Synthesis and cytotoxic activity of 2-acyl-1H-indole-4,7-diones on human cancer cell lines

Article abstract of DOI:10.1016/j.ejmech.2004.10.007

Synthesis and cytotoxic activity of a series of 2-acyl-1H-indole-4,7-diones on human cancer cell lines are described. Due to close structural relationship to 2-acylindoles, potent inhibitors of tubulin polymerization, the mode of action of these novel com

Full text of DOI:10.1016/j.ejmech.2004.10.007

European Journal of Medicinal Chemistry 40 (2005) 85–92
www.elsevier.com/locate/ejmech
Original article
Synthesis and cytotoxic activity of 2-acyl-1H-indole-4,7-diones
on human cancer cell lines
Siavosh Mahboobi a,*, Andreas Sellmer a, Emerich Eichhorn a, Thomas Beckers b,1
,
Heinz-Herbert Fiebig c, Gerhard Kelter c,2
a Department of Pharmaceutical Chemistry I, University of Regensburg, 93040 Regensburg, Germany
b Therapeutic Area Oncology, ALTANA Pharma AG, 78467 Konstanz, Germany
c Oncotest GmbH, Am Flughafen 12-14, 71908 Freiburg, Germany
Received 1 September 2004; received in revised form 15 October 2004; accepted 21 October 2004
Available online 16 December 2004
Abstract
Synthesis and cytotoxic activity of a series of 2-acyl-1H-indole-4,7-diones on human cancer cell lines are described. Due to close structural
relationship to 2-acylindoles, potent inhibitors of tubulin polymerization, the mode of action of these novel compounds has been investigated.
Cytotoxicity, the influence on tubulin polymerization, and cell cycle dependent cytotoxicity on colon carcinoma cells by investigation of RKO
exo p27 versus RKO p27kip1 cells are described. IC50 values of arrested versus proliferating cells differ only in a range of two to fourfold and
therefore cellular targets, predominantly relevant for mitotic progression, are excluded. As shown by the significant difference in the IC90
values on different tumor cell lines, the investigated compounds seem to act selectively on mammary and renal cancer cells.
© 2004 Elsevier SAS. All rights reserved.
Keywords: Indole-4,7-diones; Cytotoxic activity; Cell cycle specificity; Tubulin
1. Introduction
search for new, simple chinoide systems with potential phar-
macological value, we prepared a series of 2-acyl-1H-indole-
4,7-diones, structurally related to 3 and investigated the bio-
logical properties of these systems, combining the structural
features of the 2-indolyl-methanone and a chinoide system.
Reflecting the diversity in structure, synthetic and natu-
rally occurring indoles exhibit antibacterial, fungicide, cyto-
toxic and antiproliferative activity. We recently reported on
two classes of 2-indolylmethanones 1 and 2, being potent
inhibitors of receptor tyrosine kinases [1] and highly potent
antiproliferative agents by acting as destabilizing tubulin
inhibitors with anti-angiogenic potential [2] (Fig. 1).
Moreover, scientists have noted on a large number of anti-
cancer agents containing chinoide structures [3–6], includ-
ing the 2-acetyl-naphtho[2,3-b]furan-4,9-dione (3) [7], a natu-
rally occurring potent inhibitor of proliferation in a human
keratinocyte cell system [8], being promising candidates for
the treatment of proliferative disorders [9]. Therefore, in
2. Results and discussion
2.1. Chemistry
According to Scheme 1 the desired 2-acyl-1H-indole-4,7-
diones were prepared from commercially accessible 2,5-
dimethoxybenzaldehyde (5) employing the strategy of Bene-
teau and Besson [10], which includes nitration of the aldehyde
5, Henry reaction of 6 and hydrogenolytic ring closure. After
protection of 4,7-dimethoxyindol (8) with benzene sulfonyl
chloride, lithiation of 9 was performed with n-BuLi at –78 °C
in THF. Position and amount of metallation (≥90%) was
proved by quenching the 2-indolyl-lithium with MeOD and
1H-NMR spectroscopy of the resulting 1-benzenesulfonyl-2-
deutero-4,7-dimethoxy-1H-indole (9a). Reaction of the result-
* Corresponding author. Tel.: +49 941 943 4824; fax: +49 941 943 1737.
E-mail addresses: siavosh.mahboobi@chemie.uni-regensburg.de
(S. Mahboobi), thomas.beckers@altanapharma.com (T. Beckers),
gerhard.kelter@oncotest.de (G. Kelter).
1 Tel./fax: +49 7531 849 2974.
2 Tel.: +49 761 515 5920; fax: +49 761 515 5955.
0223-5234/$ - see front matter © 2004 Elsevier SAS. All rights reserved.
doi:10.1016/j.ejmech.2004.10.007

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S. Mahboobi et al. / European Journal of Medicinal Chemistry 40 (2005) 85–92
Fig. 1
.
