Studies on a Galactan from Tension Wood of Beech (Fagus silvatica L.).

Abstract

Chlorite holocellulose was prepared from beech tension wood and extracted with dimethylsulphoxide, hot water and sodium hydroxide. The hemicellulose mixture extracted with the latter was fractionated with Fehling''s solution and with cetyl-trimethyl ammonium hydroxide and a galactan was isolated with DPn 380 and a uronic acid content of 28%. On hydrolysis it yielded D-galactose, 69.3%, L-arabinose, 6%, D-xylose 4.2% and L-rhamnose 20.5%. From a partial hydrolysate of the galactan there were isolated (by carbon column chromatography and by chromato-graphy on thick filter paper) the following neutral oligosaccharides: 6-O-[BETA]-D-galactopyranosyl-D-galactose, 4-O-[BETA]-D-galactopyranosyl-D-galactose, 6-O-[BETA]-D-galactopyranosyl-6-O-[BETA]-D-galactopyranosyl-D-galactose, 6-O-[BETA]-D-galactopyranosyl-4-O-[BETA]-D-galactopyranosyl-D-galactose, 6-O-[BETA]-D-galactopyranosyl-6-O-[BETA]-D-galactopyranosyl-D-galactose, and the following acidic sugars: D-galacturonic acid, 4-O-methyl-D-glucuronic acid, 2-O-[alpha]-D-galacturonopyranosyl-l-rhamnose, 6-O-(4-O-methyl-[BETA]-D-glucuronopyranosyl)-D-galactose as well as a few others which were identified tentatively. The galactan thus obviously contains both [BETA]-1,4- as well as [BETA]-1,6-linked galactose units, a combination which has not previously been demonstrated to occur in a natural polysaccharide.