Riboflavin with H₂‐Driven or Electrochemical Recycling: A Cheap Cofactor System for Supporting Biocatalytic Alkene Reduction

Abstract This study shows 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 H 2 ‐driven or electrochemical recycling system. We employ the robust NiFe hydrogenase, Escherichia coli Hyd1, for H 2 ‐driven riboflavin reduction and show the feasibility of unmediated electrochemical recycling of reduced riboflavin at a simple carbon electrode. We show that H 2 ‐driven reduction of riboflavin can be extended to continuous flow with a packed bed reactor comprising of Hyd1 immobilized on a carbon support. These findings demonstrate that there is 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.