Polysaccharides of Fabaceae. I. Galactomannan of Astragalus sericeocanus seeds

Galactomannan (yield 3.58% of seed mass) of molecular weight 876 kDa was isolated from seeds of Astragalus sericeocanus Gontsch. (Fabaceae). Its solutions had high viscosity [eta], 764.6 mL/g, and optical density [alpha](D) +65.3A degrees. The polysaccharide consisted of galactose and mannose in molar ratio 1:1.58. The main chain of the galactomannan macromolecule was constructed of 1,4-beta-D-mannopyranose units, 63% of which were substituted at C-6 by single alpha-D-galactopyranose units. C-13 NMR spectroscopy established that the galactomannan contained units of differently substituted galactose mannobiose units: Man-Man, (Gal)Man-Man, and/or Man-Man(Gal) in addition to (Gal)Man-Man(Gal), the ratio of which was 0.15:0.51:0.34.