Acta Pharm. 59 (2009) 431–440
Original research paper
10.2478/v10007-009-0040-9
Synthesis, anticancer and cytostatic activity
of some 6H-indolo[2,3-b]quinoxalines
SUBHAS S. KARKI1*
RAHUL HAZARE1
SUJEET KUMAR1
VIVEK S. BHADAURIA1
JAN BALZARINI2
ERIK DE CLERCQ2
1Department
of Pharmaceutical Chemistry
KLE College of Pharmacy, 2nd Block
Rajajinagar, Bangalore-560010, India
2Rega
Institute for Medical Research
Katholieke Universiteit Leuven
B-3000 Leuven, Belgium
Accepted October 22, 2009
Various 6-aralkyl-9-substituted-6H-indolo[2,3-b]quinoxalines were synthesized by reaction of 1,5-disubstituted
2,3-dioxo-2,3-dihydroindole and orthophenylene diamine. Appreciable anticancer activity of compounds 5b, 5d,
5g and 5l at various cell lines among 59 human tumor
cell panels was observed. All the synthesized compounds
were evaluated for cytostatic activity against human
Molt 4/C8 and CEM T-lymphocytes as well as for murine L1210 leukemia cells. Compound 5h exhibited an
IC50 of 71 mmol L–1 against Molt 4/C8 and 117 mmol L–1
against CEM compared to melphalan 3.2 mmol L–1 and
2.5 mmol L–1, respectively. The IC50 for compound 7i against L1210 was 7.2 mmol L–1 compared to melphalan 2.1
mmol L–1.
Keywords: indolo[2,3-b]quinoxaline, cytostatic activity, anticancer activity
Quinoxaline derivatives seem to have very interesting biological properties (1–3). The
plant alkaloid ellipticine (5,11-dimethyl-6H-pyrido[4,3-b]carbazole) has DNA-intercalating and antitumor activity and is active against the herpes simplex virus (4, 5). Graslund
et al. (6) have studied ellipticine and the derivatives 2,3-dimethyl-6-(2-dimethyl-aminoethyl)6H-indolo[2,3-b]quinoxaline and 6-(2-dimethylaminoethyl)6H-indolo[2,3-b] quinoxaline for their interaction with oligodeoxynucleotide duplexes. They reported that compounds were intercalated in a non-specific fashion and by an AT-specific interaction.
Recently, Sauvain et al. (7) reported that 3-(4’-chloro)phenylquinoxaline-2-carbonitrile-1,4-di-N-oxide had potent antimalarial activity particularly against a chloroquine-resistant strain of Plasmodium falciparum. Moarbess et al. (8) examined imidazo[1,2-a]quinoxaline, imidazo[1,5-a]quinoxaline and pyrazolo[1,5-a]quinoxaline derivatives for their
in vitro and in vivo anti-tumoral activities. Toshima et al. (9) have designed and evaluated
quinoxaline-carbohydrate hybrids as novel and selective photo-induced DNA cleaving
and cytotoxic agents.
* Correspondence; e-mail: subhasskarki@gmail.com
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S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
H3 C
N
N
N
H
N
CH 3
N
Ellipticine
5,11-dimethyl-6H-pyrido[4,3-b]carbazole
CH 3
N
N
CH 3
CH 3
H3C
6(2-dimethylaminoethyl)
6H-indolo[2,3-b]quinoxalines
N
N
N
H3C
CH 3
2,3-dimethyl-6(2-dimethylaminoethyl)
6H-indolo[2,3-b]quinoxaline
Fig. 1. Structures of ellipticine and other indolo[2,3-b]quinoxalines.
Some quinoxalin-2-ones have shown antifungal activity (10, 11) whereas quinoxalin-1-oxides have antibacterial activity (12). 6H-indolo[2,3-b]quinoxaline can be regarded as
an aza analogue of ellipticine. It was therefore of interest to test 6,9-disubstituted-6H-indolo[2,3-b]quinoxalines for their anticancer and cytostatic activity.
