Research paper Discovery of novel quaternary ammonium compounds based on quinuclidine-3-ol as new potential antimicrobial candidates Linda Bazina a, 1 , Ana Maravi c b, 1 , Lucija Krce c , Barbara Soldo a , Renata Od zak a , Viljemka Bu cevi c Popovi c a , Ivica Aviani c , Ines Primo zi c d , Matilda Sprung a, * a University of Split, Faculty of Science, Department of Chemistry, R. Boskovica 33, 21 000, Split, Croatia b University of Split, Faculty of Science, Department of Biology, R. Boskovica 33, 21 000, Split, Croatia c University of Split, Faculty of Science, Department of Physics, R. Boskovica 33, 21 000, Split, Croatia d University of Zagreb, Faculty of Science, Department of Chemistry, Horvatovac 102a, 10 000, Zagreb, Croatia article info Article history: Received 13 November 2018 Received in revised form 6 December 2018 Accepted 11 December 2018 Available online 12 December 2018 Keywords: Quaternary ammonium compounds Antimicrobial activity Quinuclidine Cytotoxicity abstract Quaternary ammonium compounds (QACs) are amphiphilic molecules displaying a broad-spectrum of antibacterial activity. QACs are commonly used antiseptics in industrial, home and hospital settings. Given the emergence of the QAC-resistant bacteria, there is an urgent need to design new QACs with good antimicrobial activity, able to escape the host resistance mechanism. Therefore, a series of QACs derived from quinuclidine-3-ol and an alkyl chain of variable length (QOH-C3 to -C14), was designed and synthesized. The antimicrobial potential of the new monoquaternary QACs was surveyed against seventeen strains of emerging food spoilage and pathogenic microorganisms, including clinical multidrug-resistant ESKAPE isolates. The QOH-C14 proved to have the strongest antimicrobial activity. It was highly active against all pathogens tested, particularly against the Gram-positive bacteria with minimal inhibitory concentrations (MICs) ranging from 0.06 to 3.9 mg/mL, and fungi exerting the MIC 90 between 0.12 and 3.9 mg/mL. The potency of QOH-C14, confirmed that alkyl chains are an important part of the structure with their lengths playing a critical role in bioactivity of these compounds. The atomic force microscopy images show the disruption of a cell membrane upon the treatment with QOH-C14. These results were additionally confirmed by flow cytometry and fluorescence microscopy. A relatively low toxicity toward healthy human cells underline that QOH-C14 has a potential as new QAC antimi- crobial candidate. © 2018 Elsevier Masson SAS. All rights reserved. 1. Introduction Quaternary ammonium compounds (QACs) have long ago been recognised and still are some of the most powerful antimicrobial agents. It has been proposed that their mode of action is based on electrostatic interactions between a positively charged QACs nitrogen and a negatively charged bacterial cell membrane that leads to membrane perforation and ultimately cell death [1]. Therefore, these agents are considered as antimicrobials with a broad-spectrum activity [2]. Given their good antimicrobial po- tential, QACs are often used as antiseptics in hospitals and homes worldwide [3]. QACs such as benzalkonium chloride (BAC), dime- thyldodecylammonium chloride and cetylpyridinium chloride are among the most used antiseptics in many pharmaceutical and personal care products [4]. Considering their mode of action, it was originally believed that the bacterial resistance toward QACs is not possible [2]. However, qac genes encoding series of efflux pumps have recently been discovered [4]. More research on this subject has shown that sub- lethal concentrations of QACs in the environment triggers not only the qac-dependent resistance but also yet another unknown mechanism [5]. Therefore, development of new QACs able to escape bacterial resistance and identification of new resistance Abbreviations: QACs, quaternary ammonium compounds; AMPs, antimicrobial peptides; PI, propidium iodide; PBS, phosphate buffer saline; DMSO, dimethyl sulfoxide; MHB, Muller-Hinton broth; MIC, minimal inhibitory concentration; MBC, minimal bactericidal concentration; AFM, atomic force microscopy; BAB, benzyl- dodecyldimethylammonium bromide; BAC, benzalkonium chloride. * Corresponding author. E-mail addresses: linbaz@pmfst.hr (L. Bazina), amaravic@pmfst.hr (A. Maravic), lkrce@pmfst.hr (L. Krce), barbara@pmfst.hr (B. Soldo), rodzak@pmfst.hr (R. Odzak), viljemka@pmfst.hr (V.B. Popovic), iaviani@pmfst.hr (I. Aviani), ines. primozic@chem.pmf.hr (I. Primozic), msprung@pmfst.hr (M. Sprung). 1 These authors contributed equally to this work. Contents lists available at ScienceDirect European Journal of Medicinal Chemistry journal homepage: http://www.elsevier.com/locate/ejmech https://doi.org/10.1016/j.ejmech.2018.12.023 0223-5234/© 2018 Elsevier Masson SAS. All rights reserved. European Journal of Medicinal Chemistry 163 (2019) 626e635