| Sumario: | 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 (0.2 M) 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-erythrose1 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. © 2016 Elsevier Ltd
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