Effect of New Analogs of Hexyloxy Phenyl Imidazoline on Quorum Sensing in Chromobacterium violaceum and In Silico Analysis of Ligand-Receptor Interactions

Abstract

The increasing common occurrence of antibiotic-resistant bacteria has become an urgent public health issue. There are currently some infections without any effective treatment, which require new therapeutic strategies. An attractive alternative is the design of compounds capable of disrupting bacterial communication known as quorum sensing (QS). In Gram-negative bacteria, such communication is regulated by acyl-homoserine lactones (AHLs). Triggering of QS after bacteria have reached a high cell density allows them to proliferate before expressing virulence factors. Our group previously reported that hexyloxy phenylimidazoline (9) demonstrated 71% inhibitory activity of QS at 100 μM (IC50 = 90.9 μM) in Chromobacterium violaceum, a Gram-negative bacterium. The aim of the present study was to take 9 as a lead compound to design and synthesize three 2-imidazolines (13–15) and three 2-oxazolines (16–18), to be evaluated as quorum-sensing inhibitors on C. violaceum CV026. We were looking for compounds with a higher affinity towards the Cvi receptor of this bacterium and the ability to inhibit QS. The binding mode of the test compounds on the Cvi receptor was explored with docking studies and molecular dynamics. It was found that 8-pentyloxyphenyl-2-imidazoline (13) reduced the production of violacein (IC50 = 56.38 μM) without affecting bacterial growth, suggesting inhibition of quorum sensing. Indeed, compound 13 is apparently one of the best QS inhibitors known to date. Molecular docking revealed the affinity of compound 13 for the orthosteric site of N-hexanoyl homoserine lactone (C6-AHL) on the CviR protein. Ten amino acid residues in the active binding site of C6-AHL in the Cvi receptor interacted with 13, and 7 of these are the same as those interacting with AHL. Contrarily, 8-octyloxyphenyl-2-imidazoline (14), 8-decyloxyphenyl-2-imidazoline (15), and 9-decyloxyphenyl-2-oxazoline (18) bound only to an allosteric site and thus did not compete with C6-AHL for the orthosteric site.

N-Heterocycles Scaffolds as Quorum Sensing Inhibitors. Design, Synthesis, Biological and Docking Studies

“…Imidazoline 32b was QSI at all concentrations and displayed IC 50 = 65.09 µM. The QS inhibition activity of 32b is comparable to other synthesized bioisosteres [ 21 ]. Imidazoline 32c at 1000 μM afforded 46% activity and compound 32a behaved as an antimicrobial at the latter concentration.…”

“…Furthermore there are reports of its replacement with cyclopentane, cyclopentanol, cyclopentanone, oxazolidinone, benzothiazol and thiadiazol [ 13 ]. Our group reported a substitution with imidazoline and oxazoline in prior studies [ 20 , 21 ]. In the design of the present bioisosteres, the amido group and the lateral chain were conserved but the length of the latter varied.…”

“…Activity as QSI of benzimidazole 18a (85% QS inhibition at 100 µM, IC 50 of 36.67 µM) is comparable than 2-[4-(hexyloxy)phenyl]-4,5-dihidro-1 H -imidazole (65% QS inhibition at 90 µM, IC 50 = 56.38 µM) [ 21 ], more active than 4-nitro-pyridine- N -oxide (active at 100 µM), the best synthetic quorum sensing inhibitor (QSI) in a screening of 27 synthetic compounds and 27 natural extracts [ 11 , 45 ]. However benzimidazole 18a is not QSI like 2-(4′-chlorophenoxy)- N -butanoyl homoserine lactone (IC 50 = 377 nM) [ 7 ].…”

Computational and Biological Evaluation of β-Adrenoreceptor Blockers as Promising Bacterial Anti-Virulence Agents

“…These promising natural-based hits exhibit preferential polar interactions with Trp84, Asp97, Met135, and Ser155, in addition to relevant hydrophobic contacts towards Tyr80, Leu85, Tyr88, Met89, Trp111, Phe115, and Phe126, which have been successfully translated into high biological findings. Comparable residue-wise binding interactions were reported for several chemically synthesized 2-imidazoline/oxazoline-based analogues through molecular docking and dynamics simulations [59]. The compounds predict favourable polar binding contributions for Trp84, Asp97, Tyr88, Ser155, and Pro189 residues with the ligands' 2-imidazoline/oxazoline polar heads.…”

Repurposing α-Adrenoreceptor Blockers as Promising Anti-Virulence Agents in Gram-Negative Bacteria

“…Another study showed promising CviR-based anti-virulence biological activity for flavonoid- and chalcone-based hits, predicting favorable polar interactions with Trp84, Asp97, Met135, and Ser155, as well as non-polar contacts to Tyr80, Leu85, Tyr88, Met89, Trp111, Phe115, and Phe126 [ 59 ]. Comparable residue-wise bindings were also demonstrated for several synthetic oxazoline/2-imidazoline-based derivatives through molecular docking-coupled dynamics simulations [ 60 ]. Similarly, isolates from Passiflora edulis showed the relevant accommodation of the CviR binding site which is mediated through balanced hydrophilic–hydrophobic contacts with Ile57, Tyr80, Tyr84, Leu85, Tyr88, Ile99, Trp111, Phe115, Met135, and Ile153 [ 61 ].…”