A new closed-loop flow reaction system improves the yield and speed of enzymatic reaction sequences that convert amines—including dopamine and other biogenic amines—to alcohols with the same chirality. The system, devised by Francesca Paradisi and Martina L. Contente at the University of Nottingham, creates alcohols that are currently difficult and expensive to produce but are widely used in agrochemicals, food additives, fragrances, and drugs (Nat. Catal. 2018, DOI: 10.1038/s41929-018-0082-9). Enzyme sequences can be used in batch mode to carry out the conversions, but Paradisi and Contente enhanced the efficiency of batch processing about 20-fold by carrying out the reactions in a continuous-loop flow system. By-products and final products are removed during each cycle. The system’s significantly reduced reaction times are due to its use of locally high catalyst concentrations, reuse of the aqueous phase, and recirculation of enzyme cofactors. “This strategy mimics an in vivo system and leads to an ultra-efficient, zero-waste, and closed-loop process with excellent atom efficiency and automation,” the researchers note.