Scaffold‐Hopping of Multicationic Amphiphiles Yields Three New Classes of Antimicrobials

Quaternary ammonium compounds (QACs) are a vital class of antiseptics. Recent investigations into their construction are uncovering novel and potent multicationic variants. Based on a trisQAC precedent, we have implemented a scaffold‐hopping approach to develop alternative QAC architectures that display 1–3 long alkyl chains in specific projections from cyclic and branched core structures bearing 3–4 nitrogen atoms. The preparation of 30 QAC structures allowed for correlation of scaffold structure with antimicrobial activity. We identified QACs with limited conformational flexibility that have improved bioactivity against planktonic bacteria as compared to their linear counterparts. We also confirmed that resistance, as evidenced by an increased minimum inhibitory concentration (MIC) for methicillin‐resistant Staphylococcus aureus (MRSA) compared to methicillin‐susceptible Staphylococcus aureus (MSSA), can reduce efficacy up to 64‐fold for monocationic QACs. Differentiation of antimicrobial and anti‐biofilm activity, however, was not observed, suggesting that these compounds utilize a non‐specific mode of eradication.     

Efflux Pumps Might Not Be the Major Drivers of QAC Resistance in Methicillin‐Resistant Staphylococcus aureus

Quaternary ammonium compounds (QACs) are commonly used antiseptics that are now known to be subject to bacterial resistance. The prevalence and mechanisms of such resistance, however, remain underexplored. We investigated a variety of QACs, including those with multicationic structures (multiQACs), and the resistance displayed by a variety of Staphylococcus aureus strains with and without genes encoding efflux pumps, the purported main driver of bacterial resistance in MRSA. Through minimum inhibitory concentration (MIC)‐, kinetic‐, and efflux‐based assays, we found that neither the qacR/qacA system present in S. aureus nor another efflux pump system is the main reason for bacterial resistance to QACs. Our findings suggest that membrane composition could be the predominant driver that allows CA‐MRSA to withstand the assault of conventional QAC antiseptics.     

Analysis of the Destabilization of Bacterial Membranes by Quaternary Ammonium Compounds: A Combined Experimental and Computational Study

The mechanism of action of quaternary ammonium compound (QAC) antiseptics has long been assumed to be straightforward membrane disruption, although the process of approaching and entering the membrane has little modeling precedent. Furthermore, questions have more recently arisen regarding bacterial resistance mechanisms, and why select classes of QACs (specifically, multicationic QACs) are less prone to resistance. In order to better understand such subtleties, a series of molecular dynamics simulations were utilized to help identify these molecular determinants, directly comparing mono-, bis-, and triscationic QACs in simulated membrane intercalation models. Three distinct membranes were simulated, mimicking the surfaces of Escherichia coli and Staphylococcus aureus, as well as a neutral phospholipid control. By analyzing the resulting trajectories in the form of a timeseries analysis, insight was gleaned regarding the significant steps and interactions involved in the destabilization of phospholipid bilayers within the bacterial membranes. Finally, to more specifically probe the effect of the hydrophobic section of the amphiphile that presumably penetrates the membrane, a series of alkyl- and ester-based biscationic quaternary ammonium compounds were prepared, tested for antimicrobial activity against both Gram-positive and Gram-negative bacteria, and modeled.     

Interaction of Hyaluronic Acid (HA) with Organosilicon (Si‐QAC) Modified Magnetite for HA Recovery

Abstract

Cetylpyridinium chloride (CPC) is commonly used to precipitate hyaluronic acid (HA) from crude extract in a HA purification process. 3‐(Trimethoxysilyl)‐propyldimethyl octadecyl ammonium chloride (Si‐QAC) has a structure very similar to CPC when it is bonded to surfaces through its silane base. By taking advantage of its easy surface bonding property, Si‐QAC was bonded to the silica‐coated magnetite to facilitate HA recovery. The effects of pH, salt concentration, and the temperature on HA adsorption to Si‐QAC‐magnetite were studied. Not only the positively charged nitrogen but also hydrophobic long tail of Si‐QAC contributed to the strong interaction between HA and Si‐QAC‐magnetite. The maximum HA adsorption capacity was 38 mg/g‐dry magnetite and the equilibrium dissociation constant was 0.016 g/l at pH 4 under 37°C. The adsorbed HA could be effectively desorbed by 1 N NaCl supplemented with 0.1% Triton X100.     

