Purification, structural features and inhibition activity on α-glucosidase of a novel polysaccharide from Lachnum YM406

•LEP-2a from fermentation broth of Lachnum YM406 was a novel heteroglycan.•Backbone of LEP-2a was mainly composed of α-(1 → 3,4)-d-Manp, α-(1 → 2)-d-Manp, α-(1 → 2,6)-d-Manp.•LEP-2a had significant effects on reducing blood glucose in vivo.

A novel Lachnum sp. exopolysaccharide (LEP-2a) was separated and purified by DEAE-52 cellulose and Sephadex G-100 chromatographic columns, with relative molecular weight of 2.3 × 104 Da. One- and two-dimensional nuclear magnetic resonance analysis combined with methylation analysis results revealed that LEP-2a was a galactomannan with a backbone structure composed of α-(1 → 3,4)-d-Manp, α-(1 → 2)-d-Manp, α-(1 → 2,6)-d-Manp and β-(1 → 3)-d-Galp residues, which was substituted at O-3, O-4, O-2, O-6 by branches. Side chains were composed of α-(1 → 3,4)-d-Manp, α-(1 → 2)-d-Manp, α-(1 → 2,6)-d-Manp and β-(1 → 3)-d-Galp terminated by terminal α-d-Manp. Activities researches enlightened that LEP-2a could play a role in reducing blood glucose as one α-glucosidase inhibitor.

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