Combining Electro-, Photo-, and Biocatalysis for One-Pot Selective Conversion of Furfural into Value-Added C4 Chemicals

Chemobiocatalysis has emerged as a powerful tool in synthetic chemistry, but one-pot multistep syntheses incorporating multiple types of catalysts remain challenging because of the greatly increased incompatible issues between different catalysts. In this work, we reported the combination of electro-, photo-, and biocatalysis for one-pot selective valorization of biomass-derived furfural into various C4 chemicals including maleic acid (MA), fumaric acid (FA), d- and l-malic acid (MalA), and l-aspartic acid (l-Asp). MA was concurrently synthesized from furfural via a cascade of electrochemical oxidations with 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl (ACT) and photo-oxygenation with eosin Y (EY) with up to a 97% yield. ACT is a versatile catalyst capable of oxidizing both furfural and intermediate 5-hydroxy-2-(5H)-furanone. Then, biocatalysis was harnessed to produce enantiopure chemicals after photoelectrocatalysis. Furfural was selectively converted to d-MalA via sequential photoelectrooxidation and biocatalytic hydration with a 91% yield as maleate hydratase was readily inactivated under light irradiation. Also, maleate cis–trans isomerase (MaiA) was found to be highly sensitive to chemical oxidation; thus, two-step synthesis of FA and its derivatives l-MalA and l-Asp was performed by sequentially using ACT/EY and one/dual-enzyme with 79–97% yields. Both catalyst and reaction engineering strategies were applied to address the incompatibility between MaiA and photoelectrooxidation. Consequently, FA was produced from furfural in a concurrent manner with a 67% yield. The present work demonstrates the great power of chemobiocatalysis in the valorization of platform chemicals.