Structure of a water-insoluble D-glucan isolated from a streptococcal organism

The structure of the extracellular polysaccharide (water-insoluble D-glucan) from an anaerobic, Gram-positive coccus organism (Streptococcus) has been investigated. Acid hydrolysis of the methylated glucan yielded 2,3,4,6-tetra-, 2,3,4-tri-, 2,4,6-tri, and 2,4-di-O-methyl-D-glucose in the molar ratios of 1.13:3.99:1.00:1.02, indicating that the D-glucan has a branched structure containing (1 leads to 6)- and (1 leads to 3)-alpha-D-glucosidic bonds with an average repeating unit of seven sugar residues. The D-glucan-polyalcohol, derived by successive periodate oxidation and borohydride reduction, gave, on complete hydrolysis with acid, glycerol and D-glucose (molar ratio, 2.2:1.0). Methylation of the D-glucan-polyalcohol yielded, upon hydrolysis, 2,4,6-tri-, and 2,4-di-O-methyl-D-glucose (molar ratio, 1.0:1.1). Methylation of the D-glucan-polyalcohol following Smith degradation (mild acid hydrolysis) gave 2,4,6-tri-O-methyl-D-glucose as the principal hydrolysis product, in addition to a trace of 2,3,4,6-tetra-O-methyl-D-glucose.