Enzymatic oxidation of ellagitannin and a new ellagitannin metabolite from Camellia japonica leaves

Abstract

Polyphenols in the leaves of Camellia japonica L. at different stages of growth were analyzed by HPLC. Pedunculagin [2,3; 4,6-bis-(S)-hexahydroxydiphenoyl-d-glucose] was the major polyphenol in the youngest leaves. The levels of this compound and (+)-catechin decreased as the leaves matured. The level of (−)-epicatechin did not change with leaf maturity. Enzymatic oxidation of pedunculagin was examined to investigate the mechanism of the decrease. Pedunculagin was not directly oxidized by treatment with oxidative enzymes. However, when (+)-catechin was added to the reaction mixture, the pyrogallol rings of the 4,6-hexahydroxydiphenoyl group was oxidatively cleaved to give 2H-2-oxo-pyran-6-carboxylic acid. The in vitro oxidation products were not detected in fresh leaves, but two pedunculagin oxidation products conjugated with flavan-3-ol were isolated. A new metabolite, camelliatannin I, was isolated and characterized by spectroscopic and density functional theory calculation of NMR chemical shifts.