Plant proanthocyanidins. Part 4. Biosynthesis of procyanidins and observations on the metabolism of cyanidin in plants

Abstract

Evidence based on the results of feeding experiments with labelled (³H,¹⁴C) cinnamic acids is presented to show that the various procyanidin dimers are biosynthesised from two metabolically distinct units. One is the flavan-3-ol [(+)-catechin (10) or (–)-epicatechin (9)] and the other is the C-4 carbocation (7) or (8). It is postulated that the carbocations are derived by protonation of the flav-3-en-3-ol (6) and are intermediates in the reduction to the flavan-3-ols (9) and (10). The relationship of procyanidin biosynthesis to anthocyanidin formation in certain plants is briefly discussed.