Oligomeric isoflavonoids. Part 2. Structure and synthesis of xanthocercin A and B, the first isoflavono-lignoids

Abstract

The structures of xanthocercin A and B, the first Isoflavono-lignoids, have been established as 2,3-trans-3-(4-hydroxy-3,5-dimethoxyphenyl)-8-(3-hydroxy-4-methoxyphenyl)-2-hydroxymethyl-2,3-dihydro-7H-1,4-dioxino[2,3-h]chromen-7-one (1) and 2,3-trans-8-(3-hydroxy-4-methoxyphenyl)-3-(4-hydroxy-3-methoxyphenyl)-2-hydroxymethyl-2,3-dihydro-7H-1,4-dioxino[2,3-h]chromen-7-one (3) respectively by spectroscopic methods. These structures have been confirmed by synthesis via phenol oxidative coupling of the appropriate 7,8-dihydroxyisoflavone and respectively sinapyl and coniferyl alcohol. The natural occurrence of xanthocercin A and B as single regioisomers and their regiospecific formation during synthesis presumably originate from marked differences in susceptibility to oxidation of the hydroxy functions in their ‘catechol precursors’.