Synthesis of novel imidazo[2,1-b][1,3,4]thiadiazoles appended to sydnone as anticancer agents

Article abstract of DOI:10.1007/s00044-012-0441-z

A novel series of 3-aryl-4{6′-(6′′-substituted-coumarin- 3′′-yl) imidazo[2,1-b][1,3,4]thiadiazol-2′-yl}-sydnones 5h-5s were synthesized and screened for their anticancer and DNA cleavage activities and analyzed for pharmacological parameters such as toxicity, drug-likeliness, and drug score for oral bioavailability. In vitro toxicity assay was carried out by assessing the survival E. coli AB1157 (wild type) cultures. Some of the compounds have shown significant anticancer activities also.

Full text of DOI:10.1007/s00044-012-0441-z

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:4367–4375
DOI 10.1007/s00044-012-0441-z
ORIGINAL RESEARCH
Synthesis of novel imidazo[2,1-b][1,3,4]thiadiazoles appended
to sydnone as anticancer agents
•
Gireesh Tegginamath Ravindra R. Kamble
•
•
Tasneem Taj Pramod P. Kattimani
•
Gangadhar Y. Meti
Received: 28 October 2012 / Accepted: 18 December 2012 / Published online: 9 January 2013
Ó Springer Science+Business Media New York 2013
Abstract A novel series of 3-aryl-4{60-(600-substituted-cou-
marin-300-yl) imidazo[2,1-b][1,3,4]thiadiazol-20-yl}-sydnones
5h–5s were synthesized and screened for their anticancer and
DNA cleavage activities and analyzed for pharmacological
parameters such as toxicity, drug-likeliness, and drug score for
oral bioavailability. In vitro toxicity assay was carried out by
assessing the survival E. coli AB1157 (wild type) cultures.
Some of the compounds have shown significant anticancer
activities also.
(Terzioglu and Gursoy, 2003), antitubercular (Gadad et al.,
2004), antimicrobial (Gadad et al., 2000; Andotra et al.,
1997), analgesic (Khazi et al., 1996), and antisecretory
(Andreani et al., 2000) activities. Moreover, much work was
reported on the anti-inflammatory (Andreani et al., 1982),
cardiotonic (Andreani et al., 1986), diuretic (Andreani et al.,
1987), and herbicidal (Andreani et al., 1991) activities dis-
played by compounds incorporated with this heterocyclic
system. Imidazo[2,1-b][1,3,4]thiadiazole is also structurally
analogous in part to Levamisole, a well-known immuno-
modulator (Amery et al., 1984). Several sydnone derivatives
were associated with broad range of physiological activities
and exhibit pharmacological actions (Dunkley and Thoman,
2003; Moustafa et al., 2004). Also, coumarin derivatives
possess a wide spectrum of biological activities and most of
these compounds were proved to be active as antitumor (Raev
et al., 1990; Nofal et al., 2000), anticoagulant (Manolov and
Danchev, 1995), and anti-inflammatory agents (Emmanuel-
Giota et al., 2001). Hence, chemists have been enthusiasti-
cally pursuing the synthesis of these derivatives. It is envis-
aged that the two pharmacophores if linked together would
generate novel molecular templates which are likely to
exhibit interesting pharmacological properties.
Keywords Sydnone ꢀ Coumarin ꢀ
Imidazo[2,1-b][1,3,4]thiadiazole ꢀ Anticancer ꢀ
DNA cleavage
Introduction
It is well known that the utility of cancer chemotherapy is
considerably restricted by toxic side effects of anticancer drugs.
This restriction results from the fact that the anticancer drugs
used in the present chemotherapy lack efficient selectivity for
malignant cells. Itis an established fact thatdeoxyribose nucleic
acid (DNA) is the primary target molecule for anticancer and
antiviral therapies. Design of molecules that can bind or cleave
DNA provides a formidable opportunity for pharmacochemist
which can offer new prospects for controlled manipulation of
genome (Jarrahpour et al., 2007; Zhang et al., 2008).
In view of all of the above, we herein report the syn-
thesis some new imidazo[2,1-b][1,3,4]thiadiazoles 5h–5s
derivatized with coumarin and substituted at the 4-position
of the 3-arylsydnone ring from 3-aryl-4-formylsydnone
(1a–1d). The present study also includes analyzing target
compounds for their anticancer activity against human
colorectal adenocarcinoma cell line HT-29 and their DNA
cleavage property. Further, these newly synthesized mol-
ecules were subjected for their toxicity, permeability
through membranes (clogP) and hence calculated drug
score for their bioavailability using OSIRIS Property
Explorer. The in vitro toxicity assay was also performed on
Imidazo [2,1-b][1,3,4]thiadiazole derivatives have been of
interest since from many years due to their antineoplastic
G. Tegginamath ꢀ R. R. Kamble (&) ꢀ T. Taj ꢀ
P. P. Kattimani ꢀ G. Y. Meti
Department Studies in Chemistry, Karnatak University,
Dharwad 580003, India
e-mail: kamchem9@gmail.com
123

4368
Med Chem Res (2013) 22:4367–4375
the E. coli AB1157 (wild type) cultures to check for the
IR spectra of the title compounds (5h–5s) showed mainly
two strong absorption bands around 1,757–1,768 and
1,680–1,691 cm-1 due to sydnone and coumarin carbonyl
groups, respectively. Another medium absorption band was
observed around 1,602–1,630 cm-1 due to C=N stretching.
The C–H stretching vibrations were observed around
2,915–3,138 cm-1 in all the compounds.
survivability.
Chemistry
A typical synthetic strategy employed to obtain the title
compounds 5h–5s is given in Scheme 1. Thiosemicarba-
zone 2a–2d was prepared by condensation of 3-aryl-4-
formylsydnone (1a–1d) and thiosemicarbazide. The com-
pound 2a–2d was then cyclized in the presence of FeCl3
and sodium citrate/citric acid to 3-aryl-4-[50-amino-
[1,3,4]thiadiazol-20-yl]sydnone (3a–3d) which was then
condensed with 3-bromoacetyl-6-substituted-coumarin
(4e–4g) to get the title compounds (5h–5s).
1
The H NMR spectral analyses of the title compounds
(5h–5s) displayed a characteristic singlet in the range d
0
8.38–8.68 ppm due to imidazole proton (C5 –H). The pro-
tons of substituents viz., methyl (5k–5m), methoxy (5n–
5p), and the remaining aromatic protons appeared at their
respective regions. 13C NMR of all these compounds
showed number of signals which are consistent with the
number of carbons in the respective molecules. So also, in
electron impact studies, all the title compounds showed the
molecular ion peaks at their respective m/z.
