Synthesis and biological evaluation of imidazopyridine-oxindole conjugates as microtubule-targeting agents

Article abstract of DOI:10.1002/cmdc.201300308

A library of imidazopyridine-oxindole conjugates was synthesised and investigated for anticancer activity against various human cancer cell lines. Some of the tested compounds, such as 10 a, 10 e, 10 f, and 10 k, exhibited promising antiproliferative activity with GI₅₀ values ranging from 0.17 to 9.31 μM. Flow cytometric analysis showed that MCF-7 cells treated by these compounds arrested in the G₂/M phase of the cell cycle in a concentration-dependent manner. More particularly, compound 10 f displayed a remarkable inhibitory effect on tubulin polymerisation. All the compounds depolarised mitochondrial membrane potential and caused apoptosis. These results are further supported by the decreased phosphorylation of Akt at Ser473. Studies on embryonic development revealed that the lead compounds 10 f and 10 k caused delay in the development of zebra fish embryos. Docking of compound 10 f with tubulin protein suggested that the imidazo[1,2-a]pyridine moiety occupies the colchicine binding site of tubulin. Arrested development: A library of imidazopyridine-oxindole conjugates was synthesised and investigated for anticancer activity against various human cancer cell lines. Some of the tested compounds, such as 10 a, 10 e, 10 f, and 10 k, exhibited promising antiproliferative activity. Copyright

Full text of DOI:10.1002/cmdc.201300308

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DOI: 10.1002/cmdc.201300308
Synthesis and Biological Evaluation of Imidazopyridine–
Oxindole Conjugates as Microtubule-Targeting Agents
[
a]
[a]
[b]
[a, c]
Ahmed Kamal,* Vangala Santhosh Reddy, Santosh Karnewar, Sumit S. Chourasiya,
[a]
[a]
[b]
[a]
Anver Basha Shaik, G. Bharath Kumar, Chandan Kishor, M. Kashi Reddy,
M. P. Narasimha Rao, Ananthamurthy Nagabhushana, Kallaganti V. S. Ramakrishna,
Anthony Addlagatta,* and Srigiridhar Kotamraju*
[a]
[e, f]
[d]
[b]
[b]
A library of imidazopyridine–oxindole conjugates was synthes-
ised and investigated for anticancer activity against various
human cancer cell lines. Some of the tested compounds, such
as 10a, 10e, 10 f, and 10k, exhibited promising antiprolifera-
tive activity with GI50 values ranging from 0.17 to 9.31 mm.
Flow cytometric analysis showed that MCF-7 cells treated by
polymerisation. All the compounds depolarised mitochondrial
membrane potential and caused apoptosis. These results are
further supported by the decreased phosphorylation of Akt at
Ser473. Studies on embryonic development revealed that the
lead compounds 10 f and 10k caused delay in the develop-
ment of zebra fish embryos. Docking of compound 10 f with
tubulin protein suggested that the imidazo[1,2-a]pyridine
moiety occupies the colchicine binding site of tubulin.
these compounds arrested in the G /M phase of the cell cycle
2
in a concentration-dependent manner. More particularly, com-
pound 10 f displayed a remarkable inhibitory effect on tubulin
Introduction
Cancer, the uncontrolled growth of cells, has become a major
cause of death throughout the world. Every year more than
related to apoptosis. The microtubules are in dynamic equilib-
rium with tubulin dimers as tubulin is assembled into microtu-
[3–5]
20% of the population is affected by cancer, and the mortality
bules, which in turn are disassembled to tubulin.
Tubulin
rate is increasing annually, making it a major area of focus for
polymerisation inhibition, therefore results in an increase in
[
1,2]
[6]
researchers.
Microtubules are dynamic polymers of a and
the number of cells in metaphase arrest in the cell cycle.
b tubulin present in eukaryotic cells that play a decisive role in
several fundamental cellular processes, including cell division,
motility, transport, and maintenance of cell shape. In addition
microtubules are involved in a host of cell-signalling pathways
Consequently, microtubules have become an important
target for the design of new antimitotic anticancer agents.
Drugs that inhibit microtubule polymerisation are effective in
the treatment of lung, breast, ovarian, and other cancers. How-
ever, occurrence of peripheral neuropathy is a major complica-
tion in the development of microtubule depolymerising agents
[a] Dr. A. Kamal, V. S. Reddy, S. S. Chourasiya, A. B. Shaik, G. B. Kumar,
[7]
as drugs. Therefore, the discovery of new molecules to over-
come neuropathies are required immediately. There has been
considerable interest in the discovery and development of
M. K. Reddy, M. P. Narasimha Rao
Medicinal Chemistry & Pharmacology Division
Indian Institute of Chemical Technology, Hyderabad 500007 (India)
E-mail: ahmedkamal@iict.res.in
[2]
small molecules that affect tubulin polymerisation. Colchi-
[b] S. Karnewar, C. Kishor, Dr. A. Addlagatta, Dr. S. Kotamraju
cines (1a), podophyllotoxins (1b), and combretastatins, CA-4
Centre for Chemical Biology
Indian Institute of Chemical Technology, Hyderabad 500007 (India)
E-mail: anthony@iict.res.in
(
1c) are notable examples of compounds that inhibit microtu-
[8–10]
bule assembly by binding to tubulin.
(Figure 1) CA-4, in
giridhar@iict.res.in
particular, is an extensively studied natural cis-stilbene that
[
c] S. S. Chourasiya
strongly inhibits tubulin polymerisation by binding to the col-
Department of Medicinal Chemistry
National Institute of Pharmaceutical Education & Research (NIPER)
Hyderabad 500034 (India)
[11–13]
chicine binding pocket of tubulin.
However, the success of
tubulin polymerisation inhibitors as anticancer agents has
stimulated significant interest in the identification of new com-
pounds that may be more potent or more selective in targeted
tissues or tumours. Oxindoles are versatile moieties that dis-
[d] K. V. S. Ramakrishna
Centre for NMR & SC, Indian Institute of Chemical Technology
Hyderabad 500007 (India)
[
e] Dr. A. Nagabhushana
Centre for Cellular & Molecular Biology, Hyderabad 500007 (India)
play diverse biological activities, including anticancer activi-
[14–16]
ty.
Indirubin (3), which possess an oxindole moiety as its
[
f] Dr. A. Nagabhushana
Centre of Excellence in Epigenetics
Indian Institute of Science Education and Research, Pune 411021 (India)
basic scaffold, is reported as a potent anticancer agent that in-
hibits cyclin dependent kinase (CDK). Recently has been report-
ed that oxindoles not only inhibited CDK but also tubulin poly-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cmdc.201300308.
[5,17]
merisation by binding at the colchicine binding site.
More-
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7
cells. The results of cell cycle and mitotic arrest
showed that these compounds affect the G /M phase
2
along with the inhibition of tubulin assembly.
Results and Discussion
Chemistry
The imidazopyridine–oxindole conjugates 10a–t
were synthesised by employing the Knoevenagel re-
action between equimolar mixtures of substituted
imidazo[1,2-a]pyridine aldehydes (8a–e) and oxin-
doles (9a–d). The compound structures were con-
1
13
firmed by means of H NMR, C NMR, HRMS, and IR
spectra. All the compounds were obtained in pure E
Figure 1. Structures of standard anticancer molecules colchicine (1a), podophyllotoxin
(
1b), CA-4 (1c), imidazopyridines 2, indirubin (3), and imidazopyridine–oxindole ana-
isomeric forms and conformed with those previously
1
2
3
[22,23]
logues 10a–t; see Scheme 1 for R , R , and R groups.
reported.
The key intermediates, imidazo[1,2-
Table 1. In vitro cytotoxic effect of conjugates 10a, 10e, and10 f against a panel of 60 human cancer cell
over another class of com-
pounds, namely imidazopyridine
lines.
[
a]
[a]
Panel/cell lines
GI50 [mm]
Panel/cell lines
GI50 [mm]
10e
(
2) (Figure 1), possess many bio-
[
b]
[c]
[d]
[b]
[c]
[d]
1
0a
10e
10 f
10a
10 f
logical activities such as antipy-
retic, anti-inflammatory, antipla-
Leukaemia
HL-60 (TB)
MOLT-4
Ovarian cancer
2.59
4.20
4.98
2.57
2.67
1.88
2.89
2.92
2.31
2.25
0.34
0.59
0.29
0.58
0.92
IGROV1
OVCAR-3
OVCAR-4
OVCAR-5
OVCAR-8
2.59
4.26
6.21
4.39
4.90
2.01
1.95
3.06
1.89
2.30
2.21
2.28
2.30
2.18
1.09
0.28
1.28
1.76
1.08
0.29
1.32
[
18]
telet aggregation,
and anti-
[
19]
cancer activities. Some of the
potent hybrid molecules that
have been recently developed
as new anticancer agents are
obtained by the combination of
SR
CCRF-CEM
RPMI-8226
NCI/ADR-RES
SK-OV-3
Non-small-cell lung cancer
A549/ATCC
EKVX
3.90
2.14
3.08
2.35
1.86
2.07
2.37
3.69
2.35
2.17
0.61
2.47
1.03
[
20,21]
3.10
2.70
3.98
4.50
3.77
3.68
3.24
1.83
Renal cancer
786-0
different pharmacophores.
