Chemo-biocatalytic regioselective one-pot synthesis of different deprotected monosaccharides

A simple and straightforward chemo-enzymatic approach has been developed to synthesize a small library of different monohydroxy tetraacetylated monosaccharides useful as building blocks for the synthesis of oligosaccharides. The strategy is based on the combination of a regioselective hydrolysis catalyzed by immobilized lipases with a subsequent mild chemical acyl migration. Thus immobilized lipases were highly regioselective towards the hydrolysis in C-6 position allowing, in most cases, yields up to 95%. The hydrolysis was particularly efficient using Candida rugosa lipase (CRL) with the alpha anomers of the peracetylated monosaccharides tested. The hydrolysis of the beta anomers resulted much slower.An acyl chemical migration of C-6 products at pH 8.5–9.5 and 4 °C allowed the preparation of glycopyranosides bearing a free hydroxy group at the C-4 and C-3 position. In the optimal conditions, these products can be obtained in yields from 30 up to 80% depending on the monosaccharides used.