EXPERIMENTAL
Melting points were determined in open capillaries and were uncorrected. Rf values
were obtained using silica gel thin layer chromatography plates and a solvent system of
chloroform/methanol (9:1). 2,3-Dioxy-2,3-dihydroindoles/5-substituted 2,3-dioxy-2,3-dihydroindoles and 1-(4-substituted)arylmethyl-2,3-dioxy-2,3-dihydroindoles were prepared according to literature (13, 14). The infrared spectra of all compounds were determined by a diffuse reflectance technique using potassium bromide powder on a Jasco
460 FTIR machine (Jasco, Japan). 13C NMR for 5i and 5j and 1H NMR spectra (400 MHz)
of all compounds were generated in dimethylsulfoxide-d6/CDCl3 on a Bruker Ultraspec
spectrophotometer (Germany). FAB mass spectra for 5c and 5j were obtained by using a
Jeol SX-102 instrument (Jeol, Japan). CHN for all compounds were generated on an elemental analyzer Vario EL III (Germany).
432
S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
General procedure for the synthesis of
6-aralkyl-9-substituted-6H-indolo[2,3-b]quinoxalines (5a-m)
A mixture of 1-arylmethyl-2,3-dioxy-2,3-dihydroindole (0.005 mol), orthophenylene
diamine (0.005 mol), glacial acetic acid (0.5–1.0 mL) and anhydrous ethanol (100 mL) was
heated under reflux until the reaction was complete (4 h). Approximately half of the ethanol was removed in vacuo and the solution was left overnight at room temperature. The
solid that precipitated was collected, washed with cold ethanol and recrystallized from
suitable solvent. Products obtained were: 9-fluoro-6-(4-fluorobenzyl)-6H-indolo[2,3-b]quinoxaline (5a), 6-benzyl-9-fluoro-6H-indolo[2,3-b]quinoxaline (5b), 9-methyl-6-(4-methylbenzyl)-6H-indolo[2,3-b]quinoxaline (5c), 6-benzyl-9-methyl-6H-indolo[2,3-b]quinoxaline (5d), 9-chloro-6-(4-fluorobenzyl)-6H-indolo[2,3-b]quinoxaline (5e), 6-benzyl-9-chloro-6H-indolo[2,3-b]quinoxaline (5f), 6-(4-fluorobenzyl)-6H-indolo[2,3-b]quinoxaline (5g),
6-(4-methylbenzyl)-6H-indolo[2,3-b]quinoxaline (5h), 9-bromo-6-(4-methylbenzyl)-6H-indolo[2,3-b]quinoxaline (5i), 9-chloro-6-(4-methylbenzyl)-6H-indolo[2,3-b]quinoxaline (5j),
Table I. Physicochemical data of synthesized compounds
Compd. Yield (%)
M.p. (°C)
5a
65
218–220
5b
68
220–222
5c
72
220–225
5d
75
215–218
5e
75
235–240
5f
68
198–201
5g
72
162–163
5h
80
185–190
5i
75
193–195
5j
80
192–194
5k
71
212–215
5l
71
177–180
5m
76
223–225
Mol. formula
(Mr)
C21H13F2N3
345.34
C21H14FN3
327.35
C23H19N3
337.42
C22H17N3
323.39
C21H13ClFN3
361.80
C21H14ClN3
343.81
C21H14FN3
327.35
C22H17N3
323.39
C22H16BrN3
402.29
C22H16ClN3
357.84
C21H13BrN3F
406.25
C22H16FN3
341.38
C22H16FN3
341.38
Rf value
0.76
0.52
0.48
0.55
0.40
0.55
0.70
0.76
0.60
0.56
0.31
0.80
0.60
Elemental analysis calcd./found (%)
C
H
N
73.04
72.99
77.05
76.88
81.87
81.26
81.71
81.65
69.71
70.00
73.36
72.98
77.05
77.25
81.71
80.98
65.68
65.01
73.84
73.01
62.09
62.45
77.40
76.97
77.40
76.78
3.79
3.56
4.31
4.25
5.68
5.66
5.30
5.22
3.62
3.55
4.10
4.01
4.31
3.99
5.30
5.32
4.01
3.75
4.51
4.11
3.23
3.01
4.72
4.39
4.72
4.51
12.17
12.25
12.84
13.11
12.45
12.75
12.99
13.09
11.61
11.55
12.22
12.39
12.84
13.02
12.99
13.28
10.45
11.01
11.74
12.13
10.34
11.01
12.31
12.55
12.31
12.81
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S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
9-bromo-6-(4-fluorobenzyl)-6H-indolo[2,3-b]quinoxaline (5k), 9-fluoro-6-(4-methylbenzyl)-6Hindolo[2,3-b]quinoxaline (5l), 6-(4-fluorobenzyl)-9-methyl-6H-indolo [2,3-b] quinoxaline (5m).