Chemical structures of various methanone systems exhibiting antiproliferative activity. Dependent on the structural features, inhibition of growth factor
receptors with intrinsic tyrosine kinase (1) or inhibition of tubulin assembling (2) are predominantly responsible for the antiproliferative activity. The structu-
rally related chinoide furan derivative (3) was found to be a potent inhibitor of human keratinocyte growth.
ing 2-lithiated indole derivative with the respective carboxy-
lic acid chloride yielded the C-2 acylated indoles 10 in good
yields. The chinoide system 11 was generated by oxidation
of the dimethoxy indoles 10 using ceric ammonium nitrate
(CAN) [11] in acetonitrile/water. Removal of the
protection group with tetrabutylammonium fluoride (TBAF)
in THF [1] furnished the 1H-indole-4,7-diones 12. Instead of
benzoic acid chlorides (Scheme 1) also acetic acid anhydride
and 4-morpholinecarbonyl chloride were employed.
The N-protected indol-4,7-diones 11 as well as their unpro-
tected analogues 12 were candidates for a pharmacological
in vitro profiling to evaluate cytotoxicity, effects on tubulin
polymerization and specificity towards mitotic cells.
The investigated chinones exhibit significant cytotoxicity
with IC50 values ranging from 0.80 to 3.20 µM. The benzene
sulfonyl-group in position 1 is well tolerated and weakly influ-
ences the cytotoxic potential. Different substituents in the
methanone substructure from methyl (12a) to morpholine
(12b) and substituted phenyl (12c–12h) increase the cyto-
toxic potential up to threefold activity only. This indicates
the chinoide structure to be the most important pharmacoph-
ore in these compounds. Patterns of substitution in the phe-
nyl system affect the biological activity only weakly.
As already mentioned, the structurally related 2-acylin-
doles are effective antiproliferative agents by acting as desta-
bilizing tubulin inhibitors [2]. By investigation of bovine brain
tubulin polymerization in vitro using the naphthol blue assay
as described [14] some 2-substituded 1H-indole-4,7-diones
showed moderate tubulin inhibitory activity. Compounds 11a,
11b, 11f, 11h, 12a and 12b were characterized by IC50 values
of 32–50 µM.
2.2. Biological results
In vitro activity on human HeLa cervical carcinoma cells
was investigated using the Alamar Blue assay as a fast and
simple method for the determination of cellular metabolic
activity [12,13] (Table 1).
Tubulin inhibitors interfere with the M-phase of the cell
cycle by binding to tubulin, inducing a mitotic catastrophy.
Scheme 1. Synthesis of 2-substituded 1H-indole-4,7-diones.

S. Mahboobi et al. / European Journal of Medicinal Chemistry 40 (2005) 85–92
87
without p27kip expression were highly sensitive with an IC50
of 4 nM (Fig. 2). The investigated chinoide analogues did not
display a significant cell cycle dependent cytotoxicity. The
respective IC50 values of arrested versus proliferating cells
are summarized in Table 2 and differ only in a range of two to
fourfold as also observable for standard chemotherapeutic
drugs lacking cell cycle specificity as cisplatin, e.g.
Table 1
Cytotoxicity (IC50 values) of 2-substituded 1H-indole-4,7-diones on HeLa
cervical carcinoma cells
2.3. Selectivity of inhibition on the growth of human tumor
cell lines
Number
11a
IC50 (µM)
2.97
Number
12a
IC50 (µM)
2.92
R=
CH3
11b
11c
11d
11e
11f
11g
2.98
12b
12c
12d
12e
12f
12g
1.59
Morpholine
Ph
To investigate cytotoxicity of selected compounds, namely
the N-phenylsulfonated chinones 11a and 11e as well as their
deprotected analogues (12a, 12e) were studied using a panel
of different human tumor cell lines including a gastric
xenograft cell line (GXF 251L), adeno (LXFA 629L) and large
(LXFL 529L) cell lung cancer, mammary (MACL MCF7,
MAXF 401NL), melanoma (MEXF 462 NL and 514L), pros-
tate (PRCL PC3M), renal (RXF 486L and 944L) and an uterus
body cell line (UXF 1138L). IC70 and IC90 values were deter-
mined in a screening from XTT proliferation assays after incu-
bation with test compound for 48 h as described [2]. Indepen-
dent from substitution of the chinoide methanone—methyl
or 4-methoxyphenyl—as well as from N-phenylsulfonation
all investigated compounds stopped tumor growth of mam-
mary and renal cells at concentrations of 3 µg ml–1, exhibit-
ing IC90 values <3 µg ml–1. Remaining high potency in mela-
noma xenograft models also was observed for 12a and 12e,
exhibiting IC70 values <3 µg ml–1 in MEXF 462 NL and 514L
cell lines. In contrast, the IC90 values for inhibition of tumor
3.20
2.44
1.98
3.08
3-OMe-Ph
4-OMe-Ph
3-FPh
1.35
2.15
2.53
0.80
1.79
2.70
3,5-F2Ph
2,3,4,5,6-F5Ph
11h
1.45
12h
1.03
For evaluation of a mitosis dependent mode of action, selected
compounds with an IC50 < 1.5 µM in HeLa cell cytotoxicity
assay and weak activity towards tubulin in vitro were tested
in the human colon carcinoma cell line RKO exo p27 with
inducible expression of the cell division cycle kinase inhibi-
tor p27kip1 [15]. Induction of p27kip1 arrests proliferating RKO
cells in the G1 phase of the cell division cycle, thus inducing
complete resistance to anti-mitotic agents like taxol as a sta-
bilizing tubulin inhibitor [16].
As demonstrated in Fig. 2, the proliferating cell line RKO
exo p27 showed insensitivity to taxol, used as the standard,
up to 33 µM. In contrast, proliferating RKO exo p27 cells
Fig. 2.
