Structural characterisation of a water-soluble polysaccharide with high branches from the leaves of Taxus chinensis var. mairei

A large number of polysaccharides present in the leaves of Taxus chinensis var. mairei were successively extracted with hot water after preliminary treatments. The ion-exchange and gel-permeation chromatography was used to isolate and purify the major polysaccharides to afford a complex water-soluble polysaccharide, named T1 with a molecular mass of 3.44 × 106 Da determined by HPGPC. T1 consisted of 2,4-di-O-methyl-mannose, rhamnose, arabinose, xylose, galactose, mannose, galacturonic acid and glucuronic acid in a molar ratio of 2:5:24:9:3:46:1:10, and the acetyl content was estimated to be 2.1%. On the basis of methylation analysis, periodate and chromium trioxide oxidations, Smith degradation, graded acid hydrolysis, and NMR and IR spectroscopy, T1 possessed a 1,3,6-linked β-d-Manp main chain, substituted by mannose, arabinose, galactose, xylose, rhamnose, 2,4-di-O-methyl-mannose, galacturonic acid, and glucuronic acid residues. These contained non-reducing end-units of mannose, arabinose, xylose, 2,4-di-O-methyl-mannose, and glucuronic acid. This is the first report on isolation of an acid heteropolysaccharide from Taxus species.