Constituents of Geranium thunbergii Sieb. et Zucc. Part 14. Structures of didehydrogeraniin, furosinin, and furosin

Abstract

Three novel tannins, dehydrogeraniin, furosinin, and furosin, members of the dehydroellagitannins, were isolated from the aerial part of Geranium thunbergii Sieb. et Zucc., and their structures were elucidated on the basis of spectral evidence and chemical reactions. Dehydrogeraniin and furosinin were found to form equilibrium mixtures composed of four and eight tautomers, respectively, due to the equilibration of two dehydrohexahydroxydiphenoyl groups and the anomerization of the glucose moiety in the latter compound.