The chemical synthesis of 4-N-carboxybutyl-5-fluorocytosine (II) in solution phase starting from 5-fluorocytosine and the solid phase synthesis of Arg-Gln-Trp-Arg-Arg-Trp-Trp-Gln-Arg-NH(2) attached to the 4-N-carboxybutyl-5-fluorocytosine residue at the N-terminus of the peptide (III) via peptide bond formation is reported. The target compound exhibited a significant cytotoxic activity against a culture of HepG2 cells. In addition our results demonstrated that this new compound affect cell viability, produce mitochondrial dysfunction as well as interfere with intracellular calcium homeostasis control; leading to cell malfunction and death.