CLH304a (compound 14) is a specific and noncompetitive GABA B receptor negative allosteric modulator (NAM). CLH304a decreases GABA-induced IP3 production with an IC 50 of 37.9 μM. CLH304a has no effect on other GPCR Class C members such as mGluR1 , mGluR2 , and mGluR5. CLH304a acts on the heptahelical domain of GB2 subunits and non-competitively inhibits the effect of agonists with inverse agonist properties. CLH304a inhibits Baclofen -induced ERK1/2 phosphorylation in HEK293 cells overexpressing GABA B receptor.