HOP-62
HOP-92
5.98
5.87
4.45
2.70
2.75
4.91
5.05
1.95
2.18
1.21
3.25
2.25
1.86
2.88
2.95
2.10
1.04
0.32
1.05
0.66
0.36
1.12
1.04
0.44
The promising biological activity
exhibited by these conjugates
prompted us to explore some
newer conjugates by linking
two pharmacophores such as
oxindole and imidazopyridine
scaffolds to enhance the anti-
cancer activity. In this context
we have designed and synthes-
[
e]
NT
NT
A498
ACHN
CAKI-1
RXF 393
SN12C
TK-10
[e]
NCI-H226
NCI-H23
NCI-H322M
NCI-H460
NCI-H522
0.44
1.95
0.39
0.18
UO-31
Colon cancer
COLO 205
HCC-2998
HCT-116
HCT-15
2.21
4.56
3.61
3.60
3.05
2.55
3.02
4.03
2.01
2.36
3.15
2.33
2.04
3.00
0.57
1.04
0.43
0.58
0.32
0.43
0.36
Breast cancer
MCF-7
MDA-MB-231/ATCC
HS 578T
3.52
7.29
9.31
3.97
4.40
2.10
2.71
3.50
2.20
2.46
4.35
2.08
0.38
1.18
1.02
ised
imidazopyrimidine–oxin-
[
e]
dole conjugates (10a–t) that
were evaluated for their anti-
cancer potential. Interestingly,
some of the compounds such as
HT29
KM12
SW-620
BT-549
T-47D
MDA-MB-468
NT
0.95
0.25
CNS cancer
SF-268
SF-295
SF-539
SNB-19
SNB-75
U251
Melanoma
LOX IMVI
MALME-3M
M14
MDA-MB-435
SK-MEL-2
SK-MEL-28
SK-MEL-5
UACC-257
UACC-62
10a, 10e, 10 f, and 10k, could
5.23
2.34
1.87
2.09
3.33
2.08
2.05
1.25
0.38
0.88
1.43
0.39
0.45
4.34
3.88
2.48
3.86
2.35
5.53
2.83
8.96
3.88
2.06
3.80
3.02
1.99
2.66
3.33
2.38
3.11
2.58
0.86
0.58
0.54
0.17
[
e]
NT
be considered as potential lead
conjugates with impressive anti-
proliferative activities (GI50 0.17–
3.96
4.93
1.85
3.97
[e]
NT
9
.31 mm)
against
cancer
different
lines
1.13
0.41
1.17
0.73
human
cell
Prostate cancer
PC-3
(Table 1). Furthermore, flow cy-
3.14
4.47
2.43
2.67
0.81
1.12
tometric analysis was performed
to determine the effect of active
congeners in altering the cell-
cycle phase distribution in MCF-
DU-145
[
a] Compound concentration required to decrease cell growth to 50% that of untreated cells. Values are single
determinations; [b] 10a (NSC 761116); [c] 10e (NSC 761121); [d] 10 f (NSC 761130); [e] Not tested.
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a]pyridine aldehydes (8a–e) were prepared by means of Vils-
meier–Haack reaction on the corresponding imidazo[1,2-a]pyri-
dine (7a–e) that were in turn obtained by the reaction be-
tween 2-aminopyridine and substituted 2-bromo-1-phenyletha-
growth inhibitory activity with GI50 values of 0.38 and 0.17 mm
against MCF-7 and MDA-MB 435 cell lines, respectively. The
conjugate 10k, which possesses a chlorine atom at the C4 po-
sition of the C ring and at the C6 position of the B ring also
showed cytotoxicity against MCF-7 (GI =0.59 mm) and MDA-
[
24]
nones (4a–e). The sequential steps of these reactions are
50
outlined in Scheme 1.
MB 435 (GI =1.51 mm) cell lines (see Table 2). However, the
50
conjugates 10e and 10j contain
a chlorine atom at the C5 posi-
tion of the B ring instead of at
the C6 position and showed
a decreased cytotoxic effect rela-
tive to the conjugates 10 f and
10k which have the chlorine
substitution at the C6 position
of the B ring. It is also observed
that the absence of a halogen
atom on both the B and C rings
(
10a) decreased the antiprolifer-
ative activity significantly relative
to the halogenated conjugates
such as 10e, 10 f, 10j, and 10k.
Some conjugates such as 10b–d
and 10g–t showed moderate
antiproliferative
activity
as
shown in Tables 1 and 2.
Antimitotic effect in MCF-7 cells
In view of the potent antiproli-
ferative activities of these lead
conjugates (10a, 10e, 10 f, 10j,
and 10k) it was of interest to ex-
Scheme 1. Synthesis of compounds 10a–t. Reagents and conditions: a) acetone, reflux, 6–8 h; b) 2n HCl, reflux,
1
h, 85–92%; c) POCl
3 3 3
, DMF, CH Cl , 3 h at RT, 10–12 h at reflux, 75–80%; d) substituted oxindoles 9a–d, piperidine,
C
2 5
H OH, reflux 3–5 h, 50–70%.
amine
cell-cycle
alterations
caused by these conjugates in
MCF-7 breast cancer cells to un-
Biology
Antiproliferative Activity
derstand the phase distribution. Thus, cells were treated with
these conjugates at concentrations of 3 mm for a period of
24 h. Cells were harvested and analyzed by flow cytometry. It
was found that a large proportion of cells treated with conju-
Some of the imidazopyridine–oxindole conjugates 10a–t were
evaluated for their antiproliferative activity in a panel of 60
human cancer cell lines derived from nine cancer
types (breast, non-small-cell lung, colon, CNS, mela-
noma, ovarian, leukaemia, renal, and prostate cancer
cells) by the National Cancer Institute (NCI), Bethes-
da, MD, USA (see Table 1). For the selected represen-
tative compounds 10a, 10e, and 10 f, dose–re-
sponse curves for each cell line were measured at
a minimum of five concentrations. Cells were incu-
bated with compounds for a period of 48 h and then
cell viability was measured by the sulforhodamine B
Table 2. Growth inhibition data for compounds 10a–t in selected human breast
cancer cell lines.
[a]
[a]
Compd
GI50 [mm]
Compd
GI50 [mm]
MCF-7
MDA-MB-231
MCF-7
MDA-MB-231
1
10b
10c
1
1
1
10g
10h
0a
4.01Æ0.13
3.26Æ0.30
2.17Æ0.26
8.97Æ0.70
2.89Æ0.37
0.43Æ0.11
6.12Æ0.21
4.78Æ0.17
3.98Æ0.06
2.68Æ0.19
6.35Æ0.26
4.78Æ0.43
2.24Æ0.27
7.61Æ0.31
4.25Æ0.07
0.95Æ0.31
8.21Æ0.85
3.12Æ0.11
4.05Æ0.02
2.91Æ0.14
10k
10l
0.59Æ0.09
4.56Æ0.12
6.23Æ0.21
3.78Æ0.25
4.67Æ0.36
1.35Æ0.03
4.78Æ0.21
5.47Æ0.65
4.56Æ0.31
3.91Æ0.05
1.51Æ0.27
5.70Æ0.11
7.10Æ0.08
2.67Æ0.16
3.65Æ0.16
1.05Æ0.21
5.21Æ0.18
6.61Æ0.26
3.02Æ0.21
3.10Æ0.33
10m
10n
10o
10p
10q
10r
10s
10t
0d
0e
0 f
(SRB) assay. The compounds tested (10a, 10e, and
10 f) showed impressive anticancer activity against
the complete panel of 60 cell lines with GI50 values
1
1
0i
0j
ranging from 0.17–9.31 mm. In particular conjugate
10 f, which contains a fluorine substituent at the C4
[
a] Compound concentration required to decrease cell growth to 50% that of untreat-
position of the C ring and a chlorine substituent at
the C6 position of the B ring, exhibited significant
ed cells; values are mean ÆSD of three determinations performed in triplicate.
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10 f, 10j, and 10k) were employed at a concentration of 3 mm
in tubulin assembly assays. Combretastatin A-4 (1c) was used
as a positive control. Compounds 10 f and 10k exhibited
potent inhibition of microtubule assembly (72% and 65% in-
hibition, respectively). Compound 10 f in particular showed tu-
bulin polymerisation inhibition similar to combretastatin A-4
(
1c). However, compounds 10a, 10e, and 10j also appreciably
inhibited tubulin polymerisation, albeit to a lesser extent rela-
tive to CA-4. Furthermore, the IC50 values of these conjugates
was determined and the two leads 10 f and 10k showed pro-
nounced inhibition of tubulin polymerisation with IC50 values
of 1.8 mm and 2.4 mm respectively (Table 4). Thereby, these re-
sults confirm that compounds 10 f and 10k are potent inhibi-
tors of tubulin polymerisation.
Table 4. Effect of compounds 10a, 10e, 10 f, 10j, and 10k on tubulin
polymerisation.
[a]
[b]
Compd
IC50 [mm]
Inhibition [%]
1
1
1
1
1
0a
0e
0 f
0j
3.8Æ0.4
2.7Æ0.2
47Æ1.2
59Æ2
74Æ3
55Æ1
65Æ2
82Æ1
1.8Æ0.01
3.2Æ0.5
2.4Æ0.2
1.3Æ0.1
0k
CA-4 (1c)
[
a] Half maximal inhibitory concentration: compound concentration re-
quired to inhibit tubulin polymerisation by 50%; data are the mean ÆSD
of n=3 independent experiments performed in triplicate. [b] Inhibition of
tubulin polymerisation at 3 mm (final volume=10 mL); compounds were
pre-incubated with tubulin at a final concentration of 10 mm. Data are the
mean ÆSD of n=3 independent experiments performed in triplicate.