The proposed mechanism for the formation of the title
compounds is depicted in Scheme 2. The Fe?3 ion acts as a
template which helps in bringing thione (C=S) and imine CH
in the close proximity due to which the attack of sulfur is
possible. The alkaline pH of the reaction mixture (due to citric
acid and sodium citrate buffer) is responsible for the removal
of hydride ion (H-) which further transfers an electron to
Fe?3 and thus reduces it to Fe?2. This is followed by nucle-
ophilic attack of nitrogen present at 2nd position on the a-
carbon of bromoacetyl group and further nucleophilic addi-
tion-dehydration on the carbonyl carbon results into the for-
mation of imiazo[2,1-b] [1,3,4]thiadiazole skeleton (5h–5s).
Pharmacological parameters for oral bioavailability
For a compound to qualify as a drug candidate, certain
parameters are to be analyzed according to Lipinski’s rule of
five (Lipinski, 2004; Lipinski et al., 1997; Sangamwar et al.,
2007). The prediction of toxicity, drug-likeliness, and drug
score of the compounds were done using OSIRIS Property
Explorer (Emami et al., 2011; Gireesh et al., 2011; Taj et al.,
2011). The prediction is a fragment based approach and the
occurrence of frequency of each fragment is determined
within the collection of traded drugs and within the sup-
posedly non-drug like collection of commercially available
chemicals. A positive drug-likeliness value (0.1–10) states
that a molecule contains predominantly fragments which are
frequently present in traded drugs.
Results and discussion
Structures of the synthesized compounds were established
1
on the basis of IR, H NMR MS, and CHN analyses. The
Scheme 1 Synthetic pathway
of title compounds05h–5s 5h–
O
O
5s: 5h—R = C6H5 R0 = H;
O
0
5i—R = C6H5 R0 = Br; 5j—
O
EtOH/H2O
Stirr, 10min
N
R = C6H5 R0 =0Cl; 5k—
H2NSCHN
N
C
H
0
NH2NHCSNH 2
N
N
R = p-CH3C6H4 R0 = H; 5l—
OHC
N
R
R = p-CH3C6H4 R0 = Br;
0
R
0
2a-d
5m—R = p-CH3C6H4
R0 = Cl; 5n—R = p-
OCH3C6H4 R0 = H; 5o—
1a-d
i) Fe+3
ii) Citric acid,
Sodium citrate
0
R = p-OCH3C6H4, R0 = Br;
5p—R = p-OCH3C6H4,
R0 = Cl; 5q—R = p-ClC6H4,
R0 = H; 5r—R = p-ClC6H4,
R0 = Br; 5s—R = p-ClC6H4,
R’ = Cl
O
R'
CH2Br
O
O
O
4e-g
O
O
N
N
O
N
N
N
N
Dry ethanol
R'
N
N
S
S
N
R
R
H2N
O
O
5h-s
3a-d
123

Med Chem Res (2013) 22:4367–4375
4369
H
Scheme 2 Proposed
mechanism for the formation of
title compounds 5h–5s
H
H
Fe+2
N
N
Fe+3
N
N
N
N
Sod.citrate
Citric acid
H
R
H
Fe+3
S
C
C
C
C
NH2
R
NH2
R
H-
NH2
S
[H]
S
2a-d
R1
O
Br
C
H
R1
-HBr
N
N
N
N
N
N
O
H
NH2
NH
NH
R
R
S
S
S
H
H
OH
R1
N
N
N
N
-H2O
R1
R
R
N
N
S
S
5h-s
*
R'
as in Scheme 1
R1
=
R = as in Scheme 1
O
O
The drug toxicity is a factor of great importance for
a potential commercial drug since a significant number of
drugs are disapproved in clinical trials based on their
high toxicity profile. The Osiris calculations allow us
to predict the toxicity risks in terms of mutagenicity,
tumorigenicity, irritating and reproductive effects. The
clogP is an important physicochemical property which
indicates the lipophilicity and the ability of a molecule to
cross the biological membranes. According to Lipinski’s
rule of five the clogP value below 5 is feasible for a
compound to be a future drug.
value compared to other compounds. In correlation to this
behavior the compound 5h has shown comparatively good
anticancer activity.
In vitro toxicity assay of the title compounds
In vitro toxicity of the title compounds was analyzed by
carrying out inhibition assay of E. coli AB1157 (wild type).
E. coli AB1157 is a bacterial strain which is used for eval-
uating the cytotoxic/mutagenic/carcinogenic effects of var-
ious compounds with a potential of inducing DNA damage
and thereby inactivating culture growth or causing bacterial
death. At molecular level, the DNA damage caused by the
compounds (that induce point mutations leading base pair
substitution, compounds that release free radicals causing
DNA damage through oxidation, DNA–Protein cross link-
ing) can be evaluated using this bacterial strain. Hence, this
bacterial strain is widely used for obtaining preliminary
information about detrimental effects on the cells by the lead
molecules (Sikora and Grzesiuk, 2010; Pinto et al., 2012;
Yuan et al., 2008). The genotypic characteristics of the wild-
type bacterial strain E. coli AB 1157 is thr1,leuB6(pro–
gpt)62,his4,argE3,thi1,ara14,lacY1galK2,xyl5,mtl1,rpsL31,
tsx33,SupE44,kdgK51.
Depending upon this evaluation, it was observed that the
molecules 5j, 5m, and 5s did not show any mutagenic,
tumorigenic, irritant, or reproductive effect. Another
interesting point is that these molecules possess more drug-
likeliness value and hence show favorable drug score
value. Hence, these compounds may be said to exhibit
good bioavailability. It is also interesting to note that the
above molecules 5j, 5m, and 5s exhibited potent anticancer
activity compared with the standard.
The compounds 5i, 5l, and 5r have shown compara-
tively less toxicity and have considerable drug score value
(Table 1) and these compounds have exhibited moderate
anticancer activities. The remaining compounds have
shown more toxicity and less drug score value and in
correlation to this, these compounds have shown partial to
less anticancer activity as compared to the standard. It is
noteworthy to mention that the molecule 5h which does not
have any substituent on both phenyl ring as well as on
coumarin has exhibited no toxicity and more drug score
It was observed that the compounds 5h–5m and 5q–5s
did not show the inhibition of E. coli AB 1157 at all the
concentrations (viz., 125, 250, 500, 1000, and 2000 lg)
used as compared to the stannous chloride. However, the
compounds 5n–5p have exhibited the inhibition at
1,000 lg (1 mg). These results indicate that the compounds
123

4370
Med Chem Res (2013) 22:4367–4375
Solubility Drug-likeliness Drug score
Table 1 Pharmacological parameters for bioavailability
Entry no.
