Structural Analysis of Polysaccharides in Chinese Lacquer by NMR Spectroscopy

Structural characterization of the Chinese lacquer polysaccharide of Rhus vernicifera was performed by means of high resolution NMR spectroscopy involving two dimensional NMR measurements such sa field gradient DQF-COSY,TOCSY,HMQC,and HMBC experiments.Most of complicated proton and carbon absorptions were assigned.It was identified that the lacquer polysaccharide had a 1,3-linked D-galactopyranosidic main chain with complex side chains consisiting of D-galactose,4-O-methyl-D-glucuronic acid,D-glucuronic acid,L-arabinose,and L-rhamnose.The coupling constants(J1,2)of anomeric protons in the DQF-COSY spectrum suggested that galactopyranose residues,4-O-methy-D-glucuronic acid,and L-rhamnose(J1,2=7.1～12.6Hz)had a β-linkage and the terminal D-galactopyranose,D-glucuronic acid,L-arabinose(J1,2≦3.2Hz)had an α-linkage.The proportions of the component sugar units were calculated by the intensity of the anomeric carbon signals and were in good agreemennt with those by the methylation analysis reported preveiously.These results indicate that the NMR characterization can be widely used to investigate the relationship between the structure of lacquer polysaccharides and specific biological activities as well as the indentification of the place of prpduction.