Targeted Protein Degradation by Electrophilic PROTACs that Stereoselectively and Site-Specifically Engage DCAF1

Targeted protein degradation induced by heterobifunctional compounds and Molecular Glues presents an exciting avenue for chemical probe and drug discovery. To date, small-molecule ligands have been discovered for only a limited number of E3 Ligases, which is an important limiting factor for realizing the full potential of targeted protein degradation. We report herein the discovery by chemical proteomics of azetidine acrylamides that stereoselectively and site-specifically react with a cysteine (C1113) in the E3 Ligase substrate receptor DCAF1. We demonstrate that the azetidine acrylamide ligands for DCAF1 can be developed into electrophilic proteolysis-targeting chimeras (PROTACs) that mediated targeted protein degradation in human cells. We show that this process is stereoselective and does not occur in cells expressing a C1113A mutant of DCAF1. Mechanistic studies indicate that only low fractional engagement of DCAF1 is required to support protein degradation by electrophilic PROTACs. These findings, taken together, demonstrate how the chemical proteomic analysis of stereochemically defined electrophilic compound sets can uncover ligandable sites on E3 Ligases that support targeted protein degradation.