Manufacture of the PI3K β-Sparing Inhibitor Taselisib. Part 2: Development of a Highly Efficient and Regioselective Late-Stage Process

A highly efficient and regioselective manufacturing route for the phosphoinositide 3-kinase β-sparing inhibitor taselisib was developed. Highlights of the synthesis include: (1) magnesium-mediated formation of a challenging cyclic amidine; (2) regioselective imidazole construction via alkylation/condensation with bromopyruvic acid; and (3) triazole formation with 2-isopropyl acetamidrazone to generate the key bromobenzoxazepine core intermediate. Subsequent highly efficient one-pot palladium-catalyzed Miyaura borylation/Suzuki cross-coupling/saponification, followed by a 1,1′-carbonyldiimidazole-mediated coupling with ammonia, led to the pentacyclic taselisib. This new synthetic approach provides a more efficient route to taselisib with a significant decrease in process mass intensity compared to the previous early development routes to the bromobenzoxazepine core. Finally, implementation of a controlled crystallization provided the active pharmaceutical ingredient with the desired polymorphic form.