Two new lignan-iridoid glucoside diesters from the leaves of Vaccinium bracteatum and their relative and absolute configuration determination by DFT NMR and TDDFT-ECD calculation

Abstract

Two new lignan-iridoid glucoside diesters (2 and 3), together with their putative biosynthetic precursor 10-O-trans-caffeoyl-6α-hydroxyl-dihydromonotropein (1), were characterized from the leaves of Vaccinium bracteatum. Their planar structures and relative configuration were elucidated by spectroscopic measurements and DFT C NMR calculations, and their absolute configurations were determined by time-dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The plausible biosynthetic pathways of new compounds were also proposed.