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Quaternary ammonium compounds (QACs) are amphiphilic molecules known for their broadspectrum antibacterial activity. Although they have potent biological potential, they are often highly toxic to living organisms and ecosystems. Recent studies show that the addition of polar groups results in soft QACs that are more susceptible to hydrolysis, and therefore less toxic. [1] The aim of this study was to synthesize the new soft 3-acetamidoquinuclidine (QAc) and 3- benzamidoquinuclidine (QBn) QACs, both of which contain a naturally-derived quinuclidine backbone. [2, 3] The quaternization reactions were carried out using suitable alkyl halide chains of different lengths (12, 14 and 16 C atoms). The antibacterial activity of the new compounds was tested against a panel of Gram- positive and Gram- negative bacteria. We found that the QACs of 3- benzamidoquinuclidine exhibited better antibacterial activity in both bacterial panels (MIC between 3.9 and 62.5 μM) than the QACs of 3- acetamidoquinuclidine, which were active only against Gram-positive bacteria (MIC between 7.8 and 62.5 μM). Because we suspected that the composition of the culture medium might affect the activity of the QACs, we additionally determined the activity in CA-MHB and DMEM media. The MIC values in the cation-adjusted medium, i.e., CA- MHB, decreased 1- to 10-fold, and in the DMEM medium decreased 10- to 20-fold compared with the initial MIC values determined in MHB. These results indicate that the addition of an amide group and the composition of the culture medium strongly influence the antibacterial activity of the synthesized soft QACs.

Listeriosis is a serious disease caused by food contaminated with Listeria monocytogenes. This bacterium is found in soil and surface water samples, but can also be found in dairy products, meat and seafood. Membrane-active antimicrobials such as quaternary ammonium salts (QASs), represent an important class of bacteriostatic and biocidal amphiphilic agents that are widely used in daily life. Given the widespread use of QASs, there have been reports of L. monocyogenes isolates resistant to these compounds. Here, we present the synthesis of a new series of quaternary amidoquinuclidine salts with potent antibacterial activity against L. monocytogenes. The antibacterial activity was determined for bacteria in the form of suspension and biofilm in the low micromolar range. The newly synthesized 3- aminoquinuclidines (C10, C12, C14, and C16) were quaternized with allyl or methyl substituents. We found that regardless of the type of substituent, the derivatives with longer alkyl chains had minimal inhibitory concentrations against L. monocytogenes that were almost identical to those of the standards (BAB, CPC, and cefotaxime). The identified candidates had low toxicity to healthy human cell lines with potent genotoxic activity against bacterial cells. In addition to the mechanism of action, we demonstrated that these agents target the cell membrane and cause membrane perforation and cell death. Parallel artificial membrane permeability assays mimicking human skin showed that candidates with longer alkyl chains did not penetrate the membrane, highlighting their potential application as disinfectants against this and other highly pathogenic bacteria.

Quaternary ammonium compounds (QACs) are amphiphilic compounds with exceptional properties and a wide range of applications. They display very good biological activities. Due to the development of bacterial resistance to QACs, the current aim is to synthesize new QACs which are biodegradable, but still efficient.1 Quaternization of heterocyclic quinuclidine and its derivatives has proven to be a good solution since its quaternary salts have great antibacterial and antifungal properties. For this research, the antibacterial activity of synthesized 3- aminoquinuclidine quaternary salt with an alkyl chain of 16 carbon atoms has been investigated by microdilution method on seven bacterial strains: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Enterococcus faecalis, Salmonella enteritidis, Listeria monocytogenes and Bacillus cereus. The best MIC value obtained was 9 nM against two Gram- positive bacteria: L. monocytogenes ATCC 7644 and S. aureus ATCC 25923. The second-best MIC was against Gram-positive E. faecalis ATCC 29212 at 36 nM. Obtained values are considered the potential for future investigations of that quaternary ammonium salt.

