Stereoselective Synthesis of Boat-Locked Glycosides Designed as Glycosyl Hydrolase Conformational Probes

A general method for the preparation of galactose derivatives locked in a B-1,B-4 boat conformation has been developed. The boat scaffold was stereoselectively functionalized at the C-1' position by aliphatic and aromatic groups along with azido or hydroxy groups. The configuration at the new stereogenic center was controlled and determined by X-ray diffraction. These molecules were designed to probe the conformational itinerary of the substrate of glycosyl hydrolases. Inhibition assays were performed against a series of commercially available glycosidases, which showed that these enzymes do not harness a B-1,B-4-boat-like transition state.