Di- and tri-saccharide glycosyl donors for the synthesis of fragments of the O-specific antigen of Shigella dysenteriae type 1

Article abstract of DOI:10.1016/0008-6215(93)80073-N

Methyl O-(2,4-di-O-benzoyl-3-O-bromoacetyl-α-L-rhamnopyranosyl)-(1->3)-2,4-di-O-benzoyl-α-L-rhamnopyranoside was treated with dichloromethyl methyl ether and ZnCl2 to give O-(2,4-di-O-benzoyl-3-O-bromoacetyl-α-L-rhamnopyranosyl)-(1->3)-2,4-di-O-benzoyl-α-L-rhamnopyranosyl chloride.Similar treatment of methyl O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-glucopyranosyl)-(1->3)-2,4-di-O-benzoyl-α-L-rhamnopyranoside (13) gave crystalline O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-glucopyranosyl)-(1->3)-2,4-di-O-benzoyl-α-L-rhamnosyl chloride (14), which was also obtained by treatment of methyl O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-glucopyranosyl)-(1->3)-2,4-di-O-benzoyl-1-thio-α-L-rhamnopyranoside (12) with chlorine.In contrast to the conversion 12 -> 14, which was stereospecific, the reaction of methyl O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-D-glucopyranosyl)-(1->3)-(O-2,4-di-O-benzoyl-α-L-rhamnopyranosyl)-(1->3)-2,4-di-O-benzoyl-1-thio-α-L-rhamnopyranoside with chlorine gave a mixture of the corresponding α- (16) and (β)- 17 glycosyl chlorides.Condensation of the mixed chlorides 16 and 17 with 1,3,4,6-tetra-O-acetyl-α-D-galactopyranose, followed by reduction-acetylation of the product, gave a fully protected derivative of the tetrasaccharide of α-D-GlcpNAc-(1->3)-α-L-Rhap-(1->3)-α-L-Rhap-(1->2)-α-D-Galp.