Pushing the limits: Cyclodextrin-based intensification of bioreductions

• Published in: Journal of biotechnology Vol. 325; pp. 57 - 64
• Main Authors: Rapp, Christian, Nidetzky, Bernd, Kratzer, Regina
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 10.01.2021
• Subjects: (S)-1-(2-Chlorophenyl)ethanol; 2-Hydroxypropyl-β-cyclodextrin; Biocatalyst stabilization; Biotransformation additive; Solvent-free bioreduction; 2-Hydroxypropyl-β-cyclodextrin; Biotransformation additive; Solvent-free bioreduction; Biocatalyst stabilization; (S)-1-(2-Chlorophenyl)ethanol
• ISSN: 0168-1656; 1873-4863
• DOI: 10.1016/j.jbiotec.2020.11.017

[Display omitted] •Addition of 2-hydroxypropyl-β-cyclodextrin intensifies a bioreduction substantially.•Main effect of 2-hydroxypropyl-β-cyclodextrin is stabilization of the biocatalyst.•Biocatalyst-toxic (S)-1-(2-chlorophenyl)ethanol is produced in 292 g/L and 99.97 % e.e. The asymmetric reduction of ketones is a frequently used synthesis route towards chiral alcohols. Amongst available chemo- and biocatalysts the latter stand out in terms of product enantiopurity. Their application is, however, restricted by low reaction output, often rooted in limited enzyme stability under operational conditions. Here, addition of 2-hydroxypropyl-β-cyclodextrin to bioreductions of o-chloroacetophenone enabled product concentrations of up to 29 % w/v at full conversion and 99.97 % e.e. The catalyst was an E. coli strain co-expressing NADH-dependent Candida tenuis xylose reductase and a yeast formate dehydrogenase for coenzyme recycling. Analysis of the lyophilized biocatalyst showed that E. coli cells were leaky with catalytic activity found as free-floating enzymes and associated with the biomass. The biocatalyst was stabilized and activated in the reaction mixture by 2-hydroxypropyl-β-cyclodextrin. Substitution of the wild-type xylose reductase by a D51A mutant further improved bioreductions. In previous optimization strategies, hexane was added as second phase to protect the labile catalyst from adverse effects of hydrophobic substrate and product. The addition of 2-hydroxypropyl-β-cyclodextrin (11 % w/v) instead of hexane (20 % v/v) increased the yield on biocatalyst 6.3-fold. A literature survey suggests that bioreduction enhancement by addition of cyclodextrins is not restricted to specific enzyme classes, catalyst forms or substrates.