EP300/CBP ligand 2 (compound S19) serves as a specific ligand for the bromodomain of CREB binding protein (CBP) and E1A-associated protein (EP300). It plays a critical role in PROTAC technology by acting as a target protein ligand. By linking to an E3 ubiquitin ligase ligand via the PROTAC Linker, it facilitates the synthesis of PROTAC molecules capable of targeted protein degradation. For instance, when EP300/CBP ligand 2 is connected to the conjugate (E3 ubiquitin enzyme ligand + Linker) Thalidomide-NH-C10-Boc, it results in the formation of the PROTAC molecule dCE-2.