PD144723, S-(+)-3-isobutyl GABA, is structurally related to both the inhibitory neurotransmitter γ-aminobutyric acid and the novel anticonvulsant gabapentin. That the S-enantiomer is more potent than the R-(-)-enantiomer, PD144550, for in vitro displacement of [ 3 H]gabapentin at the gabapentin binding site illustrates the stereoselectivity of this site. The two enantiomers were prepared by Evans' chiral oxazolidinone alkylation chemistry.