Rational design of amphiphilic pyrrolidinium derivatives: structure–activity correlation and alkyl chain tuning for superior antimicrobial activity

A novel amphiphilic pyrrolidine derivatives, 1-alkyl-1-(2-(hexyl carbamoyloxy)ethyl)pyrrolidinium bromides (CPS-n-6, where n = 12, 14, 16, and 18), were synthesized and characterized. Comprehensive investigations demonstrated that the amphiphiles synthesized exhibit multifunctional properties and meet stringent biomedical criteria. CPS-n-6 possess membranotropic activity and are capable of forming mixed lipid/surfactant bilayers, imparting a positive surface charge and stabilizing biological membranes. Surfactant-based supramolecular systems exhibit the properties of micellar nanocontainers, demonstrate enhanced solubilization capacity toward hydrophobic probe Orange OT and antibiotic amphotericin B, and are characterized by nanoscale dimensions of 2-10 nm along with a high positive zeta potential of up to +89 mV. Encapsulation of amphotericin B into CPS-n-6 results in a significant enhancement of its antifungal activity against C. albicans. The amphiphiles also exhibit high antimicrobial activity against both Gram-positive and Gram-negative bacteria, including methicillin resistant strains. The most pronounced effect was observed for the dodecyl and tetradecyl homologues, which significantly surpassed the activity of amoxicillin and ciprofloxacin. Investigation of the mechanisms of antimicrobial action revealed that CPS-n-6 do not disrupt the cell wall of S. aureus at the MIC and MBC; however, they impair cytoplasmic membrane permeability and induce membrane depolarization, particularly in the case of CPS-12-6. The amphiphiles demonstrated moderate hemotoxicity (HC50 = 37-50 µM), which showed a weak dependence on the alkyl tail length. CPS-14-6 exhibited the highest selectivity against S. aureus (SI = 39), whereas CPS-18-6 was markedly less selective (SI = 2), indicating a higher risk of hemolysis at a comparable MIC.