Stereoselective synthesis of N-glycosyl amino acids by traceless Staudinger ligation of unprotected glycosyl azides

The stereoconservative Staudinger ligation of unprotectedα- and β-glycosyl azides with 2-(diphenylphosphanyl)-4-fluorophenyl esters to afford α- and β-N-glycosyl amino acids is described. The ligation method works reliably well for unprotected β-azides of the gluco, galacto and fuco series. Lower yields (ca. 50 %) were obtained with a β-glucosyl-N-acetyl azide. The reaction of an α-glucosyl azide also led to major improvements compared with the use of non-fluorinated phosphanes. All the N-glycosyl amino acid products can be isolated and byproducts removed from the crude reaction mixtures by simple water extraction.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)