7-Octynoic acid (compound 42) is a PROTAC linker and can be used in the synthesis of a series of PROTACs. PROTACs contain two different ligands connected by a linker; one is a ligand for an E3 ubiquitin ligase and the other is for the target protein. PROTACs exploit the intracellular ubiquitin-proteasome system to selectively degrade target proteins^[1].