Understanding and Sensitizing Density-Dependent Persistence to Quinolone Antibiotics.

Physiologic and environmental factors can modulate antibiotic activity and thus pose a significant challenge to antibiotic treatment. The quinolone class of antibiotics, which targets bacterial topoisomerases, fails to kill bacteria that have grown to high density; however, the mechanistic basis for this persistence is unclear. Here, we show that exhaustion of the metabolic inputs that couple carbon catabolism to oxidative phosphorylation is a primary cause of growth phase-dependent persistence to quinolone antibiotics. Supplementation of stationary-phase cultures with glucose and a suitable terminal electron acceptor to stimulate respiratory metabolism is sufficient to sensitize cells to quinolone killing. Using this approach, we successfully sensitize high-density populations of Escherichia coli, Staphylococcus aureus, and Mycobacterium smegmatis to quinolone antibiotics. Our findings link growth-dependent quinolone persistence to discrete impairments in respiratory metabolism and identify a strategy to kill non-dividing bacteria.

Heterogeneity of SOS response expression in clinical isolates of Escherichia coli influences adaptation to antimicrobial stress.

In recent years, new evidence has shown that the SOS response plays an important role in the response to antimicrobials, with involvement in the generation of clinical resistance. Here we evaluate the impact of heterogeneous expression of the SOS response in clinical isolates of Escherichia coli on response to the fluoroquinolone, ciprofloxacin. In silico analysis of whole genome sequencing data showed remarkable sequence conservation of the SOS response regulators, RecA and LexA. Despite the genetic homogeneity, our results revealed a marked differential heterogeneity in SOS response activation, both at population and single-cell level, among clinical isolates of E. coli in the presence of subinhibitory concentrations of ciprofloxacin. Four main stages of SOS response activation were identified and correlated with cell filamentation. Interestingly, there was a correlation between clinical isolates with higher expression of the SOS response and further progression to resistance. This heterogeneity in response to DNA damage repair (mediated by the SOS response) and induced by antimicrobial agents could be a new factor with implications for bacterial evolution and survival contributing to the generation of antimicrobial resistance.

Chance Favors the Prepared Genomes: Horizontal Transfer Shapes the Emergence of Antibiotic Resistance Mutations in Core Genes.

Bacterial lineages acquire novel traits at diverse rates in part because the genetic background impacts the successful acquisition of novel genes by horizontal transfer. Yet, how horizontal transfer affects the subsequent evolution of core genes remains poorly understood. Here, we studied the evolution of resistance to quinolones in Escherichia coli accounting for population structure. We found 60 groups of genes whose gain or loss induced an increase in the probability of subsequently becoming resistant to quinolones by point mutations in the gyrase and topoisomerase genes. These groups include functions known to be associated with direct mitigation of the effect of quinolones, with metal uptake, cell growth inhibition, biofilm formation, and sugar metabolism. Many of them are encoded in phages or plasmids. Although some of the chronologies may reflect epidemiological trends, many of these groups encoded functions providing latent phenotypes of antibiotic low-level resistance, tolerance, or persistence under quinolone treatment. The mutations providing resistance were frequent and accumulated very quickly. Their emergence was found to increase the rate of acquisition of other antibiotic resistances setting the path for multidrug resistance. Hence, our findings show that horizontal gene transfer shapes the subsequent emergence of adaptive mutations in core genes. In turn, these mutations further affect the subsequent evolution of resistance by horizontal gene transfer. Given the substantial gene flow within bacterial genomes, interactions between horizontal transfer and point mutations in core genes may be a key to the success of adaptation processes.

Oral quinolones versus intravenous ß-lactam for the treatment of acute focal bacterial nephritis: a retrospective cohort study.

