2-Octyl gamma-bromoacetoacetate (O gamma Br), an endogenous compound originally isolated from human cerebrospinal fluid (CSF), has previously been demonstrated to increase REM sleep duration in cats. Based on the chemical structure of O gamma Br and its reported sleep-inducing effects, we synthesized O gamma Br along with chemically related analogs and tested these compounds as inhibitors of fatty acid amide hydrolase (FAAH), a brain enzyme that degrades neuromodulatory fatty acid amides. O gamma Br was found to competitively inhibit FAAH activity with IC50 and Ki values of 2.6 microM and 0.8 microM, respectively [for the (R)-enantiomer of O gamma Br (1)]. A set of synthetic analogs of O gamma Br was examined to define the structural features required for FAAH inhibition and inhibitor potencies were assessed at pH 9.0 (near the pH optimum of FAAH) and pH 7.0. Interestingly, at pH 7.0 the gamma-halo beta-keto ester inhibitors proved to be significantly more potent than the trifluoromethyl ketone of oleic acid, one of the most potent FAAH inhibitors described to date. This study supports the possibility that O gamma Br may be a physiological regulator of FAAH activity and fatty acid amide levels in vivo. Additionally, the characterization of gamma-halo beta-keto esters as powerful FAAH inhibitors near physiological pH may aid in future studies of the enzymology and biological properties of FAAH.