 – isopropyl),
14.94 (CH3) ppm.
5.1.2. General procedure for the synthesis of N-(substituted)-4-
isopropyl-thiazole-2-carbohydrazide (2a–2g)
Equimolar quantities of 4-isopropyl-1,3-thiazole-2-carbohy-
drazide 1 and different substituted ketones were refluxed in
alcohol for 4 h in the presence of few drops of glacial acetic acid.
The solvent was evaporated and the product was poured onto cold
water, filtered and dried. The crude solid was recrystallised in
appropriate solvent systems to give the products.
MS (%) 332.09 (Mþ 100.0), 333.10 (16.5), 334.09 (4.8), 333.09
(2.3), 334.10 (2.0).
5.1.2.5. Synthesis of 4-isopropyl-N-(1-(4-bromophenyl)ethylidene)-
thiazole-2-carbohydrazide (2e). Recrystallised from ethanol as
yellow crystals in 66% yield.
5.1.2.1. Synthesis of 4-isopropyl-N-(propan-2-ylidene)thiazole-2-
carbohydrazide (2a). Recrystallised from ethanol and obtained as
pale yellow crystals in 75% yield.
M.p. 196–199 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3341 (NH), 1643 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 10.19 (s,1H, NH, disappeared on
M.p. 208–210 ꢂC.
D2O exchange), 7.65 (s, 1H, thiazole C5), 7.51 (m, 4H, phenyl), 3.43
IR (KBr)
n
max, cmꢀ1: 3251 (NH), 1623 (amide C]O).
(m, 1H, isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3), 0.9 (s, 3H, CH3) ppm.
1H NMR (DMSO-d6, 300 MHz)
d: 10.21 (s, 1H, NH, disappeared
13C NMR (DMSO-d6, 300 MHz)
d: 176.32 (amide C]O), 162.43
on D2O exchange), 7.41 (s, 1H, thiazole C5), 3.23 (m, 1H, isopropyl),
(thiazole C4), 155.34 (thiazole C2), 133.32 (C1 – phenyl), 131.11 (C2
and C6), 129.08 (C3 and C5), 122.22 (C4 – phenyl), 112.56 (thiazole
C5), 38.09 (tertiary-1C-isopropyl), 23.32 (terminal 2CH3 – iso-
propyl), 19.07 (CH3) ppm.
1.31 (d, J ¼ 8.5 Hz, 6H, CH3), 0.91 (s, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 170.21 (amide C]O), 162.21
(thiazole C4), 152.13 (thiazole C2), 114.19 (thiazole C5), 38.12
(tertiary-1C-isopropyl), 23.12 (terminal 2CH3 – isopropyl), 22.12
(CH3), 15.51 (CH3) ppm.
MS (%) 367.02 (Mþ 100.0), 365.02 (97.7), 366.02 (17.8), 368.02
(17.1), 369.01 (4.3), 369.02 (1.7), 367.03 (1.2), 368.01 (1.1).
MS (%) 225.09 (Mþ 100.0), 226.10 (11.0), 227.09 (4.7), 226.09 (1.9).
5.1.2.6. Synthesis of 4-isopropyl-N-(1-p-tolylethylidene)thiazole-2-
carbohydrazide (2f). Recrystallised from ethanol as yellow crystals
in 60% yield.
5.1.2.2. Synthesis of 4-isopropyl-N-(phenylethylidene)thiazole-2-car-
bohydrazide (2b). Recrystallised from aqueous DMF as yellow
crystals in 65% yield.
M.p. 185–188 ꢂC.
M.p. 234–236 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3332 (NH), 1621 (amide C]O).
IR (KBr)
n
max, cmꢀ1: 3302 (NH), 1639 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 10.54 (s, 1H, NH, disappeared
1H NMR (DMSO-d6, 300 MHz)
d: 10.69 (s, 1H, NH, disappeared
on D2O exchange), 7.51 (d, 2H, phenyl), 7.23 (s, 1H, thiazole C5), 7.13
(d, 2H, phenyl), 3.21 (m, 1H, isopropyl), 1.38 (d, J ¼ 8.5 Hz, 6H, CH3),
2.12 (s, 3H, CH3), 0.94 (s, 3H, CH3) ppm.
on D2O exchange), 7.24 (s, 1H, thiazole C5), 3.21 (m, 1H, isopropyl),
1.24 (d, J ¼ 8.5 Hz, 6H, CH3), 0.93 (s, 3H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 168.27 (amide C]O), 162.21
13C NMR (DMSO-d6, 300 MHz)
d: 170.11 (amide C]O), 161.19
(thiazole C4), 131.23 (C4 – phenyl), 134.23 (C1 – phenyl), 129.14 (C2
and C6), 128.53 (C3 and C5), 114.19 (thiazole C5), 38.13 (tertiary-1C-
isopropyl), 23.12 (terminal 2CH3 – isopropyl), 19.5 (CH3) ppm.
