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Some bacterial proteins involved in cell division and oxidative phosphorylation are tightly bound to cardiolipin. Cardiolipin is a non-bilayer anionic phospholipid found in bacterial inner membrane. It forms lipid microdomains located at the cell poles and division plane. Mechanisms by which microdomains are affected by membrane-acting antibiotics and the impact of these alterations on membrane properties and protein functions remain unclear. In this study, we demonstrated cardiolipin relocation and clustering as a result of exposure to a cardiolipin-acting amphiphilic aminoglycoside antibiotic, the 3′,6-dinonyl neamine. Changes in the biophysical properties of the bacterial membrane of P. aeruginosa, including decreased fluidity and increased permeability, were observed. Cardiolipin-interacting proteins and functions regulated by cardiolipin were impacted by the amphiphilic aminoglycoside as we demonstrated an inhibition of respiratory chain and changes in bacterial shape. The latter effect was characterized by the loss of bacterial rod shape through a decrease in length and increase in curvature. It resulted from the effect on MreB, a cardiolipin dependent cytoskeleton protein as well as a direct effect of 3′,6-dinonyl neamine on cardiolipin. These results shed light on how targeting cardiolipin microdomains may be of great interest for developing new antibacterial therapies.

International audience; It has been shown that diverse strains of bacteria can be separated according to their characteristic surface properties by means of CE. We employed here this analytical technique to the study of colistin-resistance in Gram-negative bacteria, which involves the selection of mutants with modified outer membrane composition resulting in changes of surface cell properties. In the same way as with molecular entities, we performed firstly the validation of an ITP-based CE method for three common pathogenic Gram-negative bacteria namely Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Secondly, we compared the electrophoretic profiles of bacterial samples from a colistin-susceptible clinical isolate of K. pneumoniae and from the corresponding colistin-resistant derivative. By a simple CE run taking a few minutes, the coexistence of several bacterial subpopulations in the colistin-resistant derivative was clearly evidenced. This work encourages further research that would allow applications of CE in clinical laboratory for a daily monitoring of bacterial population in cared patients when "last-chance" colistin treatment is initiated against multidrug-resistant bacteria.

SDS is commonly employed as BGE additive in CZE analysis of non-enveloped icosahedral viruses. But the way by which SDS interacts with the surface of such viruses remains to date poorly known, making complicate to understand their behavior during a run. In this article, two related bacteriophages, MS2 and Qβ, are used as model to investigate the migration mechanism of non-enveloped icosahedral viruses in SDS-based CZE. Both phages are characterized by similar size and surface charge but significantly different surface hydrophobicity (Qβ > MS2, where ‘>’ means ‘more hydrophobic than’). By comparing their electrophoretic mobility in the presence or not of SDS on both sides of the CMC, we show that surface hydrophobicity of phages is a key factor influencing their mobility and that SDS-virus association is driven by hydrophobic interactions at the surface of virions. The CZE analyses of heated MS2 particles, which over-express hydrophobic domains at their surface, confirm this finding. The correlations between the present results and others from the literature suggest that the proposed mechanism might not be exclusive to the bacteriophages examined here. This article is protected by copyright. All rights reserved

Aminoglycosides (AGs) constitute a major family of potent and broad-spectrum antibiotics disturbing protein synthesis through binding to the A site of 16S rRNA. Decades of widespread clinical use of AGs strongly reduced their clinical efficacy through the selection of resistant bacteria. Recently, conjugation of lipophilic groups to AGs generated a novel class of potent antibacterial amphiphilic aminoglycosides (AAGs) with significant improved activities against various sensitive and resistant bacterial strains. We have identified amphiphilic 3′,6-dialkyl derivatives of the small aminoglycoside neamine as broad spectrum antibacterial agents targeting bacterial membranes. Here, we report on the synthesis and the activity against sensitive and resistant Gram-negative and/or Gram-positive bacteria of new amphiphilic 3′,4′-dialkyl neamine derivatives and of their smaller analogues in the 6-aminoglucosamine (neosamine) series prepared from N-acetylglucosamine.

