Azido-C1-PEG4-C3-NH2 is a PROTAC linker within the PEG class, utilized in the synthesis of PROTAC molecules. Serving as a click chemistry reagent, it features an azide group capable of engaging in copper-catalyzed azide-alkyne cycloaddition reactions (CuAAC) with alkyne-containing molecules. Additionally, it can undergo strain-promoted azide-alkyne cycloaddition (SPAAC) with molecules containing DBCO or BCN groups.