Syntheses of (−)-8-epi-Swainsonine and (−)-1,8-Di-epi-swainsonine, Stereoisomers of Physiologically Interesting Indolizidine Alkaloid, Swainsonine

Abstract Two stereoisomers of the indolizidine alkaloid swainsonine, (−)-8-epi-swainsonine (2) and (−)-1,8-di-epi-swainsonine (3), have been synthesized from the known methyl 3-acetamido-2-O-acetyl-4,6-O-benzylidene-3-deoxy-α-d-glucopyranoside and methyl 3-acetamido-2-O-acetyl-3-deoxy-4,6-di-O-mesyl-α-d-glucopyranoside (14), respectively. The key pyrrolidine ring formation was achieved by intramolecular cyclization of a 6-O-tosyl derivative or a di-O-mesyl derivative 14 efficiently. The α-mannosidase inhibitory activity of the synthetic 2 and 3 was also evaluated.