Design and synthesis of new quinazolinone derivatives: investigation of antimicrobial and biofilm inhibition effects

Abstract

New quinazolin-4-ones 9-32 were synthesized in an attempt to overcome the life-threatening antibiotic resistance phenomenon. The antimicrobial screening revealed that compounds 9, 15, 16, 18, 19, 20 and 29 are the most broad spectrum antimicrobial agents in this study with safe profile on human cell lines. Additionally, compounds 19 and 20 inhibited biofilm formation in Pseudomonas aeruginosa, which is regulated by quorum sensing system, at sub-minimum inhibitory concentrations (sub-MICs) with IC₅₀ values 3.55 and 6.86 µM, respectively. By assessing other pseudomonal virulence factors suppression, it was found that compound 20 decreased cell surface hydrophobicity compromising bacterial cells adhesion, while both compounds 19 and 20 curtailed the exopolysaccharide production which constitutes the major component of the matrix binding biofilm components together. Also, at sub-MICs Pseudomonas cells twitching motility was impeded by compounds 19 and 20, a trait which augments the cells pathogenicity and invasion potential. Molecular docking study was performed to further evaluate the binding mode of candidates 19 and 20 as inhibitors of P. aeruginosa quorum sensing transcriptional regulator PqsR. The achieved results demonstrate that both compounds bear promising potential for discovering new anti-biofilm and quorum quenching agents against Pseudomonas aeruginosa without triggering resistance mechanisms as the normal bacterial life cycle is not disturbed.

Keywords: Pseudomonas aeruginosa; Antimicrobial; Biofilm inhibition; Quinazolinones.

Fig. 1

2-Alkyl-4-quinolone (AQ) molecules acting as autoinducers of pqs system in Pseudomonas aeruginosa

Fig. 2

Examples of 4(3H)-quinazolinones hybrids having antimicrobial and anti-biofilm effect

Fig. 3

Antibacterial drugs containing alicyclic amines

Fig. 4

Rational design of our candidates 9–32

Scheme 1

Synthesis of target compounds 9–32 and key intermediates

Fig. 5

Biofilm inhibition assay results depicting the effect of compounds 19 and 20 on the aggregation of Gram (-) P. aeruginosa ATCC 27953, in comparison to ciprofloxacin as positive control

Fig. 6

Hydrophobicity index of Pseudomonas aeruginosa ATCC 27953 as affected by different concentrations of compounds 19, 20. One way ANOVA test (with Tukey’s correction for multiple comparisons) shows significant difference between control and each test compound. Mean of 3 independent experiments ± SD triplicates, the asterisk indicates the significance of P-value < 0.0001

Fig. 7

Twitching motility reduction of Pseudomonas aeruginosa ATCC 27953 via different concentrations of compounds 19, 20. (I) Comparison of twitching motility zones in comparison to the negative control (DMF). One way ANOVA test (with Tukey’s correction for multiple comparisons) shows significant difference between control and test compounds. Mean of 3 independent experiments ± SD triplicates, the asterisk indicates the significance of P-value < 0.0001. (II) Illustration of motility under the influence of the addition of compounds 19, 20 at (a) 1/4 concentration of MIC, (b) 1/2 concentration of MIC, and (c) MIC

Fig. 8

A Superimposition of the co-crystalized (cyan) and the docking pose (pink) of M64 in the LBD PqsR of P. aeruginosa with RMSD of 0.5036 Å. B Binding of the co-crystalized inhibitor M64 in the LBD of PqsR of P. aeruginosa

Fig. 9

2D diagram (A) and 3D representation (B) illustrating the interactions of compound 19 within the active site of the LBD of PqsR of P. aeruginosa

Fig. 10

2D diagram (A) and 3D representation (B) illustrating the interactions of compound 20 within the active site of the LBD of PqsR of P. aeruginosa