Application Notes on Absolute Configuration of Chiral Natural Products

Absolute Configuration of Chiral Natural Products

Within the past few years it has been conclusively demonstrated that vibrational circular dichroism (VCD) is a reliable method for AC determinations. VCD offers a novel alternative to X-ray crystallography, permitting AC determinations on neat liquid, oil, and solution samples. VCD requires no derivatization of the sample or growth of a pure single crystal. VCD is defined as the difference in infrared (IR) absorption for left versus right circular polarization for a chiral molecule during a vibrational transition. VCD combines the structural specificity of vibrational IR absorption spectroscopy with the stereochemical sensitivity of a chi-roptical spectroscopy such as CD. The absolute stereochemistry is established by comparing the solution-phase VCD spectrum to the results of an ab initio quantum chemistry calculation. The calculations are easily carried out in commercial packages such as Gaussian (Gaussian, Inc., Pittsburgh, Pennsylvania).