BACKGROUND: Evidence regarding the best antibiotic regimen and the route of administration to treat acute focal bacterial nephritis (AFBN) is scarce. The aim of the present study was to compare the effectiveness of intravenous (IV) ß-lactam antibiotics versus oral quinolones. METHODS: This is a retrospective single centre study of patients diagnosed with AFBN between January 2017 and December 2018 in Hospital Universitari Vall d'Hebron, Barcelona (Spain). Patients were identified from the diagnostic codifications database. Patients treated with oral quinolones were compared with those treated with IV ß-lactam antibiotics. Therapeutic failure was defined as death, relapse, or evolution to abscess within the first 30 days. RESULTS: A total of 264 patients fulfilled the inclusion criteria. Of those, 103 patients (39%) received oral ciprofloxacin, and 70 (26.5%) IV ß-lactam. The most common isolated microorganism was Escherichia coli (149, 73.8%) followed by Klebsiella pneumoniae (26, 12.9%). Mean duration of treatment was 21.3 days (SD 7.9). There were no statistical differences regarding therapeutic failure between oral quinolones and IV ß-lactam treatment (6.6% vs. 8.7%, p = 0.6). Out of the 66 patients treated with intravenous antibiotics, 4 (6.1%) experienced an episode of phlebitis and 1 patient (1.5%) an episode of catheter-related bacteraemia. CONCLUSIONS: When susceptible, treatment of AFBN with oral quinolones is as effective as IV ß-lactam treatment with fewer adverse events.

Discovery of a new class of potent pyrrolo[3,4-c]quinoline-1,3-diones based inhibitors of human dihydroorotate dehydrogenase: Synthesis, pharmacological and toxicological evaluation.

Twenty N-substituted pyrrolo[3,4-c]quinoline-1,3-diones 3a-t were synthesized by a cyclization reaction of Pfitzinger's quinoline ester precursor with the selected aromatic, heteroaromatic and aliphatic amines. The structures of all derivatives were confirmed by IR, 1H NMR, 13C NMR and HRMS spectra, while their purity was determined using HPLC techniques. Almost all compounds were identified as a new class ofpotent inhibitors against hDHODH among which 3a and 3t were the most active ones with the same IC50 values of 0.11 µM, about seven times better than reference drug leflunomide. These two derivatives also exhibited very low cytotoxic effects toward healthy HaCaT cells and the optimal lipophilic properties with logP value of 1.12 and 2.07 respectively, obtained experimentally at physiological pH. We further evaluated the comparative differences in toxicological impact of the three most active compounds 3a, 3n and 3t and reference drug leflunomide. The rats were divided into five groups and were treated intraperitoneally, control group (group I) with a single dose of leflunomide (20 mg/kg) group II and the other three groups, III, IV and V were treated with 3a, 3n and 3t (20 mg/kg bw) separately. The investigation was performed in liver, kidney and blood by examining serum biochemical parameters and parameters of oxidative stress.

Effect of WQ-3334 on Campylobacter jejuni carrying a DNA gyrase with dominant amino acid substitutions conferring quinolone resistance.

INTRODUCTION: Campylobacteriosis stands as one of the most frequent bacterial gastroenteritis worldwide necessitating antibiotic treatment in severe cases and the rise of quinolones-resistant Campylobacter jejuni poses a significant challenge. The predominant mechanism of quinolones-resistance in this bacterium involves point mutations in the gyrA, resulting in amino acid substitution from threonine to isoleucine at 86th position, representing more than 90% of mutant DNA gyrase, and aspartic acid to asparagine at 90th position. WQ-3334, a novel quinolone, has demonstrated strong inhibitory activity against various bacteria. This study aims to investigate the effectiveness of WQ-3334, and its analogues, WQ-4064 and WQ-4065, with a unique modification in R1 against quinolones-resistant C. jejuni. METHODS: The structure-activity relationship of the examined drugs was investigated by measuring IC50 and their antimicrobial activities were accessed by MIC against C. jejuni strains. Additionally, in silico docking simulations were carried out using the crystal structure of the Escherichia coli DNA gyrase. RESULT: WQ-3334 exhibited the lowest IC50 against WT (0.188 ± 0.039 mg/L), T86I (11.0 ± 0.7 mg/L) and D90 N (1.60 ± 0.28 mg/L). Notably, DNA gyrases with T86I substitutions displayed the highest IC50 values among the examined WQ compounds. Moreover, WQ-3334 demonstrated the lowest MICs against wild-type and mutant strains. The docking simulations further confirmed the interactions between WQ-3334 and DNA gyrases. CONCLUSION: WQ-3334 with 6-amino-3,5-difluoropyridine-2-yl at R1 severed as a remarkable candidate for the treatment of foodborne diseases caused by quinolones-resistant C. jejuni as shown by the high inhibitory activity against both wild-type and the predominant quinolones-resistant strains.

