Gallotannins. Part XIII. The structure of Chinese gallotannin: evidence for a polygalloyl chain

Abstract

Evidence is presented relating to the disposition of the depsidically linked galloyl groups on the penta-O-galloyl-β-D-glucose core of Chinese gallotannin. Interpretation of the n.m.r. spectra of methylated gallotannin fractions using the spectra of model depsides and several tri-O-methylgalloyl sugar derivatives permits the tentative formulation of Chinese gallotannin as a 1,3,4,6-tetra-O-galloyl-β-D-glucose with a m-trigalloyl chain (on average) at the 2 position. Analysis of the rate of formation and disappearance of methyl m-digallate during the methanolysis of the tannin supports in outline the m-trigallate ester structure.