Structural characterisation of a highly branched galactomannan from the lichen Peltigera canina by methylation analysis and NMR-spectroscopy

An alkali-extractable water-soluble polysaccharide, Pc-4, was isolated from the lichen Peltigera canina using ethanol fractionation and size exclusion chromatography. The average molecular weight of Pc-4 was estimated to be 53 kDa. Structural characterisation of Pc-4 was performed by methanolysis, methylation analysis and NMR-spectroscopy (1D proton, COSY, NOESY, TOCSY and HSQC).According to data obtained, Pc-4 is a highly branched galactomannan, with (1→6)-linked α-mannopyranosyl units in the main chain, which are mainly disubstituted at O2 and O4 by single unsubstituted units of α-Manp and β-Galp, respectively. Pc-4 resembles the lichen galactomannans described previously; however, Pc-4 has higher degree of branching.