Biocatalytic Furfuryl Alcohol Production with Ethanol as the Terminal Reductant Using a Single Enzyme

Traditionally, furfuryl alcohol (FOL) is produced from biomass-derived furfural (FAL) by hydrogenation using metal-based chemocatalysts. It is challenging due to high metal toxicity, high hydrogen partial pressure, and the need for organic solvents. NAD(P)H-dependent yeast alcohol dehydrogenase I (YADH), which offers high atom economy and up to 100% product selectivity at room temperature in an aqueous medium, is used in this study for the biocatalytic production of FOL from FAL using ethanol (EtOH) as the terminal reductant for in situ regeneration of NAD(P)H. Up to 74% FAL conversion was observed at pH 8 with 40 and 160 mM initial FAL and EtOH concentrations, respectively. The conversion was determined to be equilibrium-limited. Circular dichroism spectroscopy and differential scanning fluorimetry studies of YADH show a significant change in the secondary structure upon treatment with increasing concentrations of aldehydes resulting in loss of catalytic activity. Benign reaction conditions support efforts toward sustainable processing, but opportunities for further improvement by increasing product titer and catalyst stability have been identified. This study lays the framework for developing the science and process for alternatives to biomass-derived ethanol.