N3-C3-NHS ester is a noncleavable ADC linker used in the synthesis of antibody-drug conjugates (ADCs). N3-C3-NHS ester is a click chemistry reagent, it contains an Azide group and can undergo copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing Alkyne groups. Strain-promoted alkyne-azide cycloaddition (SPAAC) can also occur with molecules containing DBCO or BCN groups.