Mono-N-glycosidation of beta-Cyclodextrin-Synthesis of 6-(beta-Cyclodextrinyl-amino)-6-deoxy-D-galactosides and of N-(6-Deoxy-beta-cyclodextrinyl)-galacto-azepane

摘要

An 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-beta-cyclodextrin by reductive amination in the presence of NaBH_3CN in DMSO.When methyl alpha-D- and p-nitrophenyl alpha-and beta-d-gal-acto-hexodialdo-1,5-pyranosides (1,2 and 3,respectively) were used as substrates,6-(beta-cyclodextrinylamino)-6-deoxy-D-galactopyranosides were obtained in 25-50% yields.The same was true in the cases of 6~II-oxolactose 4 and of 6~II-deoxy-D-galactopyranosides were obtained in 25-50% yields.The same was true in the cases of 6~II-oxolactose 4 and of 6~II-oxo-melibiose 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 polygal-actomannan 6.The behaviour of galacto-hexodialdo-1,5-pyr-anose 7 was different,since further intramolecular cyclisation and reduction resulted in a N-(6-deoxy-beta-cyclodextrinyl)-gal-acto-azepane in good yield.Molecular modelling was also used to explain the course of this reacdtion.Calculations indicated that the formation of the cis D-form of the intermediate N-beta-CD imine of 7 was strongly preferred.