(S)-α-[[(4-Ethyl-2,3-dioxo-1-piperazinyl)carbonyl]amino]benzeneacetic Acid is an intermediate used in the synthesis of DL-Phenylglycyl)-piperacilloic Acid (P327400), which is a racemic degradation product of Piperacillin (P479950), a new β-lactam antibiotic.