Tannins and related compounds. Part 9. Isolation and characterization of polygalloylglucoses from Turkish galls (Quercus infectoria)

Abstract

Two structural isomers of pentagalloylglucose and four isomers of hexagalloylglucose have been isolated from Turkish galls (Quercus infectoria), in addition to 1,2,3,6-tetra-O-galloyl-β-D-glucose (2), and their structures were established on the basis of ¹³C n.m.r. analysis, methanolysis, and partial hydrolysis. Trihepta-, and octa-galloylglucoses were partially purified, and their structures were also characterized mainly by ¹³C n.m.r. spectroscopy. From the isolation and structural studies of these galloylglucoses Turkish gallotannin has been shown to be a mixture of two types of polygalloylglucoses; one type has a 1,2,3,6-tetra-O-galloyl-β-D-glucose core with depside galloyl group(s) at the C-2 and/or C-6 position of the glucose moiety, and the other has a 1,2,3,4,6-penta-O-galloyl-β-D-glucose core with depside galloyl group(s) randomly distributed at the C-2, -3, -4, and -6 positions. H.p.l.c. analysis showed that Turkish gallotannin has an average molecular weight of 1 032 and the composition ranges from trito nona-galloylglucoses.