Structural characterization and antitumor activity of a pectic polysaccharide from Codonopsis pilosula

A pectic polysaccharide (CPP1b) was at first isolated from Codonopsis pilosula. Sugar analysis revealed that CPP1b is composed of rhamnose (Rha), arabinose (Ara), galactose (Gal) and galacturonic acid (GalA) with a molar ratio of 0.25:0.12:0.13:2.51. The result of esterification assay showed that about 46.7 ± 0.4% of carboxylic groups in GalA residues existed as methyl ester. Combined with chemical and spectroscopic analyses, a preliminary structure of CPP1b was proposed as follows: 1,4-linked α-d-GalpA and 1,4-linked α-d-GalpA6Me interspersed with rare 1,2-linked β-l-Rhap, 1,2,6-linked α-d-Galp and terminal α-l-Arap. CPP1b had an average molar mass and root-mean square radius (RMS) of 1.45 × 105 Da and 29.7 nm, respectively, and presented a linear random coil conformation in 0.9% NaCl. The ultrastructure of CPP1b was further investigated by transmission electron microscope (TEM) and scanning electron microscope (SEM). CPP1b exhibited obvious cytotoxicity to human lung adenocarcinoma A549 cells in a dose- and time-dependent manner.