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  • 1
    ISSN: 0170-2041
    Keywords: Glycosylation ; Koenigs-Knorr reaction ; Acyl-group migration ; Transesterification ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-O-[2,2,2-D3]Acetyl-3,4,6-tri-O-acetyl-α-D-galactopyranosyl bromide (3) was prepared and used as the glycosyl donor in studying the silver trifluoromethanesulfonate-promoted reaction with methyl 2,3,4-tri-O-benzoyl-β-D-galactopyranoside (4) and methyl 2,4,6-tri-O-benzoyl-β-D-galactopyranoside (7). In addition to the expected β-linked disaccharides, methyl 6-O-[2,2,2-D3]acetyl-2,3,4-tri-O-benzoyl-β-D-galactopyranoside (6) and methyl 3-O-[2,2,2-D3]acetyl-2,4,6-tri-O-benzoyl-β-D-galactopyranoside (9), respectively, were formed. The latter compounds were isolated from the reaction mixture and their structures were confirmed based on spectral data. Thus, it has been proven that, with fully acetylated glycosyl halides as glycosyl donors, in silver trifluoromethanesulfonate-promoted couplings, O-acetylation of the nucleophile occurs as a side reaction, the acetyl group involved originating from position 2 of the glycosyl halide.
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  • 2
    ISSN: 0170-2041
    Keywords: Anomerization ; Glycosides ; Glycosyl donors, pyruvylated ; Carbohydrates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of 4,6-O-(1-methoxycarbonylethylidene)-D-glycopyranosides 5 starting from 2,3-di-O-benzoyl-D-glycopyranosides 1 and their 4,6-bis-O-trimethylsilyl ethers 2 using methyl 2,2-bis(phenylthio)propionate (4) and methyl pyruvate (3), respectively, under Lewis acid catalysis conditions is described. In the D-gluco series anomerisation of alkyl β-D-glucopyranosides is observed as a side reaction, giving complex mixtures and low yields of the title compounds whereas alkyl-α-D-glucopyranosides and alkyl or phenyl 1-thio-β-D-glucopyranosides react without anomerisation. The reactions are accompanied by isomerisation of the initially formed diastereomer (R)-5 having an equatorial methoxycarbonyl group to the thermodynamically favoured diastereomer (S)-5 having the methoxycarbonyl group in an axial position. In the D-galacto series similar side reactions are observed accompanied by rearrangement to furanosides 9 of alkyl and phenyl β-D-galactopyranosides. The results are used for efficient syntheses of two protected disaccharides 8 and 11 representing structural fragments of the polysaccharide repeating units of Mycobacteria and Rhizobia via pyruvate acetal-containing glucosyl and galactosyl donors 7 and 10.
    Additional Material: 5 Tab.
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  • 3
    ISSN: 0170-2041
    Keywords: Glycosyl halides ; Haloacetates ; Koenigs-Knorr reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chloroacetylation of alkyl glycopyranosides of β-D-galactose, β-D-glucose and α-D-mannose as well as of free D-glucose, D-galactose, D-mannose and D-xylose, using chloroacetic anhydride as acylating reagent, gave the corresponding fully chloroacetylated pyranose derivatives in excellent yields. From D-glucose, 1,2,3,6-tetra-O-chloroacetyl-α-D-glucopyranose (9) was also obtained. Subsequent treatment of the fully chloroacetylated α-D-glycopyranoses 3, 8, 13 and 15 of galactose, glucose, mannose, and xylose, respectively, with HBr resulted in 2,3,4,6-tetra-O-chloroacetyl-α-D-galactopyranosyl bromide (4, 98%), -glucopyranosyl bromide (10, 92%), -mannopyranosyl bromide (14, 72%) and 2,3,4-tri-O-chloroacetyl-α-D-xylopyranosyl bromide (16, 68%). 10 reacted with D-pantholactone (17) and silver trifluoromethanesulfonate under acidic conditions to give the corresponding α-linked (18, 45%) and β-linked (20, 38%) glucopyranosides. Under basic conditions the corresponding ortho ester product 21 was formed (92%) which upon treatment with BF3 gave the glucosides 18 and 20. Silver silicate as the catalyst gave only traces of 18. Thus, 20 was isolated in 80% yield. Reaction of 10 with silver crotonate and silver laurate gave 1-O-crotonoyl- (22) and 1-O-lauroyl-2,3,4,6-tetra-O-chloroacetyl-β-D-glucopyranose (24), respectively. 18 and 22 were dechloroacetylated with thiourea, affording the corresponding deblocked glucose derivatives 19 and 23, respectively.
    Additional Material: 1 Tab.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 163-170 
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycosides ; Glycosylation, intramolecular ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Iodosuccinimide activation of prearranged glycosides constructed out of phenyl 2,3,4-tri-O-benzyl-1-thio-α-L- and -D-mannopyranosides which are linked by a succinyl spacer via position 6 to position 3 of the benzyl 2-O-benzoyl-6-O-benzyl-α-L- and -D-glucopyranosides (6,3-prearranged L-Man/L-Glc, D-Man/D-Glc, L-Man/D-Glc, and D-Man/L-Glc) affords α/β-mixtures of the corresponding 3,6′-succinyl bridged disaccharides Man-(1→4)-Glc in 70-78% yield. The diastereoselectivity of the intramolecular glycosylation is independent of the topographic properties of the prearranged glycosides (the α-anomers predominate for L-Man/L-Glc and D-Man/D-Glc) but depends on the geometric properties (the β-anomers predominate for L-Man/D-Glc and D-Man/L-Glc). Thus, a double asymmetric induction is operative during intramolecular glycosylation of prearranged glycosides. Furthermore, the diastereoselectivity strongly depends on the topological properties and on the donor moiety of the prearranged glycosides, since 2,3-prearranged L-Man/D-Glc affords solely the disaccharide α-L-Man-(1→4)-D-Glc whereas the corresponding L-Rha/D-Glc was previously shown to give predominantly the disaccharide β-L-Rha-(1→4)-D-Glc.
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