Hexavalent glycoclusters having tris-bipyridine ferrous complex cores as minimum combinatorial libraries for probing carbohydrate–carbohydrate interactions

Abstract 2,2′-Bipyridines having two lactoside- or maltoside-appendages were prepared and then, complexed with ferrous ion to afford the corresponding tris-bipyridine ferrous complexes presenting hexavalent lactoside/maltoside clusters. Each of these complexes provided a simple dynamic combinatorial library composed of two diastereomeric stereoisomers (Δ and Λ) whose ratios depend on their relative stabilities. These tris-bipyridine ferrous complexes showed different responses from each other towards alkaline/alkaline-earth metal salts. For example, the lactoside cluster showed unique two-step binding profiles, whereas the maltoside cluster did simple Langmuir-type ones. Our referential experiments revealed that intermolecular lactoside–lactoside interactions mediated by the alkaline/alkaline-earth metal cations play essential roles in the two-step binding profiles.