Title
The “racemic approach” in the evaluation of the enantiomeric NorA efflux pump inhibition activity of 2-phenylquinoline derivatives
Author
Andrea Carotti, Federica Ianni, Stefano Sabatini, Alessandro Di Michele, Roccaldo Sardella, Glenn W. Kaatz, Wolfgang Lindner, Violetta Cecchetti, Benedetto Natalini
Year
2016
Journal
Journal of Pharmaceutical and Biomedical Analysis
Abstract
Among the mechanisms adopted by bacteria, efflux pumps (EPs) have been recognized as being significantly involved in contributing to resistance to commonly used antibacterial agents. However, little is known about their three-dimensional structures or the steric requirements for their inhibition. Lack of such knowledge includes NorA, one of the most studied Staphylococcus aureus EPs. In the present study, the use of two commercialized Cinchona alkaloid-based zwitterionic chiral stationary phases allowed the enantioseparation of four 2-((2-(4-propoxyphenyl)quinolin-4-yl)oxy)alkylamines 1–4previously found to be potent S. aureus NorA efflux pump inhibitors when tested as racemates. In the identified optimal polar-ionic conditions (MeOH/THF/H2O-49/49/2 (v/v/v) + 25 mM formic acid, 12.5 mM diethylamine), repeated consecutive injections of 1allowed the isolation of sufficient amount of its enantiomers (2.6 mg and 2.8 mg, for (R)-1and (S)-1, respectively) and then to evaluate their ability to inhibit the S. aureus NorA efflux pump. The biological evaluation highlighted the main contribution of the (R)-1enantiomer to both the EtBr efflux inhibition and synergistic effect with against SA-1199B (norA+/A116E GrlA) respect to the racemate activity. The comparison between the experimental electronic circular dichroism and the time-dependent density functional theory calculations spectra of the two isolated enantiomeric fractions allowed for all compounds a clear and easy assignment of the enantiomeric elution order.
Instrument
J-810
Keywords
Circular dichroism, Absolute configuration, Pharmaceutical