[2′,2′]-(+)-Catechin-(+)-taxifolin from commercial willow bark: structure, bonding positions and oxidative cleavage

Abstract

[2′,2′]-(+)-Catechin-(+)-taxifolin, a novel biflavonoid from commercial willow bark (Salix spp.), is characterized by spectrometric methods. The bonding positions are established by nuclear Overhauser effect difference spectroscopy of the methyl ether acetates of the bi-(+)-taxifolin analogues, which represent products of oxidation of the methylene function of the (+)-catechin moiety and which undergo methylene insertion reactions with diazomethane. Photoinduced oxidative cleavage of the biphenyl-type interflavonoid linkage involving singlet oxygen, accompanied by intermolecular transfer of an acetyl group of the peracetate, yielding a range of flavan-3-ols and dihydroflavonols, provides the first example of this type of biflavonoid photofragmentation.