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Issue 1, 2009
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Thio-arylglycosides with various aglyconpara-substituents: a probe for studying chemical glycosylation reactions

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Abstract

Three series of thioglycosyl donors differing only in their respective aglycon substituents within each series have been prepared as representatives of typical glycosyl donors. The relative anomeric reactivities of these donors were quantified under competitive glycosylation conditions with various reaction time, promoters, solvents and acceptors. Over three orders of magnitude reactivity difference were generated by simple transformation of the para-substituent on the aglycon with methanol as the acceptor, while chemoselectivities became lower with carbohydrate acceptors. Excellent linear correlations were attained between relative reactivity values of donors and σp values of the substituents in the Hammett plots. This indicates that the glycosylation mechanism remains the same over a wide range of reactivities and glycosylation conditions. The negative slopes of the Hammett plots suggested that electron donating substituents expedite the reactions and the magnitudes of slopes can be rationalized by neighboring group participation as well as electronic properties of the glycon protective groups. Within the same series of donors, less nucleophilic acceptors gave smaller slopes in their Hammett plots. This is consistent with the notion that acceptor nucleophilic attack onto the reactive intermediate is part of the rate limiting step of the glycosylation reaction.

Graphical abstract: Thio-arylglycosides with various aglyconpara-substituents: a probe for studying chemical glycosylation reactions

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Supplementary files

Article information


Submitted
29 Jul 2008
Accepted
09 Sep 2008
First published
20 Oct 2008

Org. Biomol. Chem., 2009,7, 117-127
Article type
Paper

Thio-arylglycosides with various aglyconpara-substituents: a probe for studying chemical glycosylation reactions

X. Li, L. Huang, X. Hu and X. Huang, Org. Biomol. Chem., 2009, 7, 117
DOI: 10.1039/B813048E

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