Safety, tolerability and biological responses of Oreochromis niloticus juveniles upon oral oxolinic acid administration.

In aquaculture, oxolinic acid (OA) is used as a second-line treatment at 12 mg/kg biomass/day for seven consecutive days. The present study evaluated the biosafety of 21 days of dietary administration of OA at 0, 12, 36, 60 and 120 mg by assessing the growth, biochemical, erythrocytic morphological and histopathological alterations and residue levels in Oreochromis niloticus. A significant dose-dependent reduction in feed intake and biomass and an increase in mortalities and erythrocytic cellular and nuclear changes were recorded. Significant elevations in plasma glucose, creatinine, alkaline phosphatase, alanine transaminase and aspartate transaminase and a decline in calcium and chloride levels were documented. The kidney, liver and intestine histoarchitecture showed mild to marked alterations. The edible tissue OA residues peaked on day 21 and decreased upon cessation of administration in all the dosing groups. The residue levels in the muscle of the recommended dose group were well within the maximum residue limit set by the European Medicines Evaluation Agency. Although the current study hinted at the safety and tolerability of OA even during long-term usage in O. niloticus in Indian conditions, care must be exercised for its aquacultural application because of its listing as a critically important medicine for humans.

Photocatalytic Degradation of Quinolones by Magnetic MOFs Materials and Mechanism Study.

With the rising incidence of various diseases in China and the constant development of the pharmaceutical industry, there is a growing demand for floxacin-type antibiotics. Due to the large-scale production and high cost of waste treatment, the parent drug and its metabolites constantly enter the water environment through domestic sewage, production wastewater, and other pathways. In recent years, the pollution of the aquatic environment by floxacin has become increasingly serious, making the technology to degrade floxacin in the aquatic environment a research hotspot in the field of environmental science. Metal-organic frameworks (MOFs), as a new type of porous material, have attracted much attention in recent years. In this paper, four photocatalytic materials, MIL-53(Fe), NH2-MIL-53(Fe), MIL-100(Fe), and g-C3N4, were synthesised and applied to the study of the removal of ofloxacin and enrofloxacin. Among them, the MIL-100(Fe) material exhibited the best photocatalytic effect. The degradation efficiency of ofloxacin reached 95.1% after 3 h under visible light, while enrofloxacin was basically completely degraded. The effects of different materials on the visible photocatalytic degradation of the floxacin were investigated. Furthermore, the photocatalytic mechanism of enrofloxacin and ofloxacin was revealed by the use of three trappers (▪O2-, h+, and ▪OH), demonstrating that the role of ▪O2- promoted the degradation effect of the materials under photocatalysis.

Imidazopyridine Family: Versatile and Promising Heterocyclic Skeletons for Different Applications.

