Constructing a chemoenzymatic strategy for enhancing the efficiency of selectively transforming 5-hydroxymethylfurfural into furan carboxylic acids

Abstract

Furan carboxylic acids including 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA) are important bio-based chemicals and widely applied in the fields of pharmaceuticals and materials. However, selectively obtaining these value-added compounds from biomass-derived 5-hydroxymethylfurfural (HMF) is difficult due to the readily reactive alcohol/aldehyde groups of the generated intermediates during the oxidative process. Biotransformation using enzyme catalysis is a sustainable and promising approach, but there are remaining challenges including low efficiency and selectivity due to the chaotic and complex biocatalytic process, loss of enzyme activity and inevitable increase in reaction volume caused by exogenous addition of H₂O₂. In these contexts, a natural flavin cofactor mimic (NFCM)-mediated chemoenzymatic system consisting of H₂O₂-dependent peroxygenase, NAD⁺-dependent alcohol dehydrogenase and galactose oxidase was constructed for the first time for selectively converting HMF to each furan carboxylic acid. The bifunctional catalyst NFCM enabled the in situ generation of H₂O₂ and regeneration of NAD⁺, which skillfully alleviated the problems caused by exogenous addition of H₂O₂. Each furan carboxylic acid was achieved with excellent yield (>99%) and selectivity (>99%). Furthermore, an immobilization technique based on a hydrogel material was employed for the first time, which greatly promoted the stability and reusability of each biocatalyst.