Studies of chiral molecules using chiroptical spectroscopies

UnrestrictedRecently, a new methodology based on the three chiroptical properties, namely vibrational circular dichroism (VCD), electronic circular dichroism (ECD) and optical rotation (OR), was developed toward determining the Absolute Configurations (ACs) of chiral molecules. This new methodology determines the AC of a chiral molecule via comparison of the ab initio Density Functional Theory (DFT) calculations of VCD, ECD or OR with the experimental results. Prior studies have shown that this method is quite straightforward and reliable, and readily applicable to a variety of chiral molecules. Although either one of the three chiroptical properties is capable of determining the AC by its own self, simultaneous applications of all three are more favorable and will undoubtedly increase the certainty of the AC determined. Our group has reported the first study of this kind and unambiguously determined the ACs of four cytotoxic sesquiterpene natural products. In an effort to further extend the applicability and demonstrate the reliability of this concerted method, we report here the determination of the ACs of several natural products with previously unknown ACs by the VCD, ECD and OR spectroscopies. They are schizozygane alkaloid: schizozygine; iso-schizozygane alkaloids: iso-schizogaline and iso-schizogamine; iridoids: plumericin, iso-plumericin and prismatomerin. In addition, the AC determination and conformational analysis of two chiral organic molecules, phenyl sulfoxides-d5 and 2-hydroxy-3-pinanone, using VCD spectroscopy are also reported.; In the second part of this thesis, the monomethyl-[16O, 17O, 18O]-phosphate and [16O, 17O, 18O]-thiophosphate have been synthesized and characterized by 31P and 17O NMR and by MS. Their ECD spectra have then been re-examined in order to evaluate the potential of ECD as a means to determine the ACs of these isotopically-chiral phosphate compounds. Measurable ECD was confirmed for monomethyl-[16O, 17O, 18O]-phosphate, although of somewhat weaker magnitude than previously reported. No significant ECD was detected for [16O, 17O, 18O]-thiophosphate