Synthesis and anti-tubercular activity of a series of 2-sulfonamido/ trifluoromethyl-6-substituted imidazo[2,1-b]-1,3,4-thiadiazole derivatives

Article abstract of DOI:10.1016/j.bmc.2004.07.060

A series of 2-sulfonamido/trifluoromethyl-6-(4′-substituted aryl/heteroaryl)imidazo[2,1-b]-1,3,4-thiadiazole derivatives (II) have been synthesized by reaction of 2-amino-5-sulfonamido/trifluoromethyl-1,3,4- thiadiazoles and an appropriate α-haloaryl/hete

Full text of DOI:10.1016/j.bmc.2004.07.060

Bioorganic & Medicinal Chemistry 12(2004) 5651–5659
Synthesis and anti-tubercular activity of a series of
2-sulfonamido/trifluoromethyl-6-substituted imidazo-
[2,1-b]-1,3,4-thiadiazole derivatives
Andanappa K. Gadad,* Malleshappa N. Noolvi and Rajshekhar V. Karpoormath
Department of Medicinal Chemistry, College of Pharmacy, JN Medical College, Nehru Nagar, Belgaum 590 010, Karnataka, India
Received 18 June 2004; revised 28 July 2004; accepted 28 July 2004
Available online 3 September 2004
This paper is dedicated to Professor C. S. Mahajanshetti on the occasion of his 73rd birthday
Abstract—A series of 2-sulfonamido/trifluoromethyl-6-(40-substituted aryl/heteroaryl)imidazo[2,1-b]-1,3,4-thiadiazole derivatives
(II) have been synthesized by reaction of 2-amino-5-sulfonamido/trifluoromethyl-1,3,4-thiadiazoles and an appropriate a-halo-
aryl/heteroaryl ketones. Further 5-bromo (III), 5-thiocyanato (IV), 5-gaunylhydrazone (V) derivatives were synthesized in order
1
to study the effect of these substituents on biological activity. Structures of these compounds were established by IR, H NMR,
13C NMR, Mass and HRMS. The selected compounds were evaluated for their preliminary in vitro anti-tuberculosis activity against
Mycobacterium tuberculosis H37Rv strain using radiometric BACTEC and broth dilution assay methods. The results show that
compounds 5, 7, 8, 10 and 12 exhibited moderate to good anti-tubercular activity with percentage inhibition of 29, 43, 58, 31
and 41, respectively, at a MIC of > 6.25lg/mL. Compound 18 showed a MIC of 20lg/mL.
ꢀ 2004 Elsevier Ltd. All rights reserved.
1. Introduction
gency in 1993, for the first time an infectious disease
achieved that dubious distinction.3–5 Approximately,
80% of TB cases are found in 23 countries; the highest
rates of incidence being found in South-East Asia and
Africa.6
Tuberculosis (TB) is a chronic necrotizing bacterial
infection with wide variety of manifestations caused by
Mycobacterium tuberculosis, which has been a scourge
of humanity for thousands of years and remains one
of the prevalent health tribulations in the world.1 To-
day, TB is among the top five causes of global mortality.
The history of TB highlights manꢀs struggle for existence
against a disease that dates from antiquity and is the
story of failures and successes of disaster and hope.2
This saddle is further augmented by HIV infection,
which impairs the immune system and allows large num-
ber of people already infected with TB to progress to ac-
tive disease. The exponential increase in TB cases has
been greatest in areas with high prevalence of HIV
infections.7 The active TB is currently treated with a
four-drug regimen comprising isoniazid, rifampicin, pyr-
azinamide and ethambutol for a period of at least six
months.8–10 The long treatment regimen can be difficult
to fully complete, fueling the development of more infec-
tious and virulent multidrug resistant (MDR) strains of
TB, which shows very high mortality.11 Such MDR-TB
is difficult and expensive to treat and is not always
curable, alternative combination treatment of five-drug
regimen is recommended initially, including both
ethambutol and rifampicin. Later, the treatment will
be modified on the basis of results of susceptibility tests.
In such patients, other anti-tubercular drugs so called
second line drugs (ethionamide, cycloserine, capreomy-
cin, kanamycin, p-aminosalicylic acid and some time
It has been estimated that approximately one third of
the worldꢀs population is infected with the bacillus,
and that each year 8 million people develop active dis-
ease and 2million die of the disease. In developing coun-
tries where rates of both infection and active disease
have always been high, the number of cases skyrocketed,
so dramatic was the increase that the World Health
Organization (WHO) declared TB a global health emer-
Keywords: Imidazo[2,1-b]-1,3,4-thiadiazoles; a-Haloaryl/heteroaryl
ketones; Anti-tubercular activity; BACTEC assay.
*
Corresponding author. Tel.: +91 831 2471399/2470674; fax: +91 831
2472387; e-mail: akgadad@rediffmail.com
0968-0896/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2004.07.060

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A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
clofazimine) are variably combined with each other and
with first line drugs with the aim to overcome resistance.
MDR-TB often requires prolonged treatment some-
times up to 24 months12 and thus poses a major chal-
lenge to the control of the disease worldwide.
2. Chemistry
The synthesis of the imidazo[2,1-b]-1,3,4-thiadiazoles
(II, Scheme 1) was carried out by the condensation of
(I) with a a-haloaryl/heteroaryl ketone under reflux in
ethanol. It is well established35 that this reaction pro-
ceeds via the intermediate iminothiadiazole (IA), which
under reflux temperature spontaneously underwent ring
closer to form the desired fused heterocycle (II) with
good yields. The electronic and steric factors at 5th posi-
tion of 2-amino-5-substituted-1,3,4-thiadiazole are cru-
cial in determining the course of its reaction with
substituted a-haloaryl/heteroaryl ketones.36 The sulfo-
namido and trifluoromethyl groups are strongly electro-
negative and consequently its inductive effects impart
less nucleophilic character to the nitrogen at 4th position
of the 1,3,4-thiadiazole. Thus the alkylation of this thia-
diazole occurs at 3rd nitrogen with subsequent ring clo-
ser to form the corresponding bridgehead nitrogen
heterocyclic system. The various a-haloaryl/heteroaryl
ketones were prepared by the bromination of corre-
sponding ketones using well-established Friedel–Craftꢀs
reaction.37 Thus obtained 2-sulfonamido/trifluoro-
methyl-6-aryl/heteroaryl-imidazo[2,1-b]-1,3,4-thiadiazole
derivatives were subjected to electrophilic substitution
reaction38 at the fifth position with bromine in the pres-
ence of sodium acetate in acetic acid to obtain 5-bromo
derivative (III). 5-Thiocyanato (IV), 5-guanylhydrazone
(V) derivatives were prepared by earlier reported
methods.33–35
There is now recognition that innovative drugs to com-
bat TB are urgently required. With the completion of
the genome of M. tuberculosis comes the promise of a
new generation of potent drugs to combat the emerging
epidemic of TB. The emphasis of mycobacterial research
now has shifted from gene hunting to interpretation of
the biology of the whole organism in an effort to better
define which activities is likely to be critical to survival
and thus amenable to the development of new drugs.13
In this regard, however, there have been few additions
of some promising new anti-tuberculosis agents, such
as the long acting rifamycins,14,15 fluoroquinolones,16–18
oxazolidinones19,20 and nitroimidazopyrans21 to the
existing main-line drugs.