Building a Better Quaternary Ammonium Compound (QAC): Branched Tetracationic Antiseptic Amphiphiles

Bacteria contaminate surfaces in a wide variety of environments, causing severe problems across a number of industries. In a continuation of our campaign to develop novel antibacterial quaternary ammonium compounds (QACs) as useful antiseptics, we have identified a starting material bearing four tertiary amines, enabling the rapid synthesis of several tris‐ and tetracationic QACs. Herein we report the synthesis and biological activity of a series of 24 multiQACs deemed the “superT” family, and an investigation of the role of cationic charge in antimicrobial and anti‐biofilm activity, as well as toxicity. This class represents the most potent series of QACs reported to date against methicillin‐resistant Staphylococcus aureus (MRSA), with minimum inhibitory concentrations (MICs) and minimum biofilm eradication concentrations (MBECs) as low as 0.25 and 25 μm , respectively. Based on the significant cell‐surface‐charge differences between bacterial and eukaryotic cells, in certain cases we observed excellent efficacy‐to‐toxicity profiles, exceeding a 100‐fold differential. This work further elucidates the chemical underpinnings of disinfectant efficacy versus toxicity based on cationic charge.     

Derivatives of Di-O-octanoylglycerol and mono-O-octylglycerol as modulators of protein kinase C and diacylglycerol kinase activities

Twelve analogs of 1,2-di-O-octanoylglycerol modified at C-3 and three quaternaryN-alkyl-ammonium derivatives of glycerol were synthesized. The compounds were testedin vitro as potential modulators of the calcium activated, phospholipid dependent protein kinase C (PKC) and diacylglycerol (DAG) kinase activities in order to understand the molecular interactions of these enzymes with their natural activators, inhibitors, or substrates. PKC activity was assayed by measuring histone H₁ phosphorylation, and the compounds synthesized were tested either in the presence (inhibitors) or in the absence (activators) of 1,2-di-O-octanoyglycerol analogs with the phosphatidylserine/Ca²⁺ mixture. DAG kinase activity was measured by the incorporation of phosphate into 1,2-di-O-oleoyl-sn-glycerol in the presence of the various analogs synthesized. In regard to PKC activity, the assays revealed that 1,2-di-O-octanoylglycerol analogs are inactive when modified at C-3 with groups which do not permit hydrogen bonding. Under our conditions, di-O-octanoylthioglycerol, which has been reported as inactive, was able to activate PKC in the presence of phosphatidylserine. It has been shown to give a synergistic activation with diacylglycerol and had no affinity for the phorbol ester receptor binding site, suggesting thatO-octanoylthioglycerol interacts with the enzyme at a different site from the phorbol ester receptor binding site. PKC and DAG kinase activities are inhibited byN-alkyl-ammonium compounds (IC₅₀ 24 μM) only when either two 8-carbon alkyl or acyl chains are present at the 1- and 2-positions of the glycerol backbone. The fact that these compounds have a strong effect on the binding of [³H]phorbol 12,13-dibutyrate to protein kinase C, and also inhibit DAG kinase, may suggest binding to the DAG site of the regulatory domain of PKC.     

Inhibitory pheromonal activity promoted by sulfur analogs of the sex pheromone of the female processionary mothThaumetopoea pityocampa (Denis and schiff)

New sulfur analogs of the sex pheromone of the female processionary mothThaumetopoea pityocampa have been found to be effective inhibitors of the natural pheromone activity both in EAG bioassays and field tests. The structures of these analogs have been derived from replacement of the oxygen atom(s) of the acetate group by sulfur (compounds 3-5) and the olefinic moiety of the enyne function by the isosteric SCH₂ group (compounds 6 and 7). The synthesis and biological activity of 3-[(Z)-12-pentadecen-10-ynylthio]-1,1,1-trifluoropropan-2-one (8), a closely related structure to the pheromone is also described.     

