Pyrimidine nucleosides and their monophosphate prodrugs for treatment of viral infections and cancer

A compound of Formula (I):

• or a pharmaceutically acceptable salt or prodrug thereof, wherein:
• X1 is H, C1-C6 alkyl, C1-C6haloalkyl, C1-C6 alkoxy, C2-C6 alkenyl, C2-C6 alkynyl, COR1, or COOR1;
• X2 is hydrogen, COR1, or COOR1
• wherein each R1 is, independently, CH2—O(CO)—X5;
• CH2—O(CO)O—X5, C1-20 alkyl, the carbon chain derived from a fatty alcohol or C1-20 alkyl substituted with a C1-C6 alkyl, alkoxy, di(C1-C6 alkyl)-amino, fluoro, C3-10 cycloalkyl, cycloalkyl alkyl, cycloheteroalkyl, aryl, heteroaryl, substituted aryl, or substituted heteroaryl;
• wherein the substituents are C1-6 alkyl, or C1-6 alkyl substituted with a C1-C6 alkyl, C1-C6 alkoxy, di(C1-C6 alkyl)-amino, fluoro, or C3-10 cycloalkyl
• X5 is independently, C1-20 alkyl, the carbon chain derived from a fatty alcohol or C1-20 alkyl substituted with a C1-C6 alkyl, alkoxy, C3-10 cycloalkyl, cycloalkyl alkyl, cycloheteroalkyl, aryl, heteroaryl, substituted aryl, or substituted heteroaryl;
• wherein the substituents are C1-6 alkyl, or C1-6 alkyl substituted with a C1-C6 alkyl, C1-C6 alkoxy, di(C1-C6 alkyl)-amino, fluoro, or C3-10 cycloalkyl
• each X3 and X4 is independently H, C1-6 alkyl, C2-6 alkenyl, C2-6alkynyl, aryl, alkylaryl, halogen, NH2, OH, SH, CN, or NO2.