Synthesis, in vitro anticancer evaluation and in silico studies of novel imidazo[2,1-b]thiazole derivatives bearing pyrazole moieties

Article abstract of DOI:10.1016/j.ejmech.2013.12.010

A series of imidazo[2,1-b]thiazoles bearing pyrazole moieties 4-6(a-c) was synthesized through the reaction of 6-hydrazinylimidazo[2,1-b]thiazoles 3a-c with different β-dicarbonyl compounds. Eleven compounds were screened at the National Cancer Institute (NCI), USA for anticancer activity at a single dose (10 μM). The in vitro anticancer evaluation revealed that compounds 2a and 4-6(a) exhibited increased potency towards CNS SNB-75 and Renal UO-31 cancer cell lines. COMPARE analyses showed strong to considerable correlations with rapamycin (mTOR inhibitor). The results of assessment of toxicities, druglikeness, and drug score profiles of compounds 2a and 4-6(a) are promising. Some of the target compounds showed good docking scores with potential anticancer targets, chosen based on pharmacophore mapping of the established derivatives.

Full text of DOI:10.1016/j.ejmech.2013.12.010

European Journal of Medicinal Chemistry 75 (2014) 492e500
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Synthesis, in vitro anticancer evaluation and in silico studies of novel
imidazo[2,1-b]thiazole derivatives bearing pyrazole moieties
*
Ahmed R. Ali , Eman R. El-Bendary, Mariam A. Ghaly, Ihsan A. Shehata
Department of Medicinal Chemistry, Faculty of Pharmacy, University of Mansoura, Mansoura 35516, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of imidazo[2,1-b]thiazoles bearing pyrazole moieties 4e6(aec) was synthesized through the
Received 3 August 2013
Received in revised form
22 October 2013
Accepted 8 December 2013
Available online 23 January 2014
reaction of 6-hydrazinylimidazo[2,1-b]thiazoles 3aec with different
compounds were screened at the National Cancer Institute (NCI), USA for anticancer activity at a single
dose (10 M). The in vitro anticancer evaluation revealed that compounds 2a and 4e6(a) exhibited
b-dicarbonyl compounds. Eleven
m
increased potency towards CNS SNB-75 and Renal UO-31 cancer cell lines. COMPARE analyses showed
strong to considerable correlations with rapamycin (mTOR inhibitor). The results of assessment of tox-
icities, druglikeness, and drug score profiles of compounds 2a and 4e6(a) are promising. Some of the
target compounds showed good docking scores with potential anticancer targets, chosen based on
pharmacophore mapping of the established derivatives.
Keywords:
Aminothiazole
Imidazo[2,1-b]thiazole
Pyrazole
Ó 2013 Elsevier Masson SAS. All rights reserved.
Anticancer evaluation
In silico studies
1. Introduction
Prompted by the above considerations, and in view of the need
for new antitumor agents, it was of interest to prepare imidazo[2,1-
The global burden of cancer continues to increase largely
because of aging and growth of the world population. Based on the
GLOBOCAN estimates, about 12.7 million cancer cases and 7.6
million cancer deaths have occurred in 2008 [1]. The development
of new anticancer agents is becoming the major interest in many
academic and industrial research laboratories all over the world
with the aim to develop more potent molecules with higher spec-
ificity and reduced toxicity. Levamisole I, the imidazo[2,1-b]thiazole
derivative, was reported as a potential antitumor agent in patients
with small tumor burdens [2]. In addition, numerous imidazo[2,1-b]
thiazole derivatives were reported to possess antitumor activities
[3e7]. Furthermore, it was found that the incorporation of pyrazole
ring into different aryl or heteroaryl ring systems was reported to
exhibit significant anticancer activities [8e13].
b]thiazoles bearing different pyrazole moieties to be evaluated for
their antitumor activity.
2. Results and discussion
2.1. Chemistry
The synthesis of the target compounds 2e6(aec) is outlined in
Scheme 1. 2-Amino-4-arylthiazoles 1aec were prepared utilizing
either phenacyl chloride or phenacyl bromide according to a re-
ported procedure [14] which is considered to be an easy, rapid and
purification-free procedure. From literature survey, it was reported
that a variety of aminoheterocyclic systems could yield fused ring
systems containing keto group through reaction with chloroacetyl
chloride [15,16], 4-chlorobutyryl chloride [17], ethyl chloroacetate
[18,19], or 3-bromopropionic acid [20]. Recently, it was demon-
strated that the reaction between 2-amino-4-phenylthiazole and
chloroacetic acid could be furnished in ethanol yielding fused
imidazothiazole derivatives [21]. In the present study, 2-amino-4-
arylthiazoles 1aec were reacted with chloroacetic acid in glacial
acetic acid in the presence of anhydrous sodium acetate via pro-
longed heating up to 40 h, and the products were obtained in 72e
82% yield [22]. The structures of compounds 2aec were confirmed
on the basis of spectral data. The 1H NMR spectra showed a broad
singlet at 3.48e3.85 ppm for the imidazoeCH2 protons. Heating
* Corresponding author. Tel.: þ20 1098384072 (mobile).
E-mail addresses: ahmed_reda551988@yahoo.com, ahmed_reda5588@mans.
edu.eg (A.R. Ali).
0223-5234/$ e see front matter Ó 2013 Elsevier Masson SAS. All rights reserved.
http://dx.doi.org/10.1016/j.ejmech.2013.12.010

A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
493
Scheme 1. Synthesis of the title compounds 2e6 (aec).
compounds 2aec in ethanol with hydrazine hydrate afforded 6-
hydrazinyl-3-(un)substituted phenylimidazo[2,1-b]thiazoles 3aec
in 56e65% yield. Compounds 3aec were confirmed by their 1H
NMR spectra, which showed CHeimidazole proton signal as a
singlet peak at the expected region with D2O exchangeable peaks
for the NH2 and NH protons. It was reported that the reaction be-
tween hydrazinoheterocycles and diethyl malonate, ethyl acetoa-
cetate or acetylacetone could be performed through refluxing in
ethanol [11,23,24], DMF and fused sodium acetate [25] and glacial
acetic acid [26]. Compounds 3aec were refluxed with diethyl
malonate, ethyl acetoacetate or acetylacetone in glacial acetic acid.
The structures of the synthesized compounds 4e6(aec) were
confirmed by microanalyses and spectral data (IR, 1H NMR, 13C NMR
and EI-MS) which showed full agreement with their structures
(Experimental section).
based on their ability to add diversity to the NCI small molecule
compound collection. The operation of this screen utilizes 60
different human tumor cell lines, representing leukemia, mela-
noma and cancers of the lung, colon, brain, ovary, breast, prostate,
and kidney. The compounds were added at single high dose
(10 mM) and the culture was incubated for 48 h. End point de-
terminations were made with a protein binding dye, Sulforhod-
amine B [28e30].
Results for each compound are reported as a mean graph of the
percent growth of the treated cells when compared to the un-
treated control cells. The percentage growth of the tested com-
pounds against the full 60-cell line panel is illustrated in Table 1.
The mean percentage growth against the full 60-cell line panel
and the screening data of the tested compounds against the most
sensitive cell lines are illustrated in Table 2.
