Biocatalyst substrate-coupled regeneration

Alcohol dehydrogenase-catalyzed regeneration of NAD(P)H by oxidation of alcohols certainly represents the most widespread regeneration method currently applied. Especially if the desired production reaction is an ADHsubstrate-coupled regeneration approach excels in simplicity, as only one biocatalyst has to be used for the whole reaction (Scheme 8.8). Another advantage of this methodology is that the nicotinamide cofactor does not have to leave the... 

The use of organic solvents as reaction media for biocatalytic reactions can not only overcome the substrate solubility issue, but also facilitate the recovery of products and biocatalysts as well. This technique has been widely employed in the case of lipases, but scarcely applied for biocatalytic reduction processes, due to the rapid inactivation and poor stability of redox enzymes in organic solvents. Furthermore, all the advantages for nonaqueous biocatalysis can take effect only if the problem of cofactor dependence is also solved. Thus, bioreductions in micro- or nonaqueous organic media are generally restricted to those with substrate-coupled cofactor regeneration. 

Single diastereomers of the diol products were obtained by a two-step process after careful selection of the biocatalysts. In the first reduction step, the starting substrate was completely converted into the corresponding P-hydroxy ketone by the first KRED enzyme without any further reduction to the 1,3-diol. Reduction reactions were coupled with the glucose/glucose dehydrogenase (GDH) system for the in situ regeneration of the reduced cofactor. The second KRED enzyme was then added to... 

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