Fig. 1.

E3 ligase ligands used for PROTACs: thalidomide derivatives targeting Cereblon. Bestatin and compound 7 are ligands of cIAP [34], nutlin is a ligand of MDM2 [26]. The VHL ligand 9 was optimized starting from a peptide using structure guided design [35]. The asterisk shows the attachment point for the linker.