P-COUMAROYLATED SYRINGYL UNITS IN MAIZE LIGNIN - IMPLICATIONS FOR BETA-ETHER CLEAVAGE BY THIOACIDOLYSIS

Recent NMR studies of lignin isolated from maize demonstrated that p-c oumarate esters are attached exclusively to the gamma-position of phen ylpropane side chains. Thioacidolysis/desulphuration experiments have revealed that p-coumarate units are attached primarily (ca 90%) to syr ingyl moieties in maize lignin. In model studies with guaiacylglycerol and syringylglycerol-beta-guaiacyl ethers, cleavage of beta-ether lin kages by thioacidolysis was reduced 40% by gamma-acylation of phenylpr opane side chains with p-coumarate. Our results indicate that gamma-p- coumarate esters significantly reduce the yields of syringyl products recovered after thioacidolysis of grass lignins.