Iodine-catalyzed condensation of isatin with indoles: A facile synthesis of di(indolyl)indolin-2-ones and evaluation of their cytotoxicity

Article abstract of DOI:10.1016/j.bmcl.2012.02.011

Isatin reacts smoothly with indoles in the presence of a catalytic amount of molecular iodine under mild conditions to afford a novel class of di(indolyl)indolin-2-one derivatives in good yields. These molecules are found to possess a promising cytotoxici

Full text of DOI:10.1016/j.bmcl.2012.02.011

Bioorganic & Medicinal Chemistry Letters 22 (2012) 2460–2463
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Bioorganic & Medicinal Chemistry Letters
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Iodine-catalyzed condensation of isatin with indoles: A facile synthesis
of di(indolyl)indolin-2-ones and evaluation of their cytotoxicity
B.V. Subba Reddy a, , N. Rajeswari b, M. Sarangapani b, Y. Prashanthi a, Roopa Jones Ganji c,
⇑
Anthony Addlagatta c,
⇑
a Natural Product Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
b College of Pharmacy, Kakatiya University, Warangal, India
c Chemical Biology, Indian Institute of Chemical Technology, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Isatin reacts smoothly with indoles in the presence of a catalytic amount of molecular iodine under mild
conditions to afford a novel class of di(indolyl)indolin-2-one derivatives in good yields. These molecules
are found to possess a promising cytotoxicity against cancer cells only but not on normal cells.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 12 January 2012
Revised 28 January 2012
Accepted 3 February 2012
Available online 13 February 2012
Keywords:
Isatin
Molecular iodine
Indoles
Cytotoxicity
Di(indolyl)indolin-2-one
Indoles and its derivatives are found abundantly in Nature and
are known to exhibit potent physiological properties.1 In particular,
3,3-diaryloxindole is frequently found in clinical drugs and
biologically active compounds and are known to possess anti-pro-
liferative, antibacterial, anti-protozoal and anti-inflammatory
activities.2 They have also been used as laxatives3 and some lead
molecules are known to facilitate Ca2+ depletion mediated inhibi-
tion of translation initiation.4 Furthermore, a large number of
bis(indolyl)methanes have been isolated from natural sources.5
Some of these natural products for example, vibrindole A have
shown promising biological activity.6 Generally, 3,3-di(indol-
y)indolin-2-ones are prepared by coupling of isatin with indoles
under acidic conditions.7,8 However, only a few methodologies
has been reported for the synthesis of di(indolyl)indolin-2-ones.9
Therefore, the development of simple and efficient methods is
desirable to generate structurally varied di(indolyl)indolin-2-ones
with a variety of substituents.
In continuation of our interest on catalytic use of molecular
iodine for various transformations,11 we herein report for the first
time, a direct and metal-free condensation of isatin with indoles
using a catalytic amount of molecular iodine. Accordingly, we first
attempted the coupling of 1 equiv of isatin (1) with 2 equiv of
indole (2) in the presence of 10 mol % of molecular iodine. The
reaction proceeds well in dichloromethane at room temperature
and the corresponding di(indolyl)indolin-2-one 3a was obtained
in 82% yield (Scheme 1).
Next we examined the scope of this method with respect
to various indoles. Interestingly, substituted indoles such as
5-cyano-, 2-methyl-5-nitro-, methyl 5-carboxylate, 2-methyl-, 5-
nitro-, 2-phenyl-, 5-bromo-, 5-chloro-, and 1-methyl derivatives
underwent a smooth coupling with isatin to furnish the corre-
sponding di(indolyl)indolin-2-one derivatives in good yields
(Table 1, entries b–j). Notably, electron-deficient indoles such as
2-methyl-5-nitro-, 5-cyano-, methyl 5-carboxylate and 5-nitro-,
derivatives also participated well coupling with isatin under
similar conditions (Table 1, entries b, c, d and f). Furthermore, N-
methylindole also gave the desired product in 85% yield (Table 1,
entry j). This method works well with both electron-rich as well
as electron-deficient indoles. The products were characterized
and confirmed by NMR, IR, and mass spectroscopy. In all cases,
the reactions proceeded well at room temperature affording the
corresponding di(indolyl)indolin-2-ones in good yields. However,
in the absence of iodine, the reaction failed to give the desired
Recently, molecular iodine has received considerable attention
in organic synthesis because of its high tolerance to air and mois-
ture, low-cost, nontoxic nature and ready availability, affording the
corresponding products in excellent yields with high selectivity.
The mild Lewis acidity associated with iodine has led to its use
in organic synthesis using catalytic to stoichiometric amounts.10
⇑
Corresponding authors.
E-mail address: basireddy@iict.res.in (B.V. Subba Reddy).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.02.011