Concentration dependent viability of RKO exo p27 colon carcinoma cells proliferating (left) and non-proliferated (right) by p27kip1 induced cell cycle
arrest. The cells treated with taxol (top) are only sensitive in a proliferative state without expression of p27kip (IC50 = 4 nM). Compound 12f exhibits cytotoxic
potential independent on the proliferative status of the RKO exo p27 cells (bottom).

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S. Mahboobi et al. / European Journal of Medicinal Chemistry 40 (2005) 85–92
Table 2
Cytotoxicity (IC50 values) on proliferating RKO exo p27 and non-proliferating cells with expression of p27kip1
Number
IC50 Alamar Blue assay (µM)
Proliferating
Arrested (+p27kip1
Number
IC50 Alamar Blue assay (µM)
Proliferating
Arrested (+p27kip1
)
)
R=
11e
11f
11h
Taxol
1.37
–
2.18
–
12e
12f
12h
–
–
4-OMe-Ph
3-FPh
0.61
0.52
1.80
1.88
0.47
0.004
2.09
>0.1
2,3,4,5,6-F5-Ph
growth of gastric, lung, prostate and uterus cell lines differed
in general at least a 10-fold in potency (IC90 > 30 µg ml–1).
GraphPad Prism software. Colchicine or Vincristine were
included as positive controls.
2.4. Conclusion
3.1.2. Cell viability assay
Metabolic activity correlating with cell proliferation/
viability was quantified using the Alamar Blue assay as
described [13] and HeLa (ATCC CCL2) cervical as well as
RKO exo p27 colon carcinoma cell lines [15]. The com-
pounds were dissolved in dimethylsulfoxide (DMSO; 20 mM)
and subsequently diluted in semi-logarithmic steps. DMSO
dilutions were further diluted 1:100 into Dulbecco’s modi-
fied Eagle’s medium (DMEM) containing 10% inactivated
fetal calf serum (FCSi) to a final concentration twice as high
as the final concentration in the test. RKO exo p27 or HeLa
cells were seeded into 96 well flat bottom plates at a density
of 5000 cells or 1000 cells per well, respectively, in a volume
of 50 µl per well. To determine the effect on arrested RKO
exo p27 cells, these cells were seeded at a density of
15,000 cells per well and pretreated with 10 µM Ponasterone
A. Twenty-four hours after seeding, 50 µl each of the com-
pound dilutions in DMEM were added per well with 1%
DMSO treated cells as a control. After incubation with the
compounds for 72 h at 37 °C in a humidified atmosphere con-
taining 5% CO2, 10 µlAlamar Blue solution (Biosource) were
added and the fluorescence measured (ex 544 nm, em
590 nm). For calculation of cell viability, the emission value
from untreated cells was set as 100% viability and the emis-
sion rates of treated cells were set in relation to the values of
untreated cells. The corresponding IC50 values were deter-
mined from the concentration–effect-curves using the pro-
gram GraphPad Prism.
The 2-acyl-1H-indole-4,7-diones represent a novel series
of chinoide compounds exhibiting significant cytotoxic activ-
ity towards human cancer cell lines represented by the RKO
colon and HeLa cervical carcinoma models. Considering the
moderate tubulin polymerization interference as well as the
lack of correlation between the IC50 values of tubulin inhibi-
tion and cytotoxicity of the investigated compounds, tubulin
polymerization seems not to be the main cellular target respon-
sible for cytotoxicity—in contrast to the structurally related
2-aroylindoles 2, lacking a chinoide system.
In general chinoide agents were considered to exhibit cyto-
toxic activity by DNA intercalation [3,5], interference with
topoisomerase II DNA-complexes as well as by generating
free radicals or reactive oxygen species through redox cycling
[6]. Our data as presented in this study do not rule out the
possibility that 2-acyl-1H-indole-4,7-diones might act by one
of these mechanisms. The lack of significant cell cycle speci-
ficity suggests a more common mode of interference with
cell viability and a target(s) irrelevant for mitotic progres-
sion.
As shown by the significant difference in the IC90 values
on different tumor cell lines, the investigated compounds seem
to act selectively on mammary and renal cancer cells.
3. Experimental section
3.1. Biological methods
3.2. Chemistry
3.1.1. Tubulin polymerization assay
3.2.1. General
The assay was performed as described [14]. Bovine brain
tubulin heterodimers (5 µg µl–1; 50 µg per assay), provided
by Cytoskeleton/TEBU (MAP-rich, order No. ML-113F),
were incubated with test compounds in PEM buffer pH
6.6 containing 1 mM GTP in a total volume of 100 µl at 37 °C
for 1 h. Concentration dependent inhibition of GTP/heat
induced tubulin polymerization was calculated using the
1H-NMR and 13C-NMR spectra were recorded with a
Bruker Avance 300 spectrometer at 300 K, using TMS as an
internal standard. AA′BB′ and AA′XX′ spectra as well as
AB-spectra are characterized by the center of the respective
AA′, BB′ or XX′ part. ForAB-spectra the coupling constants
are given in addition. Elemental analyses were performed by

S. Mahboobi et al. / European Journal of Medicinal Chemistry 40 (2005) 85–92
89
the Analytical Laboratory, University of Regensburg. Melt-
ing points were determined with a Büchi Melting Point B-545
device. IR spectra (KBr or pure solid) were measured with a
Bruker Tensor 27 spectrometer, MS spectra were measured
with a Finnigan MAT 95 (EI, 70 eV). All reactions were car-
ried out under nitrogen.
