Structural analysis of carrageenans from Burmese and Thai samples of Catenella nipae Zanardini

The carrageenans extracted from samples of the red seaweed Catenella nipae Zanardini from Burma and Thailand have been characterised by recently developed chemical derivatisation procedures (utilising reductive hydrolysis and reductive partial-hydrolysis techniques) combined with GLC-MS analysis and by IR and NMR spectroscopy. Both polysaccharides are linear polymers composed primarily of 4-linked 3,6-anhydro-α-d-galactopyranosyl-2-sulfate residues alternating with 3-linked β-d-galactopyranosyl residues that are either unsubstituted (α-carrageenan) or 4-sulfated (ι-carrageenan). The Burmese sample has a somewhat higher proportion of α-carrageenan residues. The Thai C. nipae carrageenan was shown to have minor proportions of β- and ϰ-carrageenan residues. 1H-1H COSY, 13C-1H COSY and TOCSY NMR spectroscopic examinations of polymer segments produced from this polysaccharide as well as ι-carrageenan itself, have permitted the 1H and 13C NMR assignments for ι-carrageenan to be independently verified and for characteristic 1H and 13C chemical shifts for α-carrageenan to be identified and assigned for the first time.