R
R0 ClogP Toxicity
Mutagenic Tumorigenic Irritant Reproductive effect
5h
5i
C6H5
H
3.44
?
?
?
?
?
?
?
?
?
?
?
?
?
?
???
?
-2.03
-2.87
-2.77
-2.38
-3.21
-3.11
-2.05
-2.89
-2.79
-2.77
-3.6
-1.82
-4.11
-1.83
-3.13
-5.42
-3.14
-2.85
-5.14
-2.88
-1.01
-3.25
-1.08
1.26
0.24
0.37
0.22
0.22
0.32
0.11
0.14
0.16
0.25
0.20
0.34
C6H5
Br 4.14
Cl 4.05
??
?
?
5j
C6H5
?
?
5k
5l
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-OCH3C6H4
H
3.76
?
?
???
?
Br 4.45
Cl 4.37
??
?
?
5m
5n
5o
5p
5q
5r
5s
?
?
H
3.34
???
???
???
?
??
??
??
?
???
?
p-OCH3C6H4 Br 4.03
p-OCH3C6H4 Cl 3.95
?
p-ClC6H4
p-ClC6H4
p-ClC6H4
H
4.05
???
?
Br 4.75
Cl 4.67
??
?
?
?
?
-3.51
? Non toxic, ?? mild toxic, ??? highly toxic
anticancer activity as compared to reference drug CISPL in
case of activity against HT-29-human colorectal adeno-
carcinoma cell line.
Table 2 In vitro toxicity assay of title compounds against E. coli
AB1157 (wild type)
Entry no. Zone of inhibition at various
concentrationsa
MIC lg (mg)
The compounds 5j, 5m, and 5s (chloro substituted
compounds) have shown good anticancer property with
LC50 values [80, TGI (Total Growth Inhibition) values
[40, and GI50 values 7.7, 7.9, and 8.0, respectively
(Table 3). Bromo substituted compounds viz, 5i, 5l, 5r on
coumarin ring have exhibited moderate activity against this
cell line with LC50 values [70 and TGI [ 30 and GI50
value of 5.6, 6.1, and 5.25, respectively. The compounds
5k and 5q have shown partial anticancer activity and
remaining compounds 5n, 5o, and 5p have shown less
anticancer activity. Moderate and partial activity of 5l and
5k may be attributed to the hydrophobic character of
methyl moiety present on the phenyl group of the sydnone
ring. The very weak activity of the compounds 5n, 5o, and
5p is attributed to methoxy group present on the N-2
position of sydnone ring which increases the toxicity and
chemotherapeutic index. Figure 1 depicts the activity of
compounds plotted against GI50 values.
250 lg 500 lg 1,000 lg 2,000 lg
5h
5i
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.30
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.50
0.00
0.00
0.00
0.00
0.00
0.00
0.50
0.50
0.50
0.00
0.00
0.00
0.80
0.00
0.00
0.00
0.00
0.00
0.00
0.80
0.80
0.80
0.00
0.00
0.00
1.50
[2
[2
[2
[2
[2
[2
1.0
1.0
1.0
[2
[2
[2
0.25
5j
5k
5l
5m
5n
5o
5p
5q
5r
5s
SnCl2
Bold values indicate the toxicity of the compounds at that
concentration
No inhibition at 125 lg
a
DNA cleavage activity
Zone of inhibition in cm
5h–5m and 5q–5s were not capable in interfering the
survival of an E. coli culture AB1157 (Table 2) thus
demonstrating the absence of cytotoxic effect in the con-
ditions used during the experiments.
The DNA cleavage activity was determined using gel
electrophoresis according to reported method (Sambrook
et al., 1989). The picture of the gels is presented in Fig. 2.
This indicates that the control DNA alone does not show
any apparent cleavage as the title compounds did. The gel
after electrophoresis clearly revealed that the compound 5s
with chloro substituent on the phenyl ring of sydnone as
well as coumarin moiety has exhibited potent DNA
cleavage as shown in the Fig. 2. The compounds 5m and
Anticancer activity
The compounds were divided into four categories (good,
moderate and partial activity) based on the results of
123

Med Chem Res (2013) 22:4367–4375
4371
compound 5s inhibits the growth of the pathogenic
organism by cleaving the genome.
Table 3 LC50, TGI, and GI50 values against cell line—HT-29-human
colorectal adenocarcinoma concentrations (lg/mL)
Entry no.
R
R0
LC50
TGI
GI50
Activity
5h
5i
C6H5
H
[70
[30
[30
>40
\30
[30
>40
\30
\30
\30
\30
[40
>40
43
6.3
Active
Ma
Ga
Pa
Experimental procedure
C6H5
Br [70
5.6
5j
C6H5
Cl
H
>80
7.7
Chemistry
5k
5l
p-CH3C6H4
p-CH3C6H4
p-CH3C6H4
p-OCH3C6H4
p-OCH3C6H4
p-OCH3C6H4
p-ClC6H4
p-ClC6H4
p-ClC6H4
[80
4.23
6.1
Br [70
Ma
Ga
Pa
Melting points were determined in open capillaries. IR
1
(KBr) spectra were recorded on FT-IR spectrometer. H
5m
5n
5o
Cl
H
>80
>70
7.9
3.14
3.04
3.68
4.00
5.25
8.00
8.27
NMR spectra (DMSO-d6) were recorded on a Bruker
Avance-300 (300 MHz, FT-NMR) and 13C NMR spectra
(CDCl3 or DMSO-d6) were recorded on FT-NMR Bruker
Avance-II 400 MHz spectrometer with TMS as an internal
reference. Mass spectra were recorded on a GCMS-
SC\AD\17-004. All the reagents and solvents used were of
analytical grade, and were used as supplied unless other-
wise stated. TLC was performed on silica gel coated plates
for monitoring the reactions (Toluene: Methanol, 80:20).