MS (%) 287.11 (Mþ 100.0), 288.11 (18.2), 289.11 (5.0), 289.12 (1.3).
(thiazole C4), 157.32 (thiazole C2), 143.1(C4 – phenyl), 129.00 (C2,3,5,6
– phenyl), 114.21 (thiazole C5), 38.11 (tertiary-1C-isopropyl), 24.11
(CH3), 23.47 (terminal 2CH3 – isopropyl), 19.13 (CH3) ppm.
MS (%) 301.12 (Mþ 100.0), 302.13 (17.6), 303.12 (4.5), 303.13
(2.0), 302.12 (1.9).
5.1.2.3. Synthesis of 4-isopropyl-N-(1-(4-chlorophenyl)ethy-
lidene)thiazole-2-carbohydrazide (2c). Recrystallised from ethanol
as yellow crystals in 61% yield.
5.1.2.7. Synthesis of 4-isopropyl-N-(1-(4-hydroxyphenyl)ethy-
lidene)thiazole-2-carbohydrazide (2g). Recrystallised from ethanol
as yellow crystals in 56% yield.
M.p. 183–186 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3323 (NH), 1636 (amide C]O).
M.p. 176–178 ꢂC.

4744
B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
IR (KBr)
n
max, cmꢀ1: 3494 (OH), 3329 (NH), 1613 (amide C]O).
: 10.23 (s, 1H, NH, disappeared
room temperature. The deposited pale yellow solid was filtered,
1H NMR (DMSO-d6, 300 MHz)
d
washed and recrystallised from ethanol and obtained as yellow
crystals in 75% yield. M.p. 202–204 ꢂC.
on D2O exchange), 7.12 (d, 2H, phenyl), 7.11 (s, 1H, thiazole C5), 6.02
(d, 2H, phenyl), 5.11 (s, 1H, OH), 3.21 (m, 1H, isopropyl), 1.32
(d, J ¼ 8.5 Hz, 6H, CH3), 0.91 (s, 3H, CH3) ppm.
IR (KBr)
(amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 10.21 (s, 1H, NH, disappeared
n
max, cmꢀ1: 3347 (NH), 1687 (acetyl C]O), 1623
13C NMR (DMSO-d6, 300 MHz)
d: 170.54 (amide C]O), 164.54
(C4 – phenyl), 162.34 (thiazole C4), 153.45 (thiazole C2), 130.08
(C2 and C6), 119.66 (C3 and C5), 114.87 (thiazole C5), 38.97 (tertiary-
1C-isopropyl), 23.11 (terminal 2CH3 – isopropyl), 19.13 (CH3) ppm.
MS (%) 303.10 (Mþ 100.0), 304.11 (16.5), 305.10 (4.7), 304.10
(1.9), 305.11 (1.8).
on D2O exchange), 9.76 (s, 1H, amide NH, disappeared on D2O
exchange), 7.23 (s, 1H, thiazole C5), 3.15 (m, 1H, isopropyl), 2.14 (s,
3H, CH3), 1.29 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 171.34 (acetyl C]O), 167.54
(amide C]O), 162.75 (thiazole C4), 155.34 (thiazole C2), 111.34
(thiazole C5), 36.22 (tertiary-1C-isopropyl), 25.3 (CH3), 23.12
(terminal 2CH3 – isopropyl) ppm.
5.1.3. Synthesis of 5-(4-isopropylthiazol-2-yl)-1,3,4-oxadiazole-2-
thiol (3)
MS (%) 227.07 (Mþ 100.0), 228.08 (10.0), 229.07 (4.6%), 228.07
(1.9).