Figure 2. Antimitotic effects of 10a, 10e, 10 f, 10j, and 10k by FACS analy-
sis. MCF-7 cells were treated with 10a, 10e, 10 f, 10j, and 10k (3 mm) for
24 h. Untreated cells and DMSO-treated cells served as controls. Cell-cycle
analysis was performed with propidium iodide as indicated in the Experi-
mental Section. The cell-cycle phase distribution was determined, and the
percentage of cells in each phase was analyzed by FCS express 4 plus.
Effect on mitochondrial membrane depolarisation
Measurement of mitochondrial membrane potential (DYm)
gates 10e, 10 f, and 10k accumulated in the G /M phase (68,
serves as a marker to estimate the overall function of mito-
2
63, and 58%, respectively; see Figure 2 and Table 3).
chondria and during induction of apoptosis, DY is depolar-
m
[25]
ised. Therefore, in this study we examined the effect of oxin-
dole conjugates on DY . MCF-7 cells were treated with com-
m
Table 3. Cell cycle phase distribution of MCF-7 cells following treatment
with compounds 10a, 10e, 10 f, 10j, and 10k.
pounds 10a, 10e, 10 f, 10j, and 10k at a 1 mm concentration
for 24 h and stained with JC-1 dye. In control cells the dye con-
centrates in the mitochondrial matrix where it forms red fluo-
rescent aggregates (J-aggregates) because of to the electro-
chemical potential gradient. In cells treated with compounds
which induce apoptosis, the mitochondrial membrane is depo-
larized thus preventing the accumulation of the JC-1 dye in
the mitochondria. Therefore the dye in the monomeric form is
dispersed throughout the entire cell leading to a shift from red
Phase
Compd
Control
G
1
S
2
G /M
71.69
65.91
31.11
34.65
29.30
30.29
8.59
13.05
5.36
6.49
19.20
6.49
19.72
20.99
63.53
58.86
53.71
49.62
1
1
0a
0e
1
0 f
0j
0k
1
1
(
J-aggregates) to green fluorescence (JC-1 monomers). Thus,
apoptotic cells showing primarily green fluorescence are easily
differentiated from healthy cells which show red and green
fluorescence. It was observed that these conjugates significant-
ly depolarize the mitochondrial membrane potential (Figure 3)
as well as causing significant inhibition of tubulin polymeri-
sation and thereby induce cell death in MCF-7 cells.
Inhibition of tubulin polymerisation
To investigate whether the antiproliferative activity of the syn-
thesised congeners was related to an interaction with tubulin,
we evaluated their effect on the inhibition of tubulin polymeri-
sation. The imidazopyrimidine–oxindole conjugates (10a, 10e,
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was observed that compounds 10e, 10 f, and 10k, which
caused tubulin depolymerisation, also significantly decreased
Akt phosphorylation (Ser473), thereby suggesting that Akt also
plays some role in MCF-7 cell death mediated by these conju-
gates (Figure 5).
Effect on the development of zebra fish embryo
Zebra fish (Danio rerio) has emerged as a powerful model
system for chemical genetic screening owing to several advan-
tages, especially its external development and optically clear
[27–29]
embryos.
Our results indicate that these conjugates have
potent antimitotic activity by destabilising microtubules. To
further validate these observations, the effect of these com-
pounds on the development of zebra fish embryos was exam-
ined. Zebra fish embryos treated with 10 f and 10k showed
severe delay in development relative to DMSO-treated control
embryos. Whereas the control embryos progress through
prim5 stage, both the conjugate (10 f and 10k) treated em-
bryos were arrested at the 10 somite stage. A similar develop-
mental delay was observed with embryos treated with com-
bretastatin A-4 (1c), a known inhibitor of microtubule polymer-
isation. However, embryos treated with 10a, 10e, or 10j
showed little phenotypic abnormalities. These observations
suggest that both 10 f and 10k act as potent antimitotic com-
pounds in zebra fish embryos and could be considered as po-
tential chemotherapeutic leads (Figure 6).
Molecular docking studies
AutoDock version 4.2 was used to dock imidazo[1,2-a]pyridine
[30,31]
derivatives into the colchicine binding site of b-tubulin.
Re-
sults suggest that the docking position of the imidazo[1,2-
a]pyridine moiety bind well in the colchicine binding pocket
with extensive hydrophobic contacts within the binding
pocket of the b-chain (Figure 7). The imidazo[1,2-a]pyridine
Figure 3. Imidazopyridine–oxindoles cause mitochondrial membrane depo-
larisation in MCF-7 cells. Cells were treated with 10a, 10e, 10 f, 10j, and
1
0k (1 mm) for 24 h, and mitochondrial membrane potential was measured
by JC-1 staining as described in the Experimental Section.
Effect on chromatin condensation
Apoptosis is an important, continuous process of de-
struction of undesirable cells during development or
[
26]
homeostasis in multicellular organisms.
During
apoptosis, mitochondrial membrane potential is de-
polarised and chromatin condensation takes place.
Hoechst-33258 staining was used to visualise nuclear
condensation and it was found that the oxindole
conjugates 10a, 10e, 10 f, 10j, and 10k caused sig-
nificant nuclear condensation in MCF-7 cells upon
treatment at 3 mm concentration for 24 h (Figure 4).
Studies on Akt signaling pathway
It is known that cancer cells possess higher levels of
Akt (Ser473), which in turn is responsible for the in-
creased proliferation rates in these cells by inducing
Figure 4. Imidazopyridine–oxindoles cause apoptosis in MCF-7 cells. Cells were treated
with 10a, 10e, 10 f, 10j, and 10k (3 mm) for 24 h, then washed with PBS and incubated
with Hoechst-33258 stain (4 mgmL ) for 20 min to measure nuclear condensation. Fluo-
À1
downstream cell survival pathways. Interestingly, it rescence images were captured with a DAPI filter.
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a chlorine atom (Table 4). The cyclic amide group on indoline
(
B ring) participates in two hydrogen bonds with Asn101 of
the a-chain. The small variation in the substitution at the C5
and C6 positions of B rings shows clear distinction activity. For
example, conjugates with a substitution at the C6 position dis-
play better inhibition than a conjugate with a substitution at
the C5 position. From the modelling it is clear that this ring oc-
cupies the interface between the a- and b-chains. The substi-
tution near the C5 position experiences steric clashes with
Ly352 of the b-chain, however, the substitution at the C6 posi-
tion is exposed to solvent and does not have any steric issues
and as such they become more favourable to binding. This
study further confirms the improved activity of the conjugates
Figure 5. Effect of imidazopyridine–oxindole conjugates on phosphorylation
of Akt. MCF-7 cells were treated with 10e, 10 f, and 10k (5 mm) for 24 h.
Proteins were resolved by SDS-PAGE and immunoblot analysis was per-
formed with Akt and phospho-Akt(Ser473) specific antibodies. The bands
were detected by enhanced chemiluminescence as described in the Experi-
mental Section.
10e and 10 f.
Conclusions
In conclusion, a library of substituted imidazopyridine–oxindole
conjugates 10a–t were synthesised and biologically evaluated
for their cytotoxic activity against breast cancer cell lines.
Some representative conjugates were evaluated for their anti-
proliferative potential in the 60 human cancer cell line panel of
the NCI. Almost all the synthesised compounds showed excel-
lent to moderate antiproliferative activity, in particular, conju-
gates 10 f and 10k showed potent anticancer activity with GI50
values as low as 0.6 mm in breast cancer cells. Flow cytometry
results demonstrated that these conjugates (10a, 10e, 10 f,
Figure 6. Effect of microtubule inhibitors on the development of zebra fish
embryos. Embryos were treated with DMSO (1%), 10 f, 10k (5 mm) or CA-4
(
1c) at 5 hpf and imaged at 26 hpf to observe morphology.
10j, and 10k) caused cell-cycle arrest and accumulated cells in
the G /M phase. These compounds inhibited microtubule as-
2
sembly as shown by the tubulin polymerisation assay. Interest-
ingly, it was observed that the IC50 value of compound 10 f
was similar to that of combretastatin A-4 (1c), a well-known
microtubule assembly disrupter. The docking studies of com-
pounds 10e and 10 f reveal that the imidazopyridine ring ex-
hibited binding interactions similar to that of the colchicines.
SAR results confirm that the conjugates containing a chlorine
atom at C6 of the B ring and a halogen atom (F or Cl) at C4 of
the C ring showed potent anticancer activity. Based on these
results it is evident that compound 10 f is a suitable template
for the design of newer tubulin polymerisation inhibitors.
Figure 7. A) Docking pose of 10e (light sticks) and 10 f (dark sticks). The
grey surface represents the b-chain with the blue ribbon indicating the
a-chain of tubulin. The imidazo[1,2-a]pyridine moiety of compounds is
buried in the hydrophobic pocket of the colchicine binding domain.
B) Amino acids of a-and b-chain tubulin interacting with compounds 10e
and 10 f. Dashed lines indicate hydrogen bonds.
Experimental Section
Biology
Cell-cycle analysis: Breast cancer cells (MCF-7) were incubated for
2
1
4 h in the presence or absence of test compounds 10a, 10e, 10 f,
0j, and 10k (3 mm). Cells were harvested with trypsin EDTA and
moiety binds in the pocket where the A ring of colchicine nor-
mally binds and amino acids in proximity to this moiety in-
clude Cys241, Leu242, Ala250, Leu255, Val318, and Ile378.
