Arabinogalactan A from Japanese larch (Larix leptolepis)

Abstract

Fractionation of the water-soluble polysaccharides from Japanese larch wood affords two homogeneous arabinogalactans A and B. Mild acid hydrolysis of arabinogalactan A furnishes 3-O-β-L-arabinopyranosyl-L-arabinose. Hydrolysis of methylated arabinogalactan A gives 2,3,4- and 2,3,5-tri-, and 2,5-di-O-methyl-L-arabinose, 2,3,4,6-tetra-, 2,3,4- and 2,4,6-tri-, 2,4- and 2,6-di-, and 2-O-methyl-D-galactose. Two successive degradations of the periodate-oxidised polysaccharide result in the formation of an essentially linear 1→3′ linked galactan. From these and other experiments it is concluded that the highly branched arabinogalactan contains interior chains of 1→3′ linked β-D-galactopyranose residues to which are attached as side-chains other D-galactopyranose residues joined by 1→6′ linkages and, less frequently, single L-arabinofuranose or 3-O-β-L-arabinopyranosyl-L-arabinofuranose units.