Adventures in Atropisomerism: Development of a Robust, Diastereoselective, Lithium-Catalyzed Atropisomer-Forming Active Pharmaceutical Ingredient Step

The final step in the route to BMS-986142, a reversible inhibitor of the BTK enzyme, involves the diastereoselective construction of a chiral axis during the base-mediated cyclization of the quinazolinedione fragment. Optimization of the reaction to minimize formation of the undesired atropisomer led to the discovery that the amount of base and nature of the counterion play a vital role in the diastereoselectivity of the reaction. The highest diastereoselectivities were observed with a catalytic amount of LiOt-Bu. Development of a crystallization to selectively purge the undesired atropisomer is reported. Interestingly, ripening of the crystalline API was observed and further investigated, leading to a significant increase in the purity of the active pharmaceutical ingredient.