Spectral and Chromatographic Analyses of Tannins. I. ¹³C Nuclear Magnetic Resonance Spectra of Hydrolyzable Tannins

Abstract

The ¹³C nuclear magnetic resonance (¹³C-NMR) spectra of hydrolyzable tannins, in which D-glucopyranose takes the ⁴C₁ conformation, have been analyzed and the ¹³C resonances of the glucose carbons fully assigned. The peak sequences of carbons in glucose are different among several types of hydrolyzable tannins, reflecting differences of the acyl (galloyl, hexahydroxy-diphenoyl and dehydrohexahydroxydiphenoyl) groups, as found upon comparison of penta-O-galloyl-β-D-glucose (1), casuarictin (7), tellimagrandin II (13) and isoterchebin (15). The additive character of galloylation and hexahydroxydiphenoylation shifts can be used for locating the positions of the acyl groups. The substituents and substitution mode at C-1 and C-2 of glucose in these tannins can be deduced from the diagnostic ¹³C chemical shift of the anomeric carbon. The ¹³C resonances of the dimeric hydrolyzable tannins were assigned on the basis of the data for their monomeric units.