Structural studies on a galactomannan isolated from the lichen Stereocaulon ramulosum.

Abstract

Stereocaulon ramulosum (SW.) Raüsch, a lichen that grows in Southern Brazil, was treated with hot aqueous alkali, the extract fractionated with Fehling solution, and the resulting insoluble copper complex regenerated. The polysaccharide was fractionated stepwise in the presence of Cetavlon, and at pH 8.5, in the presence of borate, the predominant component was precipitated. From this, galactomannan B was obtained and shown to contain a main chain of (1→6)-linked α-D-mannopyranosyl units, which were unsubstituted (1), monosubstituted with single-unit side-chains of β-D-Galp-(1→4)-(2), and disubstituted with β-D-Galp-(1→4)- and α-D-Manp-(1→2)- (3). These principal components were arranged sequentially, with the structure 3→2 making a large contribution.