colorless crystals, m.p.: 168.8–168.9 °C. IR (solid):
1689 cm–1. 1H-NMR (DMSO-[D6]): d (ppm) = 2.62 (s, 3H,
CH3), 3.61 (s, 3H, OCH3), 3.86 (s, 3H, OCH3), 6.77 (d, 1H,
3J = 8.7 Hz, aromat.), 6.95 (d, 1H, 3J = 8.7 Hz, aromat.), 7.69
(s, 1H, aromat.), 7.71–7.78 (m, 3H, aromat.), 8.31–8.35 (m,
2H, aromat.). EI-MS (70 eV) m/z (%): 359 (23) [M]+•, 218
(98), 188 (42), 160 (18), 148 (88), 77 (33), 43 (100). Anal.
(C18H17NO5S) Calc. C 60.16, H 4.77, N 3.90. Found: C 59.80,
H 4.89 N 3.43.
3.2.2. 1-Benzenesulfonyl-4,7-dimethoxy-1H-indole (9)
During 20 min, NaH (2.37 g, 59.3 mmol) (60% in paraf-
fin) was added to a stirred solution of 4,7-dimethoxy-1H-
indole (8) (10.0 g; 56.4 mmol) in 200 ml of anhydrous THF
at 0 °C. After stirring at room temperature for 1 h, benzene-
sulfonyl chloride (7.59 ml, 59.3 mmol) was added slowly.
The reaction mixture was stirred for additional 3 h, poured
into 500 ml of 10% aq NaHCO3 and extracted with ether (3 ×
250 ml). The combined organic layers were dried (Na2SO4),
and the solvent was removed under reduced pressure to give
a beige solid. Recrystallization from ethanol afforded 9 as
colorless crystals.Yield: 15.43 g (82%), m.p.: 105.1–105.4 °C.
1H-NMR (DMSO-[D6]): d (ppm) = 3.54 (s, 3H, OCH3), 3.81
3.2.4.2. (1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
morpholin-4-yl-methanone (10b). Yield: 2.34 g (69%) col-
orless crystals, m.p.: 187.9–188.0 °C. IR (KBr): 2978,
1633 cm–1. 1H-NMR (DMSO-[D6]): d (ppm) = 3.57 (s, 3H,
OCH3), 3.66 (s, br., 8H), 3.83 (s, 3H, OCH3), 6.74 (d, 1H,
3J = 8.7 Hz, aromat.), 6.83 (d, 1H, 3J = 8.7 Hz, aromat.), 6.95
(s, 1H, aromat.), 7.70–7.78 (m, 3H, aromat.), 8.28–8.32 (m,
2H, aromat.). EI-MS (70 eV) m/z (%): 330 (14) [M]+•, 289
(13), 204 (100), 176 (24), 77 (8). Anal. (C21H22N2O6S) Calc.
C 58.59, H 5.15, N 6.51. Found: C 58.41, H 5.42, N 6.10.
3
3.2.4.3. (1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
phenyl-methanone (10c). Yield: 2.82 g (85%) light yellow-
ish crystals, m.p.: 182.0–184.6 °C. IR (KBr): 3068, 1658 cm–1.
1H-NMR (DMSO-[D6]): d (ppm) = 3.62 (s, 3H, OCH3), 3.83
(s, 3H, OCH3), 6.65 (d, 1H, J = 8.6 Hz, aromat.), 6.71 (d,
1H, 3J = 8.6 Hz, aromat.), 6.78 (d, 1H, 3J = 3.8 Hz, aromat.),
3
7.59–7.74 (m, 3H, aromat.), 7.79 (d, 1H, J = 3.8 Hz, aro-
mat.), 7.84–7.87 (m, 2H, aromat.). EI-MS (70 eV) m/z (%):
317 (94) [M]+•, 176 (100), 148 (60), 146 (58), 133 (79).Anal.
(C16H15NO4S) Calc. C 60.55, H 4.76, N 4.41. Found: C 60.51,
H 4.89 N 4.53.
3
(s, 3H, OCH3), 6.80 (d, 1H, J = 8.7 Hz, aromat.), 6.96 (d,
3
1H, J = 8.7 Hz, aromat.), 7.11 (s, 1H, aromat.), 7.60–7.71
(m, 2H, aromat.), 7.72–7.79 (m; 4H, aromat.), 8.02–8.05 (m,
2H, aromat.), 8.27–8.30 (m, 2H, aromat.). EI-MS (70 eV)
m/z (%): 421 (11) [M]+•, 280 (40), 265 (12), 105 (100), 77
(40). Anal. (C23H19NO5S) Calc. C 65.55, H 4.54, N 3.32.
Found: C 65.69, H 4.72, N 3.21.
