Action of acid on 6-thio-hexose derivatives. Synthesis of 1,6-epithio-hexofuranoses

Reaction of 5,6-anhydro-1,2-O-isopropylidene-3-O-methanesulfonyl-3-L-idofuranose+ ++ with thioacetic acid in pyridine gave 6-S-acetyl-1,2-O-isopropylidene-3-O-methanesulfonyl-6-thio-3-L-idofur anose, which was deacetylated and the resultant thiol was converted into 1,2-O:5,6-O,S-diisopropylidene-3-O-methanesulfonyl-3-L-idofuran ose. Alkaline cleavage of the mesyl group gave 1,2-O: 5,6-O,S-diisopropylidene-3-L-idofuranose, which on treatment with hot dilute hydrochloric acid gave, after acetylation, 2,3,5-tri-O-acetyl-1,6-dideoxy-1,6-epithio-alpha-L-idofuranose+ ++ and not the expected idopyranose isomer. 1,2:3,5-Di-O-isopropylidene-6-O-toluene-p-sulfonyl-alpha-D-glucofuranose was converted into 6-S-acetyl-1,2:3,5-di-O-isopropylidene-6-thio-alpha-D-glucofuranose; conversion into the 6-thiol and isomerisation in acidified acetone gave 1,2-O:5,6-O,S-diisopropylidene-6-thio-alpha-D-glucofuranose. Acid treatment of this diacetal, or the isomeric 1,2:3,5-di-O-isopropylidene-6-thio-alpha-D-glucofuranose, followed by acetylation gave 2,3,5-tri-O-acetyl-1,6-dideoxy-1,6-epithio-beta-D-glucofuranose. Similar treatment of 1,2:3,4-di-O-isopropylidene-6-thio-alpha-D-galactopyranose gave 2,3,5-tri-O-acetyl-1,6-dideoxy-1,6-epithio-alpha-D-galactofuranose .