The development of sulfonamides is one of the most fas-
cinating and useful areas in medicinal chemistry. The
discovery of sulfonamides as antibacterial agents in
early 1930ꢀs was the beginning of the present chemothera-
peutic agents. The sulfonamides have a relatively broad
antibacterial spectrum with high activity profile against
pneumococci, streptococci, staphylococci, meningococci
and shigelle.22 The sulfonamido group (–SO2NH2) is a
common pharmacophore found in various biologically
active molecules, enzyme inhibitors and receptor
antagonists.23,24
3. Biological activity
Fluorinated compounds in general and fluorinated
heterocyclic compounds in particular are the focus of
much interest in modern medicinal chemistry. The tri-
fluoromethyl group (–CF3) is an important structural
moiety in diverse classes of bioactive organic molecules,
which exhibited wide ranging biological properties.25–27
Many efficient methods for the introduction of a tri-
fluoromethyl group into organic molecules have been
developed. The electronegativity of fluorine can have a
significant effect on the basicity or acidity of neighbour-
ing groups and on the electron distribution, and can
change the overall reactivity and stability of a mole-
cule.28 The CF3 group has a larger van der Waals radius
than that of a CH3 group and the same electronegativity
as oxygen. The CF3 substituted compounds have been
reported to possess biological activities such as herbi-
cides, fungicides, analgesic agents, antipyretic agents
and anticancer agents.29–32
In vitro evaluation of the anti-tuberculosis activity was
carried out at NIH within the Tuberculosis Acquisition
Antimicrobial Coordinating Facility (TAACF) screen-
ing program, Alabama, USA and Haffkine Institute
for Training, Research and Testing, Mumbai, India.
Minimum Inhibitory Concentration (MIC) was deter-
mined against M. tuberculosis strain H37Rv by using
the radiometric BACTEC39,40 and broth dilution41,42
assay methods, respectively. The purpose of the screen-
ing program is to provide a resource whereby new exper-
imental compounds can be tested for their capacity to
inhibit the growth of virulent M. tuberculosis.
4. Results and discussion
We have synthesized a series of nineteen derivatives of
imidazo[2,1-b]-1,3,4-thiadiazole 1–19 containing sulfon-
amido/trifluoromethyl groups at 2nd position by react-
ing 2-amino-5-substituted-1,3,4-thiadiazole of general
formula (I) with substituted a-haloaryl/heteroarylke-
tones as depicted in Scheme 1. Further, compounds 4–
8 were obtained by bromination, thiocyanation and
guanylation. Structures of the synthesized compounds
were established on the basis of IR, 1H NMR, 13C
NMR and mass spectral data. HRMS data provided
additional proof in order to substantiate the structures
of the compounds.
In view of the above facts and in continuation of our
search for various biologically active molecules33,34
and encouraging antibacterial activity of some imid-
azo[2,1-b]-1,3,4-thiadiazole derivatives35 has prompted
us to synthesize some novel molecules of fused imid-
azo[2,1-b]-1,3,4-thiadiazole and carry out their prelimi-
nary anti-tubercular activity. In this paper we report
the synthesis and spectral studies of a novel series
of 2-sulfonamido/trifluoromethyl-6-(40-substituted aryl/
heteroaryl)imidazo[2,1-b]-1,3,4-thiadiazole derivatives
and evaluation of in vitro anti-tuberculosis activity.

A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
5653
N
N
O
Br
+
NH2
N
S
a
R1
S
N
CH2-C Aryl/Het
R1
I
NH2
IA
R1 = SO2NH2, CF3
Br
N
N
b
Aryl/Het.
R1
S
N
III
Aryl = 3,4,5-OCH3 Ph
'
'
'
R1 = SO2NH2
S
CN
Aryl/Het.
3
N
5
4
N
c
N
2
N
Aryl/Het.
6
R1
R1
S
a
7
N
S
N
7
1
IV
II
R1 = SO2NH2 Aryl = 4-Me Ph; 4-Cl Ph
'
'
R1 = SO2NH2, CF3
'
'
'
'
Aryl = Ph; 4-OCH3 Ph; 3,4,5-OCH3 Ph;
H
C
NH
C
H
'
'
'
4-F Ph; 4-Me Ph; 4-Cl Ph;
N
N
NH2
'
'
'
.
4-NO2 Ph; 4-Br Ph; 4-OH Ph.
N
S
d, e
N
Het = furyl, coumarinyl.
Aryl/Het.
R1
N
V
R1 = -SO2-N=CH-N(CH3)2
Aryl = 4'-MePh; 4'-Cl Ph
O
Br–H C–C–Aryl/Het
Scheme 1. Reagents and conditions: (a)
, EtOH, reflux, 12h, Na2CO3; (b) Br2, CH3COONa, CH3COOH; (c) KSCN, Br2,
2
CH3COOH, 0–5ꢁC; (d) Vilsmeier reagent, 80–90ꢁC, 4h; (e) aminoguanidineÆHCl, EtOH, reflux, 0.5h.
Compounds 1–6 showed, absorption bands ranging
from 3300 to 3400cmꢀ1 for NH2, compounds 5 and 6
showed peaks at 2150 to 2195cmꢀ1 for SCN, compound
16 showed broad absorption band at 3422cmꢀ1 for OH,
compound 19 showed strong absorption band at
1728cmꢀ1 for C@O group of coumarin, in their respec-
tive IR spectra.
tively. Electron impact mass spectra showed an accurate
molecular ion peaks at m/z 310.2, 370.95, 298.1, 448.1,
351.1, 371.1, 433.3, 453.2, 299.2, 314.9, 303.8, 349.8,
283.1, 259.1 and 337.2 for compounds 1–8, 10, 12, 14,
15 and 17–19, respectively.
Imidazo[2,1-b]-1,3,4-thiadiazoles are planar and rigid
aromatic system with two condensed heterocycle, which
have different p conjugation. The mesomorphic proper-
ties of new mesogens are strictly dependent not only on
the nature of substituents but also on their position in
the thiadiazolic or imidiazolic part of the molecule, con-
sequently, which influences the biological activity.43
1
In particular, it must be pointed out that in H NMR
the presence of a singlet between d 8.0 and 8.9ppm indi-
cates the formation of bridgehead nitrogen heterocycle
(II) by cyclodehydration process via IA. Further the ab-
sence of this singlet in compounds 4–8 confirms that 5-
substituted derivatives have been formed. Compounds
1–6 showed a singlet around d 8.8ppm indicating the
presence of –SO2NH2 and the characteristic peaks at d
5.01, 3.8–3.9, 2.3ppm indicated the presence of OH,
OMe and Me groups in their respective structures. The
compounds 1–17 showed prominent signals for aromatic
protons around d 8.27–6.89ppm and in case of com-
pound 18 and 19 heterocyclic protons appeared between
d 8.79–6.49ppm.
The synthesized compounds were evaluated for their in
vitro anti-tuberculosis activity against M. tuberculosis
strain H37Rv by using radiometric BACTEC and broth
dilution assays. The result of anti-mycobacterial activity
is presented in Table 1. We studied the effects of various
substituents at 40 position of the aromatic ring. Amongst
them 40-nitro, 40-methyl, 40-chloro substituted deriva-
tives showed encouraging activity. The results showed
that compounds 5, 10 and 12 exhibited moderate anti-
tubercular activity with percentage inhibition of 29, 31
and 41, respectively, at a MIC of > 6.25lg/mL.