In recent years, there has been increasing attention focused on various products belonging to the imidazopyridine family; this class of heterocyclic compounds shows unique chemical structure, versatile optical properties, and diverse biological attributes. The broad family of imidazopyridines encompasses different heterocycles, each with its own specific properties and distinct characteristics, making all of them promising for various application fields. In general, this useful category of aromatic heterocycles holds significant promise across various research domains, spanning from material science to pharmaceuticals. The various cores belonging to the imidazopyridine family exhibit unique properties, such as serving as emitters in imaging, ligands for transition metals, showing reversible electrochemical properties, and demonstrating biological activity. Recently, numerous noteworthy advancements have emerged in different technological fields, including optoelectronic devices, sensors, energy conversion, medical applications, and shining emitters for imaging and microscopy. This review intends to provide a state-of-the-art overview of this framework from 1955 to the present day, unveiling different aspects of various applications. This extensive literature survey may guide chemists and researchers in the quest for novel imidazopyridine compounds with enhanced properties and efficiency in different uses.

Synergistic Effect of SOS Response and GATC Methylome Suppression on Antibiotic Stress Survival in Escherichia coli.

The suppression of the SOS response has been shown to enhance the in vitro activity of quinolones. Furthermore, Dam-dependent base methylation has an impact on susceptibility to other antimicrobials affecting DNA synthesis. Here, we investigated the interplay between these two processes, alone and in combination, in terms of antimicrobial activity. A genetic strategy was used employing single- and double-gene mutants for the SOS response (recA gene) and the Dam methylation system (dam gene) in isogenic models of Escherichia coli both susceptible and resistant to quinolones. Regarding the bacteriostatic activity of quinolones, a synergistic sensitization effect was observed when the Dam methylation system and the recA gene were suppressed. In terms of growth, after 24 h in the presence of quinolones, the Δdam ΔrecA double mutant showed no growth or delayed growth compared to the control strain. In bactericidal terms, spot tests showed that the Δdam ΔrecA double mutant was more sensitive than the ΔrecA single mutant (about 10- to 102-fold) and the wild type (about 103- to 104-fold) in both susceptible and resistant genetic backgrounds. Differences between the wild type and the Δdam ΔrecA double mutant were confirmed by time-kill assays. The suppression of both systems, in a strain with chromosomal mechanisms of quinolone resistance, prevents the evolution of resistance. This genetic and microbiological approach demonstrated the enhanced sensitization of E. coli to quinolones by dual targeting of the recA (SOS response) and Dam methylation system genes, even in a resistant strain model.

Norfloxacin prophylaxis effect on multidrug resistance in patients with cirrhosis and bacterial infections.

It is unclear whether norfloxacin predisposes to infections by multidrug-resistant organisms (MDROs). We aimed to evaluate if patients with cirrhosis receiving norfloxacin prophylaxis at the time of the diagnosis of bacterial infections were more likely to present a multidrug-resistant isolate than those without prophylaxis. This is a cross-sectional study of hospitalized patients with cirrhosis and bacterial infections from Argentina and Uruguay (NCT03919032) from September 2018 to December 2020. The outcome variable was a multidrug-resistant bacterial infection. We used inverse probability of treatment weighting to estimate the odds ratio (OR) of norfloxacin on infection caused by MDROs considering potential confounders. Among the 472 patients from 28 centers, 53 (11%) were receiving norfloxacin at the time of the bacterial infection. Patients receiving norfloxacin had higher MELD-sodium, were more likely to have ascites or encephalopathy, to receive rifaximin, beta-blockers, and proton-pump inhibitors, to have a nosocomial or health-care-associated infection, prior bacterial infections, admissions to critical care units or invasive procedures, and to be admitted in a liver transplant center. In addition, we found that 13 (24.5%) patients with norfloxacin and 90 (21.5%) of those not receiving it presented infections caused by MDROs (adjusted OR 1.55; 95% CI: 0.60-4.03; p = 0.360). The use of norfloxacin prophylaxis at the time of the diagnosis of bacterial infections was not associated with multidrug resistance. These results help empiric antibiotic selection and reassure the current indication of norfloxacin prophylaxis in well-selected patients.Study registration number: NCT03919032.

Preparation of a hydrophobic deep eutectic solvent and its application in the detection of quinolone residues in cattle urine.

