Identification, Synthesis, Characterization, and Control Strategy Establishment for Process Impurities of Baloxavir Marboxil

This manuscript provides a comprehensive summary of 12 process impurities in baloxavir marboxil, including four previously unreported impurities. Through identification, synthesis, and characterization using MS and NMR techniques, the formation pathways of each impurity were proposed to enhance the understanding of the process. Corresponding control strategies were established. Three batches of kilogram-scale demonstrations were conducted, resulting in baloxavir marboxil with a yield of 51%, purity exceeding 99.8%, and a single impurity detected at <0.10%, all achieved from chiral starting material A-1. Notably, the two genotoxic impurities were effectively purged to levels below detection limits, meeting the criteria specified by the Threshold of Toxicological Concern (TTC).