Effect of the position of a methoxy substituent on the antimicrobial activity and crystal structures of 4-methyl-1,6-diphenylpyrimidine-2(1H)-selenone derivatives

Derivatives of pyrimidine-2(1H)-selenone are a group of compounds with very strong antimicrobial activity. In order to study the effect of the position of the methoxy substituent on biological activity, molecular geometry and intermolecular interactions in the crystal, three derivatives were prepared and evaluated with respect to their antimicrobial activities, and their crystal structures were determined by X-ray diffraction. The investigated compounds, namely, 1-(X-methoxyphenyl)-4-methyl-6-phenylpyrimidine-2(1H)-selenones (X = 2, 3 and 4 for 1, 2 and 3, respectively), C₁₈H₁₆N₂OSe, showed very strong activity against selected strains of Gram-positive bacteria and fungi. Two compounds, 1 and 2, crystallize in the monoclinic space group P2₁/c, while 3 crystallizes in the space group P2₁/n; 1 has two molecules in the asymmetric unit and the other two (2 and 3) have one molecule. The geometries of the investigated compounds differ slightly in the mutual orientations of the aromatic and pyrimidineselenone rings. The O atom in 1 stabilizes the conformation of the molecules via intramolecular C-H...O hydrogen bonding. The packing of molecules is determined by weak C-H...N and C-H...Se intermolecular interactions and additionally in 1 and 2 by C-H...O intermolecular interactions. The introduction of the methoxy substituent results in greater selectivity of the investigated compounds.