Tetracyclic diterpenoids with isomerized isospongian skeleton and labdane diterpenoids from the fruits of Amomum kravanh

Four novel Diterpenoids, including three tetracyclic diterpenes with isomerized isospongian skeletons, kravanhins A-C (1-3), and kravanhin D (4), and three new labdane diterpenes (5-7) were isolated from the fruits of Amomum kravanh. Compounds 1-4 had unprecedented isospongian diterpene skeletons with a trans-anti-cis fused tricyclic ring system. The structures of compounds 1-7 were established on the basis of extensive analysis of NMR spectra, CD, and X-ray crystallography. Compound 2 showed inhibitory activity on nitric oxide production in lipopolysaccharide-induced RAW264.7 macrophages with an IC(50) value of 36.2 μM.