Quinols as Novel Therapeutic Agents
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 2 643
To a stirring solution of n-butyllithium (3.3 mL, 1.6 M in
hexanes, 5.2 mmol) in THF (7 mL) at -78 °C was added a
solution of sulfonylindole (5a, 5b, 3.5 mmol) in THF (7 mL)
dropwise, under a nitrogen atmosphere. Following addition,
the solution was stirred at -78 °C for 1.5 h. The resultant
solution was added via cannula to a stirring solution of freshly
prepared 4,4-dimethoxy-4H-naphthalen-1-one (0.54 g, 3.5
mmol) in THF (14 mL) at -78 °C. Following addition, the
solution was stirred at -78 °C for 2 h. After this time, the
resultant solution was poured into brine (25 mL) and extracted
with CH2Cl2 (3 × 25 mL). The combined organic layer was
washed with water (3 × 20 mL), brine (2 × 20 mL), dried
(MgSO4), filtered, and evaporated to dryness. The dark oil was
redissolved in acetone (20 mL) and 10% aqueous acetic acid
(20 mL) and heated at reflux for 1 h. After this time, the
solution was allowed to cool to room temperature and extracted
with CH2Cl2 (3 × 25 mL). The combined organic layer was
washed with water (3 × 20 mL) and brine (2 × 20 mL), dried
(MgSO4), filtered, and evaporated to dryness. Purification by
flash column chromatography (4:1 hexane: EtOAc) gave the
required benzo-annelated (indolyl)quinol (7a, 7b) as white
solids.
Synthesis of 4-(Benzimidazol-2-yl)-4-hydroxy-2,5-cy-
clohexadien-1-one (10). To N-(N-pyrrolidinomethyl)benz-
imidazole10 (0.571 g, 2.84 mmol) in dry THF (20 mL) under
nitrogen was added n-butyllithium (1.25 mL of 2.5 M solution,
3.12 mmol) dropwise with stirring at -78 °C. After 1 h, 4,4-
dimethoxycyclohexadienone (0.437 g, 2.84 mmol) was added
dropwise with stirring. After a further 2 h, the reaction was
allowed to rise to room temperature, 2 M HCl (20 mL) was
added, and the volume was reduced under vacuum. The pH
was adjusted to 6-7 with 1 M sodium hydrogen carbonate
solution to form a white precipitate which was collected by
filtration, washed with water, and dried under vacuum to give
a white solid (0.30 g, 47%).
tially more potent than the recently reported antitumor
4-substituted 4-hydroxycyclohexa-2,5-dien-1-ones1 with
similar patterns of selectivity against colon, renal, and
breast cell lines. For example, the most potent com-
pound in the series, the 6-fluoro analogue 1h, exhibits
a mean GI50 value of 16 nM and mean LC50 value of
2.24 µM in the NCI 60-cell-line screen, with LC50
activity in the HCT 116 human colon cancer cell line
below 10 nM. In vivo, significant antitumor activity was
recorded (day 28) in mice bearing subcutaneously
implanted MDA-MB-435 xenografts, following intra-
peritoneal treatment of mice with compound 1a at 50
mg/kg.
Experimental Section
All new compounds were characterized by elemental micro-
analysis (C, H, and N values within 0.4% of theoretical values).
Melting points were determined using a Gallenkamp melting
point apparatus and are reported uncorrected. 1H and 13C
NMR spectra were recorded on a Bruker ARX250 spectrom-
eter. IR spectra (as KBr disks) were determined on a Perkin-
Elmer Spectrum One FT-IR spectrometer. Mass spectra were
recorded on an AEI MS-902 or a VG Micromass 7070E
spectrometer. TLC systems for routine monitoring of reaction
mixtures and for confirming the homogeneity of analytical
samples used Kieselgel 60F254 (0.25 mm) silica gel TLC
aluminum sheets. Sorbsil silica gel C 60-H (40-60 µm) was
used for flash chromatographic separations. All reactions were
carried out under inert atmosphere using anhydrous reagents
and solvents. THF was dried and purified before use by
distillation from sodium-benzophenone. All other commercial
materials were used as received.
General Method for the Synthesis of 1-(Arylsulfonyl)-
indoles (5a-i).6 To a vigorously stirring solution of indole (8.5
mmol, 3a-d) and tetrabutylammonium hydrogen sulfate
(TBAHS) (1.28 mmol) in toluene (25 mL) at 0 °C was added
50% aqueous sodium hydroxide (25 mL) and sulfonyl chloride
(12.8 mmol, 4a-e). The resultant solution was stirred at room
temperature for 16 h. After this time, the organic layer was
separated; washed with 1 N HCl (2 × 25 mL), saturated
aqueous NaHCO3 (2 × 25 mL), water (25 mL), brine (25 mL);
dried (MgSO4); and evaporated to dryness to yield 1-(arylsul-
fonyl)indoles (5a-h), which were used in subsequent steps
without further purification. 1-(2-Naphthylsulfonyl)indole (5i)
was prepared in a similar manner from indole and 2-naphthyl-
sulfonyl chloride.
