4 years ago

Regioselective Galactofuranosylation for the Synthesis of Disaccharide Patterns Found in Pathogenic Microorganisms

Regioselective Galactofuranosylation for the Synthesis of Disaccharide Patterns Found in Pathogenic Microorganisms
Olivier Tasseau, Yari Cabezas, Charles Tellier, Laurent Legentil, Vincent Ferrières, Franck Daligault
Koenigs–Knorr glycosylation of acceptors with more than one free hydroxyl group by 2,3,5,6-tetrabenzoyl galactofuranosyl bromide was performed using diphenylborinic acid 2-aminoethyl ester (DPBA) as inducer of regioselectivity. High regioselectivity for the glycosylation on the equatorial hydroxyl group of the acceptor was obtained thanks to the transient formation of a borinate adduct of the corresponding 1,2-cis diol. Nevertheless formation of orthoester byproducts hampered the efficiency of the method. Interestingly electron-withdrawing groups on O-6 or on C-1 of the acceptor displaced the reaction in favor of the desired galactofuranosyl containing disaccharide. The best yield was obtained for the furanosylation of p-nitrophenyl 6-O-acetyl mannopyranoside. Precursors of other disaccharides, found in the glycocalix of some pathogens, were synthesized according to the same protocol with yields ranging from 45 to 86%. This is a good alternative for the synthesis of biologically relevant glycoconjugates.

Publisher URL: http://dx.doi.org/10.1021/acs.joc.7b00565

DOI: 10.1021/acs.joc.7b00565

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