Elaeocarpus Alkaloids. V. The Alkaloids of Elaeocarpus kaniensis

Abstract

The leaf alkaloids of Elaeocarpus kalziensis Schltr. are a complex mixture, from which eight new alkaloids have been separated. Spectroscopic evidence has shown that these alkaloids are a closely interrelated group of indolizidines and structures have been assigned to elaeokanine A (1), elaeokanine B (8), elaeokanine C (10), elaeokanine D (12), elaeokanine E (17), and elaeokanidine A (18), Elaeokanidine B and elaeokanidine C are stereoisomers of elaeokanidine A, but the spectroscopic evidence is insufficient for the structures of these alkaloids to be assigned unequivocally. The assigned structures in all cases indicate relative and not absolute stereochemistry. The structures established for elaeokanine A, elaeokanine B, and elaeokanine C by spectroscopic methods have been confirmed by synthesis. Catalytic hydrogenation of synthetic 8-n-butyryl-7-oxoindolizidine (22) over platinum oxide in ethanol afforded (±)elaeokanine C in 30% yield. Under these hydrogenation conditions a major product was 8-n-butyryl-7-oxo-8,9-dehydroindolizidine (23) formed by loss of hydrogen from (22).