TCO-PEG1-Val-Cit-PABC-PNP is a 1-unit PEG ADC linker that facilitates the synthesis of antibody-drug conjugates (ADCs) [1]. Serving as a click chemistry reagent, it features a TCO group capable of partaking in an inverse electron demand Diels-Alder reaction (iEDDA) with Tetrazine-grouped molecules.