3.2.3. 1-Benzenesulfonyl-2-deutero-4,7-dimethoxy-1H-
indole (9a)
Lithiation of 9 and work up of 9a were performed as
described for 10a–10h. The lithiated species was quenched
with CD3OD, and 1H-NMR measurements were performed
to determine the amount of H/D-exchange (>90%). 1H-NMR
(DMSO-[D6]): d (ppm) = 3.54 (s, 3H, OCH3), 3.81 (s, 3H,
3.2.4.4. (1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
(3-methoxyphenyl)-methanone (10d). Yield: 2.85 g (80%)
light yellowish crystals, m.p.: 101.5–102.2 °C. IR (solid):
1660 cm–1. 1H-NMR (DMSO-[D6]): d (ppm) = 3.62 (s, 3H,
OCH3), 3.83 (s, 3H, OCH3), 3.86 (s, 3H, OCH3), 6.80 (d, 1H,
3J = 8.7 Hz, aromat.), 6.96 (d, 1H, 3J = 8.7 Hz, aromat.), 7.12
(s, 1H, aromat.), 7.32–7.36 (m, 1H, aromat.), 7.49–7.86 (m,
6H, aromat.), 8.27–8.31 (m, 2H, aromat.). Anal.
(C24H21NO6S) Calc. C 63.85, H 4.69, N 3.10. Found: C 63.80,
H 4.81, N 2.84.
3
OCH3), 6.65 (d, 1H, J = 8.6 Hz, aromat.), 6.71 (d, 1H,
3J = 8.6 Hz, aromat.), 6.78 (s, 1H, aromat.), 7.59–7.74 (m,
3H, aromat.), 7.84–7.87 (m, 2H, aromat.).
3.2.4.
(1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
ones (10a–10h)
To a stirred solution of 9 (2.50 g; 7.88 mmol) in 50 ml of
dry THF, n-butyllithium (5.41 ml 1.6 M in hexane; 8.66 mmol)
was added at –78 °C. The solution was stirred at this tempera-
ture for 2 h, until the indole-2-yl lithium precipitates. The
respective carbonic acid chloride (8.66 mmol) was added—in
case of solid carboxylic acid chlorides a solution in THF
(10.0 ml), pre-cooled to –78 °C—all at once. The mixture
was stirred for additional 2 h and allowed to reach room tem-
perature over night. Na2CO3 solution (200 ml; 2%) was added
to the stirred solution, the precipitating product removed by
filtration, purified (cc SiO2, CH2Cl2) and crystallized from
ethanol.
3.2.4.5. 1-(1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
(4-methoxyphenyl)-methanone (10e). Yield: 2.03 g (57%),
1
m.p.: 161.1–161.7 °C. IR (Solid): 1669 cm–1. H-NMR
(DMSO-[D6]): d (ppm) = 3.34 (s, 3H, OCH3), 3.83 (s, 3H,
3
OCH3), 3.90 (s, 3H, OCH3), 6.79 (d, 1H, J = 8.8 Hz, aro-
3
mat.), 6.94 (d, 1H, J = 8.7 Hz, aromat.), 7.06 (s, 1H, aro-
mat.), 7.16 (d, 2H, 3J = 8.8 Hz, aromat.), 7.70–7.82 (m, 3H,
3
aromat.), 8.04 (d, 2H, J = 8.8 Hz, aromat.), 8.32 (d, 2H,
3J = 8.0 Hz, aromat.). EI-MS (70 eV) m/z (%): 451 (35) [M]+•,
310 (100). Anal. (C24H21NO6S) Calc. C 63.85, H 4.69, N
3.10. Found: C 64.51, H 4.99, N 2.83.
3.2.4.1. 1-(1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
ethanone (10a). Instead of the carbonic acid chloride acetic
acid anhydride was used for condensation.Yield: 2.00 g (70%)
3.2.4.6. (1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
(3-fluorophenyl)-methanone (10f). Yield: 2.25 g (65%), m.p.:
1
172.5–172.6 °C. IR (KBr): 1655 cm–1. H-NMR (DMSO-

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S. Mahboobi et al. / European Journal of Medicinal Chemistry 40 (2005) 85–92
[D6]): d (ppm) = 3.62 (s, 3H, OCH3), 3.83 (s, 3H, OCH3),
6.81 (d, 1H, 3J = 8.8 Hz, aromat.), 6.98 (d, 1H, 3J = 8.8 Hz,
aromat.), 7.22 (s, 1H, aromat.), 7.60–7.84 (m, 6H, aromat.),
7.90 (d, 1H, 3J = 7.4 Hz, aromat.), 8.29 (d, 2H, 3J = 7.6 Hz,
aromat.). EI-MS (70 eV) m/z (%): 439 (33) [M]+•, 298 (78),
123 (100). Anal. (C23H18FNO5S) Calc. C 62.86, H 4.13, N
3.19. Found: C 62.77, H 4.28, N 3.17.
3H, aromat.), 8.41–8.44 (m, 2H, aromat.). Anal.
(C19H16N2O6S) Calc. C 56.99, H 4.03, N 7.00. Found: C
56.81, H 3.80, N 6.90.
