Synthesis of antisense oligonucleotides carrying modified 2-5A molecules at their 5'-termini and their properties.

The synthesis of 8-methyladenosine-substituted 2-5A tetramers with hydroxyalkyl groups at the 5'-phosphates and the corresponding 2-5A-antisense chimeras is described. These oligonucleotides were synthesized by the phosphoramidite method with a DNA/RNA synthesizer. These 2-5A tetramers with hydroxyethyl and hydroxybutyl groups at their 5'-phosphates were more resistant to hydrolysis by alkaline phosphatase than those without the hydroxyalkyl groups. Incorporation of the hydroxyethyl group into the 2-5A tetramer and 2-5A-antisense chimera slightly reduced the abilities of their analogues to activate recombinant human RNase L, but the abilities of the 2-5A tetramer and the 2-5A-antisense chimera both with the hydroxyethyl group and 8-methyladenosine returned to 80 and 50% relative to those of the oligonucleotides without the hydroxyethyl group and 8-methyladenosine, respectively. Furthermore, the enzyme activated by 8-methyladenosine-substituted 2-5A-antisense chimera with the hydroxyethyl group cleaved the complementary RNA as efficiently as that activated by 2-5A-antisense chimera without the hydroxyethyl group and 8-methyladenosine. Thus, the 2-5A-antisense chimera carrying the hydroxyethyl group and 8-methyladenosine will be a candidate for a novel antisense molecule.