The starting compound 3-aryl-4-formylsydnone 1a–1d was
prepared by formylation of the 3-arylsydnone (Thoman
et al., 1964) using N-methylformanilide in POCl3. The
compound 1a–1d was condensed with thiosemicarbazide to
obtain the corresponding thiosemicarbazone 2a–2d. The
compound 2a–2d was converted into the 3-aryl-4-[50-
amino-[1,3,4]-thiadiazol-20-yl]sydnone 3a–3d in the pres-
ence of FeCl3 as catalyst under the influence of citric acid
and sodium citrate. The cell lines were procured from
National centre for cell science (NCCS), Pune, Maha-
rashtra, India.
Br [80
Pa
5p
5q
5r
Cl
H
>70
Pa
[80
Pa
Br [70
Ma
Ga
5s
Cl
>80
CISPL
135
Bold values indicate the compounds having good anticancer activity
Ga good activity, Ma moderate activity, Pa partial activity
General procedure for the preparation of 4-{60-(coumarin-
300-yl)-imidazo-[2,1-b][1,3,4]thiadiazol-20-yl}-3-
arylsydnone (5h–5s)
Fig. 1 Anticancer activity of the synthesized compounds against
HT-29-human colorectal adenocarcinoma cell line 5h–5s
A mixture of equimolar quantities of 3-phenyl-4-[50-
amino-60-phenyl-[1,3,4]-thiadiazol-20-yl]sydnone (3a–3d)
(0.263 g, 1 mmol) and 3-bromoacetyl-6-(substituted)-cou-
marin (4e–4g) (1 mmol) was refluxed in dry ethanol
(20 mL) for 12 h. The excess solvent was distilled off and
poured into ice cold water and the solid hydrobromide salt
separated was neutralized by aqueous sodium carbonate
solution to get free base 5h. It was filtered, washed with
water, dried, and recrystallized using ethanol. The other
imidazo[2,1-b][1,3,4]thiadiazole derivatives 5i–5s were
prepared analogously.
4-{60-(Coumarin-300-yl)-imidazo-[2,1-b][1,3,4]thiadiazol-
20-yl}-3-phenylsydnone (5h)
Fig. 2 DNA cleavage activity of the title compounds
5q have shown moderate cleavage. The difference was
observed in bands of all the compounds compared to the
control DNA. With this, it can be concluded that the
Light yellow crystals. Yield 80 % mp (°C) 219–220. IR
(KBr in cm-1); 3135 (–CH), 2920, 1760 (–CO), 1682
1
(C=O), 1602 (C=N), 1483. H NMR (300 MHz, d ppm,
123

4372
Med Chem Res (2013) 22:4367–4375
0
126.6, 127.5, 128.4, 128.8, 129.4, 137.4 (C2 –C), 143.3,
CDCl3); 7.46–7.63 (m, 5H, N3–ArH), 7.76–7.92 (m, 4H,
Ar–H), 8.32 (s, 1H, C4–H), 8.68 (s, 1H, C5 –H), 13C NMR
0
155.2 (C4–C), 164.4. Mass m/z (%) 443. Analysis; Cal-
culated for C22H15N5O4S: C, 59.32; H, 3.39; N, 15.72.
Found: C, 59.25; H, 3.42; N, 15.70.
(300 MHz, d ppm, CDCl3); 102 (C5–C), 116.30, 118.2,
0
120.2 (C5 –C), 121.4, 122.3, 125.5, 126.8, 127.5 (C6 –C),
0
00
0
0
128.4, 129.6 (C3 –C), 129.8, 138.1 (C2 –C), 141.3 (C8 –C),
150.2, 154.7 (C4–C), 162.00. Mass m/z (%) 429 (M?1,
18.3), 194 (48.2), 44 (100). Analysis; Calculated for
C21H11N5O4S: C, 58.52; H, 3.12; N, 16.19. Found: C,
58.46; H, 3.04; N, 16.23.
4-{60-(600-Bromocoumarin-300-yl)-imidazo-[2,1-
b][1,3,4]thiadiazol-20-yl}-3-p-tolylsydnone (5l)
Pale yellow needles. Yield 85 % mp (°C) 202–203. IR
(KBr in cm-1); 3137 (–CH), 2938, 2916, 1762 (–CO), 1686
1
4-{60-(600-Bromocoumarin-300-yl)-imidazo-[2,1-
b][1,3,4]thiadiazol-20-yl}-3-phenylsydnone (5i)
(C=O), 1618 (C=N), 1484. H NMR (300 MHz, d ppm,
CDCl3); 2.53 (s, 3H, CH3), 6.88–7.48 (m, 4H, N3–ArH),
7.63–7.92 (m, 3H, Ar–H), 8.25 (s, 1H, C4–H), 8.48 (s, 1H,
C5 –H). 13C NMR (300 MHz, d ppm, CDCl3); 34.3 (CH3–
0
C), 103.4 (C5–C), 116.6, 117.4, 119.8, 123.6, 124.3 (C5 –
0
Light yellowish brown crystals. Yield 85 % mp (°C)
248–249. IR (KBr in cm-1); 3128 (–CH), 2932, 1752
(–CO), 1685 (C=O), 1615 (C=N), 1471. 1H NMR
(300 MHz, d ppm, CDCl3); 7.38–7.50 (m, 5H, N3–ArH),
7.55-8.02 (m, 3H, Ar–H), 8.22 (s, 1H, C4–H), 8.50 (s, 1H,
0
C), 127.5, 128.4, 129.3, 129.9, 130.3, 131.6, 138.4 (C2 –C),
143.4, 146.3, 149.6, 155.6 (C4–C), 163.2. Mass m/z (%)
525 (M?2, 15.6), 523 (M?, 17.2). Analysis; Calculated for
C22H12N5BrO4S (523): C, 50.39; H, 2.69; N, 13.36. Found:
C, 50.32; H, 2.62; N, 13.40.
C5 –H); 13C NMR (300 MHz, d ppm, CDCl3); 98.0 (C5–C),
0
0
116.50, 119.1, 121.6 (C5 –C), 122.2, 123.7, 124.3, 126.4,
0
0
129.2, 129.8, 130.3, 131.3, 140.2 (C2 –C), 146.4 (C8 –C),
149.5, 153.3 (C4–C), 163.3. Mass m/z (%) 511 (M?2,
17.4), 509 (M?, 19.8). Analysis; Calculated for C21H10
N5BrO4S: C, 49.42; H, 2.37; N, 13.72. Found: C, 49.46;
H, 2.44; N, 13.68.