In light of the NCI-60 results, the following could be considered:
In this study, compounds 5b and 6b exhibited the lowest mean
percentage growth against the full 60-cell line panel. Regarding
sensitivity against individual cell lines, both compounds 5b and 6b
showed observed low cell growth promotion against several Leu-
kemia and Non-Small Cell Lung cancer cell lines, while compound 4a
decreased growth promotion with several Non-Small Cell Lung and
Renal cancer cell lines. By comparing the results from different
series, it was found that introduction of methyl pyrazolone moiety
in compounds 5aec proved to enhance the potency towards Renal
UO-31 cancer cell line. It is worth mentioning that compounds 2a
and 4e6(a) showed increased potency towards CNS SNB-75 and
Renal UO-31 cancer cell lines with growth percentages ranging from
58.95 to 64.07%. In particular, compound 5a, bearing methyl pyr-
azolone moiety, exhibited considerable potency with Non-Small
Cell Lung HOP-92, CNS SNB-75 and Renal UO-31 cancer cell lines. In
addition, compounds 2b and 4e6(b) demonstrated considerable
2.2. Biological evaluation
2.2.1. In vitro anticancer screening
The synthesized compounds 2a, b and 4e6(aec) were selected
by the National Cancer Institute (NCI) [27], Bethesda, Maryland,
USA, under the Developmental Therapeutic Program (DTP) which
is designed to screen up to 3000 compounds per year for potential
anticancer activity. The screening is a two-stage process, begin-
ning with the evaluation of all compounds against the 60 cell
lines at a single dose of 10 mM. The output from the single dose
screen is reported as a mean graph and is available for analysis by
the COMPARE program. Compounds which exhibit significant
growth inhibition are evaluated against the 60 cell panel at five
concentration levels. Compounds with drug-like properties,
based on computer-aided design, are to be prioritized in the NCI
screening service. Eleven compounds were selected for screening

494
A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
Table 1
Percentage cell growth of sixty human tumor cell line anticancer screening data of the tested compounds at single dose assay (10ꢀ5 M concentration).
Subpanel tumor cell lines
Percentage cell growth
2a
2b
4a
4b
4c
5a
5b
5c
6a
6b
6c
Leukemia
CCRF-CEM
HL-60(TB)
K-562
MOLT-4
RPMI-8226
SR
96.26
114.37
88.78
95.38
94.40
85.96
91.53
98.69
119.92
94.24
101.34
93.00
82.99
89.47
95.64
95.90
84.40
94.05
109.67
80.53
78.88
93.56
73.33
95.39
87.79
96.02
94.17
79.72
79.10
89.20
77.82
88.13
88.10
78.97
84.97
74.04
107.29
94.74
90.30
98.13
84.39
89.19
83.39
84.36
94.19
84.55
92.53
71.37
65.78
75.94
73.28
104.66
76.85
93.87
93.05
80.88
90.21
83.10
81.32
68.15
65.83
105.89
108.61
98.39
90.26
81.05
Non-small cell lung cancer
A549/ATCC
HOP-62
98.34
93.62
77.98
101.74
94.88
115.64
105.38
94.28
92.50
107.38
111.42
110.36
103.57
93.84
92.87
85.91
63.49
89.96
91.46
98.07
104.31
74.91
88.88
104.11
99.44
102.56
97.79
83.28
104.17
74.09
101.84
104.83
75.09
94.39
96.87
108.04
110.69
95.90
100.61
95.34
66.54
100.72
91.58
92.13
106.96
89.17
79.56
97.48
73.63
95.36
91.97
99.77
103.29
84.55
98.30
99.16
65.52
89.74
95.54
104.88
104.79
88.86
98.99
91.39
86.04
88.30
95.42
91.13
103.73
88.40
85.77
97.10
74.69
81.47
91.04
90.97
101.28
75.28
98.61
103.83
77.99
94.85
93.33
96.36
101.67
91.76
HOP-92
NCIeH226
NCIeH23
NCIeH322M
NCIeH460
NCIeH522
Colon cancer
COLO 205
HCC-2998
HCT-116
HCT-15
106.25
87.50
102.01
97.85
97.59
95.89
109.07
111.45
94.81
107.90
101.15
97.12
93.29
88.41
100.40
103.09
95.51
100.54
102.03
93.24
92.86
91.35
106.73
101.53
107.73
100.09
111.21
114.88
102.67
102.28
97.33
96.53
102.89
100.25
97.07
88.73
85.68
104.52
99.31
106.35
102.92
94.42
103.34
117.53
104.05
105.30
105.84
105.33
101.22
94.95
97.58
103.54
101.74
100.19
102.08
89.79
95.55
87.04
99.93
100.40
105.61
106.71
96.97
101.14
103.52
107.83
106.17
91.24
96.68
HT29
KM12
SW-620
103.85
101.16
106.63
106.26
102.38
103.50
100.39
100.65
106.11
103.83
CNS cancer
SF-268
SF-295
SF-539
SNB-19
110.43
NTa
97.50
99.66
61.00
93.89
100.09
80.02
94.76
100.32
75.77
94.33
99.50
NTa
88.22
90.95
63.13
84.15
105.43
84.42
101.26
90.22
74.16
91.89
105.75
91.21
101.39
102.29
73.33
99.29
69.36
89.71
90.75
59.39
90.73
96.32
85.56
94.70
88.01
65.32
91.72
111.30
NTa
102.43
100.49
79.10
94.06
98.39
77.49
94.00
96.51
64.07
94.69
101.66
82.48
104.27
92.78
69.22
87.79
111.50
88.51
108.66
100.35
85.89
SNB-75
U251
98.07
94.95
Melanoma
LOX IMVI
MALME-3M
M14
MDA-MB-435
SK-MEL-2
SK-MEL-28
SK-MEL-5
UACC-257
UACC-62
Ovarian cancer
IGROV1
OVCAR-3
OVCAR-4
OVCAR-5
OVCAR-8
NCI/ADR-RES
SK-OV-3
Renal cancer
786-0
89.40
101.88
99.94
98.88
99.35
97.04
87.82
98.15
95.70
105.10
96.31
88.66
86.89
141.10
100.94
99.88
101.90
96.41
89.58
97.60
85.00
96.45
97.08
100.10
93.72
101.00
95.71
99.65
96.89
118.22
105.40
90.01
116.24
101.85
95.89
90.77
107.15
100.26
92.94
101.88
102.44
101.76
101.53
91.11
96.76
102.05
96.23
87.44
103.79
96.35
92.42
94.93
81.88
93.01
107.40
99.25
83.58
114.42
98.52
90.04
100.48
74.11
91.90
94.08
95.36
96.89
97.61
102.42
94.18
104.85
89.44
91.91
93.14
101.37
94.49
113.34
97.94
85.48
92.77
113.53
103.67
94.60
125.13
94.82
98.86
108.31
90.51
95.09
113.94
104.72
99.82
102.96
90.29
102.61
90.13
109.47
91.76
104.07
86.86
103.87
110.53
97.73
113.22
97.86
99.61
89.46
95.21
105.26
90.35
97.04
95.97
101.78
98.24
91.47
98.97
81.20
103.88
89.77
94.33
86.83
117.44
109.55
87.39
115.07
100.64
99.31
105.27
113.24
99.12
107.89
99.34
88.02
99.81
98.04
96.68
104.97
92.50
88.91
99.28
105.92
77.19
105.89
94.22
101.33
109.76
99.90
124.33
102.01
99.30
76.48
100.66
93.01
95.40
95.88
95.47
89.91
107.51
107.01
81.89
109.27
91.51
106.95
114.96
97.77
112.78
96.05
107.97
101.17
100.28
100.47
100.05
93.44
98.47
100.81
103.15
95.50
104.48
111.20
97.86
78.74
101.55
91.53
93.96
70.24
94.99
81.31
111.06
94.89
79.93
92.67
103.52
78.40
81.46
75.88
89.67
92.23
130.54
59.58
96.40
75.20
101.79
78.89
111.56
88.42
94.95
103.12
97.97
90.53
96.64
96.57
91.20
79.90
108.59
96.04
124.73
58.95
94.09
74.06
89.14
79.28
104.15
90.87
98.75
80.94
101.01
99.21
96.88
84.53
95.88
96.40
134.53
71.63
98.00
111.15
83.84
77.38
93.38
96.47
124.03
59.16
101.78
85.72
91.00
78.63
93.47
88.99
128.30
89.64
104.52
102.68
90.72
83.54
104.57
98.14
A498
ACHN
CAKI-1
RXF 393
SN12C
TK-10
UO-31
90.13
100.77
103.92
139.24
74.68
124.72
61.27
140.69
94.43
110.76
Prostate cancer
PC-3
DU-145
82.43
112.39
101.36
101.64
76.37
105.83
89.98
104.83
87.33
118.36
77.57
106.34
79.39
105.05
75.26
113.22
88.65
104.76
79.09
112.85
84.73
115.53
Breast cancer
MCF78
MDA-MB-231/ATCC
HS 578T
BT-549
T-47D
88.54
96.67
103.17
111.82
84.40
90.89
102.16
110.60
89.05
92.10
106.41
85.84
85.68
100.93
97.61
82.73
102.08
88.99
106.75
98.28
95.35
87.34
93.87
103.79
107.23
112.56
85.68
89.58
89.89
105.52
89.72
89.39
114.34
93.54
96.46
101.13
101.20
73.71
91.82
79.03
108.67
111.26
80.63
88.70
86.29
105.70
95.32
87.19
102.40
85.06
86.43
94.30
113.37
80.72
88.55
89.72
88.80
97.03
125.41
98.15
111.59
MDA-MB-468
106.39
104.39
105.50
97.94
102.05
a
NT: not tested.