Physico-chemical data for synthesized compounds 5a-m are reported in Table I.
Anticancer activity
Compounds 5b, 5d, 5g and 5l were submitted to in vitro disease-oriented antitumor
screen (15). This assay involves determination of a test agent’s effect on growth parameters against a panel of approximately 60 human tumor cell lines, derived largely from
solid tumors, including non-small cell lung, colon, central nervous system, melanoma,
ovarian, prostate and breast cancers, plus a few leukemia and renal cell lines. Compounds
were tested at a 1.0 ´ 10–5 mol L–1 using DMSO as solvent; a 48-h continuous drug exposure protocol was applied and a sulforhodamine B (SRB) protein assay was used to estimate cell viability or growth. The measured effect of the compound on a cell line was
calculated according to one of the following two expressions:
if
(Atest – Atzero) ³ 0,
then
percentage growth = 100 (Atest – Atzero) / Actrl – Atzero)
if
(Atest – Atzero) < 0,
then
percentage growth = 100 (Atest – Atzero) / Atzero
where, Atzero is the average of absorbance measurements of SRB-derived color just before exposure of cells to the test compound, Atest is the average absorbance measurements of SRB-derived color just after 48-h exposure of cells to the test compound, Actrl is
the average of absorbance measurements of SRB-derived color just after 48 h with no exposure of cells to the test compound.
Cytostatic activity
The methodology for cytostatic activity assays in Molt 4/C8, CEM and L1210 assays
has been published previously (16). In brief, varying concentrations of compounds were
incubated at 37 °C with the cells for 72 h (human Molt 4/C8 or CEM T-lymphocytes) or
48 h (murine L1210 cells). After the incubation period cell number was counted by a
coulter counter (Harpenden Herz, UK).
RESULTS AND DISCUSSION
We have synthesized a series of thirteen derivatives of 6H-indolo[2,3-b]quinoxalines
(5a-m) containing an N-aralkyl group at the 6th position by reacting N-aralkylisatin with
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S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
NH 2
NH2
O
HO
NH
HN
R
R
O
N
NH
R
O
NH 2
O
N
alcohol
N
CH 3COOH
R'
R'
1
R'
2
3
H2O
H2 N
N
R
N
N
R
N
O
N
–H 2O
R'
R'
5a-m
4
5
R
R'
5
R
R'
a
F
F
h
H
CH3
b
F
H
i
Br
CH3
c
CH3
CH3
j
Cl
CH3
d
CH3
H
k
Br
F
e
Cl
F
l
F
CH3
f
Cl
H
m
CH3
F
g
H
F
Scheme 1
orthophenylene diamine, as depicted in Scheme I. The reaction of isatin with orthophenylene diamine has been reported to give spirobenzimidazoline, isatin-3-imine and/or 6H-indolo[2,3-b]quinoxaline in various kinds of solvents. No spiro compound or Schiff’s base
Table II. Spectral data of synthesized compounds
Compd.
