New Adenosine Kinase Inhibitors with Oral Antiinflammatory Activity: Synthesis and Biological Evaluation

Article abstract of DOI:10.1021/jm00074a024

Several 5-iodotubercidin analogues in the pyrazolo<3,4-d>pyrimidine ring system were synthesized as potential inhibitors of adenosine kinase by a direct Lewis acid-catalyzed glycosylation procedure using both the preformed carbohydrate and the heterocyclic base as starting materials.The 5'-hydroxyl, -chloro, -azido, -deoxy, -amino, and -fluoro derivatives were prepared and evaluated in three systems for biological activity relative to adenosine, the true substrate, and 5-iodotubercidin, a known inhibitor.First, each compound was studied kinetically for inhibition of purified human placental adenosine kinase activity.The order of potency was: iodotubercidin > hydroxyl > amino <*> deoxy > fluoro > chloro >> azido.The K_i values for the 5'-hydroxyl and 5'-amino compounds, the two most potent inhibitors, were 80 and 150 nM, respectively.The inhibition appeared to be essentially competitive in nature, although a noncompetitive component of significance for the more potent inhibitors cannot be ruled out.Second, a bioassay was conducted in which the toxicity of 6-methylmercaptopurine riboside toward human CEM lymphoblasts was reversed by varying concentrations of the compounds.The order of effectiveness of the compounds in this system, representing a functional inhibition of adenosine kinase in cultured cells, was about the same as that with the purified enzyme, except that the 5'-chloro and 5'-fluoro compounds were ineffective.Third, the 5'-hydroxyl derivative was evaluated in vivo in a rat pleurisy inflammation model and displayed biological activity at a dose of 30 mg/kg given orally.Finally, the in vitro toxicity of each compound was assessed in CEM lymphoblasts.Results indicated that the two most potent inhibitors in the pyrazolo<3,4-d>pyrimidine ring system, the 5'-hydroxyl (7) and the 5'-amino (20), were 15-fold and 75-fold, respectively, less growth inhibitory than 5-iodotubercidin.