Synthesis and evaluation of avermectin–imidazo[1,2-a]pyridine hybrids as potent GABAA receptor modulators

Abstract

The γ-aminobutyric acid type A (GABAA) receptors are pentameric transmembrane protein complexes. They have attracted extensive attention from the scientific community due to their significant pharmacological potential. Here we report the first synthesis of avermectin–imidazo[1,2-a]pyridine hybrids promising as GABAA receptor positive allosteric modulators (PAMs). An efficient multi-step protocol was elaborated for the installation of the 6-methyl-2-(p-tolyl)imidazo[1,2-a]pyridine pendant to the Avermectin B1a and Ivermectin skeletons through a linker. A variety of linkers were used in order to study the effect of disturbances in the hybrid structure on the GABAA receptor affinity. In vitro experiments showed that the lead compounds exhibited high potency (IC50 = 207 and 359 nM) for binding at the benzodiazepine site of GABAA receptors. In silico studies suggest that the hybrids are able to bind at the Ivermectin binding site of the GABAA receptor. The functional properties of the highest-affinity hybrid (compound 15e) as GABAAR PAM were evaluated by patch-clamp electrophysiological recordings of GABA-mediated currents in rat cerebellar Purkinje neurons. The results obtained suggest that the potentiating effect of hybrid compound 15e is due to its interaction both with benzodiazepine- and Ivermectin-binding sites of GABAARs. Drug-induced behavioral responses in adult zebrafish for hybrids correlate with an alternative mode of action of avermectin and imidazo[1,2-a]pyridine pharmacophores. The investigation of avermectin–imidazo[1,2-a]pyridine hybrid molecules with activity as GABAA receptor modulators is important for the discovery of safe and effective drugs for the treatment of neurological disorders and pest control agents.