Methyltetrazine-DBCO TEA is a non-cleavable ADC linker utilized in the synthesis of antibody-drug conjugates (ADC). This compound serves as a click chemistry reagent featuring a DBCO group that facilitates strain-promoted alkyne-azide cycloaddition (SPAAC) with azide-containing molecules. In addition, Methyltetrazine-DBCO TEA includes a Tetrazine group, enabling the inverse electron-demand Diels-Alder reaction (iEDDA) with TCO-containing molecules.