Azido-PEG3-amino-OPSS is a PROTAC linker of the PEG class, utilized in the synthesis of PROTAC molecules. This reagent participates in click chemistry due to its azide group, enabling copper-catalyzed azide-alkyne cycloaddition reactions (CuAAc) with alkyne-containing molecules. It also engages in strain-promoted azide-alkyne cycloaddition reactions (SPAAC) with molecules that have DBCO or BCN groups.