A preponderantly 4-sulfated, 3-linked galactan from the green alga Codium isthmocladum

The green algae of the genus Codium have recently been demonstrated to be an important source of sulfated galactans from the marine environment. Here, a sulfated galactan was isolated from the species Codium isthmocladum and its structure was studied by a combination of chemical analyses and NMR spectroscopy. Two fractions (SG 1, approximately 14 kDa, and SG 2, approximately 20 kDa) were derived from this highly polydisperse and heterogeneous polysaccharide. Both exhibited similar structures in (1)H 1D NMR spectra. The structural features of SG 2 and its desulfated derivative were analyzed by COSY, TOCSY, DEPT-HSQC, HSQC, and HMBC. This sulfated galactan is composed preponderantly of 4-sulfated, 3-linked beta-D-galactopyranosyl units. In minor amounts, it is sulfated and glycosylated at C-6. Pyruvate groups are also found, forming five-membered cyclic ketals as 3,4-O-(1'carboxy)-ethylidene-beta-D-galactose residues. A comparison of sulfated galactans from different marine taxonomic groups revealed similar backbones of 3-beta-D-Galp-1.