DISACCHARIDE AND TRISACCHARIDE GLYCOSYL DONORS FOR THE SYNTHESIS OF FRAGMENTS OF THE O-SPECIFIC ANTIGEN OF SHIGELLA-DYSENTERIAE TYPE-1

Methyl O-(2,4-di-O-benzoyl-3-0-bromoacetyl-alpha-L-rhamnopyranosyl)-(l --> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranoside was treated with dichloromethyl methyl ether and ZnCl2 to give O-(2,4-di-O-ben-zoyl-3-0-bromoacetyl-alpha-L-rhamnopyranosyl)-(l --> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl chloride. Similar treatment of methyl O-(3,4,6-tri-O-acetyl-2-azido-2-deoXY-alpha-D-glucopyranosyl)-(l --> 3)-2,4-di-0-benzoyl-alpha-L-rhamnopyranoside (13) gave crystalline O-(3,4,6-tri-O-acetyl-2-azido-2-deoxy-alpha-D-gluco-pyranosyl)-(l --> 3)-2,4-di-O-benzoyl-alpha-L-rhamnopyranosyl chloride (14), which was also obtained by treatment of methyl O-(3,4,6-tri-O-acetyl-2-azido-2-deoxoy-alpha-D-glucopyranosyl)-(l --> 3)-2,4-di-0-benzoyl-1-thio-alpha-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-alpha-D-glucopyranosyl)-(l --> 3)-(O-2,4-di-O-benzoYl-alpha-L-rhamnopyranosyl)-(l --> 3)-2,4-di-O-benzoyl-1-thio-alpha-L-rhamnopyranoside with chlorine gave a mixture of the corresponding alpha- (16) and beta- (17) glycosyl chlorides. Condensation of the mixed chlorides 16 and 17 with 1,3,4,6-tetra-0-acetyl-alpha-D-galactopyranose, followed by reduction-acetylation of the product, gave a fully protected derivative of the tetrasaccharide alpha-D-Glc pNAc-(1 --> 3)-alpha-L-Rha p-(l --> 3)-alpha-L-Rha p-(l --> 2)-alpha-D-Gal p.