In 13C NMR spectrum we have observed most charac-
teristic signals appeared at around d 21.0, 42.0, 56.0–
60.0, 120.0 and 148.0ppm, for CH3, N(CH3)2, OCH3,
CF3, SCN, respectively. The signals appeared at around
d 102.0, 110.0, 140.0, 165.0ppm for C-5, C-6, C-7a, C-2
and carbons of Ph group at d 128.0–132.0ppm, respec-
The activity is considerably affected by substituents
at position-5 on the imidazo[2,1-b]-1,3,4-thiadiazole
nucleus. It has been observed that compounds 7 and 8

5654
A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
Table 1. The in vitro anti-tuberculosis activity of compounds 1–19 against M. tuberculosis H37Rv
R2
3
N
4
N
5
2
Aryl/Het.
6
R1
a
7
N
7
S
1
Sl. no.
R1
Aryl/Het
R2
H
MIC in lg/mL
SO2NH2
>6.25
OMe
OMe
1
2
SO2NH2
SO2NH2
SO2NH2
H
H
Br
>6.25 (5)
50
OMe
OMe
3
4
F
OMe
NDa
OMe
OMe
5b
6b
7b
SO2NH2
SCN
SCN
>6.25 (29)
>6.25 (3)
>6.25 (43)
CH3
SO2NH2
Cl
O
S
H3C
NH
C
N
C N
CH3
C
H
N
N
N
H
NH2
H
H3C
O
O
H3C
H3C
NH
C
8b
9
N
C
N
S
>6.25 (58)
NDa
Cl
C
H
N
H
NH2
H
O
CF3
CF3
CF3
H
H
H
10
11
>6.25 (31)
40
OMe
OMe
OMe
OMe
12
CF3
H
>6.25 (41)
NO2
13
14
CF3
CF3
H
H
50
40
F
Cl
15
16
17
18
CF3
CF3
CF3
CF3
H
H
H
H
50
50
40
2
Br
OH
CH3
O
19
CF3
––
H
40
O
––
O
INH
––
0.044
Values in bracket indicate % inhibition.
a Not determined.
b Prepared by the method given in literature.35

A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
5655
having a gaunylhydrazone group at 5th position,
showed a better anti-mycobacterial activity with per-
centage inhibition of 43 and 58, respectively, at a MIC
of >6.25lg/mL. We have also studied the effect of sulfo-
namido group in compounds 1–6 and trifluoromethyl
group in compounds 9–19 on the biological activity,
we observed that replacement of trifluoromethyl for sul-
fonamido group at 2nd position did not alter the anti-
tuberculosis activity to a greater extent.
NMR spectra were recorded at 75.5MHz on a Bruker
AM spectrometer and their chemical shifts are reported
in d ppm units with respect to TMS as internal standard;
Mass spectra were recorded on a VG-Quattro II, Micro-
mark Mass Spectrometer under the electron impact at
70eV.
6.2. General procedure for the synthesis of substituted
imidazo[2,1-b]-1,3,4-thiadiazoles (Scheme 1)
When the 6-substituted phenyl group is replaced by a
heterocyclic group, the moderate anti-tuberculosis activ-
ity was observed. In two cases we have replaced the aro-
matic ring with furan 18 and coumarin 19 ring systems,
furan-substituted derivative showed better activity with
a MIC of 20lg/mL.
A mixture of I (30mmol) and an appropriate quantity of
a-halo aryl/heteroaryl ketones (30mmol) in ethanol
(150mL) was heated to reflux on a water bath for 10–
12h. Excess of solvent was removed under reduced pres-
sure and the solid hydrobromide separated was filtered,
washed with cold ethanol and dried. Neutralization of
hydrobromide salts with cold aqueous solution of
Na2CO3 yielded the corresponding free bases II, which
was purified by recrystallisation from ethanol.
5. Conclusion
In the present paper, we report the synthesis, spectral
studies and anti-tuberculosis activity of novel series of
imidazo[2,1-b]-1,3,4-thiadiazoles. These fused hetrocy-
clic compounds were prepared by the cyclodehydration
6.2.1. 2-Sulfonamido-6-(40-methoxyphenyl)imidazo[2,1-
b]-1,3,4-thaidiazole (1). This was obtained by reacting
2-amino-5-sulfonamido-1,3,4-thiadiazole (5.41g, 30
mmol) and 40-methoxy phenacyl bromide (6.87g,
30mmol) as described above and isolated as pale yellow
solid crystals: yield 6.1g (65 %); mp 235–238ꢁC; kmax
(ethanol) 316, 264, 232nm; IR (KBr) mmax 3334, 3141,
process
between
2-amino-5-sulfonamido/trifluoro-
methyl-1,3,4-thiadiazole derivatives and a-haloaryl/
heteroaryl ketones. The preliminary in vitro anti-tuber-
culosis screening of these novel series of 2-sulfonam-
1
2924, 2853, 1549, 1496, 1286, 1196, 1050, 784cmꢀ1; H
ido/trifluoromethyl-6-(40-substituted
phenyl)imidazo-
NMR (DMSO-d6) d 8.72(s, 1H, 5H)), 8.68 (d,
J = 4Hz, 2H, SO2NH2), 7.85 (d, J = 9Hz, 2H, aryl-H),
7.0 (d, J = 8Hz, 2H, aryl-H), 3.80 (s, 3H, 40-OCH3)
ppm; 13C NMR (DMSO-d6) d 164.3, 159.9, 147.6,
145.7, 127.1, 126.7, 115.0, 110.6, 56.0ppm; EIMS m/z
[2,1-b]-1,3,4-thiadiazoles has evidenced that phenyl
substitution at 6th position and gaunylhydrazone group
at 5th position, have emerged as potential compounds
endowed with moderate to good anti-tuberculosis activ-
ity. On the contrary, the replacement of sulfonamido by
trifluoromethyl group at 2nd position showed no greater
change in the anti-tuberculosis activity. The possible
improvement of anti-tuberculosis activity of this basic
imidazo[2,1-b]-1,3,4-thiadiazole structure through mod-
ulation of ring substituents and/or additional functiona-
tion warrants further investigations. In summary, we
have identified a novel series of imidazo[2,1-b]-1,3,4-thia-
diazoles, which may develop into the potential class of
anti-tubercular agents.
+
(relative intensity) 310.2(M , 60%), 284.4 (52%), 272.4
(61%), 257.3 (97%), 243.3 (96%), 161.2 (50%), 147.2
(65%), 135.2(80%), 119.1 (90%), 107.1 (91%), 91.1
(92%), 81.2 (94%), 79.2(92%), 53.2 (93%), 41.3 (100%);
HRMS (EI) m/z calcd for C11H10O3N4S2: 310.0189;
found: 310.0186.
