Synthesis of oligonucleotides terminally modified by bulky and negatively charged substituents and their hybridization with RNA targets.

2'-O-methyl RNAs having phosphorylated cyclohexane groups at the 5' and 3'-terminal bases were synthesized and their hybridization properties toward RNA targets were studied. It was proved that the duplex of the modified 2'-O-methyl RNAs and the target RNA longer than the 2'-O-methyl RNA was less stable than that with the short target. In addition, it was also clarified that the selectivity toward the short target was improved by the introduction of the phosphate group in comparison with that without the phosphate group.