Structure of two glucans and a galactofuranomannan from the lichen Umbilicaria mammulata

Abstract: The three main polysaccharides from the lichenized fungus Umbilicaria mammulata were isolated and characterized. Their structures were determined using GC-MS of derived alditol acetates, GC-MS-methylation analysis and 13C NMR spectroscopy. Two of them were (1→3)-and (1→6)-linked β-glucans, namely laminaran and pustulan, respectively. The other was a galactofuranomannan, which was analyzed as well as a galactose-free polysaccharide formed on partial hydrolysis. The former consisted of a main chain of (1→6)-linked α-mannopyranosyl residues, part of them being substituted at O-2, O-4, and O-2,4 by complex, branched side chains containing α-mannopyranosyl and β-galactofuranosyl units. This heteropolysaccharide is related to those of other Umbilicariaceae, and its chemical characterization presents a useful tool for the systematics of lichenized fungi. [Copyright &y& Elsevier]