Series of N-substituted diethyl aspartates and Nsubstituted-3-oxo-l,4-piperazine-2-acetic acid esters were synthesized as potential inhibitors of aspartate transcarbamoylase. The aspartates were obtained by addition of substituted alkyl amines to diethyl maleate, or conversion of the hydroxy ethyl amino adduct to other functions. The 3-0X0-1,4-piperazine-2-acetic acid esters were prepared by addition of ethylene diamine to diethyl maleate, followed by cyclization. Addition of 1,2-diamino-2-methylpropane gave the corresponding 5,bdimethyl-3-0X0-1,4-piperazine-2-acetic acid ester. N-Acyl derivatives in each series were obtained using the bromoacyl chlorides. A majority of the compounds in each series showed antimicrobial activity against five representative microorganisms, as well as significant activity against aspartate transcarbamoylase. Four of the compounds were found to have significant specificity against several tumor cell lines. A distance of two carbons between Nand a reactive function was found to give the best activity for either antimicrobial, antienzyme, or tumor cell specificity activities, in either the open chain aspartates or cyclic piperazines. Little difference in anti-enzyme activity was found between the aspartates and piperazines, but introduction of the planar phenyl substituents lowered inhibitory activity.