Modified 2′ and 3′ nucleoside prodrugs for treating flaviviridae infections

A compound of the Formula (XIII):

• or a pharmaceutically acceptable salt thereof, wherein:
• R3 is selected from the group consisting of H;
• mono-, di-, and tri-phosphate or a stabilized phosphate prodrug;
• acyl;
• a sulfonate ester;
• optionally substituted alkyl sulfonyl;
• optionally substituted arylsulfonyl;
• a lipid;
• an amino acid;
• a carbohydrate;
• a peptide;
• cholesterol;
• and a pharmaceutically acceptable leaving group which when administered in vivo is capable of providing a compound wherein R3 is independently H, or mono-, di- or triphosphate;
• B is an optionally substituted 3-7 membered heterocyclic ring consisting of C, O and/or S atoms;
• Base is selected from the group consisting of:
• wherein
• each R′, R″, R′″ and R″″ are independently selected from the group consisting of H, OH, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, cycloalkyl, Br-vinyl, —O-alkyl, O-alkenyl, O-alkynyl, O-aryl, O-aralkyl, —O-acyl, O-cycloalkyl, NH2, NH-alkyl, N-dialkyl, NH-acyl, N-aryl, N-aralkyl, NH-cycloalkyl, SH, S-alkyl, S-acyl, S-aryl, S-cycloalkyl, S-aralkyl, F, Cl, Br, I, CN, COOH, CONH2, CO2-alkyl, CONH-alkyl, CON-dialkyl, OH, CF3, CH2OH, (CH2)mOH, (CH2)mNH2, (CH2)mCOOH, (CH2)mCN, (CH2)mNO2 and (CH2)mCONH2;
• m is 0 or 1;
• W is C—R″ or N;
• T and V independently are CH or N;
• Q is CH, —CCl, —CBr, —CF, —CI, —CCN, —C—COOH, —C—CONH2, or N;
• Q1 and Q2 independently are N or C—R;
• R is H, alkyl, or acyl;
• and
• Q3, Q4, Q5 and Q6 independently are N or CH.