Structural characterization of rhamnan sulfate isolated from commercially cultured Monostroma nitidum (Hitoegusa)

Abstract

A rhamnan sulfate was extracted from green seaweed, Monostroma nitidum (Hitoegusa), which is commercially cultured on the coast of the Okinawa Island, Japan. The yield of rhamnan sulfate was 3.5% (W/W), and the total carbohydrate, uronic acid, ash, sulfuric acid and moisture of the polysaccharide was 67.2%, 11.8%, 27.3%, 24.7% and 3.5%, respectively. L-rhamnose (L-Rha), D-xylose (D-Xyl), D-glucose (D-Glc), D-galactose (D-Gal) and D-glucuronic acid (D-GlcA) residues were identified by liquid chromatography (HPLC), and the molar ratio of L-Rha : D-GlcA : D-Xyl : D-Glc : D-Gal : sulfuric acid for the polysaccharide was estimated to be 7.0 : 1.0:0.5:0.1:0.5:5.0. From the results of methylation analysis and NMR ( 1H and 13C) studies of native and desulfated rhamnan, the polysaccharide was found to include (1→3)-linked α-L-rhamnopyranosyl residues on the main chain and β-D- GlcAp(1→2)-α-L-Rhap(1→2)-α-L-Rhap(1→linked tri-saccharide side chains at the C2position. The sulfate groups substituted at C4and C2position of the L-rhamnosyl residues on the main and side chain, respectively.