5a
5b
5c
IR (n, cm–1)
3100–3030,
2917–2849,
1604, 1584,
1508, 1486
3066–3004,
2904–2849,
1618, 1582,
1511, 1489
3052–3019,
2920–2851,
1615, 1578,
1513, 1487
1H/ 13C
NMR (d, ppm) (DMSO-d6)
MS
5.73 (s, 2H, -CH2-), 7.02–7.06 (m, 2H, Ar-H), 7.40–7.43
(m, 2H, Ar-H), 7.52–7.57 (m, 1H, Ar-H), 7.62 (d, 1H, J = 8.0,
Ar-H), 7.75–7.79 (m, 1H, Ar-H), 7.83–7.87 (m, 1H, Ar-H),
8.19–8.24 (m, 2H, Ar-H), 8.38 (d, 1H, J = 8.0, Ar–H)
5.77 (s, 2H, -CH2-), 7.28–7.31 (m, 4H, Ar-H), 7.32–7.39
(m, 2H, Ar-H), 7.42 (d, 1H, Ar-H), 7.74–7.79 (m, 1H, Ar-H),
7.82–7.86 (m, 1H, Ar-H), 8.19–8.24 (m, 2H, Ar-H), 8.38 (d,
1H, J = 8.0, Ar-H)
2.34 (s, 3H, CH3), 2.59 (s, 3H, CH3), 5.71 (s, 2H, -CH2-),
7.14 (d, 2H, J=7.6, Ar-H), 7.27 (d, 2H, J = 8.0, Ar-H),
7.30–7.32 (m, 2H, Ar-H), 7.49 (d, 1H, J = 8.4, Ar-H), 7.74
338 (100)
(t, 1H, J = 14.8, Ar-H), 7.81 (t, 1H, J = 14.8, Ar-H), 8.20
(d, 1H, J = 8.0, Ar-H), 8.35–8.37 (m, 1H, Ar-H)
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S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
5d
5e
5f
5g
3059–3024,
2966–2850,
1616, 1578,
1508, 1489
3066,
2917–2848,
1605, 1581,
1509, 1474
3062,
2918–2849,
1609, 1581,
1509, 1455
3045–3013,
2954–2849,
1610, 1583,
1513, 1469.
5h
3053–3022,
2964–2920,
1612, 1583,
1510, 1471
5i
3053–3021,
2918–2849,
1609, 579,
1516, 1453
5j
3054-3022,
2972-2849,
1613, 1581,
1516, 1467
5k
5l
5m
436
3066-3024,
2917-2848,
1605, 1578,
1508, 1475
3054-3029,
2917-2849,
1613, 585,
1515, 1485
3055-3026,
2919-2849,
1603, 579,
1506, 1488
2.59 (s, 3H, -CH3), 5.76 (s, 2H, -CH2-), 7.29–7.38 (m, 6H,
Ar-H), 7.49 (d, 1H, J = 8.4, Ar-H), 7.72–7.76 (m, 1H, Ar-H),
7.79–7.83 (m, 1H, Ar-H), 8.18–8.20 (m, 1H, Ar-H), 8.36–8.38
(m, 2H, Ar-H)
5.73 (s, 2H, -CH2-), 7.01–7.37 (m, 4H, Ar-H), 7.61–7.64
(m, 2H, Ar-H), 7.76–7.80 (m, 1H, Ar-H), 7.84–7.88 (m, 1H,
Ar-H), 8.22 (d, 1H, J = 8.0, Ar-H), 8.39 (d, 1H, J = 8.0,
Ar-H), 8.52–8.53, (m, 1H, Ar-H)
5.77 (s, 2H, -CH2-), 7.28–7.35, (m, 6H, Ar-H), 7.57–7.62,
(m, 1H, Ar-H), 7.75–7.87 (m, 2H, Ar-H), 8.19–8.22 (m, 1H,
Ar-H), 8.36–8.38, (m, 1H, Ar-H), 8.53, (s, 1H, Ar-H)
5.69 (s, 2H, -CH2-), 7.00 (t, 2H, J = 16, Ar-H), 7.31–7.41
(m, 4H, Ar-H), 7.63 (t, 1H, J = 16.0, Ar-H), 7.69–7.73 (m, 1H,
Ar-H), 7.76–7.80 (m, 1H, Ar-H), 8.16 (d, 1H, J = 8.8, Ar-H),
8.32–8.34 (m, 1H, Ar-H), 8.51 (d, 1H, J = 7.6, Ar-H)
2.34 (s, 3H, CH3), 5.74 (s, 2H, -CH2-), 7.15 (d, 2H, J = 8.0,
Ar-H), 7.27–7.34 (m, 2H, Ar-H), 7.44 (d, 2H, J = 8.0, Ar-H),
7.68 (t, 1H, J = 15.6, Ar-H), 7.73–7.77 (m, 1H, Ar-H), 7.83
