Employing a simple synthetic protocol, a series of highly effective halogen-substituted imidazole-thiosemicarbazides with anti-Toxoplasma gondii effects against the RH tachyzoites, much better than sulfadiazine, were obtained (IC50s 10.30-113.45 µg/mL vs. ~2721.45 µg/mL). The most potent of them, 12, 13, and 15, blocked the in vitro proliferation of T. gondii more potently than trimethoprim (IC50 12.13 µg/mL), as well. The results of lipophilicity studies collectively suggest that logP would be a rate-limiting factor for the anti-Toxoplasma activity of this class of compounds.
Keywords: anti-Toxoplasma gondii activity; cytotoxicity; selectivity ratio; structure-activity relationship (SAR) analysis; thiosemicarbazides.