Proof of the presence of racemic forms of arylglycerol-Β-aryl ether structure in lignin: studies on the stereo structure of lignin by ozonation

Abstract

Recent rapid progress of the biosynthetic study of lignan, especially finding a new type of protein that regulates the stereo structure of lignan, z seems to re-create an interest in the investigation of optical activity of lignin, although lignin has long been assumed to be optically inactive. The arylglycerol-/3-aryl ether substructure in lignin is known to consist of two diastereomers: erythro and threo forms. Each diastereomer is assumed to be a mixture of two enantiomers: the D form and the L form. If this structure is produced as a dimer by simple radical coupling of two coniferyl alcohol radicals and no other factor affects this process, the formation of asymmetric carbon at the /3position must be a racemic process. However, when a monomer radical combines with the already grown oligomeric structure, the formation of asymmetric carbon at the /?-position of this structure must be affected by other asymmetric carbons already present in oligomer parts. Lignin synthesis is believed to proceed in the polysaccharide matrix. In such a situation, formation of an asymmetric carbon in lignin could be affected by optically active carbohydrates,