A high methyl ester pectin polysaccharide from the root bark of Aralia elata: Structural identification and biological activity

In this study, a high methyl ester pectin polysaccharide, AER-A3 (Mw, 1.12 × 105 g/mol; O-methyl ester groups (wt%), 3.81%), was isolated and purified from the root bark of Aralia elata by ion exchange and gel-filtration chromatography. Its planar structure was investigated in combination with UPLC-ESI+-MS, FT-IR, HILIC-UPLC-ESI−-HCD-MS/MS, GC–MS and NMR techniques. The main chain of AER-A3 was unambiguously determined to be smooth region and hairy region with a chain length ratio of 1:1, characterized by occurrence of (1 → 2)-α-Rhap, (1 → 2,3)-α-Rhap, (1 → 2,4)-α-Rhap, (1 → 2,3,4)-α-Rhap, and (1 → 4)-α-GalpA, whereas the branched chain included T-α-Rhap, T-α-Araf, (1 → 5)-α-Araf, (1 → 3,5)-α-Araf, T-β-Galp, (1 → 3)-β-Galp, (1 → 3,4,6)-β-Galp, (1 → 4)-Glcp, (1 → 3)-Glcp, and (1 → 3)-Manp. Meanwhile, SEC-MALLS-RID, CD and Congo red assays showed that AER-A3 had no helical conformations but existed as a globular shape with branching. In addition, AER-A3 had good scavenging activities against DPPH, hydroxyl, and superoxide radicals. Anti-tumor assay investigated the effects of AER-A3 on human A549 and HepG2 cancer cell lines in vitro. These results provided a scientific basis for the use of the polysaccharides in A. elata root barks in pharmaceuticals.