N-substituted-4-(pyridin-4-ylalkyl)piperazine-1-carboxamides and related compounds as Leishmania CYP51 and CYP5122A1 inhibitors

CYP5122A1, an enzyme involved in sterol biosynthesis in Leishmania, was recently characterized as a sterol C4-methyl oxidase. Screening of a library of compounds against CYP5122A1 and CYP51 from Leishmania resulted in the identification of two structurally related classes of inhibitors of these enzymes. Analogs of screening hit N-(3,5-dimethylphenyl)-4-(pyridin-4-ylmethyl)piperazine-1-carboxamide (4a) were generally strong inhibitors of CYP51 but were less potent against CYP5122A1 and typically displayed weak inhibition of L. donovani promastigote growth. Analogs of screening hit N-(4-(benzyloxy)phenyl)-4-(2-(pyridin-4-yl)ethyl)piperazine-1-carboxamide (18a) were stronger inhibitors of both CYP5122A1 and L. donovani promastigote proliferation but also remained selective for inhibition of CYP51. Two compounds in this series, N-(4-((3,5-bis(trifluoromethyl)benzyl)oxy)phenyl)-4-(2-(pyridin-4-yl)ethyl)piperazine-1-carboxamide (18e) and N-(4-((3,5-di-tert-butylbenzyl)oxy)phenyl)-4-(2-(pyridin-4-yl)ethyl)piperazine-1-carboxamide (18i) showed modest selectivity for inhibiting L. donovani promastigote proliferation compared to J774 macrophages and were effective against intracellular L. donovani with EC₅₀ values in the low micromolar range. Replacement of the 4-pyridyl ring present in 18e with imidazole resulted in a compound (4-(2-(1H-imidazol-1-yl)ethyl)-N-(4-((3,5-bis(trifluoromethyl)benzyl)oxy)phenyl)piperazine-1-carboxamide, 18p) with approximately fourfold selectivity for CYP5122A1 over CYP51 that inhibited both enzymes with IC₅₀ values ≤ 1 µM, although selective potency against L. donovani promastigotes was lost. Compound 18p also inhibited the proliferation of L. major promastigotes and caused the accumulation of 4-methylated sterols in L. major membranes, indicating that this compound blocks sterol demethylation at the 4-position in Leishmania parasites. The molecules described here may therefore be useful for the future identification of dual inhibitors of CYP51 and CYP5122A1 as potential antileishmanial drug candidates and as probes to shed further light on sterol biosynthesis in Leishmania and related parasites.