¹³C Nuclear Magnetic Resonance Spectra of Hydrolyzable Tannins. III.¹⁾ Tannins Having ¹C₄Glucose and C-Glucosidic Linkage

Two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy was utilized for the assignments of the glucose carbon signals in the ¹³C-NMR spectra of hydrolyzable tannins in which the glucopyranose core takes a ¹C₄or related boat conformation, and of tannins possessing a C-glucosidic linkage. Remarkable changes in the sequences of glucose carbons were observed with change in the conformation of the glucose core, and with the formation of a C-glucosidic linkage. The chemical shifts of the C-2 signals of the glucose cores adopting the open-chain form in C-glucosidic tannins and in complex tannins can be utilized for the discrimination of the configurations at C-l in these tannins.