Stereoselective biotransformation of cyclic imines in recombinant cells of Synechocystis sp. PCC 6803

Light-driven biotransformations in recombinant cyanobacteria allow to employ photosynthetic water-splitting for cofactor-regeneration and thus, to save the use of organic electron donors. The genes of three recombinant imine reductases (IREDs) were expressed in the cyanobacterium Synechocystis sp. PCC 6803 and eight cyclic imine substrates were screened in whole-cell biotransformations. While initial reactions showed low to moderate rates, optimization of the reaction conditions in combination with promoter engineering allowed to alleviate toxicity effects and achieve full conversion of prochiral imines with initial rates of up to 6.3 mM h(-1). The high specific activity of up to 22 U g(CDW)(-1) demonstrates that recombinant cyanobacteria can provide large amounts of NADPH during whole cell reactions. The excellent optical purity of the products with up to >99 %ee underlines the usefulness of cyanobacteria for the stereoselective synthesis of amines.