Synthesis of 5,8-dihydroxy-6,7-dimethoxyflavones and revised structures for some natural flavones
1995
Horie, T. | Kawamura, Y. | Yamamoto, H. | Kitou, T. | Yamashita, K.
Six 5,8-dihydroxy-6,7-dimethoxyflavones and three 8-hydroxy-5,6,7-trimethoxyflavones were synthesized from 2',5'-dihydroxy-3',4',6'-trimethoxyacetophenone by adapting the selective O-alkylation and dealkylation, and the differentiation between the flavones and their isomeric 6-hydroxyflavones was clarified by 1HNMR and UV spectra. Four natural flavones proposed as 5,8-dihydroxy-6,7-dimethoxyflavones, must have other structures and three are shown to be the isomeric 5,7-dihydroxy-6,8-dimethoxyflavones. A flavone, isolated from Ageratum conyzoides, is correctly identified as 8-hydroxy-5,6,7,3',4',5'-hexamethoxyflavone, but the structure of a flavone, isolated from Helichrysum, is revised to the isomeric 7-hydroxy-5,6,8-trimethoxyflavone.
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