4-{60-(600-Chlorocoumarin-300-yl)-imidazo-[2,1-
b][1,3,4]thiadiazol-20-yl}-3-p-tolylsydnone (5m)
Pale yellowish needles. Yield 60 % mp (°C) 175–176. IR
(KBr in cm-1); 3134 (–CH), 2933, 2911, 1762 (–CO), 1683
1
(C=O), 1613 (C=N), 1481. H NMR (300 MHz, d ppm,
CDCl3); 2.42 (s, 3H, CH3), 6.85–7.40 (m, 4H, N3–ArH),
4-[60-(600-Chlorocoumarin-300-yl)-imidazo-[2,1-
b][1,3,4]thiadiazol-200-yl]-3-phenylsydnone (5j)
7.56–7.93 (m, 3H, Ar–H), 8.18 (s, 1H, C4–H), 8.46 (s, 1H,
C5 –H). 13C NMR (300 MHz, d ppm, CDCl3); 34.1 (CH3–
0
Pale yellow crystals. Yield 75 % mp (°C) 224–225. IR
0
C), 103.2 (C5–C), 116.3, 117.6, 122.9, 123.7, 126.9 (C5 –
(KBr in cm-1); 3131 (–CH), 2935, 1758 (–CO), 1683
0
C), 127.8, 128.7, 128.8, 129.4, 129.9, 131.2, 138.4 (C2 –C),
1
(C=O), 1610 (C=N), 1468. H NMR (300 MHz, d ppm,
CDCl3); 7.42–7.59 (m, 5H, N3–ArH), 7.62–7.79 (m, 3H,
Ar–H), 8.28 (s, 1H, C4–H), 8.57 (s, 1HC5 –H). 13C NMR
143.3, 146.2, 148.3, 157.3 (C4–C), 162.7. Mass m/z (%)
480 (M?2, 7.3), 478 (M?, 22.4). Analysis; Calculated for
C22H12N5ClO4S (478): C, 55.06; H, 2.94; N, 14.59. Found:
C, 55.00; H, 2.90; N, 14.51.
0
(300 MHz, d ppm, CDCl3); 103.6 (C5–C), 117.10, 118.8,
0
122.6 (C5 –C), 122.9, 123.2, 126.9, 127.8, 128.5, 129.4,
0
129.6.3, 131.0, 139.4 (C2 –C), 146.7, 148.3, 154.2 (C4–C),
3-(p-Anisyl)-4-{60-(coumarin-30-yl)-imidazo[2,1-
b][1,3,4]thiadiazol-20-yl}-sydnone (5n)
163.3. Mass m/z (%) 466 (M?2, 9.4), 464 (M?, 27.7).
Analysis; Calculated for C21H10N5ClO4S: C, 54.14; H,
2.60; N, 15.03. Found: C, 54.20; H, 2.52; N, 14.98.
Yellowish crystals. Yield 70 % mp (°C) 213–214. IR (KBr
in cm-1); 3128 (–CH), 2938, 2917, 1751 (–CO), 1680
4-{60-(Coumarin-3-yl)-imidazo-[2,1-b][1,3,4]thiadiazol-
20-yl}-3-p-tolylsydnone (5k)
1
(C=O), 1613 (C=N), 1472. H NMR (300 MHz, d ppm,
CDCl3); 3.70 (s, 3H, OCH3), 6.77–7.12 (m, 4H, N3–ArH),
7.54–7.76 (m, 4H, Ar–H), 8.12 (s, 1H, C4–H), 8.38 (s, 1H,
C5 –H). 13C NMR (300 MHz, d ppm, CDCl3); 64.4
(OCH3–C), 102.6 (C5–C), 115.4, 115.8, 117.3, 117.9,
Yellow needles. Yield 70 % mp (°C) 289–290. IR (KBr in
0
cm-1); 3130 (–CH), 2932, 2910, 1755 (–CO), 1678 (C=O),
1
1610 (C=N), 1480. H NMR (300 MHz, d ppm, CDCl3);
2.38 (s, 3H, CH3), 6.80–7.36 (m, 4H, N3–ArH), 7.50–7.88
0
121.6, 122.3, 123.4 (C5 –C), 125.7, 126.2, 127.3, 128.4,
0
129.8, 138.6, 139.4 (C2 –C), 146.6, 150.7, 158.6 (C4–C),
0
(m, 4H, Ar–H), 8.14 (s, 1H, C4–H), 8.44 (s, 1H, C5 –H).
162.7. Mass m/z (%) 459. Analysis; Calculated for
C22H15N5O5S (459): C, 57.26; H, 3.28; N, 15.18. Found:
C, 57.20; H, 3.22; N, 15.15.
13C NMR (300 MHz, d ppm, CDCl3); 32.6 (CH3–C), 102.8
0
(C5–C), 116.5, 116.9, 121.5, 122.3, 123.4 (C5 –C), 125.3,
123

Med Chem Res (2013) 22:4367–4375
4373
1
3-p-Anisyl-4-{60-(600-bromocoumarin-300-yl)-imidazo-
[2,1-b][1,3,4]thiadiazol-20-yl}-sydnone (5o)
(C=O), 1617 (C=N), 1480. H NMR (300 MHz, d ppm,
CDCl3); 7.54–7.75 (m, 4H, N3–ArH), 7.89–8.05 (m, 3H,
Ar–H), 8.37 ( s, 1H, C4–H), 8.63 (s, 1H, C5 –H). 13C NMR
0
Yellowish brown crystals. Yield 65 % mp (°C) 221–222.
(300 MHz, d ppm, CDCl3); 102.9 (C5–C), 117.6, 119.8,
0
123.7 C5 –C), 124.2, 124.5, 125.3, 127.2, 128.6, 129.3,
IR (KBr in cm-1); 3124 (–CH), 2933, 2914, 1759 (–CO),
1
0
130.4, 131.6, 138.2, 139.6 (C2 –C), 146.3, 149.6, 156.4,
1685 (C=O), 1622 (C=N), 1475. H NMR (300 MHz, d
ppm, CDCl3); 3.82 (s, 3H, –OCH3), 6.81–7.17 (m, 4H, N3–
157.4 (C4–C), 164.3. Mass m/z (%) 548 (M?4, 8.3), 546
(M?2, 25.4), 544 (M?, 17.2). Analysis; Calculated for
C21H9N5BrClO4S (544): C, 46.30; H, 2.04; N, 12.86.
Found: C, 46.26; H, 2.00; N, 12.80.
