Nitric oxide inhibitors with a spiro diterpenoid skeleton from Scutellaria formosana: Structures, NO inhibitory effects, and interactions with iNOS

A phytochemical investigation to obtain new NO inhibitors resulted in the isolation of five new spiro diterpenoids (1 −5) from the aerial parts of Scutellaria formosana. The structures were elucidated on the basis of extensive 1D and 2D NMR spectroscopic data analysis, and the absolute configurations of these compounds were established via comparison of experimental and calculated electronic circular dichroism (ECD) spectra. The nitric oxide (NO) inhibitory effects were evaluated and all of the compounds showed inhibitory effects on lipopolysaccharide-induced NO production in murine microglial BV-2 cells. The possible mechanism of NO inhibition of bioactive compounds was also investigated using molecular docking, which revealed the interactions of bioactive compounds with the iNOS protein.