Stereoselective Bio‐Organocatalytic Cascade to Chiral Amides as Active Pharmaceutical Ingredient Intermediates Using ω ‐Transaminase and Choline Chloride Under Microwave Irradiation

Amide bond formation is a key transformation in organic synthesis, especially for the preparation of active pharmaceutical ingredients (APIs). In this work, we report the development of a bio‐organocatalytic cascade, combining stereoselective transamination catalyzed by ω ‐transaminases ( ω ‐TAs) in neat organic solvent and choline chloride (ChCl)‐mediated direct amidation. This strategy enables the synthesis of chiral amides from prochiral carbonyl compounds and carboxylic acids under solvent‐free microwave conditions. After optimizing the biocatalytic transamination in MTBE, we applied the method to the synthesis of key intermediates of Racecadotril and AVR‐48, achieving full conversions and enantiomeric excess above 99%. The amidation step, promoted by ChCl without traditional activating agents, proved highly efficient for a wide range of aliphatic and aromatic carboxylic acids, affording the target amides in 60%–86% yields. Solvent evaporation after the transamination step was essential to remove interfering byproducts such as acetone, thus improving amidation yields. Overall, this integrated methodology provides a green, efficient, and scalable route to access amide‐based building blocks in high optical purity, opening new avenues for sustainable pharmaceutical manufacturing.