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.