Alkali modification of carrageenans. Part IV. Porphyrans as model compounds

The rate of alkaline cyclization of porphyran is in the same order as those of carrageenan model compounds containing non-sulfated beta-D-galactose units, showing that the cyclization of the alpha-galactosyl units does not depend on the beta-D-adjacent sugar residues when they carry no sulfate groups. It also suggests that there is no influence of the alpha-D-galactose 2-sulfate on the cyclization rate, in spite of its change from the equatorial to the axial position during the conversion of the 4C1 to 1C4 chair conformation