Ac4ManNAz is an azido-containing metabolic glycoprotein labeling reagent. Ac4ManNAz can be used to selectively modify proteins. Ac4ManNAz can be used in cell labeling, tracking and proteomic analysis. Ac4ManNAz 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. It can also undergo strain-promoted alkyne-azide cycloaddition (SPAAC) reactions with molecules containing DBCO or BCN groups.