The stereoselective preparation of the β-d-GlcNAc-(1→4)-D-Glc disaccharide starting from known 4-O-[6-O-(1-methoxy-1-methylethyl)-3,4-O-isopropylidene-β-d-talopyranosyl]-2,3:5,6-di-O-isopropylidene-aldehydo-D-glucose dimethyl acetal (2), in turn easily obtained from lactose, is reported. Key steps of this new procedure, that avoids the glycosylation reaction, are (a) a first epimerization at C-4' through an unusual procedure involving a completely stereospecific hydroboration-oxidation of the enol ether group of the hex-4-enopyranoside 4, obtained from 3 by base promoted acetone elimination, (b) an amination with inversion by S(N)2 reaction on an imidazylate intermediate, and, finally, (c) N-acetylation followed by complete deprotection.

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http://dx.doi.org/10.1016/j.carres.2014.01.020DOI Listing

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