Pharmacophore\nEstablishment and Optimization\nof Saturated 1,6-Naphthyridine-Fused Quinazolinones that Inhibit Meningoencephalitis-Causing Naegleria fowleri

Primary amoebic meningoencephalitis (PAM) is a human\nbrain infection\ncaused by Naegleria fowleri with a\n97% mortality rate. Quinazolinones resulting from a Mannich-coupled\ndomino rearrangement were recently identified as inhibitors of the\namoeba. Herein, we resolved the effective concentrations for 25 pilot\ncompounds and then, using the Mannich protocol and a key late-stage, <i>N</i>-demethylation/functionalization, we synthesized 53 additional\nanalogs to improve potency, solubility and microsomal stability. We\nestablished an antiamoebic quinazolinone pharmacophore, culminating\nin (±)-<i>trans</i>-<b>57b</b> which featured\nthe best combination of potency, selectivity index, solubility, and\nmicrosomal stability. Enantiomeric separation afforded (4a<i>S</i>,13b<i>R</i>)-<b>57b</b> (<b>BDGR-20237</b>) with a 41-fold potency advantage over its enantiomer. ADME and\nmouse pharmacokinetic profiling for <b>BDGR-20237</b> revealed\nhigh brain penetrance but a limited half-life which did not statistically\nenhance the mouse survival in a pilot efficacy study. The pharmacophoric\nmodel, supported by 88 quinazolinones, several of which exhibit subnanomolar\npotency, will guide further scaffold optimization.