A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
495
Table 2
Mean percentage growth and screening data of the tested compounds with the most sensitive cell lines represented as percent cell growth.
Comp. No.
NSC code
Mean percentage
growth
Leukemia SR
Non-Small cell
lung cancer HOP-92
CNS cancer
SNB-75
Renal cancer
UO-31
2a
2b
4a
4b
4c
5a
5b
5c
6a
6b
6c
768188
768168
768190
768169
768179
768170
768171
768180
768176
768177
768185
98.20
95.40
93.33
95.56
100.84
94.06
91.25
97.12
93.89
92.28
100.62
85.96
77.82
82.99
74.04
84.39
84.55
73.28
73.33
80.88
65.83a
81.05
77.98
111.42
63.49a
99.44
75.09
66.54a
73.63
65.52a
86.04
74.69
77.99
61.00a
75.77
63.13a
74.16
73.33
59.39a
65.32a
79.10
64.07a
69.22
85.89
61.27a
92.67
59.58a
110.76
74.68
58.95a
80.94
71.63
59.16a
89.64
94.43
a
Underlined values are those below 70.00%.
potency towards Leukemia MOLT-4 and SR and Renal A498 cancer
cell lines than other compounds in the same series.
target compounds 2aec and 4e6(aec) have TPSA value ranging
from 26.50 to 43.17 (Table 3), they theoretically should present
good passive oral absorption.
We performed COMPARE [31] analyses for compounds 2a, b and
4e6(aec) in order to investigate the similarity of their cytotoxicity
pattern (mean graph fingerprints) with those of known anticancer
standard agents, NCI active synthetic compounds and natural ex-
tracts, which are present in public available databases. Such anal-
ysis is based on comparing the patterns of differential growth
inhibition for cultured cell lines and can potentially gain insight
into the mechanism of the cytotoxic action. If the data pattern
correlates well with that of compounds belonging to a standard
agent database (Pearson’s correlation coefficient (PCC > 0.6)), the
compound of interest may have the same mechanism of action
[32,33]. On the other hand, if the activity pattern does not correlate
with any standard agent, it is possible that the compound has a
novel mechanism of action. Standard COMPARE analyses were
performed at the GI50 level.
It was established that compounds 4c and 6a demonstrated high
correlation levels with rapamycin (NSC S226080) with PCC values
of 0.615 and 0.648, respectively. Considerable correlations between
compounds 2a, 4a, 5a, 5b, 5c and 6b, and rapamycin were noted
with PCC values of 0.574, 0.572, 0.58, 0.587, 0.557 and 0.514,
respectively. Such similarity in COMPARE results could indicate the
resemblance in mechanisms of action with rapamycin. Rapamycin
is reported to be mTOR inhibitor which is considered to be a key
enzyme in regulation of cellular metabolism, growth, and prolif-
eration [34e36]. In addition, compound 5c exhibited a considerable
correlation with merbarone (NSC S336628) with PCC value of
0.563. Merbarone is a catalytic inhibitor of topoisomerase II and so
inhibit DNA cleavage [37]. Compounds 2b, 4b and 6c did not display
high correlation levels with the NCI tested drugs or other biological
active substances. It can be assumed that this compound may have
a unique mechanism of action that differs from other known
anticancer agents.
Based on the reported data that nearly 40% of drug candidates
fail in clinical trials because of poor ADME [40], we evaluated
the compliance of the designed compounds to the Lipinski’s
rule of five, calculated by Canvas [38] and Osiris [41] programs.
Molecules violating more than one of these rules may have
problems with bioavailability. Predictions of ADME properties for
the studied compounds are given in Table 3. The results showed
that all the targeted compounds comply with these rules sug-
gesting that the synthesized compounds would be possible drug
molecules.
2.2.3. Assessment of toxicities, druglikeness, and drug score profiles
Osiris program [41] was used for prediction of the overall
toxicity of the designed derivatives as the prediction process relies
on a predetermined set of structural fragments that give rise to
toxicity alerts in case they are encountered in the structure. All
target compounds 2aec and 4e6(aec) showed low in silico
possible toxicity risks as shown in Table 4. Osiris program was also
used for calculating the fragment-based druglikeness of the
designed compounds and a positive value indicates that the
designed molecule contains fragments which are frequently pre-
sent in commercial drugs.
Table 3
Solubility, total polar surface area, and calculated Lipinski’s rule of five for tested
compounds.
Comp. No. Log Sa TPSAb MWc
cLog Pd nHBAe nHBDf RBg nVioh
2a
2b
2c
4a
4b
4c
5a
5b
5c
6a
6b
6c
ꢀ2.46 26.50 216.26 1.56
3
3
3
3
3
3
3
3
3
2
2
2
0
0
0
1
1
1
0
0
0
0
0
0
1
1
1
2
2
2
2
2
2
2
2
2
0
0
0
0
0
0
0
0
0
0
0
0
ꢀ3.38 28.47 250.70 2.18
ꢀ2.99 28.34 230.29 1.88
ꢀ2.55 36.62 298.32 0.41
ꢀ3.29 38.59 332.76 1.03
ꢀ2.89 38.45 312.35 0.73
ꢀ3.10 37.95 296.35 2.64
ꢀ3.83 39.92 330.79 3.25
ꢀ3.44 39.78 310.37 2.95
ꢀ1.73 41.20 294.37 3.27
ꢀ2.47 43.17 328.82 3.89
ꢀ2.08 43.04 308.40 3.59
2.2.2. Total polar surface area and Lipinski’s rule of five
It is well established that more than 80% of the drugs on the
market have an estimated log S value greater than ꢀ4. Typically, a
low solubility goes along with a bad absorption and therefore
the general aim is to avoid poorly soluble compounds. As shown
in Table 3, the entire target compounds 2aec and 4e6(aec),
having log S values above ꢀ4, are expected to have good aqueous
solubility which significantly affects its absorption and distribution
characteristics.
The total polar surface area (TPSA) was calculated using Canvas
[38] program since it is a key property that has been linked to drug
bioavailability. Thus, passively absorbed molecules with a TPSA
>140 are thought to have low oral bioavailability [39]. Since all the
a
Solubility parameter.
