Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran in Biphasic Media using Immobilized Galactose Oxidase: Proof of Concept and Limitations

The oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) is a key reaction in valorizing biomass. DFF is hardly soluble in water, while HMF is often obtained from biorefineries in crude wet organic fractions. Thus, the reaction is challenging for both biocatalysis performed in aqueous media, and for chemocatalysis where the presence of water often results in catalyst poisoning. Galactose oxidase (GalOx) can selectively oxidize HMF to DFF and displays promising activity in aqueous-organic media. In this study, GalOx was immobilized on ten carriers, assessing the immobilization yield, activity, and stability. Covalently immobilized GalOx catalyzed the oxidation of HMF to DFF in neat and water-saturated EtOAc, and in biphasic systems of various water contents. At 50 % v/v H2O, the reaction was conducted at a semi-preparative scale (50 mL) with no adverse effect on DFF yield. Some limitations arise, such as enzyme deactivation, and adsorption of DFF to the support, particularly in the aqueous fraction. Future options to upgrade the route may include designed stable enzymes under the presence of HMF/DFF, and the setup of microaqueous systems where DFF adsorption is minimized. The use of wet EtOAc media would be a promising approach in future biorefineries employing inexpensive crude wet organic fractions.将5-羟甲基糠醛（5-hydroxymethylfurfural，HMF）氧化为2,5-二甲酰基呋喃（2,5-diformylfuran，DFF）是生物质增值过程中的关键反应。DFF几乎不溶于水，而HMF通常从生物炼制厂的粗湿有机组分中获取，因此该反应无论是在水相介质中开展的生物催化过程，还是水易引发催化剂中毒的化学催化体系中，均存在较大挑战。半乳糖氧化酶（Galactose oxidase，GalOx）可选择性催化HMF氧化生成DFF，且在水-有机混合介质中展现出优异的催化活性。本研究将GalOx固定于十种载体之上，对其固定化回收率、催化活性与稳定性进行了系统评估。共价固定化的GalOx能够在纯乙酸乙酯、水饱和乙酸乙酯，以及不同水含量的双相体系中催化HMF氧化为DFF。当水相体积占比为50%（v/v）时，反应以半制备规模（50 mL）进行，DFF收率未受到不利影响。该体系仍存在部分局限，如酶失活以及DFF在载体上的吸附，尤其在水相组分中更为显著。未来可通过以下方向优化该工艺路线：设计在HMF/DFF存在条件下稳定性更强的酶，以及构建可最大程度减少DFF吸附的微水相体系。采用湿乙酸乙酯介质有望在未来使用低成本粗湿有机组分的生物炼制厂中得到应用。