Chemical structure characterization of polysaccharides using diffusion ordered NMR spectroscopy (DOSY)

The potential of DOSY NMR spectroscopy to distinguish the linkage pattern of chemically related polysaccharides was evaluated using β-glucans isolated from yeast (Saccharomyces cerevisiae) and mushroom (Pleurotus eryngii). Laminarin from Laminaria digitata was included for chemical shift comparison. Characterization through methylation and 1D/2D NMR analysis showed that all the samples were constituted by $\to$3)-Glcp-(1$\to$; →3,6)-Glcp-(1$\to$; Glcp-(1$\to$ and $\to$6)-Glcp-(1$\to$ linkages. The results obtained allowed the identification of the well-known chemical structure of laminarin. Moreover, DOSY demonstrated that the units $\to$3)-Glcp-(1$\to$ and $\to$6)-Glcp-(1$\to$ from yeast β-glucans, presented the same diffusion time. For the mushrooms β-glucans, the diffusion time of these units were different, confirming that they belong to distinct polysaccharides. The yeast and the mushroom polysaccharide samples presented the same NMR correlations, but after DOSY analysis, different structures could be proposed. Therefore, DOSY NMR spectroscopy could be a tool for the identification of different linkage patterns of polysaccharides belonging to the same group and may be a useful contribution to the chemical structure and biological activity correlation studies of such structures.