Non‐Enzymatic Oxidation of a Pentagalloylglucose Analogue into Members of the Ellagitannin Family

Abstract

AbstractThe occurrence of more than 1000 structurally diverse ellagitannins has been hypothesized to begin with the oxidation of penta‐O‐galloyl‐β‐d‐glucose (β‐PGG) for the coupling of the galloyl groups. However, the non‐enzymatic behavior of β‐PGG in the oxidation is unknown. Disclosed herein is which galloyl groups tended to couple and which axial chirality was predominant in the derived hexahydroxydiphenoyl groups when an analogue of β‐PGG was subjected to oxidation. The galloyl groups coupled in the following order: at the 4,6‐, 1,6‐, 1,2‐, 2,3‐, and 3,6‐positions with respective S‐, S‐, R‐, S‐, and R‐axial chirality. Among them, the most preferred 4,6‐coupling reflected the what was observed for natural ellagitannins. A new finding was that the second best coupling occured at the 1,6‐positions. With the detection of a 3,6‐coupled product, this work demonstrated that even ellagitannin skeletons with an axial‐rich glucose core may be generated non‐enzymatically.