Introduction : The use of the pharmacophoric approach is a promising direction for modifying the chemical structure of 2-propylpentanoic (valproic) acid in order to obtain new drugs.
Materials and methods : In the experiments on mice, acute toxicity, neurotoxicity, antiepileptic activity and analgesic effect of N-(5-ethyl-1,3,4-thiadiazol-2-yl)-2-propylpentanamide (valprazolamide) were evaluated. LD 50 was determined by probit analysis. Neurotoxicity was determined in a rotarod test and a bar test in mice. The effects of valprazolamide on the exploratory behavior of mice in open field test and in a light/dark transition test were evaluated. Its antiepileptic activity was tested in mice against seizures induced by maximal electroshock, pentylenetetrazole (scPTZ); isoniazid, thiosemicarbazide, pilocarpine, and camphor. The analgesic effect was studied in a hot plate test.
Results and discussion : N-(5-ethyl-1,3,4-thiadiazol-2-yl)-2-propylpentanamide was obtained by introducing pharmacophores into the structure of 2-propylpentanoic acid: a substituted amide group and an electron-donor domain of 1,3,4-thiadiazole. The LD 50 value for intraperitoneal administration of a new 2-propylpentanoic acid: derivative to mice was 924.8 mg/kg, and the TD 50 value in the rotarod test and the bar test were 456.7 mg/kg and 546.7 mg/kg, respectively. The suppression of orienting responses in the animals was noted when it was administered in neurotoxic doses. Valprazolamide showed the most antiepileptic activity on models of MES, scPTZ and isoniazid antagonism tests. The ED 50 values were 138.4 mg/kg, 74.5 mg/kg, and 126.8 mg/kg, respectively. The therapeutic indices for these models of epilepsy were 6.7; 12.4; 7.3, and protective index – 3.3; 6.1 and 3.6, respectively. In the hot plate test, valprazolamide increased the latency period before a defensive response to a thermal stimulus (ED 50 165 mg/kg).
Conclusion : N-(5-ethyl-1,3,4-thiadiazol-2-yl)-2-propylpentanamide is a new 1,3,4-thiadiazolylamide derivative of 2-propylpentanoic acid with antiepileptic and analgesic activities, which belongs to the group of low-toxic agents.
LD 50 =924.8 mg/kg (mice, intraperitoneally)
TD 50 =456.7 mg/kg (rotarod, mice, intraperitoneally)
ED 50 =138.4 mg/kg (MES, mice, intraperitoneally)
ED 50 =74.5 mg/kg (scPTZ, mice, intraperitoneally)