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  • Glycosylations of Simple Acceptors with 2-O-Acyl l-Idose or l-Iduronic Acid Donors Reveal Only a Minor Role for Neighbouring-Group Participation

    Author(s)
    Mohamed, Shifaza
    He, Qi
    Lepage, Romain
    Krenske, Elizabeth
    Ferro, Vito
    Griffith University Author(s)
    Lepage, Romain
    Year published
    2018
    Metadata
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    Abstract
    Several l‐idose and l‐iduronic acid glycosyl donors (mostly thioglycosides but also halides and trichloroacetimidates) with acyl protecting groups at the C‐2 position were prepared and evaluated in glycosylation reactions with simple acceptors. In glycosaminoglycan oligosaccharide syntheses in the literature, the presence of C‐2 acyl protecting groups in l‐ido‐configured glycosyl donors generally results in exclusive formation of 1,2‐trans glycosidic linkages, a finding that has typically been attributed to neighbouring‐group participation. However, glycosylations of simple alcohols with l‐ido‐configured donors (particularly ...
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    Several l‐idose and l‐iduronic acid glycosyl donors (mostly thioglycosides but also halides and trichloroacetimidates) with acyl protecting groups at the C‐2 position were prepared and evaluated in glycosylation reactions with simple acceptors. In glycosaminoglycan oligosaccharide syntheses in the literature, the presence of C‐2 acyl protecting groups in l‐ido‐configured glycosyl donors generally results in exclusive formation of 1,2‐trans glycosidic linkages, a finding that has typically been attributed to neighbouring‐group participation. However, glycosylations of simple alcohols with l‐ido‐configured donors (particularly thioglycosides), reported here, generally displayed incomplete stereocontrol and gave mixtures of the 1,2‐trans and 1,2‐cis products, suggesting that neighbouring‐group participation has lesser importance in these reactions. Glycosyl donors and reaction conditions were identified that gave improved, but not exclusive, selectivity for the desired α‐l‐anomer (1,2‐trans) as the major product. Interestingly, glycosylations under the same reaction conditions with more complex monosaccharide acceptors gave exclusively the expected 1,2‐trans products. The role of neighbouring‐group participation in these glycosylations was explored with density functional theory (DFT) calculations, which revealed that the non‐stereoselective addition of the acceptor alcohol to the intermediate oxocarbenium ion is competitive with the stereospecific addition of the acceptor to the acyloxonium ion intermediate.
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    Journal Title
    European Journal of Organic Chemistry
    Volume
    2018
    Issue
    19
    DOI
    https://doi.org/10.1002/ejoc.201800318
    Subject
    Medicinal and Biomolecular Chemistry not elsewhere classified
    Medicinal and Biomolecular Chemistry
    Organic Chemistry
    Publication URI
    http://hdl.handle.net/10072/380164
    Collection
    • Journal articles

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