Probability of β-O-4 Bond Formation between Monolignol Dimers and Coniferyl Alcohol in the Enzymatic Dehydrogenative Polymerization

Abstract

Lignin is a natural polymer formed through the complex coupling of monolignols via various linkage types. Among these, approximately 50% are β-O-4 linkages, however, when and to what extent these linkages are formed during the polymerization process remains unclear. In this study, enzymatic dehydrogenative polymers (DHPs) were synthesized using β-O-4, β-5 and β-β dimers together with ［3-OCD₃］coniferyl alcohol (D-CA), and the probability of forming a β-O-4 linkage during trimer formation by the addition of a monomer to a dimer was investigated. The obtained DHPs were subjected to thioacidolysis and analysis of the degradation products revealed that the proportion of β-O-4 linkage formation showed little difference among the three dimers, while the amount of unreacted β-5 dimer was higher than that of the other dimers.