Discovery of a Negative Allosteric Modulator of GABAB Receptors

Initialized from the scaffold of CGP7930, an allosteric agonist of GABA(B) receptors, a series of non-competitive antagonists were discovered. Among these compounds, compounds 3, 6, and 14 decreased agonist GABA-induced maximal effect of IP3 production in HEK293 cells overexpressing GABA(B) receptors and Gq(j9) proteins without changing the EC50. Compounds 3, 6, and 14 not only inhibited agonist baclofen-induced ERK1/2 phosphorylation but also blocked CGP7930-induced ERK1/2 phosphorylation in HEK293 cells overexpressing GABA(B) receptors. The results suggested that compounds 3, 6, and 14 are negative allosteric modulators of GABA(B) receptors. The representative compound 14 decreased GABA-induced IP3 production with IC50 of 37.9 mu M and had no effect on other GPCR Class C members such as mGluR1, mGluR2, and mGluRS. Finally, we showed that compound 14 did not bind to the orthosteric binding sites of GABA(B) receptors, demonstrating that compound 14 negatively modulated GABA(B) receptors activity as a negative allosteric modulator.