Inhibition of nitric oxide production by clerodane diterpenoids from leaves and stems of Croton poomae Esser.

Chromatographic separation of crude extracts from the leaves and stems of Croton poomae Esser led to the isolation of two new clerodane diterpenes crotonolide K (1) and furocrotinsulolide A acetate (2) and six known clerodane diterpenes (3-8), together with twelve known compounds (9-20). Their structures were established from spectroscopic analysis. The clerodane diterpenoids 1-8 were evaluated for inhibition of nitric oxide (NO) production in LPS-activated RAW 264.7 macrophages. Compounds 1, 2, 5, 7 and 8 showed potent inhibitory effects, with IC50 values ranging from 32.19 to 48.85 μM, which is better than both the standard drugs indomethacin (154.5 μM) and dexamethasone (56.28 μM).