Synthesis, Antimicrobial, Anti-Virulence and Anticancer Evaluation of New 5(4 H)-Oxazolone-Based Sulfonamides

Abstract

Since the synthesis of prontosil the first prodrug shares their chemical moiety, sulfonamides exhibit diverse modes of actions to serve as antimicrobials, diuretics, antidiabetics, and other clinical applications. This inspiring chemical nucleus has promoted several research groups to investigate the synthesis of new members exploring new clinical applications. In this study, a novel series of 5(4H)-oxazolone-based-sulfonamides (OBS) 9a-k were synthesized, and their antibacterial and antifungal activities were evaluated against a wide range of Gram-positive and -negative bacteria and fungi. Most of the tested compounds exhibited promising antibacterial activity against both Gram-positive and -negative bacteria particularly OBS 9b and 9f. Meanwhile, compound 9h showed the most potent antifungal activity. Moreover, the OBS 9a, 9b, and 9f that inhibited the bacterial growth at the lowest concentrations were subjected to further evaluation for their anti-virulence activities against Pseudomonas aeruginosa and Staphylococcus aureus. Interestingly, the three tested compounds reduced the biofilm formation and diminished the production of virulence factors in both P. aeruginosa and S. aureus. Bacteria use a signaling system, quorum sensing (QS), to regulate their virulence. In this context, in silico study has been conducted to assess the ability of OBS to compete with the QS receptors. The tested OBS showed marked ability to bind and hinder QS receptors, indicating that anti-virulence activities of OBS could be due to blocking QS, the system that controls the bacterial virulence. Furthermore, anticancer activity has been further performed for such derivatives. The OBS compounds showed variable anti-tumor activities, specifically 9a, 9b, 9f and 9k, against different cancer lines. Conclusively, the OBS compounds can serve as antimicrobials, anti-virulence and anti-tumor agents.

Keywords: anti-virulence; antibiofilm; anticancer; antimicrobial; oxazolone; sulfonamide.

Figure 1

Some drugs containing oxazolone scaffold.

Figure 2

Selected FDA-approved anti-cancer agents containing sulfonamide moiety.

Scheme 1

Synthesis of acid 7.

Scheme 2

Synthesis of the target compounds 9a–k.

Figure 3

Antibiofilm activities of the synthesized compounds. The antibiofilm activities of the synthesized compounds were evaluated at their sub-MIC concentrations to avoid any influence on the bacterial growth. The crystal violet method was used to quantify the inhibition activity of compounds on (A) S. aureus and (B) P. aeruginosa. The synthesized compounds showed variable abilities to inhibit the biofilm formation, however, compounds 9a, 9b and 9f showed the highest abilities to inhibit biofilm formation in both tested bacterial strains. Representative image for the inhibitory effect of compound 9e on the biofilm formation by (C) S. aureus and (D) P. aeruginosa were taken. The formed biofilms were markedly reduced showing scattered thinner layers of bacterial biofilms. (*** = p < 0.001; ** = p < 0.01; * p < 0.05; ns = non-significant).

Figure 4

Selected active synthesized compounds decreased the production of extracellular enzymes. The anti-virulence activities were assessed for the selected compounds 9a, 9b and 9f at their sub-MIC against P. aeruginosa and S. aureus. The three tested compounds significantly diminished the hemolytic activity of (A) S. aureus and (B) P. aeruginosa. Moreover, the tested compounds significantly reduced the production of protease of (C) S. aureus and (D) P. aeruginosa. (*** = p < 0.001, ** = p < 0.01).

Figure 5

Anti-virulence activities of the active synthesized compounds. Selected compounds 9a, 9b and 9f at sub-MIC were tested for their ability to decrease the production of QS-controlled bacterial virulence factors. The tested compounds significantly decreased the production of (A) S. aureus pigment staphyloxanthin and (B) P. aeruginosa pigment pyocyanin. (*** = p < 0.001).

Figure 6

Structure activity relationship for the newly synthesized compounds 9a–k concerning the antibacterial activity.

Figure 7

Apoptotic effect of the active synthesized compounds. Quantification of caspase 3/7 levels was used to assess the apoptotic activities of tested compounds on cancer cells. The tested compounds, particularly 9b, significantly triggered the cancer cells’ apoptosis by increasing the dose. The experiment was conducted in triplicate and the date are shown as mean ± error values. (*** = p < 0.001, ** = p < 0.01).

Figure 8

Docking and binding mode of the ligand; 2-(1,3-dioxo-1,3-dihydro-2H-isoindol-2-yl)ethyl-4-(4-ethoxy [1,1-biphenyl]-4-yl)-4-oxobutanoic acid (yellow) into the active site active site of the Escherichia coli QS protein (PDB: 1ROS). (A) 3D structure of the ligand (yellow), (B) 2D structure of the ligand (yellow).

Figure 9

Docking and binding mode of 9a (blue), 9b (cyan) and 9f (red) into the active site of the Escherichia coli QS protein (PDB: 1ROS). (A) 3D structure of 9a (blue), (B) 2D structure of 9a (blue), (C) 3D structure of 9b (cyan), (D) 2D structure of 9b (cyan) (E) 3D structure of 9f (red), and (F) 2D structure of 9f (red).