Sulfur-enriched alkaloids from the root of Isatis indigotica

摘要

Five new sulfur-enriched alkaloids isatithioetherins A–E(1–5), and two pairs of scalemic enantiomers(t)-and( à)-isatithiopyrin B(6 a and 6 b) and isoepigoitrin and isogoitrin(7 a and 7 b), along with the known scalemic enantiomers epigoitrin and goitrin(8 a and 8 b), were isolated and characterized from an aqueous extract of the Isatis indigotica roots. Their structures were determined by extensive spectroscopic data analysis, including 2 D NMR and theoretical calculations of electronic circular dichroism(ECD) spectra based on the quantum-mechanical time-dependent density functional theory(TDDFT). Compounds 1–5 represent a novel group of sulfur-enriched alkaloids, biogenetically originating from stereoselective assemblies of epigoitrin-derived units. Isolation and structure characterization of 6 a and 6 b support the postulated biosynthetic pathways for the diastereomers 9 a and 9 b via a rare thio-Diels–Alder reaction. Compounds 2 and 4 showed antiviral activity against the influenza virus A/Hanfang/359/95(H3 N2, IC500.60 and 1.92 μmol/L) and the herpes simplex virus 1(HSV-1, IC503.70 and 2.87 μmol/L), and 2 also inhibited Coxsackie virus B3(IC500.71 μmol/L).& 2018 Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).