Synthesis and evaluation of febrifugine derivatives as anticoccidial agents

A series of new febrifugine derivatives with a 4(3H)-quinazolinone scaffold were synthesized and evaluated for their anticoccidial activity both in vitro and in vivo. The targets' in vitro activity against Eimeria tenella was studied using quantitative real-time reverse transcription polymerase chain reaction and Madin-Darby bovine kidney cells. Most of these compounds demonstrated anticoccidial efficacy, with inhibition ratios ranging from 3.3% to 85.7%. Specifically, compounds 33 and 34 showed significant inhibitory effects on the proliferation of E. tenella and exhibited lower cytotoxicity compared to febrifugine. The IC₅₀ values of compounds 33 and 34 were 3.48 and 1.79 μM, respectively, while the CC₅₀ values were >100 μM for both compounds. Furthermore, in a study involving 14-day-old chickens infected with 5 × 10⁴ sporulated oocysts, treatment with five selected compounds (22, 24, 28, 33, and 34), which exhibited in vitro inhibition rate of over 50% at 100 μM, at a dose of 40 mg/kg in daily feed for 8 consecutive days showed that compound 34 possessed moderate in vivo activity against coccidiosis, with an anticoccidial index of 164. Structure-activity relationship studies suggested that spirocyclic piperidine may be a preferable substructure to maintain high effectiveness in inhibiting Eimeria spp., when the side chain 1-(3-hydroxypiperidin-2-yl)propan-2-one was replaced.