Synthesis, Characterization and In Vitro Antibacterial Evaluation of Novel 4-(1-(Pyrimidin-4-yl)Ethyl)-12H-Pyrimido[4′,5′:5,6][1,4]Thiazino[2,3-b]Quinoxaline Derivatives

A new methodology for the synthesis of 4-(1-(pyrimidin-4-yl)ethyl)-12H-pyrimido[4 ',5 ':5,6][1,4]thiazino[2,3-b]quinoxaline derivatives 5a-g was introduced. Condensation of 5-bromo-4-[1-(5-bromo-2,6-dichloropyrimidin-4-yl)ethyl]-2-chloro-6-methylpyrimidine 2 and 3-aminoquinoxaline-2-thiol 3 gave either regioisomers 4 or 4 '. The computational and spectral data of both regioisomers confirmed the occurrence of the S/N type Smiles rearrangement during the course of the reaction. Treatment of the foregoing compound with various secondary amines gave several new 4-(1-(pyrimidin-4-yl)ethyl)-12H-pyrimido[4 ',5 ':5,6][1,4]thiazino[2,3-b]quinoxaline derivatives 5a-g. The newly synthesized compounds were evaluated for their potential antibacterial activity and the results exhibit two of the derivatives are moderately valuable compounds in comparison with three reference drugs.