ISOLATION OF THE ALDOBIURONIC ACID, 3-(XYLOPYRANOSYL) -α-<scp>D</scp>-GLUCURONOPYRANOSIDE, FROM WHEAT STRAW HOLOCELLULOSE AND SYNTHESIS OF ITS β-ISOMER

Abstract

Extraction of wheat straw holocellulose with 4% potassium hydroxide removed a polysaccharide fraction containing D-xylose (77.2%), L-arabinose (6.9%), and uronic acid anhydride (7.9%). Hydrolysis of this polysaccharide with dilute acid produced a degraded polysaccharide which was precipitated by ethanol after removing free D-xylose from the hydrolyzate by fermentation with Hansenulasuaveolans. Prolonged hydrolysis of the degraded polysaccharide yielded an aldobiuronic acid which was shown to be 3-(xylopyranosyl)-α-D-glucuronopyranoside. The β-isomer of this compound was synthesized from D-glucurone and D-xylose and its structure was confirmed by degradative studies after methylation. The enzyme β-glucuronidase did not hydrolyze the α- or β-isomers of this aldobiuronic acid.