Thio and epidithio derivatives of methyl β-lactoside

Abstract

Treatment of methyl β-lactoside with triphenylphosphine-carbon tetrabromide in pyridine gave the 3′,6′-anhydro-6-bromo-6-deoxy derivative, from which 6-thio derivatives were prepared, and methyl 3′,4′-O-isopropylidene-β-lactoside gave the 6,6′-dibromo-6,6′-dideoxy derivative. A dibromide was prepared also from methyl 4′,6′-O-benzylidene-β-lactoside by bromination with Ph3P-CBr4, acetylation, and then treatment with N-bromosuccinimide. Various 6,6′-dithio derivatives were prepared from the 6,6′-dibromide by nucleophilic substitution reactions. Reaction of the 6,6′-dibromide with thiourea led to the 6,6′-epidithio derivative and, with potassium trithiocarbonate, the bridged 6,6′-trithiocarbonate was formed. The 6,6′-dibromo derivative underwent selective nucleophilic substitution to give a variety of 6′-bromo-6-thio derivatives. Likewise, with azide, the 6-azide was formed first, followed by the 6,6′-diazide and the product of elimination, the 6-azido-5′-ene. Raney nickel-mediated desulphuration of the various 6,6′-dithio derivatives afforded methyl 6,6′-dideoxy-β-lactoside, and desulphuration of the 6′-bromo-6-thio derivatives could be accomplished without reductive dehalogenation to give methyl 6′-bromo-6,6′-dideoxylactoside.