Novel-Substituted Heterocyclic GABA Analogues. Enzymatic Activity against the GABA-AT Enzyme from Pseudomonas fluorescens and In Silico Molecular Modeling.

γ-Aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the central nervous system, and a deficiency of GABA is associated with serious neurological disorders. Due to its low lipophilicity, there has been an intensive search for new molecules with increased lipophilicity to cross the blood-brain barrier to raise GABA concentrations. We have designed and evaluated in vitro and in silico some new analogues of GABA, where the nitrogen atom at the γ-position is embedded in heterocyclic scaffolds and determined their inhibitory potential over the GABA-AT enzyme from Pseudomonas fluorescens. These modifications lead to compounds with inhibitory activity as it occurs with compounds 18a and 19a. The construction of Pseudomonas fluorescens and human GABA-AT models were carried out by homology modeling. Docking assays were done for these compounds over the GABA-AT enzyme models where 19a showed a strong interaction with both GABA-AT enzymes.

QSAR and Molecular Docking Studies of the Inhibitory Activity of Novel Heterocyclic GABA Analogues over GABA-AT.

We have previously reported the synthesis, in vitro and in silico activities of new GABA analogues as inhibitors of the GABA-AT enzyme from Pseudomonas fluorescens, where the nitrogen atom at the γ-position is embedded in heterocyclic scaffolds. With the goal of finding more potent inhibitors, we now report the synthesis of a new set of GABA analogues with a broader variation of heterocyclic scaffolds at the γ-position such as thiazolidines, methyl-substituted piperidines, morpholine and thiomorpholine and determined their inhibitory potential over the GABA-AT enzyme from Pseudomonas fluorescens. These structural modifications led to compound 9b which showed a 73% inhibition against this enzyme. In vivo studies with PTZ-induced seizures on male CD1 mice show that compound 9b has a neuroprotective effect at a 0.50 mmole/kg dose. A QSAR study was carried out to find the molecular descriptors associated with the structural changes in the GABA scaffold to explain their inhibitory activity against GABA-AT. Employing 3D molecular descriptors allowed us to propose the GABA analogues enantiomeric active form. To evaluate the interaction with Pseudomonas fluorescens and human GABA-AT by molecular docking, the constructions of homology models was carried out. From these calculations, 9b showed a strong interaction with both GABA-AT enzymes in agreement with experimental results and the QSAR model, which indicates that bulky ligands tend to be the better inhibitors especially those with a sulfur atom on their structure.