New acyclic receptors containing pyridazine units. The influence of π-stacking on the selective transport of lipophilic phenethylamines

The synthesis of four new series of acyclic heteroaromatic receptors is described. They are built by two flexible polyether chains functionalised at their end with pyridazinone or methylpyridazine rings and connected by pyridine or benzene units. Their ability as carriers of lipophilic and hydrophilic phenethylamines and metallic cations has been evaluated. Transport rates show that, in general, these compounds are much more efficient carriers of lipophilic amines than of dopamine and Na+, K+ and Ca2+ ions. Their transport selectivities towards phenethylamine and homoveratrylamine are discussed on the basis of their structural features. Molecular modelling studies suggest that interaction of the aromatic moiety of the guest with the pyridazinone rings via double π-stacking, or with the pyridine ring by single π-stacking, should be responsible of their enhanced efficacy and selectivity in the transport of lipophilic phenethylamines.