Process Development and Scale Up of a Selective JAK3 Covalent Inhibitor PF-06651600

A scalable process for PF-06651600 (1) has been developed through successful enabling of the first generation syntheis. The synthesis highlights include the following: (1) replacement of costly PtO2 with a less expensive 5% Rh/C catalyst for a pyridine hydrogenation, (2) identification of a diasteroemeric salt crystallization to isolate the enantiomerically pure cis-isomer directly from a racemic mixture of cis/trans isomers, (3) a high yielding amidation via Schotten–Baumann conditions, and (4) critical development of a reproducible crystallization procedure for a stable crystalline salt (1·TsOH), which is suitable for long-term storage and tablet formulation. All chromatographic purifications, including two chiral SFC chromatographic separations, were eliminated. Combined with other improvements in each step of the synthesis, the overall yield was increased from 5% to 14%. Several multikilogram batches of the API have been delivered to support clinical studies.