B. V. Subba Reddy et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2460–2463
2461
indole on a conjugated 3H-indol-3-ylidene (B) would give the
desired di(indolyl)indolin-2-one (Scheme 2).
O
HN
Cytotoxicity: Cellular viability in the presence of test com-
pounds was determined by MTT-microcultured tetrazolium assay
following the reported protocol.13 Human lung cancer cell line,
A549; human breast cancer cell line, MDA-MB-231; (estrogen
receptor-negative); and a human neuroblastoma cell line, SK-N-
SH along with a MRC5, human normal lung cell line are employed
in the current study.
10 mol% I2
CH2Cl2, r.t.
NH
O
+
N
N
H
O
H
N
1
2
3a
H
Scheme 1. Synthesis of di(indolyl)indolin-2-one 3a.
products. This clearly indicates that molecular iodine is essential
to facilitate the reaction. The scope and generality of this process
is illustrated with respect to various indoles and the results are
presented in Table 1.12 The salient features of this method are
good yields, mild reaction conditions and low-cost of the
catalyst.
Mechanistically, we assume that the reaction proceeds by
the activation of isatin by molecular iodine. This is followed by a
nucleophilic attack of indole on isatin led to the formation of 3-hy-
droxy-3,3’-biindolin-2-one. A subsequent dehydration of 3-hydro-
xy-3,3’-biindolin-2-one (A) and addition of another equivalent of
All the four types of cell lines were seeded to flat bottom 96
(10,000 cells/100 ll) well plate and cultured in the medium
containing 10% serum and incubated for 24 h in a 5% CO2 humid
chamber so that the cells can adhere to the surface. 3-(4,5-
dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT)
was dissolved in PBS at 5 mg/mL and sterile filtered. Different con-
centrations of the compounds were added to the adhered cells.
After 48 h, MTT solution (10
plate. Cells were further incubated in the CO2 chamber for 2 h. Fol-
lowing this, media was removed and 100 l of DMSO was added.
Absorbance was measured at 562 nm in a multimode microplate
ll per well) was added to the culture
l
Table 1
Synthesis of di(indolyl)indolin-2-one derivatives from isatin and indoles
Entry
Isatin (1)
Indole (2)
Product (3)a
NH
Time (h)
14
Yieldb (%)
O
N
H
N
H
O
a
82
3a
NH
NH
N
O
H
O
O2N
Me
O2N
N
Me
NO2
3b
N
H
O
b
c
d
e
f
16
18
15
16
18
20
78
85
80
75
80
H
NH
O
N
H
Me
O
NC
NH
CN
N
N
H
O
H
3c
CN
NH
N
O
H
O
MeO2C
NH
MeO2C
3d
N
N
H
O
H
CO2Me
NH
N
H
O
O
NH
Me
3e
N
H
Me
N
H
O
NH
O
N
Me
H
O
O2N
NH
3f
O2N
N
H
N
H
O
NO2
NH
N
O
H
O
NH
Ph
3g
N
H
Ph
N
H
O
g
82
NH
O
N
Ph
H
(continued on next page)

2462
B. V. Subba Reddy et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2460–2463
Table 1 (continued)
Entry
Isatin (1)
Indole (2)
Product (3)a
Time (h)
18
Yieldb (%)
O
Br
NH
3h
Br
N
H
N
H
O
h
85
Br
Cl
NH
NH
N
H
O
O
Cl
NH
3i
Cl
N
H
N
H
O
i
j
22
19
70
85
N
H
Me
O
O
N
N
Me
N
H
O
3j
N
N
O
Me
NH
H
O
Cl
3k
N
H
N
O
Cl
k
12
14
13
14
68
70
75
74
H
NH
N
O
H
O
O2N
NH
Cl
Cl
Cl
Me
O2N
Cl
3l
N
Me
NO2
N
H
O
l
H
NH
Me
O
N
H
O
NH
Ph
3m
N
H
Ph
Cl
N
H
O
m
NH
O
N
Ph
H
O
MeO2C
NH
MeO2C
Cl
3n
N
N
H
O
n
H
CO2Me
NH
N
H
O
O
Br
NH
Cl
3o
Cl
Br
N
N
H
O
o
15
80
H
Br
NH
N
H
O
a
The products were characterized by NMR, IR and mass spectroscopy.
Yield refers to pure products after chromatography.
b
O
I2
reader (Tecan GENios). All the experiments were carried out in
triplicates.
The IC50 values are calculated from the percentage of cytotoxic-
ity and are presented in Table 2. Except compound 3m (Table 2,
entry 13), all compounds in the present study display systematic
HN
..
H
O
I2
O
+
N
N
O
H
H
N
1
2
H
A
cytotoxicity at near
lines (SK-N-SH). More than 50% of the compounds inhibit the cell
growth in the A549 cell lines near one M concentration. Only five
compounds affect the breast cancer cell lines (MDA-MB 231) in the
sub-micromolar range. Surprisingly, none of the compounds
(Table 2) possess any cytotoxicity on the non-cancerous breast
cells (MRC5). Biochemical studies are underway to understand
lM concentration on the neuroblasoma cell
N
l
HN
+
NH
N
..
H
O
O
N
N
B
H
H
Scheme 2. A plausible reaction pathway.