Moth responses to selectively fluorinated sex pheromone analogs

Partially fluorinated analogs of the European corn borer (Ostrinia nubilalis) female sex pheromone, 11-tetradecenyl acetate (97:3Z:E), having mono- and trifluorsubstitutions at the terminal carbon of the pheromone chain, mimicked the biological activity of the pheromone, while analogs with fluorine at either side of the double bond and a pentafluoro analog were essentially inactive. Comparison of the pheromonal activity of these analogs with the previously reported activity of similarly fluorinated pheromones in five other species of moths revealed an unpredictable relationship between fluorine substitution pattern and pheromone-mimicking activity. Fluorine substitution patterns that rendered pheromonal analogs biologically inactive in the European corn borer had no detrimental influence upon pheromonal activity in other species and the converse was also true. This is evidence that the relative importance of electronic qualities of sites within a pheromone molecule differ from species to species. Furthermore, it indicates that the biochemical components (pheromone receptor proteins, binding proteins, and enzymes) that make up moth olfactory chemosensory systems must also vary structurally from species to species, despite the fact that they are involved in olfactory sensing of compounds having very similar chemical structure.     

Metallocene QACs: The Incorporation of Ferrocene Moieties into monoQAC and bisQAC Structures

Inspired by the incorporation of metallocene functionalities into a variety of bioactive structures, particularly antimicrobial peptides, we endeavored to broaden the structural variety of quaternary ammonium compounds (QACs) by the incorporation of the ferrocene moiety. Accordingly, 23 ferrocene-containing mono- and bisQACs were prepared in high yields and tested for activity against a variety of bacteria, including Gram-negative strains and a panel of clinically isolated MRSA strains. Ferrocene QACs were shown to be effective antiseptics with some displaying single-digit micromolar activity against all bacteria tested, demonstrating yet another step in the expansion of structural variety of antiseptic QACs.     

Biosynthesis and Structure–Activity Relationship Investigations of the Diazeniumdiolate Antifungal Agent Fragin

Only a few natural products incorporating a diazeniumdiolate moiety have been isolated, and these compounds usually display a broad range of biological activities. Only recently has the first diazeniumdiolate natural product biosynthetic gene cluster been identified in Burkholderia cenocepacia H111, which produces the fungicide (−)-fragin and the signal molecule rac-valdiazen. In this study, l -valine was identified as the initial substrate of (−)-fragin biosynthesis with the aid of feeding experiments using isotopically labelled amino acid. The formation of the diazeniumdiolate was chemically studied with several proposed intermediates. Our results indicate that the functional group is formed during an early stage of the biosynthesis. Furthermore, an oxime compound was identified as a degradation product of (−)-fragin and was also observed in the crude extract of the wild-type strain. Moreover, a structure–activity relationship analysis revealed that each moiety of (−)-fragin is essential for its biological activity.     

Synthesis,Surface-Active Properties,and Emulsification Efficiency of Trimeric-Type Nonionic Surfactants Derived From Tris(2-aminoethyl)amine

Trimeric-type nonionic surfactants based on tris(2-aminoethyl)amine were prepared. N-alkyl chloride (namely, octanoyl chloride, n-decanoyl chloride, n-dodecanoyl chloride) was reacted with tris(2-aminoethyl)amine in the presence of toluene and triethylamine. The products were partially reduced and then ethoxylated by poly(ethylene glycol) of molecular weights 400, 1,000, and 2,000 g mol⁻¹. The structures were confirmed by infrared (IR) and ¹HNMR spectroscopy. The molecular weights of the surfactants were measured by gel permeation chromatography (GPC). The properties of the prepared compounds were investigated by the surface tension, interfacial tension, and cloud point. The emulsification power of the prepared surfactants for oil-in-water emulsions was also studied and the emulsion stability was monitored by an optical microscope and the bottle testing method. Some factors affecting the emulsion stability were investigated     

Preparation and surface-active properties of sulfopropylated N-alkylperfluorooctanamides

Sulfopropylation of perfluorooctanamide or its N-alkyl substituted derivatives gave products which were valuable as anionic surfactants. The amides were prepared by the reaction of ethyl perfluorooctanoate with ammonia orn-alkyl amines (C₁-C₁₂), and then treated with 1,3-propanesultone to obtain the desired products. The surfaceactive properties of these compounds were investigated to elucidate the correlation with the chain length of the N-alkyl group. Thus, generally speaking, the N-butyl derivative was found to exhibit properties superior to the others.     