Quaternary ammonium salts (QASs) are irreplaceable membrane- active antimicrobial agents that have been widely used for almost a century. Cetylpyridinium chloride (CPC) is one of the most potent QASs, however, recent data from the literature indicate a 2- to 4-fold decrease in CPC activity against resistant bacterial strains. Given the growing demand for effective antimicrobials, especially in times of current and future spread of infectious diseases, the number of resistant isolates is expected to increase. One plausible approach to address this problem is to structurally modify the CPC structure by adding other biologically active functional groups. Here, a series of QASs based on pyridine-4-aldoxime were synthesized, characterized, and tested for antimicrobial activity in vitro. Although we obtained several potent antiviral candidates, Py- C12Br, Py-C12, and Py-C14, these candidates had lower antibacterial activity than commercial CPC. AFM images showed damage to the cell membrane and no viable cells after the bacteria were exposed to 4xMIC of Py-C12 for 3 hours. We found that the addition of an oxime group to the pyridine backbone resulted in an unfavorable electron density distribution and cLogP values and disrupted the interaction with the QacR dimer that regulates efflux pump expression. MD simulations showed that binding of Py-C16 to QacR leads to dissociation of the dimer within 50 ns, whereas the same was not observed in the case of the QacR dimer and the QacR dimer bound to CPC. This explains the lower bioactivity of our compounds, as they are likely to induce premature expression of the efflux pumps.

Quaternary ammonium compounds (QACs) are known for their potent antimicrobial activity, however, new data show that environmental bacteria developed resistance pointing to the importance for new QACs discovery. Our previous studies have shown that quaternary salts of heterocyclic derivatives, 3- substituted quinuclidine and benzylimidazole, have good antimicrobial activity acting on the bacterial membrane and binding to DNA. Led by these findings, we used pyridinium-4-aldoxime as biologically active heterocyclic precursor known for its antidote application. For reactions of quaternization we used different aryl/alkyl bromides obtaining corresponding QACs in very good yields. New compounds were tested against a panel of pathogenic Gram-positive and Gram-negative bacteria including standard benzyldodecyldimetylammonium bromide (BAB). Preliminary data show that quaternization of pyridinium-4-aldoxime significantly affect its antimicrobial activity irrespective of the quaternization agent. Also, all QACs obtained with alkyl reagents show lower MIC values for both Gram negative and positive bacteria, however observed values (312 µg/mL) were 100-fold higher than for BAB (2 µg/mL). Regardless, refinement of these structures, using other reagent(s) for quaternization might lead to better biological activities of pyridinium-4-aldoxime.

Reduced space of multi-target antimicrobial activities was used as a dependent variable for estimation of Cinchona alkaloids derivatives [1] activities. A panel of various Gram- positive and Gram-negative bacteria provided activity data whose principal components were extracted by 2nd-order tensor decomposition. These principal components were regressed on the theoretically computed energy fingerprints of all compounds. Extensive machine learning procedure was applied for generation of multivariate linear regression models with linear combination of original variables as well as their higher- order polynomial terms. Regression models of antimicrobial activity in dependence on molecular dynamics data were builded and thoroughly validated by leave-one- out cross- validation technique (LOO-CV) [2]. The most optimal representation was selected on the basis of R2 values and LOO-CV mean squared error and is presented on Fig. 1.

Quaternary ammonium compounds (QACs) are biologically active amphiphiles displaying potent antimicrobial properties (M.D. Joyce et al., 2015). Given the alarming number of QACs resistant environmental isolates, the aim of further QACs research is to synthetise soft QACs variants more prone to either spontanious or enzymatic degradation. Our previous studies on QACs have shown that quinuclidine is a good starting structure for quaternization and that its derivatives have potent antimicrobial activity (Bazina et al., 2019). It is also known that amide bond is susceptible to peptidase degradation. This fact implies that compounds containing such bond could be degraded more easily in the environment by enzymatic decomposition. For these reasons, we were set to synthesize new amido-quinuclidine derivatives with long alkyl chains to yield biologically active and more environmental friendly QACs variants. A series of six new compounds QAd12, MeQAd12, AlyQAd12, QAd14, MeQAd14 and AlyQAd14 were synthesized and analyzed for their antimicrobial activity using a panel of pahtogenic bacteria and fungus. All compounds display good antimicrobial potential at concentrations in μM range. To investigate if those compounds are succesfully degraded by cellular peptidases, enzymatic digestion of compounds using cell lysates will be preformed. This finding might shed light on new potential mechanism for production of environmental friendly QACs.

