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) 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. 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 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.
The monoterpenoid lactone derivative (+)‐dihydrocarvide ((+)‐DHCD) can be polymerised to form shape‐memory polymers. Synthetic biology routes from simple, inexpensive carbon sources are an attractive, alternative route over chemical synthesis from (R)‐carvone. We have demonstrated a proof‐of‐principle in vivo approach for the complete biosynthesis of (+)‐DHCD from glucose in Escherichia coli (6.6 mg L−1). The pathway is based on the Mentha spicata route to (R)‐carvone, with the addition of an ′ene′‐reductase and Baeyer–Villiger cyclohexanone monooxygenase. Co‐expression with a limonene synthesis pathway enzyme enables complete biocatalytic production within one microbial chassis. (+)‐DHCD was successfully produced by screening multiple homologues of the pathway genes, combined with expression optimisation by selective promoter and/or ribosomal binding‐site screening. This study demonstrates the potential application of synthetic biology approaches in the development of truly sustainable and renewable bioplastic monomers.
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