摘要：

An oligosaccharide alditol, dHex-GalNAc-Gal-Gal-GalNAcol, has been isolated from polysialoglycoprotein, which was derived from the unfertilized eggs of Savelinus leucomaenis pluvius (a salmonid fish, Iwana in Japanese), by alkaline borohydride treatment followed by exhaustive digestion with sialidase. First, the structure of the terminal dHex residue in the above pentasaccharide has been assigned as 6-deoxyaltrose (= dAlt in pyranoid form) by a combination of structural methods (GLC, TLC, mass spectrometry, and 400-MHz 1 H-NMR spectroscopy). The occurrence of a 6-deoxyhexose other than l -fucose in glycoprotein has not been previously reported. Next, the absolute configuration of this unusual sugar residue has been assigned as d on the basis of the exciton-splitting study of tris- p -bromobenzoate derivatives of methyl 6-deoxyaltrosides. The usefullness of this circular dichroic exciton-splitting method in the determination of the absolute configuration of carbohydrate components, only available in minute amounts, is emphasized. The anomeric configuration of the glycosidic linkage of the d -altropyranosyl residue was deduced from 400-MHz 1 H NMR spectroscopy. The 6-deoxy-- d -altropyranosyl residue thus established has the same configuration as ±- l -fucose but with the C-5 methyl group inverted, suggesting that the biosynthetic incorporation of d -dAlt parallels that of l -fucose, and a possible pathway is also considered.

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