Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with an alkyne spacer as GABA uptake inhibitors

Screening for New Inhibitors of Glycine Transporter 1 and 2 by Means of MS Binding Assays

A straightforward screening of a compound library comprising 2439 substances for the identification of new inhibitors for the neurotransmitter transporters GlyT1 and GlyT2 is described. Screening and full-scale competition experiments were performed using recently developed GlyT1 and GlyT2 MS Binding Assays. That way for both targets, GlyT1 and GlyT2, ligands were identified, which exhibited affinities (pKi values) in the low micromolar to sub-micromolar range. The majority of these binders exhibit new chemical scaffolds in the class of GlyT1 and GlyT2 inhibitors, which could be of interest for the development of new ligands with improved affinities for the target proteins. Additionally, compounds with excellent fluorescent properties were found for GlyT2, which renders them promising compounds for future fluorescence-based techniques. All in all, this study demonstrates that MS Binding Assays represent a powerful technology platform also well suited for the screening of compound libraries in a highly reliable and effective manner.

Synthesis and biological evaluation of novel N-substituted nipecotic acid derivatives with tricyclic cage structures in the lipophilic domain as GABA uptake inhibitors

A new class of GABA reuptake inhibitors with sterically demanding, highly rigid tricyclic cage structures as the lipophilic domain was synthesized and investigated in regard to their biological activity at the murine GABA transporters (mGAT1–mGAT4). The construction of these compounds, consisting of nipecotic acid, a symmetric tricyclic amine, and a plain hydrocarbon linker connecting the two subunits via their amino nitrogens, was accomplished via reductive amination of a nipecotic acid derivative with an N-alkyl substituent displaying a terminal aldehyde function with tricyclic secondary amines. The target compounds varied with regard to spacer length, the bridge size of one of the bridges, and the substituents of the tricyclic skeleton to study the impact of these changes on their potency. Among the tested compounds nipecotic acid ethyl ester derivates with phenyl residues attached to the cage subunit showed reasonable inhibitory potency and subtype selectivity in favor of mGAT3 and mGAT4, respectively.

L-menthol exhibits antidepressive-like effects mediated by the modification of 5-HTergic, GABAergic and DAergic systems

Major depression disorder, also known as depression, with a significant and persistent low mood as the main clinical features, is the main type of mood disorders. L-menthol (LM), the main active ingredient of mint, has been considered as safe and healthy natural ingredient by the Food and Drug Administration in the USA. In this study, LM (40 mg/kg, i.g.) produced antidepressant-like effect in the forced swimming test (FST) in mice. The sub-effective dose (5 mg/kg, i.g.) of LM combined with the sub-effective dose of fluoxetine (5 mg/kg, i.p.) or reboxetine (2.5 mg/kg, i.p.) could significantly shorten the immobility time in the FST. Pretreatment with ondansetron (a highly selective 5-HT₃ receptor antagonist, 8 mg/kg, i.p.), bicuculline [a competitive γ-aminobutyric acid (GABA) antagonist, 4 mg/kg, i.p.] and haloperidol (a non-selective D₂ receptor antagonist, 0.2 mg/kg, i.p.) significantly reversed the antidepressant-like effect of LM (40 mg/kg, i.g.). In contrast, prazosin (a α1-adrenoceptor antagonist, 1 mg/kg, i.p.) and N-methyl-d-aspartic acid (an agonist at the glutamate site, 75 mg/kg, i.p.) did not eliminate the antidepressant-like effect of LM. All of these above indicated that LM is able to induce an antidepressant-like effect mediated by the modification of 5-HTergic, GABAergic and DAergic systems in the FST. LM might be used as combination therapy in depressed patients and is a potential antidepressant.