Condensed tannins: determination of the point of linkage in ‘terminal’(+)-catechin units and degradative bromination of 4-flavanylflavan-3,4-diols

Abstract

Data for a variety of 8- and 6-substituted 3′,4′,5,7-tetra-O-methyl-(+)-catechins show that the chemical shifts for the residual A-ring protons at C-6 and C-8 fall into narrow ranges without overlap [τ(CDCl₃) 3·76–3·93; 3·51–3·70, respectively]; degradative bromination of novel flavanyl[6,4]- and -[8,4]flavan-3,4-diols, in which bromine serves as ‘marker’ for the point of attachment of the ‘lower’ flavanyl unit, also provides a method for determining the absolute configurations of both constituent flavonoids at C-2 and C-3.