Synthesis, Biological Evaluation, and Quantitative Receptor Docking Simulations of 2-Acylaminoethyl-1,4-benzodiazepines as novel Tifluadom-Like Ligands with High Affinity and Selectivity for k-Opioid Receptors

The synthesis and biological evaluation of a series of 2-substitued 5-phenyl-l,4-benzodiazepines, structurally related to tifluadom (5), the only benzodiazepine that acts simultaneously as a κ-opioid agonist and a cholecystokinin-A (CCK-A) antagonist, are reported. The radioligand binding models used in these studies were [125I](BH)-CCK-8 in rat pancreas (CCK-A), [3H]-(MeNLE28.31)-CCK-8 in guinea pig cerebral cortex (CCK-B), and [3H]U-69593 (κ1), [3H]DAMGO (μ), and [3H]DADLE (δ) in guinea pig brain. All the title compounds were devoid of significant affinity for both CCK-A and CCK-B receptors, while some of them bound with nanomolar affinity and high selectivity for κ-opioid receptors. In particular, the 2-thienyl derivative 7a (X = H) with a K1 = 0.50 nM represents a clear improvement with respect to tifluadom, showing a comparable potency but higher selectivity. The application of computational simulations and linear regression analysis techniques to the complexes between guinea pig κ (κ1)-receptor and the title compounds allowed the identification of the structural determinants for recognition and quantitative elucidation of the structure-affinity relationships in this class of receptors.