The Structure of a Synthetic Glucan: I. General Structural Features

Abstract

Only D-glucoSe was obtained on acid hydrolysis of the glucan. Periodate oxidation released formaldehyde, which was believed to arise from Cc of D-glucofuranose units. From the additional formaldehyde liberated from the borohydride-reduced glucan the degree of polymerization was estimated to be about 165. Complete hydrolysis of the derived polyalcohol gave glycerol, erythritol, D-glucose, and D-xylose. Partial hydrolysis gave glycerol, erythritol, and a t least seven non-reducing oligosaccharides. Direct evidence for the existence of relatively large nu~nbers of 1 4 6 and 1 4 4 linkages was found, together with smaller numbers of 1 + 2 linkages. The methylated glucan was freely soluble in chloroform -petroleum ether (5:05), and hydrolysis gave tetra, tri, di, and mono-0-methyl-D-glucoses in a 6:6:3:1 molar ratio.There are many reports in the literature on the polymerization of D-glucose and a few papers on other monosaccharides (e.g. 1-10). Most of these polynierizations have been acid catalyzed a t temperatures ranging froin rooin temperature to about 200" C and the yields of polymeric material have varied greatly. There appears to have been no detailed study 011 the structures of these synthetic glucans, although there is general agreement that 1 --, G liilltages are co~ninonly present and that there is a high proportion of a-glucosidic bonds. In a paper (6) on the glucan obtained by polymerization in the presence of metaboric acid it was inferred, on the grounds of hydrolytic behavior, that there were 110 glucofuranose units present. I t was further stated that the polymer was highly branched, as shown by the large ainouilt of 2,3,4,G-tetra-0-methyl-~-glucose obtained. Another recent paper on the glucan obtained by poly~uerization of 1,G-anhydro-D-glucose again demonstrated the branched nature of the polymer on the basis of periodate oxidation (1 1).Since 1958 there has been a group of papers published by Mora and his associates a t the National Institutes of Health on the preparation of several synthetic polysaccharides (2-4). Since sollie derivatives of these synthetic ~llaterials have been shown to be biologically active (12, 13) it was of interest to look more closely a t the structures of these polymers. The present paper reports the general structural features of the glucan designated as polyglucose I1 in Table I of reference 3. Complete hydrolysis of the glucan by boiling it with 1 N sulphuric acid followed by chromatography of the product showed only glucose, which was isolated in the crystalline state. Alkaline oxidation or bromine oxidation of the sugar to the corresponding aldonic acid followed by adsorption of the acid on an anion exchange resin left no residue which reacted with Tollens (23) or 9-anisidine trichloroacetate (24) spray reagents when the effluent was evaporated, thus de~noilstrating the absence of ally sugar alcohols. The low optical rotation of the glucan, [aID2' 65" (c, 1.0 in water), compared with the high positive rotation of alpha-linked glucans, such as amylose (195-21...