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  • Organic Chemistry  (14)
  • Carbohydrates  (7)
  • Glycosylation, intramolecular  (3)
  • Koenigs-Knorr reaction  (2)
  • 11
    ISSN: 0947-3440
    Keywords: Carbohydrates ; Disaccharides ; Glycosylation, intramolecular ; β-L-Rhamnoside ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Disaccharides containing a β-L-rhamnosyl residue were prepared by a novel intramolecular glycosylation strategy. Thus, suitably benzyl-protected L-rhamnosyl donors (ethyl and phenyl 1-thiorhamnoside 7, 18) were prearranged in positions 2 and 3 with benzyl 2-O-benzoyl-4,6-O-benzylidene-α-D-glucopyranoside 8 in position 3 by a malonyl, succinyl and phthaloyl bridge, respectively, to give the corresponding connected saccharides 9, 12, 16 and 20. After regioselective opening of the benzylidene ring of the glucoside residue to give compounds 10, 13, 17 and 21, the latter afforded the 3,2′- and 3,3′-bridged disaccharides 22-25 upon intramolecular glycosylation with a thiophilic reagent. The anomeric selectivity of this intramolecular glycosylation is strongly influenced by the nature of the alkanoyl and aroyl bridge, its position at the rhamnosyl residue and the solvent used for the coupling. Best results were obtained in acetonitrile with the succinyl „spacer“ attached to position 2 of the phenyl 1-thiorhamnoside and position 3 of the glucoside that afforded the corresponding β-(1→4)-linked disaccharide 22β in 76% yield.
    Additional Material: 1 Tab.
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  • 12
    ISSN: 0947-3440
    Keywords: Carbohydrates ; Tetrasaccharide, bacterial ; Glycosylation, intramolecular ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The blockwise synthesis of the pyruvated tetrasaccharide 4,6-(S)-pyruvic-acetal-β-d-GlcNAcp-(1→3)-α-d-Galp-(1→4)-β-l-Rhap-(1→4)-β-d-Glcp-O(CH2)5NH2 (32), related to the repeating unit of the capsular polysaccharide of Streptoccus pneumoniae type 27, by coupling of the suitably protected disaccharide blocks 4,6(S)-pyruvic-acetal-β-d-GlcNAcp-(1→3)-α-d-Galp-trichloroacetimidate (13) and β-l-Rhap-(1→4)-β-d-Glcp-O(CH2)5NHZ (29β) is described. The latter disaccharide acceptor was prepared via prearranged glycosides by intramolecular glycosylation of a protected 5-aminopentyl β-d-glucopyranoside linked by a succinyl bridge at C-3 to C-2 of ethyl 1-thio-α-l-rhamnopyranoside. The dependence of the anomeric selectivity of the coupling on the nature of the protecting group at C-4 of the rhamnosyl moiety is studied.
    Additional Material: 1 Ill.
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  • 13
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 338 (1996), S. 238-242 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pyruvated di- and trisaccharide fragments representing the immunodominant side chains of Klebsiella K26 capsular polysaccharides are prepared. Phenyl 4′,6′-O-benzylidene-1-thio-β-D-lactoside (1) is converted in 4 steps into the corresponding pyruvated 1-thio-lactoside (2) and transformed into the imidate (4). Coupling of the latter with Z-protected 5-aminopentanol gives the pyruvated disaccharide fragment (6) upon deblocking. Similarly, imidate (4) is coupled to allyl 2,3-di-O-benzoyl-3-O-(1-fluoro-1,1,3,3-tetraisopropyl-1,3-disiloxane-3-yl)-α-D-glucopyranoside (8) to give the corresponding trisaccharide fragment upon deblocking.
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  • 14
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 340 (1998), S. 204-213 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of 1-O-trimethylsilyl-glycoses, 1-O-acylglycoses and glycosyl fluorides, respectively, with silylated alcohols (glycodesilylations) are summarized. Synthetic strategies toward oligosaccharides using glycodesilylations are discussed as well and some typical experimental procedures are given.
    Additional Material: 3 Tab.
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  • 15
    ISSN: 0947-3440
    Keywords: Glycosides, pyruvated ; Sponge, marine ; Microciona prolifera ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of phenyl 2,3,6,2′,3′-penta-O-benzoyl-1-thio-β-D-lactoside (7) with BF3 in methyl pyruvate afforded the corresponding phenyl 4′,6′-O-[(R)-1-(methoxycarbonyl)ethylidene]-1-thio-β-D-lactoside (9) in 91% yield. The latter was converted via bromide 10 into the corresponding lactal 11 the azidonitration of which afforded an unseparable mixture of the „gluco“- and „manno“-configurated azido nitrates 12 (97%). As an alternative, benzyl O-(β-D-galactopyrnosyl)-(1→4)-2-azido-2-deoxy-α-D-glucopyranoside (15) was prepared in two steps and 91% yield from the corresponding fully acetylated 2-azido-2-deoxylactosyl bromide 13 and was further modified in four steps to give the benzoylated benzyl 4′,6′-O-benzylidene-2-deoxy-2-[(2,2,2-trichloroethoxycarbonyl)amino]-α-D-lactoside 18 in 78% overall yield. The benzylidene acetal of the latter was cleaved to give the diol 19 the pyruvation of which as for compound 9 afforded the corresponding pyruvated lactosamine derivative 20 (81%). Hydrogenolysis of 20 followed by treatment with trichloroacetonitrile gave the corresponding pyruvated disaccharide trichloroacetimidate 22 (77%). Coupling of the latter with Z-protected 5-amino-1-pentanol followed by deblocking of the intermediates furnished 5-aminopentyl 2-acetamido-4′,6′-O-[(R)-1-carboxyethylidene]-2-deoxy-β-D-lactoside (2). Similarly, condensation of 22 with 5-[(benzyloxycarbonyl)amino]-pentyl 2,4-di-O-benzyl-β-L-fucopyranoside (25) followed by deblocking of the intermediate trisaccharide afforded 5-aminopentyl O-{4,6-O-[(R)-1-carboxyethylidene]-β-D-galactopyranosyl}-(1→4)-2-acetamido-2-deoxy-β-D-glucopyranoside-(1→3)-β-L-fucopyranoside (3). Saccharides 2 and 3, represent fragments of the Microciona prolifera aggregation factor.
    Additional Material: 2 Tab.
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  • 16
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1990 (1990), S. 613-615 
    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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