STRUCTURAL STUDIES ON THE GALACTOMANNANS OF LICHENS OF THE GENUS CLADONIA

Galactomannans were isolated from Cladonia signata, C. furcata, C. imp erialis, and C. clathrata via successive alkaline extraction and preci pitation with Fehling solution and Cetavlon. They were investigated us ing C-13-NMR spectroscopy, methylation analysis, and Smith degradation , and their specific rotations and monosaccharide compositions determi ned. As with galactomannans of other Cladonia species, they contained (1-->6)-linked main chains of alpha-mannopyranose, which were non-subs tituted (structure 4 in Fig. 2), mono-substituted at O-2 with alpha-ma nnopyranose (structure 6) or alpha-galactopyranose (structure 1), O-4 with beta-galactopyranose (structure 2), and disubstituted at O-2 and O-4 with alpha-mannopyranosyl and beta-galactopyranosyl units, respect ively (structure 5). Disubstitution was present to a greater extent in the galactomannans of C. clathrata and C. imperialis than in those of C. signata and C. furcata. In the case of the galactomannans of C. fu rcata, C. clathrata, and C. imperialis, substitution also occurred at O-2 with ta-galactofuranosyl-(1-->6)-O-alpha-mannopyranosyl units (str ucture 7). As observed in previous investigations, the C-1 portion of the C-13-NMR of mannose-containing polysaccharides is typical of the l ichen species. However, those of galactomannans of C. imperialis and C . clathrata are almost identical and, although other chemical data sho wed many structures in common, some differences were evident. (C) 1997 The British Lichen Society.