Preparation and antibacterial properties of waterborne UV cured coating modified by quaternary ammonium compounds

In this article, the antibacterial properties and mechanism of waterborne UV cured acrylic coatings (WUV) modified by quaternary ammonium compounds (QAC) is discussed, as well as the changes in the antibacterial properties of QAC under the action of different additives. (60 wt% methanol, 60 wt% ethanol, and 75 wt% ethanol). And the chemical cross-linking method is used to combine WUV with QAC. The scanning electron microscopy (SEM), Fourier transforms infrared spectrometer (FTIR), and X-ray photoelectron spectroscopy (XPS) was employed to characterize the modified WUV. The antibacterial properties of three antibacterial agents in liquid coatings (WUV-L) and cured coating films (WUV-C) are investigated. The SEM images showed many irregular wrinkles appeared on the surface of modified coating films. The FTIR result showed the hydroxyl groups promoted the binding ability of the antibacterial agents and coating, and the XPS result revealed that the increase of −NR₄⁺ concentration enhanced the antibacterial properties of coating films. The antibacterial properties of WUV-L and WUV-C improved with the increase of QAC. Theoretical antibacterial agents mass fraction of 5% or higher was found to have the highest antibacterial rate (>90.00%) for WUV modification, among, the WUV modified by QAC-m60 is the best with the antibacterial rate reaching to 99.73% in WUV-L and 99.67% in WUV-C.     

Identification of Male-Produced Aggregation Pheromone of the Curculionid Beetle <Emphasis Type="Italic">Sternechus subsignatus</Emphasis>

Analyses of the headspace volatiles produced by males and females of Sternechus subsignatus Boheman (Coleoptera: Curculionidae) revealed seven male-specific compounds. The major component was (E)-2-(3,3-dimethylcyclohexylidene)-ethanol, and the minor components were 1-(2′-hydroxyethyl)-1-methyl-2-isopropenylcyclobutane (grandisol), 7-methyl-3-methyleneoct-6-en-1-ol, (Z)-2-(3,3-dimethylcyclohexylidene)-ethanol, (Z)- and (E)-2-(3,3-dimethylcyclohexylidene)-acetaldehyde, and (E)-2-(3,3-dimethylcyclohexylidene) acetic acid. The latter compound is described for the first time as a natural product. Only four of the seven identified compounds showed electrophysiological activity. Enantioselective gas chromatography showed that the natural grandisol is the (1R,2S)-stereoisomer. The major component, (E)-2-(3,3-dimethylcyclohexylidene)-ethanol, attracted S. subsignatus in olfactometer bioassays. Studies are in progress to evaluate the biological activity of the major component and the EAD-active mixture under field conditions.     

The l-Alanosine Gene Cluster Encodes a Pathway for Diazeniumdiolate Biosynthesis

N-Nitroso-containing natural products are bioactive metabolites with antibacterial and anticancer properties. In particular, compounds containing the diazeniumdiolate (N-nitrosohydroxylamine) group display a wide range of bioactivities ranging from cytotoxicity to metal chelation. Despite the importance of this structural motif, knowledge of its biosynthesis is limited. Herein we describe the discovery of a biosynthetic gene cluster in Streptomyces alanosinicus ATCC 15710 responsible for producing the diazeniumdiolate natural product l -alanosine. Gene disruption and stable isotope feeding experiments identified essential biosynthetic genes and revealed the source of the N-nitroso group. Additional biochemical characterization of the biosynthetic enzymes revealed that the non-proteinogenic amino acid l -2,3-diaminopropionic acid (l -Dap) is synthesized and loaded onto a free-standing peptidyl carrier protein (PCP) domain in l -alanosine biosynthesis, which we propose may be a mechanism of handling unstable intermediates generated en route to the diazeniumdiolate. These discoveries will facilitate efforts to determine the biochemistry of diazeniumdiolate formation.     

