CHEMICAL STRUCTURE OF CONDENSED TANNINS FROM 8 DIFFERENT TREE SPECIES STUDIED BY NMR TECHNIQUES

摘要

NMR techniques were applied to study and to compare the chemical structure of tannins from 8 different tree species, i.e., Norway spruce (Picea abies), Scots pine (Pinus sylvestris), larch (Larix gmelini), French maritime pine bark extractive, Quebracho (Schinopsis lorentzii), black wattle (Acacia mearnsii), Mangium (Acacia mangium) and Chinese Bayberry tree (Myrica rubra). The tannins from Norway spruce bark and Scots pine bark were extracted in our laboratory by using fresh bark harvested in Stockholm area. The other tannins were obtained as commercial samples. It was found in this study that the complicated chemical structures of condensed tannins can be elucidated by applying ~13C, DEPT90, and 2D HSQC NMR techniques. The tannins from pines and larch were found to be structurally similar to each other, containing mainly the procyanidins. In the case of Norway spruce tannin, stilbene polymer or stilbene- procyanidin co-polymer were found to comprise about half of the tannin content together with procyanidins. Quebracho tannin was found to contain predominantly the profisetinidins, in agreement with results of other earlier studies. Black wattle tannin was also found to contain profisetinidins as the major components, and proanthocyanidins and probably prorobinetinidins as the minor components. Tannin from Mangium was found to contain the prorobinetinidins as the major components. The Chinese Bayberry (Myrica rubra) tannin, however was found to contain mainly the prorobinetinidins and also small amount of the prodelphinidins.