Synthesis, characterization and antiamoebic activity of 1-(thiazolo[4,5-b]quinoxaline-2-yl)-3-phenyl-2-pyrazoline derivatives

A new series of 1-N-thiocarboxamide-3-phenyl-2-pyrazolines 1–6 was synthesized by cyclization of different Mannich bases with unsubstituted thiosemicarbazide. The reaction of cyclized pyrazoline derivatives 1–6 with 2,3-dichloroquinoxaline afforded the title compounds 7–12. The structures of the new compounds were confirmed by elemental analyses as well as 1H, 13C NMR, IR and electronic spectral data. The HM1:IMSS strain of Entamoeba histolytica parasite was cultured in vitro and the sensitivity of the parasite to the synthesized compounds was evaluated using the microdilution method. Among all the pyrazoline derivatives 1–6, none was found to be a better inhibitor as compared to the reference drug, metronidazole. The quinoxaline derivatives, 9, 11 and 12 were found to be potent inhibitors of E. histolytica.