Isolation and structural characterization of a non-competitive α-glucosidase inhibitory polysaccharide from the seeds of Litchi chinensis Sonn

Abstract In this study, a novel homogeneous polysaccharide (LSP-W-4, MW = 6.70 kDa) was isolated and purified from the seeds of Litchi chinensis Sonn. Monosaccharide composition analysis indicated that LSP-W-4 is a heteropolysaccharide consisting of arabinose, mannose, glucose and galactose in a molar ratio of 6.33:3.88:10.35:1.00. A detailed structural analysis revealed that LSP-W-4 has a backbone consisting of 1,4-α-Glcp and 1,4-β-Manp, as well as four branched chains including of T-α-Galp, T-α-Araf, α-Araf-(1 → 5)-α-Araf-(1 → and α-Araf-(1 → 5)-α-Araf-(1 → 5)-α-Araf-(1 → attached to O6 of 1,4-β-Manp and 1,4-α-Glcp. LSP-W-4 exhibited significant inhibitory activity both against yeast (Saccharomyces cerevisiae) and mammalian (rat-intestinal acetone powder) α-glucosidase, with IC50 values of 75.24 μM and 66.97 μM, respectively, with both such inhibitory activities being more powerful than those of acarbose. A kinetic analysis revealed that LSP-W-4 inhibited the activities of both yeast and mammalian α-glucosidase in a typical non-competitive manner, with KM values of 0.43 mmol/L and 0.53 mmol/L, respectively.