Partial methanolysis of the agar-type sulfated galactan of the red seaweed Laurencia gemmifera

Abstract

This report describes the use of paper chromatography (PC), fast-flow liquid chromatography (FFLC) and reversed-phase high-performance liquid chromatography (RP-HPLC) for analysis of the products of mild methanolysis of the sulfated galactan of the red seaweed Laurenciu gemrnifera. The complex mixture of methyl glycosides of neutral monosaccharides, acetals of agarobiose, and acetals of 3,6anhydro-L-galactose was completely resolved. The method provides an alternative to GLC for determining xylose and other minor constituents in red-seaweed galactans. Partial methanolysis has been used for structural studies of galactans of red seaweedsld5, employing PC, TLC, and adsorption chromatography for separation and identification of the products. HPLC (normal phase) was particularly useful for the assignment of agar or carrageenan structures to red-algal polysaccharide@, based on identification of the dimethyl acetals of agarobiose and carrabiose, respectively. No attempt has yet been made to analyze the methanolysis products of agar-type polysaccharides by RP-HPLC, although methanolysis studies of various complex carbohydrates have been carried out by RP-HPLC’,*. Chromatographic analysis of the products of mild methanolysis of agar-type polysaccharides is particularly complicated because of the complex pattern of substitution with non-carbohydrate’ (sulfate, O-methyl, and pyruvate acetal groups) and carbohydrate (D-xylose” and 4-U-methyl-L-galactose”) substituents for the agarose disaccharide repeating-units, and also because of the presence of the labile 3,6-anhydrogalactosyl residue, which affords dimethyl acetal derivatives’ under controlled conditions. The present paper is a first approach to obtain useful information on the main