Structural Studies on the Galactomannans of Lichens of the Genus Cladonia

Abstract

Galactomannans were isolated from Cladonia signata, C. furcata, C. imperialis, and C. clathrata via successive alkaline extraction and precipitation with Fehling solution and Cetavlon. They were investigated using ⊃13C-NMR spectroscopy, methylation analysis, and Smith degradation, and their specific rotations and monosaccharide compositions determined. As with galactomannans of other Cladonia species, they contained (l →6)-linked main chains of α-mannopyranose, which were non-substituted (structure 4 in Fig. 2), monosubstituted at O-2 with α-mannopyranose (structure 6) or α-galactopyranose (structure 1), O-4 with β-galactopyranose (structure 2), and disubstituted at O-2 and O-4 with α-mannopyranosyl and β-galactopyranosyl units, respectively (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. furcata, C. clathrata, and C. imperialis, substitution also occurred at O-2 with O-β-galactofuranosyl-(l→6)-O-α-mannopyranosyl units (structure 7). As observed in previous investigations, the C-l portion of the ⊃13C-NMR of mannose-containing polysaccharides is typical of the lichen species. However, those of galactomannans of C. imperialis and C. clathrata are almost identical and, although other chemical data showed many structures in common, some differences were evident.