Discovery of [1,2,4]-triazolo [1,5-a]pyrimidine-7(4H)-one derivatives as positive modulators of GABAA1 receptor with potent anticonvulsant activity and low toxicity

In searching for more effective and safer antiepileptic drugs, a series of 2,5-disubstituted [1,2,4]-triazolo[1,5-a]pyrimidine-7(4H)-one derivatives were designed and synthesized. Spontaneous Ca²⁺ oscillations (SCOs) of cortical neurons were used for in vitro phenotypic screening. Maximal electroshock test (MES) and pentylenetetrazole (PTZ) test were used to access their anticonvulsant activity, and rotarod test was used to estimate their neurotoxicity. The active compounds in in vitro model are specifically effective in pentylenetetrazole (PTZ)-induced epilepsy model but not maximal electroshock (MES) model, more importantly with lower neurotoxicity as compared to commonly used drugs. Among them, compound 5c and 5e showed significant anticonvulsant activities in PTZ-induced epilepsy model with ED₅₀ values at 31.81 mg/kg and 40.95 mg/kg, respectively. These compounds have improved neurotoxicity with protective index (PI = TD₅₀/ED₅₀) values at 17.22 and 9.09, respectively. Finally we demonstrated that compound 5c and 5e mainly acted on GABA_A receptor as positive modulators but not sodium channels. Thus the present study has provided potential candidates for further investigation in epilepsy.