In recent years, the demand for development of new and more effective antiseptics and disinfectants has risen. One reason for this is the COVID-19 pandemic and the widespread use of these formulations provoking higher incidence of bacterial resistance in future years [1]. Quaternary ammonium compounds (QACs) have been shown to be effective antimicrobial candidates that tend to disrupt the bacterial membrane, leading to leakage of cytoplasm and subsequent cell lysis [2]. We and others have shown that natural products could be used as chemical scaffolds for quaternization to yield QACs of potent antimicrobial activities [3, 4]. Here we report the new series of such natural scaffold- guided structures containing amide bond as a potential substrate for protease degradation. The introduction of amide bond might result in biodegradable QACs, hence variants that have much shorter lifetime in the environment. The 3- aminoquinuclidine was substituted with alkyl chains of different length (10, 12 and 14 C-atoms) to yield precursors for quaternization (Figure 1). The quaternization was performed with appropriate alkyl halide reagents to obtain amidoquinuclidine QACs in good yields (Figure 2). The minimum inhibitory concentrations (MICs) were determined for both, amidoquinuclidines and their QACs, against a panel of Gram-positive and Gram-negative bacteria. As expected, the activity of the QACs was significantly better than for corresponding amidoquinuclidines which is in good correlation with calculated lipophilicity coefficients (cLogP). Our results suggest that amidoquinuclidine QACs could be good antibacterial candidates. The future experiments will elucidate weather these candidates are substrates for protease degradation.

Antimicrobial activity of Cinchona alkaloids derivatives [1] was previously evaluated by using disc diffusion assay against a panel of various Gram-positive and Gram-negative bacteria. Principal components of the activity data were extracted by 2nd-order tensor decomposition and used as dependent variables for multivariate linear regression, whereas theoretically computed energy fingerprints of all compounds were used as independent variables. Potential energy surfaces (PES) of compounds were sampled by performing molecular dynamics simulations and then decomposed by principal component analysis. Regression models were generated by extensive machine learning multivariate linear regression – linear combinations of original variables were used as well as their higher-order polynomial terms. Obtained models were thoroughly validated by leave-one-out cross- validation technique (LOO- CV) [2]. The optimal activity/PES model based on the adjusted and the predicted R2 values as well as LOO-CV mean squared error will be presented.

Quaternary ammonium compounds (QACs) are group of chemical compounds with broad spectrum applications. Owing to their amphiphilic nature, QACs reduce surface tension and form micelles allowing dispersion in a liquid. Due to this ability QACs are incorporated into soaps, cosmetics, hair dyes and detergents. Previously synthesized QACs consisting of a quinuclidine-3-ol core and long side alky chains (C10, C12, C14) have shown promising antimicrobial potential and low cytotoxicity. Given their potential application, here we have additionally investigated thermodynamic properties and self-assembly of these surfactants (Figure 1.) by measuring conductivity, dynamic light scattering (DLS) and Zeta-potential.

Quaternary ammonium compounds (QACs) have long been praised for their powerful antimicrobial potential. With a wide range of application, from different industries to pharmacy and medicine, these compounds are omnipresent ingredients of many commercial products. However, recent studies show that as much as 83% of MRSA isolates are resistant toward most of the commonly used QACs. Therefore, elucidation of resistance mechanism(s) and development of new potent QACs are in the centre of further research in the field. Quinuclidine is a bicyclic part of alkaloids isolated from a bark of the Cinchona trees. Even though these alkaloids have long been used in a traditional medicine, the biological potential of quinuclidine derivatives is still underexplored. Apart from its anticholinergic, antiparasitic, antioxidative and antitumor activity, some quinuclidine derivatives have been shown to act on FitZ protein, known to be essential for bacterial cell division. All this motivated us to synthesize new quinuclidine containing QACs in order to further explore its antimicrobial potential and to develop new and powerful naturally derived QACs. Our studies have shown that quaternisation of substituted quinuclidine improves its antimicrobial activity by several hundred folds and that this activity depends on the type of substituent used for quaternisation. Aryl- quinuclidines typically had lower antimicrobial activity than their alkyl counterparts. Also, somewhat better antimicrobial activity was observed toward Gram-positive bacteria, suggesting that bacterial membrane might be involved in the mode of action mechanism. Therefore, the PI- uptake measurements were performed along with atomic force microscopy (AFM) and indeed, obtained results indicated bacterial membrane perforation. Moreover, alkyl-quinuclidines, more specifically an identified candidate with the longest alkyl chain, exhibited the best antimicrobial activity with the lowest MIC values across selected panel of the bacteria and good activity toward S. aureus biofilms. In addition, this compound had lower toxicity toward healthy human cell lines than the referent QACs, suggesting that quinuclidine could serve as a new possible core molecule for future QACs development.

