71(P-61) 振動円二色性(VCD)スペクトルによる複合糖質等の立体化学研究(ポスター発表の部)

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Chiral molecules exhibit circular dichroism (CD), the differential absorption of left versus right circularly polarized light, and the spectroscopies have been useful method for determining the absolute configuration. Recently, the measurement of CD in an infrared region, i.e. vibrational circular dichroism (VCD), has been advanced instrumentally and theoretically. VCD has some advantages over conventional electronic circular dichroism (ECD) by the applicability to all organic molecules and the reliability of ab initio quantum calculations. We apply this powerful technique to the determination of the absolute stereochemistry of some cruciferous phytoalexin-related compounds and to analysis of glycoconjugates. The determination of the absolute configuration of cruciferous phytoalexin-related compounds A number of cruciferous phytoalexin studies have been reported so far, but most of their absolute stereochemistry is still to be investigated. So we applied the VCD spectroscopy to determine the absolute configuration of dioxibrassinin (1) and 3-cyanomethyl-3-hydroxyoxindole (2). Compounds 1 and 2 were synthesized and their VCD spectra were measured. The comparison of observed VCD spectra and calculated ones indicated that their stereochemistry are both S. This is the first case of the determination of absolute stereochemistry of chiral tertiary alcohols by VCD. Application of VCD to carbohydrates Recently, the biological significance of carbohydrates have been recognized and analytical studies of carbohydrates have been widely investigated. Most analyses have been based on achiral methods such as NMR or MS in spite of their chiral properties. We considered that the detailed stereochemical information could be extracted using VCD. Various carbohydrates have been measured to construct an extensive database aiming to create a methodology for VCD pattern discrimination of the carbohydrates. The database in the fingerprint region indicated that sugars with the axial glycosidic linkage showed a negative, sharp and intense VCD band, named "Glycoside band" at around 1145 cm^<-1>. The applicability of the Glycoside band was demonstrated by quantifying α-β ratio of mixture samples and monitoring of an enzymatic reaction. In the C-H stretching region, we found the stereochemistry of single chiral center in the presence of multiple such centers could be extracted through the vibrational chirality transfer phenomenon. Also, VCD in this region was indicated to be a sensitive probe of glycosidic linkage sites. In conclusion, by using the VCD database and the proposed spectra-structure correlations, VCD will be an effective tool in carbohydrate analysis.
天然有機化合物討論会の論文
2004-10-01

71(P-61) 振動円二色性(VCD)スペクトルによる複合糖質等の立体化学研究(ポスター発表の部)

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