t-Boc-Aminooxy-PEG4-azide is a click chemistry reagent with a t-Boc-aminooxy group. The azide group is reactive with alkyne, such as BCN, DBCO via Click Chemistry to yield a stable triazole linkage. The protected aminooxy can be deprotected under mild acidic conditions. The hydrophilic PEG spacer increases solubility in aqueous media.