Discovery of 17-imidazo[1,2-a]pyridinyl-3α-hydroxy-5α-androstanes (17IPAs) as novel potent positive allosteric modulators of the GABAA receptor: Synthesis, in vitro and in silico studies.

Neuroactive steroids (NASs) have attracted considerable interest as novel treatments for various central nervous system (CNS) disorders and as new intravenous general anesthetics. Herein, we report the synthesis, biological evaluation, and in silico studies of a series of promising NASs, 17-imidazo[1,2-a]pyridinyl-3α-hydroxy-5α-androstanes (17IPAs). It was shown that 17IPAs can be synthesized by the condensation of 21-bromo-3α-hydroxy-5α-androstan-20-one with substituted 2-aminopyridines under mild conditions. A representative series of 17IPAs was evaluated for their ability to alter the amplitude of currents evoked by 1 µM γ-aminobutyric acid (GABA) in isolated rat cerebellar Purkinje neurons. The compounds were found to be potent and efficacious positive allosteric modulators of GABA type A receptors (GABAARs), with EC50 values ranging from 0.34 to 3.2 µM. Interactions of the most potent compound (EC50 = 0.34 ± 0.1 µM) with the GABAAR were investigated using molecular docking calculations. Our model predicts that the imidazo[1,2-a]pyridine moiety at the C17 position of the 5α-androstan-3α-ol core does not prevent the binding of the compound to the neurosteroid site at the β(+)/α(-) intersubunit interfaces. We conclude that 17IPAs retain their ability to potentiate α1β2γ2 GABAARs despite the changes in the profile of interacting residues. Experiments with [3H]flunitrazepam displacement in rat cortical membranes excluded any possible competitive binding of 17IPAs to the benzodiazepine binding site of GABAAR. Overall, 17-imidazo[1,2-a]pyridinyl-5α-androstanes may serve as the starting point for the rational design of novel selective NASs for CNS indications and anesthesia.