Quaternary ammonium compounds (QACs), as cationic amphiphiles, show broad-spectrum antibacterial activity due to a mechanism based on membrane disruption. Since previously synthesized monoQACs containing quinuclidine-3- ol showed promising antimicrobial potential, we have further developed a new series of bisQACs containing quinuclidine-3-ol. In this series, we bind two quinuclidine centers by long alkyl chains of variable length (C8, C10 and C12), assuming that two-headed (bicephalic) QACs would possess even better ability of bacterial membrane disruption. These compounds were screened for antimicrobial activity against Gram-positive and Gram- negative bacterial strains, both ATCC and clinical isolates, as well as fungi and molds. Activity toward inhibition of the biofilm structures and cytotoxicity were also tested.

Emerging antibiotic resistance is one of the biggest threats to public health and there is a crucial need for development of new effective antibiotics. Quaternary ammonium compounds (QACs), as cationic amphiphiles, have been recognized as broad-spectrum antibacterial agents. In this paper, we have designed and synthesized cationic surfactant systems based on quinuclidine bearing an amino group and a long side alkyl chain (C12 and C14) assuming that amino group would upgrade ability of bacterial membrane disruption (Figure 1). These compounds are characterized by FT-IR, 1H NMR and 13C NMR analysis and are evaluated for antimicrobial activity against representative Gram-positive and -negative bacterial strains. The minimal inhibitory and bactericidal concentrations (MIC and MBC) are determined by using the method of a serial dilution. Our results show a positive correlation between antimicrobial activity and an alkyl chain length. Tested compounds exhibit noteworthy antibacterial activity, especially, QNH2-C14 with considerably low minimal inhibitory concentration against S. aureus (MIC = 3.9 μg mL-1), S. pyogenes (MIC = 3.9 μg mL-1) and E. faecalis (MIC = 1.95 μg mL-1). The work on cytotoxicity measurements toward different human cell lines is currently in progress.

In an attempt to identify a new class of antimicrobial agents, the antimicrobial potential of quaternary quinuclidinium derivativeswith N-alkyl substituent on the position 3 of quinuclidine was evaluated.We were guided bythe results of our previouswork which showedthatquaternary derivatives of 3- substituted quinuclidineshavevery good biological activity.1Therefore, newseriesof quaternary quinuclidiniumsalts were designed and synthetized by the quaternization of quinuclidin-3-yl(dodec-1-yl)aminewith different benzyl bromides. All compounds were obtained in very good yields after which they were further characterized by physico-chemical methods includingFTIR, 1H and 13C NMR spectroscopies.The antibacterial activities of all compounds were evaluated against series of recent clinical isolates of antibiotic susceptible Gram-positive and resistant Gram- negative pathogens by determining their minimum inhibitory concentrations. All compounds showed good to strong broad-spectrum activity displaying MIC values between1.95-3.9 μg/mL.Cytotoxicity of compounds with different cell lines in human cell culture was determinedand it was determined that HaCat cell line is less tolerant that RPE1 displaying IC50values between 0.97-24.3 μM/mL. Based on these results, quaternary quinuclidine with long alkyl chain can be considered as promising new class of antimicrobials and further investigations should be performed.

Listeria monocytogenes is a rapidly growing Gram-positive food pathogen that causes listeriosis in humans which, if untreated, can lead to serious and often fatal consequences. Once L. monocytogenes are organized in biofilm structures, they are more resistant to antibiotics and as such pose a great challenge to scientists [1]. One of the most powerful antimicrobial agents are quaternary ammonium compounds (QAC) that are widely used as antiseptics in homes and hospitals worldwide. As amphiphilic compounds, these agents interact with negative bacterial membranes causing an osmotic imbalance that subsequently leads to perforation of the cell wall structure. For this reason, QAC are considered as agents of a broad spectrum antibacterial activity. However, a worrisome number of bacterial strains isolated from the environment have become resistant to commercial QAC highlighting the importance of new drug discoveries [2]. An underexplored natural QAC that has promising medicinal and pharmaceutical potential is a quinuclidine isolated from the cinchona tree. Our group has previously shown that quinuclidine based QAC have good antibacterial potential, especially toward Gram-positive bacterial strains [3]. Motivated by these observations, we were interested whether QAC consisting of a quinuclidine core and long side alkyl chains (C12 and C14) exhibit antimicrobial activity against L. monocytogenes and whether these compounds have an effect on a biofilm formation. Our results indicate that quinuclidine derived QAC have a promising antimicrobial activity against L. monocytogenes with MIC and MBC values of up to 3.9 µg mL-1. An upcoming research on the fractional inhibitory concentration and antimicrobial activity against biofilm structures will showcase its benefit in manifold applications.

