Discovery of a Series of Covalent Ligands That Bind to Cys77 of the Von Hippel–Lindau Tumor Suppressor Protein (VHL)

Most ligands for the Von Hippel-Lindau tumor suppressor (VHL) bind at the HIF-1α binding site. Ligands that bind to allosteric sites on VHL could be highly valuable for the field of protein degradation, therefore, a covalent hit identification campaign was run targeting Cys77 on VHL. Hit <b>2</b> bound selectively to Cys77 on VHL and did not alkylate the reactive Cys89 on Elongin B. It showed time- and concentration-dependent labeling, with a <i>k</i> _inact/<i>K</i> _I of 0.30 M^-1 s^-1, and does not affect binding at the HIF-1α site. This hit ligand was optimized to afford compound <b>15</b> which showed improved potency and labeling of VHL. An X-ray structure of a close analogue was determined revealing the compound binding in a shallow groove on the surface of VHL. These are the first small molecules that bind covalently to an allosteric site on VHL and provide a suitable starting point for further optimization.