(±)-2-propyl-4-Pentenoic acid (4-ene VPA) is a major metabolite of valproic acid.[1] It undergoes β-oxidation to form reactive metabolites that induce hepatotoxicity in rats. 4-ene VPA is also neuroteratogenic, reducing forebrain size and inducing deformation of the neural tube in mouse embryos.[2]
Reference:
[1]. Tang, W., and Abbott, F.S. A comparative investigation of 2-propyl-4-pentenoic acid (4-ene VPA) and its α-fluorinated analogue: Phase II metabolism and pharmacokinetics. Drug Metab. Dispos. 25(2), 219-227 (1997).
[2]. Gofflot, F., Nassogne, M.C., Etzion, T., et al. In vitro neuroteratogenicity of valproic acid and 4-en-VPA. Neurotoxicol. Teratol. 17(4), 425-435 (1995).