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Abstract: We reported here a new synthesis of C-2 and C-3 sulfated guar gum (SRSGG) with low degree of substitution (DSS) of 0.58, employing triphenylchloromethane (TrCl) as a protected precursor. The yield and DSTr (calculated from the weight of triphenylmethanol) of triphenylmethylated GG (GGTr) was 165.6% and 0.71, respectively. In addition, low ratio (1:4) of chlorosulfuric acid to pyridine (1:4) was chosen in sulfation reaction since the protecting group was slightly sensitive to acid. Results of FT-IR and 13C NMR spectroscopy indicated that C-2 and C-3 substitution was predominant but not fully sulfated in SRSGG. Size-exclusion chromatograph combined with multi-angle laser photometer (SEC-LLS) showed a decrease in molecular weight in the reaction. This might be due to the degradation in sulfation and deprotection process. Finally, we investigated the effect of structure features on the antioxidant activities in vitro. Vitro antioxidant experiments revealed that the regioselective sulfation at C-2 and C-3 and low molecular weight afforded strong antioxidant activities showing a much higher scavenging abilities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical than that by the known C-6-sulfated derivative. The antioxidant activities of sulfated polysaccharides were not a function of a single factor but a combination of molecular weight, DSS and substitution positions. [Copyright &y& Elsevier]

Abstract: We reported here a regioselective synthesis of non-C-6 phosphorylated guar gum (PRSGG) with a degree of substitution (DS) 0.34. Triphenylchloromethane (TrCl) was employed as a key protected precursor. Detritylation was performed by treatment with an excess of dichloroacetic acid. Phosphorylated GG was successfully characterized by FT-IR and 13C NMR spectroscopies. It was indicated that C-2 and C-3 substitution was predominant in phosphorylated polysaccharide. A decrease in weight average molar mass (M w) was observed in the reaction due to the acid environment in deprotection procedure. The results of vitro antioxidant experiments revealed that regioselective phosphorylation at C-2/C-3 and low M w afforded strong antioxidant activities. Non-C-6 phosphorylated guar gum showed a much higher scavenging abilities of 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radical than C-6-phosphorylated derivative. [Copyright &y& Elsevier]

Abstract: It was essential to understand the chemical structure of polysaccharides for further research and biochemical or medical application of this natural biopolymer. In the present study, sulfated derivatives of guar gum with high degree of sulfation (DS) were synthesized using 4-dimethylaminopyridine (DMAP)/dimethylcyclohexylcarbodiimide (DCC) as catalyst in homogeneous conditions. The effects of the ratio of chlorosulfuric acid to pyridine, the content of catalyst and reaction temperature were investigated. Results of FT-IR, 1H and 13C NMR indicated that C-6 substitution was predominant in sulfated polysaccharide. In the sulfation reaction, a sharp decrease in M W was observed. The enhanced antioxidant activities of sulfated polysaccharides were not a function of a single factor but a combination of high DS and low molecule weight. [Copyright &y& Elsevier]

Abstract: Sulfated polysaccharides exerted potential biological property which was relative to degree of sulfation (DS), M w, substitution position and chain conformation. In the present study, commercial guar gum was purified and its sulfated derivates with different DS and M w were synthesized. FT-IR and 13C NMR analysis indicated that C-6 substitution was predominant in sulfated samples compared with other positions. In the sulfation reaction, a sharp decrease in M w was observed. The d f values from 1.92 to 2.85 indicated that the –SO3H groups led to the relatively expanded conformation of sulfated polysaccharides. Antioxidant assays showed that sulfated polysaccharides had better antioxidant activities. The data obtained in in vitro models indicated that high DS and low M w showed the best antioxidant capacities. [Copyright &y& Elsevier]