Acid hydrazide 1 (0.003 mol) was dissolved in a solution of
potassium hydroxide (0.006 mol) in water (2 mL) and ethanol
(20 mL). Carbon disulfide (2 mL) was then added while stirring and
the reaction mixture was heated under reflux for 8 h. The solvents
were removed under reduced pressure; the residue was treated
with water and then filtered. The filtrate was cooled, neutralized to
pH 6 using dilute hydrochloric acid and the separated product was
filtered, washed with water, dried and recrystallised from benzene
as yellow crystals in 86% yield.
5.1.6. General procedure for the synthesis of N-(arylidene)-4-
isopropyl-1,3-thiazole-2-carbohydrazide (6a–6f)
Equimolar quantities of 4-isopropyl-1,3-thiazole-2-carbohy-
drazide 1 and substituted aldehydes were refluxed in alcohol for
3 h in the presence of few drops of glacial acetic acid. The solvent
was evaporated and the product was poured on cold water, filtered
and dried. The crude solid was recrystallised in appropriate solvent
systems to give the products.
M.p. 208–210 ꢂC.
IR (KBr)
1H NMR (DMSO-d6, 300 MHz)
thiazole C5), 3.21 (m,1H, isopropyl),1.24 (d, J ¼ 8.5 Hz, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
: 177.5 (oxadiazole C2), 162.49
n
max, cmꢀ1: 2765 (SH), 1670 (C]N).
d: 14.31 (s, 1H, SH), 7.41 (s, 1H,
5.1.6.1. Synthesis of N-benzylidene-4-isopropylthiazole-2-carbohy-
drazide (6a). Recrystallised from aqueous DMF as yellow crystals in
d
84% yield.
(thiazole C4), 154.45 (thiazole C2), 148.32 (oxadiazole C5), 112.33
(thiazole C5), 39.04 (tertiary-1C-isopropyl), 23.45 (terminal 2CH3 –
isopropyl) ppm.
M.p. 198–200 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3194 (NH), 1643 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 11.97 (s,1H, NH, disappeared on
MS (%) 227.02 (Mþ 100.0), 228.02 (11.5), 229.01 (9.0).
D2O exchange), 8.32 (s,1H, –N]CH–Ar), 7.2–7.8 (5H of phenyl), 7.28
(s, 1H, thiazole C5), 3.24 (m, 1H, isopropyl) ppm.
5.1.4. Synthesis of 4-amino-5-(4-isopropyl-1,3-thiazol-2-yl)-4H-
1,2,4-triazole-3-thiol (4)
To a solution of potassium hydroxide (0.0067 mol) in absolute
ethanol (30 mL), 4-isopropyl-1,3-thiazole-2-carbohydrazide
13C NMR (DMSO-d6, 300 MHz)
d: 164.54 (thiazole C4), 161.22
(amide C]O), 155.33 (thiazole C2), 147.64 (CH]N),), 134.2 (phenyl
C1), 131.2 (phenyl C4), 129.7 (phenyl C2 and C6), 126.12 (phenyl C3
and C5), 122.34 (thiazole C5), 36.22 (tertiary-1C-isopropyl), 23.12
(terminal 2CH3 – isopropyl) ppm.
1
(0.003 mol) and carbon disulphide (0.006 mol) were added and the
mixture was agitated for 16 h. To the resulting solution anhydrous
ether was added and the precipitated potassium dithiocarbazinate
was collected by filtration, washed with ether and dried under
vacuum. The potassium salt was obtained in quantitative yield and
was used in the next step without further purification. A suspension
of the potassium salt, hydrazine hydrate (1.5 mL) and water (1.0 mL)
was heated under reflux for 5 h, hydrogen sulphide evolved and
homogeneous solution resulted which was diluted with 50 mL water
and subsequent acidification with dilute acetic acid gave a white
precipitate which was filtered, washed with water and recrystallised
from aqueous DMF and obtained as pale yellow crystals in 61% yield.
M.p. 250–252 ꢂC.
MS (%) 275.11 (Mþ 100.0), 276.11 (17.1), 277.11 (5.0%), 277.12
(1.1).
5.1.6.2. N-(3,4,5-Trimethoxybenzylidene)-4-isopropyl-1,3-thiazole-2-
carbohydrazide (6b). Recrystallised from aqueous DMF as yellow
crystals in 81% yield.
M.p. 210–212 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3180 (NH), 1616 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 11.97 (s,1H, NH, disappeared on
D2O exchange), 8.32 (s, 1H, –N]CH–Ar), 7.81 (d, 2H, J ¼ 8.5 Hz, C2
and C5-H), 7.28 (s, 1H, thiazole C5), 3.24 (m, 1H, isopropyl), 2.33
(s, 9H, OCH3) ppm.
