DBCO-PEG4-SS-TCO is a cleavable 4 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs) [1]. DBCO-PEG4-SS-TCO is a click chemistry reagent, it contains a TCO group that can undergo an inverse electron demand Diels-Alder reaction (iEDDA) with molecules containing Tetrazine groups.