Abstract The preparation of N-(2-phosphonylmethoxyethyl) derivatives of purine and pyrimidine bases, IV, as analogs of the antiviral 9-(2-phosphonylmethoxyethyl) adenine (PMEA, I), is described. The synthesis consists in alkylation of alkali metal salts of heterocyclic bases or their N-or O-substituted derivatives with diethyl 2-p- toluenesulfonyloxyethoxymethylphosphonate (IIa), 2-chloroethoxymethylphosphonate (IIb ...