There is currently considerable interest in the intensification of biocatalytic processes to reduce the cost of goods for biocatalytically produced chemicals, including pharmaceuticals and advanced pharmaceutical intermediates. Continuous-flow biocatalysis shows considerable promise as a method for process intensification; however, the reliance of some reactions on the use of diffusible cofactors (such as the nicotinamide cofactors) has proven to be a technical barrier for key enzyme classes. This minireview covers attempts to overcome this limitation, including the cofactor recapture and recycling retention of chemically modified cofactors. For the latter, we also consider the state of science for cofactor modification, a field reinvigorated by the current interest in continuous-flow biocatalysis.

Biocatalysis is used for many chemical syntheses due to its high catalytic rates, specificities and operation under ambient conditions. Continuous-flow chemistry offers advantages to biocatalysis, avoiding process issues caused by substrate/product inhibition, equilibrium controlled limitations on yield and allosteric control. Modular continuous-flow biochemistry would also allow the flexible assembly of different complex multistep reactions. Here we tackle some technical challenges that currently prohibit the wide-spread use of continuous flow biocatalysis; cofactor immobilization and site-specific immobilization. We provide the first example of enzymes engineered to retain and recycle their cofactors, and the use of these enzymes in continuous production of chiral pharmaceutical intermediates.