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)