– Amino-PEG4-bis-PEG3-N3, a cleavable 7-unit PEG ADC linker, is used in synthesizing antibody-drug conjugates (ADCs) [1]. As a click chemistry reagent, it contains an Azide group and can participate in copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules possessing Alkyne groups. Additionally, strain-promoted alkyne-azide cycloaddition (SPAAC) can occur with molecules containing DBCO or BCN groups.