Oligomeric hydrolyzable tannins having a valoneoyl group as linking unit of monomeric constituents have been classified into three types, based on the location of hexahy-droxydiphenoyl (HHDP) moiety of valoneoyl group on the glucose residue [HHDP part at O-4/O-6 (Type-A), O-2/O-3 (Type-B) and O-3/O-6 (Type-C) of glucose core]. The orientation of valoneoyl group in several dimers, representing those of each type, were determined by ^1H-^<13>C long-range COSY. A convenient and generally applicable method, for assigning the orientation of valoneoyl group in each type of oligomers, was established based on the difference of the chemical shifts of valoneoyl proton signals of the above-mentioned dimers and known oligomers of related structures. The behaviors of the oligomers upon partial hydrolysis at the valoneoyl moiety, under various conditions, were shown to be different depending on the location of valoneoyl group on the glucose core. The optimal condition was determined for the ether cleavage in the valoneoyl group and other related structural units, which is frequently observed upon partial hydrolysis of oligomers in hot water. This is applicable to chemical correlations of the oligomers with their monomeric constituents.
