Glycosylation of α-amino acids by sugar acetate donors with InBr3. Minimally competent Lewis acids

A simplified method for the preparation of Fmoc-serine and Fmoc-threonine glycosides for use in O-linked glycopeptide synthesis is described. Lewis acids promote glycoside formation, but also promote undesired reactions of the glycoside products. Use of ‘minimally competent’ Lewis acids such as InBr3 promotes the desired activation catalytically, and with greatly reduced side products from sugar peracetates.

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