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)