Binding and transport properties of a benzo[b]thiophene-based mono-(thio)urea library

Abstract

Using the chemical versatility of the benzo[ b ]thiophene motif, an extensive library of 24 (thio)urea receptors, with different binding properties and lipophilicities was prepared and included α,α-, α,β-, β,β-, β,γ-, α,γ-, and γ,γ-benzo[ b ]thiophene positional isomers, as well as β- or γ-benzo[ b ]thiophene-based molecules decorated with aliphatic chains or aryl moieties with different fluorination degrees. 1 H NMR titrations, X-ray crystallography studies, and DFT calculations showed that the receptors with higher chloride binding affinities were the β,β- and γ,γ-bis-benzo[ b ]thiophene and fluorinated aryl β- or γ-benzo[ b ]thiophene derivatives that synergistically bind chloride with the urea and one or two C β/γ -H ancillary binding groups. Experimental efflux studies showed that, among these small drug-like molecules, only the highly fluorinated analogues displayed anion transmembrane transport activity, suggesting that this property is dependent on the receptors' lipophilicity and hydrogen bonding ability. Moreover, LUV based assays, undertaken under electroneutral and electrogenic conditions, together with NMDG-Cl assays, indicated that anion efflux occurs mainly through an uniport mechanism. Further MD simulations showed that anion transport is highly dependent on the orientation and interactions of the receptors at the water/lipid interface.