Optimization of selenylation conditions for a pectic polysaccharide and its structural characteristic

• CPP1b is a pectic polysaccharide isolated from Codonopsis pilosula.
• A HNO3–Na2SeO3 method was performed for selenylation modification of CPP1b.
• The optimal modification conditions were determined and obtained sCPP1b.
• Selenylation modification could raise CPP1b antitumor activity in vitro.
• sCPP1b’ structure was characterized.

CPP1b is a pectic polysaccharide isolated from Codonopsis pilosula, and it possesses potent antitumor activity. In this study, a HNO3–Na2SeO3 method was performed to synthesize selenium–CPP1b (sCPP1b). The effects of BaCl2 usage amount and HNO3 concentration on the yield and selenium content of sCPP1b were investigated by single-factor experiments. Reaction time, reaction temperature and the ratio of polysaccharide to Na2SeO3 were optimized by orthogonal experimental design at three levels of each of the three factors (L9(3)4) based on antitumor activity, selenium content and yield of sCPP1b. Our results showed that 5 h of reaction time, 60 °C of reaction temperature, and 2:2 ratio of polysaccharide to Na2SeO3 were the optimal selenylation modification conditions. The validation experiments completed under the optimal conditions gave the mean selenium content and yield of sCPP1b were 478.17 μg/g (RSD = 5.7%) and 595 mg/g (RSD = 1.6%), respectively. Selenylation modification can significantly increase the antitumor activity of CPP1b in vitro. The structural characterization of sCPP1b was further characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, and high-performance gel permeation chromatography coupled with multi-angle laser light scattering. These structure analysis results indicated that sCPP1b has been successfully selenylation modified with similar structure to polysaccharide of CPP1b.