A Retro‐biosynthesis‐Based Route to Generate Pinene‐Derived Polyesters

Abstract

Significantly increased production of biobased polymers is a prerequisite to replace petroleum‐based materials towards reaching a circular bioeconomy. However, many renewable building blocks from wood and other plant material are not directly amenable for polymerization, due to their inert backbones and/or lack of functional group compatibility with the desired polymerization type. Based on a retro‐biosynthetic analysis of polyesters, a chemoenzymatic route from (−)‐α‐pinene towards a verbanone‐based lactone, which is further used in ring‐opening polymerization, is presented. Generated pinene‐derived polyesters showed elevated degradation and glass transition temperatures, compared with poly(ϵ‐decalactone), which lacks a ring structure in its backbone. Semirational enzyme engineering of the cyclohexanone monooxygenase from Acinetobacter calcoaceticus enabled the biosynthesis of the key lactone intermediate for the targeted polyester. As a proof of principle, one enzyme variant identified from screening in a microtiter plate was used in biocatalytic upscaling, which afforded the bicyclic lactone in 39 % conversion in shake flask scale reactions.

Chemo-enzymatic pathways toward pinene-based renewable materials

“…[13][14][15] Still, achieving controlled polymerization of pinene monomers remains a challenge, which has spurred an increased interest towards unlocking their inherent potential by activation through oxidation by chemical and biocatalytic methods. [16][17][18] Biocatalysis displays a great potential to replace harsh chemical synthesis with green options for the sustainable generation of medicines, biochemicals and materials. 19 In particular, by capitalizing on synthetic-biology approaches, mild oxidations required for monomer activation which would be challenging to access by traditional organic synthesis 20 can be achieved in water with oxygen as co-substrate.…”

Lactone monomers obtained by enzyme catalysis and their use in reversible thermoresponsive networks

“…The very different structural and physicochemical features (e.g., crystallinity, flexibility, and miscibility) between the original homopolymers PCL, PDL, and PNCL would yield exciting properties of their corresponding block copolymers. Others and in our recently reported work, we showed that PDL is a fully amorphous polymer with a glass‐transition temperature ( T g ) of about −57 °C . In addition, PNCL homopolymer was synthesized and characterized (Figure S5).…”

“…reported the synthesis of norcamphor lactone on 80 mmol scale, in 81% yield and 5 days reaction time which opened the door to further investigations to modulate the entire process in order to further scale it up to a better yield. We have previously reported that an engineered thermostable variant of CHMO Acineto , harboring four substitutions and referred to as CHMO Acineto _QM, was able to fully convert the nonnatural bulky substrate norcamphor (the major product is the normal lactone, 93.4%) and act on the more substituted substrate (−)‐ cis ‐verbanone . Scaling up this transformation from 2 to 33 mM of the substrate norcamphor in shake‐flask enabled the biosynthesis of norcamphor lactone in 0.5 g scale, stressing the high potential of the enzyme CHMO Acineto _QM to be used for the production of industrially relevant products (Scheme ).…”

“…Interestingly, using Methanesulfonic acid (MSA) as a catalyst readily afforded polymerization of the more sterically hindered monomers. MSA is considered as an efficient and ecofriendly catalyst . In this investigation, we aim to evaluate the possibility of ROP to occur using the base → acid “ catalyst switch ” approach .…”

“…The enzyme CHMO Acineto _QM was expressed as previously described . Briefly, freshly transformed E. coli cells were cultivated in 30 mL 2xYT medium containing 40 μg mL −1 kanamycin sulfate overnight at 37 °C and 200 rpm.…”