Boc-L-Tyr(PEG(3)-N3)-OH is a click chemistry agent containing azide. It contains an azide group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing alkyne groups. It can also undergo ring strain-promoted alkyne-azide cycloaddition (SPAAC) with molecules containing DBCO or BCN groups.