Syntheses of the methyl glycosides of the repeating units of chondroitin 4- and 6-sulfate
摘要:
3,4,6-Tri-O-acetyl-D-galactal was transformed into methyl 6-O-acetyl-2-azido-4-O-benzyl-2-deoxy-beta-D-galactopyranoside and its 4-O-acetyl-6-O-benzyl analogue, each of which was glycosylated with activated, O-acetylated derivatives of methyl D-glucopyranosyluronate. The resulting beta-(1----3)-linked disaccharide derivatives were each reductively N-acetylated, hydrogenolysed, O-sulfated, and saponified to afford the disodium salts of methyl 2-acetamido-2-deoxy-3-O-(beta-D-glucopyranosyluronic acid)-4-O-sulfo-beta-D-galactopyranoside and the 6-O-sulfo analogue. D-Galactal was also transformed into activated derivatives of 2-azido-3,6-di-O-benzyl-2-deoxy-D-galactopyranose and their 3,4-di-O-benzyl analogues with various substituents at O-4 and O-6. These glycosyl donors were condensed with 6-O-protected derivatives of methyl 2,3-di-O-benzyl-beta-D-glucopyranoside to give the beta-(1----4)-linked disaccharide derivatives, which were selectively deprotected, then oxidised at C-6 of the gluco unit, reductively N-acetylated, selectively deprotected, O-sulfated at C-4 or C-6 of the galacto unit, and hydrogenolysed to give the disodium salts of methyl 4-O-(2-acetamido-2-deoxy-4-O-sulfo-beta-D-galactopyranosyl)-beta-D- glucopyranosiduronic acid and the 6-O-sulfo analogue.
derivatives, respectively, as a result of a syn epoxidation directed by the allylic hydroxyl group, and consecutive ring-opening by m-ClBzOH. When glucal and allal derivatives are fully protected, initial epoxidation proceeds mainly anti to the allylicgroup to give, after ring-opening, the corresponding pyranosyl chlorobenzoates. Stereoselectivity in the reaction of fully protected galactal derivatives
tert.-Butyldimethylsilyl chloride is a useful reagent for direct 3,6-di--protection of D-glucal and D-galactal. The unprotected 4-hydroxy group is still accessible to other protective groups providing after selective 3,6--desilylation 4--protected derivatives. 2-Azido group introduction does not even require 4--protection thus affording valuable 2-azido-2-deoxy-gluco- and -galactopyranosyl donors for
either the selective TBDMS protection of secondary alcohols or the fast per-O-trimethylsilylation of saccharide polyols. In the second part of the paper the scope of the silylation approach was significantly extended with the development of unprecedented "one-pot" and "solvent-free" sequences allowing the regioselective silylation/alkylation (or the reverse sequence) of saccharide polyols in short times
A nonclassical, totally stereoselective synthesis of orthogonally protected 1,3-disaccharides is reported. Enantiomericallypure beta-keto-delta-lactones, efficiently obtained from glucal and galactal, are transformed into electron-poor heterodienes and chemo-, regio-, and stereoselectively cycloadded to glycals as electron-rich dienophiles, to directly afford 2-thiodisaccharides. The reductive desulfurization
[4+2] Cycloaddition reaction of bis (trichloroethyl) azodicarboxylate and glycals: preparation of a C1-C1 2-amino disaccharide
作者:Yves Leblanc、Brian J. Fitzsimmons
DOI:10.1016/s0040-4039(00)99150-0
日期:1989.1
Bis (trichloroethyl) azodicarboxylate is an efficient diene in the [4+2] cycloaddition reaction with glycals. It offers several advantages over the previously described dibenzyl azodicarboxylate (DBAD) which was used to prepare 2-amino glycosides.