Synthesis of 5-epi-deoxynojirimycin from methyl α-d-glucoside

A simple method for the preparation of 5-epi-nojirymycin (5-epi-DNJ) by a reductive amination of sugar derived alkoxyamines is presented. The latter were prepared in situ from the respective alkylated sugar oximes, which were obtained from the readily available methyl α-d-glucoside in a few well defined steps. The stereoselectivity of the reductive amination/cyclisation step depended on the size of the alkyl group in the oxime moiety and was best for the derivative decorated with a bulky tert-butoxyl group (5-epi-DNJ:DNJ=82:18). The stereochemical outcome of this reaction was rather surprising since the analogous process performed for sugar alkylamines usually provides predominantly derivatives of DNJ.