An α-N-acetylneuraminic acid (Neu5Ac) ligand equipped with an azide handle through a hydrophilic PEG3 spacer. The terminal azide couples to alkynes via copper-catalyzed azide-alkyne cycloaddition (CuAAC) or to DBCO and related strained alkynes via copper-free click chemistry, forming stable 1,2,3-triazole linkages. This terminal sialic acid (Neu5Ac) residue is a recognition element for Siglecs and sialic-acid-binding proteins, and serves as a building block and substrate for sialidase and sialyltransferase studies.