Mechanism of anomerization of cyclohexyl 2-deoxy-3,4,6-tri-O-methyl-2-(N-methylacetamido)-alpha- and beta-D-hexopyranosides under reductive-cleavage conditions

Carbohydrate Research
Y M Ahn, G R Gray

Abstract

The fully methylated cyclohexyl glycosides of 2-acetamido-2-deoxy-alpha- and beta-D-hexopyranoses having the gluco, manno, and galacto configurations were each subjected to reductive-cleavage conditions using one of three promoters, namely trimethylsilyl trifluoromethanesulfonate, a mixture of trimethylsilyl methanesulfonate and boron trifluoride etherate, or boron trifluoride etherate alone. As expected, the fully methylated 1,2-trans-linked acetamido sugar derivatives were rapidly converted to their respective oxazolinium ions with all three promoters. Surprisingly, however, the fully methylated 1,2-cis-linked acetamido sugar derivatives were also converted to their respective oxazolinium ions, albeit at a much slower rate. In the latter case, evidence was obtained for anomerization to the 1,2-trans-linked isomers under reductive-cleavage conditions. Since the anomerization was relatively slow at room temperature in dichloromethane, a modified procedure was developed in which the reaction was carried out at 70 degrees C in 1,2-dichloroethane. Using the modified procedure, all 1,2-cis- and 1,2-trans-linked acetamido sugar derivatives were rapidly converted into their respective oxazolinium ions and subsequent quenching of the ...Continue Reading

Citations

Jan 12, 2001·Oral Microbiology and Immunology·S I FarquharsonG R Gray

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