Chemistry, properties, and phylogenetic implications of the methylated carrageenans from red algae of the genus Areschougia (Areschougiaceae, Gigartinales, Rhodophyta)

Abstract

The three Australian-endemic species comprising the genus Areschougia have been examined to determine the structure of their nonfibrillar wall components. The polysaccharide extracted from the most widely distributed species, A. congesta (Turner) J. Agardh, was shown by compositional analyses, Fourier transform infrared (FTIR) spectroscopy, linkage analysis, and 13C-NMR spectroscopy to be a carrageenan composed predominantly of the repeating disaccharides 6′-O-methylcarrabiose 2,4′-disulfate, carrabiose 2,4′-disulfate (the repeating unit of ι-carrageenan), 4′,6′-O-(1-carboxyethylidene)carrabiose 2-sulfate, and 6′-O-methylcarrabiose 2-sulfate. The carrageenan also contained small amounts of 4..