Carrageenans. Part IX. Methylation analysis of galactan sulphates from Furcellaria fastigiata, Gigartina canaliculate, Gigartina chamissoi, Gigartina atropurpurea, Ahnfeltia durvillaei, Gymnogongrus furcellatus, Eucheuma isiforme, Eucheuma uncinatum, Aghardhiella tenera, Pachymenia hymantophora, and Gloiopeltis cervicornis. Structure of ξ-carrageenan
In continuation of the search for polysaccharide structures with which to develop conformational analysis, the sixteen polysaccharides for which a preliminary characterization was described in the preceding paper have been investigated by the methylation method. The earlier conclusions are confirmed and extended, with few qualifications. Amongst the structural variations in the χ and ιcarrageenans are undersulphation on C(4) of the 3-linked residue and on C(6) of the 4-linked residue. A new polysaccharide type is discovered in certain Gigartina species and the (as yet hypothetical) idealized form of it is named ξ-carrageenan. It is the polymer of D-galactose 2-sulphate in which the glycosidic linkages are 1,4 and 1,3, probably arranged alternately with β- and α-configurations respectvely
Two polysaccharides emerge with exceptional promise for conformational analysis, namely an agarose sulphate from Gloiopeltis furcata and a possible ξ-carrageenan from Gigartina atropurpurea.