Further branching of valproate-related carboxylic acids reduces the teratogenic activity, but not the anticonvulsant effect.

In the present study, compounds derived from the anticonvulsant drug valproic acid (VPA, 2-n-propylpentanoic acid) and analogues known to be teratogenic were synthesized with an additional carbon-branching in one of the side chains. The substances were tested for their ability to induce anticonvulsant activity and sedation in adult mice, and neural tube defects (exencephaly) in the offspring of pregnant animals (Han:NMRI mice). In all cases, the rates of exencephaly, embryolethality, and fetal weight retardation induced by the methyl-branched derivatives were very low when compared to those of the parent compounds. These novel compounds exhibited anticonvulsant activity which was not significantly different from that of VPA. Neurotoxicity was considerably lower for some compounds as compared to VPA. Anticonvulsant activity and neurotoxicity of branched short chain fatty acids are far less structure-dependent and not related to teratogenic potency. Within this series of compounds, (+/-)-4-methyl-2-n-propyl-4-pentenoic acid and (+/-)2-isobutyl-4-pentenoic acid exhibited the most favorable profile in regard to high anticonvulsant effect, low sedation, and teratogenicity. Valproic acid analogues with additional methyl branching may be valuable antiepileptic agents with low teratogenic potential.