Use of imidazo[1,5-a]quinoline scaffold as the pharmacophore in the design of bivalent ligands of central benzodiazepine receptors

• Published in: Bioorganic & medicinal chemistry 2025-01, Vol.117, p.118006, Article 118006
• Main Authors: Paolino, Marco, Saletti, Mario, Venditti, Jacopo, Castriconi, Federica, Giuliani, Germano, Maramai, Samuele, Toti, Alessandra, Ghelardini, Carla, Matucci, Rosanna, Villalobos, Narcy Alcazar, Anzini, Maurizio, Cappelli, Andrea
• Format: Article
• Language: English
• Subjects: Animals; Cerebral Cortex - drug effects; Cerebral Cortex - metabolism; Drug Design; Humans; Imidazoles - chemical synthesis; Imidazoles - chemistry; Imidazoles - pharmacology; Ligands; Male; Mice; Molecular Structure; Pharmacophore; Quinolines - chemical synthesis; Quinolines - chemistry; Quinolines - pharmacology; Receptors, GABA-A - chemistry; Receptors, GABA-A - metabolism; Structure-Activity Relationship
• ISSN: 0968-0896; 1464-3391
• DOI: 10.1016/j.bmc.2024.118006

[Display omitted] •Monovalent and Bivalent CBR ligands bearing different spacers were synthesized by exploiting the imidazo[1,5-a]quinoline scaffold.•Binding affinity was tested in: (1) hum. recomb. α1β3γ2 and α2β3γ2 GABAARs in mouse L(tk-) cells; (2) cerebral cortex from male CD-1 albino mice.•In binding condition 1, compounds showed Ki values from the sub-micromolar up to the nanomolar range without selectivity for a specific isoforms.•In binding condition 2, most of the compounds showed biphasic curves, suggesting the presence of two well-distinct populations of binding sites.•Selected monovalent (i. e. 7a) and bivalent (i. e. 6a,c) CBR ligands were tested in vivo. The imidazo[1,5-a]quinoline scaffold of central benzodiazepine receptor (CBR) ligands was used as the pharmacophore in the design of bivalent ligands bearing spacers showing variable length and different physicochemical features. The newly designed compounds were synthesized along with the corresponding reference monovalent compounds bearing the corresponding spacers terminated with a tert-butoxycarbonyl group. The novel compounds were tested in binding assays with different CBR preparations such as the cerebral cortex from male CD-1 albino mice or the human recombinant α1β3γ2 and α2β3γ2 γ-aminobutyric acid type A receptors (GABAARs) stably expressed in mouse L(tk-) cells. The tested compounds showed IC50 values from the sub-micromolar up to the nanomolar range with very similar inhibition constants values for the two isoforms of GABAARs. The similarity in the affinity between the bivalent ligands and the corresponding monovalent ones appeared to rule out any bivalent interactions of these ligands with the two isoforms of GABAARs. Similarly, both series were able to inhibit the binding of radiolabeled flumazenil to GABAARs in cortical membranes of albino CD-1 mice, but most of the tested compounds showed biphasic inhibition curves, suggesting the existence of two well-distinct populations of binding sites. Finally, some CBR ligands selected from the bivalent ligands (i.e. 6a,c) and from the reference monovalent ligands (i.e. 7a) were then tested in vivo for their potential pharmacological effects, evaluating four classical benzodiazepine actions such as anticonvulsant, anxiolytic, locomotor, and anti-amnesic activities. All the tested compounds showed anticonvulsant and anxiolytic properties with neither muscle relaxant effect nor learning and memory impairments.