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Quantitative determination of 3,6-anhydrogalactose derivatives and specific fragmentation of the red algal galactans under reductive hydrolysis conditions
A. I. Usov, M. Ya. Elashvili
N. D. Zelinsky Institute of Organic Chemistry, Academy of Sciences of the USSR, Moscow
Abstract: The complete acid hydrolysis of the red algal galactans in the presence of 4-methyl-morpholine – borane is shown to proceed with quantitative reduction of 3,6-anhydrogalactose derivatives to the corresponding 3,6-anhydrogalactitols, whereas all the other monosaccharides are liberated essentially in the non-reduced form. The reaction allows one to determine separately 3,6-anhydrogalactose and its 2-O-methyl derivative together with other monosaccharides in one sample of hydrolyzate by g.l.c. The method gives the possibility to analyse the 3,6-anhydrogalactose content in algal biomass before the isolation of polysaccharides. Partial acid hydrolysis in the presence of the same reducing agent gives rise to a series of oligosaccharides having a 3,6-anhydrogalactitol residue at the "reducing" end; sulfate groups are substantially retained. These oligosaccharides are stable and convenient for chromatographic separation; their structures may be elucidated by 13C NMR spectroscopy. Partial reductive hydrolysis of polysaccharides or al-g al biomass can be used as micro-scale method for assignment of agar or carrageenan structures to unknown galactans, since the resulting agarobiitol or carrabiitol are unambiguously identified as acetates by g.l.c.
Russian Journal of Bioorganic Chemistry 1991, 17 (6):839-848