Bicyclic nucleosides and nucleotides as therapeutic agents

1. A compound of the formula (I) which may be a D-or L-nucleoside or nucleotide, or a salt thereof;

wherein:

each R is independently selected from the group consisting of H, CF 3 , optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted acyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted heteroaryl, optionally substituted heterocyclyl, and optionally substituted arylalkyl;

or C-5 monophosphate, diphosphate and triphosphate derivatives thereof, or C-5 mono, di or triphosphate mimics;

B is a group of formula (II)

wherein, if Z is a participant in a π bond (double bond), Z is independently selected from N or C-G; or, if Z is not a participant in a π bond (double bond), Z is independently selected from O, S, Se, NR, NOR, NNR 2 , CO, CS, CNR, SO, S(O) 2 , SeO, Se(O) 2 or C(G) 2 , wherein each G is independently selected from the group consisting of H, halogen, OR, SR, NR 2 , NROR, N 3 , COOR, CN, CONR 2 , C(S)NR 2 , C(═NR)NR 2 , and R; and

where any two adjacent Z are not both selected from O, S, and Se, or not both selected from CO, CS, CNR, SO, S(O) 2 , SeO, and Se(O) 2 ;

wherein, if X is a participant in a π bond (double bond), X is C; or if X is not a participant in a π bond (double bond), X is CR or N;

wherein, if R″ is a participant in a π bond (double bond), R″ is O, S, Se, NR, NOR, and NNR 2 ; or if R″ is not a participant in a π bond (double bond), R″ is OR, SR, F, Cl, R, or SeR; and

dashed lines (- - -) indicate a possible π or double bond.

2. A compound according to claim 1 , or a salt thereof, wherein the base structure B is selected from the following formulae (XI) to (XXI)

wherein Z, X and R″ are as defined in claim 1 .

3. A compound according to claim 1 , or a salt thereof, wherein X is N.

4. A compound according to claim 1 , or a salt thereof, wherein the base structure B is selected from the following:

wherein G and R are as defined in claim 1 .

5. A compound according to claim 1 , or a salt thereof, wherein the base structure B is represented by formula IIa:

wherein each Z′ is independently N (if a participant in a π bond) or NR (if not a participant in a π bond), and R″, R and Z are as defined in claim 1 .

6. A compound according to claim 1 , or a salt thereof, wherein the base structure B is represented by the formula IIb:

wherein each Z′ is independently N (if a participant in a π bond) or NR (if not a participant in a π bond), and each Z is independently CG (if a participant in a π bond) or >C(G) 2 (if not a participant in a π bond), and wherein R″ and G is as defined in claim 1 .

7. A compound according to claim 1 , or a salt thereof, wherein the base structure B is represented by formula IIc:

wherein R and G are as defined in claim 1 .

8. A compound according to claim 1 , or a salt thereof, wherein the base structure B is represented by the formula IId:

wherein R and G are as defined in claim 1 .

9. A compound according to claim 1 , or a salt thereof, wherein the base structure B is represented by the formula IIe:

wherein R and G are as defined in claim 1 .

10. A compound of formula (I) selected from the following formulae, or a salt thereof:

wherein:

each R on the sugar moiety is independently selected from H, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted aryl, optionally substituted acyl and optionally substituted arylalkyl;

each R on the base moiety is independently selected from H, optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocyclyl, and optionally substituted arylalkyl;

each G is independently selected from H, halogen, CF 3 , optionally substituted alkyl, optionally substituted aryl, optionally substituted heteroaryl, optionally substituted heterocyclyl, and optionally substituted arylalkyl; and

C-5 monophosphate, diphosphate and triphosphate derivatives thereof, or C-5 mono, di or triphosphate mimics.

11. A compound according to claim 1 , or a salt thereof, wherein the sugar moiety is represented by the formula:

or C-5 monophosphate, diphosphate and triphosphate derivatives thereof, or C-5 mono, di or triphosphate mimics, wherein R is as defined in claim 1 .

12. A compound according to claim 1 , or a salt thereof, wherein the sugar moiety is represented by the formula:

or C-5 monophosphate, diphosphate and triphosphate derivatives thereof, or C-5 mono, di or triphosphate mimics.

13. A compound according to claim 1 , or a salt thereof, which is a β anomer.

14. A compound according to claim 1 , or a salt thereof, selected from

15. A pharmaceutical composition comprising a compound according to claim 1 or a salt thereof, and at least one pharmaceutically acceptable carrier or diluent.

16. A pharmaceutical composition according to claim 15 for use in the treatment of a viral infection.

17. A pharmaceutical composition according to claim 16 , wherein the virus is the hepatitis C virus.

18. A pharmaceutical composition according to claim 15 further comprising one or more antiviral or antibacterial agents.

19. A pharmaceutical composition according to claim 18 , wherein the antiviral agents are selected from the group selected from interferon and interferon derivatives, IMPDH inhibitors, antiviral nucleosides, polymerase inhibitors and protease inhibitors.

20. A pharmaceutical composition according to claim 19 , wherein the composition comprises interferon or ribavirin.