6.2.2. 2-Sulfonamido-6-(30,40,50-trimethoxyphenyl)imid-
azo[2,1-b]-1,3,4-thaidiazole (2). This was obtained
by reacting 2-amino-5-sulfonamido-1,3,4-thiadiazole
(5.41g, 30mmol) and 30,40,50-trimethoxy phenacyl bro-
mide (8.67g, 30mmol) as described above and isolated
as pale yellow solid crystals: yield 5.8g (52%); mp 240–
242ꢁC; kmax (ethanol) 326, 268, 232nm; IR (KBr) mmax
3325, 3154, 2944, 2838, 1591, 1494, 1286, 1196, 1048,
6. Experimental
6.1. Chemistry protocols
1
784cmꢀ1; H NMR (DMSO-d6) d 8.9 (s, 1H, 5H), 8.77
All research chemicals were purchased from Sigma-Ald-
rich or Lancaster Co. and used as such for the reactions.
Solvents except LR grade were dried and purified
according to the literature when necessary. Reactions
were monitored by thin layer chromatography (TLC)
on silica gel G plates and compounds visualized by
exposure to iodine vapours.
(d, J = 4Hz, 2H, SO2 NH2), 7.24 (s, 2H, aryl-H), 3.86
(s, 6H, 30-, 5-OCH3), 3.69 (s, 3H, 40-OCH3) ppm; 13C
NMR (DMSO-d6) d 164.7, 154.0, 153.8, 147.5, 145.3,
143.2, 138.4, 128.6, 111.8, 104.5, 60.9, 56.7ppm; EIMS
m/z (relative intensity); 370.95 (M+, 100%), 292.0 (5%),
217.01 (6%), 196.91 (5%), 139.98 (12%), 99.0 (12%),
74.06 (27%).
Melting points were determined using open capillary
tube method and are uncorrected. Spectra were obtained
as follows: UV spectra were recorded using Jasco V-530
spectrophotometer; Infra red (IR) spectra were recorded
using KBr disk on a Nicolet MX-1 FTIR spectrometer;
1H NMR spectra were recorded at 300MHz and 13C
6.2.3. 2-Sulfonamido-6-(40-fluorophenyl)imidazo[2,1-b]-
1,3,4-thaidiazole (3). This was obtained by reacting
2-amino-5-sulfonamido-1,3,4-thiadiazole (5.41g, 30
mmol) and 40-fluoro phenacyl bromide (6.51g, 30mmol)
as described above and isolated as pale yellow solid
crystals; yield 4.2g (47%); mp 264–265ꢁC; kmax (ethanol)

5656
A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
316, 254, 232nm; IR (KBr) mmax 3361, 3141, 2923, 2855,
6.2.6. 2-Sulfonamido-5-thiocyanato-6-(40-chlorophenyl)-
imidazo[2,1-b]-1,3,4-thaidiazole (6). This was obtained
by following the procedure as described for compound
5, by reacting 2-amino-5-sulfonamido-1,3,4-thiadiazole
(5.41g, 30mmol) and 40-chloro phenacyl bromide
(7.36g, 30mmol), as colourless needles; yield 2.48g
(65%); mp 211–213ꢁC; kmax (ethanol) 314, 256, 232;
IR (KBr) mmax 3332, 3153, 2925, 2196, 1634, 1578,
1
1584, 1496, 1360, 1285, 1195, 1040, 859cmꢀ1; H NMR
(DMSO-d6) d 8.86 (s, 1H, 5H), 8.73 (d, J = 4Hz, 2H,
SO2NH2), 7.9 (d, J = 8Hz, 2H, aryl-H), 7.3 (d,
J = 9Hz, 2H, aryl-H) ppm; 13C NMR (DMSO-d6) d
164.9, 161.0, 146.5, 146.0, 130.7, 127.8, 116.7,
111.7ppm; EIMS m/z (relative intensity) 298.1 (M+,
100%), 121.1 (16%), 94.2 (8%), 80.1 (95%), 70.1 (21%),
1
64.2(02%), 48.2(44%); HRMS (EI) m/z calcd for
C10H7O2N4FS2: 297.9989; found: 297.9985.
1481, 1368, 1164, 1089, 829cmꢀ1; H NMR (CDCl3) d
8.80 (s, 2H, SO2NH2), 7.37 (d, J = 8Hz, 2H, aryl-H),
7.75 (d, J = 9Hz, 2H, aryl-H) ppm; 13C NMR
(DMSO-d6) d 167.4, 152.5, 149.2, 134.9, 131.5, 130.0,
129.9, 129.7, 110.9ppm; EIMS m/z (relative intensity)
371.1 (M+, 100%), 102(10%), 80.1 (94%), 64.2(15%),
48.2(15%); HRMS (EI) m/z calcd for C11H6O2N5ClS3:
370.9367; found: 370.9370.
6.2.4. 2-Sulfonamido-5-bromo-6-(30,40,50-trimethoxyphen-
yl)imidazo[2,1-b]-1,3,4-thaidiazole
(4).
To
1.85g
(5.0mmol) of compound 2, 0.82g (10mmol) of sodium
acetate and 10mL of acetic acid stirred together at room
temperature was added drop wise 0.96g (6.0mmol) of
bromine. After the addition, stirring was continued for
30min. The mixture was poured into 100mL of water
from which a solid separated. The solid was collected,
washed with water and dried. Recrystallisation from
acetonitrile gave colourless crystals of compound 4:
yield 0.8g (36%); mp 200–202ꢁC; kmax (ethanol) 314,
270, 232nm; IR (KBr) mmax 3350, 3153, 2941, 2840,
6.2.7. 2-[N-(Dimethylaminomethino)]sulfonamido-5-guan-
ylhydrazone-6-(40-methylphenyl)imidazo[2,1-b]-1,3,4-thai-
diazole (7). This was obtained by following the proce-
dure described in the literatures.33,35 2-Sulfonamido-6-
(40-methylphenyl)imidazo[2,1-b]-1,3,4-thaidiazole was
prepared in 51% yield as yellow needles by reacting
2-amino-5-sulfonamido-1,3,4-thiadiazole (5.41g, 30
mmol) and 40-methylphenacyl bromide (6.39g, 30mmol)
in presence of ethanol (150mL) under reflux for 12h.
Then 2-sulfonamido-5-formyl-6-(40-methylphenyl)imid-
azo[2,1-b]-1,3,4-thaidiazole was prepared in 81% yield
as yellow needles by slow addition of 2-sulfonamido-6-
(40-methylphenyl)imidazo[2,1-b]-1,3,4-thaidiazole (2.94g,
10mmol) to the freshly prepared Vilsmeier reagent. Fur-
ther the 2-sulfonamido-5-formyl-6-(40-methyl phe-
nyl)imidazo[2,1-b]-1,3,4-thaidiazole (3.78g, 10mmol)
and aminoguanidine hydrochloride (1.1g, 10mmol)
was refluxed for 30min in presence of ethanol
(150mL). The resultant precipitate was collected by fil-
tration, followed by basification with aqueous ammonia,
title compound 7 was isolated as yellow needles; yield
3.13g (70%); mp 215–220ꢁC; kmax (ethanol) 294, 248,
226; IR (KBr) mmax 3425 (b), 3129, 2913, 1678, 1641,
1591, 1495, 1286, 1196, 1050, 784cmꢀ1 1H NMR
;
(CDCl3) d 8.75 (br, 2H, SO2NH2), 7.24 (s, 2H, Ar–H),
3.86 (s, 6H, 30-, 50-OCH3), 3.73 (s, 3H, 40-OCH3) ppm;
13C NMR (DMSO-d6) d 165.9, 153.8, 145.3, 143.2,
138.4, 128.5, 110.8, 104.5, 93.9, 60.9, 56.7ppm; EIMS
m/z (relative intensity) 450.1 (M + 2,100), 448.1 (M+,
95%), 370.1 (94%), 355.1 (93%), 327.1 (61%), 297.1
(38%), 290.1 (42%), 193.1 (54%), 178.1 (58%), 135.1
(50%), 120.1 (52%), 79.9 (96%), 64.1 (93%), 48.2
(63%); HRMS (EI) m/z calcd for C13H13O5N4BrS2:
447.9505; found: 447.9498.
