The Fe(III) and Ga(III) coordination chemistry of 3-(1-hydroxymethylidene) and 3-(1-hydroxydecylidene)-5-(2-hydroxyethyl)pyrrolidine-2,4-dione: novel tetramic acid degradation products of homoserine lactone bacterial quorum sensing molecules

NMR and EPR study of the interaction of tris(3-hydroxy-4-pyridinonato) Ga(III) complexes with liposomes that mimic plant membranes

We performed an NMR and EPR study of the interaction of four [Ga(3,4-HPO)₃] chelates with liposomes derived from a soybean extract (SEL) and simpler formulations using POPC (100%) and POPE:POPC (50%). Parent [Fe(3,4-HPO)₃] chelates are eligible to prevent Iron Deficiency Chlorosis and we took advantage of the likenesses of the ions Fe (III) and Ga (III), and the fact their metal ion complexes are isostructural, to perform a combined NMR and EPR study to get information about the permeation properties of the complexes. The results demonstrate the presence of liposomes loaded with Ga-chelates and that the distribution of complexes alongside the bilayer is dependent on their structure. Two compounds, [Ga(mpp)₃] and [Ga(etpp)₃], have a higher affinity for the polar region of the liposome bilayer thus suggesting that their structure facilitates their permanence at the root-rhizosphere interface. Chelates [Ga(dmpp)₃] and [Ga(mrb13)₃] interact with all types of protons of the lipid bilayer thus implying that they travel all along the bilayer structure indicating their higher permeation properties through soybean membranes. The results obtained for compound, [Ga(mrb13)₃], which has been included in this work but was not yet tested in plant supplementation experiments, encourage its testing in in vivo plant studies once this study revealed that it interacts strongly with the model membranes. If the results of the future experiments in plants are positive and consistent with the present membrane-interaction studies the latter could constitute a good screening test for future compounds thus saving reagents and time.

Iron metabolism in Pseudomonas aeruginosa biofilm and the involved iron-targeted anti-biofilm strategies

Pseudomonas aeruginosa is a gram-negative bacterium that exists in various ecosystems, causing severe infections in patients with AIDS or cystic fibrosis. P. aeruginosa can form biofilm on a variety of surfaces, whereby the bacteria produce defensive substances and enhance antibiotic-resistance, making themselves more adaptable to hostile environments. P. aeruginosa resistance represents one of the main causes of infection-related morbidity and mortality at a global level. Iron is required for the growth of P. aeruginosa biofilm. This review summarises how the iron metabolism contributes to develop biofilm, and more importantly, it may provide some references for the clinic to achieve novel anti-biofilm therapeutics by targeting iron activities.

Unstable Tetramic Acid Derivatives from the Deep-Sea-Derived Fungus Cladosporium sphaerospermum EIODSF 008

Seven new unstable tetramic acid derivatives, cladosporiumins I-O (1–7), together with the known analogue cladodionen (8) were isolated from the extract of the deep-sea-derived fungus Cladosporium sphaerospermum EIODSF 008. Their structures were elucidated by spectroscopic analysis, quantum chemical calculations and ECD spectra. Compound 4 was a Mg complex of tetramic acid derivative. In acidic solvent, 4 could change to 1 and 6, and 7 could change to 5. In addition, 1, 5 and 8 existed as two exchangeable isomers, respectively. The structures of cladosporiumins E-H were reassigned as their Na complexes. The antibacterial and cytotoxic activities of 1–8 were also evaluated. However, because of their instability, all of the isolated compounds did not show significant antibacterial activity as the preliminary EtOAc extracts of the fungal strain.

Chemical and Biological Aspects of Nutritional Immunity-Perspectives for New Anti-Infectives that Target Iron Uptake Systems

Upon bacterial infection, one of the defense mechanisms of the host is the withdrawal of essential metal ions, in particular iron, which leads to "nutritional immunity". However, bacteria have evolved strategies to overcome iron starvation, for example, by stealing iron from the host or other bacteria through specific iron chelators with high binding affinity. Fortunately, these complex interactions between the host and pathogen that lead to metal homeostasis provide several opportunities for interception and, thus, allow the development of novel antibacterial compounds. This Review focuses on iron, discusses recent highlights, and gives some future perspectives which are relevant in the fight against antibiotic resistance.

