Industry-Oriented Route Evaluation and Process Optimization for the Preparation of Brexpiprazole

Efforts toward route evaluation and process optimization for the preparation of brexpiprazole (1) are described. Starting from commercially available dihydroquinolinone 11, a three-step synthesis route composed of O-alkylation, oxidation, and N-alkylation was selected for industry-oriented process development aiming to reduce side reactions and achieve better impurity profiles. The reaction conditions of the three steps were investigated, and the control strategy for the process-related impurities was established. The optimized process was validated on the kilogram scale and now is viable for commercialization, with the results of not less than 99.90% purity of 1 (by HPLC) and not more than 0.05% of persistent impurities 15 and 16.