Biocatalytic Routes to Lactone Monomers for Polymer Production

Abstract

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.

From Bugs to Bioplastics: Total (+)‐Dihydrocarvide Biosynthesis by Engineered Escherichia coli

“…The CHMO from Rhodococcus species Phi1 (CHMO WT ) catalyses the oxidation of (2 R ,5 R )‐dihydrocarvone; however, it generates the unwanted abnormal lactone (3 S ,6 S )‐6‐isopropenyl‐3‐methyl‐2‐oxo‐oxepanone . Site‐directed mutagenesis studies of this enzyme generated a triple variant (F249A/F280A/F435A; CHMO 3M ) that successfully produced the required “normal” (+)‐DHCD lactone . Therefore, we selected CHMO 3M as the catalyst for the final lactone production step in E .…”

“…Gene synthesis and subcloning : The genes encoding the C‐terminally His 6 ‐tagged proteins pentaerythritol tetranitrate reductase (PETNR C‐His 6 ) from E . cloacae (UNIPROT: P71278) and cyclohexanone monooxygenase (CHMO WT ) from Rhodococcus species Phi1 (UNIPROT: Q84H73) were synthesised and subcloned into pET21b, as described previously. The CHMO triple variant F249A/F280A/F414A (CHMO 3M ) was generated by PCR mutagenesis, as described previously .…”

“…For example poly‐ϵ‐caprolactone and polylactide are employed in drug delivery and tissue engineering, and are often major components in polyurethane biopolymers . A variety of limonene‐based monoterpenoids found in Mentha essential oils can be converted into the lactone monomers menthide, carvomenthide and (+)‐dihydrocarvide ((+)‐DHCD) . Subsequent polymeric forms have uses as thermoplastic elastomers (shape‐memory polymers) and pressure‐sensitive adhesive components …”

“…A variety of limonene‐based monoterpenoids found in Mentha essential oils can be converted into the lactone monomers menthide, carvomenthide and (+)‐dihydrocarvide ((+)‐DHCD) . Subsequent polymeric forms have uses as thermoplastic elastomers (shape‐memory polymers) and pressure‐sensitive adhesive components …”

“…Synthetic routes to monomeric (+)‐DHCD include hydrogenation and subsequent Baeyer–Villiger oxidation of the natural product ( R )‐carvone . However, a synthetic biology route could serve as an alternative approach (Scheme ) given that the enzymes responsible for ( R )‐carvone biosynthesis in Mentha spicata are known, and prior studies with Baeyer–Villiger cyclohexanone monooxygenases (CHMO) have demonstrated (+)‐DHCD production . An early attempt at in vivo ( R )‐carvone production was to incorporate the C5 isoprenoid precursor (geranyl pyrophosphate) production and subsequent spearmint pathway genes into recombinant Escherichia coli .…”