Re-examining the stereochemistry of polycyclic suffruticosine via TDDFT calculations, ECD spectroscopy, and chemical synthesis

Abstract

The determination of complex natural product structures involves two main steps: (1) establishing atom connectivity, and (2) assigning stereochemistry. While the former step is now routinely accomplished using H-1 and C-13 NMR data, supplemented with various 2D NMR experiments, assigning relative and absolute stereochemistry to complex natural products continues to present a significant challenge. In this study, we employ time-dependent density functional theory (TDDFT) computations to analyze electronic circular dichroism (ECD) spectra and elucidate the structure of polycyclic suffruticosine. By combining TDDFT-assisted ECD spectral assignment with experimental ECD spectra obtained from the eastern fragment (securinine and allosecurinine) and the chemically synthesized western fragment of suffruticosine, we demonstrate that the true structure of natural suffruticosine is the enantiomer of the initially reported structure in the isolation paper.