Modified 2' and 3'-nucleoside prodrugs for treating flaviviridae infections

A method for the treatment of a host infected with a hepatitis C virus, comprising administering to the host infected with a hepatitis C virus an effective amount of a compound of the formula:

• or a pharmaceutically acceptable salt thereof, wherein:
• Base is selected from the group consisting of thymine, cytosine, 5-fluorocytosine, 5-methylcytosine, 6-azapyrimidine, 6-azacytosine, 2- and/or 4-mercaptopyrimidine, uracil, 5-halouracil, 5-fluorouracil, C5-alkylpyrimidine, C5-benzylpyrimidine, C5-halopyrimidine, C5-vinylpyrimidine, C5-acetylenic pyrimidine, C5-acyl pyrimidine, C5-amidopyrimidine, C5-cyanopyrimidine, C5-iodopyrimidine, C6-iodo-pyrimidine, C5-Br-vinyl pyrimidine, C6-Br-vinyl pyrimidine, C5-nitropyrimidine, C5-amino-pyrimidine, 5-azacytidinyl, 5-azauracilyl;
• R7 is F;
• R1 is H;
• phosphate;
• monophosphate, diphosphate;
• triphosphate;
• a stabilized phosphate prodrug;
• acyl;
• lower acyl;
• alkyl;
• lower alkyl;
• sulfonate ester;
• alkyl or arylalkyl sulfonyl;
• methanesulfonyl;
• benzylsulfonyl;
• a lipid;
• a phospholipid;
• an amino acid;
• a carbohydrate;
• a peptide;
• a cholesterol;
• or other pharmaceutically acceptable leaving group which when administered in vivo provides a compound wherein R1 is H or phosphate;
• R2 is phosphate;
• monophosphate;
• diphosphate;
• triphosphate;
• a stabilized phosphate prodrug;
• acyl;
• lower acyl;
• alkyl;
• lower alkyl;
• sulfonate ester;
• alkyl or arylalkyl sulfonyl;
• methanesulfonyl;
• benzylsulfonyl;
• a lipid;
• a phospholipid;
• an amino acid;
• a carbohydrate;
• a peptide;
• a cholesterol;
• or other pharmaceutically acceptable leaving group which when administered in vivo provides a compound wherein R2 is H or phosphate;
• and
• wherein each Y3 is H.