Stereoselective Synthesis of N-Glycosyl Amino Acids by Traceless Staudinger Ligation of Unprotected Glycosyl Azides

摘要

The stereo conservative Staudinger ligation of unprotected alpha- and beta-glycosyl azides with 2-(diphenylphosphanyl)-4-fluorophenyl esters to afford alpha- and beta-N-glycosyl amino acids is described. The ligation method works reliably well for unprotected beta-azides of the gluco, galacto and fuco series. Lower yields (ca. 50 %) were obtained with a beta-glucosyl-N-acetyl azide. The reaction of an alpha-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.