Synthesis and structural features of phosphorylated Artemisia sphaerocephala polysaccharide

Phosphorylation is a key route to achieve varieties of biological activities for polysaccharides. Currently, conventional phosphorylation reagents are characterized by long processing times and high reaction temperatures. Here, we reported phosphorylation of Artemisia sphaerocephala polysaccharides (PASP) with the degrees of substitution (DS) of 0.34-0.54 in mild reaction conditions (3-4h and 25°C) by employing POCl₃/pyridine technique. FT-IR spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis confirmed the appearance of phosphate ester (P⁵⁺) groups in PASP. Size exclusion chromatography combined with multi-angle laser light scattering (SEC-MALLS) result clearly showed temperature-dependent increment of weight average molecular mass (M_W). High temperature facilitated the reaction of phosphoryl chloride with primary and secondary hydroxyl groups, favoring the crosslinking of polysaccharide chains by phosphate di-esters as further confirmed in ¹³C NMR determination. Our results provide insight into the relationship between the structure and reaction conditions of phosphorylated polysaccharide, which is important for understanding and exploiting these derivatives in a wide range of applications.