Studies on the Polysaccharides of Lichens. III. The Structure of Alkali-Soluble Polysaccharides in Umbilicaria pustulata (L.) Hoffm. and Umbilicaria spodochroa (Ach.) Hoffm.

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Abstract
D-Galacto-D-mannans have been isolated from two species of lichen, Umbilicaria pustulata and Umbilicaria spodochroa, by extraction with alkali. The polysaccharide composition of the various fractions is dependent on the sequence and vigour of the extraction procedures. One fraction from each lichen was purified and investigated in detail. The glycans in these fractions were found to have closely related structures, comprising a main chain of (1 .fwdarw. 6)-linked .alpha.-D-mannopyranosyl units with side chains attached to approximately every other mannose unit at positions O-2, O-4 or both. The side chains were short stubs consisting mainly of 2- and 3-linked .alpha.-D-mannopyranosyl and 3-linked .alpha.-D-glucopyranosyl units. All galactose existed as .beta.-D-galactofuranosyl units, as non-reducing end groups attached to the main chain at O-4, or as sequences of 5- and 3-linked .beta.-D-galactofuranosyl units. All galactose existed as .beta.-D-galactofuranosyl units, as non-reducing end groups attached to the main chain at O-4, or as sequences of 5- and 3-linked .beta.-D-galactofuranosyl units in the side chains. The major fractions of the polysaccharides were found to have a molecular weight of about 50 000 (Mw).