Azido-PEG1-Val-Cit-PABC-PNP, a 1 unit PEG ADC linker, is utilized in the development of antibody-drug conjugates (ADCs) [1]. This compound serves as a click chemistry reagent featuring an Azide group, facilitating copper-catalyzed azide-alkyne cycloaddition reactions (CuAAc) with molecules bearing Alkyne groups. Additionally, it can participate in strain-promoted alkyne-azide cycloaddition (SPAAC) with molecules containing DBCO or BCN groups.