Novel 2,6-bis(4-methoxyphenyl)-1-methylpiperidin-4-one oxime esters: synthesis and a new insight into their antioxidant and antimicrobial potential

A simple and efficient protocol for the synthesis of novel 2,6-bis(4-methoxyphenyl)-1-methylpiperidin-4-one oxime esters 4(a-q) is described. Initially, p-anisaldehyde 1 was condensed (Mannich reaction) with acetone and ammonium acetate trihydrate afforded 2,6-bis(4-methoxyphenyl)piperidin-4-one 2. Then, methylation followed by oximation with hydroxylamine hydrochloride (NH(2)OHa (TM) HCl) furnished a key scaffold 4. Further, to explore the enhanced biological properties of the piperidin-4-one core i.e. the key scaffold 4 was conjugated with substituted benzoyl chlorides in the presence of anhydrous K2CO3 as base to obtain novel 2,6-bis(4-methoxyphenyl)-1-methylpiperidin-4-one oxime esters 4(a-q) in excellent yields. The newly synthesized compounds were characterized by elemental analysis, IR, H-1 NMR, C-13 NMR and mass spectroscopic techniques, and screened for their in vitro antioxidant and antimicrobial activities. Most of the compounds exerted positive efficacy towards the biological assays performed. Among the synthesized analogues, compounds 4l and 4m exhibited promising antioxidant activity and on the other hand compounds 4b and 4d manifested persuasive antibacterial activity, whereas compound 4b displayed stupendous antifungal activity against A. flavus strain.

Antibacterial activities of naturally occurring compounds against Mycobacterium avium subsp. paratuberculosis.

The antibacterial activities of 18 naturally occurring compounds (including essential oils and some of their isolated constituents, apple and green tea polyphenols, and other plant extracts) against three strains of Mycobacterium avium subsp. paratuberculosis (a bovine isolate [NCTC 8578], a raw-milk isolate [806R], and a human isolate [ATCC 43015]) were evaluated using a macrobroth susceptibility testing method. M. avium subsp. paratuberculosis was grown in 4 ml Middlebrook 7H9 broth containing 10% oleic acid-albumin-dextrose-catalase, 0.05% Tween 80 (or 0.2% glycerol), and 2 µg/ml mycobactin J supplemented with five concentrations of each test compound. The changes in the optical densities of the cultures at 600 nm as a measure of CFU were recorded at intervals over an incubation period of 42 days at 37°C. Six of the compounds were found to inhibit the growth of M. avium subsp. paratuberculosis. The most effective compound was trans-cinnamaldehyde, with a MIC of 25.9 µg/ml, followed by cinnamon oil (26.2 µg/ml), oregano oil (68.2 µg/ml), carvacrol (72.2 µg/ml), 2,5-dihydroxybenzaldehyde (74 µg/ml), and 2-hydroxy-5-methoxybenzaldehyde (90.4 µg/ml). With the exception of carvacrol, a phenolic compound, three of the four most active compounds are aldehydes, suggesting that the structure of the phenolic group or the aldehyde group may be important to the antibacterial activity. No difference in compound activity was observed between the three M. avium subsp. paratuberculosis strains studied. Possible mechanisms of the antimicrobial effects are discussed.

Design, synthesis and photodynamic antimicrobial activity of ruthenium trischelate diimine complexes

In this study, we describe, for the first time, the synthesis and photophysical and microbiological investigation of ruthenium trischelate diimine complexes designed so as to possess properties specifically suited for use in Photodynamic antimicrobial chemotherapy (PACT). Of the three compounds investigated, one ([Ru(dmob)(3)]Cl-2) has demonstrated considerable promise as a photosensitiser for use in PACT. As a result, this compound is now the subject of comprehensive chemical, toxicological and formulation studies.

Antimicrobial and antibiofilm activities of 1-alkylquinolinium bromide ionic liquids

Quinoline derivatives are known to possess a range of bioactive and medicinal activities, which have been exploited in the design of antibacterial, antifungal and antimalarial compounds. In this study, we report on the microbiological toxicity of a series of 1-alkylquinolinium bromides against a range of clinically relevant microorganisms, in both planktonic and sessile (biofilm) cultures. A comparison of antimicrobial activity against planktonic bacteria and established biofilms is presented. In general, 1-alkylquinolinium ionic liquids possess excellent, broad spectrum antimicrobial activity against microorganisms grown in both the planktonic and sessile, or biofilm, mode of growth. Importantly, these compounds are potent against Gram positive and Gram negative bacteria, as well as fungi, with a clear dependency on length of the alkyl substituent for activity, with compounds containing twelve and fourteen carbons in the alkyl group exhibiting highest antimicrobial and antibiofilm activity. © 2010 The Royal Society of Chemistry.

