Studies of the selective O-alkylation and dealkylation of flavonoids. VIII. Synthesis of pedaliin.
作者:TOKUNARU HORIE、MASAO TSUKAYAMA、HIROKI KOURAI、YOSHIKAZU NAKAYAMA、MITSURU NAKAYAMA
DOI:10.1248/cpb.34.30
日期:——
3', 4'-Bis(benzyloxy)-6-hydroxy-5, 7-dimethoxyflavone (15) was obtained from 6-hydroxy-2, 4-dimethoxy-3-(methoxymethoxy)acetophenone (13) via 6'-hydroxy-2', 4'-dimethoxy-3'-methoxy-methoxy-2-[3, 4-bis(benzyloxy)benzoyl]acetophenone (14). The 5-methoxyl group of the acetate (16) of the flavone (15) was selectively split with about 5% (w/v) anhydrous aluminum chloride in acetonitrile to give 6-acetoxy-3', 4'-bix(benzyloxy)-5-hydroxy-7-methoxyflavone (17). The 5-hydroxyflavone (17) was converted into 3', 4', 5-tris(benzyloxy)-6-hydroxy-8-methoxyflavone (20) by benzylation and hydrolysis. Condensation of the 6-hydroxyflavone (20) with 2, 3, 4, 6-tetra-O-acetyl-α-D-glucosyl bromide, folowed by hydrolysis of the resultant compound afforded the corresponding 6-O-β-D-glucoside (22), which was converted into 3', 4', 5, 6-tetrahydroxy-7-methoxyflavone 6-O-β-D-glucoside (pedaliin) (1) by hydrogenolysis. The process should be useful as a general method for synthesizing 6-O-glucosides of 5, 6-dihydroxy-7-methoxyflavones.
3', 4'-双(苄氧基)-6-羟基-5, 7-二甲氧基黄酮(15)是由6-羟基-2, 4-二甲氧基-3-(甲氧基甲氧基)苯乙酮(13)通过6'-羟基得到-2', 4'-二甲氧基-3'-甲氧基-甲氧基-2-[3, 4-双(苄氧基)苯甲酰基]苯乙酮(14)。黄酮(15)的乙酸酯(16)的5-甲氧基用约5%(w/v)无水氯化铝的乙腈溶液选择性裂解,得到6-乙酰氧基-3',4'-联(苄氧基) -5-羟基-7-甲氧基黄酮(17)。通过苄基化和水解将5-羟基黄酮(17)转化为3',4',5-三(苄氧基)-6-羟基-8-甲氧基黄酮(20)。 6-羟基黄酮(20)与2,3,4,6-四-O-乙酰基-α-D-葡萄糖基溴缩合,然后水解所得化合物,得到相应的6-O-β-D-葡萄糖苷(22),通过氢解转化为3',4',5,6-四羟基-7-甲氧基黄酮6-O-β-D-葡萄糖苷(pedaliin)(1)。该方法应可作为合成 5, 6-二羟基-7-甲氧基黄酮的 6-O-葡萄糖苷的通用方法。