Anticonvulsant and neurotoxic activities of twelve analogues of valproic acid.

Twelve racemic analogues of the antiepileptic drug valproic acid (VPA) were tested and compared with VPA for anticonvulsant activity by the subcutaneous pentylenetetrazol (PTZ) seizure threshold test and for neurotoxicity by the rotorod test. Four compounds produced maximal anticonvulsant activity (100% protection) in equimolar doses (1.5 mmol/kg) to VPA and two compounds showed a similar effect with lower doses (1.0 mmol/kg). Four compounds produced lower activity (38-80% protection), and two compounds showed no anticonvulsant activity at the dose used (1.5 mmol/kg). Two of the 12 compounds, (+/-)-2-n-propyl-4-hexynoic acid (11) and (+/-)-4-methyl-2-n-propyl-4-pentenoic acid (12), showed no sedation at doses that produced the maximum anticonvulsant effect. For the first time we succeeded to develop two compounds with higher protective index and safety ratios than VPA. Compound 11 had a longer duration of action and higher protective index but a lower safety ratio than 12. Comparisons of the anticonvulsant and minimal neurotoxic effects of these compounds with their calculated lipophilicity (C log P) revealed that compounds with the desired high anticonvulsant activity and minimal neurotoxicity showed C log P values between 1.84 and 2.64 and had nine carbon atoms (in contrast to eight carbon atoms for VPA).