STRUCTURAL STUDIES ON THE GALACTOMANNANS OF LICHENS OF THE GENUSCLADONIA

Abstract

Galactomannans were isolated fromCladonia signata,C. furcata,C. imperialis, andC. clathratavia successive alkaline extraction and precipitation with Fehling solution and Cetavlon. They were investigated using13C-NMR spectroscopy, methylation analysis, and Smith degradation, and their specific rotations and monosaccharide compositions determined. As with galactomannans of otherCladoniaspecies, they contained (1→6)-linked main chains of α-mannopyranose, which were non-substituted (structure4in Fig. 2), mono-substituted at O-2 with α-mannopyranose (structure6) or α-galactopyranose (structure1), O-4 with β-galactopyranose (structure2), and disubstituted at O-2 and O-4 with α-mannopyranosyl and β-galactopyranosyl units, respectively (structure5). Disubstitution was present to a greater extent in the galactomannans ofC. clathrataandC. imperialisthan in those ofC. signataandC. furcata. In the case of the galactomannans ofC. furcata,C. clathrata, andC. imperialis, substitution also occurred at O-2 withO-β-galactofuranosyl-(1→6)-O-α-mannopyranosyl units (structure7). As observed in previous investigations, the C-1 portion of the13C-NMR of mannose-containing polysaccharides is typical of the lichen species. However, those of galactomannans ofC. imperialisandC. clathrataare almost identical and, although other chemical data showed many structures in common, some differences were evident.