Trigonostemons G and H, dinorditerpenoid dimers with axially chiral biaryl linkage from Trigonostemon chinensis

Abstract

Trigonostemons G and H, two novel dimeric dinorditerpenoids, were isolated from the stem barks of Trigonostemon chinensis. Their planar structures and relative configurations were established by extensive analysis of spectroscopic data. Trigonostemons G and H possess a homodimeric biaryl skeleton obtained from two rearranged chiral nonracemic abietane‐type dinorditerpenes through an axially chiral biaryl 11,11′‐linkage. Torsional scan and computation of the transition states were carried out to estimate the rotational energy barrier, and the axial chirality (aS) was determined by time‐dependent density functional theory (TDDFT) electronic circular dichroism (ECD) calculations. The positive n‐π* ECD transitions of the isolated carbonyl chromophore above 300 nm could be used to determine the central chirality of trigonostemon G independently by ECD calculations of the diastereomers.

Biogenetic and biomimetic synthesis of natural bisditerpenoids: hypothesis and practices

“…Their unique axial chirality was established by ECD calculations. 142 Compounds 236 and 237 are other examples of totarane dimers that were rst observed in sediments from the Lower Oligocene of the Rhine Ri Valley by GC-MS and their structures were established by NMR. Their formation was thought to involve free radical coupling.…”