Syntheses of Legionaminic Acid, Pseudaminic Acid, Acetaminic Acid, 8- epi -Acetaminic Acid, and 8- epi -Legionaminic Acid Glycosyl Donors from N -Acetylneuraminic Acid by Side Chain Exchange.

Metaperiodate cleavage of the glycerol side chain from an N -acetyl neuraminic acid-derived thioglycoside and condensation with the two enantiomers of the Ellman sulfinamide afford two diastereomeric N -sulfinylimines from which bacterial sialic acid donors with the legionaminic and acetaminic acid configurations and their 8- epi -isomers are obtained by samarium iodide-mediated coupling with acetaldehyde and subsequent manipulations. A variation on the theme, with inversion of the configuration at C5, similarly provides two differentially protected pseudaminic acid donors.