Piperazine-2-carboxylic acid (1) is a conformationally restricted nonproteinogenic amino acid which has been incorporated into a number of medicinally useful compounds. N-methyl- D-aspartate (NMDA) antagonist 21 and HIV protease inhibitor 32 provide examples. Piperazine-2-carboxylic acid is commercially available only in racemic form. Homochiral material has been obtained from racemic preparations by separating enantiomers through ...