(4-O-methyl-α-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 precipitation, ion-exchange chromatography, and gel filtration. The results of compositional and linkage analyses, supported by those of H-1 and C-13 NMR measurements of oligomers generated on partial acid hydrolysis, showed the (1 --> 4)-linked beta-D-xylopyranosyl backbone with about 18% of 4-O-methyl-D-glucuronic acid attached to O-2 of the xylose residues. From the mean distance of adjacent carboxyl groups, obtained from experimentally determined single-ion activity coefficients of calcium counterions, it followed that the uronic acid units are separated and distributed regularly along the xylan chain, i.e. approximately each sixth D-xylose unit bears a 4-O-methyl-D-glucuronic acid residue. (C) 1998 Elsevier Science Ltd. All rights reserved.