Oligomeric compounds comprising tricyclic nucleosides and methods for their use

1. An oligomeric compound comprising at least one tricyclic nucleoside having formula II:

wherein independently for each of said tricyclic nucleosides having formula II:

Bx is a heterocyclic base moiety;

one of T 1 and T 2 is an internucleoside linking group attaching said tricyclic nucleoside of formula II to said oligomeric compound and the other of T 1 and T 2 is hydroxyl, a protected hydroxyl, a 5′ or 3′-terminal group selected from one or more conjugate groups, capping groups and phosphate moieties or an internucleoside linking group attaching said tricyclic nucleoside of formula II to said oligomeric compound;

q 1 , q 2 , q 3 and q 4 are each H;

z 1 is H and z 2 is F; and

wherein said oligomeric compound comprises from about 8 to about 40 linked monomeric subunits and is complementary to at least a portion of a target RNA.

2. The oligomeric compound of claim 1 wherein each Bx is, independently, uracil, thymine, cytosine, 5-methylcytosine, adenine or guanine.

3. The oligomeric compound of claim 1 wherein said oligomeric compound further comprises said 5′ or 3′-terminal group.

4. The oligomeric compound of claim 1 wherein each monomeric subunit is, independently, a β-D-2′-deoxyribonucleoside or a tricyclic nucleoside having formula II.

5. The oligomeric compound of claim 1 wherein each linked monomeric subunit that is not a β-D-2′-deoxyribonucleoside or a tricyclic nucleoside having formula II is a modified nucleoside independently selected from a bicyclic modified nucleoside, a 2′-modified nucleoside, a 4′-thio modified nucleoside or a 4′-thio-2′modified nucleoside.

6. The oligomeric compound of claim 1 wherein said oligomeric compound comprises a motif selected from a gapped motif, a hemimer motif, a blockmer motif, a fully modified motif, a positionally modified motif and an alternating motif.

7. The oligomeric compound of claim 1 wherein said oligomeric compound comprises a gapped oligomeric compound comprising two external regions separated by an internal region wherein each external region independently comprises from 1 to 5 contiguous tricyclic nucleosides of formula II and the internal region comprises from 6 to about 23 contiguous monomeric subunits independently selected β-D-ribonucleosides and β-D-2′-deoxyribonucleosides.

8. The oligomeric compound of claim 7 wherein essentially each monomeric subunit in the internal region is a β-D-2′-deoxyribonucleoside.

9. The oligomeric compound of claim 7 wherein the internal region comprises from about 8 to about 12 β-D-2′-deoxyribonucleosides.

10. The oligomeric compound of claim 9 wherein each external region comprises from 1 to 3 tricyclic nucleosides of formula II.

11. The oligomeric compound of claim 10 wherein the internal region comprises 10 β-D-2′-deoxyribonucleosides.

12. The oligomeric compound of claim 1 wherein said oligomeric compound comprises a 5′-terminal tricyclic nucleoside of formula II wherein T 1 is a 5′-phosphate moiety.

13. The oligomeric compound of claim 1 wherein each internucleoside linking group is, independently, a phosphodiester or a phosphorothioate.

14. The oligomeric compound of claim 1 comprising from 10 to about 16 linked monomeric subunits.

15. The oligomeric compound of claim 1 comprising from 18 to about 21 linked monomeric subunits.

16. A tricyclic nucleoside having formula III:

wherein:

Bx is a heterocyclic base moiety;

one of T 3 and T 4 is H or a hydroxyl protecting group and the other of T 3 and T 4 is H, a hydroxyl protecting group or a reactive phosphorus group;

q 1 , q 2 , q 3 and q 4 are each H; and

z 1 is H and z 2 is F.

17. The tricyclic nucleoside of claim 16 wherein Bx is uracil, thymine, cytosine, 5-methylcytosine, adenine or guanine.

18. The tricyclic nucleoside of claim 16 wherein T 3 is 4,4′-dimethoxytrityl and T 4 is diisopropylcyanoethoxy phosphoramidite.