7, 8 and 9-substituted tetracycline compounds

1. A compound of formula (I):

or a pharmaceutically acceptable salt thereof, wherein:

R 4 and R 4′ are each methyl;

R 5 is hydrogen or hydroxyl;

R 6 and R 6′ are each independently hydrogen, methyl, or hydroxyl;

R 7 is dioxenyl;

R 8 is hydrogen, phenyl, nitrophenyl, halo or lower alkynyl; and

R 9 is hydrogen, amino, acetamide or lower alkynyl.

2. The compound of claim 1 , wherein R 5 is hydroxyl, R 6 is methyl, and R 6′ is hydrogen.

3. The compound of claim 2 , wherein R 8 and R 9 are each hydrogen.

4. The compound of claim 3 , wherein said compound is 7-(1,4-dioxenyl) doxycycline or a pharmaceutically acceptable salt thereof.

5. The compound of claim 2 , wherein R 8 is phenyl or ethynyl, and R 9 is amino.

6. A pharmaceutical composition comprising a therapeutically effective amount of a compound of claim 1 and a pharmaceutically acceptable carrier.

7. The pharmaceutical composition of claim 6 , wherein said compound is 7-(1,4-dioxenyl) doxycycline or a pharmaceutically acceptable salt thereof.

8. A method for treating a bacterial infection in a mammal, comprising administering to said mammal a compound of claim 1 .

9. The method of claim 8 , wherein said compound is 7-(1,4-dioxenyl) doxycycline or a pharmaceutically acceptable salt thereof.

10. The method of claim 8 , wherein said bacterial infection is associated with E. coli.

11. The method of claim 8 , wherein said bacterial infection is associated with S. aureus.

12. The method of claim 8 , wherein said bacterial infection is associated with E. faecalis.

13. The method of claim 8 , wherein said compound is administered with a pharmaceutically acceptable carrier.