IR (KBr)
n
max, cmꢀ1: 3353 (NH), 3248 (NH2).
:14.09(s,1H,NH–C]S), 7.11(s,1H,
13C NMR (DMSO-d6, 300 MHz)
d: 164.33 (amide C]O), 162.67
1HNMR(DMSO-d6, 300 MHz)
d
(thiazole C4), 155.43 (thiazole C2), 151.1 (phenyl C3 and C5), 143.23
(CH]N), 141.3 (phenyl C4), 128.2 (phenyl C1), 115.23 (thiazole C5),
106.2 (phenyl C2), 51.2 (3ꢂ CH3), 38.91 (tertiary-1C-isopropyl), 23.23
(terminal 2CH3 – isopropyl) ppm.
thiazole C5), 6.01 (s, 2H, NH2, disappeared on D2O exchange), 3.15
(m, 1H, isopropyl), 1.23 (d, J ¼ 8.5 Hz, 6H, CH3), 0.9 (s, 6H, CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 185.24 (C]S), 162.21 (thiazole
C4), 155.45 (thiazole C2), 153.15 (triazole C5), 144.27 (triazole C2),
114.19 (thiazole C5), 38.123 (tertiary-1C-isopropyl), 23.12 (terminal
2CH3 – isopropyl), 22.12 (CH3) ppm.
MS (%) 363.13 (Mþ 100.0), 364.13 (18.8), 365.12 (4.5), 365.13
(2.8), 364.12 (1.9).
MS (%) 241.05 (Mþ 100.0), 243.04 (9.1), 242.05 (8.8), 242.04
(3.4), 244.04 (1.0).
5.1.6.3. N-(4-Dimethylaminobenzylidene)-4-isopropyl-1,3-thiazole-
2-carbohydrazide (6c). Recrystallised from aqueous DMF as yellow
crystals in 82% yield.
5.1.5. Synthesis of N-acetyl-4-isopropylthiazole-2-carbohydrazide
(5)
Acid hydrazide 1 (0.003 mol) was warmed with acetic anhy-
dride (5 mL) for 1 h and then the mixture was allowed to attain
M.p. 194–200 ꢂC.
IR (KBr)
1H NMR (DMSO-d6, 300 MHz)
D2O exchange), 8.11 (s, 1H, –N]CH–Ar), 7.32 (d, 2H, J ¼ 8.5 Hz,
n
max, cmꢀ1: 3194 (NH), 1606 (amide C]O).
d: 11.65 (s,1H, NH, disappeared on

B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
4745
phenyl C2 and C6-H), 7.12 (s, 1H, thiazole C5), 6.62 (d, 2H, phenyl C3
and C5-H), 3.26 (m, 1H, isopropyl), 2.87 (s, 6H, N–(CH3)2) ppm.
water and the mixture was stirred for further 30 min. The separated
product was filtered, washed with water, dried and recrystallised in
appropriate solvent systems to give the products.
13C NMR (DMSO-d6, 300 MHz)
d: 164.11 (amide C]O), 163.51
(thiazole C4), 155.43 (thiazole C2), 141.12 (CH]N), 139.09 (phenyl
C4), 134.87 (phenyl C3 and C5), 130.6 (phenyl C1), 126.09 (phenyl C2
and C6), 113.54 (thiazole C5), 40.3 (N–(CH3)2), 35.21 (tertiary-1C-
isopropyl), 22.12 (terminal 2CH3 – isopropyl) ppm.
MS (%) 316.14 (Mþ 100.0), 317.14 (18.4), 318.13 (4.5), 318.14 (2.0),
317.13 (1.5).
5.1.7.1. 1-(5-(4-Isopropylthiazol-2-yl)-2-phenyl-1,3,4-oxadiazol-
3(2H)-yl)ethanone (7a). Recrystallised from ethanol as pale brown
crystals in 60% yield.
M.p. 154–156 ꢂC.
IR (KBr)
n
max, cmꢀ1: 1665 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 7.32 (s, 1H, thiazole C5), 7.23
5.1.6.4. N-(4-Hydroxybenzylidene)-4-isopropyl-1,3-thiazole-2-car-
bohydrazide (6d). Recrystallised from aqueous DMF as pale yellow
crystals in 72% yield.
