A β-D-lactose ligand equipped with a thiol-functionalized linker through a short ethyl spacer. The thiol group can be reacted with other thiol-modified substrates to form disulfide bonds, or reacted with maleimides to form stable thioether conjugates. 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.