Antisense Oligonucleotides

2'-5' Linked Oligonucleotides

Cellular DNA and RNA are made up of ribo- and 2'-deoxyribonucleic acids linked together via 3'-5' phosphodiester linkages and by far comprise the bulk of polynucleic acids found in cells. Much less common are oligonucleotides which have 2'-5' linkages. However, a unique feature of 2'-5' linked oligonucleotides is their ability to bind selectively to complementary RNA (12-13). These features suggest a number of interesting uses for 2'-5' linked oligos such as their use as RNA specific probes or in antisense oligos.

Chimeric oligos have been synthesized using 3'-deoxy-2'-phosphoramidites and 2'-deoxy-3'-phosphoramidites. Using these amidites the authors synthesized phosphorothioate oligos with 2'-5' linkages and chimeras with 2'-5' linked ends and 3'-5' linked central regions. They found that 2'-5' phosphorothioate oligos: 1) bind selectively to complementary RNA with the same affinity as phosphodiester oligos; 2) exhibit much nonspecific binding to cellular proteins; 3) do not activate RNase H. In experiments with Chinese hamster ovary cells transfected with human 5a-reductase-II (5aR-II), chimeric antisense oligos complementary to the 5' untranslated region of 5aR-II, containing seven 3'-5' linkages in the center, were effective in inhibiting 5aR-II protein in a dose dependent manner. The same oligos with 2'-5' linkages only were ineffective in inhibiting 5aR -II protein synthesis (14).

3'-dA-CE Phosphoramidite