1. The process of purifying a compound of the formula   comprising, treating an impure reaction product containing an amount of said compound of formula I and less polar impurities, with a hydrophobic resin. 2. A process according to claim 1, wherein said less polar impurities have a retention time of about 2.1 to about 30 minutes. 3. A process according to claim 1, wherein one of said less polar impurities has a retention time of about 9 to about 12 minutes. 4. A process according to claim 1, wherein one of said less polar impurities has the formula   5. A process according to claim 1, wherein said impurities, after treatment, comprise less than about 60 ppm relative to the total weight of the purified product. 6. A process according to claim 1, wherein said impurities, after treatment, comprise less than about 20 ppm relative to the total weight of the purified product. 7. A process according to claim 1, wherein said hydrophobic resin is a crosslinked polystyrene resin. 8. A process according to claim 1, wherein said hydrophobic resin is Diaion HP-20<(RTM)> or Amberchrom CG-161<(RTM)>. 9. A process according to claim 3, wherein said hydrophobic resin is Diaion HP-20<(RTM)> or Amberchrom CG-161<(RTM)>. 10. A compound of the formula   substantially free of less polar impurities. 11. A compound according to claim 10, wherein said compound of formula I is substantially free of the compound of formula II. 12. A parenteral composition, comprising an antibacterially effective amount of a compound of the formula I, or a pharmaceutically acceptable salt thereof, substantially free of less polar impurities, and a pharmaceutically acceptable carrier. 13. A parenteral composition, comprising an antibacterially effective amount of a compound of the formula I, or a pharmaceutically acceptable salt thereof, substantially free of a compound of formula II, and a pharmaceutically acceptable carrier. 14. A parenteral composition according to claim 10, comprising a compound of formula I and water. 15. A parenteral composition according to claim 10, wherein the compound of formula I is a lyophylate. 16. A parenteral composition according to claim 11, wherein the compound of formula I comprises about 10mg to about 700mg of compound in a unit dosage container. 17. A parenteral composition according to claim 11, wherein the compound of formula I comprises about 275mg to about 500mg of compound in a unit dosage container 18. A parenteral composition according to claim 10, wherein the compound of formula I comprises about 10mg to about 700mg of compound in a unit dosage container. 19. A parenteral composition according to claim 10, wherein the compound of formula I comprises about 275mg to about 500mg of compound in a unit dosage container. 20. A compound of the formula   21. A pharmaceutical composition, comprising an antibacterially effective amount of a compound according to claim 20, or a pharmaceutically acceptable salt thereof. 22. A method of treating a bacterial infection, comprising administering to a subject affected by a bacterial infection an antibacterially effective amount of a compound according to claim 20. 23. A compound of formula Ill   24. A pharmaceutical composition, comprising an antibacterially effective amount of a compound according to claim 23, or a pharmaceutically acceptable salt thereof. 25. A method of treating a bacterial infection, comprising administering to a subject affected by a bacterial infection an antibacterially effective amount of a compound according to claim 23.