Thalidomide -O-C5-azide is a click chemistry modification of the cereblon (CRBN) inhibitor Thalidomide. Thalidomide -O-C5-azide contains an azide group and can undergo copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing alkyne groups. Thalidomide -O-C5-azide can be used as a ligand of E3 ubiquitin ligase and Linker conjugates ( E3 Ligase Ligand-Linker Conjugates ) for the synthesis of PROTACs.