Surfactants, including quaternary ammonium salts (QAS), are organic compounds composed of a hydrophilic head and a hydrophobic tail. Thanks to this structure, they are very readily soluble in many solvents. Owing to their foaming, wetting, softening and emulsifying abilities, and thermal stability, quaternary ammonium salts are widely used in many industries (such as food, paper and cosmetics). These compounds are also applied as biocides which are highly efficient against lipophilic viruses, bacteria or fungi at very low concentrations. Besides these, they are used for destruction of biofilms formed by microorganisms in cooling systems. They find application in medicine as antimicrobial agents and even medications. When applied according to the manufacturer's recommendations, QASs are not toxic to humans, do not corrode surfaces when used for cleaning and are biodegradable. In an attempt to find a new class of antimicrobial agents, a series of benzylimidazolium derivatives with different length of alkyl chains were synthesized. The compounds were characterized by FT- IR, 1H NMR and LC-MS analysis and evaluated for antimicrobial activity against representative Gram- positive and -negative bacterial strains as well as toward the Candida albicans fungi. The minimal inhibitory and bactericidal concentrations (MIC and MBC) were determined by using the method of a serial dilution. All newly synthesized compounds display significantly lower MIC and MBC values for Gram- positive than the Gram-negative bacteria. Among the tested compounds, N- tetradecylbenzylimidazolium bromide exhibited a considerable antibacterial efficiency against S. pyogenes (MIC=MBC=0.03 μg mL- 1). The cytotoxicity measurements toward different human cell lines are currently underway.

The bark of the Cinchona trees is the source of a variety of alkaloids, the most famous being cinchonine, cinchonidine, quinine and quinidine. They are useful in organic chemistry as organocatalysts in stereoselective syntheses, but also in medicine, since they possess various analgesics, anti-inflammatory and anti–arrhythmic properties. To investigate a new class of antimicrobials that could direct to the discovery of a novel scaffold, a series of quaternary derivatives of cinchonines and their corresponding pseudo-enantiomeric cinchonidines were synthesized. All compounds were prepared in good yields and characterized by standard analytical spectroscopy methods. The antibacterial activities of all compounds were evaluated against seven recent clinical isolates of antibiotic susceptible Gram- positive and resistant Gram-negative pathogens. The bioactive assays, antibacterial efficiency, cytotoxicity and classification model build by principal component analysis for all compounds will be discussed. Supported by Croatian Science Foundation, Project No 3775 ADESIRE

Quinuclidine, bicyclic alkaloid, easily forms quaternary ammonium compounds (QACs) which exhibit diverse biological and pharmacological activity. Given their amphiphilic nature, cationic part of salts electrostatically interacts with the negatively charged phospholipids of the bacterial cell wall so that long alkyl tails of salts can penetrate into the membrane of bacteria. [1] In order to explore antimicrobial activity we have synthesized quaternary 3- hydroxyquinuclidinium salts with different lengths of alkly chains (C10, C12 and C14). Compounds were acquired in significant yields and their structures were affirmed by 1H NMR, 13C NMR and IR spectral data. The antimicrobial activity was tested against Gram-positive, Gram-negative bacteria both ATCC and clinical isolates as well against fungal strains, using broth microdiluton method to determine minimum inhibitory concentrations (MICs). Activity toward inhibition of the biofilm structures was also tested. Our preliminary results indicate that the tested compounds have a better activity against Gram-positive bacteria and the compound displaying the highest antibacterial activity is the one with the longest alkyl chain.

