A fast and efficient route for introduction of methylene bridged-amine (morpholinomethyl) functionality in the C5 position of the sulfonylated cytosine nucleobase has been developed. First, novel N1-sulfonylcytosine derivatives 3-6 were prepared by the condensation of silylated cytosine with selected sulfonyl chlorides. They were subsequently transformed to 5-morpholinomethyl-N1-sulfonylcytosine derivatives (8, 12-15) using microwave irradiation. As a result of the cytosine ring opening in N1-tosylcytosine, depending on the reaction conditions, peculiar tosyl-urea derivative 9 has been isolated, which provided additional insight into reaction pathway. The influence of the C5-substituent on the antiproliferative activity has been evaluated by MTT test on U251, MCF-7 and MOLT-4 tumor cell-lines.