Sulfation of arabinogalactan with ammonium sulfamate

Arabinogalactan is a biologically active water-soluble polysaccharide contained in great amounts in larch wood. A sulfate group introduced into the arabinogalactan molecule increases its biological activity and imparts new anticoagulant and hypolipedemic properties. A new method for the catalytic sulfation of arabinogalactan with ammonium sulfamate is proposed. The catalytic activity in the reaction of arabinogalactan sulfation with ammonium sulfamate has been investigated for both the base activators (urea and thiourea) and oxidants (KMnO₄ and K₂Cr₂O₇). It has been shown that, in this process, the most effective activator is KMnO₄, which ensures the highest (11.3 wt %) sulfur content in sulfated arabinogalactan. The effect of temperature and time of the arabinogalactan sulfation with ammonium sulfamate and the nature of solvents used on the sulfur content in sulfated arabinogalactan has been examined. It has been found that the highest (11.3%) sulfur content in the product is obtained by sulfation of arabinogalactan in 1,4-dioxane at a temperature of 90 °C for 4 h with the KMnO₄ activator. The introduction of a sulfate group into the arabinogalactan molecule has been confirmed by the FTIR and NMR spectroscopy data. The FTIR spectrum of sulfated arabinogalactan, in contrast to that of the initial arabinogalactan, includes an absorption band at 1249 cm⁻¹. According to the ¹³C NMR spectroscopy data, the sulfate groups are located at carbon atoms C2 and C4 of the main galactan chain and at carbon atom C6 of the end galactose units of the main and side arabinogalactan chains. It has been established by gel permeation chromatography that, during the sulfation, the molecular mass of arabinogalactan molecules increases proportionally to the introduced sulfate groups. The absence of low molecular weight fractions is indicative of the absence of depolymerization under the conditions of sulfation and evolution of sulfated arabinogalactan.