5-Aminouridine can modify nucleobases and can be incorporated into the target DNA. 5-Aminouridine exhibits a wide range of biological activity and it inhibits the growth of tumors, fungi and viruses^[1][2][3]. In Vitro: This modified nucleobase, 5-Aminouridine, must exhibit a low enough potential to be oxidized by Os(bpy)₃³⁺. These modified nucleobases can be inserted into the target DNA by direct synthesis using modified phosphoramidites^[4]. In Vivo: 5-Aminouridine inhibits incorporation of carbamylaspartate into pyrimidines of both RNA and DNA in rat lived and [³²P]phosphate into phospholipids and RNA nucleotides of rat liver slices and hepatoma^[1].