3.2.5.3. 1-Benzenesulfonyl-2-benzoyl-1H-indole-4,7-dione
(11c). Yield: 1.08 g (92%) yellow crystals, m.p.: 184.5–
1
186 °C. IR (solid): 1668, 1658 cm–1. H-NMR (DMSO-
[D6]): d (ppm) = 6.82 (d, 1H, 3J = 10.3 Hz, quinone), 6.85 (d,
1H, 3J = 10.3 Hz, quinone), 7.11 (s, 1H, pyrrole), 7.60–7.90
(m, 6H, aromat.), 7.98–8.02 (m, 2H, aromat.), 8.33–8.37 (m,
2H, aromat.). EI-MS (70 eV) m/z (%): 391 (34) [M]+•, 250
(61), 77 (100).Anal. (C21H13NO5S) Calc. C 64.44, H 3.35, N
3.58. Found: C 64.42, H 3.42, N 3.49.
3.2.4.7. (1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
(3,5-difluorophenyl)-methanone (10g). Yield: 2.94 g (82%)
yellow crystals, m.p.: 159.0–159.1 °C. IR (KBr): 1655 cm–1.
1H-NMR (DMSO-[D6]): d (ppm) = 3.62 (s, 3H, OCH3), 3.84
3
(s, 3H, OCH3), 6.81 (d, 1H, J = 8.7 Hz, aromat.), 6.99 (d,
3
1H, J = 8.7 Hz, aromat.), 7.33 (s, 1H, aromat.), 7.68–7.82
3.2.5.4. 1-Benzenesulfonyl-2-(3-methoxybenzoyl)-1H-indole-
4,7-dione (11d). Yield: 1.06 g (84%) orange crystals, m.p.:
(m, 6H, aromat.), 8.26–8.30 (m, 2H, aromat.). EI-MS (70 eV)
m/z (%): 457 (50) [M]+• , 316 (86), 141 (100). Anal.
(C23H17F2NO5S) Calc. C 60.39, H 3.75, N 3.06. Found: C
60.80, H 3.69, N 2.84.
1
195.1–196.2 °C. IR (solid): 1663 cm-1. H-NMR (DMSO-
[D6]): d (ppm) = 3.85 (s, 3H, OCH3), 6.81 (d, 1H, 3J = 10.3 Hz,
3
quinone), 6.85 (d, 1H, J = 10.3 Hz, quinone), 7.11 (s, 1H,
pyrrole), 7.33–7.39 (m, 1H, aromat.), 7.36–7.58 (m, 3H, aro-
mat.), 7.74–7.90 (m, 3H, aromat.), 8.33–8.38 (m, 2H, aro-
mat.). EI-MS (70 eV) m/z (%): 421 (14) [M]+•, 280 (93), 77
(100). Anal. (C22H15NO6S) Calc. C 62.70, H 3.59, N 3.32.
Found: C 62.47, H 3.51, N 2.95.
3.2.4.8. (1-Benzenesulfonyl-4,7-dimethoxy-1H-indol-2-yl)-
(pentafluorophenyl)-methanone (10h). Yield: 1.70 g (42%)
yellow crystals, m.p.: 203.4–203.7 °C. IR (KBr): 1680 cm–1.
1H-NMR (DMSO-[D6]): d (ppm) = 3.64 (s, 3H, OCH3), 3.83
3
(s, 3H, OCH3), 6.83 (d, 1H, J = 8.8 Hz, aromat.), 7.07 (d,
1H, 3J = 8.8 Hz, aromat.), 7.72–7.84 (m, 4H, aromat.), 8.32–
8.36 (m, 2H, aromat.). EI-MS (70 eV) m/z (%): 511 (24)
[M]+•, 370 (56), 195 (100). Anal. (C23H13F5NO5S) Calc. C
54.02, H 2.76, N 2.74. Found: C 54.09, H 2.85, N 2.76.
3.2.5.5. 1-Benzenesulfonyl-2-(4-methoxybenzoyl)-1H-indole-
4,7-dione (11e). Yield: 0.87 g (69%) yellow crystals, m.p.:
1
153.3–155.4 °C. IR (KBr): 1673 cm–1. H-NMR (DMSO-
[D6]): d (ppm) = 3.90 (s, 3H, OCH3), 6.81 (d, 1H, 3J = 10.3 Hz,
3
quinone), 6.84 (d, 1H, J = 10.3 Hz, quinone), 7.06 (s, 1H,
pyrrole), 7.15 (d, 2H, 3J = 7 Hz, aromat.), 7.75–7.96 (m, 3H,
aromat.), 7.99 (d, 2H, 3J = 7 Hz, aromat.), 8.37–8.41 (m, 2H,
aromat.). EI-MS (70 eV) m/z (%): 421 (7) [M]+•, 280 (100).
Anal. (C22H15NO6S) Calc. C 62.70, H 3.59, N 3.32. Found:
C 62.73, H 3.89, N 3.58.
3.2.5. (1-Benzenesulfonyl-1H-indole-4,7-dione-2-yl)-ones
(11a–11h)
To a stirred solution of 10a–10h (3.00 mmol) in 30 ml of
CH3CN, ceric(IV)ammonium nitrate (4.93 g in 9 ml H2O;
9.00 mmol) was added at 20 °C. The solution/suspension was
stirred at room temperature for 30 min, diluted with water
(200 ml), and the precipitated yellow to orange product was
removed by filtration and purified by cc (SiO2, CH2Cl2). Crys-
tallization from CH2Cl2 by addition of hexane and remove-
ment of a part of the solvent under reduced pressure yielded
the desired products.
