The stereochemistry of oxindole alkaloids: uncarines A, B (formosanine), C (pteropodine), D (speciophylline), E (isopteropodine), and F

Abstract

A study of the N.M.R. spectra, circular dichroism, and equilibration reactions of the four stereoisomeric oxindole alkaloids, uncarines C (pteropodine), D (speciophylline), E (isopteropodine), and F, isolated from Ulzcaria berlzaysii F. Muell, and Uncaria ferrea D.C., has allowed assignment of the configuration at all five asymmetric centres. Partial synthesis of uncarines C, D, E, and F from tetrahydroalstonine has provided proof for the assigned stereochemistry of the rings D and E. Comparison of the spectra of uncarines C, D, E, and F, mitraphylline, and isomitraphylline with those of formosanine (uncarine B) has shown that in formosanine and uncarine A the D/E ring junction is trans, and not cis, as previously reported. Formosanine and uncarine A are therefore the C19 epimers of mitraphylline and isomitraphylline respectively.