Stereocontrolled synthesis of sulfur-linked analogues of the branched tetrasaccharide repeating-unit of the immunostimulant polysaccharide schizophyllan and of its β-(1 → 3)-branched, β-(1 → 6)-linked isomer

Abstract

The branched, sulfur-linked tetrasaccharide S-(β- d- glucopyranosyl)-(1 → 3)-S-[(6-S-β- d- glucopyranosyl)-3,6- dithio-β- d- glucopyranosyl]-(1 → 3)-S-3- thio- d- glucopyranose ( 9) has been conveniently prepared by S N2 displacement of the triflate group in 1,2:5,6- di-O- isopropylidene-3-O- trifluoromethylsulfonyl-α- d- allofuranose with the sodium salt of 2,4- di-O- acetyl-3,6- di-S-(2,3,4,6- tetra-O- acetyl-β- d- glucopyranosyl)-1,3,6- trithio-β- d- glucopyranose ( 5). Conversely, reaction of the sodium salt of 5 with 1,2,3,4- tetra-O- acetyl-6- deoxy-6- iodo-β- d- glucopyranose afforded the positional isomer S-(β- d- glucopyranosyl)-(1 → 6)-S-[(3-S-β- d- glucopyranosyl)-3,6- dithio-β- d- glucopyranosyl]-(1 → 6)-S-6- thin- d- glucopyranose ( 12).