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

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 C-13 NMR spectroscopy. Two of them were (1 -> 3)and (1 -> 6)-linked beta-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 a-mannopyranosyl residues, part of them being substituted at O-2, O-4, and O-2,4 by complex, branched side chains containing a-mannopyranosyl and beta-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. (c) 2005 Elsevier Ltd. All rights reserved.