6.2.5. 2-Sulfonamido-5-thiocyanato-6-(40-methylphenyl)-
imidazo[2,1-b]-1,3,4-thaidiazole (5). This was obtained
by following the procedure described in the literature.35
2-sulfonamido-6-(40-methyl phenyl)imidazo[2,1-b]-1,3,4-
thaidiazole was prepared in 51% yield as yellow needles
by reacting 2-amino-5-sulfonamido-1,3,4-thiadiazole
(5.41g, 30mmol) and 40-methyl phenacyl bromide
(6.39g, 30mmol) in presence of ethanol (150mL) under
reflux for 12h. Then to a mixture of 2-sulfonamido-
1
1511, 1418, 1326, 1147, 1091, 918, 850cmꢀ1; H NMR
(DMSO-d6) d 12.10 (s, 1H, @N–NH–), 8.55 (s, 1H, 5-
CH@N), 8.40 (s, 1H, –CH@N–SO2), 7.71 (d, J = Hz,
2H, aryl-H), 7.23 (d, J = 8Hz, 2H, aryl-H), 3.00, 3.25
(s, 6H, –N(CH3)2), 2.30 (s, 3H, Ar CH3) ppm; 13C
NMR (DMSO-d6) d 165.5, 152.2, 145.4, 139.7, 131.4,
130.3, 128.9, 110.3, 102.3, 74.7, 42.4, 36.6, 21.7ppm;
EIMS m/z (relative intensity) 434.3 (M + 1, 30%),
433.3 (M+, 100%), 374.2 (5%), 215.1 (12%), 161.1
(13%), 135.1 (58%), 117.2(34%), 99.2(60%), 84.2
(84%), 72.2 (72%), 64.0 (95%); HRMS (EI) m/z calcd
for C16H19O2N9S2: 433.1098; found: 433.1097.
6-(40-methyl
phenyl)imidazo[2,1-b]-1,3,4-thaidiazole
(2.94g, 10mmol) and potassium thiocyanate (1.56g,
16mmol) in glacial acetic acid (50mL) was added (at
0–5ꢁC) bromine (1.6g, 10mmol) in glacial acetic acid
(20mL) dropwise with stirring. Then stirring was contin-
ued for 30min at 15–18ꢁC and then at room tempera-
ture for 30min. The reaction mixture was poured into
ice water, filtered and recrystallised from ethanol and
isolated as colourless solid crystals of compound 5; yield
2.52g (72%); mp 220–222ꢁC; kmax (ethanol) 322, 266,
234; IR (KBr) mmax 3363, 3147, 2924, 2166, 1610, 1554,
6.2.8. 2-[N-(Dimethylaminomethino)]sulfonamido-5-guan-
ylhydrazone-6-(40-chlorophenyl)imidazo[2,1-b]-1,3,4-thai-
diazole (8). This was obtained by following the proce-
dure as described for compound 7, by reacting 2-
amino-5-sulfonamido-1,3,4-thiadiazole (5.41g, 30mmol)
and 40-chloro phenacyl bromide (7.36g, 30mmol), as
yellow needles; yield 2.94g (65%); mp 228–232ꢁC dec;
kmax (ethanol) 289, 257, 225; IR (KBr) mmax 3443 (b),
2923, 1677, 1634, 1498, 1405, 1313, 1152, 1084,
1
1486, 1369, 1171, 1054, 832cmꢀ1; H NMR (CDCl3),
d 8.80 (s, 2H, SO2NH2), 7.23 (d, J = 8Hz, 2H, aryl-H),
7.71 (d, J = Hz, 2H, aryl-H),2.13 (s, 3H, 40-CH3) ppm;
13C NMR (CDCl3) d 166.6, 152.0, 148.7, 139.6, 130.0,
129.5, 127.9, 110.9, 102.4, 21.4ppm; EIMS m/z (relative
intensity) 351.1 (M+, 100%), 116.2 (12%), 102 (29%),
80.1 (95%), 70.2(18%), 64.2(15%); HRMS (EI)
calcd for C12H9O2N5S3: 350.9913; found: 350.9917.
m/z

A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
5657
1
917, 846cmꢀ1; H NMR (DMSO-d6) d 12.10 (s, 1H,
2H, aryl-H), 8.1 (s, 1H, 5H), 7.98 (d, J = 8Hz, 2H,
aryl-H) ppm; 13C NMR (CDCl3) d 153.4, 147.8, 146.5,
143.1, 139.4, 130.2, 126.3, 124.7, 112.1ppm; EIMS m/z
(relative intensity) 315.94 (M + 1, 45%), 314.98 (M+,
100%), 256.14 (10%), 217.01 (10%), 102.6 (6%), 74.06
(23%).
@N–NH–), 8.55 (s, 1H, 5-CH@N), 8.40 (s, 1H,
–CH@N–SO2), 7.75 (d, J = 9Hz, 2H, aryl-H), 7.37 (d,
J = 8Hz, 2H, aryl-H), 3.00, 3.25 (s, 6H, –N(CH3)2)
ppm; 13C NMR (DMSO-d6) d 163.9, 152.3, 145.6,
139.1, 131.8, 130.3, 128.9, 110.2, 102.2, 75.1, 42.4, 36.6
ppm; EIMS m/z (relative intensity) 455.2(M +,2
46%), 453.2(M +, 100%), 411.2(15%), 325.1 (6%),
181.1 (8%), 135.1 (37%), 99.2(45%), 84.2(58%), 72.2
(43%), 64.1 (95%), 44.3 (92%); HRMS (EI) m/z calcd
for C15H16O2N9ClS2: 453.0551; found: 453.0545.
6.2.13. 2-Trifluoromethyl-6-(40-fluorophenyl)imidazo[2,1-
b]-1,3,4-thaidiazole (13). This was obtained by reacting
2-amino-5-trifluoromethyl-1,3,4-thiadiazole (5.07g, 30
mmol) and 40-fluoro phenacyl bromide (6.51g, 30mmol)
as described in the general procedure and isolated as col-
ourless solid crystals; yield 4.64g (54%); mp 153–154ꢁC;
kmax (ethanol) 312, 250, 232nm; IR (KBr) mmax 3138,
2925, 2854, 1609, 1517, 1486, 1335, 1287, 1165, 1016,
6.2.9. 2-Trifluoromethyl-6-(phenyl)imidazo[2,1-b]-1,3,4-
thaidiazole (9). This was obtained by reacting 2-amino-
5-trifluoromethyl-1,3,4-thiadiazole (5.07g, 30mmol)
and phenacyl bromide (5.97g, 30mmol) as described in
the general procedure and isolated as colourless solid
crystals; yield 4.43g (55%); mp 160–161ꢁC; kmax (etha-
nol) 310, 270, 232nm; IR (KBr) mmax 3138, 2933, 2854,
839cmꢀ1 1H NMR (CDCl3) d 8.07 (s, 1H, 5H), 7.8
;
(m, 2H, J = 5, 4Hz, aryl-H), 7.1 (m, 2H, J = 9, 8Hz,
aryl-H) ppm.
