Isolation and structural elucidation of novel homogenous polysaccharide from Mactra veneriformis

Crude polysaccharide, possessing immune-enhancing and anti-hyperglycemic activities, was extracted from Mactra veneriformis by water extraction and alcohol precipitation. Three homogeneous polysaccharides (MVPS-1, MVPS-2 and MVPS-3) were successfully purified from the crude polysaccharide of M. veneriformis by DEAE-cellulose column chromatography. The average molecular weights (Mw) of the three polysaccharides were 446, 426 and 452 kDa, respectively. Monosaccharide analysis indicated that the homogeneous polysaccharides contained only d-glucose residue. Fourier-transform infrared spectra (FTIR) revealed the typical characteristics of carbohydrate polymer and the typical peak of α-type glycosidic bond. The MVPS-2 was selected to characterize its absolute chemical structure by analysis of nuclear magnetic resonance (NMR) in this article. According to 1H NMR, 13C NMR and 2D-NMR analysis, MVPS-2 contains two kinds of α-linkages for the glucose residue with a ratio of 6:1. One is α-(1 → 4) and the other is α-(1 → 2) linkage. The H–H correlation spectrometry (COSY) and heteronuclear single-quantum coherence (HSQC) result showed that MVPS-2 was consisted by a repeating structure unit as [→4Glc1 → 4Glc1 → 4Glc1 → 2Glc1 → 4Glc1 → 4Glc1 → 4Glc1]n.