Synthesis and structure characterization of sulfated galactomannan from fenugreek gum

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 SO₃^- 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 SO₃^- groups and the decrease in M_W could have a significant effect on its biological activity.