General Method for the Synthesis of 4-(1-Arylsulfonyl-
1H-indol-2-yl)-4-hydroxycyclohexa-2,5-dienones (1a-i).
To a stirring solution of n-butyllithium (3.3 mL, 1.6 M in
hexanes, 5.2 mmol) in THF (7 mL) at -78 °C was added a
solution of 1-(arylsulfonyl)indole (3.5 mmol, 5a-i) in THF (7
mL) dropwise, under a nitrogen atmosphere. Following addi-
tion, the solution was stirred at -78 °C for 1.5 h. After this
time, the resultant solution was added via cannula to a stirring
solution of 4,4-dimethoxycyclohexa-2,5-dienone (0.54 g, 3.5
mmol) in THF (14 mL) at -78 °C. Following addition, the
solution was stirred at -78 °C for 2 h. After this time, the
resultant solution was poured into brine (25 mL) and extracted
with CH2Cl2 (3 × 25 mL). The combined organic layer was
washed with water (3 × 20 mL) and brine (2 × 20 mL), dried
(MgSO4), filtered, and evaporated to dryness. The resulting
oil (6a-i) was redissolved in acetone (20 mL), and 10%
aqueous acetic acid (20 mL) added followed by heating at reflux
for 1 h. After this time, the solution was allowed to cool to
room temperature and extracted with CH2Cl2 (3 × 25 mL).
The combined organic layer was washed with water (3 × 20
mL) and brine (2 × 20 mL), dried (MgSO4), filtered, and
evaporated to dryness. Purification by flash column chroma-
tography (4:1 hexane: EtOAc) yielded products 1a-i in low to
moderate yields.
Synthesis of 4-(Indol-2-yl)-4-hydroxy-2,5-cyclohexa-
dien-1-one (11). To N-(dimethylaminomethyl)indole11 (0.57
g, 3.2 mmol) dissolved in THF (10 mL) under nitrogen was
added n-butyllithium (2.02 mL of 1.6 M solution, 3.2 mmol)
at -78 °C. After 10 min the reaction was warmed to 0 °C over
35-40 min and then cooled again to -78 °C, and 4,4-
dimethoxycyclohexadienone (0.5 g, 3.2 mmol) was added. After
stirring at -78 °C for 1 h, the reaction was warmed to room
temperature over several hours, quenched by the addition of
water (20 mL), and then extracted with diethyl ether (2 × 20
mL). The organic fractions were combined, dried over sodium
sulfate, and concentrated in vacuo. The residue was dissolved
in ethanol:THF (1:1, 10 mL), sodium borohydride (0.135 g, 3.5
mmol, 1.1 equiv) added, and the reaction stirred at reflux for
5 h. After cooling to room temperature, the solvent was
removed in vacuo. The residue was dissolved in acetone (20
mL), 10% aqueous acetic acid (20 mL) was added, and the
reaction was stirred overnight. After cooling to room temper-
ature, the acetone was removed under reduced pressure and
the aqueous phase extracted with ether (2 × 20 mL). The
combined organic layers were washed with saturated sodium
hydrogen carbonate solution (20 mL) and water (20 mL), dried,
and concentrated under vacuum. The crude product was
purified by flash column chromatography (ethyl acetate/hexane
1:4) to give a white solid (0.19 g, 26%).
In Vitro Assays. Compounds were prepared as 10 mM top
stocks, dissolved in DMSO, and stored at 4 °C, protected from
light for a maximum period of 4 weeks. Human-derived cell
lines (HCT 116, HT29 colon carcinoma; MCF-7 (ER+), MDA
468 (ER-) breast carcinoma) were routinely cultivated at 37
°C in an atmosphere of 5% CO2 in RPMI 1640 medium
supplemented with 2 mM L-glutamine and 10% fetal calf
serum and subcultured twice weekly to maintain continuous
logarithmic growth. Cells were seeded into 96-well microtiter
plates at a density of 5 × 103 per well and allowed 24 h to
adhere before drugs were introduced (final concentration 0.1-
100 µM, n ) 8). Serial drug dilutions were prepared in medium
immediately prior to each assay. At the time of drug addition
and following 72 h of exposure, MTT was added to each well
General Method for the Synthesis of 4-(1-Arylsulfonyl-
1H-indol-2-yl)-4-hydroxy-4H-naphthalen-1-ones (7a,b).