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  • Organic Chemistry  (14)
  • Carbohydrates  (7)
  • 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
    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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  • 14
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Oligosaccharides ; Glycosylations ; Organic synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetrasaccharide 5-aminopentyl glycoside β-D-Manp-(1→4)-β-D-Glcp-(1→4)-α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NH2(22) related to the exopolysaccharide of Arthrobacter sp. CE-17 was synthesized by coupling of the properly protected disaccharide blocks β-D-Manp-(1→4)-β-D-Glcp-1-S-Ph (11) and α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NHZ (20). Building block 11 was obtained by intramolecular β-mannosylation of a malonyl-tethered disaccharide glycoside which was prepared from phenyl 4,6-O-benzylidene-1-thio-β-D-glucopyranoside (1) and ethyl 2,3,4-tri-O-benzyl-1-thio-α-D-mannopyranoside (5) in 5 steps. Building block 20 was obtained by coupling N-Z-protected 5-aminopentyl 2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (14) obtained from the non-benzylated counterpart 12 with ethyl 2,3-di-O-benzoyl-4-O-chloroacetyl-1-thio-α-L-rhamnopyranoside (18) obtained in 3 steps from ethyl 2,3-O-isopropylidene-1-thio-α-L-rhamnopyranoside (15).
    Additional Material: 1 Ill.
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  • 15
    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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  • 16
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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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