THE HEMICELLULOSES PRESENT IN ASPEN WOOD (POPULUS TREMULOIDES): PART III. THE CONSTITUTION OF PENTOSAN AND HEXOSAN FRACTIONS

Extractive-free aspen wood (Populustremuloides) was extracted with water, followed by alkaline solutions of successively increasing concentration, and finally with alkaline borate solution. Hemicellulose fractions (I–IX) were thus obtained, and some of these were further subdivided into components which formed water-insoluble copper complexes (A) and those which did not (B). Analytical data are recorded for each fraction.One of the fractions (V) represented 19% by weight of the original wood. Hydrolysis of the methylated material gave 2,3,5-tri-O-methyl-L-arabinose, 2,3,4-tri-O-methyl-D-xylose, 2,3-di-O-methyl-D-xylose, 2- and 3-mono-O-methyl-D-xyloses, and three acidic fragments as the major components.When V was treated with an enzyme preparation, 80% by weight of the material was hydrolyzed to simple sugars, and an enzyme-resistant polysaccharide fraction remained. Methylation of the latter, followed by hydrolysis, afforded, in addition to those methylated sugars described above, 2,3,4,6-tetra-O-methyl-D-mannose.A mannose-rich hemicellulose fraction (VIIIA) was also methylated and then hydrolyzed. The major products were 2,3,4,6-tetra-O-methyl-D-mannose, 2,3,6-tri-O-methyl-D-mannose, and 2,3,6-tri-O-methyl-D-glucose. The significance of these results is discussed.