Methyl ferulate, a model feruloyl ester, was reacted with H2O2 and peroxidase in order to simulate the possible fate of such esters in the primary cell wall. The major dimeric product was identified as a cyclic dimer with a beta-5 linkage and an alpha-O-4 linkage. This compound, which exceeded the yield of 5,5'-dehydrodiferulic acid dimethyl ester, could arise by nucleophilic substitution of an intermediary beta-5 quinone methide with the neighbouring phenolic hydroxyl group. Inclusion in the reaction mixture of high concentrations of sugars as alternative nucleophiles, such as would occur in the plant cell wall, resulted in very little or no bonding of aromatic material to the sugar. In contrast to these in vitro findings, 5,5'-dehydrodiferulate is the only oxidatively-coupled dimer of ferulate to have been reported in vivo; the apparent formation of ether bonds between ferulate oxidation products and cell wall polysaccharides has been reported. Mechanisms are proposed which may facilitate bonding of ferulate-derived quinone methides to carbohydrates in vivo.
- Methyl ferulate
- plant cell walls