(t, 1H, J = 15.2, Ar-H), 8.22 (d, 1H, J = 8.4, Ar-H), 8.39
(d, 1H, J = 8.4, Ar-H), 8.55 (d, 1H, J = 7.6, Ar-H)
2.29 (s, 3H, CH3), 5.66 (s, 2H, -CH2-), 7.10 (d, 2H, J = 8.0,
Ar-H), 7.20 (d, 2H, J = 7.6, Ar-H), 7.24 (s, 1H, Ar-H),
7.67–7.73 (m, 2H, Ar-H), 7.79 (t, 1H, J = 13.8, Ar-H), 8.16 (d,
1H, J = 8.0, Ar-H), 8.32 (d, 1H, J = 8.0, Ar-H), 8.61 (s, 1H,
Ar-H). 21.17 (s), 29.79 (s), 44.90 (s), 111.72 (s), 114.02 (s),
121.31 (s), 125.40 (s), 126.48 (s), 127.21 (s), 128.01 (s), 129.32
(s), 129.58 (s), 133.09 (s), 133.48 (s), 137.64 (s), 138.71 (s),
139.69 (s), 140.92 (s), 142.73 (s)
2.34 (s, 3H, -CH3), 5.72 (s, 2H, -CH2-), 7.15 (d, 2H, J=8,
Ar-H), 7.25 (d, 2H, J=8, Ar-H), 7.34-7.36 (m, 1H, Ar-H),
7.59-7.61 (m, 1H, Ar-H), 7.75-7.86 (m, 2H, Ar-H), 8.19-8.22
(m, 1H, Ar-H), 8.35-8.38 (m, 1H, Ar-H), 8.51 (d, 1H, Ar-H).
357 (100)
21.18 (s), 29.80 (s), 44.90 (s), 111.27 (s), 120.80 (s), 122.39 (s),
126.44 (s), 126.80 (s), 127.22 (s), 128.01 (s), 129.29 (s), 129.52
(s), 129.01 (s), 130.81 (s), 133.15 (s), 137.62 (s), 138.84 (s),
139.65 (s), 140.90 (s), 142.35 (s), 145.83 (s).
5.67 (s, 2H, -CH2-), 7.00 (t, 2H, J=16, Ar-H), 7.23-7.31 (m,
4H, Ar-H), 7.69-7.75 (m, 2H, Ar-H), 7.78-7.82 (m, 1H, Ar-H),
8.16 (d, 1H, J=8.8, Ar-H), 8.33 (d, 1H, J=8, Ar-H).
2.30 (s, 3H, CH3), 5.68 (s, 2H, -CH2-), 7.12 (d, 2H, Ar-H),
7.22 (d, 2H, Ar-H), 7.29-7.37 (m, 3H, Ar-H), 7.69-7.73 (m,
1H, Ar-H), 7.77-7.81 (m, 1H, Ar-H), 8.15-8.18 (m, 1H, Ar-H),
8.33 (d, 1H, J=8.4, Ar-H).
2.55 (s, 3H, CH3), 5.66, (s, 2H, -CH2-), 6.95-6.98 (m, 2H,
Ar-H), 7.23-7.32 (m, 3H, Ar-H), 7.45 (d, 1H, J=8.4, Ar-H),
7.68-7.71 (m, 1H, Ar-H), 7.75-7.79 (m, 1H, Ar-H), 8.14 (d,
1H, J=8.8, Ar-H), 8.32 (d, 2H, J=6.8, Ar-H).
S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
were detected. Compounds 5a-m showed absorption bands ranging from 3052–3000 cm–1
for C-H aromatic stretching, 2960–2900 cm–1 for C-H aliphatic stretching; there were also
some bands for C=C and C=N at 1580–1575 cm–1 and 1505–1480 cm–1, respectively (Table
II). In 1H NMR spectra, the presence of a singlet between d 5.8–5.6 ppm was observed
for the methylene group and multiplets were observed between d 8.55–7.00 ppm for aromatic protons. In the 13C NMR spectra, signals from d 142.73 to 111.72 ppm were observed for aromatic carbon and d 44.90 to 21.12 ppm for alkyl carbons. Fast atomic bombardment (FAB) mass spectra showed accurate molecular ion peaks at m/z 338 and 357
for 5c and 5j, respectively (Table II).
