Trisaccharides of Lolium and Festuca.

Abstract

IN the course of an investigation into the distribution of water-soluble carbohydrates in seeds of the Gramineae1, it was observed that two species of grass (Lolium perenne L. and Festuca pratensis Huds.) contained in their caryopses substantial amounts of a trisaccharide which was not detected in any of the thirty other wild grasses and cereals examined. This non-reducing trisaccharide (Fig. 1, X) had a specific rotation of + 90.5° (without recrystallization), yielded equal amounts of galactose, glucose and fructose on acid hydrolysis and was readily broken down to fructose and a reducing disaccharide in the presence of invertase or very dilute acid. This ease of hydrolysis suggests that the trisaccharide resembles raffinose in containing a terminal β-fructofuranoside residue. Iodine oxidation2 indicated that the galactose residue was at the non-reducing end of the disaccharide, and electrophoretic mobility of the disaccharide in borate was intermediate between the mobilities of laminari-biose and melibiose. Movement in borate is allied to the mode of linkage of sugar residues3, disaccharides containing 1,2 or 1,4 linkages being of much lower mobility than those containing 1,3 or 1,6 linkages. The disaccharide under consideration would therefore appear to contain either a 1,3 or a 1,6 linkage. Although the electrophoretic behaviour in borate does not distinguish between α and β linkages, the high positive rotation of the trisaccharide suggests that the galactose and glucose residues are α-linked, and, since 6-glucose-α-galactoside is melibiose, it seems probable that the newly isolated disaccharide is 3-glucose-α-galactoside. The trisaccharide from Lolium perenne and Festuca pratensis is therefore tentatively described as α-D-galactopyranosyl-3-α-D-glucopyranosy 1-2- β-D- fructofuranoside.