Whereas the aromatic C ring is sandwiched between Lys352
fixed in ice-cold 70% ethanol at 48C for 30 min; ethanol was re-
moved by centrifugation, and cells were stained with 1 mL of DNA
staining solution (2 mg of RNase A and 0.2 mg of propidium iodide
[32]
(
PI)) for 30 min. The DNA content of 20000 events were mea-
1
and Asn258 of the b-chain, the R substituent at the C4 posi-
sured by flow cytometry (BD FACS Canto II). Histograms were ana-
lyzed using FCS express 4 plus.
tion interacts with the main chain at Asn350. Any larger or hy-
drophobic groups, such as methyl groups, cannot be accom-
modated at this position. Compounds that show the highest
inhibition against tubulin polymerisation have either no substi-
tution or small atoms such as fluorine or in exceptional cases
Tubulin polymerisation assays: The tubulin polymerisation assay
was performed employing a fluorescence-based tubulin polymeri-
sation assay kit (Cytoskeleton, Inc.) according to the manufacturer’s
[33,34]
À1
protocol.
The reaction mixture contained, 2 mgmL bovine
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brain tubulin, 10 mm fluorescent reporter, and 1 mm GTP in the
presence or absence of test compounds in PEM buffer (80 mm
PIPES, 0.5 mm EGTA, 2 mm MgCl2, pH 6.9) at 378C in a final
volume of 10 mL. Fluorescence readings were recorded on a Tecan
multimode reader at l 360/420 nm (excitation/emission) every
Docking studies
Molecular docking simulations were performed using AutoDock 4.2
and the atomic coordinates of b-tubulin as the target (PDB code
3
E22). After removing the ligand and solvent molecules, hydrogen
atoms and Kollman charges were added to each protein atom. Co-
ordinates for each compound were obtained from Chemdraw11
followed by MM2 energy minimisation. Docking was carried out by
2
min for up to 3 h. Combretastatin A-4 (1c) was used as positive
control under similar conditions. To evaluate the IC50 values of the
compounds against tubulin assembly, the compounds 10a, 10e,
[
30,31]
AutoDock 4.2 in the colchicine binding pocket.
Grid map in
1
5
0 f, 10j, and 10k were incubated at various concentrations (1–
mm) with tubulin.
AutoDock was used to define the interaction of protein and ligand
in the binding pocket. The grid map was used with 60 points in
each x, y, and z direction, equally spaced at 0.375 ꢁ. Docking was
[36]
Analysis of mitochondrial membrane potential: MCF-7 cells were in-
cubated for a period of 24 h in the presence or absence of test
compounds 10a, 10e, 10 f, 10j, and 10k (1 mm). At the end of
treatment, the medium was aspirated, cells were washed with
medium without FBS, and JC-1 stain (Sigma cat. no. CS0390) was
added to the cells for 20 min at 378C under humidified atmos-
phere. Cells were washed again with medium. The cells were cov-
ered with medium and observed under a fluorescence microscope
performed using the Lamarckian genetic algorithm. Each dock-
ing experiment was performed 100 times, yielding 100 docked
conformations. Parameters used for the docking were as follows:
population size of 150; random starting position and conforma-
tion; maximal mutation of 2 ꢁ translation and 50degrees rotation;
elitism of 1; mutation rate of 0.02 and crossover rate of 0.8; and
local search rate of 0.06. Simulations were performed with a maxi-
mum of 1.5 million energy evaluations and a maximum of 50000
generations. Final docked conformations were clustered using a tol-
erance of 1 ꢁ root mean square deviation (RMSD). The best model
was chosen based on the most favourable stabilisation energy.
[25]
equipped with rhodamine and FITC filters.
Hoechst-33258 staining: MCF-7 cells were incubated for a period of
4 h in the presence or absence of test compounds 10a, 10e, 10 f,
0j and 10k (3 mm). At the end of treatment, the medium was as-
2
1
pirated, cells were washed with medium without FBS, and
Hoechst-33258 stain (Invitrogen cat. no. H3570) was added to the
cells for 20 min at 378C under humidified atmosphere. Cells were
washed again with medium. The cells were covered with medium
and observed under a fluorescence microscope equipped with
Chemistry
General: All chemicals and reagents were obtained from Lancaster
(
Alfa Aesar, Johnson Matthey Company, Ward Hill, MA, USA),
Sigma–Aldrich (St. Louis, MO, USA), and Spectrochem Pvt. Ltd.
Mumbai, India) and were used without further purification. Reac-
(
[26]
DAPI filter.
tions were monitored by TLC performed on silica gel coated glass
plates containing 60 GF254 with visualisation achieved by UV light
or iodine indicator. Column chromatography was performed with
Western blot analysis: After the treatment of MCF-7 cells with com-
pounds 10e, 10 f and 10k at 3 mm, cells were washed with ice-
cold phosphate-buffered saline (PBS) and homogenised in 100 mL
of radioimmunoprecipitation assay (RIPA) buffer (20 mm Tris·HCl,
pH 7.4, 2.5 mm EDTA, 1% Triton X-100, 1% sodium deoxycholate,
1
13
Merck 60–120 mesh silica gel. H and C NMR spectra were record-
ed on Bruker UXNMR/XWIN-NMR (300 MHz) or Inova Varian VXR
Unity (500 MHz) instruments. Chemical shifts (d) are reported in
ppm downfield from an internal TMS standard. ESI mass spectra
were recorded on a Micro mass Quattro LC using ESI+ software
with a capillary voltage of 3.98 kV and an ESI mode positive ion
trap detector. High-resolution mass spectra were recorded on
a QSTAR XL Hybrid MS–MS mass spectrometer. Melting points
were determined with an Electro thermal melting point apparatus,
1
% SDS, 100 mm NaCl, 100 mm NaF) containing 1 mm sodium or-
[35]
thovanadate and a mixture of protease inhibitors. The homoge-
nate was centrifuged at 750 g for 10 min at 48C to pellet out the
nuclei. The remaining supernatant was centrifuged for 30 min at
1
2000 g. Proteins were resolved on SDS-PAGE and blotted onto ni-
1
13
and are uncorrected. H NMR, C NMR, and HRMS spectra of final
compounds 10a–t are provided in the Supporting Information.
trocellulose membranes. Membranes were probed with AKT and
phospho-AKT (Ser473) procured from Millipore. The detection was
carried out with HRP-labelled rabbit anti-mouse IgG (Amersham)
using an enhanced chemiluminescence detection system (ECL Ad-
vanced Kit, GE Health care).
2
1
(
5
-Phenylimidazo[1,2-a]pyridine (7a): 2-Aminopyridine
0 mmol) was dissolved in acetone (100 mL) and treated with 4a
2.1 g, 10 mmol). The reaction mixture was heated at reflux for 4–
h, and the resulting salt (6a) was collected by filtration, washed
5 (1 g,
with acetone, and then dissolved in 3n HCl (200 mL) and heated
at reflux for 1 h. Before complete cooling, the solution was cau-
Zebra fish maintenance and screening: Wild-type zebra fish (Danio
rerio) were raised and maintained at 28.58C with 14/10 h light–
dark cycle. Two or three pairs of zebra fish were synchronously
mated and embryos were pooled. The embryos were dechorionat-
ed and 3–4 embryos were dispensed in 200 mL of E3 embryo
medium (5 mm NaCl, 0.17 mm KCl, 0.44 mm CaCl , 0.68 mm MgCl )
tiously basified by dropwise addition of 15% aq NH OH to pH 8.
4
The resulting base was collected by filtration and crystallised from
EtOH to afford compound 7a as a white solid (1.75 g, 85% yield);
1
mp: 144–1468C; H NMR (300 MHz, CDCl ): d=6.70 (t, J=6.7 Hz,
3
2
2
1
H), 7.10 (dt, J=6.7, 1.5 Hz, 1H), 7.25 (dt, J=6.7, 1.5 Hz, 1H), 7.37
into each well of a 96-well plate. The embryos were treated with
compounds 10a, 10e, 10 f, 10j, 10k, and combretastatin A-4 (1c)
(
7
.
t, J=7.5 Hz, 2H), 7.57 (d, J=9.0 Hz, 1H), 7.79 (s, 1H), 7.89 (d, J=
.5 Hz, 2H), 8.05 ppm (d, J=6.7 Hz, 1H); MS (ESI): m/z 195 [M+H]
+
(
5, 10, and 25 mm) and DMSO (1%) at 5 h post-fertilisation (hpf)
and incubated at 28.58C. Approximately 50 embryos were
screened for each compound in biological replicates. They were
observed after 28 hpf with a Leica stereomicroscope. Only those
compounds that resulted in similar phenotypic defects in most of
the embryos were considered active.
2-(4-Chlorophenyl)imidazo[1,2-a]pyridine (7c): Compound 7c
was prepared according to the method described for compound
7a, employing 2-Bromo-1-(4-chlorophenyl)ethanone 4c (2.46 g,
10 mmol) and 2-aminopyridine 5 (1 g, 10 mmol) to obtain the pure
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+
+
product 7c as a white solid (2.6 g, 89% yield); mp: 171–1738C;
(ESI): 338 [M+H] ; HRMS (ESI) calcd for C H N O [M+H]
22 16 3
1
H NMR (300 MHz, CDCl ): d=6.77 (t, J=6.6 Hz, 1H), 7.07–7.21 (m,
338.1287; found: 338.1286.
