Studies have shown that functionalized amino acids (FAA) exhibit outstanding activity in the maximal electroshock-induced seizure (MES) test in rodents. Affinity labels patterned in part after the potent antiepileptic (R)-N-benzyl-2-acetamido-3-methoxypropionamide ((R)-2) have been prepared as mechanistic probes to learn the pharmacological basis for FAA function. The chemical reactivity of the affinity labels with nucleophiles was assessed, and the labels were evaluated in in vitro radioligand assays and in the MES tests in rodents. The affinity labels did not bind to receptors known to effect seizure spread. Three affinity labels, (R,S)-N-benzyl-2-acetamido-6-isothiocyanatohexanamide ((R,S)-5), (R)-N-(4-isothiocyanatobenzyl)-2-acetamido-3-methoxypropionamide ((R)-6), and (R)-N-(3-isothiocyanatobenzyl)-2-acetamido-3-methoxypropionamide ((R)-7), possessed excellent in vivo anticonvulsant activity and exhibited maximal activity at later time periods than typically observed for FAA. The anticonvulsant activity of 6 and 7 resided primarily in the (R)-enantiomer and the activity of (R)-6 and (R)-7 in rats (po) exceeded that of phenytoin. The chemical properties, pharmacological profile, and marked stereospecificity associated with 6 and 7 anticonvulsant activity make these compounds useful pharmacological tools for the study of the mode of action of FAA.