1860
H. GAO and J. KAWABATA
1
360.0845); H-NMR ꢁ (DMSO-d6) ppm: 3.73 (3H, 40-
OMe), 3.89 (6H, 30 and 50-OMe), 6.64 (1H, s, 8-H), 7.01
(1H, s, 3-H), 7.31 (2H, s, 20 and 60-H), 12.67 (1H, s,
5-OH).
eluent, to yield crude 11. This was further purified by
preparative HPLC (mobile phase, water–methanol–for-
mic acid (40:60:0.1); flow rate, 4.5 ml/min; detection,
UV 254 nm) to give 11 (tR 18 min, 79 mg, 82%) as
yellow powder: mp > 300 ꢁC; FD-HR-MS m=z
30,40,5,50,6,7-Hexahydroxyflavone (9). A mixture of 8
(75.6 mg, 0.21 mmol), 47% aqueous hydrobromic acid
(1.4 ml, 12.6 mmol) and acetic acid (11.2 ml) was heated
under reflux for 23 hr. After cooling to room temper-
ature, the reaction mixture was extracted with 1-butanol
(2 ꢀ 50 ml). The organic phase was washed with water
and concentrated to dryness. The residue was dissolved
in a small amount of methanol and subjected to reverse-
phase column chromatography, using water–methanol–
formic acid (50:50:0.1) as the eluent, to yield crude 9.
This was further purified by preparative HPLC (mobile
phase, water–methanol–formic acid (50:50:0.1); flow
rate, 5.0 ml/min; detection, UV 254 nm) to give 9 (tR
18 min, 52 mg, 82%) as pale yellow powder: mp >
300 ꢁC; FD-HR-MS m=z 318.0389 (calcd. for C15H10O8,
302.0400 (calcd. for C15H10O7, 302.0426); H-NMR ꢁ
1
(DMSO-d6) ppm (J in Hz): 6.51 (1H, s, 3-H), 6.55 (1H,
s, 8-H), 6.88 (2H, d, J ¼ 8:9, 50-H), 7.36–7.37 (2H, m, 20
and 60-H).
5,7-Dihydroxy-40-methoxyflavone (12a). 4-Methoxy-
benzoyl chloride (4.08 g, 24 mmol) was reacted with
20,40,60-trihydroxyacetophenone (3.36 g, 20 mmol) in a
similar way to that described for 8a to give 12a (2.56 g,
45%) as yellow crystals: mp 260–261 ꢁC; FD-HR-MS
m=z 284.0666 (calcd. for C16H12O5, 284.0685); 1H-
NMR ꢁ (DMSO-d6) ppm (J in Hz): 3.85 (3H, s, 40-
OMe), 6.19 (1H, d, J ¼ 2:0, 6-H), 6.49 (1H, d, J ¼ 2:0,
8-H), 6.86 (1H, s, 3-H), 7.10 (2H, d, J ¼ 8:9, 30 and 50-
H), 8.02 (2H, d, J ¼ 8:9, 20 and 60-H), 10.88 (1H, s, 7-
OH), 12.92 (1H, s, 5-OH).
1
318.0375); H-NMR ꢁ (DMSO-d6) ppm: 6.48 (1H, s, 3-
H), 6.49 (1H, s, 8-H), 6.94 (2H, s, 20 and 60-H), 12.78
(1H, s, 5-OH).
5,6,7-Trihydroxy-40-methoxyflavone (12). By the same
method as that used for 10, 12a (1.7 g, 6 mmol) was
converted to 12. After separating by reverse-phase
column chromatography, using water–methanol–formic
acid (60:40:0.1) as the eluent, the crude material was
further purified by preparative HPLC (mobile phase,
water–methanol–formic acid (30:70:0.1); flow rate,
4.5 ml/min; detection, UV 254 nm) to give 12 (tR
26 min, 84 mg, 28%) as yellow powder: mp 274 ꢁC;
FD-HR-MS m=z 300.0644 (calcd. for C16H12O6,
300.0634); 1H-NMR ꢁ (DMSO-d6) ppm (J in Hz):
3.85 (3H, s, 40-OMe), 6.59 (1H, s, 8-H), 6.82 (1H, s, 3-
H), 7.10 (2H, d, J ¼ 8:8, 30 and 50-H), 8.02 (2H, d,
J ¼ 8:8, 2 and 60-H), 12.75 (1H, s, 5-OH).
