1164
Vol. 52, No. 10
anticancer properties. In this study, compound modification FAB-MS: m/z [MꢅH]ꢅ 360. Anal. (C18H17NO7) Calcd C, 60.17; H, 4.74.
Found C, 60.46; H, 4.59.
6ꢀ-Hydroxy-2,2ꢀ,3ꢀ,4ꢀ-tetramethoxychalcone (7c) According to gen-
eral procedure A, the title compound was obtained as an orange solid: mp
at B-ring of the trimethylbaicalein skeleton, e.g. 8b (4ꢃ-NO2),
8e (4ꢃ-OCH3), 8f (3ꢃ-OH), and 9 (4ꢃ-NH2) showed impres-
sive potency against Hep G2 cells, whereas 8a, 8b and 8f
128—131 °C; UV (EtOH): lmax nm (log e)ꢀ363 (4.05), 282 (4.04); IR
(KBr): n cmꢄ1ꢀ3419 (OH), 1608 (CO), 1541 (CꢀC); H-NMR (300 MHz,
DMSO-d6): d 3.77 (3H, s, OCH3) , 4.00 (3H, s, OCH3) , 4.01 (3H, s, OCH3),
4.09 (3H, s, OCH3), 6.59 (1H, s, H-5ꢃ), 7.12 (1H, t, Jꢀ8.4 Hz, H-5), 7.23
(1H, d, Jꢀ8.4 Hz, H-3), 7.60 (1H, t, Jꢀ8.4 Hz, H-4), 7.86 (1H, d, Jꢀ8.1 Hz,
H-6) , 8.22 (1H, d, Jꢀ15.6 Hz, H-a), 8.46 (1H, d, Jꢀ15.6 Hz, H-b); FAB-
MS (NBA as matrix): m/z [MꢅH]ꢅ 345. Anal. (C19H20O6) Calcd C, 66.27;
H, 5.85. Found C, 66.52; H, 5.58.
1
also exhibited potent inhibition of proliferation of Hep 3B
cells. These results suggested that triple methoxy groups at
A-ring of baicalein skeleton could be a suitable lead toward
potent inhibitors against certain Hep cancers. Modification of
B-ring with certain common electrowithdrawal or elec-
trodonating groups at the 4ꢃ-position would provide im-
proved antiproliferative activities. Recently, Chan and
co-workers reported that baicalein caused a 50% inhibition
of DU145 cells only at a concentration of 150 mM or above.12)
In our study, derivatives 8b and 8f showed more potency
against DU145 cells than baicalein.
6ꢀ-Hydroxy-2ꢀ,3,3ꢀ,4ꢀ-tetramethoxychalcone (7d) According to gen-
eral procedure A, the title compound was obtained as an orange solid: mp
174—176 °C; UV (EtOH): lmax nm (log e)ꢀ322 (3.02), 209 (3.36); IR
(KBr): n cmꢄ1ꢀ3061 (OH), 1635 (CO), 1598 (CꢀC); H-NMR (300 MHz,
1
DMSO-d6) d 3.72 (3H, s, OCH3), 3.83 (3H, s, OCH3), 3.85 (3H, s, OCH3),
3.86 (3H, s, OCH3), 6.41 (1H, s, H-5ꢃ), 7.14 (1H, d, H-4), 7.23—7.30 (3H,
H-2, 5, 6), 7.57 (2H, s, H-a, b); FAB-MS (NBA as matrix): m/z [MꢅH]ꢅ
345.1. Anal. (C19H20O6) Calcd C, 66.27; H, 5.85. Found C, 66.49; H, 5.67.
6ꢀ-Hydroxy-2ꢀ,3ꢀ,4ꢀ,4-tetramethoxychalcone (7e) According to gen-
eral procedure A, the title compound was obtained as a golden yellow solid:
