Bioactive diterpenoids from Croton laevigatus.

Eight previously undescribed diterpenoids, crolaevinoids A-H, including two halimanes, four clerodanes, and two laevinanes, along with six known analogues were isolated from the twigs of Croton laevigatus. The structures of the previously undescribed were elucidated by spectroscopic analysis, and their absolute configurations were determined by combination of a single crystal X-ray diffraction and CD analysis (exciton chirality and Rh2(OCOCF3)4-induced methods). Crolaevinoids A and B represent the first halimane diterpenoids with a unique lactone bridge between C-12 and C-17. All compounds were evaluated for their inhibitory effects on the nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW264.7 macrophage cells. Furocrotinsulolide A and 3,4,15,16-diepoxy-cleroda-13(16),14-diene-12,17-olide exhibited pronounced inhibition of NO production with IC50 values of 10.4 ± 0.8 and 6.0 ± 1.0 μM, respectively, being more potent than the positive control, quercetin (IC50 = 13.1 ± 1.9 μM).