Synthesis of the C'D' disaccharide of aureolic acid

Arylbis(arylthio)sulfonium salts have been used to activate glycals towards nucleophilic addition to form principally 2-deoxy-beta-glycosides. This method was applied to the synthesis of the 2-(methylphenylthio)-2'-phenylthio derivative (22) of methyl O-(4-O-benzyl-2,6-dideoxy-beta-D-arabino- hexopyranosyl)-(1-->3)-3,4-di-O-benzyl-2,6-dideoxy-2,6-beta-D-arabino- hexopyranoside, the C'D' ring analog of an aureolic acid disaccharide. The condensation of 1,5-anhydro-2,6-dideoxy-D-arabino-hex-1-enitol with methanol in the presence of the phenylbis(phenylthio)sulfonium salt resulted in formation of the first beta-glycoside linkage. The methyl 6-deoxyglucoside obtained was deprotected at HO-3 to give the 2-thiophenyl-substituted 2,6-dideoxy-beta-glucoside. This was coupled with 1,5-anhydro-3,4-di-O-benzyl-2-deoxy-D-arabino-hex-1-enitol in the presence of 4-methylphenyl[bis(4-methylphenyl)thio]sulfonium salt to give the (1-->3)-linked disaccharide 22. Finally, desulfurization of 22 using WII Raney nickel generated the required 2,2'-dideoxydisaccharide.