Hyperolactone C: Determination of its absolute configuration by comparison of experimental and calculated CD spectra

Abstract

A detailed conformational analysis of hyperolactone C diastereomers and enantiomers ((5R,9R),(5S,9S) and (5S,9R),(5R,9S)) was done with molecular mechanics and density functional theory methods. Time-dependent density functional theory (B3PW91/TZVP) was used to calculate electronic transition energies (UV/vis spectra) and rotational strengths of the respective conformations. The effect of solvation (acetonitrile solution) on excitation energies and electronic circular dichroism was approximated by the polarizable continuum model. By comparison of the simulated CD spectrum with that measured for hyperolactone C isolated from Hypericum lloydii, its absolute configuration can be assigned as (5S,9S).

Determination of Absolute Configuration of Natural Products: Theoretical Calculation of Electronic Circular Dichroism as a Tool

“…The principle is simply based on the comparison of the calculated and experimental ECD spectra: the more closely they match, the more reliable conclusion for the AC assignment can be drawn. Extensive studies on the application of the TDDFT method to the ECD calculation of chiral molecules, for example, of natural 5,34,35,38,39, 62-75 or synthetic 32,33,35-37,76-81 origin have been reported over the past few years. The purpose of this review is to use several examples representing different classes of natural products to illustrate the applicability of this approach in determining the AC of natural products.…”

Absolute configuration of eremophilane sesquiterpenes from Petasites hybridus: Comparison of experimental and calculated circular dichroism spectra

“…18,19 Most of the older publications show CD spectra of Petasites compounds beginning far above 200 nm and/or only indicate the sign and De values of the most important extrema. Therefore, we aimed to present complete CD spectra of several quite similar eremophilane type sesquiterpenes and to achieve certain knowledge how the minimal structural differences of these compounds could contribute to the spectroscopic influence of the carbonyl group.…”

Absolute Configurations of Globosuxanthone A and Secondary Metabolites from Microdiplodia sp. – A Novel Solid‐State CD/TDDFT Approach

“…The first six computed transitions (see vertical bars reproducing the rotational strengths in Figure 4) are well below the estimated ionization potential; they are mainly due to excitations from the five highest oc- [15][16][17]19] for safe use in configurational assignment. [20][21][22][23] The dihydroxanthenone globosuxanthone A (1), isolated from Chaetomium globosum Ames [1] and in this study from the endophytic strain Microdiplodia sp., is therefore assigned as methyl (1R,2R)-1,2,8-trihydroxy-9-oxo-2,9-dihydro-1H-xanthene-1-carboxylate.…”