ArH), 7.43–7.94 (m, 3H, Ar–H), 8.21 (s, 1H, C4–H), 8.42
(s, 1H, C5 –H). 13C NMR (300 MHz, d ppm, CDCl3); 64.8
(OCH3–C), 103.2 (C5–C), 115.8, 116.2, 117.2, 119.8, 123.7
0
0
(C5 –C), 124.6, 127.5, 129.3, 130.4, 131.3, 138.2, 139.6
4-[60-(600-Chlorocoumarin-300-yl)-imidazo[2,1-
0
(C2 –C), 146.4, 149.4, 157.4 (C4–C), 163.6. Mass m/z (%)
b][1,3,4]thiadiazol-20-yl]-3-p-chlorophenyl sydnone (5s)
541 (M?2, 18.6), 539 (M?, 20.3). Analysis; Calculated for
C22H12N5BrO5S (539): C, 48.90; H, 2.61; N, 12.96. Found:
C, 48.86; H, 2.56; N, 13.00.
Straw yellow crystals. Yield 65 % mp (°C) 290–291. IR
(KBr in cm-1); 3124 (–CH), 2921, 1764 (–CO), 1686
1
3-p-Anisyl-4-[60-(600-chlorocoumarin-300-yl)-imidazo-
[2,1-b][1,3,4]thiadiazol-20-yl]-sydnone (5p)
(C=O), 1611 (C=N), 1479. H NMR (300 MHz, d ppm,
CDCl3); 7.53–7.74 (m, 4H, N3–ArH), 7.85–8.01 (m, 3H,
Ar–H), 8.36 (s, 1H, C4–H), 8.62 (s, 1H, C5 –H). 13C NMR
0
Yellow crystals. Yield 80 % mp (°C) 217–218. IR (KBr in
(300 MHz, d ppm, CDCl3); 102.6 (C5–C), 117.2, 118.9,
0
123.4 C5 –C), 123.8, 124.3, 125.6, 126.8, 128.2, 129.1,
cm-1); 3126 (–CH), 2935, 2916, 1755 (–CO), 1681 (C=O),
1
0
130.2, 131.3, 137.8, 138.6 (C2 –C), 145.8, 148.9, 155.9,
1618 (C=N), 1473. H NMR (300 MHz, d ppm, CDCl3);
3.76 (s, 3H, OCH3), 6.79–7.13 (m, 4H, N3–ArH),
156.7 (C4–C), 163.8. Mass m/z (%) 504 (M?4, 6.3), 502
(M?2, 25.2), 500 (M?, 33.5). Analysis; Calculated for
C21H9N5Cl2O4S (500): C, 50.41; H, 2.22; N, 14.00. Found:
C, 50.38; H, 2.18; N, 14.06.
7.48–7.87 (m, 3H, Ar–H), 8.15 (s, 1H, C4–H), 8.40 (s, 1H,
C5 –H). 13C NMR (300 MHz, d ppm, CDCl3); 64.6
(OCH3–C), 102.8 (C5–C), 115.2, 117.3, 118.4, 122.9, 123.4
0
0
C5 –C), 124.3, 126.8, 127.5, 129.4, 131.3, 136.3, 137.3,
0
139.2 (C2 –C), 146.1, 148.4, 150.4, 157.2 (C4–C), 162.0.
Mass m/z (%) 496 (M?2, 10.2), 494 (M?, 31.6). Analysis;
Calculated for C22H12N5ClO5S (494): C, 53.28; H, 2.85; N,
14.12. Found: C, 53.22; H, 2.90; N, 14.05.
Pharmacological evaluation
In vitro cytotoxicity assay (De Lemos et al., 2011)
3-(p-Chlorophenyl)-4-[60-(coumarin-300-yl)-imidazo
[2,1-b][1,3,4]thiadiazol-20-yl]-sydnone (5q)
The E. coli AB 1157, a wild-type strain, proficient to repair
DNA damage is considered for this study. Initially, the
stock culture of bacteria was revived by inoculating in
broth medium and grown at 37 °C for 18 h. The LB Agar
plates were prepared and wells were made in the solidified
LB agar plate. Each plate was inoculated with 18 h old
cultures (100 ll, 10-4 cfu) and spread evenly on the plate.
After 20 min, the wells were filled with compound at dif-
ferent concentrations. Standard compound plate was also
prepared in the same manner. All the plates were incubated
at 37 °C for 24 h and the diameter of inhibition zone were
noted. Media was prepared using tryptone (10.00 g), NaCl
(10.00 g), and yeast extract (5.00 g); agar (20.00 g) in
distilled water (1,000 mL). The results were presented as
diameter of inhibition zones in cm (Table 2).
Yellow needles. Yield 50 % mp (°C) 179–190. IR (KBr in
cm-1); 3128 (–CH), 2924, 1763 (–CO), 1685 (C=O), 1608
(C=N), 1478. 1H NMR (300 MHz, d ppm, CDCl3);
7.52–7.73 (m, 4H, N3–ArH), 7.82–7.98 (m, 4H, Ar–H),
8.35 (s, 1H, C4–H), 8.61 (s, 1H, C5 –H). 13C NMR
0
(300 MHz, d ppm, CDCl3); 102.2 (C5–C), 117.3, 117.8,
0
121.5, 122.3, 123.2 C5 –C), 124.6, 125.4, 126.8, 127.4,
0
128.4, 129.3, 129.9, 137.4, 138.8 (C2 –C), 144.4, 146.2,
150.6, 155.4 (C4–C), 163.5. Mass m/z (%) 466 (M?2, 8.1),
464 (M?, 25.3). Analysis; Calculated for C21H10N5ClO4S
(464): C, 54.14; H, 2.60; N, 15.03. Found: C, 54.10; H,
2.58; N, 15.10.