Antimicrobial/cytolytic peptides from the venom of the North African scorpion, Androctonus amoreuxi: Biochemical and functional characterization of natural peptides and a single site-substituted analog

The venoms of scorpions are complex cocktails of polypeptide toxins that fall into two structural categories: those that contain cysteinyl residues with associated disulfide bridges and those that do not. As the majority of lethal toxins acting upon ion channels fall into the first category, most research has been focused there. Here we report the identification and structural characterization of two novel 18-mer antimicrobial peptides from the venom of the North African scorpion, Androctonus amoreuxi. Named AamAP1 and AamAP2, both peptides are C-terminally amidated and differ in primary structure at just two sites: Leu?Pro at position 2 and Phe?Ile at position 17. Synthetic replicates of both peptides exhibited a broad-spectrum of antimicrobial activity against a Gram-positive bacterium (Staphylococcus aureus), a Gram-negative bacterium (Escherichia coli) and a yeast (Candida albicans), at concentrations ranging between 20µM and 150µM. In this concentration range, both peptides produced significant degrees of hemolysis. A synthetic replicate of AamAP1 containing a single substitution (His?Lys) at position 8, generated a peptide (AamAP-S1) with enhanced antimicrobial potency (3-5µM) against the three test organisms and within this concentration range, hemolytic effects were negligible. In addition, this His?Lys variant exhibited potent growth inhibitory activity (ID(50) 25-40µm) against several human cancer cell lines and endothelial cells that was absent in both natural peptides. Natural bioactive peptide libraries, such as those that occur in scorpion venoms, thus constitute a unique source of novel lead compounds with drug development potential whose biological properties can be readily manipulated by simple synthetic chemical means.

The major facilitator superfamily transporter MdtM contributes to intrinsic resistance of Escherichia coli to quaternary ammonium compounds

OBJECTIVES:
Quaternary ammonium compounds (QACs) are used extensively as biocides and their misuse may be contributing to the development of bacterial resistance. Although the major intrinsic resistance to QACs of Gram-negative bacteria is mediated by the action of tripartite multidrug transporters of the resistance-nodulation-division family, we aimed to test if the promiscuity of the recently characterized major facilitator superfamily multidrug transporter, MdtM, from Escherichia coli enabled it also to function in the efflux of QACs.
METHODS:
The ability of the major facilitator mdtM gene product, when overexpressed from multicopy plasmid, to protect E. coli cells from the toxic effects of a panel of seven QACs was determined using growth inhibition assays in liquid medium. Interaction between QACs and MdtM was studied by a combination of substrate binding assays using purified protein in detergent solution and transport assays using inverted vesicles.
RESULTS:
E. coli cells that overproduced MdtM were less susceptible to the cytotoxic effects of each of the QACs tested compared with cells that did not overproduce the transporter. Purified MdtM bound each QAC with micromolar affinity and the protein utilized the electrochemical proton gradient to transport QACs across the cytoplasmic membrane. Furthermore, the results suggested a functional interaction between MdtM and the tripartite resistance-nodulation-division family AcrAB-TolC efflux system.
CONCLUSIONS:
The results support a hitherto unidentified capacity for a single-component multidrug transporter of the major facilitator superfamily, MdtM, to function in the efflux of a broad range of QACs and thus contribute to the intrinsic resistance of E. coli to these compounds.

Halophilic microorganisms as a source of novel antibiofilm compounds

Objectives: There is great urgency for alternate sources of antibiotics to be identified. One relatively untapped source of novel bioproducts, including antimicrobials, is organisms derived from extreme environments. Halophiles (which require high salt concentrations) are one such group which is being increasingly explored for their biotechnological potential. The aim of this study was to identify halophilic environmental isolates which possessed in vitro and in vivo antimicrobial and antibiofilm activities. Methods: 73 halophilic bacteria and archaea were isolated from Kilroot salt mine in Northern Ireland. Culture extracts of each isolate were screened for antimicrobial and antibiofilm activity against numerous pathogenic bacteria, including Staphylococcus species and Pseudomonas aeruginosa, both model strains and clinical isolates. The methods used included disc diffusion assays of crude extracts, MIC screening, the MBEC assay, and an in vivo model based on the Greater Wax Moth (Galleria mellonella). Results: The assays indicated >50% of extracts displayed antimicrobial and antibiofilm activity against at least one pathogen, the majority being Staphylococcus species, but also E. coli and P. aeruginosa. Biofilms were either reduced or eradicated by halophile extracts when tested with the MBEC device. Further experiments demonstrated that these effects could be replicated in vivo, with extracts reducing the severity of infections and enhancing the survival of infected G. mellonella. Conclusions: The importance of extremophiles to pharmaceutical research should not be underestimated. While not yet fully characterised, based on the data obtained, the halophiles isolated during this study may provide a promising reservoir of novel antimicrobial and antibiofilm compounds.

