Kinetic insights into ϵ-caprolactone synthesis: Improvement of an enzymatic cascade reaction.

A computational approach for the simulation and prediction of a linear three-step enzymatic cascade for the synthesis of ϵ-caprolactone (ECL) coupling an alcohol dehydrogenase (ADH), a cyclohexanone monooxygenase (CHMO), and a lipase for the subsequent hydrolysis of ECL to 6-hydroxyhexanoic acid (6-HHA). A kinetic model was developed with an accuracy of prediction for a fed-batch mode of 37% for substrate cyclohexanol (CHL), 90% for ECL, and >99% for the final product 6-HHA. Due to a severe inhibition of the CHMO by CHL, a batch synthesis was shown to be less efficient than a fed-batch approach. In the fed-batch synthesis, full conversion of 100 mM CHL was 28% faster with an analytical yield of 98% compared to 49% in case of the batch synthesis. The lipase-catalyzed hydrolysis of ECL to 6-HHA circumvents the inhibition of the CHMO by ECL enabling a 24% higher product concentration of 6-HHA compared to ECL in case of the fed-batch synthesis without lipase. Biotechnol. Bioeng. 2017;114: 1215-1221. © 2017 Wiley Periodicals, Inc.

An enzyme cascade synthesis of ε-caprolactone and its oligomers.

Poly-ε-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 ε-caprolactone (ε-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 ε-CL. Key to success was a subsequent direct ring-opening oligomerization of in situ formed ε-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-ε-CL at more than 20 g L(-1) when starting from 200 mM cyclohexanol. This oligomer is easily chemically polymerized to PCL.