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

Abstract

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.