Nucleotides for the treatment of cancer

1. A compound according to Formula I:

or a pharmaceutically acceptable salt thereof, wherein:

one of R 1 and R 2 is hydrogen and the other is

or R 1 and R 2 together with the two oxygen atoms to which they are attached form the ring structure:

R 3 is hydrogen, C 1-10 alkyl, C 2-11 alkenyl, C 2-11 alkynyl, C 1-10 alkoxycarbonylC 1-10 alkyl, C 1-10 alkylcarbonylthioC 1-10 alkyl, C 1-10 alkyldisulfideC 1-6 alkyl, aryl, or heteroarylC 1-10 alkyl, wherein alkyl is optionally substituted by one, two, or three substituents independently selected from halogen and hydroxy, and heteroaryl is substituted by one or two substituents selected from C 1-10 alkyl and nitro;

R 4 is hydrogen or C 1-10 alkyl;

R 5 is C 1-10 alkoxycarbonyl, C 3-10 cycloalkoxycarbonyl, C 1-10 alkylcarbonyloxyC 1-10 alkyl, C 3-10 cycloalkylcarbonyoxy, aryl, aryloxy, C 1-10 alkylaryl, arylC 1-10 alkyl, arylC 1-10 alkoxycarbonyl, aryloxycarbonyl, heteroaryl, heteroarylC 1-10 alkyl, or C 1-10 alkylheteroaryl;

R 6 is

and

W is O or S,

providing that the compounds of the following formula are excluded:

wherein R 3′ is aryl or an optionally substituted heteroaryl, R 4′ is C 1-10 alkyl, R x is C 1-6 alkyl, C 3-10 cycloalkyl, arylC 1-10 alkyl or aryl, and W is O.

2. The compound of claim 1 , wherein R 1 and R 2 together with the two oxygen atoms to which they are attached form the ring structure:

or a pharmaceutically acceptable salt thereof.

3. The compound of claim 1 , wherein the compound has a formula II:

or a pharmaceutically acceptable salt thereof,

providing that the compounds of the following formula are excluded:

wherein R 3 is aryl or an optionally substituted heteroaryl, R 4 is C 1-10 alkyl, R x is C 1-6 alkyl, C 3-10 cycloalkyl, arylC 1-10 alkyl or aryl, and W is O or S.

4. The compound of claim 1 , wherein the compound has a formula IV:

or a pharmaceutically acceptable salt thereof.

5. The compound of claim 1 , wherein W is O.

6. The compound of claim 1 , wherein the compound is selected from:

or a pharmaceutically acceptable salt thereof.

7. A pharmaceutical composition comprising the compound of claim 1 or a pharmaceutically acceptable salt thereof together with a pharmaceutically acceptable carrier or diluent.

8. A method for the treatment of a cancer comprising administering an effective treatment amount of a compound according to Formula I:

or a pharmaceutically acceptable salt thereof, wherein:

one of R 1 and R 2 is hydrogen and the other is

or R 1 and R 2 together with the two oxygen atoms to which they are attached form the ring structure:

R 3 is hydrogen, C 1-10 alkyl, C 2-11 alkoxycarbonylC 2-11 alkyl, C 1-10 alkylcarbonylthioC 1-10 alkyl, C 1-10 alkyldisulfideC 1-6 alkyl, aryl or heteroarylC 1-10 alkyl, wherein alkyl is optionally substituted by one, two, or three substituents independently selected from halogen and hydroxy, and heteroaryl is substituted by one or two substituents selected from C 1-10 alkyl and nitro, provided that both occurrences of R 3 , when present, are not simultaneously hydrogen;

R 4 is hydrogen or C 1-10 alkyl;

R 5 is C 1-10 alkoxycarbonyl, C 3-10 cycloalkoxycarbonyl, C 1-10 alkylcarbonyloxyC 1-10 alkyl, C 3-10 cycloalkylcarbonyoxy, aryl, aryloxy, C 1-10 alkylaryl, arylC 1-10 alkyl, arylC 1-10 alkoxycarbonyl, aryloxycarbonyl, heteroaryl, heteroarylC 1-10 alkyl, or C 1-10 alkylheteroaryl;

R 6 is

and

W is O or S,

providing that the compounds of the following formula are excluded:

wherein R 3′ is aryl or an optionally substituted heteroaryl, R 4′ is C 1-10 alkyl, R x is C 1-6 alkyl, C 3-10 cycloalkyl, arylC 1-10 alkyl or aryl, and W is O, or a pharmaceutically acceptable salt thereof.

9. The method of claim 8 , wherein said compound or composition is administered in combination with one or more other therapeutic agents.

10. A combination comprising the compound of claim 1 , or a pharmaceutically acceptable salt thereof, and one, two, three, or more other therapeutic agents.