Hylaranins: prototypes of a new class of amphibian antimicrobial peptide from the skin secretion of the oriental broad-folded frog, Hylarana latouchii

Amphibian skin secretions contain a broad spectrum of biologically active compounds, particularly antimicrobial peptides, which are considered to constitute a first line of defence against bacterial infection. Here we describe the identification of two prototype peptides representing a novel structural class of antimicrobial peptide from the skin secretion of the oriental broad-folded frog, Hylarana latouchii. Named hylaranin-L1 (GVLSAFKNALPGIMKIIVamide) and hylaranin-L2 (GVLSVIKNALPGIMRFIAamide), both peptides consist of 18 amino acid residues, are C-terminally amidated and are of unique primary structures. Their primary structures were initially deduced by MS/MS fragmentation sequencing from reverse-phase HPLC fractions of skin secretion that demonstrated antimicrobial activity. Subsequently, their precursor-encoding cDNAs were cloned from a skin secretion-derived cDNA library and their primary structures were confirmed unequivocally. Synthetic replicates of both peptides exhibited broad-spectrum antimicrobial activity with mean inhibitory concentrations (MICs) of 34 µM against Gram-negative Escherichia coli, 4.3 µM against Gram-positive Staphylococcus aureus and 4–9 µM against the yeast, Candida albicans. Both peptides exhibited little haemolytic activity (<6 %) at the MICs for S. aureus and C. albicans. Amphibian skin secretions thus continue to provide novel antimicrobial peptide structures that may prove to be lead compounds in the design of new classes of anti-infection therapeutics.

Cationicity-Enhanced Analogues of the Antimicrobial Peptides, AcrAP1 and AcrAP2, from the Venom of the Scorpion, Androctonus crassicauda, Display Potent Growth Modulation Effects on Human Cancer Cell Lines

The non disulphide-bridged peptides (NDBPs) of scorpion venoms are attracting increased interest due to their structural heterogeneity and broad spectrum of biological activities. Here, two novel peptides, named AcrAP1 and AcrAP2, have been identified in the lyophilised venom of the Arabian scorpion, Androctonus crassicauda, through “shotgun” molecular cloning of their biosynthetic precursor-encoding cDNAs. The respective mature peptides, predicted from these cloned cDNAs, were subsequently isolated from the same venom sample using reverse phase HPLC and their identities were confirmed by use of mass spectrometric techniques. Both were found to belong to a family of highly-conserved scorpion venom antimicrobial peptides - a finding confirmed through the biological investigation of synthetic replicates. Analogues of both peptides designed for enhanced cationicity, displayed enhanced potency and spectra of antimicrobial activity but, unlike the native peptides, these also displayed potent growth modulation effects on a range of human cancer cell lines. Thus natural peptide templates from venom peptidomes can provide the basis for rational analogue design to improve both biological potency and spectrum of action. The diversity of such templates from such natural sources undoubtedly provides the pharmaceutical industry with unique lead compounds for drug discovery.

The antimicrobial potential of ionic liquids: A source of chemical diversity for infection and biofilm control

Although described almost a century ago, interest in ionic liquids has flourished in the last two decades, with significant advances in the understanding of their chemical, physical and biological property sets driving their widespread application across multiple and diverse research areas. Significant progress has been made through the contributions of numerous research groups detailing novel libraries of ionic liquids, often ‘task-specific’ designer solvents for application in areas as diverse as separation technology, catalysis and bioremediation. Basic antimicrobial screening has often been included as a surrogate indication of the environmental impact of these compounds widely regarded as ‘green’ solvents. Obviating the biological properties, specifically toxicity, of these compounds has obstructed their potential application as sophisticated designer biocides. A recent tangent in ionic liquids research now aims to harness tuneable biological properties of these compounds in the design of novel potent antimicrobials, recognising their unparalleled flexibility for chemical diversity in a severely depleted antimicrobial arsenal. This review concentrates primarily on the antimicrobial potential of ionic liquids and aims to consolidate contemporary microbiological background information, assessment protocols and future considerations necessary to advance the field in light of the urgent need for antimicrobial innovation.

