This application proposes the synthesis of two series of imidazothiadiazines that can potentially act as transition state analogs of two critical enzymes in purine biosynthesis, adenylosuccinate synthetase and guanylate synthetase. Although transition state analogs have proven to be potent, specific inhibitors of certain enzymes, the use of such agents has received little attention in cancer chemotherapy. A successful application of the principle of drug design based on transition state affinity would have broad implications for rational design of new drugs with predictable specificities.