B. V. Subba Reddy et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2460–2463
2463
Table 2
Cytotoxic study of products 3a–o
S. No.
Product (3)
MDA-MB 231 (
lM)
SK-N-SH (lM)
A549 (
l
M)
MRC5 (lM)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
Isatin
>100
0.90 0.06
0.94 0.04
0.94 0.06
0.98 0.04
0.98 0.03
0.99 0.03
9.6 0.72
0.93 0.10
1.31 0.08
1.32 0.24
1.28 0.01
1.23 0.11
>100
1.23 0.030
0.89 0.037
0.97 0.127
0.75 0.04
0.92 0.06
7.90 0.26
8.91 0.17
0.96 0.4
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
>100
99.42 7.5
99.14 5.5
>100
>100
9.98 0.31
>100
9.95 0.32
10.00 0.18
>100
9.99 0.20
10.05 0.34
>100
10.00 0.13
>100
>100
>100
76.3 0.7
69.4 0.264
>100
71.5 0.751
>100
13.5 0.3
>100
15.07 0.13
9.9 0.24
1.04 0.14
9.84 0.16
1.78 0.42
0.97 0.03
Indole
Standard (Doxorubicin)
>100
8.14 0.14
15.58 0.35
14.84 0.25
Meraj, S.; Prasad, A. R. Synthesis 2006, 4121; (f) Praveen, C.; Sagayaraj, Y. W.;
Perumal, P. T. Tetrahedron Lett. 2009, 50, 644.
the biological pathways that are affected by these compounds spe-
cifically in cancer cells and not in normal cell lines.
10. (a) Togo, H.; Iida, S. Synlett 2006, 2159; (b) Lin, X.-F.; Cui, S.-L.; Wang, Y.-G.
Tetrahedron Lett. 2006, 47, 4509; (c) Chen, W.-Y.; Lu, J. Synlett 2005, 1337; (d)
Royer, L.; De, S. K.; Gibbs, R. A. Tetrahedron Lett. 2005, 46, 4595; (e) Banik, B. K.;
Fernandez, M.; Alvarez, C. Tetrahedron Lett. 2005, 46, 2479; (f) Wang, S.-Y.
Synlett 2004, 2642; (g) Bandgar, B.-P.; Shaikh, K.-A. Tetrahedron Lett. 2003, 44,
1959; (h) Ko, S.; Sastry, M. N. V.; Lin, C.; Yao, C.-F. Tetrahedron Lett. 2005, 46,
5771.
11. (a) Yadav, J. S.; Reddy, B. V. S.; Hashim, S. R. J. Chem. Soc., Perkin Trans. 1 2000,
3082; (b) Yadav, J. S.; Reddy, B. V. S.; Premalatha, K.; Swamy, T. Tetrahedron
Lett. 2005, 46, 2687; (c) Yadav, J. S.; Reddy, B. V. S.; Rao, C. V.; Chand, P. K.;
Prasad, A. R. Synlett 2001, 1638; (d) Yadav, J. S.; Reddy, B. V. S.; Reddy, M. S.;
Prasad, A. R. Tetrahedron Lett. 2002, 43, 9703.
In summary, we have developed a novel method for the synthesis
of di(indolyl)indolin-2-one derivatives by means of a coupling of
isatin with indoles using a catalytic amount of molecular iodine un-
der mild conditions. This method is simple and convenient to pre-
pare a wide range of di(indolyl)indolin-2-one derivatives which
are found to possess strong cytotoxicity against only cancer cell
lines and not normal ones. This provides a platform for further
development of these compounds into promising anticancer agents.
12. General procedure: To a stirred solution of isatin (1 mmol) and indole (2 mmol)
in dry dichloromethane (4 mL) was added molecular iodine (26 mg, 10 mol %)
at room temperature. The resulting mixture was stirred at room temperature