The anti-cancer activity of compounds 5b, 5d, 5g and 5l at concentrations 1.0 ´ 10–5
mol L–1 was tested against 59 human tumor cell lines representing leukemia, melanoma
and cancers of the lung, colon, brain, ovary, breast, prostate and kidney. The data for anticancer activity, in terms of the percent growth of treated cells, is given in Table III.
Table III. Growth of cancer cells (%) when treated with compounds 5b, 5d, 5g and 5la
Panel/cell line
Non-small cell lung cancer
HOP-92
Colon cancer
HCC-2998
HCT-116
Breast cancer
HS 578T
Ovarian cancer
IGROV1
Leukemia
HL-60(TB)
K-562
MOLT-4
RPMI-8226
SR
Renal cancer
UO-31
Melanoma
SK-MEL-2
SK-MEL-5
Prostate cancer
PC-3
CNS cancer
SF-539
SNB-75
a
Percentage of growth (%)
5b
5d
5g
5l
34.69
47.75
–
57.14
55.67
69.24
–
–
–
–
–
69.57
–
–
54.68
68.94
69.90
–
44.75
55.85
–
–
7.31
50.03
–
–
32.40
45.51
58.90
–
–
–
–
–
–
30.11
69.85
–
–
18.70
–
–
66.05
–
–
–
–
–
37.12
59.20
–
–
–
–
–
58.63
–
–
–
–
–
–
66.09
60.96
c = 1.0 ´ 10–1 mol L–1
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S. S. Karki et al.: Synthesis, anticancer and cytostatic activity of some 6H-indolo[2,3-b]quinoxalines, Acta Pharm. 59 (2009) 431–440.
Table IV. Cytostatic activity: IC50 values
Compd.
L1210a
Molt4/C8a
CEMa
5a
289 ± 14
381 ± 136
303 ± 191
5b
91 ± 45
> 610
189 ± 52
5c
285 ± 24
272 ± 24
246 ± 59
5d
260 ± 78
389 ± 161
290 ± 22
> 552
³ 552
5e
85 ± 2.8
5f
75 ± 17
513 ± 23
119 ± 55
5g
199 ± 27c
170 ± 18 c
188 ± 40c
5h
117 ± 74
71 ± 31
117 ± 19
5i
7.2 ± 5.3
222 ± 25 c
247 ± 28c
5j
5k
5l
32 ± 25
50 ±
27b
164 ± 2.9c
5m
32 ± 16
Melphalan
2.1 ± 0.02
284 ± 8
c
279 ± 7c
> 500
400 ± 142c
³ 1465
764 ± 179c
424 ±
81c
3.2 ± 0.6
> 500
2.5 ± 0.2
DMSO – negative control.
IC50 – 50 % inhibitory concentration (mmol L–1) required to inhibit tumor cell proliferation by 50 %.
a Values are mean ± SEM, n = 2 to 3.
Significant difference vs. melphalan: b p < 0.05, c p < 0.01.
Synthesized compounds and melphalan as a standard were also evaluated for their in
vitro cytostatic activity against human Molt 4/C8 and CEM T-lymphocytes as well as murine leukemia L1210 cells. The results of cytostatic activity are presented in Table IV.
Only melphalan showed IC50 values consistently lower than 10 mmol L–1 (IC50 range
2.1–3.2 mmol L–1). The test compounds had IC50 values ranging between 23 and ³ 1465
mmol L–1 (except for 5i that had and IC50 of 7.2 mmol L–1 for L1210 cell proliferation).
Compound 5h emerged as the only compound that consistently inhibited cell proliferation of all three tumor cell lines at an IC50 ranging between 71 and 117 mmol L–1. It is unclear why 5i is markedly more cytostatic to L1210 cells than to the human lymphocyte
cell lines. Also, for 5e, 5j, 5k, 5l and 5m, there was a clear trend of higher cytostatic activity against the murine L1210 than against the human lymphocyte cell lines.