Antioxidant,antimicrobial and toxicological properties of Schinus molle L. essential oils

Ethnopharmacological relevance: Schinus molle L. has been used in folk medicine as antibacterial, antiviral, topical antiseptic, antifungal, antioxidant, anti-inflammatory, anti-tumoural as well as antispasmodic and analgesic; however, there are few studies of pharmacological and toxicological properties of S. molle essential oils. Aim of the study: The aim of this study was to evaluate the antioxidant and antimicrobial activities of S. molle leaf and fruit essential oils, correlated with their chemical composition and evaluate their acute toxicity. Materials and methods: The chemical composition of S. molle leaf and fruit essential oils were evaluated by GC-FID and GC-MS. Antioxidant properties were determined using the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) free radical and β-carotene/linoleic acid methods. Antimicrobial properties were evaluated by the agar disc diffusion method and minimal inhibitory concentration assay. Toxicity in Artemia salina and acute toxicity with behavioural screening in mice were evaluated. Results: The dominant compounds found in leaf and fruit essential oils (EOs) were monoterpene hydrocarbons, namely -phellandrene, β-phellandrene, β-myrcene, limonene and α-pinene. EOs showed low scavenging antioxidant activity by the DPPH free radical method and a higher activity by the β-carotene/linoleic acid method. Antimicrobial activity of EOs was observed for Gram+, Gram– pathogenic bacteria and food spoilage fungi. EOs showed cytotoxicity for Artemia salina and lower toxicity in Swiss mice. Conclusions: The result showed that EOs of leaves and fruits of S. molle demonstrated antioxidant and antimicrobial properties, suggesting their potential use in food or pharmaceutical industries.

Antimicrobial resistance and synergy in herbal medicine

Antimicrobial resistance (AMR) is a serious and growing threat to human health. The development of new antibiotics is limited and slow. The tradition of synergy in herbal medicine is being used as a source of research ideas. A literature review of antimicrobial research and plant synergy published in a five year period was carried out using online databases. The in vitro findings were that most of the research reported synergy both within plants and between plants and antibiotics. Whole plant extracts and combinations of compounds were shown to be more effective antimicrobials than isolated constituents. The discussion highlights that the in vitro herbal research findings are difficult to apply to practice and aren’t progressing to clinical trials. Collaborative, innovative, inter-disciplinary clinical research is recommended.

Antimicrobial activity of essential oils isolated from Portuguese endemic species of Thymus

Aims: Thymus species are wild species mostly found in the arid lands of Portugal. Possible antimicrobial properties of Thymus essential oils have been investigated. The chemical composition of the essential oils and the antimicrobial activity of Thymus mastichina (L) L. subsp. mastichina , T. camphoratus and T. lotocephalus from different regions of Portugal were analysed. Methods and Results: Hydrodistillation was used to isolate the essential oils and the chemical analyses were performed by gas chromatography (GC) and GC coupled to mass spectrometry. The antimicrobial activity was tested by the disc agar diffusion technique against Candida albicans , Escherichia coli , Listeria monocytogenes , Proteus mirabilis , Salmonella spp. and Staphylococcus aureus . Pure linalool, 1,8-cineole and a mixture (1:1) of these compounds were included. Linalool, 1,8-cineole or linalool/1,8-cineole and linalool/1,8-cineole/linalyl acetate were the major components of the essential oils, depending on the species or sampling place. The essential oils isolated from the Thymus species studied demonstrated antimicrobial activity but the micro-organisms tested had significantly different sensitivities. Conclusions: The antimicrobial activity of essential oils may be related to more than one component. Significance and Impact of the Study: Portuguese endemic species of Thymus can be used for essential oil production for food spoilage control, cosmetics and pharmaceutical use. Further studies will be required to elucidate the cell targets of the essential oil components.

Antimicrobial activity of essential oils against multiresistant aeromonads and enterococci

Tese de mestrado. Biologia (Microbiologia Aplicada). Universidade de Lisboa, Faculdade de Ciências, 2014

Brazilian fruit pulps as functional foods and additives: Evaluation of bioactive compounds

Eight tropical fruit pulps from Brazil were simultaneously characterised in terms of their antioxidant and antimicrobial properties. Antioxidant activity was screened by DPPH radical scavenging activity (126–3987 mg TE/100 g DW) and ferric reduction activity power (368–20819 mg AAE/100 g DW), and complemented with total phenolic content (329–12466 mg GAE/100 g DW) and total flavonoid content measurements (46–672 mg EE /100 g DW), whereas antimicrobial activity was tested against the most frequently found food pathogens. Acerola and açaí presented the highest values for the antioxidant-related measurements. Direct correlations between these measurements could be observed for some of the fruits. Tamarind exhibited the broadest antimicrobial potential, having revealed growth inhibition of Pseudomonas aeruginosa. Escherichia coli, Listeria monocytogenes, Salmonella sp. and Staphylococcus aureus. Açaí and tamarind extracts presented an inverse relationship between antibacterial and antioxidant activities, and therefore, the antibacterial activity cannot be attributed (only) to phenolic compounds.