Structural features and in vitro antiviral activities of sulfated polysaccharides from Sphacelaria indica

► Two families of polysaccharides were isolated for the first time from Sphacelaria. ► The xylogalactofucan has unusually low sulfate content. ► Sulfated alginate exerts strong antiviral effect towards HSV. ► Charge density appeared to be an important determinant of anti-HSV activity. ► The main mode of action was directed to HSV entry.