Sustainable Synthesis of Bio-Based Furanic and Aromatic Amines Using an Optimized Whole-Cell Transaminase-Decarboxylase Cascade in E. coli RARE.

The development of efficient biocatalytic routes for synthesizing primary amines is often hindered by the unfavorable thermodynamic equilibrium of enzymatic transamination. In this study, we present a highly effective bienzymatic cascade coupling the (S)-selective ω-transaminase from Pseudomonas psychrotolerans (PpS-TA) with pyruvate decarboxylase from Zymomonas mobilis (ZmPDC). This integrated system uses ZmPDC to irreversibly remove the pyruvate coproduct, thereby shifting the equilibrium toward the desired amine. Optimization of the purified enzyme system resulted in a twofold increase in conversion compared to the transaminase alone. The cascade exhibited broad substrate scope across various substituted benzaldehydes and simultaneously enabled the formation of valuable (R)-acyloin byproducts through the carboligation activity of ZmPDC. To enhance industrial applicability, the cascade was transferred to a whole-cell system using an engineered Escherichia coli strain (RARE), which minimizes undesired endogenous aldehyde reduction. The coexpressed whole-cell biocatalyst exhibited superior productivities at substrate loadings up to 50 mM without the need for organic cosolvents. Finally, the utility of this approach was demonstrated through the chemo-enzymatic synthesis of the bio-based platform molecule 2,5-bis(aminomethyl)furan from d-fructose, achieving an exceptional 90% conversion on a 500-mL preparative scale. This integrated strategy provides a sustainable and scalable framework for producing high-value aromatic and furanic amines.