EN
Cytotoxicity of 22 amino acid 4-N-substitued cytosine derivatives was studied on KB and HeLa human tissue cultures. The secondary modification of tryptamine substituent seems to be a determining factor of the cytotoxic activity of 4-N-pyrimidinyl amino acids. The activity of the investigated compounds was inversely dependent on their solubility limited by the results of the solubility-activity relationship analysis.