Sulfo DBCO-Amine is a water-soluble building block containing DBCO moiety. This reagent can be used to derivatize carboxyl-containing molecules or activated esters (e.g. The NHS ester) with DBCO moiety through a stable amide bond. The low mass weight will add minimal spacer to modified molecules and the hydrophilic sulfonated spacer arm will greatly improve water solubility of DBCO derivatized molecules. DBCO is commonly used for copper-free Click Chemistry reactions.