Electronic circular dichroism (ECD) and discrete wavelength resolved specific optical rotations, referred to as optical rotatory dispersion (ORD), have been remeasured for inuloxin C and analysed with corresponding quantum chemical (QC) predicted data for all diastereomers of inuloxin C. The QC‐predicted sign of ORD and of a major ECD band are found to match the experimental observations for more than one diastereomer. However, these ECD and ORD analyses combined with electronic dissymmetry factor analyses narrowed the choices of absolute configuration (AC) of inuloxin C to (5R,7S,8R,10R) and (5S,7S,8S,10S). Supplementing these analyses with corresponding analyses for acetylated inuloxin C resulted in a unique choice for the AC of inuloxin C as (5S,7S,8S,10S). This result is independent of NMR analysis. Furthermore, this AC is in full agreement with previously determined relative configuration by NMR and the AC derived therefrom using ECD and ORD. Therefore, the present study identifies a pathway for determining the ACs of chiral molecules with multiple stereogenic centers when relative configurations are not known, or when it is desired to deduce ACs independent of the known relative configurations.

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We have isolated mixtures of [5]-and [3]ladderanoic acids 1a and 2a from the biomass of an anammox bioreactor and have separated the acids and their phenacyl esters for the first time by HPLC. The absolute configurations of the naturally occurring acids and their phenacyl esters are assigned as R at the site of side-chain attachment by comparison of experimental specific rotations with corresponding values predicted using quantum chemical (QC) methods. The absolute configurations for 1a and 2a were independently verified by comparison of experimental Raman optical activity spectra with corresponding spectra predicted using QC methods. The configurational assignments of 1a and 2a and of the phenacyl ester of 1a were also confirmed by X-ray crystallography.

(1 R ,10 bR )-1′-(( R )-1,2-Dihydroxyethyl)-1-hydroxy-8,9-dimethoxy1,5,6,10 b -tetrahydropyrrolo [2,1- a ]isoquinolin-3(2 H )-one, an analogue of (−)-crispine A, with three stereogenic centers is synthesized and its absolute configuration (AC) established using the combined information derived from the synthetic scheme and single crystal X-ray diffraction data. The experimental chiroptical spectra (namely, optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD)) and the corresponding quantum chemical (QC) predicted spectra for all diastereomers are used to evaluate the AC. The AC of the synthesized compound could be correctly established using any one of the three chiroptical spectroscopic methods (ORD, ECD, or VCD) when the relative configuration is constrained to be that derived from X-ray data or when the ACs of two of the chiral centers are constrained to be those derived from the synthetic scheme. In the absence of this outside information, the QC predicted ORD, ECD, and VCD for incorrect diastereomers are also found to satisfactorily reproduce the corresponding experimental spectra. Nevertheless, incorrect diastereomers could be eliminated when combined electronic dissymmetry factor (EDF) and vibrational dissymmetry factor (VDF) spectral analyses are included, leaving the correct diastereomer as the sole choice. Thus, the combined EDF and VDF spectral analysis is seen to be a helpful diastereomer discrimination tool.

The versatility of the natural products (2S,3S)- and (2S,3R)-3-hydroxy-5-oxotetrahydrofuran-2,3-dicarboxylic acids (1 and 2), isolated in large amounts from tropical plant sources, has been demonstrated by the construction of 3-substituted and 3,4-disubstituted chiral pyrrolidine-2,5-diones. The absolute configurations of chiral pyrrolidine-2,5-diones have been ascertained using chiroptical spectroscopic methods and/or single-crystal XRD data. A combination of different reaction strategies delivering a diverse matrix of fused heterocyclic ring systems is presented. The pyrrolo­[2,1-a]­isoquinoline alkaloid (+)-crispine A possesses a wide range of pharmacological activities including antidepressant, antiplatelet, antileukemic, and anticancer activities. The analogues of indolizino­[8,7-b]­indole alkaloids (+)- and (−)-harmicine show strong antileishmanial, antinociceptive, PDE5-inhibitory, antimalarial, and antiviral activities. The bicyclic furo­[2,3-b]­pyrrolo skeleton is present in many natural products. Thus, the uniqueness of relatively cheap, naturally occurring chiral 2-hydroxycitric acid lactones as chirons has been demonstrated by the construction of some important molecular skeletons that are otherwise difficult to synthesize.