Vlasoulides A and B, a pair of neuroprotective C32 dimeric sesquiterpenes with a hexacyclic 5/7/5/5/(5)/7 carbon skeleton from the roots of Vladimiria souliei

Vlasoulides A and B (1 and 2), a pair of epimeric C32 sesquiterpene lactone dimers, featuring a 5/7/5/5/(5)/7 ring system were isolated from the roots of Vladimiria souliei. Their chemical structures were determined by comprehensive analysis of spectroscopic data, including HRESIMS and 1D and 2D NMR spectroscopic data. Their absolute configurations were established by Mosher's method and ECD experiments. Furthermore, biological studies showed that compound 1 showed prominent neuroprotective effects against glutamate-induced neurotoxicity in PC-12 cells, with EC50 values of 13.54 ± 0.33 μM, while, the EC50 value of compound 2 is greater than 30 μM.