title: Highly efficient preparation of tumor antigen-containing glycopeptide building blocks from novel pentenyl glycosides.
abstract: O-Glycosylated amino acids containing the tumor-associated T(Tf)-antigen (beta-D-Gal-(1-->3)-alpha-D-GalNAc) disaccharide unit were conveniently synthesized in seven steps starting from D-galactose via an n-pentenyl glycoside (NPG) building block. Azidonitration of 3,4,6-tri-O-acetyl-D-galactal, followed by nitrate displacement with simultaneous acetate hydrolysis with sodium 4-penten-1-oxide, afforded n-pentenyl 2-deoxy-2-azidogalactoside (3) in near quantitative yield. Subsequent high-yielding transformations resulted in the synthesis of the key glycosyl donor n-pentenyl beta-disaccharide 5 that was employed for the stereospecific preparation of glycosyl amino acids via NIS-promoted glycosylations with serine or threonine acceptors. The surprising utility of the reaction of sodium 4-penten-1-oxide with anomeric nitrates encouraged the detailed exploration of the action of a variety of nucleophiles on anomeric nitrates for the synthesis of useful 2-azido glycosyl donors directly from the 'classic' Lemieux azidonitration product of protected galactals. This expedient synthesis (28% overall yield from 1 to 7a) that makes use of heretofore rarely exploited pentenyl 2'-azidoglycosides, should be a valuable entry in the armamentarium of routes to biologically relevant glycopeptides in both mono- and multivalent forms.
mesh_terms: D000951:Antigens, Neoplasm / Q000737:chemistry*; D006020:Glycopeptides / Q000138:chemical synthesis* / Q000737:chemistry; D006027:Glycosides / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism
chemical_list: D000951:Antigens, Neoplasm; D006020:Glycopeptides; D006027:Glycosides