Metal Affinity Fusion Enzyme Immobilization: Batch Process Showcase for Cascading Alcohol Oxidation and Bayer-Villiger Oxidation in Microaqueous Media

Baeyer-Villiger monooxygenases (BVMOs) show great potential for the selective oxidation of a wide scope of ketones with exceptional regio-, chemo-, or stereoselectivity to produce diverse value-added (cyclic) esters. However, the technical application of BVMOs remains challenging due to their oxygen- and cofactor-dependency, instability, and susceptibility to substrate/product inhibition. The use of nonaqueous media is considered a straightforward solution but is limited due to enzyme instability and the unavailability of specific amounts of water required for enzyme activation and cofactor regeneration. Fusion approaches provide enzymes with the possibility of recycling cofactors even under low-water conditions by shortening the diffusion distance between active sites, whereas the stability and reusability of enzymes can be achieved by immobilization techniques. On all bases, a fusion enzyme of cyclohexanone monooxygenases (CHMOs) and alcohol dehydrogenases (ADHs) was immobilized on a newly reported resin, Chromalite MIDA (Methacrylate IminoDiAcetic) loaded with a variety of metal ions, via a one-pot metal affinity approach of simultaneous purification and immobilization. The immobilization process was rationally optimized in terms of activity and immobilization yields for both enzymes by the design of experiments (DoE). The catalytic performance of the immobilized fused enzyme was examined for the linear cascade to synthesize ϵ-caprolactone as a polymer precursor in cyclopentyl methyl ether (CPME). The immobilized fused enzyme showed an improved productivity of ϵ-caprolactone in 99.5 vol.% CPME than the buffer system (50 vs 30 mM), as well as a higher productivity and operational stability in comparison with the free enzyme (49 vs 12 mM) with prospective reusability of seven times. The upscale of the cascade in a rotating bed reactor at 125 mL in 99 vol.% CPME was established by obtaining 37 mM ϵ-caprolactone, demonstrating the feasibility of using ADH-CHMO fusion on a technical scale with further improvements.