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  • 1
    Electronic Resource
    Electronic Resource
    Glycosyl Imidates, 55. Synthesis of the Pentasaccharide Moiety of an Asterosaponin (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 817-823 
    Details
    ISSN: 0170-2041
    Keywords: Glycosyl trichloroacetimidates ; Glycosylation ; D-Xylose ; D-Quinovose ; Steroids ; Saponins ; Starfish ; Asterias amurensis ; Carbohydrates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of 2-O-acetyl-protected O-galactosyl trichloroacetimidate 3 as glycosyl donor and 2,4-di-O-unprotected xylopyranoside 2 as glycosyl acceptor furnished in the presence of Et2O · BF3 as catalyst regioselectively β-(1→4)-connected disaccharide 4 which gave upon subsequent reaction with O-quinovosyl trichloroacetimidate 5 as donor β-(1→2)-connection, thus affording trisaccharide 6. Removal of the 2-O-acetyl group from the galactosyl moiety yielded acceptor 7; its glycosylation with donor 5 furnished β-connected tetrasaccharide 8. This compound was transformed via 1-O-desilylation and then treatment with trichloroacetonitrile in the presence of a base into O-tetraosyl trichloroacetimidate 10 as glycosyl donor. Reaction of 10 with 3-O-unprotected 2,4-di-O-acetyl- and 2,4-di-O-benzyl-protected quinovosides 13 and 16 furnished the desired fully O-protected pentasaccharides 17 and 18, respectively. Hydrogenolytic O-debenzylation of 18 furnished the O-unprotected target molecule 19 which was characterized as its O-acetyl product 20.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201135
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Glycosyl Phosphatidylinositol (GPI) Anchor Synthesis Based on Versatile Building Blocks - Total Synthesis of a GPI Anchor of Yeast (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1153-1165 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Sphingosines ; Ceramides ; Ceramides-1-phosphates ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -For the design of a synthesis of target molecule 1 the retrosynthetic analysis yielded building blocks 2-5, of which ceramide 2-phosphite derivative 2 and aminoethyl phosphite derivative 5 are known. The generation of α-glucosaminyl (1→6)inositol building block 3 was based on pseudodisaccharide 6 which was selectively benzoylated at 6b-O and then selectively benzylated at 3b-O to give 3. The synthesis of tetramannosyl building block 4 started from known ortho ester derivative 8 which was transformed into versatile mannosyl donors 13 and 18 and into acceptor 22. Reaction of 13 with 22 gave α-disaccharide 23, deacetylation and then mannosylation with 18 gave trisaccharide 25; ensuing deacetylation and mannosylation with 13 gave tetrasaccharide 27; deallylation, acetylation, regioselective removal of the anomeric O-acetyl group and treatment with CCl3CN/DBU afforded 4. Glycosylation of 3 with donor 4 led to pseudohexasaccharide 31 in high yield. Replacement of the O-acyl groups by O-benzyl groups and then exchange of the menthyloxycarbonyl group by an O-acetyl group gave 36 which enabled regioselective attachment of 2 and 5. To this end, the 6e-O-silyl group was removed and then the aminoethyl phosphate residue was attached with reagent 5 to give 38 in high yield. 1a-O-Deacetylation and then reaction with 2 afforded 40 as fully protected 1 which was liberated in two steps; treatment with acid removed all acid labile protective groups and finally catalytic hydrogenation afforded the desired GPI anchor 1 which could be fully structurally assigned.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of Hetaryl Glycosides and Their Glycosyl Donor Properties (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1353-1360 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Substitution ; Carbohydrates ; Anomeric O-hetarylation ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Anomeric O-hetarylation of tetra-O-benzyl- and tetra-O-acetylglucose (1a, b) can be directly performed with electron-deficient heteroaromatic/heterocyclic systems 2-14, which contain imide halide moieties. The reactions were carried out in the presence of a base and led, through an exchange of the halide by the glucopyranosyloxy moiety, to the products 2a-14a, 7b-14b. Predominantly or exclusively β-products were obtained. Systems bearing more than one imide halide moiety, such as cyanuric fluoride (15) or 5-chloro-2,4,6-trifluoropyrimidine (16), can be employed for successive anomeric O-hetarylations. Investigation of the glycosyl donor properties of O-glucosyl heteroaromatic imidates with 6-O- and 4-O-unprotected glucose derivatives 18 and 19 as acceptors and comparison of the results obtained with data for the corresponding β-trichloroacetimidates 17aβ and 17bβ, reveals that 2,3,5,6-tetrafluoropyridin-4-yl glucopyranosides 14aβ and 14bβ exhibit similar properties. For specific tasks, for instance α-glucopyranoside formation, 14aβ may even be advantageous.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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