Total polar surface area (A).
Molecular weight.
Calculated lipophilicity.
Number of hydrogen bond acceptors.
Number of hydrogen bond donors.
Rotatable bonds.
b
c
ꢀ
d
e
f
g
h
Number of violations to Lipinski’s rule of five.

496
A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
Table 4
7000 receptor-based pharmacophore models. PharmMapper finds
the best mapping poses of the user uploaded molecules against all
the targets in PharmTarget Database [42].
Toxicity risks, druglikeness and drug scores of the designed compounds.
Comp. No.
Toxicity risks
Druglikeness
Drug score
(Mutagenicity,
Tumorigenicity,
Irritancy,
PharmMapper is available at http://59.78.96.61/pharmmapper.
The server demonstrated a variety of putative targets that might
exhibit considerable binding affinity to the target compounds.
Eight targets, involved in cancer therapy, are common between the
tested compounds. These targets might explain the observed
antiproliferative activity. Table 5 lists the scores with the top eight
targets proposed by PharmMapper.
Reproductive effects)
2a
2b
2c
4a
4b
4c
5a
5b
5c
6a
6b
6c
ea
ea
ea
ea
ea
ea
ea
ea
ea
ea
ea
ea
3.39
4.14b
2.12
0.66
1.60
0.91b
0.86b
0.86b
0.61
0.63
0.48
0.68
0.61
0.63
0.54
0.58
0.42
ꢀ0.70
2.2.5. Docking study
3.67
Docking simulations were carried out with the aid of Docking
Server [43], a web-based interface that utilizes a number of
computational chemistry software specifically aimed at correctly
calculating accurate ligand geometry optimization, energy mini-
mization, charge calculation, docking calculation and protein-
ligand complex representation. Molecular docking simulations
were performed for the target compounds to evaluate their recog-
nition profile at the binding pocket of the proposed targets.
The binary complex of the target coupled with its natural ligand
was used as a reference for docking and modeling in this
investigation.
The eight potential targets proposed by pharmacophore map-
ping approach were used to investigate their interaction with the
designed compounds. The target compounds 2aec and 4e6(aec)
were comparatively evaluated in terms of estimated free energy of
binding (kcal/mol), and inhibition constant Ki (uM) to the eight
proposed enzymes and the results are listed in Table 6.
Compounds 5b and 6b showing the lowest mean percentage
growth against the full 60-cell line panel demonstrated the best
docking score with the proposed targets.
4.57b
2.37
0.16
1.55
ꢀ1.14
a
No indication for toxic effects.
Underlined values represent the highest results in each parameter.
b
The drug score combines druglikeness, cLog P, Log S, molecular
weight and toxicity risks in one handy value. A value of 0.5 or more
makes a compound a promising lead for future development of a
safe and efficient drug. Predictions of potential toxicity, druglike-
ness and drug score for the studied compounds are given in Table 4.
Almost all of the synthesized compounds, except 4c and 6c, possess
good values of druglikeness and drug score.
2.2.4. Target fishing
An attempt was made to investigate the potential targets
involved in observed inhibition displayed by the synthesized
compounds against NCI 60 cell panel. PharmMapper server is a
freely accessed web server designed to identify potential target
candidates for the given small molecules using reverse pharma-
cophore mapping approach. The server hosts a large, in-house
repertoire of pharmacophore database annotated from all the tar-
gets information in potential drug target databases, including over
3. Conclusion
On the basis of the results obtained from in vitro anticancer
evaluation, it was found that compounds 5b (NSC 768171) and 6b
Table 5
Fit score of the synthesized compounds against the top eight targets.
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
•
•

A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
497
Table 6
Estimated free energy of binding and inhibition constants of the synthesized compounds with the top eight targets.
•
(NSC 768177) demonstrated the lowest mean percentage growth
against the full 60-cell line panel. They also manifested the lowest
inhibition constants with the targets proposed by PharmMapper.
Concerning the sensitivity against individual cell lines, compounds
2a and 4e6(a) exhibited increased potency towards CNS SNB-75
and Renal UO-31 cancer cell lines. In vitro anticancer evaluation,
together with in silico studies, revealed that compounds 2a and 4e
6(a) could be considered as promising leads for further develop-
ment of more potent anticancer agents.
on Bruker 500 MHz FT NMR spectrometer and 1H NMR spectra for
remaining compounds were carried out at the National Research
Centre using
iodimethylsulfoxide (DMSO-d6) is used as a solvent with the
chemical shift being expressed in (ppm) and downfield from
a Varian Gemini 500 MHz FT NMR. Deuter-
d
tetramethylsilane (TMS) as internal standard.
Electron impact mass spectra (EI-MS), recorded on a Shimadzu
GC/MS QP-2010 Plus mass spectrometer, and elemental analysis (in
accord with the calculated values) were carried out in the Micro-
analytical Unit, Faculty of Science, Cairo University. Anticancer
evaluation was performed at National Cancer Institute (NCI),
Bethesda, Maryland, USA.
4. Experimental
4.1. General
4.2. General procedure for the synthesis of compounds (2aec) [22]
2-Amino-4-arylthiazoles 1aec were prepared following the
procedure reported by Dighe [14]. All the reagents and solvents
were obtained from commercial suppliers, and used without pu-
rification. TLC was monitored on Fluka silica gel TLC aluminum
cards (0.2 mm thickness) with fluorescent indicator 254 nm
using a mixture of petroleum ether/ethyl acetate in various
proportions.
A mixture of 2-amino-4-arylthiazole 1aec (10 mmol), chloro-
acetic acid (1.89 g, 20 mmol) and anhydrous sodium acetate (1.64 g,
20 mmol) in glacial acetic acid (10 mL) was refluxed for 40 h. The
reaction mixture was cooled and poured onto ice water with stir-
ring. The solid formed was filtered and crystallized from ethanol.
Melting points (ꢁC) were recorded using a FischereJohns
melting point apparatus and are uncorrected. The IR spectra (KBr)
4.2.1. 3-Phenylimidazo[2,1-b]thiazol-6(5H)-one (2a)
Yield: 82%; mp 212e214 ꢁC [21]; IR (KBr, , cmꢀ1): 3169 (CH
n
were recorded on Mattson 5000 FT IR spectrophotometer (
n
in
aromatic), 3023, 2987 (CH aliphatic), 1654, 1644 (C]O), 1599,
1584 cmꢀ1 (C]N); EI-MS (70 eV) m/z (Rel. Int.): 216 (Mþ, 3.24), 199
(20.06), 176 (100.00), 134 (31.72), 98 (21.04), 77 (11.00).
cmꢀ1) in the Microanalytical Unit, Faculty of Science, Mansoura
University. 1H and 13C NMR for compounds 3e6(a) were recorded

498
A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
4.2.2. 3-(4-Chlorophenyl)imidazo[2,1-b]thiazol-6(5H)-one (2b)
Yield: 80%; mp 254e256 ꢁC [22]; 1H NMR (
, ppm, DMSO-d6):
7.31 (t, 2H, AreH), 7.43 (t, 1H, AreH), 7.58 (s, 2H, Hethiazole, CHe
imidazole), 7.77 (s, 1H, NH), 7.90 (d, 2H, AreH); 13C NMR (
, ppm,
d
d
3.48 (s, 2H, CH2), 7.46 (d, 2H, AreH), 7.63 (s, 1H, Hethiazole), 7.86
(d, 2H, AreH); EI-MS (70 eV) m/z (Rel. Int.): 252 (Mþ þ 2, 30.47),
250 (Mþ, 2.57), 210 (100.00), 168 (32.13), 132 (6.05), 111 (11.57);
Anal. for C11H7ClN2OS (250.70) C, H, N.