1511, 1444, 1311, 1286, 1144, 1020, 831cmꢀ1
;
1H
6.2.14. 2-Trifluoromethyl-6-(40-chlorophenyl)imidazo[2,1-
b]-1,3,4-thaidiazole (14). This was obtained by reacting
2-amino-5-trifluoromethyl-1,3,4-thiadiazole (5.07g, 30
mmol) and 40-chloro phenacyl bromide (7.36g,
30mmol) as described in the general procedure and iso-
lated as a colourless solid crystals; yield 4.64g (51%); mp
155–156ꢁC; kmax (ethanol) 314, 256, 232nm; IR (KBr)
mmax 3126, 2924, 2854, 1518, 1480, 1296, 1171, 1014,
NMR (CDCl3) d 78.12(s, 1H, 5H), 7.84 (d, J = 7Hz,
2H, aryl-H), 5–7.3 (m, 3H, aryl-H),ppm.
6.2.10. 2-Trifluoromethyl-6-(40-methoxyphenyl)imidazo-
[2,1-b]-1,3,4-thaidiazole (10). This was obtained by react-
ing 2-amino-5-trifluoromethyl-1,3,4-thiadiazole (5.07g,
30mmol) and 40-methoxy phenacyl bromide (6.87g,
30mmol) as described in the general procedure and iso-
lated as pale red solid crystals; yield 5.56g (62%); mp
155–156ꢁC; kmax (ethanol) 314, 268, 240nm; IR (KBr)
mmax 3121, 2924, 2854, 1514, 1436, 1305, 1286, 1196,
1
831cmꢀ1; H NMR (CDCl3) d 8.08 (s, 1H, 5H), 7.75
(d, J = 9Hz, 2H, aryl-H), 7.37 (d, J = 8Hz, 2H, aryl-
H) ppm; 13C NMR (CDCl3) d 150.2, 147.8, 145.2,
134.5, 131.8, 129.4, 127.0, 120.7, 110.3ppm; EIMS m/z
(relative intensity), 305.89 (M + 2, 70%), 303.89 (M+,
100%), 256.1 (5%), 217.01 (6%), 148.85 (3%), 86.06
(4%), 74.07 (33%).
1
1050, 784cmꢀ1; H NMR (CDCl3) d 8.03 (s, 1H, 5H),
7.75 (d, J = 9Hz, 2H, aryl-H), 6.96 (d, J = 9Hz, 2H,
aryl-H), 3.85 (s, 3H, 40-OCH3) ppm; 13C NMR (CDCl3)
d 160.2, 148.9, 144.8, 130.9, 127.1, 126.0, 120.8, 117.2,
114.6, 109.2, 55.7ppm; EIMS m/z (relative intensity)
300.2 (M + 1, 28%), 299.2 (M+, 100%), 284.1 (45%),
256.1 (43%), 177.1 (67%), 146.1 (44%), 133.1 (81%),
103.3 (35%), 90.2(52%), 76.2(43%), 63.2(50%) 44.2
(20%); HRMS (EI) m/z calcd for C12H8ON3F3S:
299.0335; found: 299.0334.
6.2.15. 2-Trifluoromethyl-6-(40-bromophenyl)imidazo[2,1-
b]-1,3,4-thaidiazole (15). This was obtained by reacting
2-amino-5-trifluoromethyl-1,3,4-thiadiazole (5.07g, 30
mmol) and 40-bromo phenacyl bromide (8.34g,
30mmol) as described in the general procedure and iso-
lated as colourless solid crystals; yield 5.53g (53%); mp
188–190ꢁC; kmax (ethanol) 304, 262, 232nm; IR (KBr)
mmax 3125, 2924, 2853, 1516, 1480, 1295, 1171, 1011,
6.2.11. 2-Trifluoromethyl-6-(30,40,50-trimethoxyphenyl)-
imidazo[2,1-b]-1,3,4-thaidiazole (11). This was obtained
by reacting 2-amino-5-trifluoromethyl-1,3,4-thiadiazole
(5.07g, 30mmol) and 30,40,50-trimethoxy phenacyl bro-
mide (8.67g, 30mmol) as described in the general proce-
dure and isolated as pale orange solid crystals; yield
3.33g (31%); mp 135–137ꢁC; kmax (ethanol) 304, 264,
232nm; IR (KBr) mmax 3121, 2935, 2847, 1590, 1519,
826cmꢀ1 1H NMR (CDCl3) d 8.1 (s, 1H, 5H), 7.68
;
(d, J = 9Hz, 2H, aryl-H), 7.53 (d, J = 9Hz, 2H, aryl-
H) ppm; 13C NMR (CDCl3) d 150.8, 147.9, 145.2,
132.4, 132.2, 127.3, 122.7, 120.7, 117.1, 110.3ppm;
EIMS m/z (relative intensity), 305.82(M + 1, 02%),
349.82(M +, 100%), 284.12 (6%), 256.14 (41%), 217.01
(7.5%), 148.94 (4%), 102.07 (4%), 74.07 (27%).
1495, 1275, 1188, 1011, 784cmꢀ1; H NMR (CDCl3) d
1
8.08 (s, 1H, 5H), 7.06 (s, 2H, aryl-H), 3.91 (s, 6H, 30-,
50- OCH3), 3.88 (s, 3H, 40-OCH3) ppm.
6.2.16.
azo[2,1-b]-1,3,4-thaidiazole (16). This was obtained by
reacting 2-amino-5-trifluoromethyl-1,3,4-thiadiazole
2-Trifluoromethyl-6-(40-hydroxyphenyl)imid-
6.2.12. 2-Trifluoromethyl-6-(40-nitrophenyl)imidazo[2,1-
b]-1,3,4-thaidiazole (12). This was obtained by reacting
(5.07g, 30mmol) and 40-hydroxy phenacyl bromide
(6.45g, 30mmol) as described in the general procedure
and isolated as colourless solid crystals; yield 4.18g
(49%); mp 152–153ꢁC; kmax (ethanol) 310, 260,
232nm; IR (KBr) mmax 3422 (b), 3125, 2924, 1517,
2-amino-5-trifluoromethyl-1,3,4-thiadiazole
(5.07g,
30mmol) and 40-nitro phenacyl bromide (7.32g,
30mmol) as described in the general procedure and iso-
lated as pale yellow solid crystals; yield 4.71g (50%); mp
192–193ꢁC; kmax (ethanol) 330, 266, 234nm; IR (KBr)
mmax 3138, 2923, 2854, 1602, 1519, 1342, 1295, 1157,
1
1480, 1295, 1171, 1012, 827cmꢀ1; H NMR (CDCl3)
d 8.02(s, 1H, 5H), 7.70 (d, J = 9Hz, 2H, aryl-H),
6.89 (d, J = 9 Hz, 2H, aryl-H), 5.01 (broad, 1H,
40-OH) ppm.
