Xylopidimers A–E, Five New Guaiane Dimers with Various Carbon Skeletons from the Roots of Xylopia vielana

[Image: see text] Five new guaiane dimers, xylopidimers A–E (1–5), were isolated and identified from the roots of Xylopia vielana. The structures of 1–5 were elucidated by spectroscopic analysis and further confirmed by single-crystal X-ray diffraction. On the basis of the results of single-crystal X-ray analysis, 1–5 showed different carbon skeletons. Among these compounds, the unique connecting patterns of 1 and 2 caused significant differences on their carbon skeletons, which have not been reported. Moreover, 3–5 were also three new guaiane dimers. Among these compounds, 4 exhibited potent inhibitory activity against the production of nitric oxide with an IC(50) value of 4.59 μM in RAW264.7 cells stimulated by lipopolysaccharide.