Synthesis and absolute stereochemistry assignment of enantiopure dihydrofuro- and dihydropyrano-quinoline alkaloids

The chiral quinoline alkaloids platydesmine 3, platydesmine methosalt 4 and edulinine 9, have been synthesised in enantiopure form via asymmetric dihy droxylation of the achiral alkaloid atanine 1. Chromatographic separation o f MTPA diastereoisomers 20 formed from racemic bromohydrin derivatives of a tanine 1 was a key step in the synthesis of geibalansine 7, edulinine 9, ri balinine 10, Psi-ribalinine 11 and araliopsine 12 as single enantiomers. Th e absolute configurations of (+)-platydesmine methosalt 4 and (-)-Psi-ribal inine 11 were unequivocally determined by X-ray crystallography while stere ochemical correlation and circular dichroism spectroscopy methods were used to assign absolute configurations to platydesmine 3, geibalansine 7, ribal inine 10, araliopsine 12 and edulinine 9. Possible errors which earlier led to the incorrect assignment of absolute configurations of the quinoline al kaloids platydesmine 3, platydesmine methosalt 4, edulinine 9, araliopsine 12 and other related chiral quinoline alkaloids are discussed.