CINNAMIC ACID BRIDGES BETWEEN CELL WALL POLYMERS IN WHEAT AND PHALARIS INTERNODES

Article abstract of DOI:10.1016/0031-9422(92)80256-E

A method has been devised for the quantitative determination of cinnamic acids participating in ester-ether bridges between cell wall polymers based on the different reactivities of free carboxylic acids and their esters towards borohydride reductants and the different susceptibilities of cinnamic acid ester and benzyl ether linkages to alkaline treatments.Lignin-poylsaccharide containing fractions extracted with dioxane-H2O from cell walls of wheat (Triticum aestivum) and phalaris (phalaris aquatica) internodes are hydrogenated using a Pd/C catalyst at room temperature to convert cinnamic acids to their corresponding dihydrocinnamic acids.The sample is subsequently reduced with LiBH4 in ether-toluene to convert ester-linked dihydrocinnamates to their corresponding alcohols, hydrolysed with 4 M NaOH at 170 deg, and the dihydrocinnamic acid derivatives released from their etherified forms determined by GC.Using model compounds it was shown that these reactions proceeded quantitatively.The results indicate that all of the etherified ferulic acid in the dioxane-H2O-soluble fractions of walls of wheat and phalaris internodes is also ester-linked.It has been calculated that there are nine to 10 ferulic acid ester-ether bridges for every 100 C6-C3 lignin monomers. p-Coumaric acid is not involved in ester-ether bridges. Key Word Index - Triticum aestivum; Phalaris aquatica; Gramineae; lignin; polysaccharide; p-coumaric acid; ferulic acid; esterified cinnamic acid; etherified cinnamic acid.