DMSO-d6): 39.98 (C4epyrazolidinedione), 107.78 (CHeimidazole, e
SeCHethiazole), 125.62, 127.70, 128.68 (AreCH), 134.31 (quater-
nary AreC, thiazoleeC), 148.69 (C6eimidazothiazole), 157.94 (2 C]
O), 168.60 (eSeC(N)]N-imidazothiazole); EI-MS (70 eV) m/z (Rel.
Int.): 298 (Mþ, 3.61), 285 (12.18), 246 (3.49), 199 (3.37), 161 (6.39);
Anal. for C14H10N4O2S (298.32) C, H, N.
4.2.3. 3-p-Tolylimidazo[2,1-b]thiazol-6(5H)-one (2c)
Yield: 70%; mp 132e134 ꢁC [22]; 1H NMR (
d, ppm, DMSO-d6):
2.29 (s, 3H, eCH3), 3.85 (s, 2H, CH2), 7.22 (d, 2H, AreH), 7.31 (s, 1H,
Hethiazole), 7.62 (d, 2H, AreH); EI-MS (70 eV) m/z (Rel. Int.): 230
(Mþ, 47.37), 198 (100), 176 (41.17); Anal. for C12H10N2OS (230.29)
C, H, N.
4.4.2. 1-(3-(4-Chlorophenyl)imidazo[2,1-b]thiazol-6-yl)pyrazolidine-
3,5-dione (4b)
Yield: 60%; mp 234e236 ꢁC; 1H NMR (
d, ppm, DMSO-d6): 3.46 (s,
2H, CH2), 7.46 (d, 2H, AreH), 7.63 (s, 1H, Hethiazole), 7.65 (s, 1H,
NH), 7.86 (d, 2H, AreH), 7.89 (s, 1H, CHeimidazole); EI-MS (70 eV)
m/z (Rel. Int.): 332 (Mþ, 0.58), 320 (0.58), 280 (1.49), 252 (30.02),
210 (100.00), 168 (30.69), 111 (9.82); Anal. for C14H9ClN4O2S
(332.76) C, H, N.
4.3. General procedure for the synthesis of compounds (3aec)
Equimolar quantities of 3-(un)substituted phenylimidazo[2,1-b]
thiazol-6(5H)-one 2aec (10 mmol) and hydrazine hydrate (99%)
(0.6 mL, 10 mmol) were dissolved in warm ethanol (10 mL) and
refluxed for 8 h. After standing for approximately 24 h at room
temperature, the solvent was distilled under reduced pressure and
the obtained solid was crystallized from aqueous ethanol.
4.4.3. 1-(3-p-Tolylimidazo[2,1-b]thiazol-6-yl)pyrazolidine-3,5-
dione (4c)
Yield: 55%; mp 126e128 ꢁC; 1H NMR (
d, ppm, DMSO-d6): 2.29 (s,
3H, eCH3), 3.50 (s, 2H, CH2), 7.22 (d, 2H, AreH), 7.31 (s, 1H, He
thiazole), 7.47 (s, 1H, NH, D2O exchangeable), 7.75 (d, 2H, AreH),
7.79 (s, 1H, CHeimidazole); EI-MS (70 eV) m/z (Rel. Int.): 312 (Mþ,
5.42), 290 (5.03), 232 (25.08), 190 (100.00), 176 (16.41), 148 (33.13),
97 (10.60); Anal. for C15H12N4O2S (312.35) C, H, N.
4.3.1. 6-Hydrazinyl-3-phenylimidazo[2,1-b]thiazole (3a)
Yield: 61%; mp 140e142 ꢁC; IR (KBr, , cmꢀ1): 3433, 3251 cmꢀ1
n
(NH, NH2), 3112 (CH aromatic), 1599, 1584 cmꢀ1 (C]N); 1H NMR
, ppm, DMSO-d6): 4.34 (s, 2H, NH2), 7.04 (t, 2H, AreH), 7.25 (t,
1H, AreH), 7.36 (s, 1H, Hethiazole), 7.75 (s, 1H, CHeimidazole),
7.80 (d, 2H, AreH), 8.67 (s, 1H, NH); 13C NMR (
, ppm, DMSO-d6):
(
d
4.4.4. 3-Methyl-1-(3-phenylimidazo[2,1-b]thiazol-6-yl)-1H-pyrazol-
d
5(4H)-one (5a)
101.48 (CHeimidazole, eSeCHethiazole), 125.50, 127.15, 128.44
(AreCH), 134.87 (quaternary AreC, thiazoleeC), 149.82 (C6eimi-
dazothiazole), 168.22 (eSeC(N)]N-imidazothiazole); EI-MS
(70 eV) m/z (Rel. Int.): 230 (Mþ, 3.75), 214 (3.32), 198 (1.85),
176 (100.00), 134 (82.10), 112 (1.57); Anal. for C11H10N4S (230.29)
C, H, N.
Yield: 51%; mp 190e192 ꢁC; IR (KBr, , cmꢀ1): 3169 (CH aro-
n
matic), 3065, 2988 (CH aliphatic), 1654, 1645 (C]O), 1596,
1583 cmꢀ1 (C]N); 1H NMR (
d, ppm, DMSO-d6): 2.18 (s, 3H, pyr-
azolineeCH3), 3.36 (s, 2H, CH2), 7.33 (t, 2H, AreH), 7.43 (t, 1H, Are
H), 7.58 (s, 1H, Hethiazole), 7.62 (s, 1H, CHeimidazole), 7.90 (d, 2H,
AreH); 13C NMR (
d, ppm, DMSO-d6): 22.46 (pyrazolineeCH3), 41.02
(C4epyrazoline), 107.78 (CHeimidazole, eSeCHethiazole), 125.63,
127.70, 128.68 (AreCH), 134.33 (quaternary AreC, thiazoleeC),
148.71 (C6eimidazothiazole), 157.95 (C3-pyrazoline,C]O), 168.59
(eSeC(N)]N-imidazothiazole); EI-MS (70 eV) m/z (Rel. Int.): 296
(Mþ, 0.01), 255 (0.06), 241 (0.10), 218 (34.91), 176 (100.00),
134 (64.90), 104 (15.39), 77 (12.20); Anal. for C15H12N4OS (296.35)
C, H, N.
4.3.2. 3-(4-Chlorophenyl)-6-hydrazinylimidazo[2,1-b]thiazole (3b)
Yield: 65%; mp 144e146 ꢁC; IR (KBr, , cmꢀ1): 3438, 3283 cmꢀ1
n
(NH, NH2), 3111 (CH aromatic), 1632, 1533 cmꢀ1 (C]N); 1H NMR (
d,
ppm, DMSO-d6): 4.33 (s, 2H, NH2), 7.02 (d, 2H, AreH), 7.37 (s, 1H,
Hethiazole), 7.76 (s, 1H, CHeimidazole), 8.01 (d, 2H, AreH), 8.78 (s,
1H, NH); EI-MS (70 eV) m/z (Rel. Int.): 266 (Mþ þ 2, 0.38), 264 (Mþ,
0.09), 210 (100.00), 168 (39.33), 146 (4.86); Anal. for C11H9ClN4S
(264.73) C, H, N.
