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Free keywords:
HIGHLY STEREOSELECTIVE GLYCOSYLATION; N-ACETYLNEURAMINIC ACID;
DIELS-ALDER REACTIONS; ORGANIC-SOLVENTS; CONCENTRATED-SOLUTIONS; LITHIUM
PERCHLORATE; 2-DEOXY-BETA-GLYCOSIDIC LINKAGES; STEREOCONTROLLING
AUXILIARY; CARDIOACTIVE STEROIDS; PROTECTING GROUPdeoxyglycosides; glycosylations; LiClO4/diethyl ether mixtures;
carbohydrates; oligosaccharides;
Abstract:
2-Deoxy- and 2,6-dideoxyglycosyl trichloroacetimidates, phosphites and fluorides are efficiently activated in 0.1M metal perchlorate/solvent mixtures, i.e, without the need for an additional promoter like a strong Lewis acid or a heavy metal salt. Under these neutral conditions they react with different glycosyl acceptors to give oligosaccharides, amino acid glycosides and cholesteryl glycosides in high yields and with pronounced stereoselectivity. For 3,4,6-tri-O-benzyl protected 2-deoxy glucose the highest yields were observed with the alpha-imidate, however, the anomer ratio was highest if the corresponding glycosyl fluoride was used. The stereoselectivity was not significantly influenced by the solvent and the metal ion, the yield was highest in 0.1M solutions of LiClO4 in diethyl ether. Under these gentle conditions also 2-deoxy-L-fucosyl fluoride and D-digitoxosyl fluoride react with different O-silylated glycosyl accepters to give sensitive 2,6-dideoxyglycosides with preparatively useful results.
