Discovery of Small-Molecule Ligands for the E3 Ligase STUB1/CHIP from a DNA-Encoded Library Screen

STIP1 homology and U-box containing protein 1 (STUB1), also known as the C-terminus of Hsc70-interacting protein (CHIP), is an E3 ligase that plays a crucial role in removal of misfolded proteins via Hsc70. A DEL screen was run against CHIP to identify small-molecule binders. Two hits were identified that were confirmed by biochemical and biophysical techniques, including 2D NMR. X-ray crystal structures were obtained, which revealed binding to the peptide binding site. Fragment-based deconstruction indicated that hit 2 was a suitable starting point for optimization. During the optimization, an unexpected rearrangement of an oxadiazole from an array hit led to the exploration of an amide vector. This resulted in the discovery of compound 5, which is the most potent small-molecule ligand for CHIP identified to date and a suitable starting point for further optimization into a tool molecule or PROTAC warhead.