4.4.5. 1-(3-(4-Chlorophenyl)imidazo[2,1-b]thiazol-6-yl)-3-methyl-
1H-pyrazol-5(4H)-one (5b)
4.3.3. 6-Hydrazinyl-3-p-tolylimidazo[2,1-b]thiazole (3c)
Yield: 48%; mp 236e238 ꢁC; 1H NMR (
d, ppm, DMSO-d6): 1.80 (s,
Yield: 56%; mp 120e122 ꢁC; IR (KBr,
n
, cmꢀ1): 3453, 3286 cmꢀ1
3H, pyrazolineeCH3), 3.31 (s, 2H, CH2), 7.46 (d, 2H, AreH), 7.63 (s,
1H, Hethiazole), 7.86 (d, 2H, AreH), 7.89 (s, 1H, CHeimidazole); EI-
MS (70 eV) m/z (Rel. Int.): 330 (Mþ, 0.23), 289 (0.26), 275 (0.40), 252
(30.17), 210 (100.00), 168 (31.68), 138 (10.84), 111 (11.08); Anal. for
(NH, NH2), 3180 (CH aromatic), 1612, 1522 cmꢀ1 (C]N); EI-MS
(70 eV) m/z (Rel. Int.): 244 (Mþ, 72.29), 228 (13.25), 213 (0.19),
168 (85.54), 126 (19.28); Anal. for C12H12N4S (244.32) C, H, N.
C15H11ClN4OS (330.79) C, H, N.
4.4. General procedure for the synthesis of compounds 4e6(aec)
4.4.6. 3-Methyl-1-(3-p-tolylimidazo[2,1-b]thiazol-6-yl)-1H-
A mixture of 6-hydrazinyl-3-(un)substituted phenylimidazo
[2,1-b]thiazole 3aec (10 mmol) and diethyl malonate, ethyl ace-
toacetate, or acetylacetone (10 mmol) in glacial acetic acid (10 mL)
was refluxed for 6e8 h. After cooling, the formed precipitate was
filtered, dried and crystallized from aqueous acetic acid to furnish
the entitled compounds.
pyrazol-5(4H)-one (5c)
Yield: 44%; mp 158e160 ꢁC; 1H NMR (
d, ppm, DMSO-d6): 1.81 (s,
3H, pyrazolineeCH3), 2.29 (s, 3H, AreCH3), 3.51 (s, 2H, CH2), 7.22 (d,
2H, AreH), 7.32 (s, 1H, Hethiazole), 7.73 (d, 2H, AreH), 7.80 (s, 1H,
CHeimidazole); EI-MS (70 eV) m/z (Rel. Int.): 310 (Mþ, 2.44), 269
(17.98), 255 (1.40), 232 (25.31), 190 (100.00), 148 (29.14), 118
(51.48), 91 (65.79); Anal. for C16H14N4OS (310.37) C, H, N.
4.4.1. 1-(3-Phenylimidazo[2,1-b]thiazol-6-yl)pyrazolidine-3,5-
dione (4a)
4.4.7. 6-(3,5-Dimethyl-1H-pyrazol-1-yl)-3-phenylimidazo[2,1-b]
Yield: 63%; mp 190e192 ꢁC; IR (KBr,
n
, cmꢀ1): 3251 (NH), 3167
thiazole (6a)
(CH aromatic), 3064, 2999 (CH aliphatic), 1654, 1645 (C]O), 1599,
Yield: 66%; mp 188e190 ꢁC; IR (KBr, , cmꢀ1): 3168 (CH aro-
n
1584 cmꢀ1 (C]N); 1H NMR (
d, ppm, DMSO-d6): 3.37 (s, 2H, CH2),
matic), 3065, 2988 (CH aliphatic), 1596, 1583 cmꢀ1 (C]N); 1H NMR

A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
499
(
d
, ppm, DMSO-d6): 2.18 (s, 3H, CH3epyrazole), 2.51 (s, 3H, CH3e
unbound dye is removed by washing five times with 1% acetic acid
and the plates are air dried. Bound stain is subsequently solubilized
with 10 mM trizma base, and the absorbance is read on an auto-
mated plate reader at a wavelength of 515 nm. For suspension cells,
the methodology is the same except that the assay is terminated by
pyrazole), 5.71 (s, 1H, CHepyrazole), 7.32 (t, 2H, AreH), 7.43 (t, 1H,
AreH), 7.58 (s, 1H, Hethiazole), 7.62 (s, 1H, CHeimidazole), 7.89 (d,
2H, AreH); 13C NMR (
d, ppm, DMSO-d6): 22.46 (2 CH3epyrazole),
107.78 (CHeimidazole, eSeCHethiazole, C4epyrazole), 125.62,
127.70, 128.67 (AreCH), 134.32 (quaternary AreC, thiazoleeC),
148.70 (C6eimidazothiazole, C5epyrazole), 157.94 (C3epyrazole),
168.59 (eSeC(N)]N-imidazothiazole); EI-MS (70 eV) m/z (Rel.
Int.): 294 (Mþ, 0.01), 252 (0.01), 218 (40.24), 195 (0.08), 176
(100.00), 134 (46.08), 104 (10.96), 77 (2.63); Anal. for C16H14N4S
(294.37) C, H, N.
fixing settled cells at the bottom of the wells by gently adding 50 mL
of 80% TCA (final concentration, 16% TCA). Using the seven absor-
bance measurements [time zero, (Tz), control growth, (C), and test
growth in the presence of drug at the five concentration levels (Ti)],
the percentage growth is calculated at each of the drug concen-
tration levels. Percentage growth inhibition is calculated as:
4.4.8. 3-(4-Chlorophenyl)-6-(3,5-dimethyl-1H-pyrazol-1-yl)
ꢂ [(Ti ꢀ Tz)/(C ꢀ Tz)] ꢃ 100 for concentrations for which Ti ꢄ Tz
ꢂ [(Ti ꢀ Tz)/Tz] ꢃ 100 for concentrations for which Ti < Tz
imidazo[2,1-b]thiazole (6b)
Yield: 70%; mp 216e218 ꢁC; 1H NMR (
d, ppm, DMSO-d6): 2.17 (s,
3H, CH3epyrazole), 2.46 (s, 3H, CH3-pyrazole), 5.86 (s, 1H, CHe
pyrazole), 7.45 (d, 2H, AreH), 7.62 (s, 1H, Hethiazole), 7.86 (d, 2H,
AreH), 7.90 (s,1H, CHeimidazole); EI-MS (70 eV) m/z (Rel. Int.): 328
(Mþ, 1.88), 286 (1.40), 252 (22.15), 229 (1.19), 210 (64.84),
168 (22.12), 138 (11.87), 111 (19.36); Anal. for C16H13ClN4S (328.82)
C, H, N.
4.6. Target fishing
The target compounds 2aec and 4e6(aec) were uploaded in
Tripos Mol2 format. PharmMapper adopts semi-rigid pharmaco-
phore mapping protocol. As a result, multiple conformations of the
query molecule were required prior to mapping which could be
achieved by online service provided by the server. PharmMapper
found the best mapping poses of the uploaded molecules against all
the targets in PharmTargetDB and top N potential drug targets
(default value is 300) as well as respective molecule’s aligned poses
were outputted [42].
4.4.9. 6-(3,5-Dimethyl-1H-pyrazol-1-yl)-3-p-tolylimidazo[2,1-b]
thiazole (6c)
Yield: 67%; mp 196e198 ꢁC; 1H NMR (
d, ppm, DMSO-d6): 2.12 (s,
3H, pyrazoleeCH3), 2.28 (s, 3H, AreCH3), 2.46 (s, 3H, pyrazoleeCH3),
5.72 (s,1H, CHepyrazole), 7.22 (d, 2H, AreH), 7.32 (s,1H, Hethiazole),
7.75 (d, 2H, AreH), 7.81 (s, 1H, CHeimidazole); EI-MS (70 eV) m/z
(Rel. Int.): 308 (Mþ, 50.68), 266 (43.15), 209 (41.10), 190 (84.93), 148
(36.99), 118 (8.90); Anal. for C17H16N4S (308.40) C, H, N.