(d, 5H, Ar-H), 6.64 (s, oxadiazole C2-H), 3.26 (m, 1H, isopropyl), 2.21
(s, 3H, CH3), 1.23 (d, 6H, terminal CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 170.11 (acetyl C]O), 160.98
M.p. 189–194 ꢂC.
(thiazole C4), 155.69 (thiazole C2), 144.76 (oxadiazole C5), 128.11
(phenyl C4), 125.98 (phenyl C3 and C5), 123.11 (phenyl C2,C6), 111.09
(thiazole C5), 76.21 (oxadiazole C2), 38.12 (tertiary-1C-isopropyl),
23.54 (acetyl CH3), 23.24 (terminal 2CH3 – isopropyl) ppm.
MS (%) 315.10 (Mþ 100.0), 316.11 (17.6), 317.10 (4.7), 317.11 (2.0),
316.10 (1.9).
IR (KBr)
n
max, cmꢀ1: 3483 (OH), 3232 (NH), 1621 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 11.21 (s,1H, NH, disappeared on
D2O exchange), 8.32 (s, 1H, –N]CH–Ar), 7.16 (d, 2H, J ¼ 8.5 Hz,
phenyl C2 and C6-H), 7.12 (s, 1H, thiazole C5), 6.82 (d, 2H, phenyl C3
and C5-H), 5.09 (s, 1H, OH), 3.26 (m, 1H, isopropyl) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 166.87 (amide C]O), 165.87
(phenyl C4), 163.11 (thiazole C4), 157.34 (thiazole C2), 141.23
(CH]N), 123.09 (phenyl C1), 121.66 (phenyl C2 and C6), 113.43
(thiazole C5), 111.1 (phenyl C3 and C5), 35.45 (tertiary-1C-isopropyl),
22.43 (terminal 2CH3 – isopropyl) ppm.
5.1.7.2. 1-(5-(4-Isopropylthiazol-2-yl)-2-(3,4,5-trimethoxyphenyl)-
1,3,4-oxadiazol-3(2H)-yl)ethanone
(7b). Recrystallised
from
ethanol as pale brown crystals in 67% yield.
M.p. 188–192 ꢂC.
MS (%) 289.09 (Mþ 100.0), 290.09 (17.3), 291.08 (4.5), 291.10 (1.1).
IR (KBr)
n
max, cmꢀ1: 1650 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 7.01 (s, 1H, thiazole C5), 6.63
5.1.6.5. N-(4-Nitrobenzylidene)-4-isopropyl-1,3-thiazole-2-carbohy-
drazide (6e). Recrystallised from aqueous DMF as pale yellow
crystals in 66% yield.
(s, oxadiazole C2-H), 6.12 (d, 2H, Ar-H), 4.01 (s, 9H, OCH3), 3.12
(m, 1H, isopropyl), 2.21 (s, 3H, CH3), 1.29 (d, 6H, terminal CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 168.11 (acetyl C]O), 162.11
M.p. 214–216 ꢂC.
(thiazole C4), 154.11 (oxadiazole C5), 152.01 (thiazole C2), 151.11
(phenyl C3,C5), 138.01 (phenyl C4), 134.34 (phenyl C1), 116.76
(thiazole C5), 103.32 (phenyl C2,C6), 76.36 (oxadiazole C2), 56.6 (3C,
OCH3) 38.91 (tertiary-1C-isopropyl), 23.41 (terminal 2CH3 – iso-
propyl), 23.21 (acetyl CH3) ppm.
IR (KBr)
n
max, cmꢀ1: 3226 (NH), 1632 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d: 11.32 (s, 1H, NH, disappeared
on D2O exchange), 8.72 (d, 2H, phenyl C3 and C5-H), 8.21 (s, 1H,
–N]CH–Ar), 7.98 (d, 2H, J ¼ 8.5 Hz, phenyl C2 and C6-H), 7.12 (s, 1H,
thiazole C5), 3.26 (m, 1H, isopropyl) ppm.
MS (%) 405.14 (100.0), 406.14 (21.8), 407.13 (4.5), 407.14 (3.5),
406.13 (1.1).
13C NMR (DMSO-d6, 300 MHz)
d: 165.76 (amide C]O), 165.42
(thiazole C4), 155.34 (thiazole C2), 154.99 (phenyl C4), 143.012
(phenyl C1), 141.88 (CH]N), 132.54 (phenyl C2 and C6), 123.1
(phenyl C3 and C5), 111.1 (thiazole C5), 33.56 (tertiary-1C-isopropyl),
23.65 (terminal 2CH3 – isopropyl) ppm.
