Abstract: Compounds represented by the formula: wherein A is selected from the group consisting of W is NH2 or H; and each X, Y and Z is individually selected from the group consisting of OH, H and halogen provided at least one of X and Y is H; tautomers, or pharmaceutically acceptable salts thereof; are provided. Compounds of the present invention are useful as inhibitors of PNP and of T-cell proliferation. Compounds of the present invention are useful for treating Cancer. Method for preparing the compounds of the present invention are also provided.