Different stereoselectivity of the enantiomers of HA-966 (3-amino-1-hydroxy-2-pyrrolidinone) for neuroprotective and anticonvulsant actions in vivo.

HA-966 is an antagonist at the glycine modulatory site of N-methyl-D-aspartate (NMDA) receptors. Neuroprotective effects of HA-966 were determined in postnatal day (PND) 7 rats that received intrastriatal injections of NMDA (15 nmol) and then were administered either racemic HA-966, or the purified (R) or (S) enantiomer 15 min later. The (R)-enantiomer dose-dependently attenuated NMDA-induced brain injury, whereas the (S)-enantiomer was ineffective. When given intravenously to mice, racemic HA-966 and the (S)-enantiomer prevented tonic extensor seizures from low-intensity electroshock (ED50 = 13.2 and 8.8 mg/kg, respectively). Anticonvulsant effects of the (R)-enantiomer were much less potent (ED50 = 105.9 mg/kg). Ataxia measured by inverted screen fall-off was 17 times more potent with the (S)-enantiomer than with the (R)-enantiomer. Since previous published work indicates that glycine-site NMDA antagonist activity is primarily due to the (R)-enantiomer, our results suggest neuroprotective action for the (R)-enantiomer and anticonvulsant action, not related to a glycine antagonist mechanism for the (S)-enantiomer.