A β-D-lactose ligand equipped with a terminal alkyne through a hydrophilic PEG3 spacer. The alkyne couples to azide-functionalized partners via copper-catalyzed azide-alkyne cycloaddition (CuAAC), forming stable 1,2,3-triazole linkages. This compound provides a lactose (Galβ1-4Glc) building block for glycoconjugate synthesis and the construction of probes for galactose-recognizing proteins, including galectins and the hepatic asialoglycoprotein receptor; it is a substrate for sialyltransferases and other glycosyltransferases.