Two tetra-p-tert-butyl- and two tetra-p-H-calix[4]arene species integrating one or two propylnalidixate esters at the lower rim have been synthesized as possible antibacterial prodrugs. As they display amphiphilic behavior, their properties at the air–water interface were evaluated using the Langmuir balance technique. It has been shown that the two tert-butyl analogues form stable monolayers. The two tert-butyl analogues were then studied at 20 and 37 °C on carbonate buffered subphases at pH 10.0, before being engaged in hydrolytic studies on “production” of monolayers so as to allow a simple treatment, a HPLC survey of nalidixate release. The latter was found to be effective at 37 °C, with formation of free nalidixate in 13% yield for the bisnalidixate derivative, and 10% yield for the mononalidixate after 3 days.

Graphical abstract, Two well-known antibiotic heterocycles, the ‘quinolone’ nalidixic acid and the β-lactam penicillin V, active at different levels of the bacterial growth process, have been attached via an ether–ester junction to the p-tert-butylcalix[4]arene lower rim, in alternate position. The resulting hydrophobic molecular drug-organisers were fully characterized, and evaluated over two Gram negative and three Gram positive reference strains, using disk diffusion assays with disks impregnated with solution of title compound in pure DMSO. An interesting activity was observed over Staphylococcus aureus ATCC 25923 with the dissymmetrical podand incorporating one penicillin and one nalidixic ester moieties.

Tetra-p-guanidinoethylcalix[4]arene trifluoroacetate salt (CX1) was synthesized recently as an antibacterial agent. It showed to be active in vitro against various Gram-positive and Gram-negative bacteria. To get more insight in the mechanism of the biological activity of this derivative, it was studied upon interactions with model lipid membranes. Langmuir monolayers were formed with zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine or 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, and with anionic 1,2-dimyristoyl-sn-glycero-3-phospho-rac-(1-glycerol) and 1,2-dimyristoyl-sn-glycero-3-phospho-L-serine. The two classes of lipids were used, respectively, as model lipids of the eukaryotic and bacterial cell membranes. The monolayers were exposed to CX1 at different concentrations around the minimum inhibitory concentration found for E. coli . The surface pressure-area and surface potential-area compression isotherms, as well as Brewster angle microscopy and polarization-modulation infrared reflection-absorption spectroscopy, were employed to study the monolayers. The results obtained show a higher affinity of CX1 for the anionic lipids, indicating importance of charge-charge interactions. On the basis of a comparative study of the behavior of CX1 and that of p-guanidinoethylphenol trifluoroacetate salt, we propose that interplay of charge-charge and apolar interactions between CX1 and lipids is responsible for the important reorganization of model membranes. This proposal may be helpful in developing new antibacterial calixarene derivatives.

International audience; The asymmetric Diels-Alder reactions between (3R)-4,4-dimethyl-2-oxopyrrolidin-3-yl acrylate derivatives and three N-Z-protected 1-aminodienes have been investigated both in solution and on a solid support. Comparable results for each reaction were observed with the formation of the corresponding constrained cyclic ß-amino acids in high yield and moderate-to-good selectivity when using optimized conditions. A detailed comparison of both solution and solid-support synthesis by conventional heating and microwave activation revealed that the microwave technique is often advantageous. We have also demonstrated that the reaction on a solid support offered an excellent resolution of the problem of low reactivity and instability of the reagents.

