Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism, and optical rotation: the iso-schizozygane alkaloids isoschizogaline and isoschizogamine.

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the concerted application of DFT calculations of VCD, ECD, and OR to the determination of the ACs of the isoschizozygane alkaloid natural products, isoschizogaline, and isochizogamine, whose ACs have not previously been determined. The ACs of naturally occurring (-)-isoschizogaline and (-)-isoschizogamine, are both determined definitively to be 2R, 7R, 20S, 21S.