Structural analysis of the polysaccharide from Pachymenia lusoria (Cryptonemiaceae, Rhodophyta)

The highly complex polysaccharide extracted from the New Zealand red alga Pachymenia lusoria (Grev.) J. Ag. has been characterised and certain structural features defined. A reductive hydrolysis procedure was used for constituent sugar and linkage analyses, with trideuteriomethylation being employed to enable the location of natural methyl ether groups to be determined. A reductive partial-hydrolysis procedure allowed agarobiosyl constituent residues to be identified. The analytical results are consistent with the polymer having a linear backbone of 3-linked d-galactopyranosyl alternating with 4-linked d- or l-galactopyranosyl residues. The 3-linked residues are nearly all 2-sulfated, with 1 in 3 also being 6-O-methylated and 1 in 5 also bearing a 4,6-pyruvic acetal residue. About one-third of the polymer is comprised of blocks of agarobiosyl repeat units that are 2-sulfated on the β-d-galactopyranosyl and one-third 2-O-methylated on the 3,6-anhydro-l-galactosyl constituents. Of the remaining 4-linked residues, half are 2-O-methyl-d-galactopyranosyl residues and half are galactopyranosyl residues, of which approximately half are in the l configuration.