Toward the automated solid-phase synthesis of oligoglucosamines: systematic evaluation of glycosyl phosphate and glycosyl trichloroacetimidate building blocks

Glucosamines are common components of many biologically important oligosaccharides. Reported is a systematic evaluation of glucosamine phosphates and trichloroacetimidates as glycosylating agents for the efficient construction of beta-(1 --> 6) glucosamine linkages. A set of differentially protected glucosamine donors incorporating a host of amine protecting groups, including 2-phthaloyl, benzyloxycarbonyl (Z), trichloroetheoxycarbonyl (Troc) and trichloroacetyl (TCA) protective groups, were prepared. Donors were initially evaluated for reactivity and protecting group compatibility in a solution-phase study with a model 6-hydroxyl galactose acceptor. Based on these results, glucosamine donor 10 was selected for the solution-phase synthesis of a beta-(1 --> 6)-glucosamine pentasaccharide. Finally, building block 10 proved well suited for use in the automated solid-phase synthesis of a repeating unit trisaccharide. An assessment of glucosamine phosphate donors as potential glycosylating agents for a variety of glucosamine linkages is also discussed.