Determination of the configuration of 3,6-anhydrogalactose and cyclizable alpha-galactose 6-sulfate units in red seaweed galactans |
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Authors: | Navarro Diego A Stortz Carlos A |
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Affiliation: | Departamento de Química Orgánica-CIHIDECAR, Facultad de Ciencias Exactas y Naturales, Univ. Buenos Aires, Pabellon 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina. |
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Abstract: | 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. |
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Keywords: | Carrageenans Agarans 3,6-Anhydrogalactose Seaweed galactans Enantiomers |
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