Riboflavin with H2‐driven or Electrochemical Recycling is a Cheap Cofactor System for Supporting Biocatalytic Alkene Reduction

We show that the organic cofactor riboflavin provides a cheap and atom‐efficient source of reducing equivalents to sustain biocatalytic alkene reductions by ene‐reductase enzymes, when coupled with a H2‐driven or electrochemical recycling system. We employ the robust NiFe hydrogenase, Escherichia coli Hyd1, for H2‐driven riboflavin reduction, and also show scope for unmediated electrochemical recycling of reduced riboflavin at a simple carbon electrode. We show that H2‐driven reduction of riboflavin can be extended to continuous flow with a packed bed reactor comprising Hyd1 immobilised on a carbon support. These findings demonstrate scope for replacing the expensive nicotinamide cofactors, NADH or NADPH, with riboflavin for applications of ene‐reductases in biotechnology in either batch or continuous flow, and in electrosynthesis.