5.1.7.3. 1-(5-(4-Isopropylthiazol-2-yl)-2-(4-dimethylaminophenyl)-
1,3,4-oxadiazol-3(2H)-yl)ethanone (7c). Recrystallised from ethanol
as pale brown crystals in 62% yield.
MS (%) 318.08 (100.0), 319.08 (17.7), 320.07 (4.5), 320.09 (1.1).
M.p. 182–185 ꢂC.
IR (KBr)
n
max, cmꢀ1: 1634 (amide C]O).
5.1.6.6. N-(2,3-Dichloro-benzylidene)-
4-isopropyl-1,3-thiazole-2-
1H NMR (DMSO-d6, 300 MHz)
d: 7.16 (s, 1H, thiazole C5), 7.01
carbohydrazide (6f). Recrystallised from aqueous DMF as pale
yellow crystals in 66% yield.
(s, 2H, Ar-H), 6.67 (m, 2H, Ar-H), 6.34 (s, oxadiazole C2-H), 3.32
(m, 1H, isopropyl), 2.91 (s, 6H, N–(CH3)2), 2.21 (s, 3H, CH3), 1.43
(d, 6H, terminal CH3) ppm.
M.p. 208–213 ꢂC.
IR (KBr)
n
max, cmꢀ1: 3216 (NH), 1632 (amide C]O).
13C NMR (DMSO-d6, 300 MHz)
d: 166.34 (acetyl C]O), 162.23
1H NMR (DMSO-d6, 300 MHz)
d
: 11.32 (s,1H, NH, disappeared on
(thiazole C4), 159.65 (oxadiazole C5), 152.12 (thiazole C2), 148.98
(phenyl C4), 129.34 (phenyl C1), 128.11 (phenyl C2, C6), 116.76
(thiazole C5), 115.36 (phenyl C3, C5), 78.87 (oxadiazole C2), 41.6
(s, 2C, N–(CH3)2), 38.41 (tertiary-1C-isopropyl), 23.33 (acetyl CH3),
23.11 (terminal 2CH3 – isopropyl) ppm.
D2O exchange), 8.43 (s, 1H, –N]CH–Ar), 7.64 (d, H, phenyl C2), 7.43
(d, H, phenyl C6), 7.13 (d, H, phenyl C5-H), 7.12 (s, 1H, thiazole C5),
3.26 (m, 1H, isopropyl) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 171.12 (amide C]O), 162.65
(thiazole C4), 155.68 (thiazole C2), 143.11(CH]N), 135.1 (phenyl C3
and C4), 133.09 (phenyl C1), 132.54 (phenyl C2), 124.32 (phenyl C5),
114.43 (thiazole C5), 38.96 (tertiary-1C-isopropyl), 23.11 (terminal
2CH3 – isopropyl) ppm.
MS (%) 358.15 (Mþ 100.0), 359.15 (20.6), 360.14 (4.5), 360.15
(2.7), 359.14 (1.5), 361.15 (1.0).
5.1.7.4. 1-(5-(4-Isopropylthiazol-2-yl)-2-(4-hydroxyphenyl)-1,3,4-
oxadiazol-3(2H)-yl)ethanone (7d). Recrystallised from ethanol as
pale brown crystals in 60% yield.
MS (%) 341.02 (Mþ 100.0), 343.01 (68.5), 342.02 (16.1), 345.01
(13.2), 344.02 (9.9), 346.01 (2.2), 344.01 (2.0), 343.02 (1.6), 342.01 (1.1).
M.p. 178–182 ꢂC.
5.1.7. General procedure for the synthesis of 3-acetyl-5-(4-
isopropylthiazole)-2-substituted-2,3-dihydro-1,3,4-oxadiazoles
(7a–7f)
A mixture of 6a–6f (0.003 mol) and acetic anhydride (10 mL)
was heated under reflux for 4 h. After the reaction mixture attained
room temperature, excess acetic anhydride was decomposed by
IR (KBr)
n
max, cmꢀ1: 3503 (OH), 1632 (amide C]O).
