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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.
    Type of Medium: Electronic Resource
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  • 2
    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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  • 3
    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.
    Type of Medium: Electronic Resource
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