An improved sol-gel process involving the use of hollow silica microspheres as a supporting additive was applied for the co-immobilization of whole cells of Escherichia coli with Chromobacterium violaceum ω-transaminase activity and Lodderomyces elongisporus with ketoreductase activity. The co-immobilized cells with two different biocatalytic activities could perform a cascade of reactions to convert racemic 4-phenylbutan-2-amine or heptan-2-amine into a nearly equimolar mixture of the corresponding enantiomerically pure R amine and S alcohol even in continuous-flow mode. The novel co-immobilized whole-cell system proved to be an easy-to-store and durable biocatalyst.

Abstract

In this study, yeast strains were screened and immobilized in a form preserving the multifaceted biocatalytic activity. Immobilization of the silica-supported whole cells of various yeasts, such as Lodderomyces elongisporus, Pichia carsonii, Candida norvegica, and Debaryomyces fabryi, by sol−gel entrapment resulted in easy-to-handle biocatalysts that mediated efficiently different types of synthetic reactions. In the present study, the enantiotope selective reduction of prochiral ketones 1a−d and the acyloin condensation of benzaldehyde 3 were studied, representing two remarkably diverse types of biotransformation. The yeast cell biocatalystsin the presence of fresh or recovered NADH cofactorcould be applied for continuous-flow bioreduction of ketones 1a−d with moderate to good yields (20 to 92%) and excellent enantiomeric purity (>99%). Immobilized L. elongisporus and P. carsonii cells could also mediate acyloin condensation of benzaldehyde 3 in batch as well as in continuousflow mode. The switchable biocatalytic activity of the immobilized yeast cells was demonstrated by consecutive biotransformations under continuous-flow conditions involving reduction of phenylacetone 1a to (S)-phenylpropane-2-ol [(S)-2a] first, followed by conversion of benzaldehyde 3 to (R)-1-hydroxy-1-phenylpropan-2-one [(R)-4] and reduction of 1a to (S)-2a again by using the same packed-bed bioreactor.

No abstract

In this study, an efficient and generally applicable 2 nd generation sol -gel entrapment method was developed for immobilization of yeast cells. Cells of Lodderomyces elongisporus, Candida norvegica, Debaryomyces fabryi, Pichia carsonii strains in admixture with hollow silica microspheres support were immobilized in sol -gel matrix obtained from polycondensation of tetraethoxysilane. As biocatalysts in the selective acyloin condensation of benzaldehyde catalyzed by pyruvate decarboxylase of the yeast, the novel immobilized whole-cell preparations were compared to other states of the cells such as freshly harvested wet cell paste, lyophilized cells and sol -gel entrapped preparations without hollow silica microspheres support. Reusability and storability studies designated this novel 2 nd generation solgel method as a promising alternative for solid formulation of whole-cells bypassing expensive and difficult downstream steps while providing easy-to-handle and stable biocatalysts with long-term preservation of the biocatalytic activity.