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Polysaccharides of the red seaweed Apophloea lyallii were extracted with hot water in a yield of 63.6% w/w of the dry seaweed. The polysaccharides were non-sulphated and were composed of various proportions of d -xylose, 2-O-methyl d -galactose, d -glucuronic acid, d - and l -galactose, 3-O-methyl galactose, and d -glucose. The aldobiuronic acid 3-O-(β- d -glucopyranosyluronic acid)- d -xylopyranose was isolated from the acid hydrolysate of the polysaccharides. The polysaccharides were fractionated by DEAE-sephadex ion exchange chromatography, and two of the fractions obtained were characterised by neutral sugar analyses, linkage analyses, and NMR spectroscopy. A major fraction obtained was shown to be largely composed of a unique (2-O-methyl galacto)–glucurono–xylo-glycan with a repeating unit represented by [α- d -(2-O-Me-Galp)-(1→4)-β- d -GlcAp-(1→3)-α- d -Xylp-(1→4)-]n. The structure of this new glycan was explored by beta-elimination analyses. A minor fraction obtained by ion exchange chromatography contained (1→4)-linked xylose, (1→4)-linked galactose, (1→4)-linked 3-O-methyl galactose, (1,3,4)-linked galactose, and terminal uronic acid in a ratio of approximately 1:0.3:0.5:0.4:0.4. |
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