An unusual juxtaposition of polysaccharide components of Collema leptosporum

The lichenised ascomycete, Collema leptosporum Malme, was extracted with aq ueous methanol to give traces of mannitol and 3-O-beta-D-glucopyranosyl-D-m annitol (2.7% yield). The residue was consecutively extracted with hot wate r to give a complex uronic acid-containing polysaccharide, and then with ho t aqueous alkali which provided a mixture of polysaccharides. This was frac tionated with Cetavlon to give a branched galactomannan, which had the lowe st content of galactose yet reported for such a lichen polysaccharide. It h as a main chain of (1-->6)-linked alpha-Manp units partly substituted at O- 2,4 by non-reducing end-units of Manp and Galp, shown by NMR spectroscopy t o have alpha- and beta-configurations, respectively. The other polysacchari de component was unexpectedly a branched (1 --> 3), (1 --> 6)-linked beta-g lucan, which is typical of a basidiomycete, whereas those of ascomycetes co ntain similar linkages but in linear glucans. (C) 1999 Elsevier Science Ltd . All rights reserved.