Synthesis of di- O-glycosyl derivatives of methyl α- l-rhamnopyranoside

Abstract

The syntheses are described of 2,3-di- O-glycosyl derivatives ( 1– 12) of methyl α- l-rhamnopyranoside where the glycosyl moieties are variously α- l-fucopyranose, β- l-fucopyranose, β- d-glucopyranose, α- d-mannopyranose. The syntheses involve stereoselective glycosylation of methyl 4- O-benzoyl-3- O-(2,3,4-tri- O-benzoyl-α- l-rhamnopyranosyl)-α- l-rhamnopyranoside ( 21), methyl 4- O-benzoyl-3- O-(2,3,4,6-tetra- O-benzoyl-α- d-mannopyranosyl)-α- l-rhamnopyranoside ( 25), methyl 4- O-benzoyl- O-(2,3,4,6-tetra- O-benzoyl-β- d-glucopyranoside ( 29), methyl 4- O-benzoyl-3- O-(2,3,4-tri- O-benzoyl-β- l-fucopyranosyl)-α- l-rhamnopyranoside ( 35), and methyl 4- O-benzyl-2- O-(2,3,4-tri- O-benzoyl-β- l-fucopyranosyl)-α- l-rhamnopyranoside ( 59). In the syntheses of compounds 7– 9, the α- l-fucopyranosyl residues are introduced stereoselectively, using 2,3,4-tri- O-benzoyl-α- l-fucopyranosyl bromide ( 17) and ethyl 2,3,4-tri- O-acetyl-1-thio-β- l-fucopyranoside ( 47) as glycosyl donors.