11 化学変換を必要としない絶対立体化学決定 : 赤外円二色性スペクトルの天然有機化合物への応用(口頭発表の部)

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Determination of absolute configuration has often required chemical derivatization. Vibrational circular dichroism (VCD), a recently developed chiroptical spectroscopy, measures differential absorption of left vs. right circularly polarized infrared light caused by molecular vibrational transition. VCD is becoming one of the most powerful and convenient technique for chiral studies, due to the applicability to all organic compounds without any derivatization in solution state with the aid of reliable theoretical calculation. We have applied this method to natural products. In this paper, we discuss VCD assignment of the absolute configurations, which are not easily determined by ordinary methods. Absolute stereochemistries of brominated marine sesquiterpenes from Laurencia 1, 2 and 4 were studied by VCD. Comprehensive conformation search followed by DFT calculation was performed to calculate VCD spectra. The observed VCD spectra showed good agreement with the calculated ones, by which compounds 1 and 2 were assigned as 7S,10S. Peroxidic diastereomers 4a and 4b were separated by chiral HPLC and their VCD spectra were measured. By comparison of experimental and theoretical VCD, their absolute stereochemistries were determined as 1R,4R,7S,10S and 1S,4S,7S,10S, respectively. This is the first case to apply VCD to determination of absolute configuration of the chiral peroxy compounds. Stereochemical studies of cruciferous phytoalexins 5-9 were also conducted by means of a nonempirical as well as an empirical manner. In this study, VCD was demonstrated to be effective also for tertiary alcohols and spiro-compounds. Stereochemistries on a glycerol moiety of lipids and glycolipids were also examined by VCD. By focusing on C=O stretching VCD, an empirical rule to distinguish the chirality of glycerol sn-2 carbon has been established.
天然有機化合物討論会の論文
2006-09-15

11 化学変換を必要としない絶対立体化学決定 : 赤外円二色性スペクトルの天然有機化合物への応用(口頭発表の部)

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