Synthesis of furanoid and pyranoid derivatives of 6-deoxy-4-thio-D-galactose

The synthesis of pyranoid and furanoid derivatives of 6-deoxy-4-thio--galactose from methyl α--glucopyranoside () is described. A key intermediate for the synthesis, methyl 2,3-di--benzoyl-6-deoxy-4-thio-α--galactopyranoside () was prepared by different approaches from . Regioselectivity for the protection or modification of the hydroxyl groups of or its derivatives was achieved by employing various reagents. The thiol group at C-4 was introduced by nucleophilic substitution of a tosylate by thiocyanate followed by reduction or alkaline methanolysis of the thiocyano group. A by-product of the latter reaction was characterized as a monothiolcarbonate derivative (), whose conformation was studied by molecular mechanics calculations. Acetolysis of methyl 6-deoxy-4-thio-α--galactopyranoside () afforded ring sulfur containing derivatives of 6-deoxy-4-thio--galactofuranose, which are described for the first time. --------------------------------------------------------------------------------