Enrichment for the detection of quinolone residues is usually cumbersome and requires large amounts of toxic organic reagents. Therefore, this study synthesized a low-toxicity hydrophobic deep eutectic solvent (DES) with DL-menthol and p-cresol, which was then characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and thermal analysis. A simple and rapid vortex-assisted liquid-liquid microextraction method was developed based on this DES for the extraction of eight quinolones from cattle urine. The optimal extraction conditions were screened by examining the DES volume, extraction temperature, vortex time, and salt concentration. Under the optimal conditions, the linear ranges of the eight quinolones were 1 ~ 100 µg/L with good linearity (r2 was 0.998 ~ 0.999), and the limits of detection and quantification were 0.08 ~ 0.30 µg/L and 0.27 ~ 0.98 µg/L, respectively. The average extraction recoveries of spiked cattle urine samples were 70.13 ~ 98.50% with relative standard deviations below 13.97%. This method can provide a reference for the pre-treatment of quinolone residue detection.

High antipersister activity of a promising new quinolone drug candidate in eradicating uropathogenic Escherichia coli persisters and persistent infection in mice.

AIMS: To develop more potent drugs that eradicate persister bacteria and cure persistent urinary tract infections (rUTIs). METHODS AND RESULTS: We synthesized eight novel clinifloxacin analogs and measured minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), the time-kill curves in uropathogenic Escherichia coli (UPEC) UTI89, and applied the candidate drugs and combinations against biofilm bacteria in vitro and in mice. Transcriptomic analysis was performed for UPEC after candidate drug treatment to shed light on potential mechanism of action. We identified Compound 2, named Qingdafloxacin (QDF), which was more potent than clinafloxacin and clinically used levofloxacin and moxifloxacin, with an MIC of < 0.04 µg ml-1 and an MBC of 0.08∼0.16 µg ml-1. In drug combination studies, QDF + gentamicin + nitrofuran combination but not single drugs completely eradicated all stationary phase bacteria containing persisters and biofilm bacteria, and all bacteria in a persistent UTI mouse model. Transcriptome analysis revealed that the unique antipersister activity of QDF was associated with downregulation of genes involved in bacterial stress response, DNA repair, protein misfolding repair, pyrimidine metabolism, glutamate, and glutathione metabolism, and efflux. CONCLUSIONS: QDF has high antipersister activity and its drug combinations proved highly effective against biofilm bacteria in vitro and persistent UTIs in mice, which may have implications for treating rUTIs.

Stir-bar sorptive extraction based on hydroxyl-functionalized zirconium-metal-organic framework for the detection of three quinolones in actual samples.

A novel analytical method based on stir-bar sorptive extraction was proposed for the determination of three trace quinolones in fish and shrimp samples. UiO-66-(OH)2 , a hydroxyl-functionalized zirconium metal-organic framework, has been coated on frosted glass rods by an in situ growth method. The product, UiO-66-(OH)2 modified frosted glass rods, has been characterized and key parameters have been optimized in combination with ultra-high-performance liquid chromatography. The detection limits of enoxacin, norfloxacin, and ciprofloxacin were 0.48-0.8 ng ml-1 , and the detection concentrations were in the range of 10-300 ng ml-1 , showing a good linear relationship. This method was used for the determination of three quinolones in aquatic organisms, and the recoveries in spiked fish and shrimp muscle tissue samples were 74.8%-105.4% and 82.5%-115.8%, respectively. The relative standard deviations were less than 6.9%. The established method combined stir-bar sorptive extraction based on UiO-66-(OH)2 modified frosted glass rods with ultra-high-performance liquid chromatography, has good application prospects for the detection of quinolone residues in fish and shrimp muscle samples.

Efficacy and safety of 1% and 2% rebamipide clear solution in dry eye disease: a multicenter randomized trial.

