An improved procedure for the analysis of linkage positions in 2- acetamido-2-deoxy-D-glucopyranosyl residues by the reductive-cleavage method

Article abstract of DOI:10.1016/0008-6215(94)84280-9

The conditions of the reductive-cleavage method were modified to allow simultaneous analysis of 2-acetamido-2-deoxy-D-glucopyranosyl residues and monosaccharides of other classes. Methyl 2-deoxy-3,4,6-tri-O-methyl-2-(N- methylacetamido)-β-D-glucopyranoside was found to undergo transglycosidation under reductive-cleavage conditions when the reaction was quenched with an alcohol. Transglycosidation proceeded via an oxazolinium-ion intermediate, which then acted as a glycosyl donor to form an anomerically pure product. Time-course studies showed that in the presence of trimethylsilyl trifluoromethanesulfonate (Me₃SiOSO₂CF₃), 4 h were required for complete conversion of the substrate into this intermediate, which was then trapped with methanol-d₄. When the reaction was conducted in the presence of a mixture of trimethylsilyl methanesulfonate (Me₃SiOSO₂Me) and boron trifluoride etherate (BF₃·OEt₂) or with BF₃·OEt₂ alone, 24 h and 48 h, respectively, were required for complete conversion. The α anomer was unreactive after 24 h under all conditions, confirming earlier results. Reaction with racemic 2-butanol yielded a pair of diastereomers, in a 1:1 ratio, which were distinguishable by their GLC retention times and their ¹H NMR spectra. Reaction with (S)-2-butanol gave only one of the diastereomeric products. These experiments demonstrated the feasibility of using the reductive-cleavage method to determine the absolute configuration of 2- acetamido sugars. The condition of the reductive-cleavage method were modified to allow simultaneous analysis of 2-acetamido-2-deoxy-D-glycopyranosyl residues and monosaccharides. These experiments demonstrated the feasibility of using the reductive-cleavage method to determine the absolute configuration of 2-acetamido sugars.