1
1011, 855cmꢀ1; H NMR (CDCl3) d 8.27 (d, J = 9Hz,

5658
A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
6.2.17.
2-Trifluoromethyl-6-(40-methylphenyl)imidazo-
tested in the BACTEC 460 radiometric system.40 The
MIC of each drug was determined and is defined as
the lowest concentration of drug, which inhibits
P99% of bacterial population present at the beginning
of the assay. Percent inhibition was calculated as
1ꢀ(growth index of test sample/growth index of
control) · 100.
[2,1-b]-1,3,4-thaidiazole (17). This was obtained by
reacting 2-amino-5-trifluoromethyl-1,3,4-thiadiazole
(5.07g, 30mmol) and 40-methyl phenacyl bromide
(6.39g, 30mmol) as described in the general procedure
and isolated as colourless solid crystals; yield 3.9g
(46%); mp 134–135ꢁC; kmax (ethanol) 322, 266,
234nm; IR (KBr) mmax 3166, 2937, 2840, 1600, 1512,
1483, 1270, 1171, 1047, 829cmꢀ1; H NMR (CDCl3) d
For the remaining test compounds (3, 11 and 13–19)
MIC of each drug was determined by broth dilution as-
say41,42 for M. tuberculosis strain H37Rv. A frozen cul-
ture in Middlebrook 7H9 broth supplemented with 10%
Albumin–Dextrose–Catalase and 0.2% glycerol was
thawed and diluted in broth to 2 · 105 cfu/mL for
M. tuberculosis and used as the inoculum. In the assay
U-tubes were used to accommodate ten compounds in
200–10lg/mL dilutions. Each test compound was dis-
solved in dimethylsulfoxide (DMSO) then diluted in
broth at twice the desired concentration. The final con-
centration of DMSO in the assay medium was 1.3%.
Each U-tube was then inoculated with 0.05mL of stand-
ardized culture and then incubated at 37ꢁC for 21days.
The growth in the U-tubes was compared with visibility
against positive control (without drug), negative control
(without drug and inoculum) and with standard
Isonaizid.
1
8.08 (s, 1H, 5H), 7.71 (d, J = Hz, 2H, aryl-H), 7.23 (d,
J = 8Hz, 2H, aryl-H), 2.39 (s, 3H, 40-CH3) ppm; 13C
NMR (CDCl3) d 149.1, 144.9, 138.7, 130.4, 129.9,
125.7, 120.8, 109.8, 102.6, 21.7ppm; EIMS m/z (relative
intensity) 283.1 (M+, 82%), 264.2 (15%), 188.1 (52%),
161.0 (91%), 117.2(100%), 89.2(7%2 ), 69.1 (68%),
44.2(51%), 39.3 (55%); HRMS (EI) m/z calcd for
C12H8N3F3S: 283.0386; found: 283.0388.
6.2.18. 2-Trifluoromethyl-6-(furoyl)imidazo[2,1-b]-1,3,4-
thaidiazole (18). This was obtained by reacting 2-ami-
no-5-trifluoromethyl-1,3,4-thiadiazole (5.07g, 30mmol)
and a-bromoacetyl furan (5.67g, 30mmol) as described
in the general procedure and isolated as brown solid
crystals; yield 3.88g (50%); mp 165–166ꢁC; kmax (etha-
nol) 320, 258 228nm; IR (KBr) mmax 3159, 2924, 1522,
1482, 1308, 1174, 1017, 888, 774cmꢀ1
;
1H NMR
(CDCl3) d 8.04 (s, 1H, 5H), 7.45 (d, J = 3Hz, 1H, furan),
6.78 (d, J = 3Hz, 1H, furan), 6.49 (q, J = 5Hz, J = 3Hz,
1H, furan) ppm; 13C NMR (CDCl3) d 148.5, 145.3,
142.7, 140.7, 112.0, 109.8, 107.4ppm; EIMS m/z (relative
intensity) 259.1 (M+, 78%), 240.1 (16%), 136.9 (100%),
109.1 (96%), 93.1 (74%), 64.2(75%), 44.2(36%), 39.3
(68%); HRMS (EI) m/z calcd for C9H4ON3F3S:
259.0022; found: 259.0023.
Acknowledgements
Authors are thankful to Dr. F. V. Manvi, Principal,
College of Pharmacy, Belgaum for providing necessary
facilities and appreciate the co-operation of Mr. Mahesh
B. Palkar in the preparation of this manuscript. We
gratefully acknowledge the support for this research
effort from All India Council for Technical Education
(AICTE), New Delhi (File No. 8018/RDII/BOR/
TAP(397)/99-2000). The authors are grateful to Tuber-
culosis Antimicrobial Acquisition and Coordinating
Facility (Sam Ananthan, Adrian Poffenberger, Cecil
Kwong, Michele Michael, NIAID, NIH, USA), and
Haffkine Institute for Research, Training and Testing,
Mumbai, India, for anti-tuberculosis activity.
6.2.19. 2-Trifluoromethyl-6-(coumarinyl)imidazo[2,1-b]-
1,3,4-thaidiazole (19). This was obtained by reacting
2-amino-5-trifluoromethyl-1,3,4-thiadiazole (5.07g, 30
mmol) and a-bromoacetyl coumarin (8.01g, 30mmol)
as described in the general procedure and isolated as
pale yellow solid crystals; yield 4.54g (45%); mp 192–
193ꢁC; kmax (ethanol) 340, 288, 234nm; IR (KBr) mmax
3176, 3072, 2922, 2847, 1728, 1516, 1299, 1191, 1108,
1
1016, 763cmꢀ1; H NMR (CDCl3) d 8.79 (s, 1H, 5H),
8.59 (s, 1H, coumarin), 7.59 (d, J = 7Hz, 1H, coumarin),
7.54 (t, J = 7Hz, 1H, coumarin), 7.36 (d, J = 8Hz, 1H,
coumarin), 7.31 (t, J = 7Hz,1H, coumarin) ppm; 13C
NMR (CDCl3) d 159.5, 153.3, 151.7, 150.4, 145.2,
138.1, 132.0, 128.7, 125.1, 120.4, 117.5, 115.8ppm;
EIMS m/z (relative intensity) 337.2(M +, 50%), 242.1
(5%), 215.1 (4%), 187.1 (35%), 155.1(31%), 143.1
(100%), 115.2 (25%), 88.2 (12%), 69.1 (20%), 44.2
(13%), 39.3 (16%); HRMS (EI) m/z calcd for
C14H6O2N3F3S: 337.0127; found: 337.0125.
References and notes
1. Dutt, A. K.; Stead, W. W. In Tuberculosis and Non-
tuberculosis Mycobacterial Infections, 4th ed.; David, S.,
Ed.; W.B. Saunders, 1999; p 3.
2. Das, R. K. JIMA 2000, 98, 112.
3. Martien, W. B. Bull. World Health Org. 2002, 80, 501.
4. Snider, D. E. J.; Raviglione, M.; Kochi, A. In Tubercu-
losis: Pathogenesis Protection and Control; Bloom, B. R.,
Ed.; American Society of Microbiology: Washington, DC,
1994; p 2.
5. Rouhi, A. M. Chem. Eng. News 1999, 77, 52 .
6. Dye, C. 4th World Congress on TB, Washington DC,
2002; p 3.