3
3
8
H), 7.62 (d, J=9.1 Hz, 1H), 7.79 (s, 1H), 7.87–7.96 (m, 2H),
.10 ppm (d, J=6.8 Hz, 1H); MS (ESI): m/z 229 [M+H] .
+
(E)-6-Chloro-3-((2-phenylimidazo[1,2-a]pyridin-3-yl)methylene)in-
dolin-2-one (10b): Compound 10b was prepared according to
the method described for compound 10a, employing
2
-para-Tolylimidazo[1,2-a]pyridine (7d): Compound 7d was pre-
pared according to the method described for compound 7a, em-
ploying 2-bromo-1-p-tolylethanone 4d (2.6 g, 10 mmol) and 2-ami-
nopyridine 5 (1 g, 10 mmol) to obtain the pure product 7d as
2-phenylimidazo[1,2-a]pyridine-3-carbaldehyde
0.9 mmol) and 6-chloroindolin-2-one 9d (150 mg, 0.9 mmol) to
obtain the pure product 10b as a yellow solid (197 mg, 59%); mp:
8a
(200 mg,
1
À1
1
a white solid (2 g, 91% yield); mp: 165–1688C; H NMR (300 MHz,
309–3108C; IR (KBr) n˜ =3408, 3004, 1712, 754 cm
;
H NMR
CDCl ): d=2.38 (s, 3H), 6.78 (dt, J=6.7 Hz, J=1.1 Hz, 1H), 7.18 (dt,
(300 MHz, CDCl ): d=6.32 (d, J=7.6 Hz, 1H), 6.78 (dd, J=2.0 Hz,
3
3
J=6.7, 1.2 Hz, 1H), 7.24 (s, 1H), 7.66 (d, J=9.1 Hz, 1H), 7.82–7.87
J=7.6 Hz, 1H), 7.10 (s, 1H), 7.44–7.48 (m, 2H), 7.55–7.63 (m, 2H),
7.68 (d, J=7.1 Hz, 2H), 7.80 (s, 1H), 8.00 (t, J=8.8 Hz, 1H), 8.04 (d,
J=8.8 Hz, 1H), 8.19 (d, J=8.8 Hz, 1H), 9.24 ppm (s,1H); C NMR
(
m, 4H), 8.11 ppm (td, J=6.7 Hz, J=1.1 Hz, 1H); MS (ESI): m/z 209
+
13
[M+H] .
(
300 MHz, CDCl + 1 drop [D]TFA): d=166.7, 143.0, 141.9, 140.7,
3
2
-Phenylimidazo[1,2-a]pyridine-3-carbaldehyde (8a): The Vilsmei-
1
37.8, 133.7, 131.7, 129.6, 129.0, 128.4, 126.3, 125.6, 123.0, 122.1,
+
er reagent was prepared at 0–58C by dropping POCl3 (2.5 mL,
120.5, 117.9, 115.3, 114.3, 113.1, 111.6 ppm; MS(ESI): 372 [M+H] ;
HRMS (ESI) calcd for C H N OCl [M+H] 372.09; found: 372.09.
+
1
0.5 mmol) into a stirred solution of DMF (2 mL, 10 mmol) in CHCl3
22
15
3
(
10 mL). The 2-phenylimidazo[1,2-a]pyridine 7a (500 mg, 2.6 mmol)
in chloroform (20 mL) was added to Vilsmeier reagent whilst main-
taining stirring and cooling. The reaction mixture was kept at RT
for 3 h and at reflux for 10–12 h (according to a TLC test). Chloro-
form was removed under reduced pressure and the resulting oily
liquid was poured onto ice. The aldehyde 8a was collected by fil-
tration and crystallised from EtOH (5 mL) to obtain the pure prod-
(E)-3-((2-(4-Fluorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)
indolin-2-one (10c): Compound 10c was prepared according to
the method described for compound 10a, employing 2-(4-
fluorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde 8b (200 mg,
0.83 mmol) and indolin-2-one 9a (111 mg, 0.83 mmol) to obtain
the pure product 10c as a yellow solid (204 mg, 69%); mp: 247–
À1
1
uct 8a as a white solid (418 mg, 73% yield); mp: 155–1588C;
2488C; IR (KBr) n˜ =3430, 3188, 1691, 757 cm ; H NMR (300 MHz,
CDCl ): d=6.35 (d, J=7.8 Hz, 1H), 6.82 (t, J=7.8 Hz, 1H), 6.98 (d,
1
H NMR (300 MHz, CDCl ): d=7.14 (t, J=6.8 Hz, 1H), 7.50–7.62 (m,
3
3
4
H), 7.81–7.86 (m, 3H), 9.68 (d, J=6.7 Hz, 1H), 10.08 ppm (s, 1H);
J=7.8 Hz, 1H), 7.22 (t, J=7.8 Hz, 1H), 7.26–7.38 (m, 2H), 7.45 (t,
J=8.9 Hz, 1H), 7.73–7.80 (m, 3H), 8.00 (t, J=8.9 Hz, 1H), 8.06 (d,
J=8.9 Hz, 1H), 8.33 (d, J=8.9 Hz, 1H), 8.98 ppm (s, 1H): C NMR
+
MS (ESI): m/z 223 [M+H] .
1
3
2
-(4-Chlorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde (8c):
(300 MHz, CDCl + 1 drop [D]TFA): d=165.5, 163.4, 142.1, 140.7,
3
Compound 8c was prepared according to the method described
for compound 8a, employing 2-(4-chlorophenyl)imidazo[1,2-a]pyri-
dine 7c (500 mg, 2.19 mmol) to obtain the pure product 8c as
136.7, 133.8, 132.33, 130.7, 128.2, 126.5, 124.8, 123.1, 122.1, 121.4,
+
119.4, 117.8, 117.2, 115.0, 114.2, 111.1 ppm; MS (ESI): 355 [M+H] ;
+
HRMS (ESI) calcd for C H N OF [M+H] 356.1194; found:
22
15
3
1
a white solid (393 mg, 70% yield); mp: 151–1538C; H NMR
356.1201.
(
300 MHz, CDCl ): d=7.16 (t, J=6.9 Hz, 1H), 7.52 (d, J=8.5 Hz, 2H),
3
(
E)-5-Fluoro-3-((2-(4-fluorophenyl)imidazo[1,2-a]pyridin-3-yl)me-
7
1
.61 (t, J=6.9 Hz, 1H), 7.75–7.85 (m, 3H), 9.66 (d, J=6.9 Hz, 1H),
0.05 ppm (s, 1H); MS (ESI): m/z 257 [M+H] .
+
thylene)indolin-2-one (10d): Compound 10d was prepared ac-
cording to the method described for compound 10a, employing
2
-para-Tolylimidazo[1,2-a]pyridine-3-carbaldehyde (8d): Com-
2-(4-fluorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
8b
pound 8c was prepared according to the method described for
compound 8a, employing 2-(4-chlorophenyl)imidazo[1,2-a]pyridine
(200 mg, 0.83 mmol) and 5-fluoroindolin-2-one 9b (126 mg,
0.83 mmol) to obtain the pure product 10d as a yellow solid
(159 mg, 51%); mp: 291–2928C; IR (KBr) n˜ =3431, 3004, 1633,
7
d (500 mg, 2.4 mmol) to obtain the pure product 8d as a white
1
À1
1
solid, yield (442 mg, 78% yield); mp: 169–1718C; H NMR
772 cm ; H NMR (300 MHz, CDCl ): d=6.16 (dd, J=2.0 Hz, J=
3
(
300 MHz, CDCl ): d=2.45 (s, 3H), 7.12 (dt, J=6.9, 1.2 Hz, 1H), 7.35
7.5 Hz, 1H), 7.02 (dd, J=2.9, 7.5 Hz, 1H), 7.17 (dt, J=2.0, 7.5 Hz,
3
(
d, J=7.9 Hz, 2H), 7.58 (dt, J=6.8 Hz, J=1.2 Hz, 1H), 7.74 (d, J=
1H), 7.26–7.31 (m, 2H), 7.45–7.48 (m, 1H), 7.69–7.75 (m, 2H), 7.82
8
1
.1 Hz, 2H), 7.80 (td, J=9.0 Hz, J=1.1 Hz, 1H), 9.66 (td, J=6.9,
.1 Hz, 1H), 10.06 ppm (s, 1H); MS (ESI): m/z 237 [M+H] .
(s, 1H), 8.00 (t, J=8.4 Hz, 1H), 8.05 (d, J=8.4 Hz, 1H), 8.18 (d, J=
+
13
8.4 Hz, 1H), 9.21 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop
3
[
1
1
D]TFA): d=165.7, 163.7, 140.7, 140.1, 137.4, 137.1, 136.9, 134.6,
(
E)-3-((2-Phenylimidazo[1,2-a]pyridin-3-yl)methylene)indolin-2-
31.4, 130.5, 128.2, 126.3, 121.6, 118.4, 117.4, 117.3, 114.2, 113.1,
one (10a): An appropriate mixture of 2-phenylimidazo[1,2-a]pyri-
dine-3-carbaldehyde 8a (200 mg 0.9 mmol) and indolin-2-one 9a
+
12.2 ppm; MS (ESI): 374 [M+H] ; HRMS (ESI) calcd for
+
C H N OF [M+H] 374.1105; found: 374.1112.
