Structural characterisation of a complex heteroglycan from the cyanobacterium Nostoc commune

► A complex high MW heteroglycan was isolated from the cyanobacterium Nostoc commune. ► Nc-5-s is composed of eleven different monosaccharidesincluding both acidic and OMe-units. ► Detailed structural characterisation of Nc-5-s using NMR spectroscopy. ► The results provide crucial data for future studies of cyanobacterial polysaccharides. An alkali-extractable O-methylated ribofuranose-containing heteroglycan, Nc-5-s, was isolated from wild-growing field colonies of the cyanobacterium Nostoc commune collected in Iceland, using ethanol fractionation and anion-exchange chromatography. The average molecular weight was estimated to be 1500kDa. Structural characterisation of the heteroglycan was performed by high-field NMR spectroscopy (1D proton, 2D-COSY, 2D-NOESY, 2D-TOCSY, 1H 13C-HSQC, HMBC, H2BC and HSQC-NOESY) as well as monosaccharide analysis after methanolysis by GC and supported by linkage analysis by GC–MS. According to the data obtained, the structure of Nc-5-s is composed of repeating units of 1, 1a, 1b and 2 and 2a in approximate molar ratio of (10:25:50:5:10). [Display omitted]