1H NMR(DMSO-d6, 300 MHz)
d:7.32(s,1H, thiazoleC5), 7.11 (m, 2H,
Ar-H), 6.64 (s, oxadiazole C2-H), 6.62 (m, 2H, Ar-H), 6.11 (s,1H, OH), 3.45
(m, 1H, isopropyl), 2.21 (s, 3H, CH3), 1.23 (d, 6H, terminal CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 166.98 (acetyl C]O), 162.21
(thiazole C4), 158.12 (oxadiazole C5), 157.21 (phenyl C4), 152.11

4746
B.P. Mallikarjuna et al. / European Journal of Medicinal Chemistry 44 (2009) 4739–4746
(thiazole C2), 131.39 (phenyl C1), 128.76 (phenyl C2, C6), 116.65
(thiazole C5), 112.43 (phenyl C3, C5), 75.76 (oxadiazole C2), 38.54
(tertiary-1C-isopropyl), 23.87 (terminal 2CH3 – isopropyl), 23.34
(acetyl CH3) ppm.
determined by broth dilution assay [22–24] and is defined as the
lowest concentration of drug, which inhibits ꢁ99% 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 ꢂC 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.
MS (%) 331.10 (Mþ 100.0), 332.10 (19.3), 333.09 (4.5), 333.11 (1.5).
5.1.7.5. 1-(5-(4-Isopropylthiazol-2-yl)-2-(4-nitrophenyl)-1,3,4-oxa-
diazol-3(2H)-yl)ethanone (7e). Recrystallised from ethanol as pale
brown crystals in 77% yield.
M.p. 168–172 ꢂC.
IR (KBr)
n
max, cmꢀ1: 1650 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d
: 8.32 (m, 2H, Ar-H), 7.87 (s, 1H,
thiazole C5), 7.32 (m, 2H, Ar-H), 6.61 (s, oxadiazole C2-H), 3.32
(m, 1H, isopropyl), 2.21 (s, 3H, CH3), 1.13 (d, 6H, terminal CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d
: 165.87 (thiazole C4), 161.01
5.2.3. MTT assay for cell viability
(acetyl C]O), 152.11 (thiazole C2), 151.34 (oxadiazole C5), 143.01
(phenyl C1, C4), 129.12 (phenyl C2, C6), 121.01 (phenyl C3, C5), 114.11
(thiazole C5), 77.65 (oxadiazole C2), 37.11 (tertiary-1C-isopropyl),
23.11 (acetyl CH3), 22.21 (terminal 2CH3 – isopropyl) ppm.
MS (%) 360.09 (Mþ 100.0), 361.09 (19.7), 362.09 (5.8), 362.10 (1.5).
Toxicity of compounds 4, 7b, and 7d in A549 cell lines in
the presence of 10% and 0.2% FBS respectively, was deter-
mined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium
bromide reduction assay [25,26]. The compounds were dissolved in
DMSO at 10 mM concentration and stored at ꢀ20ꢂ. The dilutions
were made in culture medium before treatment.
5.1.7.6. 1-(5-(4-Isopropylthiazol-2-yl)-2-(2,3-dichlorophenyl)-1,3,4-
oxadiazol-3(2H)-yl)ethanone (7f). Recrystallised from ethanol as
pale brown crystals in 56% yield.
Acknowledgements
M.p. 155–158 ꢂC.
We thank the management of St. Johns Pharmacy College, Ban-
galore, 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.
IR (KBr)
n
max, cmꢀ1: 1652 (amide C]O).
1H NMR (DMSO-d6, 300 MHz)
d
: 7.11–7.34 (m, 3H, Ar-H), 7.21
(s,1H, thiazole C5), 6.62 (s, oxadiazole C2-H), 3.65 (m,1H, isopropyl),
2.21 (s, 3H, CH3), 1.31 (d, 6H, terminal CH3) ppm.
13C NMR (DMSO-d6, 300 MHz)
d: 165.28 (acetyl C]O), 161.33
(thiazole C4), 157.43 (thiazole C2), 154.09 (oxadiazole C5), 144.23
(phenyl C1), 131.01 (phenyl C3), 128.49 (phenyl C4,5), 126.87 (phenyl
C6), 123.12 (phenyl C2,), 111.34 (thiazole C5), 76.54 (oxadiazole C2),
38.45(tertiary-1C-isopropyl), 23.35 (acetyl CH3), 21.01(terminal
2CH3 – isopropyl) ppm.
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(1.3), 384.02 (1.1).
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the lowest concentrations of compound that completely inhibited
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