Heterogeneous biocatalytic reduction of 5-(hydroxy)methyl furfural using two co-immobilised alcohol dehydrogenases

Biocatalyst heterogenisation may enable robust processes that can be applied in biorefineries to selectively valorise highly functionalised platform chemicals. In this work, we co-immobilise two dehydrogenases and successfully apply them in the selective reduction of 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl) furan (BHMF) with efficient in situ cofactor regeneration. First, we select the best enzyme candidates (an alcohol dehydrogenase from Escherichia coli together with a thermostable glucose dehydrogenase from Bacillus subtilis) and then screen a variety of carriers and chemistries to find the optimal individual immobilisation protocols for each dehydrogenase. As a result, methacrylate carriers (Purolite (TM)) functionalised with either aldehydes or with epoxy and cobalt-chelate groups co-immobilise both enzymes in high yields with a sufficient activity recovery (>20%). These optimal heterogeneous biocatalysts enable the quantitative bio-reduction of HMF to BHMF with >99% selectivity in only fifteen minutes, exhibiting an outstanding reusability of >15 batch cycles with a total volumetric productivity of similar to 5 g L-1 h(-1) of BHMF. Preliminary experiments on a semipreparative scale with HMF loadings of 40 mM also reach high product conversions (86%). Overall, the judicious selection of enzymes, carriers and reaction conditions enables the design of robust biocatalysts that may contribute to paving the way to the valorisation of highly functionalised chemicals in biorefineries.