The glucans of Ramalina celastri: relation with chemotypes of other lichens

Abstract

Several structurally different glucans were characterized as components of Ramalina celastri. Aqueous KOH extraction of the lichen at 100°C, followed by dialysis provided amylose (0.02%), identified and quantified by its blue coloration with iodine. The extract was frozen and thawed and the resulting precipitate (2% yield) shown to be a mixture of two insoluble d-glucans, with (1→3)- and (1→3),(1→4)-linkages, respectively, as shown by 13C NMR spectroscopy. On treatment with 0.5% aqueous NaOH at 50°C, the material which remained insoluble was a linear β-glucan with regularly distributed (1→3)- and (1→4)-linkages in a 1:1 molar ratio (nigeran, 1.2% yield), whereas that which solubilised was a linear β-glucan with (1→3)-linkages (laminaran, 0.8% yield). The mother liquor of the KOH extraction was treated with Fehling solution to give a precipitate and the supernatant contained an α- d-glucan (28% yield) with (1→3)- and (1→4)- linkages in a molar ratio of 3:1, and which were distributed irregularly. The structures of these two (1→3),(1→4)-linked β-glucans were characterized by methylation, controlled Smith degradation and 13C and 1H NMR spectroscopic analyses.