4.7. Docking study
Docking study was performed with the aid of Docking Server.
Gasteiger partial charges were added to the ligand atoms after energy
minimization using the MMFF94 force field. Non-polar hydrogen
atoms were merged, and rotatable bonds were defined. Essential
hydrogen atoms, Kollman united atom type charges, and solvation
parameters were added with the aid of AutoDock tools to protein
model. Affinity (grid) maps of 20 ꢃ 20 ꢃ 20 A grid points and 0.375 A
spacing were generated using the Autogrid program. Docking simu-
lations were performed using the Lamarckian geneticalgorithm (LGA)
and the Solis and Wets local search method. Initial position, orienta-
tion, and torsions of the ligand molecules were set randomly. Each
docking experiment was derived from 10 different runs that were set
to terminate after a maximum of 250,000 energy evaluations [43].
4.5. In vitro anticancer screening
Eleven of the synthesized compounds including 2a, b and 4e
6(aec) were subjected to the National Cancer Institute (NCI) in vitro
disease-oriented human cells screening panel assay for in vitro
antitumor activity [27e30]. The human tumor cell lines of the
cancer screening panel are grown in RPMI 1640 medium containing
5% fetal bovine serum and 2 mM
into 96 well microtiter plates in 100
from 5000 to 40,000 cells/well depending on the doubling time of
individual cell lines. After cell inoculation, the microtiter plates are
incubated at 37 ꢁC, 5% CO2, 95% air and 100% relative humidity for
24 h prior to addition of experimental drugs.
ꢀ
ꢀ
L
-glutamine. Cells are inoculated
mL at plating densities ranging
After 24 h, two plates of each cell line are fixed in situ with TCA, to
represent a measurement of the cell population for each cell line at
the time of drug addition (Tz). Experimental drugs are solubilized in
dimethylsulfoxide at 400-fold the desired final maximum test con-
centrationandstored frozenpriorto use. At thetimeof drugaddition,
an aliquot of frozen concentrate is thawed and diluted to twice the
desired final maximum test concentration with complete medium
Acknowledgment
We are thankful to the National Cancer Institute (NCI), Bethesda,
Maryland, USA, for performing the anticancer evaluation over the
60-cancer cell line panel.
Appendix A. Supplementary data
containing 50
serialdilutions are made to provide a totaloffive drug concentrations
plus control. Aliquots of 100 L of these different drug dilutions are
mg/mL gentamicin. Additional four, 10-fold or ½ log
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.ejmech.2013.12.
023. These data include MOL files and InChiKeys of the most
important compounds described in this article.
m
added to the appropriate microtiter wells already containing 100 mL
of medium, resulting in the required final drug concentrations.
Following drug addition, the plates are incubated for an addi-
tional 48 h at 37 ꢁC, 5% CO2, 95% air, and 100% relative humidity. For
adherent cells, the assay is terminated by the addition of cold TCA.
References
Cells are fixed in situ by the gentle addition of 50
v) TCA (final concentration, 10% TCA) and incubated for 60 min at
ꢁC. The supernatant is discarded, and the plates are washed five
times with tap water and air dried. Sulforhodamine B (SRB) solution
(100 L) at 0.4% (w/v) in 1% acetic acid is added to each well, and
plates are incubated for 10 min at room temperature. After staining,
mL of cold 50% (w/
[1] A. Jemal, F. Bray, M.M. Center, J. Ferlay, E. Ward, D. Forman, Global cancer
statistics, CA Cancer J. Clin. 61 (2011) 69e90.
[2] W.A. Remers, Antineoplastic agents, in: J.H. Block, J.M. Beale (Eds.), Text Book
of Organic, Medicinal and Pharmaceutical Chemistry, eleventh ed., Lippincott
Company, Philadeplphia, 2004, p. 441.
4
m
[3] A. Andreani, A. Leoni, A. Locatelli, R. Morigi, M. Rambaldi, M. Recanatinia,
V. Garaliene, Potential antitumor agents. Part 291: synthesis and potential

500
A.R. Ali et al. / European Journal of Medicinal Chemistry 75 (2014) 492e500
coanthracyclinic activity of imidazo[2,1-b]thiazoleguanylhydrazones, Bioorg.
Med. Chem. 8 (2000) 2359e2366.
[20] C.D. Hurd, S. Hayao, Reaction of propiolactone with heterocyclic amines, J. Am.
Chem. Soc. 77 (1955) 117e121.
[4] A. Andreani, M. Granaiola, A. Leoni, A. Locatelli, R. Morigi, M. Rambaldi,
L. Varoli, D. Lannigan, J. Smith, D. Scudiero, S. Kondapaka, R.H. Shoemaker,
Imidazo[2,1-b]thiazoleguanylhydrazones as RSK2 inhibitors, Eur. J. Med.
Chem. 46 (2011) 4311e4323.
[21] N. Swathi, T. Kumar, K. Haribabu, C. Subrahmanyam, Synthesis and biological
evaluation of substituted thiazolamines, imidazo[2,1-b]thiazol-6-(5H)-ones,
thiazolo[3,2-a]pyrimidin-5-ones and thiazolyl thioureas, Indian J. Heterocycl.
Chem. 21 (2012) 263e268.
[5] J.H. Park, M.I. El-Gamal, Y.S. Lee, C.H. Oh, New imidazo[2,1-b]thiazole de-
rivatives: synthesis, in vitro anticancer evaluation and in silico studies, Eur. J.
Med. Chem. 46 (2011) 5769e5777.
[22] Ahmed R. Ali, Eman R. El-Bendary, Mariam A. Ghaly, Ihsan A. Shehata, Novel
acetamidothiazole derivatives: synthesis and in vitro anticancer evaluation,
Eur. J. Med. Chem. 69 (2013) 908e919.
[6] S.D. Fidanze, S.A. Erickson, G.T. Wang, R. Mantei, R.F. Clark, B.K. Sorensen,
N.Y. Bamaung, P. Kovar, E.F. Johnson, K.K. Swinger, K.D. Stewart, Q. Zhang,
L.A. Tucker, W.N. Pappano, J.L. Wilsbacher, J. Wang, G.S. Sheppard, R.L. Bell,
S.K. Davidsen, R.D. Hubbard, Imidazo[2,1-b]thiazoles: multitargeted inhibitors
of both the insulin-like growth factor receptor and members of the epidermal
growth factor family of receptor tyrosine kinases, Bioorg. Med. Chem. Lett. 20
(2010) 2452e2455.
[7] E. Gursoy, N.U. Guzeldemirci, Synthesis and primary cytotoxicity evaluation of
new imidazo[2,1-b]thiazole derivatives, Eur. J. Med. Chem. 42 (2007) 320e326.
[8] Y. Xia, Z.W. Dong, B.X. Zhao, X. Ge, N. Meng, D.S. Shin, J.Y. Miao, Synthesis and
structureeactivity relationships of novel 1-arylmethyl-3-aryl-1H-pyrazole-5-
carbohydrazide derivatives as potential agents against A549 lung cancer
cells, Bioorg. Med. Chem. 15 (2007) 6893e6899.
[23] K.M. Amin, M.I. EL-Zahar, M.M. Anwar, M.M. Kamel, M.H. Mohamed, Synthesis
and anticancer activity of novel tetralin-6-ylpyridines and tetralin-6-
ylpyrimidines derivatives, Acta Pol. Pharm. Drug. Res. 66 (2009) 279e291.
