Rational Development of 4‑Aminopyridyl-Based Inhibitors Targeting Trypanosoma cruzi CYP51 as Anti-Chagas Agents

A new series of 4-aminopyridyl-based lead inhibitors targeting Trypanosoma cruzi CYP51 (<i>Tc</i>CYP51) has been developed using structure-based drug design as well as structure–property relationship (SPR) analyses. The screening hit starting point, LP10 (<i>K</i><sub>D</sub> ≤ 42 nM; EC<sub>50</sub> = 0.65 μM), has been optimized to give the potential leads <b>14t</b>, <b>27i</b>, <b>27q</b>, <b>27r</b>, and <b>27t</b>, which have low-nanomolar binding affinity to <i>Tc</i>CYP51 and significant activity against T. cruzi amastigotes cultured in human myoblasts (EC<sub>50</sub> = 14–18 nM for <b>27i</b> and <b>27r</b>). Many of the optimized compounds have improved microsome stability, and most are selective against human CYPs 1A2, 2D6, and 3A4 (<50% inhibition at 1 μM). A rationale for the improvement in microsome stability and selectivity of inhibitors against human metabolic CYP enzymes is presented. In addition, the binding mode of <b>14t</b> with the Trypanosoma brucei CYP51 (<i>Tb</i>CYP51) orthologue has been characterized by X-ray structure analysis.