22
14
3
2
(
(
3
120 mg, 0.9 mmol) was dissolved in EtOH (10 mL) and piperidine
2–3 drops) was added. The reaction mixture was held at reflux for
–5 h (according to a TLC test) and the precipitate formed on cool-
(E)-5-Chloro-3-((2-(4-fluorophenyl)imidazo[1,2-a]pyridin-3-yl)me-
thylene)indolin-2-one (10e): Compound 10e was prepared ac-
cording to the method described for compound 10a, employing
ing was collected by filtration and crystallisation with EtOH to
obtain the pure product 10a as a yellow solid (200 mg, 66%); mp:
2-(4-fluorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
8b
À1
1
2
88–2998C; IR (KBr) n˜ =3405, 3075, 1712, 745 cm
;
H NMR
(200 mg, 0.83 mmol) and 5-chloroindolin-2-one 9c (139 mg,
0.83 mmol) to obtain the pure product 10e as a yellow solid
(188 mg, 58%); mp: 299–3008C; IR (KBr) n˜ =3430, 3226, 1702,
(
300 MHz, CDCl ): d=6.37 (d, J=7.9 Hz, 1H), 6.83 (t, J=7.9 Hz, 1H),
3
7
1
.02 (d, J=7.9 Hz, 1H), 7.32 (t, J=7.9 Hz, 1H), 7.48 (t, J=8.9 Hz,
H), 7.52–7.60 (m, 3H), 7.73 (d, J=6.9 Hz, 2H), 7.79 (s, 1H), 8.03 (t,
À1
1
751 cm ; H NMR (300 MHz, CDCl ): d=6.39 (s, 1H), 6.89 (d, J=
3
J=8.9 Hz, 1H), 8.10 (d, J=8.9 Hz, 1H), 8.30 ppm (d, J=8.9 Hz, 1H),
7.8 Hz, 1H), 7.18–7.23 (m, 1H), 7.53 (t, J=8.2 Hz, 1H), 7.71–7.78 (m,
2H), 7.82 (s, 1H), 7.97–8.11 (m, 3H), 8.21 (d, J=8.2 Hz, 1H), 8.33 (d,
1
3
9
1
1
.26 (s, 1H); C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=169.6,
41.8, 140.5, 137.5, 134.2, 132.4, 131.8, 129.8, 128.9, 128.3, 126.7,
25.4, 124.9, 123.4, 121.4, 119.4, 118.1, 115.8, 114.0, 111.4 ppm; MS
3
13
J=8.2 Hz, 1H), 9.06 ppm (s, 1H); C NMR (300 MHz, CDCl3
+
1 drop [D]TFA): d=169.6, 165.7, 140.6, 139.8, 137.0, 134.8, 132.0,
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1
31.3, 130.4, 128.9, 128.2, 126.4, 125.0, 121.6, 120.5, 118.6, 117.5,
179.2, 169.6, 158.0, 140.6, 138.7, 136.5, 135.0, 133.1, 131.1, 130.3,
130.1, 129.2, 126.6, 123.7, 118.9, 118.6, 117.2, 116.0, 113.8, 112.2,
+
117.3, 113.7, 112.2, 111.4 ppm; MS (ESI): 390 [M+H] ; HRMS (ESI)
+
+
calcd for C H N OClF [M+H] 390.08; found: 390.08.
109.1 ppm; MS (ESI): 390 [M+H] ; HRMS (ESI) calcd for
2
2
14
3
+
C H N OClF [M+H] 390.08; found: 390.08.
22
14
3
(E)-6-Chloro-3-((2-(4-fluorophenyl)imidazo[1,2-a]pyridin-3-yl)me-
thylene)indolin-2-one (10 f): Compound 10 f was prepared ac-
cording to the method described for compound 10a, employing
(E)-5-Chloro-3-((2-(4-chlorophenyl)imidazo[1,2-a]pyridin-3-yl)me-
thylene)indolin-2-one (10j): Compound 10j was prepared accord-
ing to the method described for compound 10a, employing 2-(4-
chlorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde 8c (200 mg,
0.78 mmol) and 5-chloroindolin-2-one 9c (130 mg, 0.78 mmol) to
obtain the pure product 10j as a yellow solid (215 mg, 68%); mp:
2
(
0
(
-(4-fluorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
200 mg, 0.83 mmol) and 6-chloroindolin-2-one 9d (139 mg,
.83 mmol) to obtain the pure product 10 f as a yellow solid
204 mg, 63%); mp: 315–3168C; IR (KBr) n˜ =3428, 3079, 1712,
8b
À1
1
À1
1
7
6
7
8
58 cm
;
H NMR (300 MHz, CDCl3): d=6.24 (d, J=7.1 Hz, 1H),
305–3068C; IR (KBr) n˜ =3434, 3040, 1685, 756 cm
;
H NMR
.71 (d, J=7.1 Hz, 1H), 7.09–7.16 (m, 1H), 7.41 (t, J=6.9 Hz, 1H),
.64–7.70 (m, 3H), 7.89 (t, J=8.7 Hz, 1H), 7.94 (d, J=7.7 Hz, 2H),
.12 (d, J=6.9 Hz, 1H), 8.22 (d, J=6.9 Hz, 1H), 8.92 ppm (s, 1H);
(300 MHz, CDCl ): d=6.35 (s, 1H), 6.88 (d, J=7.6 Hz, 1H), 6.96 (d,
3
J=7.6 Hz, 1H), 7.39–7.44 (m, 1H), 7.54 (d, J=6.8 Hz, 2H), 7.79 (s,
1H), 7.91 (t, J=8.8 Hz, 1H), 8.01 (d, J=6.8 Hz, 2H), 8.18 (d, J=
1
3
13
C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=169.4, 163.6, 142.8,
8.8 Hz, 1H), 8.34 (d, J=8.8 Hz, 1H), 8.97 ppm (s, 1H); C NMR
3
1
1
40.6, 138.5, 136.7, 134.4, 132.3, 130.5, 128.1, 126.4, 125.6, 123.4,
22.3, 121.6, 118.3, 117.2, 115.5, 114.0, 112.0 ppm; MS (ESI): 390
(300 MHz, CDCl + 1 drop [D]TFA): d=168.8, 140.8, 140.1, 138.3,
3
136.7, 134.5, 132.8, 131.8, 130.1, 129.3, 128.3, 126.5, 124.8, 124.1,
+
+
+
[M+H] ; HRMS (ESI) calcd for C H N OClF [M+H] 390.08;
121.5, 118.3, 116.9, 114.0, 112.9, 112.1 ppm; MS (ESI): 406 [M+H] ;
22
14
3
+
found: 390.08.
HRMS (ESI) calcd for C H N OCl [M+H] 406.05; found: 406.05.
22
14
3
2
(
5
E)-3-((2-(4-Fluorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)-
-methoxyindolin-2-one (10g): Compound 10g was prepared ac-
(E)-6-Chloro-3-((2-(4-chlorophenyl)imidazo[1,2-a]pyridin-3-yl)me-
thylene)indolin-2-one (10k): Compound 10k was prepared ac-
cording to the method described for compound 10a, employing
cording to the method described for compound 10a, employing
-(4-fluorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde 8b
200 mg, 0.83 mmol) and 5-methoxyindolin-2-one 9e (136 mg,
.83 mmol) to obtain the pure product 10g as a yellow solid
154 mg, 48%); mp: 261–2628C; IR (KBr) n˜ =3457, 3053, 1709,
2
(
0
(
7
1
2-(4-chlorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
8c
(200 mg, 0.78 mmol) and 6-chloroindolin-2-one 9d (130 mg,
0.78 mmol) to obtain the pure product 10k as a yellow solid
(190 mg, 60%); mp: 278–2798C; IR (KBr) n˜ =3413, 3050, 1705,
À1
1
À1
1
46 cm ; H NMR (300 MHz, CDCl ): d=3.48 (s, 3H, OCH ), 5.94 (s,
749 cm ; H NMR (300 MHz, CDCl ): d=6.25 (d, J=7.8 Hz, 1H),
3
3
3
H), 6.86 (dd, J=2.2, 7.2 Hz, 1H), 6.91 (d, J=7.2 Hz, 1H), 7.52 (t,
6.77 (d, J=7.8 Hz, 1H), 6.97 (s, 1H),7.39 (t, J=8.7 Hz, 1H), 7.49 (d,
J=7.8 Hz, 2H), 7.69–7.79 (m, 3H), 7.92 (t, J=8.7 Hz, 1H), 7.98 (d,
J=7.6 Hz, 1H), 7.76–7.78 (m, 3H), 8.04 (t, J=7.6 Hz, 1H), 8.14 (d,
13
13
J=7.6 Hz, 1H), 8.26–8.29 (m, 3H), 9.12 ppm (s, 1H); C NMR
300 MHz, CDCl + 1 drop [D]TFA): d=169.6, 163.6, 156.0, 140.5,
J=8.7 Hz, 1H), 8.38 (d, J=8.7 Hz, 1H), 9.76 ppm (s, 1H); C NMR
(
(300 MHz, CDCl + 1 drop [D]TFA): d=169.4, 142.7, 140.6, 138.5,
3
3
1
36.5, 135.4, 134.4, 133.8, 130.5, 126.7, 121.6, 120.1, 118.2, 117.4,
136.7, 134.4, 132.3, 131.2, 130.2, 129.4, 128.0, 126.4, 125.7, 123.8,
+
+
116.2, 115.7, 113.9, 111.5, 107.6, 55.6 ppm; MS (ESI): 386 [M+H] ;
123.5, 122.3, 118.3, 117.0, 114.0, 112.1 ppm; MS (ESI): 406 [M+H] ;
+
+
HRMS (ESI) calcd for C H N O F [M+H] 386.13; found: 386.13.
