Abstract: The present application relates to a reaction system in which chemically valuable compounds can be obtained in high enantiomer purities with the aid of a coupled enzymatically operating transformation process. The coupled enzymatically operating reaction system in this context comprises an enzymatic transformation reaction which proceeds with the consumption of a cofactor, and recycling of the cofactor consumed, which proceeds enzymatically, wherein the procedure is carried out in a homogeneous aqueous solvent system comprising an organic hydrocarbon having at least two hydroxyl or ether groups.