Synthesis Of 2-Acetamido-2-Deoxy-5-Thio-α-D-Galactopyranose

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Abstract
When treated with a large excess of 2,2-dimethoxypropane in the presence of p-toluenesulfonic acid in 1,4-dioxane, 2-acetamido-2-deoxy-D-galactose gave methyl 2-acetamido-2-deoxy-5,6-0-iso-propylidene-α- and -β-D-galactofuranosides, which were converted, via benzoylation and O-deisopropylidenation, into methyl 2-acetami-do-3-O-benzoyl-2-deoxy-α- and -β-D-galactofuranosides (3,4). Selective benzoylation of 4, followed by mesylation, gave methyl 2-acetamido-3,6-di-O-benzoyl-2-deoxy-5-O-mesyl-β-D-galactofurano-side (6), which was treated with sodium methoxide to give the 5,6-anhydro derivative (7). Treatment of 7 with thiourea, followed by cleavage of the epithio ring in 8, afforded the 5-thio compound 9. Alkaline treatment of 10, derived from 9 by hydrolysis, yielded the title compound.