Diphosphates of N-(S)-(3-hydroxy-2-phosphonylmethoxypropyl) and N-(2-phosphonylmethoxyethyl) derivatives of purine and pyrimidine heterocyclic bases inhibit HSV-1 encoded ribonucleotide reductase. Of the compounds studied, the most efficient inhibitors of CDP reduction (at 5.1 mumols.l-1) by the HSV-1-encoded enzyme are HPMPApp (IC50 = 0.9 mumols.l-1) and PMEApp (IC50 = 8 mumol.l-1). PMEApp does not inhibit the enzyme isolated from the mutant HSV-1 KOS strain PMEAr which is resistant to PMEA at a concentration of 100 micrograms/ml. The enzyme isolated from the PMEA-resistant virus strain is also insensitive to inhibitory effects of hydroxyurea and HPMPApp. Thus, the inhibitory potency of HPMPApp and PMEApp toward HSV-1 encoded ribonucleotide reductase might be connected with the anti-HSV activity of HPMPA and PMEA.

Institute of Organic Chemistry and Biochemistry Czechoslovak Academy of Sciences Prague

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