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-D-galactose from methyl α-D-glucopyranoside (1) is described. A key intermediate for the synthesis, methyl 2,3-di-O-benzoyl-6-deoxy-4-thio-α-D-galactopyranoside (15) was prepared by different approaches from 1. Regioselectivity for the protection or modification of the hydroxyl groups of 1 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 (17), whose conformation was studied by molecular mechanics calculations. Acetolysis of methyl 6-deoxy-4-thio-α-D-galactopyranoside (16) afforded ring sulfur containing derivatives of 6-deoxy-4-thio-D-galactofuranose, which are described for the first time. © 1990.