Synthesis of RNA Bearing C5-polyamine Modified Pyrimidine Nucleosides at the 3´-end by T4 RNA Ligase

The incorporation of the modified nucleoside into the 3´-overhang regions of short interfering RNAs (siRNAs) has been reported to enhance their nuclease resistance and improve RNA interference activity. In this study, DNA 2-mers containing C5-polyamine-modified pyrimidine nucleosides were synthesized and then ligated to the 3´-end of the RNA by T4 RNA ligase. The modification of the base moiety with tris(2-aminoethyl)amine affected the ligation efficiency, but the DNA 2-mer containing only one modified nucleoside was ligated with sufficient efficiency. We propose a novel synthetic route to modified siRNA bearing various modified groups in the 3´-overhang region.