Bisindole alkaloids with nitric oxide inhibitory activities from an alcohol extract of the Isatis indigotica roots.

Eight bisindole alkaloids including six undescribed ones (1a/1b-5) were isolated from an alcohol extract of the Isatis indigotica roots. Their structures and absolute configurations were supported by extensive spectroscopic data analysis, including 1D, 2D NMR, HRESIMS data, specific rotation data, and comparison of the experimental and calculated ECD data. Compounds 1a and 1b were determined to be a pair of enantiomers with a ratio of approximately 1:1 by chiral-phase chromatography analysis while compound 4 was elucidated as a new type of bisindole alkaloid with the aglycone categorized as bis(indole-1'/3″-yl)methane. All the isolated compounds were tested for their nitric oxide (NO) inhibitory effects and 1-4 and 6 exhibited inhibitory effects with IC values ranging from 11.0 to 37.6 μM.