Diterpenoids from Isodon rubescens and their nitric oxide production inhibitory activity

Six new ent-kaurane diterpenoids, isodonrubescins A–F (1–6), together with twenty-five known ent-kaurane diterpenoids (7–31), a known ent-atisane diterpenoid (32), and two known ent-abietane diterpenoids (33–34), were isolated from Isodon rubescens. Their structures were established by means of extensive MS and NMR data analysis. Among the all isolates, compound 7 was found in a natural product for the first time, and ent-atisane diterpenoid was discovered from I. rubescens in Hubei Province, P. R. China for the first time. Furthermore, all the isolated compounds were tested for their NO production inhibitory activity in LPS stimulated RAW264.7 cells. Compounds 7–9, 12, 13, 16, and 17 displayed NO production inhibitory activities with IC50 values ranging from 1.36 to 18.25 μM, respectively.