From Chiral Resolution to Diastereoselective Ellman Chemistry to Biocatalysis: Route Evolution for the Efficient Synthesis of the Tetrahydrobenzoazepine Core of BTK Inhibitor BIIB091

Two improved routes to BIIB091 key tetrahydrobenzoazepine core (1) were developed to support tox and early clinical demands. The first improved route takes advantage of a diastereoselective Ellman’s sulfinimine reduction as the key step of chiral amine synthesis. This route was successfully scaled up to support API manufacturing for early clinical trials. The second improved route uses an amine transaminase (ATA) biocatalysis reaction of an N-Boc ketone (15) precursor, which was prepared by applying a trifluoroacetamide-protecting group for effective azepine ring construction and protecting group swap. The ATA route is demonstrated at a subkilogram scale and has the potential to become a late clinical and commercial route due to its significant improvements in synthetic efficiency, overall yield, and process greenness.