Synthesis of the isotopically labeled JAK1/3 inhibitor [D7]-R545 and its oxidative metabolite [D7]-R935: Protecting group-directed regioselective bromination to access 3,4,5-substituted anilines

An extensive medicinal chemistry campaign and subsequent SAR studies led to the discovery of the highly potent and selective JAK1/3 inhibitor R545. To support advanced pre-clinical DMPK studies of R545, the isotopically labeled versions of the drug and its metabolite R935 were required. Herein, we describe the development of synthetic routes to deuterium-labeled [D7]-R545 and its oxidative metabolite [D7]-R935. Deuterium atoms were introduced at several sites in the target molecules by employing a convergent synthesis strategy. The desired regiochemistry at the right-hand side of [D7]-R935 was established via a newly discovered protecting group-directed bromination. The described synthetic approach gave rise to the desired deuterium-labeled target compounds and sufficient quantities were synthesized to enable pre-clinical DMPK studies.