5,7-Dihydroxy-30,40-dimethoxyflavone (10a). 3,4-Di-
methoxybenzoyl chloride (4.8 g, 24 mmol) was reacted
with 20,40,60-trihydroxyacetophenone (3.36 g, 20 mmol)
in a similar way to that described for 8a to give 10a
(1.88 g, 30%) as yellow crystals: mp 288–289 ꢁC; FD-
HR-MS m=z 314.0789 (calcd. for C17H14O6, 314.0790);
1H-NMR ꢁ (DMSO-d6) ppm (J in Hz): 3.84 and 3.87
(3H each, s, 30 and 40-OMe), 6.20 (1H, d, J ¼ 1:3, 6-H),
6.52 (1H, d, J ¼ 1:3, 8-H), 6.96 (1H, d, J ¼ 0:5, H-3),
7.12 (2H, d, J ¼ 8:4, 50-H), 7.56 (1H, d, J ¼ 1:4, 20-H),
7.67 (1H, dd, J ¼ 1:4, 8.4, 60-H), 10.82 (1H,s,7-OH),
12.92(1H,s, 5-OH).
5,6,7-Trihydroxy-30,40-dimethoxyflavone (10). By the
same method as that used for 8b, 10a (1.9 g, 6 mmol)
was acetylated to 6-acetyl-5,7-dihydroxy-30,40-dime-
thoxyflavone, this in turn being oxidized to 10 by the
same method as that used for 5. Crude 10 was purified
by preparative HPLC (mobile phase, water–methanol–
formic acid (30:70:0.1); flow rate, 4.5 ml/min; detec-
tion, UV 254 nm) to give 10 (tR 16 min, 63 mg, 21%) as
yellow powder: mp 254 ꢁC; FD-HR-MS m=z 330.0728
6-Hydroxyapigenin (13). Compound 12 (125 mg,
0.42 mmol) was treated with 47% aqueous hydrobromic
acid (4.2 ml, 4.2 mmol) and acetic acid (4 ml) as
described for the formation of 9 from 8. After separating
by reverse-phase column chromatography, using water–
methanol–formic acid (50:50:0.1) as the eluent, the
crude material was further purified by preparative HPLC
(mobile phase, water–methanol–formic acid (40:60:0.1);
flow rate, 4.5 ml/min; detection, UV 254 nm) to give 13
(tR 15 min, 98 mg, 82%) as yellow powder: mp >
300 ꢁC; FD-HR-MS m=z 286.0502 (calcd. for C15H10O6,
1
(calcd. for C17H14O7, 330.0739); H-NMR ꢁ (DMSO-
d6) ppm (J in Hz): 3.84 and 3.87 (3H each, s, 30 and 40-
OMe), 6.61 (1H, s, 8-H), 6.92 (1H, s, 3-H), 7.11 (1H, d,
J ¼ 8:6, 50-H), 7.55 (1H, d, J ¼ 2:0, 20-H), 7.66 (1H, dd,
J ¼ 8:6, 2.0, 60-H), 12.75 (1H, s, 5-OH).
1
286.0477); H-NMR ꢁ (DMSO-d6) ppm (J in Hz): 6.56
(1H, s, 8-H), 6.55 (1H, s, 3-H), 6.91 (2H, d, J ¼ 8:7,
30 and 50-H), 7.90 (2H, d, J ¼ 8:7, 20 and 60-H), 12.78
(1H, s, 5-OH).
6-Hydroxyluteolin (11). Compound 10 (105 mg, 0.32
mmol) was treated with 47% aqueous hydrobromic acid
(1.08 ml, 9.6 mmol) and acetic acid (9 ml) as described
for the formation of 9 from 8. The resulting solid was
subjected to reverse-phase column chromatography,
using water–methanol–formic acid (50:50:0.1) as the
5,7-Dihydroxy-20-methoxyflavone (14a). 2-Methoxy-
benzoyl chloride (4.08 g, 24 mmol) was reacted with
20,40,60-trihydroxyacetophenone (3.36 g, 20 mmol) in a
similar way to that described for 8a to give 12a (1.82 g,
32%) as yellow powder: mp 279–282 ꢁC (lit.9) 281–