Stereoselective synthesis of α- and β-glycosylamide derivatives from glycopyranosyl azides via isoxazoline intermediates

Treatment of 2-acetoxy glycopyranosyl azides with Ph3P gave isoxazolines by ring closure of the phosphorimine. Coupling of in situ generated isoxazolines with acylating reagents gave mixtures of α- or β-glycopyranosyl amides. The α/β ratio depended upon the acylating reagent and metal salts employed. For example, coupling of isoxazoline 3 with Z-Asp-(SPy)-OBn in the presence of CuCl2 gave exclusively α-N-glucopyranosylasparagine derivative 8. This general procedure has been applied to mono-, di-, and trisaccharide systems. Copyright © 2003 American Chemical Society.