A β-D-N-acetylglucosamine (GlcNAcβ) ligand equipped with a terminal carboxylic acid through a hydrophilic PEG3 spacer. The carboxylic acid can be activated to NHS, sulfo-NHS, or pentafluorophenyl esters and reacted with amine-functionalized platforms or lysine residues on proteins and peptides to form amide bonds. This compound provides a β-N-acetylglucosamine (GlcNAcβ) building block for glycoconjugate synthesis and the construction of probes for GlcNAc-recognizing proteins and lectins; it is also relevant to O-GlcNAc and N-glycan biosynthesis research and a substrate for galactosyltransferases.