(4-O-METHYL-ALPHA-D-GLUCURONO)-D-XYLAN FROM RUDBECKIA-FULGIDA, VAR SULLIVANTII (BOYNTON-ET-BEADLE)

From the medicinal plant Rudbeckia fulgida, var. sullivantii (Boynton et Beadle) a low-molecular-mass (4-O-methyl-alpha-D-glucurono)-D-xylan was isolated by alkaline extraction, followed by ethanol precipitatio n, ion-exchange chromatography, and gel filtration. The results of com positional and linkage analyses, supported by those of H-1 and C-13 NM R measurements of oligomers generated on partial acid hydrolysis, show ed the (1 --> 4)-linked beta-D-xylopyranosyl backbone with about 18% o f 4-O-methyl-D-glucuronic acid attached to O-2 of the xylose residues. From the mean distance of adjacent carboxyl groups, obtained from exp erimentally determined single-ion activity coefficients of calcium cou nterions, it followed that the uronic acid units are separated and dis tributed regularly along the xylan chain, i.e. approximately each sixt h D-xylose unit bears a 4-O-methyl-D-glucuronic acid residue. (C) 1998 Elsevier Science Ltd. All rights reserved.