Novel and Neuroprotective Tetranortriterpenoids from Chinese Mangrove Xylocarpus granatum Koenig

Eight new tetranortriterpenoids (1–8) were isolated from the twigs and leaves of the Chinese mangrove plantXylocarpus granatum, together with four related known ones (9–12). The structures of new compounds were elucidated by detailed spectroscopic analysis. The absolute configuration of 9-epixylogranatin A (1) was determined by time-dependent density functional theory-electronic circular dichroism (TDDFT-ECD) calculations of the solution conformers. Xylogranatumin A (2) represents the first example of the 9, 10-secolimonoid with an unprecedented oxygen-bridged B ring (2,7-dioxabicyclo[2.2.1]-heptane). All the isolates were evaluated for thein vitroneuroprotective activity, both compounds 11 and 12 displayed moderate effects against H2O2-induced neurotoxicity in PC12 cells at the concentration of 10μM, with an increase in cell viability of 12.0% and 11.6%, respectively.