Early Development Scale-Up of a Novel CXCR Antagonist: Focus on Racemic and Stereoselective Routes of a Key Intermediate

Efforts toward a convenient and scalable process for the synthesis of a novel CXCR antagonist 1 are described, with a specific focus on a chiral key intermediate. Two generations of a racemic route have been developed for short-term deliveries, and a stereoselective process has been devised for longer term plans. Key steps involved an enzymatic resolution of racemic tetrahydrothiophene-2-carboxylic acid to install the (2R) stereocenter, the mild and efficient preparation of a sterically hindered sulfinimine under a nitrogen flow, and its stereoselective reduction to set up the (1S) amine stereocenter. The process has been scaled-up to multikilogram scale for the racemic approach, and the stereoselective route was demonstrated on multigram scale.