Electrochemical Investigations of Biologically Active 1-(3-Hydroxy-2-pyridyl)-4,4,6-trimethyl-3,4-dihydropyrimidine-2[1H]-thione at Pyrolytic Graphite Electrode

Abstract

Abstract Electrochemical behavior of a biologically active pyridinylpyrimidine derivative, 1-(3-hydroxy-2-pyridyl)-4,4,6-trimethyl-3,4-dihydropyrimidine-2[1H]-thione (1) has been investigated in aqueous phosphate buffers (1.9–10.6) at a pyrolytic graphite electrode (PGE). The oxidation occurred in a single well-defined oxidation peak, Ia, in the pH range 1.9–10.6. In the pH range 4.9–10.6, a reduction peak, IIc, was noticed in the reverse sweep that formed a quasi-reversible couple with peak IIa observed in the subsequent sweep towards positive potentials. The effect of concentration and sweep rate on peak potential and peak current of peak Ia established adsorption of 1 at the surface of PGE. Controlled potential coulometry experiments revealed the 5e− oxidation of 1 in acidic solution and 7e− oxidation in a neutral solution by an EC mechanism. UV–vis spectral and kinetic studies suggested formation of different intermediates in acidic and neutral media. The major product of oxidation at pH 2.7 was characterized as 2,2,4-trimethyl-2H-9-oxa-10-thia-1,4a,5-triazaphenanthrene 10,10-dioxide (6). At physiological pH 7.1, 1-(2,5-dioxo-6-pyridyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-thiol (7a) and 1-(3,6-dioxo-3,6-dihydro-2-pyridyl)-4,4,6-trimethyl-1,4-dihydropyrimidine-2-sulfonic acid (10) were identified as the oxidation products by GC-MS. A mechanism for the electrooxidation of 1 at PGE has also been suggested.