An N-acetyl-β-D-glucosamine derivative bearing an aminooxy (-O-NH₂) group at the anomeric or aglycone position. The aminooxy handle reacts selectively with aldehydes and ketones to form stable oxime linkages under mild aqueous conditions, providing a bioorthogonal route to conjugate the GlcNAc ligand to carbonyl-containing molecules, including oxidized glycoproteins, oxidized antibodies, and ketone-tagged biomolecules. Useful for site-specific glycoconjugation, oxime ligation chemistry, and GlcNAc-presentation studies.