Synthesis of methyl O-(3-deoxy-3-fluoro-β--galactopyranosyl)-(1→6)-β--galactopyranoside and methyl O-(3-deoxy-3-fluoro-β--galactopyranosyl)-(1→6)-O-β--galactopyranosyl-(1→6)-β--galactopyranoside |
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Authors: | Pavol Kov , Herman J. C. Yeh,Cornelis P. J. Glaudemans |
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Affiliation: | Pavol Ková, Herman J. C. Yeh,Cornelis P. J. Glaudemans |
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Abstract: | Condensation of 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-α--galactopyranosyl bromide (3) with methyl 2,3,4-tri-O-acetyl-β--galactopyranoside (4) gave a fully acetylated (1→6)-β--galactobiose fluorinated at the 3′-position which was deacetylated to give the title disaccharide. The corresponding trisaccharide was obtained by reaction of 4 with 2,3,4-tri-O-acetyl-6-O-chloroacetyl-α--galactopyranosyl bromide (5), dechloroacetylation of the formed methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β--galactopyranosyl)-(1→6)- 2,3,4-tri-O-acetyl-β--galactopyranoside to give methyl O-(2,3,4-tri-O-acetyl-β--galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β--galactopyranoside (14), condensation with 3, and deacetylation. Dechloroacetylation of methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β--galactopyranosyl)-(1→6)-O-(2,3,4-tri-O-acetyl- β--galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β--galactopyranoside, obtained by condensation of disaccharide 14 with bromide 5, was accompanied by extensive acetyl migration giving a mixture of products. These were deacetylated to give, crystalline for the first time, the methyl β-glycoside of (1→6)-β--galactotriose in high yield. The structures of the target compounds were confirmed by 500-MHz, 2D, 1H- and conventional 13C- and 19F-n.m.r. spectroscopy. |
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