4-[60-(600-Bromocoumarin-300-yl)-imidazo[2,1-b]
[1,3,4]thiadiazol-20-yl]-3-p-chloro phenylsydnone (5r)
Anticancer activity assay (Skehn et al., 1990)
Colorimetric cytotoxicity assay for anticancer screening is
a rapid, sensitive, and inexpensive method for measuring
the cellular protein content of adherent and suspension
Light yellow crystals. Yield 65 % mp (°C) 203–204. IR
(KBr in cm-1); 3122 (–CH), 2918, 1767 (–CO), 1689
123

4374
Med Chem Res (2013) 22:4367–4375
Agarose gel electrophoresis
cultures in 96-well microtiter plates. Cultures fixed with
trichloroacetic acid were stained for 30 min with 0.4 %
(w/v) sulforhodamine B (SRB) dissolved in 1 % acetic
acid. Unbound dye was removed by four washes with 1 %
acetic acid, and protein-bound dye was extracted with
10 mM unbuffered Tris base [tris(hydroxymethyl)amino-
methane] for determination of optical density in a computer
interfaced, 96-well microtiter plate reader. The SRB assay
results were linear with the number of cells and with values
for cellular protein measured by both the Lowry and
Bradford assays at densities ranging from sparse sub con-
fluence to multilayered supraconfluence. The signal-to-
noise ratio at 564 nm was approximately 1.5 with 1,000
cells per well. The sensitivity of the SRB assay compared
favorably with sensitivities of several fluorescence assays
and was superior to those of both the Lowry and Bradford
assays and to those of 20 other visible dyes. The SRB assay
provided a colorimetric end point that is nondestructive,
indefinitely stable, and visible to the naked eye. It provided
a sensitive measure of drug-induced cytotoxicity, and was
useful in quantitating clonogenicity, and is well suited to
high-volume, automated drug screening. SRB fluoresces
strongly with laser excitation at 488 nm and can be mea-
sured quantitatively at the single-cell level by static fluo-
rescence cytometry.
DNA cleavage assay was done by agarose gel electro-
phoresis method. Test samples (1 mg/mL) were prepared
in DMF. The samples (25 mg) were added to the isolated
DNA of E. coli. The samples were incubated for 2 h at
37 °C and then sample (25 mL, mixed with bromophenol
blue dye at 1:1 ratio) was loaded carefully into the elec-
trophoresis chamber wells along with standard DNA mar-
ker containing TAE buffer (4.84 g tris base, pH 8.0, 0.5 M
EDTA/1 L) and finally loaded on agarose gel and constant
electricity (50 Volts) for 45 min. The gel was then
removed carefully and stained with ETBR solution (10 lg/
mL) for 10–15 min and the bands were observed under UV
transilluminator and then photographed to determine the
extent of DNA cleavage. The results were compared with
standard DNA marker.
Conclusions
In summary, we have developed a simple, novel, and
efficient synthetic protocol for a series of imidazo[2,1-
b][1,3,4]thiadiazoles 5h–5s substituted at the 4 position of
the sydnone ring using 3-aryl-4-formylsydnone and studied
their anticancer activity against cell line HT-29-human
colorectal adenocarcinoma using cisplatin drug as standard
and DNA cleavage analyses. The compounds were also
tested for their toxicity and drug score by OSIRIS Property
Explorer. Also, in vitro cytotoxicity assay was done by
evaluating the effect of inhibition of E.coli AB 1,157 (wild
type). The compounds 5n–5p only have exhibited toxicity
at 1.0 mg (MIC). The compounds 5j, 5m, and 5s (chloro
substituted derivatives) exhibited very good anticancer
activity, and the compound 5s has completely cleaved the
DNA.
DNA cleavage activity
Preparation of culture media
DNA cleavage experiments were done according to the
literature (Barreira et al., 2008). Nutrient broth [peptone,
10; yeast extract, 5; NaCl, 10; in (g/L)] was used for
culturing the pathogen E. coli. Media (50 mL) was pre-
pared and autoclaved for 15 min at 121 °C under 15 lb
pressure. The autoclaved media was inoculated for 24 h at
37 °C.
Acknowledgments The authors are thankful to the USIC, Karnatak
University, Dharwad for carrying out the spectral (IR, 1H NMR, MS)
and elemental analyses. The authors are also thankful to Biogenics
Ltd, Hubli and NGH Institute of Dental sciences and Research centre,
Belgaum, Karnataka, India for their assistance in carrying out bio-
logical activities. One of the authors (TG) acknowledges the Uni-
versity for awarding Research Studentship.
Isolation of DNA
The fresh bacterial culture (1.5 mL) was centrifuged to
obtain the pellet which was then dissolved in lysis buffer
(100 mM tris pH 8.0, 50 mM EDTA, 10 % SDS,
0.50 mL), saturated phenol (0.50 mL) was added and
incubated at 55 °C for 10 min, and then centrifuged at
10,000 rpm for 10 min and to the supernatant, equal vol-
ume of chloroform: iso-amyl alcohol (24:1) and 1/20th
volume of 3 M sodium acetate (pH 4.8) was added. Cen-
trifuging at 10,000 rpm for 10 min and to the supernatant 3
volumes of chilled absolute alcohol was added. The pre-
cipitated DNA was separated by centrifugation and the
pellet was dried and dissolved in TAE buffer (10 mM tris
pH 8.0, 1 mM EDTA) and stored in cold condition.
References
Amery WK, Hoerig CH, Fenichel RI, Chirigos MA (eds) (1984)
Immune modulation agents and their mechanism. Marcel
Dekker, New York, p 383
Andotra CS, Langer TC, Kotha A (1997) Synthesis and antifungal
activity of some substituted 1,3,4-thiadiazolo[3,2-a]-s-triazin-5-
phenyl-7-thiones and imidazo-[2,1-b]-1,3,4-thiadiazol-5-ones.
J Indian Chem Soc 74:125–127
123

Med Chem Res (2013) 22:4367–4375
4375
Andreani A, Bonazzi D, Rambaldi M, Fabbri G, Rainsford KD (1982)
5,6-Disubstituted imidazo[2,1-b]thiazoles as potential anti-
inflammatory agents. Eur J Med Chem 17:271–274
Andreani A, Rambaldi M, Mascellani G, Bossa R, Galatulas I (1986)
Synthesis and cardiotonic activity of 5,6-disubstituted imi-
dazo[2,1-b]thiazoles. Eur J Med Chem 21:451–453
Lipinski CA (2004) Lead- and drug-like compounds: the rule-of-five
revolution. Drug Discov Today Technol 1:337
Lipinski CA, Lombardo F, Dominy PW, Feeney PJ (1997) Exper-
imental and computational approaches to estimate solubility and
permeability in drug discovery and development settings. Adv
Drug Deliv Rev 23:3–25
Andreani A, Rambaldi M, Mascellani G, Rugarli P (1987) Synthesis
and diuretic activity of imidazo[2,1-b]thiazole acetohydrazones.
