Structure activity relationship of human microsomal epoxide hydrolase inhibition by amide and acid analogues of valproic acid

Purpose. The purpose of this study was to evaluate the in vitro inhibitory potency of various amide analogues and derivatives of valproic acid toward human microsomal epoxide hydrolase (mEH). Methods. mEK inhibition was evaluated in human liver microsomes with 25 mu M (S)-(+)-styrene oxide as the substrate. Inhibitory potency expressed as t he median inhibitory concentration (IC50) was calculated from the formation rate, of the enzymatic product, (S)-(+)-1-phenyl-1,2-ethanediol. Results. Inhibitory potency was directly correlated with lipophilicity and became significant for amides with a minimum of eight carbon atoms. Branche d eight-carbon amides were more potent inhibitors than their straight chain isomer, octanamide. N-substituted valproylamide analogues had reduced or a bolished inhibition potency with the exception of valproyl hydroxamic acid being a potent inhibitor. Inhibition potency was not stereoselective in two cases of chiral valpromide isomers. Valproyl glycinamide, a new antiepilep tic drug currently undergoing phase II clinical trials and its major metabo lite valpsoyl glycine were weak mEH inhibitors. Acid isomers of valproic ac id were not potent mEH inhibitors. Conclusions. The structural requirements for valproylamide analogues for po tent in vitro mEH inhibition are: an unsubstituted amide moiety; two satura ted alkyl side chains; a minimum of eight carbons in the molecule.