Swainsonine from Astragalus

Harris et al. postulated that (liS, 8aS)-( + )-l-hydroxyindolizidine (109) and (lf ,8aS)-l-hydroxyindolizidine (110) were pivotal intermediates in the biosynthesis of slafi-amine (3) and swainsonine (cf. Section lU.C) in the fungus Rhizoctonia leguminicola (74). Compound 110 was subsequently isolated as e acetate from extracts of the diablo locoweed. Astragalus oxyphysus (75). 

Both (lS,8aS)-(- -)-indohzidin-l-ol (88) and (lR,8a -(—)-indohzidin-l-ol (89) are intermediates in the biosynthesis of slaframine (9) and swainsonine (c Section 3.5) in the fungus Rhizoctonia legutninicolaf The former has also been isolated as the acetate from the diablo locoweed. Astragalus oxyphysus7 A related compound, 8-methylindolizidin-l-ol (90), has been claimed as a new toxic principle in extracts of Oxytropis kansuensis but details are sketchy (Figure 6). AH recent publications in this area have dealt with the synthesis of 88, 89, and the enantiomer of 89. 

Swainsonine was isolated from the Australian legume Swainsonia canescens 18) and in the United States from two species of locoweed Astragalus lentiginosum and Oxytropis sericea 19), Swainsonine is a strong inhibitor of a-mannosidase. 

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