Mono-, di- and trisaccharide derivatives of 1,2-unsaturated N-acetyl-d-glucal have been synthesized and shown to function as tight-binding inhibitors/slow substrates of representative hexosaminidases. Turnover is slow and not observed in the thioamide analogue, allowing determination of the 3-dimensional structure of the complex. Inhibition is insensitive to pH and to mutation of key catalytic residues, consistent with the uncharged character of the inhibitor. These properties could render this inhibitor class less prone to development of resistance.