Synthesis and structure characterization of sulfated galactomannan from fenugreek gum.

Abstract Sulfated derivatives of the galactomannan family have multiple biological activities. In the present study, sulfated galactomannan from fenugreek gum (SFG) were prepared by chlorosulfuric acid/pyridine (CSA/Py) method. In order to acquire the derivatives with the highest degree of substitution (DS), the experiment optimum conditions of the sulfation were determined by Box-Behnken design (BBD). The quadratic regression model analysis confirmed that reaction time was the most significant parameter for the impact of DS. Under the selected conditions, maximum DS was obtained as 0.490. Results of FT-IR and X-ray photoelectron spectroscopy (XPS) indicated the present of SO 3 − group. In 13C NMR spectroscopy, the original C-6 peaks did not disappear completely and the newly peaks appeared at δ 63.2 and 64.0 illustrating the incomplete substitution were predominantly on C-6 position. After sulfation, size exclusion chromatography combined with multi-angle laser light scattering (SEC-MALLS) detected all the weight average molecular mass (M W) of sulfated derivatives decrease rapidly. The introduction of the electrostatic interaction of negatively charged SO 3 − groups and the decrease in M W could have a significant effect on its biological activity. Highlights • Sulfated galactomannan of fenugreek gum is synthesized and characterized in the present work. • Sulfation conditions are optimized by response surface methodology with a maximum degree of substitution 0.490. • Structure characterization illustrated the introduction of SO 3 − and the substitution at C-6. • All sulfated fenugreek gum derivatives showed a rapidly decrease in weight average molar mass. [ABSTRACT FROM AUTHOR]