Structure analysis of sulfated polysaccharides extracted from green seaweed Ulva lactuca: experimental and density functional theory studies

摘要

The structure of sulfated polysaccharides extracted from green seaweed Ulva lactuca has been determined using NMR experiments. The obtained results indicate that this natural product is mainly composed of disaccharide A(3S): [- 4)-beta-d-GlcA-(1 - 4)-alpha-l-Rha3S-(1 -] and B-3S: [- 4)-alpha-l-IdoA-(1 - 4)-alpha-l-Rha3S-(1 -]. The computational calculations using density functional theory (DFT) at the B3LYP/6-311+G(2d,p)//B3LYP/6-311G(d,p) model chemistries were also investigated to analyze the obtained structures based on the comparison of H-1 and C-13 NMR chemical shifts. The DFT results also confirm that the A(3S) structure is more dominating than the B-3S one with the mean absolute error of H-1 and C-13 NMR chemical shifts, respectively, equal to 0.46 and 4.98 ppm for the A(3S) and to 2.07 and 5.03 ppm for the B-3S.