Antimicrobial Investigation of Phthalimide and N-Phthaloylglycine Esters: Activity, Mechanism of Action, Synergism and Ecotoxicity

Motivated by the search for novel antimicrobials against opportunistic resistant pathogens and based on the reported antimicrobial activity of phthalimides, two series of phthalimide and <i>N</i>-phthaloylglycine esters were designed to investigate whether the addition of butyl and aryl groups enhances their antimicrobial properties. Thus, in vitro antimicrobial activity, antifungal mechanism of action, effect combined with Chloramphenicol, in silico/vitro toxicity, and a docking molecular were studied. Phthalimide and <i>N</i>-phthaloylglycine aryl esters were obtained in yields of 75-98%. Phthalimide aryl ester <b>3b</b> (R = Me) showed the best results against Gram-(+) and Gram-(-) bacteria, <i>S. aureus</i> and <i>P. aeruginosa</i>, respectively, and yeast fungi, <i>C. tropicalis</i> and <i>C. albicans</i>, with MIC values equal to 128 µg·mL^-1. Regarding the antifungal mechanism of action on <i>C. albicans</i>, the MIC values of compound <b>3b</b> changed from 128 to 1024 µg·mL^-1 in the presence of ergosterol. Furthermore, compound <b>3b</b> showed synergy with Chloramphenicol against <i>P. aeruginosa</i>, with a FICI value equal to 0.5. Finally, the four most promising compounds had their in silico/vitro toxicity evaluated, which showed moderate toxicity to non-toxicity on <i>Artemia salina</i> larvae. With the exception of Chloramphenicol, all selected compounds, including Fluconazole, are potentially hepatotoxic, but they were predicted not to cause skin sensitization, suggesting a potential application for topical use. Molecular docking revealed that compound <b>3b</b> exhibits superior binding affinity and stability with the 50S ribosomal subunit (-92.69 kcal·mol^-1) compared to Chloramphenicol, and a unique π-sulfur interaction with CYP51, suggesting its potential as a dual-action antibacterial and antifungal candidate against resistant pathogens.