The galactan sulphate of the red alga polysiphonia lanosa

The structure of the galactan sulphate of P. lanosa has been established by a combination of methylation, treatment with alkali, and partial methanolysis of the alkali-treated polysaccharide to give derivatives- of agarobiose. The polysaccharide belongs to the agar class, in which 3-linked derivatives of β- D-galactose alternate with 4-linked derivatives of α- L-galactose in a repeating sequence. In addition to D-galactose itself, the 3-linked units include 6- O-methyl- D-galactose, D-galactose 6-sulphate, and a hitherto unreported units 6- O-methyl- D-galactose 4-sulphate. The 4-linked units include L-galactose 6-sulphate, 2- O-methyl- L-galactose 6-sulphate, and 3,6-anhydro- L-galactose.