mp 201—204 °C; UV (EtOH): lmax nm (log e)ꢀ364.0 (4.41); 1H-NMR
(300 MHz , DMSO-d6) d 3.90 (3H, s, –OCH3), 3.96 (3H, s, –OCH3), 4.03
(3H, s, –OCH3), 4.10 (3H, s, –OCH3), 6.43 (1H, s, H-5ꢃ), 7.06 (2H, d,
Jꢀ9.0 Hz, H-3, 5), 7.75 (2H, d, Jꢀ8.7 Hz, H-2, 6), 8.03 (2H, d, Jꢀ15.3 Hz,
H-a), 8.44 (2H, Jꢀ15.0 Hz, H-b); FAB-MS (NBA as matrix): m/z [MꢅH]ꢅ
345. Anal. (C19H20O6) Calcd C, 66.27; H, 5.85. Found C, 66.48; H, 5.76.
3,6ꢀ-Dihydroxy-2ꢀ,3ꢀ,4ꢀ-trimethoxychalcone (7f) According to general
procedure A, the title compound was obtained as a golden yellow solid: mp
87—89 °C; UV (EtOH): lmax nm (log e) 322 (4.09), 208 (4.45); IR (KBr): n
cmꢄ1ꢀ3323 (OH), 1635 (CꢀO), 1558 (CꢀC); 1H-NMR (300 MHz, DMSO-
d6) d 3.84 (3H, s, 3ꢃ-OCH3), 3.89 (3H, s, 4ꢃ-OCH3), 3.91 (3H, s, 2ꢃ-OCH3),
6.30 (1H, s, H-5ꢃ), 6.90 (1H, d, Jꢀ7.26 Hz, H-4), 7.13 (1H, s, H-2), 7.17
(1H, d, Jꢀ7.8 Hz, H-6), 7.26 (1H, t, Jꢀ7.8 Hz, H-5), 7.74 (1H, d,
Jꢀ15.7 Hz, H-a), 7.90 (1H, d, Jꢀ15.6 Hz, H-b), EI-MS: m/z [M]ꢅ 330.
Anal. (C18H18O6) Calcd C, 65.43; H, 5.50. Found C, 65.17; H, 5.79.
Conclusion
In summary, new trimethylbaicalein derivatives 8b and 8f
were found to be much more potent than baicalein against
certain Hep cancer cells and showed moderate potency to
inhibit proliferation of DU145 cells. Although compound 9
had a much weaker inhibitory effect on prostate DU145, it
showed impressive potency against Hep G2 cells among
these derivatives. Recent investigations on the structure–ac-
tivity relationships of combretastatin A4 have come up with
some potent analogues with antimitotic activities.16) These
results suggested that baicalein would be an attractive and
promising leader in the treatment of certain Hep cancers.
Further, manipulation of baicalein derivatives with trimetho-
xyflavone pharmacophore would be worth developing poten-
tial candidates for human malignant cancers. The study is in
progress and will be reported in due course.
General Procedure B To a solution of a chalcone derivative (7) in
DMSO (30 ml) was added iodine (0.1 g, 0.4 mmol) and the mixture was
heated under reflux for 2 h and then poured into ice water to precipitate the
product. The crude product was filtered and dissolved in ethyl acetate, and
washed with 10% aqueous sodium thiosulfate (2ꢆ150 ml). The organic layer
was dried over anhydrous sodium sulfate and the solvent was evaporated in
vacuum to dryness. The resulting residue, in each case, was crystallized
from ethanol to give the desired product 8.
5,6,7-Trimethylbaicalein (8a) According to general procedure B, 7a
(3.14 g, 10 mmol) was oxidized to yield the title compound (2.81 g, 90%) as
a yellow solid: mp 161—163 °C (lit.13) 160—162 °C ); UV (EtOH): lmax nm
(log e)ꢀ306.5 (4.11), 263.5 (4.14), 214.0 (4.36); IR (KBr): n cmꢄ1ꢀ3419
(OH), 1608 (CO), 1546 (CꢀC); 1H-NMR (300 MHz, DMSO-d6) d 3.99
(3H, s, 6-OCH3), 4.05 (3H, s, 7-OCH3), 4.06 (3H, s, 5-OCH3), 6.74 (1H, s,
H-8), 6.89 (1H, s, H-3), 7.57—7.59 (3H, m, H-3ꢃ,4ꢃ,5ꢃ); 7.95 (2H, dd,
Jꢀ6.6, 1.3 Hz, H-2ꢃ,6ꢃ); EI-MS (70 eV): m/z [M]ꢅ 312. Anal. (C18H16O5)
Calcd C, 69.24; H, 5.12. Found C, 68.95; H, 4.88.
Experimental
Chemistry All reagents were commercial materials and were used di-
rectly unless otherwise noted. DMF was dehydrated over 4 Å molecular
1
sieves. NMR spectra were recorded on a Varian Gemini at 300 MHz for H
and at 75 MHz for 13C. Elemental analyses were determined using a Perkin-
Elmer 240 EA analyzer. Chromatography refers to flash chromatography on
silica gel (silica gel 60, 230—400 mesh ASTM, E. Merck). Melting points
were recorded on a Thomas Hoover capillary melting point apparatus in
open capillary tubes and are uncorrected.
General Procedure A A solution of a cinnamic acid derivative (5) in
dichloromethane (10 ml) was cooled to 0—5 °C under N2 with an ice-water
bath. Oxalyl chloride (12 mmol) was added via syringe followed by a trace
amount of anhydrous DMF. After maintaining at 0—5 °C for 2 h, the reac-
tion mixture was concentrated in vacuum to give the corresponding chloride
6, which was used directly without further purification. To a mixture of the
acyl chloride 6 and 3,4,5-trimethoxyphenol (4, 10 mmol) was slowly added
BF3–Et2O (10 ml) via syringe. The reaction mixture was then heated under
reflux for 30 min and cooled to room temperature to give a precipitate,
which was washed with ether and collected by filtration to give the desired
product 7.
