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

Several structurally different glucans were characterized as components of Ramalina celastri. Aqueous KOH extraction of the lichen at 100 degrees C, f ollowed 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-g lucans, with (1 --> 3)- and (1 --> 3),(1 --> 4)-linkages, respectively, as shown by C-13 NMR spectroscopy. On treatment with 0.5% aqueous NaOH at 50 d egrees C, the material which remained insoluble was a linear beta-glucan wi th regularly distributed (1 --> 3)- and (1 --> 4)-linkages in a 1:1 molar r atio (nigeran, 1.2% yield), whereas that which solubilised was a linear bet a-glucan with (1 --> 3)-linkages (laminaran, 0.8% yield). The mother liquor of the KOH extraction was treated with Fehling solution to give a precipit ate and the supernatant contained an alpha-D-glucan (28% yield) with (1 --> 3)- and (1 -- 4)- linkages in a molar ratio of 3:1, and which were distrib uted irregularly. The structures of these two (1 --> 3),(1 --> 4)-linked be ta-glucans were characterized by methylation, controlled Smith degradation and C-13 and H-1 NMR spectroscopic analyses. (C) 1999 Elsevier Science Ltd. All rights reserved.