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

• Published in: Journal of organic chemistry 2017-07, Vol.82 (14), p.7114-7122
• Main Authors: Legentil, Laurent, Cabezas, Yari, Tasseau, Olivier, Tellier, Charles, Daligault, Franck, Ferrières, Vincent
• Format: Article
• Language: English
• Subjects: Bacteria - chemistry; Chemical Sciences; Disaccharides - chemical synthesis; Disaccharides - chemistry; Fungi - chemistry; Furans - chemistry; Galactosides - chemistry; Glycosylation; Molecular Structure; Organic chemistry; Quantum Theory; Stereoisomerism; Trypanosomatina - chemistry
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.7b00565

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.