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

✍ Scribed by Pavol Kováč

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 1023 KB
• Volume: 245
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(93)80073-n

✦ Synopsis

Methyl O-(2,4-di-O-benzoyl-3-O-bromoacetyl-cY-~-rhamnopyranosyl)-(l + 3)-2,4-di-0-benzoyl--Lrhamnopyranoside was treated with dichloromethyl methyl ether and ZnCl, to give O-(2,4-di-O-benzoyl-3-0-bromoacetyl+L-rhamnopyranosylk(1 + 3)-2,4-di-O-benzoyl--L-rhamnopyranosyl chloride. Similar treatment of methyl 0-(3,4,6-tri-O-acetyl-2-azido-2-deo~~-o-glu~p~anosyl)-(l + 3)-2,4-di-Obenzoyl-cu-L.-rhamnopyranoside (13) gave crystalline 0-(3,4,6-tri-O-acetyl-2-azido-2-deoxye-o-glucopyranosylj-(1 + 3)-2,4-di-O-benzoyla-L-rhamnopyranosyl chloride (141, which was also obtained by treatment of methyl 0-(3,4,6-tri-0-acetyl-2-azido-2-deoxoy~-o-glucopyranosyl)-(l + 3)-2,4-di-Obenzoyl-1-thio_cY-L-rhamnopyranoside (12) with chlorine. In contrast to the conversion 12 + 14, which was stereospecific, the reaction of methyl 0-(3,4,6-tri-O-acety1-2-azido-2-deoxya-D1)-(1 + 3)-(O-2,4-di-O-benzoyl-cu-L-rhamnopyranosyl)-(1 + 3)-2,4-di-O-benzoyl-1-thio-a-L-rhamnopyranoside with chlorine gave a mixture of the corresponding (Y-(16) and p-(17) glycosyl chlorides. Condensation of the mixed chlorides 16 and 17 with 1,3,4,6-tetra-0-acetyko-galactopyranose, followed by reduction-acetylation of the product, gave a fully protected derivative of the tetrasaccharide a-D-GlcpNAc-(1 + 3)-cY-L-Rhap-(l + 3)a-L-Rhap-(1 + 2)-a-D-Galp. * Part 5 of the series Synthesis of ligands related to the O-Specific antigen of Shigelln dysenteriae type 1. For Part 4, see ref 1. * Thetwopathways1+2+4--,7andl + 5 -+ 6 + 7 were tried in the hope that one would include an intermediate purifiable by crystallization, thus reducing the number of chromatographic separations required. This hope was realized by the isolation of crystalline 6.