Scalable Atroposelective Synthesis of MRTX1719: An Inhibitor of the PRMT5/MTA Complex

MRTX1719 was identified as a potent inhibitor of the PRMT5/MTA complex, designed to selectively target MTAP-deleted cancers. A scalable synthesis of this atropisomeric compound and an efficient isolation of the desired isomer were required to support Phase 1 clinical trials, and this was established through further development of the racemic medicinal chemistry route. In the key step, the desired (M)-atropisomer of MRTX1719 was amplified from racemic API by combining crystallization (20 °C) and racemization (160 °C, 4 min). Concurrent execution of these, ostensibly incompatible, operations was enabled by a continuous flow setup (SPACE = Simultaneous Processing of Antagonistic Chemical Events) providing 98.4% e.e. of (M)-atropisomer in 75% yield from racemic API on 12 kg scale. Process development targeting earlier steps of the API synthesis led to several impactful revisions including desymmetrization of 4-chlorobenzamide to access the 6-substituted-4-(aminomethyl)phthalazin-1(2H)-one ring system, improved borylation conditions (Suzuki–Miyaura or photocatalytic), and demonstration of an economically viable route to the challenging pentasubstituted benzene from 1,4-difluorobenzene and cyclopropyl methyl ketone.