Poly-sigma-caprolactone (PCL) is chemically produced on an industrial scale in spite of the need for hazardous peracetic acid as an oxidation reagent. Although Baeyer-Villiger monooxygenases (BVMO) in principle enable the enzymatic synthesis of sigma-caprolactone (sigma-CL) directly from cyclohexanone with molecular oxygen, current systems suffer from low productivity and are subject to substrate and product inhibition. The major limitations for such a biocatalytic route to produce this bulk chemical were overcome by combining an alcohol dehydrogenase with a BVMO to enable the efficient oxidation of cyclohexanol to sigma-CL. Key to success was a subsequent direct ring-opening oligomerization of in situ formed sigma-CL in the aqueous phase by using lipase A from Candida antarctica, thus efficiently solving the product inhibition problem and leading to the formation of oligo-sigma-CL at more than 20g L(-1) when starting from 200mM cyclohexanol. This oligomer is easily chemically polymerized to PCL.
