Pyrrolopyrimidine vs Imidazole-Phenyl-Thiazole Scaffolds in Nonpeptidic Dimerization Inhibitors of Leishmania infantum Trypanothione Reductase

Abstract

Disruption of protein-protein interactions of essential oligomeric enzymes by small molecules represents a significant challenge. We recently reported some linear and cyclic peptides derived from an α-helical region present in the homodimeric interface of Leishmania infantum trypanothione reductase (Li-TryR) that showed potent effects on both dimerization and redox activity of this essential enzyme. Here we describe our first steps towards the design of non-peptidic small-molecule Li-TryR dimerization disruptors using a proteomimetic approach. The pyrrolopyrimidine and the 5-6-5 imidazole-phenyl-thiazole α-helix-mimetic scaffolds were suitably decorated with substituents that could mimic three key residues (K, Q and I) of the linear peptide prototype (PKIIQSVGIS-Nle-K-Nle). Extensive optimization of previously described synthetic methodologies was required. A library of 15 compounds bearing different hydrophobic alkyl and aromatic substituents was synthesized. The imidazole-phenyl-thiazole-based analogues outperformed the pyrrolopyrimidine-based derivatives in both inhibiting the enzyme and killing extracellular and intracellular parasites in cell culture. The most active imidazole-phenyl-thiazole compounds 3e and 3f inhibit Li-TryR and prevent growth of the parasites at low micromolar concentrations similar to those required by the peptide prototype. The intrinsic fluorescence of these compounds inside the parasites visually demonstrates their good permeability in comparison with previous peptide-based Li-TryR dimerization disruptors.

Efficient Dimerization Disruption of Leishmania infantum Trypanothione Reductase by Triazole-phenyl-thiazoles

“…In this regard, we recently disclosed the results of our first steps toward nonpeptide disruptors of Li TryR dimerization with promising leishmanicidal activity by an α-helical mimetic approach. 30 Among the reported proteomimetic scaffolds, 31 − 33 the pyrrolopyrimidine 34 and the 5-6-5 imidazole-phenyl-thiazole 35 cores were selected to dictate the spatial orientations of the side chains of three key residues (K2, Q5, and I9) in the linear peptide prototype 1 . Imidazole-based compounds 2 and 3 ( Figure 1 ), bearing a naphthalene or a biphenyl polyaromatic R 3 substituent to mimic the hydrophobic isoleucine residue, emerged as potent inhibitors of the Li TryR oxidoreductase activity, while pyrrolopyrimidines were shown to be much less active.…”

Small Molecule–Peptide Conjugates as Dimerization Inhibitors of Leishmania infantum Trypanothione Disulfide Reductase

“…Structural cavities in Li TryR dimer and monomer were calculated using the Computed Atlas of Surface Topography of proteins (CASTp) web server [ 32 ] and a probe radius of 1.4 Å. Molecular dynamics simulations were run in the AMBER force field, as described previously for Li TryR dimer and complexes [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. The molecular graphics program PyMOL (v. 1.8, Schrödinger, 2015) was employed for molecular editing, visualization, and figure preparation.…”

“… ( A ) An illustration of the Li TryR dimer (PDB entry 6I7N [ 27 ]) showing the large channel (yellow) connecting the NADPH entry site to the interfacial cavity [ 28 ], as calculated by the CASTp web server [ 32 ]; ( B ) an illustration of a Li TryR monomer showing a similar channel (yellow, 2016 Å 2 , 2550 Å 3 ) plus a second one (green, 129 Å 2 , 125 Å 3 ) that makes up the putative target site for the dimer-disrupting peptides and SMPCs; ( C ) theoretical model of the complex between prototype peptide TRL38 (C atoms in grey) and a Li TryR monomer (rainbow-colored illustration, with N - and C-termini in blue and red, respectively). …”

“…All these peptides and peptidomimetics required attachment to cell-penetrating peptides to allow their cellular uptake and subsequent killing of the parasites in cell culture [ 25 , 26 ]. To overcome the unfavorable drug-like properties of these early prototypes, our efforts were then directed towards the design of small molecules (pyrrolopyrimidine-, imidazole-, and triazole-phenyl-thiazole scaffolds) endowed with high potency and more favorable pharmacokinetic characteristics [ 27 , 28 ]. Nonetheless, our interest in peptide-based compounds did not wane because these types of compounds are gaining momentum as innovative therapies against different diseases, including leishmaniasis [ 29 , 30 ], due to their biocompatibility, versatility, low toxicity, and concise synthesis [ 30 , 31 ].…”

Recent Advancement in the Search of Innovative Antiprotozoal Agents Targeting Trypanothione Metabolism

“…Despite showing weak selectivity on parasite, the most promising imidazole‐phenyl‐thiazole ( 41 , Figure 9, Table 4) caused Li TR inhibition and antiparasitic effects on both forms of L. infantum at similar concentrations, suggesting TR as major target. Unfortunately, attempts to co‐crystalize these compounds within Li TR failed, while crystallographic studies were performed on a much less potent TRI lacking effect on TR dimerization [46a] …”