Carboxymethylation and acetylation of the polysaccharide from Cordyceps militaris and their α-glucosidase inhibitory activities

The crude polysaccharide extracted from Cordyceps militaris was chemically modified to obtain carboxymethylated derivatives (CM-CPS) and acetylated derivatives (AC-CPS). The physicochemical characterizations were comparatively investigated by chemical methods, high-performance gel permeation chromatography, FT-IR spectra, NMR analysis, Congo red test, scanning electron microscopy, atomic force microscopy and differential scanning calorimetry. Then alpha-glucosidase inhibitory activities were conducted to determine the structure-bioactivity relationship. Results indicated that carboxymethylation and acetylation modification of polysaccharide were successful with the carboxymethyl substitutions might being C-6, C-2 and acetyl substitutions at C-3, C-6 inferred from NMR analysis. In addition, the tertiary structure, ultrastructure, melting properties were also different from native polysaccharide. Besides, alpha-glucosidase inhibitory activities of derivatives exhibited differently with CM-CPS to be the lowest. Therefore, it was concluded that change of structure in polysaccharide had certain effect on bioactivity with degree of substitution and substituents position being the influence factors.