Chemoselective Synthesis of Hydrocinnamaldehyde Enabled by a Self-Sufficient Heterogeneous Redox Biocatalyst

The selective C═C bioreduction of cinnamaldehyde to hydrocinnamaldehyde is a key transformation for the fragrance, pharmaceutical, and polymer industries, but remains challenging with conventional metal catalysts. Here, we report a self-sufficient heterogeneous biocatalyst (ssHB) combining an extremophilic ene-reductase from Halomonas elongata (HeNRed) with a thermostable glucose dehydrogenase from Bacillus subtilis (BsGDH) for in situ nicotinamide adenine dinucleotide (NADH) regeneration. A consensus coimmobilization protocol was identified by microtiter plate screening, where both enzymes were reversibly coimmobilized on macroporous agarose supports activated with positively charged diethylaminoethyl (DEAE) groups. The same support also enabled NADH coimmobilization, allowing cinnamaldehyde bioreduction without exogenous cofactor supply. The resulting ssHB was thoroughly characterized and implemented in a plug-flow packed-bed reactor (PBR), enabling >90% conversion of cinnamaldehyde to hydrocinnamaldehyde under continuous flow with a 30 min residence time in the presence of 50% toluene as a cosolvent. The PBR operated continuously for 12 reactor cycles without exogenous supply of NADH before exhaustion. Translating this self-sufficient system from batch to continuous flow increased volumetric productivity 55-fold, reaching a space-time yield of 12.1 g L–1 h–1. The system also enabled full recovery of enzyme activity through streamlined reloading with fresh NADH. This work demonstrates how enzyme immobilization, cofactor recycling, and reaction intensification can be integrated into a scalable and sustainable platform for valorizing renewable feedstocks in green chemical manufacturing.