A NITRO SUGAR DERIVATIVE ROUTE TO 2-THIOEPISOPHOROSE AND 2-THIOSOPHOROSE AND THEIR REMARKABLE FACILE EPIMERIZATION

The addition of 1-thio-D-glucose sodium salt to per-O-acetylated 1,2-d ideoxy-1-nitro-D-arabino-hex-1-enitol, readily available from D-arabin ose, afforded the corresponding 2-S-glycosylated 1-deoxy-1-nitro-D-man nitol and -D-glucitol peracetates. These, after deacetylation, were tr ansformed by the Nef reaction to 2-thioepisophorose and 2-thiosophoros e, respectively. The 2-thiodisaccharides easily epimerize in aqueous s odium bicarbonate at ambient temperature to a 1:4 equilibrium mixture. The predominant 2-thiosophorose was obtained crystalline. A H-1 NMR s tudy of the epimerization in deuterium oxide showed that the reaction involves an H-2 proton exchange mechanism.