[24] F.A. Amer, M. Hammouda, A.S. El-Ahla, B.F. Abdel-Wahab, Synthesis of
important new pyrrolo[3,4-c]pyrazoles and pyrazolylepyrrolines from het-
erocyclic b-ketonitriles, J. Chin. Chem. Soc. 54 (2007) 1543e1552.
[25] S.A. Mohammed, Electron impact ionization mass spectra of fused coumarino
[4,3-d]pyrimidine derivatives, Bull. Chem. Technol. Maced. 24 (2005) 117e126.
[26] S.M. Gomha, H.M.E. Hassaneen, Synthesis and antimicrobial activity of some
new pyrazoles, fused pyrazolo[3,4-d]pyrimidine and 1,2-dihydroimidazo[2,1-
c][1,2,4]triazin-6-one derivatives, Molecules 16 (2011) 6549e6560.
[27] NCI web site, www.dtp.nci.nih.gov.
[28] M.R. Grever, S.A. Schepartz, B.A. Chabner, The National Cancer Institute:
cancer drug discovery and development program, Semin. Oncol. 19 (1992)
622e638.
[29] A. Monks, D. Scudiero, P. Skehan, R. Shoemaker, K. Paull, D. Vistica, C. Hose,
J. Langley, P. Cronise, A.V. Wolff, Feasibility of a high flux anticancer drug
screen utilizing a derive panel of human tumor cell lines in culture, J. Natl.
Cancer Inst. 83 (1991) 757e766.
[30] M.R. Boyd, K.D. Paull, Some practical consideration and applications of the
national cancer institute in vitro anticancer drug discovery screen, Drug. Dev.
Res. 34 (1995) 91e109.
[9] G. Daidone, B. Maggio, D. Raffa, S. Plescia, D. Schillaci, Maria V. Raimondi,
Synthesis and in vitro antileukemic activity of new 4-triazenopyrazole de-
rivatives, Farmaco 59 (2004) 413e417.
[10] A.R. Farghaly, Synthesis of some new indole derivatives containing pyrazoles
with potential antitumor activity, ARKIVOC 11 (2010) 177e187.
[11] E.A. Soliman, M.I. El-Zahar, A.H. El-Masry, M. Kamel, R.S. Gohar, Synthesis and
anticancer evaluation of novel tetrahydronaphthalen-6-ylthiazole heterocycles
against human HePG2 and MCF7 cell lines, Der Pharma Chem. 2 (2010) 507e521.
[12] M.I. El-Zahar, S.A. EL-Karim, M.E. Haiba, M.A. Khedr, Synthesis, antitumor
activity and molecular docking study of novel benzofuran-2-yl pyrazole py-
rimidine derivatives, Acta Pol. Pharm. Drug. Res. 68 (2011) 357e373.
[13] R. Kalirajan, L. Rathore, S. Jubie, B. Gowramma, S. Gomathy, S. Sankar, Mi-
crowave assisted synthesis of some novel pyrazole substituted benzimid-
azoles and evaluation of their biological activities, Indian J. Chem. 50B (2011)
1794e1799.
[14] S.N. Dighe, P.K. Chaskar, K.S. Jain, M.S. Phoujdar, K.V. Srinivasan, A remarkably
high-speed solution-phase combinatorial synthesis of 2-substituted-amino-4-
arylthiazoles in polar solvents in the absence of a catalyst under ambient
conditions and study of their antimicrobial activities, ISRN Org. Chem. 2011
(2011) 1e6.
[15] A.T. Taher, H.H. Georgey, H.I. El-Subbagh, Novel 1,3,4-heterodiazole ana-
logues: synthesis and in vitro antitumor activity, Eur. J. Med. Chem. 47 (2012)
445e451.
[16] M.S.K. Youssef, R.A. Ahmed, M.S. Abbady, S.A. Abdel-Mohsen, A.A. Omar, Re-
actions of 4-(2-aminothiazole-4-yl)-3-methyl-5-oxo-1-phenyl-2-pyrazoline;
synthesis of thiazolo[3,2-a]pyrimidine and imidazo[2,1-b]thiazole derivatives,
Monatsh. Chem. 139 (2008) 553e559.
[31] http://dtp.nci.nih.gov/docs/compare/compare.html.
[32] K.D. Paull, R.H. Shoemaker, L. Hodes, A. Monks, D.A. Scudiero, L. Rubinstein,
J. Plowman, M.R. Boyd, Display and analysis of patterns of differential activity
of drugs against human tumor cell lines: development of mean graph and
COMPARE algorithm, J. Natl. Cancer Inst. 81 (1989) 1088e1092.
[33] D.W. Zaharevitz, S.L. Holbeck, C. Bowerman, P.A. Svetlik, COMPARE: a web
accessible tool for investigating mechanisms of cell growth inhibition, J. Mol.
Graph. Model. 20 (2002) 297e303.
[34] Y.Y. Zaytseva, J.D. Valentino, P. Gulhati, B.M. Evers, mTOR inhibitors in cancer
therapy, Cancer Lett. 319 (2012) 1e7.
[35] C.K. Tsang, H. Qi, L.F. Liu, X.F.S. Zheng, Targeting mammalian target of rapa-
mycin (mTOR) for health and diseases, Drug. Discov. Today 12 (2007) 112e
124.
[36] R.A. Kirken, Y.L. Wang, Molecular actions of sirolimus: sirolimus and mTOR,
Transplant. Proc. 35 (2003) 227e230.
[37] J.M. Fortune, N. Osheroff, Merbarone inhibits the catalytic activity of human
topoisomerase II
17650.
a by blocking DNA cleavage, J. Biol. Chem. 273 (1998) 17643e
[17] A.A. Kadi, H.A. El-Kashef, A.A.M. Abdel-Aziz, G.S. Hassan, J. Tettey, M.H. Grant,
J. Lehmann, H.I. El-Subbagh, Synthesis, ultra-short acting hypnotic activity,
and metabolic profile of ethyl 8-oxo-5,6,7,8-tetrahydro-thiazolo[3,2-a][1,3]
diazepin-3-carboxylate (HIE-124), Arch. Pharm. Chem. Life Sci. 341 (2008)
81e89.
[18] M.F. El Shehry, A.A. Abu-Hashem, E.M. El-Telbani, Synthesis of 3-((2,4-
dichlorophenoxy)methyl)-1,2,4-triazolo(thiadiazoles and thiadiazines) as
anti-inflammatory and molluscicidal agents, Eur. J. Med. Chem. 45 (2010)
1906e1911.
[38] Canvas, Version 1.2, Schrödinger, LLC, New York, NY, 2009.
[39] D.E. Clark, S.D. Pickett, Computational methods for the prediction of ‘drug-
likeness’, Drug. Discov. Today 5 (2000) 49e58.
[40] C.A. Lipinski, F. Lombardo, B.W. Dominy, Experimental and computational
approaches to estimate solubility and permeability in drug discovery and
development settings, Drug. Deliv. Rev. 23 (1997) 3e25.
[41] http://www.organic-chemistry.org/prog/peo.
[42] X. Liu, S. Ouyang, B. Yu, K. Huang, Y. Liu, J. Gong, S. Zheng, Z. Li, H. Li, H. Jiang,
PharmMapper Server: a web server for potential drug target identification via
pharmacophore mapping approach, Nucleic Acids Res. 38 (2010) 609e614.
[43] Z. Bikadi, S. Kovacs, L. Demko, E. Hazai, DockingServer, Virtua Drug Ltd.,
Budapest, Hungary, 2007. www.dockingserver.com.
[19] H.R. Jaberi, H. Noorizadeh, Synthesis of some novel fused imidazo[2,1-b]1,3-
thiazole and imidazo[2,1-b]thiazolo[5,4-d]isoxazole derivatives, E-J. Chem. 9
(2012) 1518e1525.