Mono‐N‐glycosidation of β‐Cyclodextrin − Synthesis of 6‐(β‐Cyclodextrinylamino)‐6‐deoxy‐D‐galactosides and of N‐(6‐Deoxy‐β‐cyclodextrinyl)galacto‐azepane

Abstract

AbstractAn easy route to 6‐oxogalactose and to 6‐oxogalactosides through an oxidation reaction mediated by galactose oxidase allowed the N‐glycosidation of 6‐amino‐6‐deoxy‐β‐cyclodextrin by reductive amination in the presence of NaBH3CN in DMSO. When methyl α‐D‐ and p‐nitrophenyl α‐ and β‐D‐galacto‐hexodialdo‐1,5‐pyranosides (1, 2 and 3, respectively) were used as substrates, 6‐(β‐cyclodextrinylamino)‐6‐deoxy‐D‐galactopyranosides were obtained in 25−50% yields. The same was true in the cases of 6II‐oxolactose 4 and of 6II‐oxomelibiose 5, for which the anomeric carbon was shown to be unreactive in complexation with DMSO. This reaction was also successfully applied in water with an oxidized polygalactomannan 6. The behaviour of galacto‐hexodialdo‐1,5‐pyranose 7 was different, since further intramolecular cyclisation and reduction resulted in a N‐(6‐deoxy‐β‐cyclodextrinyl)‐galacto‐azepane in good yield. Molecular modelling was also used to explain the course of this reaction. Calculations indicated that the formation of the cis D‐form of the intermediate N‐β‐CD imine of 7 was strongly preferred. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)