The development of novel antimicrobial agents is urgently required to curb the widespread emergence of multidrug-resistant bacteria like colistin-resistant Pseudomonas aeruginosa . We previously synthesized a series of amphiphilic neamine derivatives active against bacterial membranes, among which 3′,6-di- O -[(2″-naphthyl)propyl]neamine (3′,6-di2NP), 3′,6-di- O -[(2″-naphthyl)butyl]neamine (3′,6-di2NB), and 3′,6-di- O -nonylneamine (3′,6-diNn) showed high levels of activity and low levels of cytotoxicity (L. Zimmermann et al., J. Med. Chem. 56:7691–7705, 2013). We have now further characterized the activity of these derivatives against colistin-resistant P. aeruginosa and studied their mode of action; specifically, we characterized their ability to interact with lipopolysaccharide (LPS) and to alter the bacterial outer membrane (OM). The three amphiphilic neamine derivatives were active against clinical colistin-resistant strains (MICs, about 2 to 8 μg/ml), The most active one (3′,6-diNn) was bactericidal at its MIC and inhibited biofilm formation at 2-fold its MIC. They cooperatively bound to LPSs, increasing the outer membrane permeability. Grafting long and linear alkyl chains (nonyl) optimized binding to LPS and outer membrane permeabilization. The effects of amphiphilic neamine derivatives on LPS micelles suggest changes in the cross-bridging of lipopolysaccharides and disordering in the hydrophobic core of the micelles. The molecular shape of the 3′,6-dialkyl neamine derivatives induced by the nature of the grafted hydrophobic moieties (naphthylalkyl instead of alkyl) and the flexibility of the hydrophobic moiety are critical for their fluidifying effect and their ability to displace cations bridging LPS. Results from this work could be exploited for the development of new amphiphilic neamine derivatives active against colistin-resistant P. aeruginosa .

International audience; Monolayers formed with 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] and 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] at the air/water interface were used as model membranes for studying a potential biological activity of four newly synthesized gemini amphiphilic pseudopeptides (GAPS); some of the GAPs studied showed interesting self-assembly properties. The capacity of GAPs to self-assemble in different environments let us think that these molecules may find biomedical applications in, e.g., drug delivery or transfection. The surface pressure-area and surface potential-area compression isotherms, as well as Brewster angle microscopy and polarization-modulation infrared reflection-absorption spectroscopy were used to study monolayers formed with pure GAPs, pure lipids and lipid/GAPs mixtures. The results obtained show that all four GAPs studied can be incorporated in lipid monolayers. The monolayers containing GAPs are expanded and more liquid-like compared to pure lipids. The overall results indicate that the important changes of the properties induced in the model membranes by GAPs are related to their intrinsic conformational flexibility. This feature of GAPs can be easily adjusted by engineering the structure of the spacer present in the polar head, with the aim to modify lipid membranes in a controlled way.

The two new p-tert-butylcalix[4]arene derivatives described here bear one or two nalidixic acid arms linked to the lower calixarene rim via the quinolone carboxylate moiety. These derivatives were synthesized in order to investigate two important features of molecules conceived as potential antibiotics, namely, metal cation complexation and interfacial properties, and the way in which they interrelate. The properties of the calixarene derivatives were studied in monomolecular films spread on pure water and on aqueous subphases containing biologically relevant mono- and divalent metal cations. These systems were examined via surface pressure and surface electrical potential measurements, polarization modulation infrared reflection absorption spectroscopy, and molecular modeling. Molecular modeling shows that important differences exist, first, between the structure and stability of the complexes formed with the two derivatives and, second, between their mono- and dication complexes. Correlating the properties of the monolayers with those of the modeled molecules lets us propose that the derivatives bearing one or two nalidixic pending arms form preferentially inter- and intramolecular complexes, respectively. The results obtained in this study indicate that a possible biological role of the nalidixic arms grafted on the calixarene crown may be revealed upon cation complexation.

The de novo synthesis of racemic 1′,4′-dimethyluridine was accomplished in 12 steps starting from 2,5-dimethylfuran and vinylene carbonate. Key steps of the sequence include the stereoconvergent preparation of a meso diacid, and a stereoselective glycosylation without neighboring group participation. Such 1′,4′-disubstituted ribonucleoside analogues are undisclosed compounds, which may present interesting biological activities.

Two tetra-p-tert-butyl-calix[4]arene species bearing one or two anti-HSV aciclovir units tethered via carbodiester linkages at the lower rim were synthesized as possible antiviral prodrugs. The amphiphilic properties of these derivatives were studied using Langmuir balance at the air–water and air–carbonate buffer interfaces; the monolayers formed were stable on both subphases. Monolayers formed with these molecules on a carbonate buffer subphase at pH 10 and 37 °C were then used for monitoring hydrolysis of the diester linkage. The release of free aciclovir of around 30% in 3 days was observed with both derivatives, as shown with HPLC.