BACKGROUND: To evaluate the efficacy of 1% and 2% rebamipide clear solution in the treatment of dry eye disease (DED). METHODS: Two hundred twenty patients with DED were randomly assigned to one of three groups: the 1% rebamipide, 2% rebamipide, or placebo (eye drops containing the same ingredients, except for the active components). Each eye drop was instilled four times daily for 12 weeks. Changes in tear film break-up time (TBUT), corneal and conjunctival staining score, Schirmer 1 test, and the Ocular Surface Disease Index (OSDI) from baseline to 12-week visit between the study groups were compared for efficacy assessment. RESULTS: The mean age of study patients was 43.8±14.2 years. The 1% and 2% rebamipide groups showed greater improvement in TBUT (1.99±1.87 and 2.02±2.21 s) at 12 weeks from baseline than the placebo group (1.25±2.93 s). The 2% rebamipide group showed greater improvement in the corneal staining score (- 3.15±2.00) at 12 weeks from baseline than the placebo group (- 2.85±1.80). The 1% and 2% rebamipide groups showed improvement in Schirmer 1 test (1.27±3.86 and 1.50±4.14 mm) at 12 weeks of treatment, but not the placebo group (0.55±2.99 mm). Both the rebamipide groups and the placebo group showed significantly improved OSDI after treatment for 12 weeks; however, there was no significant difference among the three groups. CONCLUSIONS: 1% and 2% rebamipide clear solutions are an effective therapeutic option for improving TBUT and tear volume, and stabilizing the corneal staining score in DED.

QTc prolongation during levofloxacin and triazole combination chemoprophylaxis: Prevalence and predisposing risk factors in a cohort of hematopoietic cell transplantation recipients.

BACKGROUND: QTc interval prolongation has been reported when combining fluoroquinolones and triazoles for chemoprophylaxis in cancer patients. Herein, we aimed to identify the prevalence and contributing factors to QTc prolongation in hematopoietic cell transplantation (HCT) recipients who received these agents during the neutropenic phase. METHODS: This is a retrospective medical chart review conducted at a university hospital in Lebanon from 2017 to 2020. It included all adult HCT inpatients on antimicrobial prophylaxis with fluoroquinolones and triazoles and whose baseline ECG monitoring done prior to chemoprophylaxis administration, then on day-3 and day-6 of therapy, were available. RESULTS: Overall, 68 HCT recipients met our inclusion criteria, of which 22% developed QTc prolongation. Based on bivariate analysis, female gender contributed to QTc prolongation (P = 0.001). There was a trend to QTc prolongation in patients with predisposing thyroid disease (P = 0.12), grade 2 vomiting and diarrhea (P = 0.16, P = 0.46, respectively), baseline hypokalemia (P = 0.18) and hypocalcemia (P = 0.3), hypomagnesemia on day-3 (P = 0.21) and day-6 hyponatremia (P = 0.36). Patients receiving two or more drugs with a known or probable risk of QTc prolongation (other than the fluoroquinolone/ triazole combination) were more prone to experience a prolonged QTc interval (P = 0.09). None of the patients that had QTc prolongation died or developed serious arrhythmias. CONCLUSION: The prevalence of QTc prolongation was 22% among HCT recipients on fluoroquinolone and triazole prophylaxis, yet we did not identify any independent risk factors for this issue. None of the patients that had QTc interval prolongation died or developed serious arrhythmias.

A 2.8 Å Structure of Zoliflodacin in a DNA Cleavage Complex with Staphylococcus aureus DNA Gyrase.