A number of procedures for the preparation of oximes are described in literature, but, only recently they are considered also from the green chemistry point of view. Traditionally, oximes are prepared by refluxing an alcoholic solution of carbonyl compound with hydroxylamine hydrochloride and a base. Accordingly, there is necessity for developing alternative efficient and less contaminating methods for the preparation of aldoximes and ketoximes. For this purpose, a series of indole oximes with a carbonyl group in different positions were synthesized. Oximes were obtained quantitatively in reactions with liquid assisted grinding and addition of an organic nitrogen base. All reactions ended within first minute. This method proved to be appropriate for the synthesis of all indole oximes from a suitable aldehydes and ketones, using just 0.4 eq or fewer base among those which are daily used in organic laboratories. Reactions were very fast and almost solvent free, which reduced cost and accumulation of toxic by-products. For all compounds, antimicrobial activity targeting resistance genes to treat infections caused by multidrug- resistant Gram-negative bacteria was estimated.

Antibiotic resistant bacteria that are difficult or impossible to treat are becoming increasingly common and are causing a global health crisis. However, the -lactam drug class, once the foundation of treatment regimens for many hospital and community acquired infections, is rapidly becoming obsolete due to the proliferation of - lactamases. To combat infection small molecules based on oxime scaffold have been developed as promising antimicrobial agent. The aim of the current study was to investigate antimicrobial profile and relationship between antimicrobial activity and structure of quaternized 4- pyridinium oxime with diverse substituents introduced into the benzyl ring to gain a better understanding of their mehanism of action. Their antimicrobial activity, kinetics, and molecular mechanism against a 14 clinically relevant bacteria, including multi-drug resistant Gram-positive and Gram-negative pathogenic bacteria were investigated in this study using multiple methods. The obtained results are very are very promising since many of the compounds demonstrated potent in vitro activity against a broad range of clinically important Gram-negative and Gram-positive bacteria, including multidrug resistant strains with MIC values from 0.48 to 125.0 μg mL-1. Structure-activity relationship analysis established that the best activities were obtained with Br and CH3 groups placed at into the benzyl ring. The inhibitory properties of oxime derivatives were measured across a wide variety of enzymes selected for their clinical relevance. Of the class A enzymes two enzymes were profiled: the widely disseminated extended-spectrum -lactamase CTX-M-15 and within class C the enzymes were chosen to represent Enterobacteriaceae with the AmpC from Enterobacter cloacae. Checkerboard assays was indicating that the combinations with ceftazidime and cefotaxime and compound with Br as p-substituent on benzyl ring showed the most potent synergistic inhibitory activity. This class of compounds could lead to an appealing class of antimicrobial agents combating multidrug resistant bacterial strains.

Food contamination by multidrug resistant Gram- negative bacteria can be a major threat to public. The prevalence of antibiotic resistance among Gram-negative foodborne pathogens and food spoilage bacteria has increased during recent decades ; therefore, the food chain has been recognized as one of the key routes of antimicrobial resistance transmission from food to human bacterial populations. Consequently, a potential way to restore some of the resistance issues is to use plant based compounds as sources of novel and promising natural antimicrobials as resistance modifying agents have attracted enormous scientific interest. Plant diversity constitutes an infinite pool of novel chemistry, making up a valuable source of highly effective phytochemicals to prevent the emergence of resistant bacteria in the food industry, by reducing or modulating the resistance and can be thereby improve the efficiency of the processed food, ensure food quality and safety of the products as well as human health. Nowadays, diterpenes are widely employed as fragrances and food additives. However, limited studies are available not only for directs antimicrobial efficacy of diterpene alcohol such as phytol, but also for resistance-modifying agents. In this study, antimicrobial screening was performed using the agar-diffusion method against a panel of both clinically relevant antibiotic susceptible Gram-positive and antibiotic resistant Gram- negative bacteria that harbours resistance genes for the most commonly important antibiotics. In addition, phytol was then evaluated in the quantitative bioassay to determinate minimum inhibitory concentration (MIC) based on broth microdilution. Finally, in vitro activities of phytol was also performed to confirm their ability to restore the resistance of the clinically and environmental Gram-negative strains producing a wide range β- lactamases from A and C molecular classes and a possible mechanism of action responsible for the antibacterial activity was also examined.

