Biotransformations with Imine Reductases: Design of a Practical Process Avoiding an Extractive Work‐Up by Entrapment of Water and Enzymes in an Immobilized Phase.

A process concept for the asymmetric biocatalytic reduction of heterocyclic imines addressing the efficiency of the reaction as well as downstream‐processing steps was studied by utilizing a "heterogenized aqueous phase", which contains the needed enzymes and cofactor within a superabsorber (polyacrylate) network, for the biotransformation. The immobilized biocatalytic system, which comprises an imine reductase (IRED), NADPH and an alcohol dehydrogenase for cofactor‐recycling, enables to run the reaction in pure organic medium. Thus, instead of an extractive work‐up as typical solution for biotransformations in aqueous medium, which, however, can be tedious due formation of emulsions, this type of IRED‐catalyzed process leads to a simplified work‐up consisting only of a decantation of the liquid organic reaction medium with the product from the heterogenized aqueous biocatalyst system. Exemplified for the (R)‐enantioselective reduction of 1‐methyl‐3,4‐dihydroisoquinoline by the IRED of Streptomyces viridochromogenes as a model reaction, a process was developed leading to 98 % conversion, 88 % yield and >99 % ee at a substrate concentration of 40 mM. [ABSTRACT FROM AUTHOR]