Design of Potent and Selective Covalent Inhibitors of Bruton’s Tyrosine Kinase Targeting an Inactive Conformation

Abstract

Bruton's tyrosine kinase (BTK) is a member of the TEC kinase family and is selectively expressed in a subset of immune cells. It is a key regulator of antigen receptor signaling in B cells and of Fc receptor signaling in mast cells and macrophages. A BTK inhibitor will likely have a positive impact on autoimmune diseases which are caused by autoreactive B cells and immune-complex driven inflammation. We report the design, optimization, and characterization of potent and selective covalent BTK inhibitors. Starting from the selective reversible inhibitor <b>3</b> binding to an inactive conformation of BTK, we designed covalent irreversible compounds by attaching an electrophilic warhead to reach Cys481. The first prototype <b>4</b> covalently modified BTK and showed an excellent kinase selectivity including several Cys-containing kinases, validating the design concept. In addition, this compound blocked FcγR-mediated hypersensitivity <i>in vivo</i>. Optimization of whole blood potency and metabolic stability resulted in compounds such as <b>8</b>, which maintained the excellent kinase selectivity and showed improved BTK occupancy <i>in vivo</i>.