for the following products
(R)-(-)-alpha-(((4-Ethyl-2,3-dioxo-1-piperazinyl)carbonyl)am)benzeneacetic acid | (R)-(-)-alpha-[[(4-Ethyl-2,3-dioxo-1-piperazinyl)carbonyl]amino]benzeneacetic acid | EPCP and (2R)-2-[(4-Ethyl-2,3-dioxopiperazinyl)carbonylamino]-2-phenylacetic acid
