Structural studies on an antitumor polysaccharide from Microellobosporia grisea.

The structure of the antitumor polysaccharide from the actinomycete Microellobosporia grisea has been investigated. By methylation and periodate-oxidation studies, the polysaccharide was shown to consist of (nonreducing) D-mannosyl groups, (1 leads to 4)-linked D-glucosyl residues, and 3,6-branched, (1 leads to 4)-linked D-glucosyl residues in the approximate molar ratios of 2:1:1. Periodate oxidation of the polysaccharide, followed by borohydride reduction and mild hydrolysis with acid yielded glycerol, erythritol, 2-O-beta-D-glucopyranosyl-D-erythritol, and 5-O-beta-D-glucopyranosyl-2,4-bis(hydroxymethyl)-1,3-dioxane, which were isolated in the molar ratios of 2.0:0.14:0.74:0.35. Partial hydrolysis of the polysaccharide gave alpha-D-Manp-(1 leads to 6)-D-Glcp, beta-D-Glcp-(1 leads to 4)-D-Glcp, alpha-D-Manp-(1 leads to 3)-D-Glcp, and beta-D-Glcp-(1 leads to 4)-[alpha-D-Manp-(1 leads to 3)-]-D-Glcp. From these results, it is proposed that the polysaccharide is mainly composed of tetrasaccharide repeating-units having the following structure. (formula: see text)