Behavioral and electroantennogram responses of periplanone analogs

The biological activities of synthetic periplanone analogs, including four candidates of periplanone-A (P-A), were evaluated by behavioral and electroantennogram (EAG) assays. Among 16 periplanone analogs, six compounds evoked pheromonal activity from the male American cockroaches. The threshold dosages of these biological active analogs were 10–10⁵ times lower than that of the known periplanone mimic, germacrene-D. The conformation required for eliciting the pheromonal activity is discussed in terms of the structure-activity relationship of these analogs. Hauptmann's P-A elicited the strongest pheromonal activity among four candidates of P-A in our bioassay, suggesting that Hauptmann's P-A is a natural P-A produced from female cockroaches.     

Sinomenine Derivatives: Synthesis,Antitumor Activity,and Apoptotic Induction in MCF-7 Cells via IL-6/PI3K/Akt/NF-κB Signaling Pathway

Natural products have been widely considered as an important resource for new drugs or lead compounds. Sinomenine (SIN) and its derivatives exert antitumor activity via regulation of inflammatory mediators. For these reasons we synthesized three series of SIN derivatives (compounds 4 a – i , 7 a – c and 11 a – c ) as antitumor agents from this natural product. All compounds were prepared by modification at the C1 and C4 positions of the A ring, the C4 position of the A ring, and the C6 and C7 positions of the C ring, respectively. All the derivatives were subjected to in vitro antitumor activity against HeLa, A549, HepG-2, MCF-7 and HT-29 cell lines. To observe the apoptotic induction of SIN derivatives and its mechanism, fluorescent staining and western blot assays were carried out for active compound against MCF-7. Based on the screening results, most of the SIN derivatives showed better antitumor activity than SIN. Some of them were found to possess broad-spectrum antitumor activity. Most notably, 11 c exhibited obvious antitumor activity in both cell lines with IC₅₀ values less than 11 μM. Besides, 11 c induced apoptosis of MCF-7 in a dose-dependent manner. Western blot assay demonstrated that 11 c inhibited IL-6-mediated activation of PI3K/Akt pathway. A docking study revealed that 11 c had stronger binding interaction with the residues of IL-6 than SIN. All these results indicate that 11 c may be a potential anti-breast cancer agent by directly targeting IL-6.     

Further Investigations into Rigidity-Activity Relationships in BisQAC Amphiphilic Antiseptics

Thirty-six biscationic quaternary ammonium compounds were efficiently synthesized in one step to examine the effect of molecular geometry of two-carbon linkers on antimicrobial activity. The synthesized compounds showed strong antimicrobial activity against a panel of both Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). While the linker geometry showed only a modest correlation with antimicrobial activity, several of the synthesized bisQACs are promising potential antiseptics due to good antimicrobial activity (MIC≤2 μM) and their higher therapeutic indices compared to previously reported QACs.     

Identification of Host-Related Volatiles Attractive to Pineapple Beetle Carpophilus humeralis

Volatiles collected from oranges fed upon by Carpophilus humeralis of either sex were consistently more attractive than volatiles from beetle-free oranges in wind-tunnel bioassays. Three compounds were identified as attractants from this system: 4-ethyl-2-methoxyphenol (1), 2,5-diisopropylpyrazine (2) (a new natural product), and 2-phenylethanol (3). Identifications were confirmed with synthetic compounds that had matching chromatographic and spectral properties. Compounds 1, 2, and 3 had only slight activity alone, but were highly synergistic with each other and with propyl acetate (PA), a fruity ester that is mildly attractive to Carpophilus beetles. Compound 2 was the most active in the wind tunnel; its threshold dose was 0.5 ng when PA was present. The structural specificity for these compounds was high. Twelve phenol analogs of 1 were tested, but only one of these, 2-methoxyphenol, was more attractive than the control. Similarly, the analogs of 2, 2-isopropylpyrazine and 2,6-diisopropylpyrazine, were completely inactive. In the field, a combination of 1, 2, and 3 was not attractive by itself, but it strongly synergized attraction to fermentation volatiles, Carpophilus pheromones, or both. Compounds 1, 2, and 3 apparently have a microbial origin because all three were detected when the host fruit was pineapples instead of oranges, because they could occur in the absence of beetles, and because autoclaved pineapple began to produce the compounds after inoculation from an attractive piece of fruit. The study demonstrated that host location for this generalist species can be far more complex than responding simply to the bouquet of low-molecular-weight volatiles normally associated with fermentation.