Thalidomide-O-C3-azide is a chemically modified version of the cereblon (CRBN) inhibitor Thalidomide through click chemistry. It features an azido group, enabling copper-catalyzed azide-alkyne cycloaddition reactions (CuAAc) with alkyne-containing molecules. Thalidomide-O-C3-azide serves as a ligand for E3 ubiquitin ligase and a component in E3 Ligase Ligand-Linker Conjugates, facilitating the synthesis of PROTACs.