Synthesis of non-natural O-glycosylamino acids derived from n-pentenyl glycosides; Model studies and proof of principle for glycopeptide synthesis

Model studies on the transformation of the olefinic unit contained in n-pen tenyl glycosides (NPGs) to glycoamino acids is described. The methodology i nvolves a Horner-Emmons olefination with a protected glycine derived phosph onate, followed by asymmetric hydrogenation using Du-PHOS catalyst system. A variety of protecting group schemes have been investigated and their ster eoselectivity in the hydrogenation reaction determined. With N-Boc and C-TS E ester protection, the diastereoselectivity in the reaction was measured b y H-1 NMR analysis with "racemic" product as a comparison. These modified g lycoamino acids are also useful for peptide synthesis. The methodology appe ars to be general and was extended to include the synthesis a glycoamino ac id containing the complex hexasaccharide Globo-H.