Minor polysaccharidic constituents from the red seaweed Hypnea musciformis. Appearance of a novel branched uronic acid

Abstract

Two polysaccharide fractions isolated from Hypnea musciformis after room temperature- and hot water extraction, soluble after KCl precipitation of the more abundant carrageenans, were subfractionated by ion-exchange chromatography eluting with increasing concentrations of NaCl. The lowest NaCl concentration (0.2M) eluted agarans. The dl-hybrids (or mixtures) eluted at intermediate concentrations of NaCl. The d/l-galactose ratio and the sulfate proportion increased with the NaCl concentration. Different types of substitution were present, mainly at C-3 with sulfate, Xyl and methylated Gal stubs, as well as low amounts of 3,6-AnGal. A novel constituent, identified as 3-C-carboxy-d-erythrose11According to the IUPAC rules for carbohydrates (Mc Naught, 1996; rule 18.3), the name of the acyclic form should be 3-C-hydroxymethyl-l-threuronic acid, whereas for the cyclic form, the ring closure takes precedence over the carboxyl group and thus, 3-C-carboxy-d-erythrofuranose should be imposed. (2R,3R)-apiuronic acid (ApiA) is used as an alternative trivial name throughout the text. in its β-furanosic form, was found linked to C-6 of β-Gal units. A search carried out in other species like Iridaea undulosa and Kappaphycus alvarezii also revealed the same constituent. Finally, the late-eluting fractions were mostly carrageenans, with a structure consistent with that of a κ/ι/ν-carrageenan hybrid.