A self-sufficient Baeyer–Villiger biocatalysis system for the synthesis of ɛ-caprolactone from cyclohexanol

In order to establish a new route for ɛ-caprolactone production from the corresponding cyclohexanol with an internal cofactor recycling for NADPH, a recently redesigned thermostable polyol dehydrogenase (PDH) and the cyclohexanone monooxygenase (CHMO) from Acinetobacter calcoaceticus were combined. First, the expression of PDH could be improved 4.9-fold using E. coli C41 with co-expression of chaperones. Both enzymes were also successfully co-immobilized on glutaraldehyde-activated support (Relizyme™ HA403). Cyclohexanol could be converted to ɛ-caprolactone (ɛ-CL) with 83% conversion using the free enzymes and with 34% conversion using the co-immobilized catalysts. Additionally, a preparative scale biotransformation of ɛ-caprolactone starting from cyclohexanol was performed using the soluble enzymes. The ɛ-CL could be isolated by simple extraction and evaporation with a yield of 55% and a purity of >99%.