Lobophytones A-G, new isobiscembranoids from the soft coral Lobophytum pauciflorum.

Seven new biscembranoids, lobophytones A-G (1-7), together with three known biscembranes were isolated from the Chinese soft coral Lobophytum pauciflorum. Their structures were elucidated by the analysis of 1D and 2D NMR (COSY, HSQC, HMBC, and NOESY) data in association with IR and MS experiments. The absolute configurations of compound 1 were determined by X-ray diffraction using the Flack parameter. Lobophytones A-G differ from the "normal" biscembranoids due to the antipodal Diels-Alder cycloaddition between cembranoid-diene and cembranoid-dienophile. The biogenetic pathway of the isolated compounds is depicted. Compound 4 showed significant inhibition toward LPS-induced nitric oxide (NO) in mouse peritoneal macrophage with IC(50) = 4.70 microM.