22 Ellagitannin,DehydroellagitanninおよびAcylated Condensed tanninの立体構造とCDスペクトル : 数種新タンニンへの応用

概要

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Chiroptical properties of tannins have been shown to offer a new reliable method for determining their stereostructures without chemical reaction. The Cotton effects at about 285, 265 and 235nm in the CD spectra of ellagitannins have been correlated with the stereostructures as follows: (1) The sign and the amplitude of the Cotton effect at about 235nm is shown to be indicative of the absolute configuration and the number of the HHDP group in a molecule. (2) The Cotton effect at 285nm which is one of the coupled Cotton effects centered at about 275nm resulting from interacting aromatic chromophores, reflects the chirality between the aromatic rings, which is predicted by the exciton chirality rule. (3) Split-type Cotton effects centered at about 220nm are also encountered in dehydroellagitannins which possess the dehydrohexahydroxydiphenoyl (DHHDP) group as well as HHDP and galloyl groups in a molecule. The Cotton effect at 200-210nm is diagnostic for the absolute configuration at the asymmetric center of DHHDP group. The absolute configuration of interflavan linkages of the condensed tannins galloylated at O-3, is determined by the Cotton effects at 200-220nm by applying the aromatic quadrant rule in analogous way as ordinary proanthocyanidins. The stereostructures of several new tannins were determined by applying this chiroptical method.
天然有機化合物討論会の論文
1981-09-10