4-O-METHYL-BETA-L-IDOPYRANOSYLURONIC ACID LINKED TO XYLAN FROM KRAFT PULP - ISOLATION PROCEDURE AND CHARACTERIZATION BY NMR-SPECTROSCOPY

The tetrasaccharide 2 ''-O-(4-O-methyl-beta-L-idopyranosyluronic acid) xylotriose was isolated from enzymatically hydrolysed, unbleached, bir ch kraft pulp by anion-exchange chromatography in two steps. The prima ry structure of the tetrasaccharide was determined by H-1 and C-13 NMR spectroscopy, using homonuclear and heteronuclear two-dimensional tec hniques. NOE data and (3)J(H,H) coupling constants show that the 4-O-m ethyl-beta-L-idopyranosyluronic acid in the tetrasaccharide is predomi nantly in the C-1(4) chair conformation. The pK(a) value (3.17) for 4- O-methyl-iduronic acid attached beta-(1-->2) to xylose was determined from the pH-dependent chemical shift of H-5. The amount of 4-O-methyli duronic acid (0.1-0.5 mol%) in surface xylan of unbleached birch and p ine kraft pulps was determined by extensive xylanase treatment and fur ther analysis by NMR spectroscopy and high-performance anion-exchange chromatography. (C) 1996 Elsevier Science Ltd.