The effect of high pressure on the stereospecificity of the glycosylation reaction

Kochetkov, Nikolay K.; Zhulin, V. M.; Klimov, E. M.; Malysheva, N. N.; Makarova, Z. G.; Ott, A. Ya.

doi:10.1016/0008-6215(87)80133-7

Cited by 25 publications

(2 citation statements)

References 2 publications

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“…Neighboring group participation leads to ions such as C . There is definitive experimental evidence for such cations in other systems. , This intramolecular participation distinguishes this mechanism from nonparticipatory mechanisms where nucleophilic assistance to formation of the oxocarbenium ion by the alcohol is probable . In our case two conformers C and C ‘ were found by optimization (see methods for details) to be 14.1 and 6.0 kcal mol -1 more stable than B , in CH 2 Cl 2 solvent.…”

Section: Resultsmentioning

confidence: 51%

Exploring the Mechanism of Neighboring Group Assisted Glycosylation Reactions

et al. 1998

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Glycosyl donors based on the 2,6-di-O-acyl-3,4-O-isopropylidene-d-galactopyranosyl-(leaving group) structure have been shown experimentally to have a high propensity for giving acyl transfer to the alcohol nucleophile as major side products in the glycosylation reaction. The corresponding cations of these relatively rigid glycosyl donors were investigated by density functional methods. The precursor cations resulting from neighboring group assistance from the 2-O-acyl group were found to be the most stable. The nucleophile methanol most favorably approaches the LUMO of such cations on the former carbonyl carbon. The resulting stable intermediate has a long C−O bond of 2.79 Å. It is suggested that such intermediates can lead to both acyl transfer and β-glycoside after passing through at least one further transition state.

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Section: Resultsmentioning

confidence: 51%

Exploring the Mechanism of Neighboring Group Assisted Glycosylation Reactions

et al. 1998

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“…23 According to several proposals 31,32 in the literature, the glycosylation reaction proceeds by activation of the glycosyl donor by silver trifluoromethanesulfonate, leading to the irreversible formation of a glycosyl oxocarbenium ion 33 that, due to neighbouring-group participation, is in equilibrium with the corresponding carbocationic species. 23,34 Nucleophilic attack of HEMA on the latter species can then result in the formation of the desired products 1a and 1b with AcEMA and monodeacetylated compounds as side products. Intramolecular neighbouring-group participation is expected to be kinetically favoured with respect to intermolecular nucleophilic attack so that the oxocarbenium ion is unlikely to have a long lifetime.…”

Section: Glycomonomersmentioning

confidence: 99%