The conversion of d-galactopyranosides into 2-amino-2-deoxy-d-talopyranosyl derivatives: Some new data

The known oxidation-oximation-reduction sequence leading from d-galactopyranosides to 2-amino-2-deoxy-d-talopyranosides through replacement of the 2-hydroxy by a 2-amino group with inversion has been reinvestigated. The easily obtainable methyl 3,4-O-isopropylidene-6-O-(1-methoxy-1-methylethyl)-β-d-galactopyranoside (1) was chosen as the suitably protected starting material. The single steps in the synthetic sequence were analyzed in some detail from the point of view of different reagents, stereoselectivities, side products, NMR spectra and conformations of intermediates. Owing to side reactions in the oxidative and reductive steps and to the incomplete diastereoselectivity in the latter, the overall yields in the conversion of 1 into methyl 2-acetamido-6-O-acetyl-2-deoxy-3,4-O-isopropylidene-β-d-talopyranoside did not exceed 50%.