Absolute configuration of 3-hydroxyisoflavanones and conjugated 2-(5H)-furanones through electronic circular dichroism

The 3-hydroxyisoflavanones and the 2-(5H)-furanones both constitute relatively small but chemically and biologically significant classes of natural products. Representatives of each class, including sedonan B (1, a 3-hydroxyisoflavanone) and 4'-O-methylpuerol (2, a 2-(5H)-furanone), were recently isolated from an extract of the dried roots of Dalea formosa Torr. (Fabaceae). As part of the structural elucidation of both compounds, their absolute configurations were determined by comparing experimental electronic circular dichroism (ECD) results with literature reports. While the absolute configurations of both compounds were established, a number of issues indicated that theoretical simulations of the ECD spectra for both compounds were warranted to further support these empirical assignments. Simulated ECD spectra were therefore generated using conformational analyses and geometric optimization followed by calculations of excitation energies and rotational energies using the TDDFT method at the B3LYP/6–31G(d,p) level. Molecular orbital analyses were also performed for 4'-O-methylpuerol. This presentation will discuss the issues that led to the need for simulated ECD spectra and the experimental and computational results for both compounds.