Biocatalysed redox reactions - Possibilities and limitations

Sammanfattning: The use of enzymes for synthetic applications is an area of increasing interest. Enzymes have been pointed out to be an environmentally friendly alternative to existing chemical methods, as well as making completely new synthetic routes possible. Over the last decades, much focus has been put on the enzyme group oxidoreductases, which can selectively introduce oxygen and hydrogen into molecules. These reactions can generate optically active molecules that are highly useful building blocks in pharmaceutical production. The limitations for a broader application of oxidoreductases are their need for expensive cofactors and limited operational stability. This thesis is based on research with the objective to improve the understanding of and develop methodology for enzymatically catalysed reduction and oxidation reactions. The problem of cofactor dependency was addressed in a study where hydrogenase and hydrogen gas were used to regenerate the NADH cofactor. A new application of hydrogenase containing Ralstonia eutropha was demonstrated, where these cells were used in combination with another whole cell catalyst for asymmetric ketone reduction. The two-cell system showed a higher specific initial reaction rate and yield, but a slightly lower enantiomeric purity of the product, in comparison with a system where a cosubstrate was used for cofactor regeneration.