Synthesis of galactomannan fragments to help NMR assignment of polysaccharides extracted from lichens

The synthesis of six model trisaccharides representative of galactomannans produced by lichens was performed through stereoselective glycosylation. These standards include linear and branched galactomannans bearing either galactofuranosyl or galactopyranosyl entities. The complete assignment of ¹H and ¹³C signals for both forms of synthetically reduced oligosaccharides was performed. The resulting NMR data were used to quickly demonstrate the structural characteristics of minor polysaccharides within different extracts of three representative lichens.