Recently we found that an antisense 2'-O-methyloligonucleotide, with two terpyridine*Cu(II) complexes at contiguous internal sites, was highly active as a site-specific (sequence-specific) artificial ribonuclease, with the activity derived from the cooperative action of the complexes. Two kinds of terpyridine-linked nucleosides were used for the construction of the RNA cleaver, including a uridine derivative with terpyridine attached to the 2'-oxygen via a short linker arm. In order to explore more efficient cleavers (practical cleavers), we have constructed a structurally similar cleaver (18-mer), but containing a novel 2'-carbon-branched uridine with a terpyridine group instead of the aforementioned 2'-oxygen-modified uridine. The reaction of a 10-fold excess of the target RNA 24-mer with the new agent, in the presence of Cu(II) ions, and at pH 7.5 and 37 degrees C, revealed that the substrate was cleaved in 92% yield after 5 h. Under similar conditions, the previous cleaver was less active and the cleavage yield was 61%.