Antioxidants play an important role as health protecting factors. Scientific evidence suggests that antioxidants reduce the risk for chronic diseases including cancer and heart disease. Primary sources of naturally occurring antioxidants are whole grains, fruits and vegetables. Plant sourced antioxidants like vitamin C, vitamin E, carotenes, phenolic acids etc. have been recognized as agents having the potential to reduce the risk for disease development. Most antioxidants from a typical diet are derived from the plant sources and belong to various classes of chemical compounds with a wide variety of physical and chemical properties. However, recent studies have shown that some synthetic organic compounds could also exhibit a strong antioxidative potential with a possible application in food and pharmaceutical industries. In this study, we have synthesized the quaternary 3- hydroxyquinuclidinium salts bearing different long alkyl chains (C8, C10, C12 and C14). All compounds were obtained in very good yields and characterized. A rapid, simple and inexpensive method to measure antioxidant capacity involving the free radical, 2, 2-diphenyl-1-picrylhydrazyl (DPPH) was utilized in order to test the ability of the synthesized compounds to act as free radical scavengers or hydrogen donors and to evaluate their antioxidant activity. Our preliminary results suggest that the compounds displaying the higher antioxidative activities are those with the longer alkyl chains. Evaluation of the biological potential including the DNA protecting ability of the newly synthesized compounds is currently underway.

Bioactive chemical scaffolds such as nitrogen bicyclic bridged-rings as quinuclidines are recognized as compounds with a broad spectrum of biological activities not only in the fields of central nervous system disorders (Alzheimer’s disease, AD) but also in infectious diseases. In this work syntheses of series of novel N-alkyl derivatives of quinucline-3-oximes are described. The possibility of mechanochemical oxime synthesis with hydroxylamine hydrochloride, without any base and with or without catalytic amount of solvent was investigated. Furthermore, quaternization of quinuclidine nitrogen atom which was carried out with methyl, ethyl, allyl and differently substituted benzyl halides resulted in a set of compounds with different conformational space and and electronic structure. All compounds were prepared in very good yields and characterized by standard analytical spectroscopy methods (1D and 2D NMR, IR, MS). pKa values were measured and compared to that of neutral oxime. For all compounds, antimicrobial activity was estimated and efficacy toward multidrug-resistant Gram- negative bacteria will be discussed. To combine experimental and theoretical data molecular modeling, docking studies and a newly developed method for application of multi-way analysis was performed.

Two series of quaternary ammonium salts were synthetized by quaternization of quinuclidine- 3-ol with a different benzyl or n-alkyl bromides. All compounds were obtained in very good yields after which they were further characterized by physical means and FTIR, 1H and 13C NMR spectroscopies. Given the previously determined role of quinuclidine as a chemical compound displaying a broad range of biological activities, we were interested how quaternization with different substituents would affect these properties. The antioxidative activities were evaluated by oxygen radical absorbance capacity (ORAC) assay and preliminary results suggest that substitution with benzyl or n-alkyl bromides at N position positively affects ORAC values. Among the tested samples, the compound with the longest alkyl chain displayed the highest ORAC value implicating a possible higher biological potential. Further evaluation of these results by DPPH method and determination of the cellular antioxidant capacity are currently underway.

Quinuclidine is part of the structure of a number of natural physiologically active compounds and some synthetic drugs. Quinuclidine easily forms quaternary ammonium salts and many of them due to the antibacterial activities were used for antiseptic, disinfectants and a variety of clinical purposes. In this study novel ammonium salts bearing quinuclidine moiety were synthesized and evaluated for their antibacterial and antifungal activities. These activities were measured in selected homologues (3-hydroxy- or 3-chloroquinuclidine) with different N-benzyl substitutent at para-position (p-bromo, p-chloro and p-nitro) in order to determine basic structure-antimicrobial activity relationship. Structure of the synthesized compounds was elucidated by 1H NMR, 13C NMR and IR spectral data. These compounds were screened against three gram-positive and three gram-negative bacterial, as well fungal strains by agar disc diffusion method. The antimicrobial activity was investigated by broth microdilution method to determine the minimum inhibitory concentrations of tested compounds.One of the newly synthesized compounds displayed most potent inhibitory activity with MIC values of 6.25, 3.12, 3.12 μg mL-1 against E. coli, P. aeruginosa and C. sakazakii respectively. Compound with 3-hydroxy substituent on the quinuclidine ring and p-chlorobenzyl substituent was found to be the most superior compounds especially against P. aeruginosa which MIC value was 160-fold better than gentamicin. The similar compound with the different substituent on position 3 of the quinuclidine ring displayed excellent activity against B. cereus with a MIC value 2.5-fold lower than gentamicin. Moreover, the antifungal profiles of these compounds were found to be most potent. Structure- activity relationship studies revealed that substituent at position 3 of quinuclidine ring as well as p-substituent at the benzyl ring have a significant effect on the antimicrobial activity of the newly synthesized quaternary ammonium salts.