for the appropriate time (Table 1). After complete conversion, as indicated by
TLC, the reaction mixture was quenched by saturated sodium thiosulphate
solution (4 mL) and extracted with dichloromethane (3 ꢀ 10 mL). The
combined organic layers were dried over anhydrous Na2SO4, concentrated in
vacuo and purified by column chromatography on silica gel (Merck, 60–
120 mesh, ethyl acetate–hexane, 3:7) to afford the pure di(indolyl)indolin-2-
one. Spectral data for the selected products: 20-Methyl-3-(2-methyl-5-nitro-
1H-indol-3-yl)-70-nitro-3,30-biindolin-2-one (3b, Table 1): White solid, mp
340–342 °C; 1H NMR (500 MHz, DMSO): d 11.26 (d, 2H, J = 7.3 Hz), 10.5–10.6
(br s, 1H), 7.82 (d, 2H, J = 9.4 Hz), 7.75 (s, 1H), 7.61 (s, 1H) 7.29 (d, 2H,
J = 7.3 Hz), 7.26 (t, 1H, J = 7.3 Hz), 7.15 (d, 1H, J = 7.3 Hz), 7.03 (d, 1H, J = 7.3 Hz),
6.91 (t, 1H, J = 7.3 Hz), 2.10 (s, 3H), 2.01 (s, 3H); 13C NMR (300 MHz,
Acknowledgments
J. S. Yadav acknowledges the partial support by King Saudi
University for Global Research Network for Organic Synthesis
(GRNOS). A.A. thanks DBT, New Delhi for a research grant.
References and notes
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CDCl3 + DMSO):
126.2, 126.0, 125.1, 121.4, 116.3, 116.1, 115.3, 115.2, 111.9, 111.5, 110.3, 109.8,
12.95, 12.9; IR (KBr):
3325, 3238, 1690, 1472, 1328 cmꢁ1; ESI (MS): m/z: 499
(M+NH4); 504(M+Na); HRMS calcd for C26H19N3O5Na: 504.1260, found,
d 178.23, 141.0, 140.0, 135.1, 137.1, 136.6, 133.4, 128.1,
m
504.1283.
Methyl
30-(5-(methoxycarbonyl)-1H-indol-3-yl)-20-oxo-3,30-
biindoline-7-carboxylate (3d, Table 1): White solid, mp 255–2570°C; 1H NMR
(500 MHz, DMSO): d 10.92–10.96 (br s, 2H), 10.11–10.55 (br s, 1H), 8.08 (s, 2H),
7.69 (d, 2H, J = 8.5 Hz), 7.35 (d, 2H, J = 8.5 Hz), 7.19 (t, 2H, J = 8.5 Hz), 7.02 (d,
1H, J = 7.6 Hz), 6.94 (d, 2H, J = 1.9 Hz), 6.91 (t, 1H, J = 7.6 Hz), 3.78 (s, 6H); 13C
NMR (300 MHz, CDCl3 + DMSO): d 178.3, 167.1, 141.2, 139.6, 133.7, 128.3,
126.2, 125.0, 124.7, 123.5, 122.1, 121.7, 119.9, 115.6, 111.7, 109.8, 51.6, 52.3;
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m
3335, 3236, 1700, 1615, 1270, 1122 cmꢁ1; ESI (MS): m/z: 497
(M+NH4); 502(M+Na); HRMS calcd for C28H21N3O5Na: 502.1358, found:
502.1378. 70-Nitro-3-(5-nitro-1H-indol-3-yl)-3,30-biindolin-2-one (3f, Table
1): White solid, mp 350–352 °C; 1H NMR (500 MHz, DMSO): d 11.27–11.39
(br s, 2H), 10.5–10.7 (br s, 1H), 8.31 (s, 2H), 7.93 (d, 2H, J = 8.3 Hz), 7.43 (d, 2H,
J = 8.3 Hz), 7.23 (d, 2H, J = 7.3 Hz), 7.10 (s, 2H), 7.06 (d, 2H, J = 7.3 Hz), 6.96 (t,
1H, J = 7.3 Hz); 13C NMR (300 MHz, CDCl3 + DMSO): d 177.7, 140.8, 139.9,
132.6, 128.3, 127.9, 124.6, 124.3, 121.8, 117.2, 116.4, 112.1, 109.8, 59.4, 51.7,
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476.097.
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