A β-D-galactose ligand equipped with a free thiol through a high-molecular-weight PEG5000 spacer. The thiol reacts with maleimides to form stable thioether conjugates or with other thiols to form disulfide bonds; it is also compatible with thiol-gold chemistry for surface immobilization. This compound provides a β-anomeric galactose building block for glycoconjugate synthesis, glycomimetic research, and the construction of probes for galactose-recognizing proteins, including galectins and other lectins. Terminal β-Gal residues are also a substrate for glycosyltransferases, including sialyltransferases and fucosyltransferases.