Design and Synthesis of Triazole-Based p-tert-Butylcalix[4]Arene Conjugates and Evaluation of Their Antimicrobial, Antibiofilm, and Anti-Quorum-Sensing Activities.

Macrocyclic calix[n]arenes have many applications, with diverse structures that can easily be functionalized either on upper or lower rims, mostly to impart solubility and improve biological activities. In this study, triazole-based p-tert-butylcalix[4]arene conjugates (AT10a and AT10b) and their p-tert-butylphenol analogs (AT10b and AT11b) were synthesized in good yields and characterized using ¹³C NMR and ¹H NMR experiments. The compounds were evaluated for their antimicrobial (AM) activity against Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis, Listeria monocytogenes), Gram-negative bacteria (Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa), and fungi (Candida albicans, Candida tropicalis), and minimal/minimum inhibitory concentration (MIC) values varied from 19 to 2500 µg/mL. The AM activities of the compounds were good against most of the strains, with S. aureus, L. monocytogenes, and C. albicans being the most susceptible. The compounds inhibited violacein synthesis in Chromobacterium violaceum CV12472 and MIC and sub-MIC concentrations. AT10a and AT11a all showed 100% inhibition at MIC and 1/2 MIC concentrations, whereas compound AT10b and compound AT11b had 85.1% ± 2.1% and 90.7% ± 1.2% inhibitions at 1/2 MIC. The compounds inhibited quorum sensing (QS) against C. violaceum CV026 at MIC and 1/2 MIC, with AT11a being the most active with inhibition diameters of 18.50 ± 0.75 mm (MIC) and 11.50 ± 0.47 mm (1/2 MIC). QS inhibition indicates that the compounds could disrupt communication and coordinated behavior in bacteria. The compounds inhibited swarming and swimming motilities against P. aeruginosa PA01 at MIC and sub-MIC concentrations, implying that they can reduce spread of bacteria and cross-infections through surface colonization. The compounds showed concentration-dependent biofilm inhibition against a range of pathogenic bacteria at MIC and sub-MIC. S. aureus, L. monocytogenes, and S. typhi biofilms were most susceptible to the compounds compared to the others. Inhibition of biofilm is an indication of possible eradication of resistance in bacteria. The results suggest that triazole-based calixarene derivatives are suitable scaffolds for the development of good AMs, which could quench cell-to-cell signaling and attenuate virulence factors in bacteria.