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

The stereoconservative Staudinger ligation of unprotected\u3b1- and \u3b2-glycosyl azides with 2-(diphenylphosphanyl)-4-fluorophenyl esters to afford \u3b1- and \u3b2-N-glycosyl amino acids is described. The ligation method works reliably well for unprotected \u3b2-azides of the gluco, galacto and fuco series. Lower yields (ca. 50\u2009%) were obtained with a \u3b2-glucosyl-N-acetyl azide. The reaction of an \u3b1-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.(\ua9 Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009