HRMS (ESI) calcd for C H N OCl [M+H] 406.05; found: 406.05.
2
3
17
3
2
22 14
3
2
(
E)-3-((2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)
(E)-3-((2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)-
5-methoxyindolin-2-one (10l): Compound 10l was prepared ac-
cording to the method described for compound 10a, employing
indolin-2-one (10h): Compound 10h was prepared according to
the method described for compound 10a, employing 2-(4-
chlorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde 8c (200 mg,
2-(4-chlorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
8c
0
.78 mmol) and indolin-2-one 9a (104 mg, 0.78 mmol) to obtain
(200 mg, 0.78 mmol) and 5-methoxyindolin-2-one 9e (127 mg,
0.78 mmol) to obtain the pure product 10l as a yellow solid
(147 mg, yield 47%); mp: 268–2698C; IR (KBr) n˜ =3214, 1710,
the pure product 10h as a yellow solid (188 mg, 65%); mp: 280–
2
CDCl ): d=6.37 (d, J=7.9 Hz, 1H), 6.84 (t, J=7.9 Hz, 1H), 7.01 (d,
J=7.9 Hz, 1H), 7.33 (t, J=7.9 Hz, 1H), 7.46–7.51 (m, 3H), 7.70–7.77
À1
1
818C; IR (KBr) n˜ =3430, 3133, 1701, 754 cm ; H NMR (300 MHz,
À1
1
758 cm ; H NMR (300 MHz, CDCl3): d=3.46 (s, 3H), 5.87 (s, 1H),
6.83–6.86 (m, 2H), 7.43 (t, J=8.9 Hz, 1H), 7.50 (d, J=6.9 Hz, 2H),
7.61 (d, J=6.9 Hz, 2H), 7.72 (s, 1H), 7.92–7.97 (m, 1H), 8.05 (d, J=
3
(
m, 3H), 8.03 (t, J=8.9 Hz, 1H), 8.08 (d, J=8.9 Hz, 1H), 8.32 (d, J=
13
13
8
.9 Hz, 1H), 9.60 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop
8.9 Hz, 1H), 8.27 (d, J=8.9 Hz, 1H), 8.55 ppm (s, 1H); C NMR
3
[
1
1
D]TFA): d=179.2, 147.6, 141.0, 139.8, 138.4, 136.9, 134.4, 133.7,
32.6, 131.2, 130.4, 129.5, 123.6, 122.4, 119.8, 118.2, 116.0, 113.9,
(300 MHz, CDCl + 1 drop [D]TFA): d=179.2, 156.1, 147.6, 140.5,
3
139.8, 136.8, 134.5, 131.2, 130.4, 130.2, 129.4, 126.7, 122.4, 119.8,
+
+
12.1, 111.5 ppm; MS (ESI): 372 [M+H] ; HRMS (ESI) calcd for
118.3, 117.6, 114.0, 113.8, 111.5, 55.6 ppm; MS (ESI): 402 [M+H] ;
+
+
C H N OCl [M+H] 372.0898; found: 372.0914.
HRMS (ESI) calcd for C H N O Cl [M+H] 402.10; found: 402.10.
2
2
15
3
23 17
3
2
(
5
E)-3-((2-(4-Chlorophenyl)imidazo[1,2-a]pyridin-3-yl)methylene)-
-fluoroindolin-2-one (10i): Compound 10i was prepared accord-
(E)-3-((2-para-Tolylimidazo[1,2-a]pyridin-3-yl)methylene)indolin-
2-one (10m): Compound 10m was prepared according to the
method described for compound 10a, employing 2-p-tolylimidazo-
[1,2-a]pyridine-3-carbaldehyde 8d (200 mg, 0.85 mmol) and indo-
lin-2-one 9a (113 mg, 0.85 mmol) to obtain the pure product 10m
as a yellow solid (205 mg, 69%); mp: 263–2648C; IR (KBr) n˜ =3428,
ing to the method described for compound 10a, employing 2-(4-
chlorophenyl)imidazo[1,2-a]pyridine-3-carbaldehyde 8c (200 mg,
0
obtain the pure product 10i as a yellow solid (212 mg, 70%); mp:
2
.78 mmol) and 5-fluoroindolin-2-one 9b (118 mg, 0.78 mmol) to
À1
1
À1
1
98–2998C; IR (KBr) n˜ =3432, 3159, 1705, 757 cm
;
H NMR
3061, 1686, 746 cm ; H NMR (300 MHz, CDCl ): d=2.40 (s, 3H),
3
(
7
(
8
300 MHz, CDCl ): d=6.13 (dd, J=1.9, 7.8 Hz, 1H), 7.01 (dd, J=3.2,
.8 Hz, 1H), 7.16 (dt, J=1.9, 7.8 Hz, 1H), 7.46 (t, J=8.7 Hz, 1H), 7.55
d, J=6.8 Hz, 2H), 7.63 (d, J=6.8 Hz, 2H), 7.80 (s, 1H), 7.99 (t, J=
6.33 (d, J=7.0 Hz, 1H), 6.83 (t, J=8.9 Hz, 1H), 6.99 (d, J=7.0 Hz,
1H), 7.29–7.32 (m, 3H), 7.42 (t, J=8.0 Hz, 1H), 7.67 (d, J=8.0 Hz,
2H), 7.75 (s, 1H), 7.97 (t, J=8.0 Hz, 1H), 8.01 (d, J=8.0 Hz, 1H),
8.36 (d, J=8.0 Hz, 1H), 8.93 ppm (s, 1H); C NMR (300 MHz, CDCl3
+ 1 drop [D]TFA): d=168.6, 142.3, 141.9, 140.8, 138.6, 133.1, 132.7,
3
13
.7 Hz, 1H), 8.05 (d, J=8.7 Hz, 1H), 8.18 (d, J=8.7 Hz, 1H),
1
3
9
.12 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=
3
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ChemMedChem 0000, 00, 1 – 12
&
9
&
ÞÞ
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1
32.0, 130.4, 129.2, 128.4, 126.3, 125.1, 123.0, 121.1, 119.7, 117.4,
126.8, 122.3, 120.2, 118.2, 117.5, 115.7, 113.6, 113.2, 111.4, 109.4,
55.6, 21.4 ppm; MS (ESI): 381 [M+H] .
+
+
114.6, 113.4, 110.9, 21.5 ppm; MS (ESI): 352 [M+H] ; HRMS (ESI)
+
calcd for C H N O [M+H] 352.14; found: 352.14.
2
3
18
3
(E)-5-Fluoro-3-((2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-yl)
methylene)indolin-2-one (10r): Compound 10r was prepared ac-
cording to the method described for compound 10a, employing
(
E)-5-Fluoro-3-((2-para-tolylimidazo[1,2-a]pyridin-3-yl)methyl-
ene)indolin-2-one (10n): Compound 10n was prepared according
to the method described for compound 10a, employing 2-p-
tolylimidazo[1,2-a]pyridine-3-carbaldehyde 8d (200 mg, 0.85 mmol)
and 5-fluoroindolin-2-one 9b (128 mg, 0.85 mmol) to obtain the
pure product 10n as a yellow solid (221 mg, 71%); mp: 305–
2
-(4-methoxyphenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
8e
(200 mg, 0.79 mmol) and 5-fluoroindolin-2-one 9b (120 mg,
0
.79 mmol) to obtain the pure product 10r as a yellow solid
À1
(
171 mg, 56%); mp: 251–2528C; IR (KBr) n˜ =3080, 1707, 744 cm
;
1
À1
1
H NMR (300 MHz, CDCl ): d=3.86 (s, 3H), 6.14 (dd, J=2.2, 7.1 Hz,
3
068C; IR (KBr) n˜ =3389, 2934, 1627, 803 cm ; H NMR (300 MHz,
3
1
7
H), 6.96–7.05 (m, 2H), 7.46–7.55 (m, 3H), 7.67 (d, J=8.4 Hz, 2H),
.85 (s, 1H), 8.04 (t, J=8.1 Hz, 1H), 8.14 (d, J=8.1 Hz, 1H), 8.24 (d,
CDCl ): d=2.45 (s, 3H), 6.12 (dd, J=2.9 Hz, J=7.8 Hz, 1H), 6.99 (d,
J=7.8 Hz, 1H), 7.14 (dt, J=2.9, 7.8 Hz, 1H), 7.38 (d, J=7.4 Hz, 2H),
7
3
13
J=8.12 Hz, 1H), 9.36 ppm (s, 1H);
C NMR (300 MHz, CDCl3
+
.49 (t, J=8.7 Hz, 1H), 7.57 (d, J=7.4 Hz, 2H), 7.83 (s, 1H), 7.95 (t,
1
drop [D]TFA): d=170.2, 162.7, 140.4, 138.2, 134.4, 131.7, 130.8,
J=8.7 Hz, 1H), 8.00 (d, J=8.7 Hz, 1H), 8.19 (d, J=8.7 Hz, 1H),
1
3
129.9, 128.4, 126.4, 120.4, 118.3, 117.6, 117.2, 115.5, 114.8, 113.8,
9
1
1
2
.11 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=
3
+
1
12.7, 112.0, 108.8, 55.5 ppm; MS (ESI): 386 [M+H] ; HRMS (ESI)
69.6, 157.8, 143.0, 140.6, 138.2, 136.7, 134.3, 132.2, 130.6, 129.0,
28.1, 126.4, 122.5, 118.2, 117.2, 115.4, 114.0, 112.5, 111.9, 108.7,
+
calcd for C H N O F [M+H] 386.13; found: 386.13.
