Evaluation of stereoselective anticonvulsant, teratogenic, and pharmacokinetic profile of valnoctylurea (capuride): A chiral stereoisomer of valproic acid urea derivative

Purpose: The purpose of this study was to evaluate the stereoselective anticonvulsant activity, neurotoxicity, pharmacokinetics, and teratogenic potential of two stereoisomers of valnoctylurea (VCU), a central nervous system (CNS)-active urea derivative of valnoctic acid, which is a constitutional isomer of valproic acid (VPA). Methods: VCU stereoisomers (2S,3S)-VCU and (2R,3S)-VCU were synthesized. Their anticonvulsant activity was determined and compared to VPA and racemic-VCU in rats utilizing the maximal electroshock seizure (MES) and the subcutaneous pentylenetetrazole (scMet) tests. Neurotoxicity was determined in rats using the positional sense test, muscle tone test, and gait and stance test. The induction of neural tube defects (NTDs) by VCU stereoisomers was evaluated in a mouse strain highly susceptible to VPA-induced teratogenicity. The pharmacokinetics of VCU was studied in a stereoselective manner following intraperitoneal (i.p.) administration to rats. Results: (2S,3S)-VCU and (2R,3S)-VCU median effective dose ED₅₀ values were 29 mg/kg [95% confidence interval (CI) = 8-60 mg/kg] and 42 mg/kg (95% CI = 36-51 mg/kg) (MES) and 22 mg/kg (95% CI = 13-51 mg/kg) and 12 mg/kg (95%CI = 7-21 mg/kg) (scMet), respectively. (2S,3S)-VCU was more potent and had a wider safety margin (p < 0.05), defined as the protective index (PI = TD₅₀/ED₅₀), at both the MES (PI > 17) and scMet (PI > 23) tests than racemic-VCU or (R,S)-VCU (PI = 2.8 and 9.9, respectively). VCU stereoisomers causedNTDs at doses > 4 times that of their anticonvulsant ED₅₀ values. At a dose of 112 mg/kg, (2R,3S)-VCU was nonteratogenic and less embryotoxic than its stereoisomer (2S,3S)-VCU. No stereoselective pharmacokinetics was observed following intraperitoneal dosing of racemic-VCU to rats. VCU was mainly eliminated by metabolism with a half-life of 2 h. Conclusions: VCU anticonvulsant activity and wide PI values make it a potential candidate for development as a new, potent antiepileptic drug (AED).