Since 2000, some thirteen quinolones and fluoroquinolones have been developed and have come to market. The quinolones, one of the most successful classes of antibacterial drugs, stabilize DNA cleavage complexes with DNA gyrase and topoisomerase IV (topo IV), the two bacterial type IIA topoisomerases. The dual targeting of gyrase and topo IV helps decrease the likelihood of resistance developing. Here, we report on a 2.8 Å X-ray crystal structure, which shows that zoliflodacin, a spiropyrimidinetrione antibiotic, binds in the same DNA cleavage site(s) as quinolones, sterically blocking DNA religation. The structure shows that zoliflodacin interacts with highly conserved residues on GyrB (and does not use the quinolone water-metal ion bridge to GyrA), suggesting it may be more difficult for bacteria to develop target mediated resistance. We show that zoliflodacin has an MIC of 4 µg/mL against Acinetobacter baumannii (A. baumannii), an improvement of four-fold over its progenitor QPT-1. The current phase III clinical trial of zoliflodacin for gonorrhea is due to be read out in 2023. Zoliflodacin, together with the unrelated novel bacterial topoisomerase inhibitor gepotidacin, is likely to become the first entirely novel chemical entities approved against Gram-negative bacteria in the 21st century. Zoliflodacin may also become the progenitor of a new safer class of antibacterial drugs against other problematic Gram-negative bacteria.

Design, Synthesis and Pharmacological Evaluation of New Quinoline-Based Panx-1 Channel Blockers.

Pannexins are an interesting new target in medicinal chemistry, as they are involved in many pathologies such as epilepsy, ischemic stroke, cancer and Parkinson's disease, as well as in neuropathic pain. They are a family of membrane channel proteins consisting of three members, Panx-1, Panx-2 and Panx-3, and are expressed in vertebrates. In the present study, as a continuation of our research in this field, we report the design, synthesis and pharmacological evaluation of new quinoline-based Panx-1 blockers. The most relevant compounds 6f and 6g show an IC50 = 3 and 1.5 µM, respectively, and are selective Panx-1 blockers. Finally, chemical stability, molecular modelling and X-ray crystallography studies have been performed providing useful information for the realization of the project.

Rapid Limit Test of Eight Quinolone Residues in Food Based on TLC-SERS, a New Limit Test Method.

Residual quinolones in food that exceed their maximum residue limit (MRL) are harmful to human health. However, the existing methods used for testing these residues have limitations; so, we developed a new limit test method called TLC-SERS to rapidly determine the levels of residues of the following: enrofloxacin (A), ciprofloxacin (B), ofloxacin (C), fleroxacin (D), sparfloxacin (E), enoxacin (F), gatifloxacin (G), and nadifloxacin (H). The residues ware preliminarily separated via TLC. The tested compounds' position on a thin-layer plate were labeled using their relative Rf under 254 nm ultraviolet light, and an appropriate amount of nanometer silver solution was added to the position. The silver on the plate was irradiated with a 532 nm laser to obtain the SERSs of the compounds. The results show significant differences in the SERS of the eight quinolones: the LODs of H, A, D, E, C, G, F, and B were 9.0, 12.6, 8.9, 19.0, 8.0, 8.7, 19.0, and 12.6 ng/mL, respectively; and the RSD was ≤4.9% for the SERS of each quinolone. The limit test results of 20 samples are consistent with those obtained via UPLC-MS/MS. The results indicate that TLC-SERS is a specific, sensitive, stable, and accurate method, providing a new reference for the rapid limit test of harmful residues in foods.

Effective Synthesis of 4-Quinolones by Reductive Cyclization of 2'-Nitrochalcones Using Formic Acid as a CO Surrogate.

4-Quinolones are the structural elements of many pharmaceutically active compounds. Although several approaches are known for their synthesis, the introduction of an aryl ring in position 2 is problematic with most of them. The reductive cyclization of o-nitrochalcones by pressurized CO, catalyzed by ruthenium or palladium complexes, has been previously reported to be a viable synthetic strategy for this aim, but the need for pressurized CO lines and autoclaves has prevented its widespread use. In this paper, we describe the use of the formic acid/acetic anhydride mixture as a CO surrogate, which allows us to perform the reaction in a cheap and commercially available thick-walled glass tube without adding any gaseous reagent. The obtained yields are often high and compare favorably with those previously reported by the use of pressurized CO. The procedure was applied to a three-step synthesis from commercially available and cheap reagents of the alkaloid Graveoline.