Structure of fructan polymers from tuberous roots of Gomphrena macrocephala (Amaranthaceae) from the cerrado

Abstract

Tuo fructo-polysaccharides, FP-I and FP-II, were separated from a soluble extract from tuberous roots of Gomphrena macrocephala St.-Hil. by gel permeation chromatography on Toyopearl HW-40S. FP-I and FP-II were mixtures of saccharides with a wide-ranging degree of polymerization; their acid hydrolysis products were fructose and glucose. The ratios of fructose to glucose in the hydrolysates of FP-I and FP-II were 38 and 60, respectively. The average molecular weights of FP-I and FP-II were estimated to be 5500 and 10000 respectively, by gel permeation HPLC. The structural confirmation of FP-I and FP-II was made by 13C-NMR analysis. Intense signals corresponding to carbon-1 (Cl), C2, C3, C4, C5 and C6 of fructose residues in FP-I and FP-II were observed at δ 60.60, 104.93, 76.99, 75.91, 81.02 and 64.11, respectively. These chemical shifts coincided with those of timothy and bacterial levans. The less intense resonances were tentatively assigned to carbons of terminal fructosyl residues and a fructosyl residue linked to a glucose residue by a β-2,1 bond in FP-I and FP-II. Also, weak signals attributed to carbons of the glucose residue in both polysaccharides were separated from those of other glycosyl residues. These findings were supported by GLC analysis of methanolysate from permethylated FP-I and FP-II. Thus FP-I and FP-II comprise fructose residues with β-2,6 linkages, and a terminal glucose bound with fructose residues at position C1, although both polysaccharides possibly contained a non-terminal glucose residue in the molecule.