title: The "racemic approach" in the evaluation of the enantiomeric NorA efflux pump inhibition activity of 2-phenylquinoline derivatives.
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 1-4 previously 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)+25mM formic acid, 12.5mM diethylamine), repeated consecutive injections of 1 allowed the isolation of sufficient amount of its enantiomers (2.6mg and 2.8mg, for (R)-1 and (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)-1 enantiomer 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.
authors.affiliation: Department of Pharmaceutical Sciences, Section of Chemistry and Technology of Drugs, University of Perugia, via del Liceo 1, 06123 Perugia, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Carotti
authors.affiliation: Department of Pharmaceutical Sciences, Section of Chemistry and Technology of Drugs, University of Perugia, via del Liceo 1, 06123 Perugia, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Ianni
authors.affiliation: Department of Pharmaceutical Sciences, Section of Chemistry and Technology of Drugs, University of Perugia, via del Liceo 1, 06123 Perugia, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Sabatini
authors.affiliation: Department of Physics and Geology, University of Perugia, Via Pascoli 1, 06123 Perugia, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Di Michele
authors.affiliation: Department of Pharmaceutical Sciences, Section of Chemistry and Technology of Drugs, University of Perugia, via del Liceo 1, 06123 Perugia, Italy. Electronic address: roccaldo.sardella@unipg.it.
authors.forename: Roccaldo
authors.initials: R
authors.lastname: Sardella
authors.affiliation: John D. Dingell Department of Veterans Affairs Medical Centre and the Department of Internal Medicine, Division of Infectious Diseases, School of Medicine, Wayne State University, Detroit, MI 48201, United States.
authors.forename: Glenn W
authors.initials: GW
authors.lastname: Kaatz
authors.affiliation: Department of Analytical Chemistry, University of Vienna, Währinger Strasse 38, 1090 Vienna, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lindner
authors.affiliation: Department of Pharmaceutical Sciences, Section of Chemistry and Technology of Drugs, University of Perugia, via del Liceo 1, 06123 Perugia, Italy.
authors.forename: Violetta
authors.initials: V
authors.lastname: Cecchetti
authors.affiliation: Department of Pharmaceutical Sciences, Section of Chemistry and Technology of Drugs, University of Perugia, via del Liceo 1, 06123 Perugia, Italy.
authors.forename: Benedetto
authors.initials: B
authors.lastname: Natalini
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors*; D001692:Biological Transport / Q000187:drug effects*; D005561:Formates / Q000494:pharmacology; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000037:antagonists & inhibitors*; D011804:Quinolines / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000378:metabolism; D013237:Stereoisomerism
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D005561:Formates; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011804:Quinolines; C541577:2-phenylquinoline; C030544:formic acid; C075040:NorA protein, Staphylococcus
keywords: Absolute configuration; Antibacterial agents; Cinchona alkaloid-derived zwitterionic chiral stationary phases; Electronic circular dichroism; Small-scale preparative enantioresolution