FORMATION OF SUBSTITUTED TRUXILLIC AND TRUXINIC ACIDS IN PLANT-CELL WALLS - A RATIONALE

The formation of phenolic cyclobutane dicarboxylic acids (truxillic an d truxinic acids) in plant cell wall materials was investigated using model compounds. Two possible mechanisms were considered-cyclodimeriza tion initiated by light or by a free radical process. Diesters formed by reaction of cinnamic acid with a series of diols had a range of dis tances separating the double bonds and, upon irradiation with ultravio let light, gave dimerization products. Dimerization did not occur when peroxidase was added to the diesters to mimic phenolic coupling react ions leading to the formation of lignin in vivo. A minimum separation of two cinnamyl moieties and an optimal relative orientation was obser ved which can be used to predict substitution patterns for unsaturated phenolic residues on the sugar backbone in plant cell walls.