Bonding of hydroxycinnamic acids to lignin: ferulic and p-coumaric acids are predominantly linked at the benzyl position of lignin, not the beta-position, in grass cell walls

A suspension in dichloromethane-water (18:1, v/v) of various Fractions cont aining hydroxycinnamic acid ester-ether bridges between lignin and polysacc harides prepared from cell walls of matured oat (Avena sativa L.) intemodes , and a solution of their acetates in the same solvent were treated with 2, 3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). This reagent selectively cle aves benzyl ether and ester linkages of negatively charged aromatic nuclei. The sample treated with DDQ was directly hydrolysed either under mild (1 M NaOH, overnight at 37 degreesC) or severe (4 M NaOH. for 2 h at 170 degree sC) conditions. The hydroxycinnamic acids released in the hydrolysate were methylated with diazomethane and analysed quantitatively rising gas chromat ography. Significant portions of ether linkages between hydroxycinnamic aci ds and lignin were cleaved with DDQ. which suggests that most of the hydrox ycinnamic acids were ether-linked at the benzyl position. and not the P-pos ition. of the lignin side chain as previously claimed. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.