2D NMR STRUCTURE ELUCIDATION OF PROANTHOCYANIDINS - THE SPECIAL CASE OF THE CATECHIN-(4-ALPHA-8)-CATECHIN-(4-ALPHA-8)-CATECHIN TRIMER

A complete and unambiguous assignment of the H-1 and C-13 NMR spectra of peracetylated catechin-(4 alpha-8)-catechin-(4 alpha-8)-catechin procyandin trimer was accomplished by reverse two-dimensional chemical shift correlation methods, An HMBC spectrum showed, for the first time, evidence of the sites of condensation between the interflavan units of a trimer. The 2,3-trans stereochemistry of the C- and F-rings are easily deduced from measurement of (3)J coupling constants, The multiplicity analysis of the protons of the i-ring in the terminal unit does not lead to such an assignment, A ROESY experiment is needed to confirm the 2,3-trans relationship, Molecular mechanics calculations explain the unexpected coupling constants of these protons.