Determination of the configuration of 3,6-anhydrogalactose and cyclizable alpha-galactose 6-sulfate units in red seaweed galactans.
A combination of two reported procedures was used in order to determine the configuration of the 3,6-anhydrogalactose present in red seaweed polysaccharides. A mild hydrolysis (to cleave only 3,6-anhydrogalactosyl linkages) was followed by a reductive amination with a chiral amine. Then, the total hydrolysis proceeded, followed by a new step of reductive amination. In this way, using (S)-alpha-methylbenzylamine as the chiral amine, it was possible to separate and quantitate both enantiomers of 3,6-AnGal and its 2-O-methyl ether as their diastereomeric acetylated aminoalditols. On the other hand, using (S)-1-amino-2-propanol, even though the derivatives of both enantiomers of 3,6-AnGal are not separated, the mixture can be safely quantitated with respect to galactose. Furthermore, a one-pot technique was developed to carry out an alkaline treatment of the polysaccharides, followed by the double hydrolysis-reductive amination procedure, which is useful to determine the proportions of both enantiomers of 6-sulfated 4-linked galactose units in the native polysaccharides. The unexpected presence of small amounts of units of this type belonging to the D-series in a porphyran sample is revealed by this novel procedure.
D000586:Amination; D002849:Chromatography, Gas; D005685:Galactans / Q000032:analysis / Q000737:chemistry*; D005690:Galactose / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism*; D006868:Hydrolysis; D010627:Phenethylamines / Q000032:analysis; D012624:Seaweed / Q000737:chemistry*
D005685:Galactans; D010627:Phenethylamines; C117625:3,6-anhydrogalactose; C086947:galactose 6-sulfate; C033198:1-phenethylamine; D005690:Galactose