Biocatalytic Routes to Lactone Monomers for Polymer Production

Monoterpenoids offer potential as biocatalytically derived monomer feedstocks for high-performance renewable polymers. We describe a biocatalytic route to lactone monomers menthide and dihydrocarvide employing Baeyer-Villiger monooxygenases (BVMOs) from Pseudomonas sp. HI-70 (CPDMO) and Rhodococcus sp. Phi1 (CHMO_Phi1) as an alternative to organic synthesis. The regioselectivity of dihydrocarvide isomer formation was controlled by site-directed mutagenesis of three key active site residues in CHMO_Phi1. A combination of crystal structure determination, molecular dynamics simulations, and mechanistic modeling using density functional theory on a range of models provides insight into the origins of the discrimination of the wild type and a variant CHMO_Phi1 for producing different regioisomers of the lactone product. Ring-opening polymerizations of the resultant lactones using mild metal-organic catalysts demonstrate their utility in polymer production. This semisynthetic approach utilizing a biocatalytic step, non-petroleum feedstocks, and mild polymerization catalysts allows access to known and also to previously unreported and potentially novel lactone monomers and polymers.