PRODRUGS OF 5-AMINO-3-(3'-DEOXY-.BETA.-D-RIBOFURANOSYL)-THIAZOLO[4,5-D]PYRIMIDIN-2,7-DIONE

The invention relates to a compound of Formula I: (see formula I) or a pharmaceutically acceptable salt thereof, wherein: R1 is NH2 or -N=CH-NR6R7, R2 is H, OH, or -OR5, R3 is OH, -OC(O)C1-C18alkyl, -OCO2R5, -OC(O)NR6R7, or a racemic, L-, or D-amino acid group -OC(O)CHR8NHR9, R4 is OH, -OC(O)C1-C18alkyl, -OCO2R5, -OC(O)NR6R7, or a racemic, L-, or D-amino acid group -OC(O)CHR8NHR9, R5 is -C1-C7alkyl, R6 and R7 are independently -C1-C7alkyl or together with nitrogen atom to which they are attached form a 5- or 6-membered heterocyclic ring, R8 is H or -C1-C7alkyl, R9 is H, -C1-C7alkyl, -C(O)R5, or -CO2R5, wherein at least one of R3 or R4 is -OCO2R5, -OC(O)NR6R7, or a racemic, L-, or D-amino acid group -OC(O)CHR8NHR9, and wherein the above alkyl is optionally substituted by 1-4 substituents. The invention also relates to the therapeutic use of such a compound and pharmaceutical compositions thereof for modulating immune cytokine activities and in treating disease states associated with abnormal cell growth, such as cancer.