6ꢀ-Hydroxy-2ꢀ,3ꢀ,4ꢀ-trimethoxychalcone (7a) According to general
procedure A, the title compound was obtained as an orange solid: mp 194—
196 °C; UV (MeOH) lmax nm (log e)ꢀ321 (4.46), 218 (4.48); IR (KBr)
n cmꢄ1ꢀ3421 (br, OH), 1618 (CꢀO), 1595 (CꢀC); 1H-NMR (300 MHz,
DMSO-d6) d 3.85 (3H, s, 3ꢃ-OCH3), 3.99 (3H, s, 4ꢃ-OCH3), 4.06 (3H, s,
2ꢃ-OCH3), 6.37 (1H, s, H-5ꢃ), 7.46—7.51 (3H, m, H-3,4,5), 7.71 (2H, d,
Jꢀ6.2 Hz, H-2,6), 8.06 (2H, d, Jꢀ15.4 Hz, H-a), 8.37 (2H, d, Jꢀ15.4 Hz,
H-b); EI-MS: m/z [M]ꢅ 314. Anal. (C18H18O5) Calcd C, 68.76; H, 5.76.
Found C, 68.55; H, 5.97.
4ꢀ-Nitro 5,6,7-Trimethylbaicalein (8b) According to general procedure
B, 7b (3.59 g, 10 mmol) was oxidized to yield the title compound (3.03 g,
85%) as
a brown solid: mp 182—185°C; UV (EtOH): lmax nm
(log e)ꢀ205.5 (4.24), 316.5 (4.08); IR (KBr): n cmꢄ1ꢀ1649 (CO); 1H-NMR
(300 MHz, DMSO-d6) d 3.91 (3H, s, 6-OCH3), 3.98 (3H, s, 7-OCH3), 3.99
(3H, s, 5-OCH3); 6.74 (1H, s, H-8), 6.82 (1H, s, H-3), 8.04 (2H, d,
Jꢀ9.3 Hz, H-2ꢃ,6ꢃ); 8.35 (2H, d, Jꢀ8.7 Hz, H-3ꢃ,5ꢃ); EI-MS (70 eV): m/z
[M]ꢅ 357. Anal. (C18H15NO7) Calcd C, 60.52; H, 4.20. Found C, 60.24, H
3.96.
2ꢀ-Methoxy-5,6,7-trimethylbaicalein (8c) According to general proce-
dure B, 7c (3.44 g, 10 mmol) was oxidized to yield the title compound
(2.94 g, 86%) as a yellow solid: mp 76—78 °C; UV (EtOH): lmax nm
(log e)ꢀ318.0 (4.64), 263.0 (4.71); IR (KBr): n cmꢄ1ꢀ1636 (CO), 1560
(CꢀC); 1H-NMR (300 MHz, DMSO-d6) d 3.91 (3H, s, OCH3), 3.92 (3H, s,
OCH3), 3.95 (3H, s, OCH3), 3.98 (3H, s, OCH3), 6.76 (1H, s, H-8), 6.96
(1H, s, H-3), 7.04 (1H, d, Jꢀ8.4 Hz, H-3ꢃ), 7.08 (1H, t, Jꢀ8.4 Hz, H-4ꢃ),
7.45 (1H, t, Jꢀ8.4 Hz, H-5ꢃ), 7.83 (1H, dd, Jꢀ7.7, 1.2 Hz, H-6ꢃ); FAB-MS
(NBA as matrix): m/z [MꢅH]ꢅ 343. Anal. (C19H18O6) Calcd C, 66.66; H,
5.30. Found C, 66.94; H, 4.98.
6ꢀ-Hydroxy-2ꢀ,3ꢀ,4ꢀ-trimethoxy-4-nitrochalcone (7b) According to
general procedure A, the title compound was obtained as an orange solid:
mp 180—182 °C; 1H-NMR (300 MHz, DMSO-d6) d 3.84 (3H, s, 3ꢃ-OCH3),
3.93 (3H, s, 4ꢃ-OCH3), 3.95 (3H, s, 2ꢃ-OCH3), 6.32 (1H, s, H-5ꢃ), 7.78 (2H,
d, Jꢀ6.2 Hz, H-2, 6), 8.03 (2H, d, Jꢀ6.2 Hz, H-3, 5), 8.28 (2H, d, H-a, b);
3ꢀ-Methoxy-5,6,7-trimethylbaicalein (8d) According to general proce-