3.2.5.6. 1-Benzenesulfonyl-2-(3-fluorobenzoyl)-1H-indole-
4,7-dione (11f). Yield: 0.95 g (77%) yellow crystals, m.p.:
1
191.9–192.0 °C. IR (KBr): 1670 cm–1. H-NMR (DMSO-
[D6]): d (ppm) = 6.78–6.86 (m, 2H), 7.31 (s, 1H, pyrrole),
7.53–7.99 (m, 7H, aromat.), 8.31–8.37 (m, 2H, aromat.).
EI-MS (70 eV) m/z (%): 409 (6) [M]+•, 269 (100). Anal.
(C21H12FNO5S) Calc. C 61.61, H 2.95, N 3.42. Found: C
61.32, H 3.85, N 3.39.
3.2.5.1.
2-Acetyl-1-benzenesulfonyl-1H-indole-4,7-dione
(11a). Yield: 0.75 g (76%) yellow crystals, m.p.: 130.9–
1
131.4 °C. IR (KBr): 1710, 1671 cm–1. H-NMR (DMSO-
3.2.5.7. 1-Benzenesulfonyl-2-(3,5-difluorobenzoyl)-1H-indole-
4,7-dione (11g). Yield: 0.95 g (96%) orange crystals, m.p.:
[D6]): d (ppm) = 2.67 (s, 3H, CH3), 6.85 (s, 2H, quinone),
7.58 (s, 1H, pyrrole), 7.75–7.90 (m, 3H, aromat.), 8.46–8.50
(m, 2H, aromat.). EI-MS (70 eV) m/z (%): 329 (3) [M]+•, 265
(57), 77 (100).Anal. (C16H11NO5S) Calc. C 58.35, H 3.37, N
4.25. Found: C 57.98, H 3.59, N 4.28.
1
216.0–216.5 °C. IR (solid): 1673 cm–1. H-NMR (DMSO-
[D6]): d (ppm) = 6.81 (d, 1H, 3J = 10.3 Hz, quinone), 6.84 (d,
1H, 3J = 10.3 Hz, quinone), 7.26 (s, 1H, pyrrole), 7.70–7.90
(m, 6H, aromat.), 8.60–8.65 (m, 2H, aromat.). EI-MS (70 eV)
m/z (%): 427 (3) [M]+•, 287 (100). Anal. (C21H11F2NO5S)
Calc. C 59.02, H 2.59, N 3.28. Found: C 58.75, H 2.90, N
3.22.
3.2.5.2. 1-Benzenesulfonyl-2-(morpholine-4-carbonyl)-1H-
indole-4,7-dione (11b). Yield: 1.07 g (89%) yellow crystals,
m.p.: 215.2–215.7 °C. IR (KBr): 1671, 1638 cm–1. 1H-NMR
(DMSO-[D6]): d (ppm) = 3.50 (s br, 2H, CH2), 3.67 (s br, 6H,
3.2.5.8. 1-Benzenesulfonyl-2-pentafluorobenzoyl-1H-indole-
4,7-dione (11h). Yield: 1.00 g (69%) orange solid, m.p.:
3
CH2), 6.74 (d, 1H, J = 10.2 Hz, quinone), 6.89 (d, 1H,
3J = 10.2 Hz, quinone), 6.99 (s, 1H, pyrrole), 7.72–7.87 (m,
143.1–144.9 °C. IR (KBr): 1677, 1652 cm–1. H-NMR
1

S. Mahboobi et al. / European Journal of Medicinal Chemistry 40 (2005) 85–92
91
(DMSO-[D6]): d (ppm) = 6.82 (d, 1H, 3J = 10.4 Hz, quinone),
6.87 (d, 1H, 3J = 10.4 Hz, quinone),7.28–7.34 (m, 3H, aro-
mat.), 7.45 (s, 1H, pyrrole), 7.56–7.67 (m, 2H, aromat.).
EI-MS (70 eV) m/z (%): 481 (2) [M]+•, 417 (32), 141 (58),
77 (100). Anal. (C21H8F5NO5S) Calc. C 52.40, H 1.68, N
2.91. Found: C 52.37, H 1.79, N 2.94.
3.2.6.5. 2-(4-Methoxybenzoyl)-1H-indole-4,7-dione (12e).
Yield: 0.27 g (65%), m.p.: 224.4–224.5 °C. IR (KBr): 1677,
1667 cm–1. 1H-NMR (DMSO-[D6]): d (ppm) = 3.87 (s, 3H,
3
OCH3), 6.78 (d, 1H, J = 10.3 Hz, quinone), 6.82 (d, 1H,
3J = 10.3 Hz, quinone), 7.02 (s, 1H, pyrrole), 7.12 (d, 2H,
3
3J = 8.9 Hz, aromat.), 7.92 (d, 2H, J = 8.9 Hz, aromat.),
13.59 (s, 1H, NH). EI-MS (70 eV) m/z (%): 281 (100) [M]+•.
Anal. (C16H11NO4) C 68.33, H 3.94, N 4.98. Found: C 68.01,
H 3.89, N 4.79.
3.2.6. 1-(1H-indole-4,7-dione-2-yl)-ones (12a–12h)
To a stirred solution of 11a–11h (1.50 mmol) in 15 ml of
THF TBAF trihydrate (0.52 g, 1.65 mmol) was added at 20 °C.
The dark red solution was stirred at room temperature for
10 min, diluted with water (100 ml), the solution/
suspension acidified with hydrochloric acid and extracted with
CH2Cl2 (3 × 50 ml). The combined organic layers were dried
(Na2SO4) and purified by cc (SiO2, CH2Cl2, ethyl acetate 8:1).