The emergence of resistant fungal pathogens has been a motivating force in the search for new antifungal agents. Inspired by their diverse biological and pharmacological activity of quinuclidine and oxime compounds we have synthesized and characterized novel class of surfactants, 3-hydroxyimino quinuclidinium bromides with different alkyl chains lengths(CnQNOH ; n = 12, 14 and 16) to evaluated antifungal activity and their mechanism of action against eight Candida albicans including both azole-resistant and azole sensitive strains. The antifungal activities were established by determination of grow inhibition zones and MIC values by disk diffusion and broth microdilution assays and compared with fluconazole and itraconazole. The synergistic interaction between C12 and C14 with fluconazole and itraconazole was also evaluated against various strains of C. albicans using a microdilution checkerboard assay. To confirm the synergistic inhibitory effects of C12 or C14 and fluconazole against the azole-resistant C. albicans strains, representative kinetic time-kill studies were performed. Mechanism of action has been also determined by performing fluorescence study where a mixture of nucleic acid binding. Results demonstrated that investigated compounds showed broad-spectrum antifungal activities against azole-resistant and azole- sensitive C. albicans strains compared with fluconazole and itraconazole. Analogues with C12 and C14 chains showed promising antifungal activities against tested fungal strains, with MIC values ranging from 3.12 to 25.00 μg/mL and 0.78 to 6.25 μg/mL, respectively. However, analogue with C16 exhibited lower activity with MIC values ranging from 12.50 to 50 μg/mL. In addition, study demonstrated the synergistic combination effects between C12 or C14 and azoles against the majority of the C. albicans strains tested. The results obtained suggest the possible use of this surfactant as an alternative antifungal agent in the medical field for applications against C. albicans responsible for diseases and infections, making it a suitable alternative to conventional antifungal agent.

The continuous emergences of multidrug-resistant Gram-negative bacterial pathogens compromise the successful treatment of serious clinical infections and call for the discovery and development of new antimicrobials agents. Potential to overcome the existing antibiotic resistance mechanisms have to be shown by new antibiotic in the discovery phase. In an effort to develop highly potent new class antibacterial agents which can restore β-lactam efficacy against Gram-negative bacterial strains producing multiple β-lactamases, new oxime compounds were designed. All new N-substituted imidazolium oximes and their monoquaternary salt were synthesized and their structure was confirmed by elemental analysis and spectral studies (IR, 1H and 13C NMR. Preliminary screening against a panel of representative Gram-positive and Gram-negative bacteria including multidrug resistant bacterial strains by the disc diffusion as well as broth microdilution assays was performed. Based on the preliminary results we discovered several compounds that demonstrated potent in vitro activity against tested microorganisms with MIC values from 6.25 to 50.0 μg mL-1. Additionally, we then used the broth microdilution assay to investigate the antiresistance efficacy of most potent compounds against ten molecularly determined extended-spectrum β- lactamase (ESBL) producing strains in comparison to eight clinically relevant antibiotics. Separate chemical-species interaction for each antimicrobial drug revealed species-specific effects elicited by a majority of the treatments explored. Among compounds tested mchlorobenzyl and 4-butenyl substituents on the imidazole ring displayed promising broadspectrum antibacterial activity against Gram-negative bacterial strains. The screen generated one promising compound exhibited remarkable, antiresistance efficacy against a wide range of β-lactamases was obtained for Escherichia coli and Enterobacter cloacae producing multiple from A and C molecular classes which was 32-fold and 128-fold more potent than ceftazidime and cefotaxime, respectively, which leads to the suggestion that may be interesting candidate for further development of new antimicrobials to restore antibacterial activity particularly among multidrug Gram-negative β-lactamase expressing bacterial pathogens.