Synthesis and pharmacological evaluation of 6-aminonicotinic acid analogues as novel GABA(A) receptor agonists.

A series of 6-aminonicotinic acid analogues have been synthesized and pharmacologically characterized at native and selected recombinant GABAA receptors. 6-Aminonicotinic acid (3) as well as 2- and 4-alkylated analogues (9–11, 14–16) display low to mid-micromolar GABAAR binding affinities to native GABAA receptors (Ki 1.1–24 μM). The tetrahydropyridine analogue of 3 (22) shows low-nanomolar affinity (Ki 0.044 μM) and equipotency as an agonist to GABA itself as well as the standard GABAA agonist isoguvacine. Cavities surrounding the core of the GABA binding pocket were predicted by molecular interaction field calculations and docking studies in a α1β2γ2 GABAA receptor homology model, and were confirmed by affinities of substituted analogues of 3. The tight steric requirements observed for the remarkably few GABAAR agonists reported to date is challenged by our findings. New openings for agonist design are proposed which potentially could facilitate the exploration of different pharmacological profiles within the GABAAR area.