Structure activity relation
Quinoxaline derivatives with substituents like F and CH3 on benzyl at 4th position
and F, CH3, Cl, Br at 9th position exhibited anticancer activity against various cell lines
of HOP-92, HCT-116, IGROV1, K-562 Molt-4 and RPMI-8226. The order of potency was
found to be 5l > 5b > 5d ³ 5g as it is evident from the overall percentage of growth inhibition. In addition, compound 5l is selective against prostate cancer.
Quinoxaline derivatives with substituents like F and CH3 on 4-aralkyl at 6th position and Cl, F, Br and CH3 at 9th position were studied for cytostatic activity against human
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Molt 4/C8 and CEM T-lymphocytes as well as murine L1210 leukemia cells. In most cases,
there was a more pronounced cytostatic activity against the murine leukemia L1210 cells
than against the human lymphocyte cells. Among the tested compounds 5b, 5e, 5f, 5h,
5i, 5j and 5k were moderately cytostatic for the leukemia cell line L1210, as it is evident
from Table IV (IC50 < 100 mmol L–1). The order of cytostatic activity for L1210 was 5i > 5f
³ 5b, therefore it suggests that by placing a halogen like bromine on the ninth position
and a methyl on the 4th position of aralkyl on the 6th position of quinoxaline produced
compounds which were less cytostatic than the standard melphalan. By keeping the electron donating groups like methyl on 6 and 9th position of aralkyl, there was not any improvement of cytostatic activity (5c).
CONCLUSIONS
The reaction of 5-substituted isatin with orthophenylene diamine provided the corresponding quinoxalines 5a-m in good yields. Investigations of cytostatic activities revealed better cytostatic activity of several compounds (5b, 5e, 5f, 5i, 5j, 5k, 5m) against the
leukemia cell line L1210 than the human lymphocytic cell lines (the lowest IC50 of 7.2
mmol L–1 was noted for 5i) compared to melphalan (IC50 2.1 mmol L–1).
Acknowledgements. – The authors thank B. G. Desai of the KLE College of Pharmacy,
Bangalore, India, for providing the necessary facilities. The authors thank V. L. Narayanan and his group at NIH, Bethesda, USA, for anti-cancer screening at the National Cancer Institute. Appreciation is extended to the Belgian Fonds voor Wetenschappelijk Onderzoek (Vlaanderen) which supported the cytostatic activity assays and to L. van Berckelaer for excellent technical assistance.
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S A @ E TA K
Sinteza, antitumorsko i citostatsko djelovanje derivata 6H-indolo[2,3-b]kinoksalina
SUBHAS S. KARKI, RAHUL HAZARE, SUJEET KUMAR, VIVEK S. BHADAURIA, JAN BALZARINI i ERIK DE CLERCQ
Reakcijom 1,5-disupstituiranih 2,3-diokso-2,3-dihidroindola s ortofenilen diaminom
sintetizirani su razli~iti 6-aralkil-9-supstituirani-6H-indolo[2,3-b]kinoksalini. Spojevi 5b,
5d, 5g i 5l pokazali su zna~ajno antitumorsko djelovanje na 59 humanih tumorskih stanica. Svi sintetizirani spojevi ispitani su na citostatsko djelovanje na stani~ne linije Molt
4/C8 i CEM T-limfocite, te na murin L1210 stanice leukemije. IC50 za spoj 5h je 71 mmol
L–1 na stani~nu liniju Molt 4/C8 i 117 mmol L–1 na CEM/0, dok su vrijednosti za melfalan 3,2, odnosno 2,5 mmol L–1. IC50 spoja 7i na stanice L1210/0 je 7,2, dok je za melfalan
2,1 mmol L–1.
Klju~ne rije~i: indolo[2,3-b]kinoksalin, citostatsko djelovanje, antitumorsko djelovanje
Department of Pharmaceutical Chemistry, KLE College of Pharmacy, 2nd Block Rajajinagar
Bangalore-560010, India
Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium
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