Fluvirosaones A and B, Two Indolizidine Alkaloids with a Pentacyclic Skeleton from Flueggea virosa

Fluvirosaones A (1) and B (2), together with virosecurinine (3), were isolated from Flueggea virosa. Their structures were determined by physical, spectroscopic, and X-ray analysis and confirmed through comparison of the calculated and experimental 13C NMR and electronic circular dichroism (ECD) data. Compounds 1 and 2 represent the first examples of a pentacyclic Securinega alkaloid containing a pentacyclic system and an α,β-unsaturated ketone. Plausible biogenetic pathways of compounds 1 and 2 are proposed.