13 C NMR spectroscopy of substituted xanthones—II: 13C NMR spectral study of polyhydroxy xanthones |
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Authors: | AW Frahm RK Chaudhuri |
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Institution: | Institut für Pharmazeutische Chemie der Universität, Kreuzbergweg 26, D-5300 Bonn 1, West Germany |
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Abstract: | The 13C NMR chemical shifts of eleven hydroxy-, two hydroxymethoxy xanthones, and xanthone-C-glucoside, mangiferin, are presented and analyzed. Hydroxy substituent effects depending on substituent position as well as on shielded ring carbon position have been evaluated. Hydroxy substituent increments for xanthones are proposed. Effects of hydroxylation on carbonyl carbon shift and the methylation of hydroxy group and the corresponding shift increments which are of diagnostic value have been observed and discussed. |
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