Engineering substrate acceptance of Resveratrol O-Methyltransferase from Vitis vinifera for the selective synthesis of O-methyl protected biobased hydroxystyrenes

Enzymatic decarboxylation of phenolic acids enables the production of biobased phenolic styrenes under mild reaction conditions. However, the free para-phenolic group can lead to undesirable side products during polymerization, giving protection of the free phenolic OH group critical importance for the application in adhesives. Here we present a one-pot two-step cascade reaction, in which phenolic acid decarboxylase from Bacillus subtilis (BsPAD) catalyzes the decarboxylation of coumaric acid, caffeic acid, ferulic acid, and sinapic acid, followed by O-methylation of the intermediate phenolic styrenes by resveratrol O-methyltransferase from Vitis vinifera (VvROMT). The reaction sequence avoids the isolation and purification of the reactive intermediate phenolic styrenes. The O-methyltransferase shows selectivity towards the phenolic styrenes. Characterization of a set of variants with amino acid substitution in the active-site cavity led to the identification of VvROMT L117F/F311W which did not show any activity towards the four phenolic acids. This avoids undesired O-methylation of the starting material, which is not desirable since the decarboxylase does not convert the formed p-methoxyphenolic acids. Furthermore, variation of amino acids in the active site led to the identification of mutants with improved activity for all four phenolic styrenes. The results constitute an important step towards the synthesis of biomass-derived methoxy styrene derivatives whose photopolymerization yields polymers with outstanding adhesion properties.