Antiviral enantiomers of a bisindole alkaloid with a new carbon skeleton from the roots of Isatis indigotica

A pair of indole alkaloid enantiomers with a novel bisindolylacetamide skeleton, insatindibisindolamides A and B (1a and 1b), was isolated from an aqueous extract of Isatis indigotica roots. The enantiomers were separated by chiral HPLC. Their structures and absolute configurations were elucidated by extensive spectroscopic analysis, including 2D NMR, X-ray crystallography, and electronic CD (ECD) calculation. The proposed biosynthetic pathway and preliminary investigations of the biological activity of compounds 1a and 1b are also discussed. (C) 2015 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.