Design, Synthesis, and Structure–Activity Relationship of 2-(Piperazin-1-yl)quinazolin-4(3<i>H</i>)-one Derivatives as Active Agents against <i>Toxoplasma gondii</i>

A novel series of quinazolin-4(3<i>H</i>)-one derivatives were synthesized using a hybridization strategy that combined the quinazolin-4(3<i>H</i>)-one scaffold, the diarylether fragment, and the piperazine ring. The <i>in vitro</i> activity evaluation of these compounds against <i>Toxoplasma gondii</i> demonstrated that most of this series of compounds showed moderate to good effectiveness, with IC₅₀ values ranging from 5.94 to 102.2 μM. Among the synthesized derivatives, compounds <b>11</b> and <b>18</b> emerged as the most potent inhibitors, significantly reducing the replication rate of <i>T. gondii</i> with IC₅₀ values of 6.33 and 5.94 μM, as well as demonstrated low cytotoxicity with CC₅₀ values of 285 and 59.2 μM, respectively. The structure-activity relationship investigation indicates that the substituent at the <i>N</i>-3 position of the quinazolin-4(3<i>H</i>)-one is important for anti-<i>T. gondii</i> activity while the replacements at the phenyl moiety of the quinazolin-4(3<i>H</i>)-one and at the diarylether fragment cannot improve activity. The invasion and proliferation assay demonstrated that compound <b>11</b> could inhibit both parasite invasion and replication ability. Further investigation of the <i>in vitro</i> efficacy revealed irreversible action of compound <b>11</b> against <i>T. gondii</i>. <i>In vivo</i> investigations conducted within a murine model of acute infection revealed that compounds <b>11</b> and <b>18</b> exhibited a remarkable capacity to significantly diminish the parasitic load in comparison to the control group while also extending the survival duration of the subjects. These results underscore the potential of compound <b>11</b> as a candidate for further exploration in the development of antitoxoplasmosis therapies.