Design, synthesis, and biological evaluation of novel BTK-targeting proteolysis targeting chimeras (PROTACs) with enhanced pharmacokinetic properties

Bruton's tyrosine kinase (BTK) has been an attractive target in the B-cell malignancies. Significant progress has been achieved in developing effective BTK-targeting small-molecule inhibitors and proteolysis targeting chimeras (PROTACs). Based on noncovalent inhibitor ARQ-531, we previously developed two potent BTK PROTACs 6e and SC-3e, which exhibited poor pharmacokinetic property. Herein, we present our extensive structureactivity relationship (SAR) studies focused on BTK binder, linker and cereblon (CRBN) ligand of SC-3e, resulting in two novel BTK PROTACs FDU28 (compound 25) and FDU73 (compound 27). Compounds 25 and 27 selectively induced rapid and robust degradation of wild type (WT) and C481S mutant BTK in a concentration-, time- and ubiquitin-proteasome system (UPS)-dependent manner without affecting CRBN neo-substrates. Furthermore, compound 27 displayed excellent cell antiproliferative activities, metabolic stability in mouse liver microsomes and improved bioavailability in mice. Overall, 27 is a highly effective and selective BTK degrader that is suitable for in vivo efficacy investigations.