5-fluorouridine monophosphate cyclic triester compounds

A compound having the structure of Formula Ia or Ib:

• or a stereoisomer or a pharmaceutically acceptable salt thereof,
• wherein:
• R1 is selected from a group of an optionally substituted aryl, and an optionally substituted heteroaryl;
• R2 is selected from a group of H, an optionally substituted C1-C10 heteroalkyl, an optionally substituted C1-C10 acyl, an optionally substituted C1-C10 heteroacyl, an optionally substituted C1-C10 alkyl-C-carboxy, and an optionally substituted C1-C10 alkyl-C-amido;
• R3 is selected from a group of H, OH, and an optionally substituted C1-C10 acyloxy;
• and
• R4 is selected from a group of H, an optionally substituted C1-C10 heteroalkyl, and an optionally substituted C1-C10 acyl.