7. Maher, D.; Floyd, K.; Ravglione, M., World Health
Organization; Geneva-Switzerland, 2002; p 1.
8. Bloom, B. R.; Murray, C. J. L. Science 1992, 257,
1055.
6.3. Biological evaluation
6.3.1. In vitro evaluation of anti-tuberculosis activity. The
preliminary anti-tuberculosis screening for test com-
pounds (1–2, 5–8, 10, and 12) was obtained for M. tuber-
culosis H37Rv in BACTEC 12B medium using a broth
microdilution assay, the microplate Alamar Blue Assay
(MABA).39 Compounds exhibiting fluorescence were
9. Snider, D. E. J.; Roper, W. L. New Engl. J. Med. 1992,
326, 703.

A. K. Gadad et al. / Bioorg. Med. Chem. 12 (2004) 5651–5659
5659
10. Bass, J. B.; Farer, L. S.; Hopewell, P. C.; OꢀBrien, R.;
Jacobs, R. F.; Ruben, F.; Dixie, E.; Snider, J.; Thornton,
G. Am. J. Respir. Crit. Care Med. 1994, 149, 1359.
11. Rattan, A.; Kalia, A.; Ahmad, N. Emerg. Infect. Dis.
1998, 4, 195.
12. Piero, S.; Giuliona, G. G. In Burgerꢀs Medicinal Chemistry
and Drug Discovery, 4th ed.; Wolff, M. E., Ed.; John Wiley
and Sons, Inc.: New York, 1996; p 575.
13. Barry, C. E.; Slayden, R. A.; Sampson, A. E.; Lee, R. E.
Biochem. Pharmacol. 2000, 59, 221.
14. Ian, O. Antimicrob. Agents Chemother. 2001, 45, 1943.
15. Temple, M. E.; Nahata, M. C. Ann. Pharmacother. 1999,
33, 1202.
16. Miyazaki, E.; Miyazaki, M.; Chen, J. M.; Chaisson, R. E.;
Bishai, W. R. Antimicrob. Agents Chemother. 1999, 43, 85.
17. Tomika, H.; Sato, K.; Akaki, T.; Kajitani, H.; Kawahara,
S.; Sakatani, M. Antimicrob. Agents Chemother. 1999, 43,
3001.
18. Ruiz Serrano, M. J.; Alcala, L.; Martinez, L.; Diaz, M.;
Marin, M.; Gonzalez-Abad, M. J.; Bouza, E. Antimicrob.
Agents Chemother. 2000, 44, 2567.
19. Zurenko, G. E.; Yagi, B. H.; Schaadt, R. D.; Allison, J.
W.; Kilburn, J. O.; Glickman, S. E.; Hutchinson, D. K.;
Barbachyn, M. R.; Brickner, S. J. Antimicrob. Agents
Chemother. 1996, 40, 839.
20. Barbachyn, M.; Huchinson, D. K.; Brickner, S. J.;
Cynamon, M. H.; Kilburn, J. O.; Klemens, S. P.;
Glickman, S. E.; Grega, K. C.; Hendges, S. K.; Toops,
D. S.; Ford, C. W.; Zurenko, G. E. J. Med. Chem. 1996,
39, 680.
25. Bravo, P.; Dillido, D.; Resnati, G. Tetrahedron 1994, 50,
8827.
26. Pilgram, K. H.; Skiles, R. D. J. Heterocycl. Chem. 1988,
25, 129.
27. Beck, J. R.; Wright, F. L. J. Heterocycl. Chem. 1987, 24,
739.
28. Harper, D. B.; OꢀHagan, D. Nat. Prod. Rep. 1994, 11, 123.
29. Jung, J. C.; Watkins, E. B.; Avery, M. A. Tetrahedron
2002, 58, 3639.
30. Kenneth, L. M.; John, J. F.; Kurt, E. S.; James, F. M.;
Brenda, M.; Theresa, T.; Diana, M.; Michael, L. M. J.
Med. Chem. 1996, 39, 3920.
31. Mutalib, A. E.; Chen, S. Y.; Espina, R. J.; Shockcor, J.;
Prakash, S. R.; Gan, L. S. Chem. Res. Toxicol. 2002, 15,
63.
32. Abdou, I. M.; Saleh, A. M.; Zohdi, H. F. Molecules 2004,
9, 109.
33. Gadad, A. K.; Karki, S. S.; Rajurkar, V. G.; Bhongade, B.
A. Arzneim.-Forsch. 1999, 49, 858.
34. Khazi, I. M.; Mahajanshetti, C. S.; Gadad, A. K.;
Tarnalli, A. D.; Sultanpur, C. M. Arzneim.-Forsch. 1996,
46, 949.
35. Gadad, A. K.; Mahajanshetti, C. S.; Nimbalkar, S.;
Raichurkar, A. Eur. J. Med. Chem. 2000, 35, 853.
36. de Stevens, G.; Eager, M.; Tarby, C. Heterocycles 1993,
35, 763.
37. Organic Synthesis Collective; Blatt, A. H., Ed.; John Wiley
and sons: New York, 1943; Vol. 2, p 480.
38. Hough, T. L. J. Heterocycl. Chem. 1983, 20, 1003.
39. Collins, L.; Franzblau, S. G. Antimicrob. Agents Chemo-
ther. 1997, 41, 1004.
40. Franzblau, S. G.; Witzig, R. S.; McLaughlin, J. C.; Torres,
P.; Madico, G.; Hernandez, A.; Quenzer, V. K.; Freguson,
R. M.; Gilman, R. H. J. Clin. Microb. 1998, 36, 362.
41. Yajko, D. M.; Madej, J. J.; Lacaster, M. V.; Sanders
C. A., V. L.; Cawthon, V. L.; Gee, B.; Babst, A.; Keith
Hardley, W. J. Clin. Microb. 1995, 33, 2324.
42. Suling, W. J.; Seitz, L. E.; Pathak, V.; Westbrook, L.;
Barrow, E. W.; Zywno-van-ginkel, S.; Renolds, R. C.;
Piper, J. R.; Barrow, W. W. Antimicrob. Agents Chemo-
ther. 2000, 44, 2784.
21. Stover, K. C.; Warrener, P.; Vandevanter, D. R.; Sher-
man, D. R.; Arain, T. M.; Langhorne, M. H.; Anderson,
S. W.; Towell, J. A.; Yuan, Y.; McMurray, D. N.;
Kreiswirth, B. N.; Barry, C. E.; Baker, W. R. Nature 2000,
405, 962.
22. Anand, N. In Burgerꢀs Medicinal Chemistry and Drug
Discovery, 4th ed.; Wolff, M. E., Ed.; John Wiley and
Sons, Inc.: New York, 1996; p 1.
ˇ
23. Krizmanic, I.; Visnjevac, A.; Luic, M.; Glavas-Obrovac,
L.; Zinic, M.; Zinic, B. Tetrahedron 2003, 59, 4049.
24. Raju, B.; Wu, C.; Kois, A.; Verner, E. J.; Castillo, R.;
Okun, I.; Stavors, F. D.; Chan, M. F. Bioorg. Med. Chem.
Lett. 1996, 6, 2651.
43. Torgova, S.; Karamysheva, L.; Strigazzi, A. Braz. J. Phys.
2002, 32, 593.