Hydroxy-1,2,5-oxadiazolyl moiety as bioisoster of the carboxy function. A computational study on gamma-aminobutyric acid (GABA) related compounds

Recently, our research group has proposed the hydroxyfurazanyl (4-hydroxy-1,2,5-oxadiazole-3-yl) moiety as a new non-classical isoster of the carboxy function in the design of γ-aminobutyric acid (GABA) analogues. Some compounds showed significant activity at the GABA-A receptor, representing the only examples of pentatomic heterocycles bearing an ω-aminoalkyl flexible side chain in the position vicinal to the hydroxy group displaying agonist activity at this receptor subtype. In this work, an ab initio analysis of the structural and electronic features of furazan-3-ol is presented, in order to provide a theoretical basis to the claimed bioisosterism with the carboxy function. An ab initio conformational study with the C-PCM implicit solvent model was carried out to elucidate the reasons of the peculiar behaviour of the furazan models. Alongside, another conformational search through molecular dynamics in explicit solvent was accomplished, in order to validate the first method. The electronic features of the 4-hydroxy 1,2,5-oxadiazole-3-yl substructure seem to account for a marked stabilizing effect of the putative bioactive conformation at the GABA-A receptor subtype. The 1,2,5-thiadiazole analogue, which shares the same conformational preference of its oxygenated counterpart, was identified as a potential candidate for synthesis and pharmacological testing.