BCN-exo-PEG3-maleimide, an ADC linker containing three PEG units, includes the lyophilic bidentate macrocyclic ligand BCN, facilitating the synthesis of macrocyclic complexes. In click chemistry, BCN reacts with azide-containing molecules to form stable triazoles without catalysts. The maleimide group (-Maleimide) degrades in aqueous media and has applications in drug delivery studies.