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Iodination of chloroform solutions of the bromides of 1H,2H,3H, 4H-pyrido[4,3-d]pyrimidinium with a threefold excess of iodine was performed to synthesize the diiodobromides of the corresponding organic cations. The composition and structure of these compounds were confirmed by UV and 1 H NMR spectroscopic and potentiometric titration methods. Values for the stability constant lgb (3.05 -4.68) allowed active iodine concentrations at the bactericidal level to be produced in solutions of 1H,2H,3H, 4H-pyrido[4,3-d]pyrimidinium diiodobromides. The minimum inhibitory concentrations (MIC) of 1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium diiodobromides against E. coli were 1.0 ± 0.25 mg/ml. Keywords: bromides and diiodobromides of 1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium derivatives, stability of iodohalogenides, antimicrobial activity.Polyhalogenides of nitrogen-containing organic cations have recently been the subject of interest as iodine in the bound state has virtually no toxicity but retains its biological activity [1]. The creation of new drugs able to release molecular iodine gradually and maintain its concentration at the bactericidal level therefore has potential [2].We have previously established the structure and coordinating capacity of 1,3-dimethyl-2,4-dioxo-R-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium (where R = phenyl or p-bromophenyl) in relation to molecular iodine [3].The studies reported here addressed the bromides and diiodobromides of organic cations based on 1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium.The aim of the present work was to prepare complexes of the bromides of 1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium derivatives with molecular iodine and study their stabilities and antimicrobial activities. = R 3 = H -1,3-dimethyl-2,4-dioxo-5,6,7-triphenyl-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide (I) and diiodobromide (I¢); R 1 = R 2 = H, R 3 = Br -5,6-diphenyl,7-(p-bromophenyl)-1,3-dimethyl-2,4-dioxo-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide (II) and diiodide (II¢); R 1 = H, R 2 = R 3 = Br -5-phenyl-6,7-bis(p-bromophenyl)-1,3-dimethyl-2,4-dioxo-1H,2H,3H, 4H-pyrido[4,3-d]pyrimidinium bromide (III) and diiodide (III¢); R 1 = R 2 = R 3 = Br -5,6,7-tri(p-bromophenyl)-1,3-dimethyl-2,4-dioxo-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide (IV) and diiodide (IV¢); R 1 = H, R 2 = R 3 = OCH 3 -6,7-bis(4-methoxyphenyl)-1,3-dimethyl-2,4-dioxo-5-phenyl-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide (V) and diiodide (V¢); R 1 = H, R 2 = R 3 = NO 2 -6,7-bis(4-nitrophenyl)-1,3-dimethyl-2,4-dioxo-5-phenyl-1H,2H,3H,4H-pyrido[4,3-d]pyrimidinium bromide (VI) and diiodide (VI¢).

Phenyl and p bromophenyl substituted 1H,2H,3H,4H pyrido[4,3 d]pyrimidinium diiodobro mides have been identified and determined by capillary zone electrophoresis on an unmodified quartz capil lary. It has been found that an increase in the number of bromine atoms in the structure of 1H,2H,3H,4H pyrido[4,3 d]pyrimidinium derivatives consecutively decreases the electrophoretic mobility of the cations. The developed method makes possible the determination pyrido[4,3 d]pyrimidinium derivatives in the con centration range (0.03-0.25) mM with the c min (3.1-10.0) μM.