GlcNAc-Thiazoline conformations.

The title compound, a powerful inhibitor of retaining N-acetylhexosaminidases, can move freely among three pyranose solution conformations of similar energy-two twist boats and the (4)C(1) chair-as revealed by NMR, calculational, and crystallographic studies. It binds in the enzyme active site only in the pseudo-(4)C(1) conformation, however, in which it most closely resembles the hypothetical bound substrate transition state, a (4)E sofa that is approximately trigonal bipyramidal at the anomeric carbon.