2016. 57, 5 – UDC 548.73:546.72:546.18:546.21 2-METHYLPYRIDINIUM 5-(2,4-DINITROPHENYL)-6-OXO-2-THIOXO-1,2,3,6TETRAHYDROPYRIMIDIN-4-OLATE: SYNTHESIS, CRYSTAL STRUCTURE, AND BIOLOGICAL EVALUATION G. Mangaiyarkarasi, G. Sridevi, P. Poornima Devi, D. Kalaivani PG and Research Department of Chemistry, Seethalakshmi Ramaswami College, Tamil Nadu, India E-mail: kalaivbalaj@yahoo.co.in Received January, 27, 2015 The titled complex is synthesized from the ethanolic solutions of 1-chloro-2,4-dinitrobenzene, 2-thiobarbituric acid, and 2-methylpyridine and characterized by spectral and elemental analyses. <...> The single crystal X-ray diffraction results for the complex are compatible with the spectral observations. <...> The titled complex exhibits anticonvulsant activity and reduces all phases of convulsion even at a low dosage. <...> Acute toxicity studies of the complex are performed to understand the safer dose concentration for clinical trials. <...> DOI: 10.15372/JSC20160519 Keywords: carbon-bonded anionic sigma complex, 2-thiobarbituric acid, 1-chloro-2,4dinitrobenzene, single crystal X-ray diffraction studies, anticonvulsant activity, maximal electroshock method. <...> Strong interactions between them result in the formation of anionic sigma complexes [ 1 ]. <...> Generally, ketones, i-diketones, and i-ketoesters form carbon-bonded anionic sigma complexes with nitroaromatics in the presence of tertiary amines [ 2—4]. <...> A series of carbon-bonded anionic sigma complexes have earlier been synthesized in our laboratories by involving chloronitroaromatic compounds and barbituric acid in the presence of tertiary amines [ 5—8]. 2-Thiobarbituric acid is an important class of heterocyclic compounds which possesses a bio-active nucleus and displays complex biological activities, such as antibacterial, sedatives, herbicidal, fungicidal and antiviral [ 9, 10 ]. <...> Since 2-thiobarbituric acid has an active methylene group, an attempt has been made to synthesize a stable carbon-bonded anionic sigma complex with an electron — deficient compound in the presence of tertiary amine. <...> In 2-thiobarbituric acid, two carbonyl groups and one thiocarbonyl group are present but it also forms a similar type of a carbon-bonded anionic sigma complex like barbituric acid which has three carbonyl groups with 1-chloro-2,4-dinitrobenzene (DNCB) in the presence of 2-methylpyridine. <...> This prompted us to synthesize a new type of a carbon-bonded anionic sigma complex of 2-thiobarbituric acid with 1-chloro-2,4-dinitrobenzene (DNCB) and 2-methylpyridine employing the one-pot synthesis guided by the observations that the presence of both pyridine and pyrimidine nuclei in a molecule remarkably increases its <...>