23 17
3
2
+
1.4 ppm; MS (ESI): 370 [M+H] ; HRMS (ESI) calcd for C H N OF
2
3
17
3
(E)-5-Chloro-3-((2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-yl)
+
[M+H] 370.14; found: 370.13.
methylene)indolin-2-one (10s): Compound 10s was prepared ac-
cording to the method described for compound 10a, employing
(E)-5-Chloro-3-((2-para-tolylimidazo[1,2-a]pyridin-3-yl)methyl-
2
(
0
(
-(4-methoxyphenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
200 mg, 0.79 mmol) and 5-chloroindolin-2-one 9c (132 mg,
.79 mmol) to obtain the pure product 10d as a yellow solid
159 mg, 50%); mp: 257–2588C; IR (KBr) n˜ =3376, 3065, 1757,
8e
ene)indolin-2-one (10o): Compound 10o was prepared according
to the method described for compound 10a, employing 2-p-
tolylimidazo[1,2-a]pyridine-3-carbaldehyde 8d (200 mg, 0.85 mmol)
and 5-chloroindolin-2-one 9c (141 mg, 0.85 mmol) to obtain the
pure product 10o as a yellow solid (209 mg, 64%); mp: 264–
À1
1
8
40 cm ; H NMR (300 MHz, CDCl ): d=3.86 (s, 3H), 6.40 (s, 1H),
3
À1
1
6.94–7.03 (m, 2H), 7.24–7.28 (m, 2H), 7.53–7.64 (m, 3H), 7.88 (s,
2
658C; IR (KBr) n˜ =3441, 3052, 1707, 751 cm ; H NMR (300 MHz,
1
H), 8.08 (t, J=8.3 Hz, 1H), 8.18–8.25 (m, 2H), 9.39 ppm (s, 1H);
CDCl ): d=2.44 (s, 3H), 6.32 (s, 1H), 6.98 (d, J=6.0 Hz, 1H), 7.30 (d,
J=6.0 Hz, 1H), 7.36–7.43 (m, 3H), 7.56 (d, J=8.0 Hz, 2H), 7.82 (s,
1
9
3
13
C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=162.7, 140.3, 139.9,
3
1
38.7, 138.0, 134.8, 131.7, 130.7, 129.7, 128.5, 126.5, 125.3, 121.5,
H), 7.93 (t, J=9.1 Hz, 1H), 7.98 (d, J=9.1 Hz, 1H), 8.18 (d, J=
13
118.5, 117.8, 115.6, 113.5, 113.0, 112.6, 109.2, 55.5 ppm; MS (ESI):
.1 Hz, 1H), 9.12 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop
3
+
+
4
02 [M+H] ; HRMS (ESI) calcd for C H N O Cl [M+H] 402.10;
23 17 3 2
[
1
D]TFA): d=166.4, 142.6, 140.7, 140.1, 138.4, 133.8, 131.4, 130.5,
28.1, 128.1, 126.4, 125.0, 122.8, 121.2, 117.9, 115.6, 114.1, 112.9,
found: 402.10.
+
1
11.8, 21.4 ppm; MS (ESI): 386 [M+H] ; HRMS (ESI) calcd for
(E)-6-Chloro-3-((2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-yl)
methylene)indolin-2-one (10t): Compound 10t was prepared ac-
cording to the method described for compound 10a, employing
+
C H N OCl [M+H] 386.13; found: 386.13.
2
3
17
3
(E)-6-Chloro-3-((2-para-tolylimidazo[1,2-a]pyridin-3-yl)methyl-
2
(
0
(
-(4-methoxyphenyl)imidazo[1,2-a]pyridine-3-carbaldehyde
200 mg, 0.79 mmol) and 6-chloroindolin-2-one 9d (132 mg,
.79 mmol) to obtain the pure product 10t as a yellow solid
187 mg, 59%); mp: 221–2228C; IR (KBr) n˜ =3463, 3079, 1713,
8e
ene)indolin-2-one (10p): Compound 10p was prepared according
to the method described for compound 10a, employing 2-p-
tolylimidazo[1,2-a]pyridine-3-carbaldehyde 8d (200 mg, 0.85 mmol)
and 6-chloroindolin-2-one 9d (141 mg, 0.85 mmol) to obtain the
pure product 10p as a yellow solid (189 mg, 58%); mp: 283–
À1
1
7
8
8
60 cm ; H NMR (300 MHz, CDCl ): d=3.89 (s, 3H), 6.33 (d, J=
3
.3 Hz, 1H), 6.82 (dd, J=1.3, 8.3 Hz, 1H), 7.10 (s, 1H), 7.19 (d, J=
.1, 2H), 7.55–7.67 (m, 3H), 7.78 (s, 1H), 7.94–8.05 (m, 2H), 8.12 (d,
À1
1
2
848C; IR (KBr) n˜ =3429, 3042, 1687, 755 cm ; H NMR (300 MHz,
CDCl ): d=2.41 (s, 3H), 6.31 (d, J=8.1 Hz, 1H), 6.82 (dd, J=1.8,
13
3
J=7.9 Hz, 1H), 9.3 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop
3
8
7
1
1
1
.1 Hz, 1H), 7.06 (s, 1H), 7.34 (d, J=7.9 Hz, 2H), 7.50–7.59 (m, 3H),
[D]TFA): d=162.6, 140.9, 139.8, 138.4, 137.2, 134.4, 130.7, 129.8,
.80 (s, 1H), 8.02–8.11 (m, 2H), 8.24 (d, J=8.8 Hz, 1H), 9.41 ppm (s,
1
28.3, 125.8, 123.9, 122.2, 120.5, 118.3, 117.4, 115.4, 113.6, 112.6,
1
3
H); C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=143.1, 140.3,
+
3
112.0, 109.1, 55.5 ppm; MS (ESI): 402 [M+H] ; HRMS (ESI) calcd for
38.2, 137.8, 134.4, 130.6, 130.5, 128.8, 128.0, 126.5, 125.7, 123.4,
+
C H N O Cl [M+H] 402.10; found: 402.10.
23
17
3
2
+
22.2, 118.3, 115.6, 113.6, 112.0, 21.4 ppm: MS (ESI): 386 [M+H] ;
+
HRMS (ESI) calcd for C H N OCl [M+H] 386.11; found: 386.11.
2
3
17
3
Acknowledgements
(E)-5-Methoxy-3-((2-para-tolylimidazo[1,2-a]pyridin-3-yl)methyl-
ene)indolin-2-one (10q): Compound 10q was prepared according
to the method described for compound 10a, employing 2-p-
tolylimidazo[1,2-a]pyridine-3-carbaldehyde 8d (200 mg, 0.85 mmol)
and 5-methoxyindolin-2-one 9e (138 mg, 0.85 mmol) to obtain the
pure product 10q as a yellow solid (139 mg, 43%); mp: 250–
V.S.R, A.B.S, G.B.K., M.P.N.R., and C.K. acknowledge the Council of
Scientific & Industrial Research (CSIR)–University Grant Commis-
sion (UGC), New Delhi (India) for the award of senior research fel-
lowships. The authors also acknowledge the CSIR for financial
support under the 12th Five-Year Plan projects “Affordable
Cancer Therapeutics (ACT)” (CSC0301) and “Small Molecules in
Lead Exploration (SMiLE)” (CSC0111). Finally, the authors thank
Dr. K. Ravinder and Dr. Rakesh K. Mishra (Centre for Cellular &
Molecular Biology, Hyderabad, India) for assistance with zebra
fish assays.
À1
1
2
518C; IR (KBr) n˜ =3395, 2927, 1627, 808 cm ; H NMR (300 MHz,
CDCl ): d=2.41 (s, 3H), 3.47 (s, 3H), 5.93 (s, 1H), 6.85 (dd, J=2.2,
3
8
.4 Hz, 1H), 6.94 (d, J=8.4 Hz, 1H), 7.35 (d, J=7.9 Hz, 2H), 7.52 (t,
J=6.9 Hz, 1H), 7.62 (d, J=7.9 Hz, 2H), 7.79 (s, 1H), 8.04 (t, J=
6
9
1
.9 Hz, 1H), 8.11 (d, J=6.9 Hz, 1H), 8.28 (d, J=6.9 Hz, 1H),
1
3
.32 ppm (s, 1H); C NMR (300 MHz, CDCl + 1 drop [D]TFA): d=
3
69.8, 156.1, 143.0, 140.3, 137.6, 135.2, 134.3, 133.4, 130.6, 128.1,
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Keywords: apoptosis
·
cytotoxicity
·
imidazopyridine–
oxindoles · molecular docking · tubulin polymerisation
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Published online on && &&, 0000
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FULL PAPERS
A. Kamal,* V. S. Reddy, S. Karnewar,
S. S. Chourasiya, A. B. Shaik, G. B. Kumar,
C. Kishor, M. K. Reddy,
Arrested development: A library of imi-
dazopyridine–oxindole conjugates was
synthesised and investigated for anti-
cancer activity against various human
cancer cell lines. Some of the tested
compounds, such as 10a, 10e, 10 f, and
M. P. Narasimha Rao, A. Nagabhushana,
K. V. S. Ramakrishna, A. Addlagatta,*
S. Kotamraju*
1
0k, exhibited promising antiprolifera-
&& – &&
tive activity.
Synthesis and Biological Evaluation of
Imidazopyridine–Oxindole Conjugates
as Microtubule-Targeting Agents
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