Aglycone anomeric configurations

Introduction to 2-D NMR experiments The purpose of the standard 1-D H NMR experiment is to achieve structure-related information about sample protons (i.e., chemical shifts, spin-spin couplings, and integration data) describing the relative number of protons. Applied to anthocyanins, this information may help to identify the aglycone (anthocyanidin), number of monosaccharides present, and anomeric configuration of the monosaccharides. However, for most anthocyanins, the information gained by a standard 1 -D H NMR experiment is insufficient for complete structure elucidation. In recent years, various 2-D NMR experiments have evolved as the most powerful tools for complete structure elucidation of anthocyanins. 

The anomeric configuration was eventually determined by NOE (studied using ROESY) experiments, establishing both inter-sugar and sugar-aglycon relations [37] (Scheme 13). 

From this preliminary review of monosaccharide glycosides, it is possible to see that the fragmentation pattern in FAB mass spectra is governed by at least three factors whose importance may vary (1) nature of the aglycone, (2) configuration of the anomeric carbon (3) remote stereochemical effects (i.e., the relative stereochemistry of the other carbohydrate carbons). 

The stmcture elucidation of saponins requires identification of the different building blocks (namely genins, monosaccharide units, substituents), determination of the sequence of the component monosaccharides in the carbohydrate moiety, the way in which monsaccharide units are attached to one another, the anomeric configuration of each glycosidically linked monosaccharide unit and the location of the carbohydrate moiety (or moieties) in the aglycone. 

There is absolute specificity with respect to the anomeric configuration of the monosaccharide residues in the substrate and the regioselectivity for linkage position is usually absolute for the glycone, but the aglycone binding interactions may be much less stringent. Quite subtle dif-... 

Chromium trioxide oxidation of fully acetylated aldopyranosides has been generally used for the determination of anomeric configurations, as the equatorial aglycones (the -anomer) are preferentially degraded (Angyal and James, 1970). However, the work of Hoffman and Lindberg... 

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