Crystallization from CH2Cl2 by addition of hexane and
removement of a part of the solvent under reduced pressure,
yielding the products as orange crystals.
3.2.6.6. 2-(3-Fluorobenzoyl)-1H-indole-4,7-dione (12f).
Yield: 0.35 g (87%), m.p.: 198.0–198.5 °C (decomp.). IR
1
(KBr): 1668, 1635 cm–1. H-NMR (DMSO-[D6]): d (ppm)
= 6.80 (d, 1H, 3J = 10.3 Hz, quinone), 6.84 (d, 1H,
3J = 10.3 Hz, quinone), 7.09 (s, 1H, pyrrole), 7.53–7.76 (m,
4H, aromat.), 13.75 (s, 1H, NH). EI-MS (70 eV) m/z (%):
269 (100) [M]+•.Anal. (C15H8FNO3) C 66.92, H 3.00, N 5.20.
Found: C 66.82, H 3.08, N 5.27.
3.2.6.7. 2-(3,5-Difluorobenzoyl)-1H-indole-4,7-dione (12g).
3.2.6.1. 2-Acetyl-1H-indole-4,7-dione (12a). Yield: 0.07 g
(26%), m.p.: 189.9–190.5 °C. IR (KBr): 1653 cm–1. 1H-NMR
(DMSO-[D6]): d (ppm) = 3.35 (s, 3H, CH3), 6.76 (d, 1H,
3J = 10.6 Hz, quinone), 6.79 (d, 1H, 3J = 10.6 Hz, quinone),
7.36 (s, 1H, pyrrole), 13.4 (s, 1H, NH). EI-MS (70 eV) m/z
(%):189 (86) [M]+•, 174 (100). Anal. (C10H7NO3) Calc. C
63.49, H 3.73, N 7.40. Found: C 62.98, H 3.98, N 7.39.
Yield: 0.15 g (35%), m.p.: 234.2–234.8 °C (decomp.). IR
1
(solid): 1660, 1644 cm–1. H-NMR (DMSO-[D6]): d (ppm)
= 6.80 (d, 1H, 3J = 10.3 Hz, quinone), 6.84 (d, 1H,
3J = 10.3 Hz, quinone), 7.14 (s, 1H, pyrrole), 7.50–7.67 (m,
3H, aromat.), 13.77 (s, 1H, NH). EI-MS (70 eV) m/z (%):
287 (100) [M]+•. Anal. (C15H7F2NO3) C 62.73, H 2.46, N
4.88. Found: C 62.80, H 2.80, N 4.93.
3.2.6.8. 2-Pentafluorobenzoyl-1H-indole-4,7-dione (12h).
Yield: 0.23 g (45%), m.p.: 185.9–186 °C. IR (KBr):
1661 cm–1. 1H-NMR (DMSO-[D6]): d (ppm) = 6.82 (d, 1H,
3J = 10.3 Hz, quinone), 6.87 (d, 1H, 3J = 10.3 Hz, quinone),
7.45 (s, 1H, pyrrole), 14.08 (s, 1H, NH). EI-MS (70 eV) m/z
(%): 341 (100) [M]+•. Anal. (C15H4F5NO3) C 52.80, H 1.18,
N 4.11. Found: C 52.83, H 1.51, N 4.14.
3.2.6.2.
2-(Morpholine-4-carbonyl)-1H-indole-4,7-dione
(12b). Yield: 0.32 g (83%), m.p.: 230.6–230.7 °C. IR (KBr):
1655 cm–1. H-NMR (DMSO-[D6]): d (ppm) = 3.61 (s, br.,
1
8H, CH2), 6.69 (d, 1H, 3J = 10.3 Hz, quinone), 6.73 (d, 1H,
3J = 10.3 Hz, quinone), 6.80 (s, 1H, pyrrole), 13.2 (s, 1H,
NH). EI-MS (70 eV) m/z (%): 260 (90) [M]+•, 174 (100).
Anal. (C13H12N2O4) Calc. C 60.00, H 4.65, N 10.76. Found:
C 59.94, H 4.88, N 10.78.
References
3.2.6.3. 2-Benzoyl-1H-indole-4,7-dione (12c). Yield: 0.24 g
(65%), m.p.: 180.2–180.4 °C. IR (KBr): 1663, 1635 cm–1.
1H-NMR (DMSO-[D6]): d (ppm) = 6.79 (d, 1H, 3J = 10.3 Hz,
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71.71, H 3.61, N 5.57. Found: C 71.32, H 3.60, N 5.45.
3.2.6.4. 2-(3-Methoxybenzoyl)-1H-indole-4,7-dione (12d).
Yield: 0.26 g (61%), m.p.: 186.0–188.0 °C. IR (Solid): 1662,
1637 cm–1. 1H-NMR (DMSO-[D6]): d (ppm) = 3.84 (s, 3H,
3
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1H, aromat.), 7.34–7.36 (m, 1H, aromat.) 7.44–7.54 (m, 2H,
aromat.), 13.65 (s, 1H, NH). EI-MS (70 eV) m/z (%): 281
(100) [M]+•. Anal. (C16H11NO4) C 68.33, H 3.94, N 4.98.
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