Vlasoulamine A, a Neuroprotective [3.2.2]Cyclazine Sesquiterpene Lactone Dimer from the Roots of Vladimiria souliei

Vlasoulamine A (1), an unprecedented sesquiterpene lactone dimer featuring a fully hydrogenated pyrrolo[2,1,5-cd]indolizine core, and vlasoulones A and B (2 and 3), a pair of epimeric dimers formed from a proposed Diels–Alder [4 + 2] cycloaddition between a germacrane sesquiterpene lactone and a eudesmane sesquiterpene, were isolated from the roots of Vladimiria souliei. Their structures and absolute configurations were established by NMR, MS, and single-crystal X-ray spectroscopic analysis. Moreover, 1 exhibited neuroprotective activity when evaluated for glutamate-induced cytotoxicity, nuclear Hoechst 33258 staining, and measuring intracellular reactive oxygen species levels, using a rat pheochromocytoma PC12 cell-based model system.