X-Ray Crystallographic Analysis, EPR Studies, and Computational Calculations of a Cu(II) Tetramic Acid Complex

In this work we present a structural and spectroscopic analysis of a copper(II) N-acetyl-5-arylidene tetramic acid by using both experimental and computational techniques. The crystal structure of the Cu(II) complex was determined by single crystal X-ray diffraction and shows that the copper ion lies on a centre of symmetry, with each ligand ion coordinated to two copper ions, forming a 2D sheet. Moreover, the EPR spectroscopic properties of the Cu(II) tetramic acid complex were also explored and discussed. Finally, a computational approach was performed in order to obtain a detailed and precise insight of product structures and properties. It is hoped that this study can enrich the field of functional supramolecular systems, giving place to the formation of coordination-driven self-assembly architectures.

3-Acylated tetramic and tetronic acids as natural metal binders: myth or reality?

Covering: up to 20153-Acylated tetramic and tetronic acids are characterized by a low pKa and are likely to be deprotonated under physiological conditions. In addition, their structure makes them excellent chelators of metallic cations. We will discuss the significance of these chemical properties with regard to the biological properties and mechanisms of action of these compounds, highlighting the importance of considering them as salts or chelates for biological purposes, rather than acids.

Targeting Staphylococcus aureus quorum sensing with nonpeptidic small molecule inhibitors

A series of 3-oxo-C₁₂-HSL, tetramic acid, and tetronic acid analogues were synthesized to gain insights into the structural requirements for quorum sensing inhibition in Staphylococcus aureus. Compounds active against agr were noncompetitive inhibitors of the autoinducing peptide (AIP) activated AgrC receptor, by altering the activation efficacy of the cognate AIP-1. They appeared to act as negative allosteric modulators and are exemplified by 3-tetradecanoyltetronic acid 17, which reduced nasal cell colonization and arthritis in a murine infection model.

Naturally occurring tetramic acid products: isolation, structure elucidation and biological activity

Natural products containing the tetramic acid core scaffold have been isolated from an assortment of terrestrial and marine species and often display wide ranging and potent biological activities including antibacterial, antiviral and antitumoral activities.

Toward implementation of quorum sensing autoinducers as biomarkers for infectious disease states

The opportunistic bacterial pathogen Pseudomonas aeruginosa causes chronic lung infections in cystic fibrosis (CF) patients. Importantly, virulence factor expression and biofilm formation in P. aeruginosa is coordinated by quorum sensing (QS) and one of the key QS signaling molecules is 3-oxo-C12-HSL. Remarkably, a tetramic acid, (C12-TA), with antibacterial properties is formed spontaneously from 3-oxo-C12-HSL under physiological conditions. Seeking to better understand this relationship, we sought to investigate whether 3-oxo-C12-HSL and C12-TA may be contributing factors to the overall pathogenicity of P. aeruginosa in CF individuals and if their detection and quantitation in sputum samples might be used as an indicator to assess disease states and monitor therapy success in CF patients. To this end, 3-oxo-C12-HSL and C12-TA concentrations were initially analyzed in P. aeruginosa flow cell biofilms using liquid chromatography coupled with mass spectrometry (LC-MS). A liquid chromatography tandem mass spectrometry (LC-MS/MS)-based method was then developed and validated for their detection and quantification in the sputa of CF patients. To the best of our knowledge, this is the first report to show the presence of both the quorum sensing molecule (3-oxo-C12-HSL) and its rearranged product (C12-TA) in human clinical samples such as sputum. A total of 47 sputum samples from 20 CF and 2 non-CF individuals were analyzed. 3-Oxo-C12-HSL was detected and quantified in 45 samples with concentrations ranging from 20 to >1000 nM; C12-TA was found in 14 samples (13-900 nM). On the basis of our findings, quorum sensing autoinducers merit further investigation as biomarkers for infectious disease states.