Analysis of oligosaccharides containing 2-deoxy-alpha-D-arabino-hexosyl residues by the reductive-cleavage method

A mixture of oligosaccharides containing (1-->4)-linked 2-deoxy-alpha-D-arabino-hexosyl ("2-deoxyglucosyl") and (1-->4)-linked alpha-D-glucosyl residues (1) was analyzed by reduction, permethylation (perethylation), degradation to monomers, and GLC-MS. Degradation was performed either by hydrolysis with subsequent reduction, by methanolysis, or by reductive cleavage, always followed by acetylation. Reductive cleavage turned out to be the method of choice for the acid-labile 2-deoxy sugars. The main degradation product formed during acid hydrolysis of 2-deoxy-D-arabino-hexosyl residues yielded, after reduction and acetylation, (4R,S)-6-O-acetyl-2,3,5-trideoxyhexono-1,4-lactone (7). By methanolysis, in addition to the expected methyl glycosides, methyl 2,3,5-trideoxy-6-O-methyl-4-hexulosonate (12) is formed as a by-product. For determination of the distribution of chain lengths, the permethylated oligomers were separated by reversed-phase HPLC. For peak assignment, one isolated oligomer was investigated by FABMS and 1H NMR spectroscopy. The average degree of polymerization (dp) calculated from the HPLC chromatogram is in good agreement with the reductive-cleavage results.