Indolizidine alkaloids absolute stereochemistry

Swainsonine is a trihydroxylated bicyclic indolizidine alkaloid with four chiral centres, whose relative stereochemistry was determined by X-ray crystallographic analysis and the absolute configuration was deduced on the basis of biosynthetic and asymmetric induction studies, and then confirmed by an enantiospecific synthesis from D-mannose [2a]. 

When first isolated from extracts from the skin of the Columbian poison frog Dendrohates histrionicus as a new alkaloid component, indolizidine 195B s (654) absolute stereochemistry needed to be established. Consequently, both enantiomers were synthesized. 

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