Eur J Med Chem 22:19–22
Manolov I, Danchev ND (1995) Synthesis, toxicological and phar-
macological assessment of some 4-hydroxy coumarin deriva-
tives. Eur J Med Chem 30:531–535
Andreani A, Rambaldi M, Locatelli A, Andreani F (1991) 5-Formy-
limidazo [2,1-b]thiazoles and derivatives with herbicidal activ-
ity. Collect Czech Chem Commun 56:2436–2447
Andreani A, Leonia A, Locatelli A, Morigi R, Rambaldi M, Simon
WA, Senn- Bilfinger J (2000) Synthesis and antisecretory
activity of 6-substituted 5-cyanomethylimidazo[2,1-b]thiazoles
and 2,6-dimethyl-5-hydroxymethylimidazo[2,1-b][1,3,4]thiadia-
zole. Arzneimittel/Drug Res 50:550–553
Moustafa MA, Nasr MN, Gineinah MM, Bayoumi WA (2004)
Synthesis and biological testing of novel analogues of sydnone
as potential antibacterial agents. Arch Pharm 337:164–170
Nofal ZM, El-Zahar MI, Abd El-Karim SS (2000) Novel coumarin
derivatives with expected biological activity. Molecules 5:
99–113
OSIRIS Property Explorer. http://www.organic-chemistry.org/prog/
peo. Accessed 17 Jan 2011
Barreira JCM, Ferreira ICFR, Oliveira MBPP, Pereira JA (2008)
Antioxidant activity and bioactive compounds of ten Portuguese
regional and commercial almond cultivars. Food Chem Toxicol
46:2230–2235
De Lemos PRG, Terra Junior ON, Amantea ML (2011) Evaluation of
the effects of an aqueous extract of Schinus terebinthifolius
involving wild bacterial culture of Escherichia coli. Asian J
Pharm Health 1:89–90
Dunkley CS, Thoman CJ (2003) Synthesis and biological evaluation
of a novel phenyl substituted sydnone series as potential
antitumor agents. Bioorg Med Chem Lett 13:2899–2901
Emami S, Kebriaeezadeh A, Ahangar N, Khorasani R (2011)
Imidazolylchromanone oxime ethers as potential anticonvulsant
agents: anticonvulsive evaluation in PTZ-kindling model of
epilepsy and SAR study. Bioorg Med Chem Lett 21:655–659
Emmanuel-Giota AA, Fylaktakidou KC, Hadjipavlou-Litina DJ,
Litinas KE, Nicolaides DN (2001) Synthesis and biological
evaluation of several 3-(coumarin-4-yl)-tetrahydroisoxazole and
Pinto NS, Carmo FS, Diniz CL, Almeida DS, Pereira MO, Santos-
Filho SD, Medeiros AC, Bernardo-Filho M (2012) Effects of an
aqueous extract of Three Ballerina on the survival of Escherichia
coli AB1157 cultures and in the action of stannous chloride.
J Med Plants Res 5:3256–3259
Raev L, Voinov E, Ivanov I, Popov D (1990) Antitumor activity of
some coumarin derivatives. Pharmazie 45:696–701
Sambrook J, Fritsch EF, Maniatis T (1989) Molecular cloning, a
laboratory manual, 2nd edn. Cold Spring Harbor Laboratory,
Cold Spring Harbor
Sangamwar AT, Deshpande UD, Pekamwar SS, Vadvalkar SM
(2007) Improving decision making for drug candidates: a
computational approach for benzthiazoles as antifungal. Indian
J Biotechnol 6:397–403
Sikora A, Grzesiuk E (2010) Reversion of argE3 to Arg? in
Escherichia coli AB1157-an informative bacterial system for
mutation detection. Acta Biochimica Pol 57:479–485
Skehn P, Storeng R, Scudiero A, Monks J, McMohan D, Vistica D,
Jonathan TW, Bokesch H, Kenney S, Boyd MR (1990) New
colorimetric cytotoxicity assay for anticancer-drug screening.
J Cancer Inst 82:1107–1112
Taj T, Kamble RR, Gireesh TM, Hunnur RK, Margankop SB (2011)
One-pot synthesis of pyrazoline derivatised carbazoles as
antitubercular, anticancer agents, their DNA cleavage and
antioxidant activities. Eur J Med Chem 46:4366–4373
Terzioglu N, Gursoy A (2003) Synthesis and anticancer evaluation of
some new hydrazone derivatives of 2,6-dimethylimidazo[2,1-
b][1,3,4]thiadiazole-5-carbohydrazide. Eur J Med Chem 38:781–786
Thoman CJ, Voaden DJ, Husnberger IM (1964) Direct formylation of
sydnones. J Org Chem 29:2044–2045
Yuan B, Cao H, Jiang Y, Hong H, Wang Y (2008) Efficient and
accurate bypass of N2-(1-carboxyethyl)-2-deoxyguanosine by
DinB DNA polymerase in vitro and in vivo. PNAS 105:
8679–8684
3-(coumarin-4-yl)-dihydropyrazole derivatives.
Chem 38:717
J Heterocycl
Gadad AK, Mahajanshetti CS, Nimbalkar S, Raichurkar A (2000)
Synthesis and antibacterial activity of some 5-guanylhydrazone/
thiocyanato-6-arylimidazo[2,1-b]-1,3,4-thiadiazole-2-sulfona-
mide derivatives. Eur J Med Chem 35:853–857
Gadad AK, Noolvi MN, Karpoormath RV (2004) Synthesis and anti-
tubercular activity of a series of 2-sulfonamido/trifluoromethyl-
6-substituted imidazo[2,1-b]-1,3,4-thiadiazole derivatives. Bio-
org Med Chem 12:5651–5659
Gireesh TM, Kamble RR, Hunnur RK, Taj T, Kariduraganavar MY
(2011) Facile TiCl4-catalyzed synthesis of novel 1,2,4-triazoles
appended to thiazoles. Chem Heterocycl Compd 47:877–885
Jarrahpour A, Khalili D, Clercq ED, Salmi C, Brunel JM (2007)
Synthesis, antibacterial, antifungal and antiviral evaluation of
some new bis-schiff bases of isatin and their derivatives.
Molecules 12:1720–1730
Khazi IAM, Mahajanshetti CS, Gadad AK, Tarnalli AD, Sultanpur
CM (1996) Synthesis, anticonvulsant and analgesic activities of
some 6-substituted imidazo[2,1-b][1,3,4]thiadiazole-2-sulfona-
mides and their 5-bromo derivatives. Arzneimittel-Forschung/
Drug Res 46:949–952
Zhang WJ, Li YT, Wu ZY, Liu ZQ, Zheng ZC (2008) Synthesis,
crystal structure and DNA-Binding study of a new Copper (II)
complex containing mixed-Ligand of iminodiacetate dianion and
6-nitro-1H-benzimidazole. J Chem Crystallogr 38:655–658
123