Characterization of Unusual Proanthocyanidins in Leaves of Bayberry (Myrica rubra Sieb. et Zucc.)

Abstract

Extractable and unextractable proanthocyanidins (EPAs and UEPAs) from leaves of bayberry were characterized. Both EPAs and UEPAs were analyzed by acid catalysis in the presence of excess phloroglucinol. The main cleavage product, epigallocatechin-3-O-gallate-(4β→2)-phloroglucinol, was successfully identified. The EPAs were of the prodelphinidin type. In fact, epigallocatechin-3-O-gallate (EGCG) and traces of epigallocatechin (EGC) were detected as the extension units, but only EGCG was present in the terminal units. All of the compounds exhibited a 2,3-cis configuration, and >98% of them were galloylated. The mean degree of polymerization (mDP) of bayberry leaf EPAs was 6.5, and the most abundant EPAs were the polymers, with mDP values of 9.5-26.7. The UEPAs were highly polymerized prodelphinidins consisting of EGCG and traces of EGC. In addition, EGCG, three EPA dimers, and two trimers were identified. The EPAs and UEPAs consisted mostly of EGCG, which is unusual in the plant kingdom.