Determination of the primary and fine structures of a galactomannan from the seed of Gleditsia triacanthos f. inermis L.

Galactomannan, a polysaccharide with a molecular weight of 660 kDa, was isolated for the first time from the seed of Gleditsia triacanthos f. inermis (yield, 15.4%). Its aqueous solutions were optically active ([alpha](D) = +31.0degrees) and highly viscous ([eta] = 578 ml/g). Analysis of this heteropolysaccharide using chemical, enzymatic, and chromatographic procedures, as well as IR and C-13 NMR spectroscopy, showed that it consists of D-mannopyranose and D-galactopyranose residues (molar ratio, 2.42 : 1). The main chain of this galactomannan comprises 1,4-beta-D-mannopyranose residues, 41% of which are substituted at C6 with single residues of alpha-D-galactopyranose. The probability of occurrence in the chain of mannobiose units substituted otherwise, determined experimentally, was 0.16 for the Man-Man unit, 0.50 for the Gal(Man-Man) and (Man-Man)Gal units, and 0.34 for the disubstituted Gal(Man-Man)Gal unit.