Water- and alkali-soluble glucans from oak lichen

Abstract

A water-soluble glucan, [α] 2 D +217° (water), and an alkali-soluble glucan, ▪ +152° (sodium hydroxide), have been isolated from the oak lichen Evernia prunastri (L.) Ach. On the basis of methylation analysis, periodate oxidation, and partial acid hydrolysis, the water-soluble polysaccharide has been shown to be a neutral, slightly branched glucan with a main chain composed of (1→3)- and (1→4)- linked glucopyranose residues in the ratio 1̃:1. Branching occurs most probably at position 2 of (1→4)-linked glucopyranose residues. On the basis of optical rotation and i.r. spectral data, and enzymic hydrolysis, the α- D configuration has been assigned to the glycosidic linkages. Likewise, the alkali-soluble polysaccharide was shown to be a neutral, branched glucan with a main chain composed of (1→3)- and (1→4)-linked α- D-glucopyranose residues in the ratio 6:1. Each of the (1→4)-linked units was a branch point involving position 6. The presence of some β- D linkages is not excluded since hydrolysis with β- D-glucosidase occurred to a small extent.