An Enzyme Cascade Synthesis of ε‐Caprolactone and its Oligomers

Abstract

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.

Enzymatic Oxyfunctionalization Driven by Photosynthetic Water-Splitting in the Cyanobacterium Synechocystis sp. PCC 6803

“…This was sustained in a control experiment with a photosynthesis inhibitor that also decelerated the reaction, albeit to a lower extent. The specific reaction rates determined in this study of 2-5 U/g CDW are similar to those achieved with the same enzyme in E. coli [2]. The possible self-shading of the cells, however, requires to operate at cell densities of a few g/L, which limits the resulting space-time yield.…”

“…Degradation of the resulting 6-phosphogluconolactone in the catabolism leads to a significant formation of NADH and subsequent respiration. A typical example of the poor efficiency is in the recent synthesis of the polymer precursor ε-caprolactone in resting cells of E. coli, in which glucose had to be added in stoichiometric amounts [2]. Several alternative solutions for this challenge are currently under consideration.…”

“…We were interested whether the concept can be extended towards the utilization of NADPH for selective oxyfunctionalisation reactions, and if side-reactions and physiological side-effects might be a problem for a catalytic application. In order to test the performance of the system, one of the most widely used Baeyer-Villiger monooxygenases (BVMO), the NADPH-specific cyclohexanone monooxygenase (CHMO) from Acinetobacter calcoaceticus NCIMB 9871 was chosen as a model (Scheme 1) [2,14]. …”

Artificial Biocatalytic Linear Cascades to Access Hydroxy Acids, Lactones, and α- and β-Amino Acids

“…Both studies show that an efficient transformation of cyclohexanol into ɛ-caprolactone is feasible (94% conversion of 60 mM 47, 80% conversion of 10 mM 47); however, both also observed reduced conversions at elevated substrate concentrations which was attributed to inhibition and deactivation of the Baeyer-Villiger monooxygenase. This issue was addressed in subsequent studies carried out as a joint effort of the two involved research groups: [76,77] The ɛ-caprolactone formed underwent in situ ring-opening oligomerisation enabled by lipase A from Candida antarctica (CAL-A), which alleviated product inhibition and produced oligo--caprolactone displaying an average molecular weight of 375 g/mol. It is worth noting that no hydrolysis of 49 to the hydroxycarboxylic acid was observed.…”

Mechanism-Guided Discovery of an Esterase Scaffold with Promiscuous Amidase Activity

“…The discovery [6][7][8] and engineering [9][10][11] of enzymes fueled by the formidable development in high-throughput biotechnology has allowed for tailored manufacturing of materials [12], medicines [13], and fine chemicals [14]. However, developing the full potential of biocatalysis and synthetic biology is dependent on exploring hitherto novel biochemistries [4,15] and reaction mechanisms [16] that expand the catalytic capabilities currently found in nature [15].…”