Isatindigodiphindoside, an alkaloid glycoside with a new diphenylpropylindole skeleton from the root of Isatis indigotica

A novel indole alkaloid glycoside with an unprecedented 2-(diphenylpropyl)-indole skeleton, isatindigodiphindoside (1), was isolated from an aqueous extract of the roots of Isatis indigotica. The structure was determined by extensive spectroscopic studies, especially by 2D NMR data analysis combined with enzymatic hydrolysis and ECD calculations. Plausible biosynthetic pathways of compound 1 are also discussed.