Evolution of a Green and Sustainable Manufacturing Process for Belzutifan: Part 5─Chemoenzymatic Diastereoselective Fluorination/DKR

A ketone fluorination/reduction dynamic kinetic resolution (DKR) was developed for a third-generation synthesis of belzutifan. This new process replaced a precious metal catalyst with a ketoreductase (KRED) in the DKR. Achieving this one-pot reaction required several rounds of enzyme evolution that improved enzyme stability in the presence of acetonitrile and methanol. To maintain development progress and satisfy program timelines, process development around the reaction, workup, and isolation operations was performed in parallel with the enzyme evolution and required ongoing modification, as new variants were made available. Additionally, opportunities for improvements to product quality and process robustness were identified by resolving issues observed in piloting experiments.