Piceatannol, a novel monomer in the lignins of palm fruit endocarps

Abstract

Lignin is derived from the oxidative radical coupling of three main p-hydroxycinnamyl alcohols, the monolignols p-coumaryl, coniferyl, and sinapyl alcohols. Recently, we discovered in grass lignins the first phenolic monomer from outside the canonical lignin biosynthetic pathway, the flavone tricin. In this work, we report the discovery of another polyphenolic compound from yet another biosynthetic pathway, the hydroxystilbene piceatannol, which also acts as a true lignin monomer in palm fruit endocarps. Piceatannol was released from these lignins upon derivatization followed by reductive cleavage (DFRC), a degradative method that cleaves ß-ether bonds, indicating that at least a fraction of it is incorporated into the lignin through labile ether bonds. 2D-NMR revealed the occurrence of other structures involving piceatannol in the lignin polymer, and demonstrated that piceatannol acts as an authentic lignin monomer participating in coupling and cross-coupling reactions during lignification of palm fruit endocarps.