Xylopsides A-D, four rare guaiane dimers with two unique bridged pentacyclic skeletons from Xylopia vielana.

Four unprecedented guaiane dimers, xylopsides A-D (1-4), were isolated and identified from the roots of Xylopia vielana. The structures of 1-4 were elucidated by spectroscopic analysis, Cu Kα X-ray crystallography and CD spectra. 1-4 showed two bridged pentacyclic skeletons between two guaiane-type sesquiterpenes, which were characterized as two different bridged ring systems. Among these compounds, 4 exhibited a moderate inhibitory activity against the production of nitric oxide with an IC50 value of 25.7 μM in RAW264.7 cells stimulated by LPS.