Seco-labdane diterpenoids from the leaves of Callicarpa nudiflora showing nitric oxide inhibitory activity.

Nine previously undescribed seco-labdane diterpenoids, nudiflopenes A-I, were isolated from the leaves of Callicarpa nudiflora. Their structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic data analysis, and the absolute configurations of these compounds were established by the modified Mosher's method and experimental and calculated electronic circular dichroism spectra. Nudiflopenes A-I belong to the class of seco-labdane diterpenoids. All of the isolates showed inhibitory activities on lipopolysaccharide-induced nitric oxide (NO) production in murine microglial BV-2 cells. The possible mechanism of NO inhibition of some bioactive compounds was also investigated using molecular docking, which revealed interactions of bioactive compounds with the inducible nitric oxide synthase (iNOS) protein.