Vincent Semetey

Helix-forming oligoureas: Temperature-dependent nmr, structure determination, and circular dichroism of a nonamer with functionalized side chains

To further investigate the degree of structural homology between γ-peptides A and N,N′-linked oligoureas B, we prepared oligourea nonamer 2 containing Ala, Val, Leu, Phe, Tyr and Lys side chains. Oligomer 2 was synthesized on solid support from activated monomers, i.e., from enantiomerically pure succinimidyl {2-{[(9H-fluoren-9-ylmethoxy)carbonyl]amino}ethyl}carbamates 3a–f that are further substituted at C(2) of the ethyl moiety. These precursors were conveniently prepared from N-Fmoc-protected β3-amino acids with corresponding side chains. Detailed NMR studies (DQF-COSY, TOCSY, and ROESY) in (D5)pyridine revealed that 2 adopts a regular (P)-2.5 helical secondary structure very similar to that previously determined for oligourea heptamer 1 and closely related to the (P)-2.614 helix of γ-peptides. Temperature-dependent NMR further demonstrated the conformational homogeneity and remarkable stability of the structure of 2 in pyridine. The CD spectrum of 2 (0.2u2005mM) was recorded in MeOH with the aim to gain more information about the conformation of oligoureas. In contrast to 2.6-helical γ-peptides, which display only a weak or no Cotton effect, oligourea 2 exhibits an intense positive Cotton effect at ca. 203u2005nm ([Θ]=+373000u2005deg cm2 dmol−1) that decreases only slowly upon increasing the temperature.

The bare skin and the nose as non-invasive routes for administering peptide vaccines

Among the different technologies currently tested for the development of novel vaccines, synthetic peptides represent a promising option, since they are chemically pure and induce immune responses of predetermined specificity. Furthermore, they can be replaced with pseudopeptides or peptide mimetics that contain changes in the amide bond, resulting in more stable and immunogenic molecules. Administration of peptide vaccines via non-invasive routes, such as the nose or the bare skin, allows the efficient uptake of antigen by antigen-presenting cells, which are abundant in the associated lymphoid tissues, ensuring the induction of effective systemic and mucosal immune responses. Using non-invasive routes could be advantageous for vaccination programs in third-world countries, since vaccine administration is simple, painless and economical. In this review, we discuss and present some preliminary data on the advantages of synthetic peptides and peptidomimetics as candidate vaccines, and their potential for administration via the skin and the nose.

Solid phase synthesis of oligoureas using O-succinimidyl-(9H-fluoren-9-ylmethoxycarbonylamino)ethylcarbamate derivatives as activated monomers

Abstract An efficient stepwise synthesis of oligoureas (up to the nonamer) on solid support using O -succinimidyl-(9 H -fluoren-9-ylmethoxycarbonylamino)ethylcarbamate derivatives as activated monomers is described. These building blocks were readily prepared starting from N -Fmoc-protected β 3 -amino acids via Curtius rearrangement of the corresponding acyl azides and treatment of the resulting isocyanate with N -hydroxysuccinimide.

Optimizing the formation of biocompatible gold nanorods for cancer research: Functionalization, stabilization and purification

We have investigated the most efficient way of preparing biocompatible gold nanorods (GNR) used as tool for cancer imaging and therapy. The surface of cetyltrimethylammonium bromide-stabilized gold nanorods (GNR-CTAB) was functionalized with various thio-polyethylene glycols of the general formula HS-PEGmX (m=356-10,000; X=-OMe, -NH(2)). The influence of several parameters such as PEG chain length, reaction conditions and purification method on long-term stability, morphology and optical properties of the produced GNR-S-PEGmX was studied, demonstrating the existence of a threshold HS-PEGmX chain length (with molecular weight m≥2000) for efficient steric stabilization of GNR. Several purification techniques were compared: dialysis, centrifugation and a rarely used technique in this field, size exclusion chromatography. While a very weak efficiency of dialysis was evidenced, both centrifugation and size exclusion chromatography were found to provide pure GNRs, though the latter method yielded nanoparticles with a significantly higher stability. Finally, the long-term stability of the produced GNRs was investigated in various media: water, PBS buffer and serum.

Preventing Biofilm Formation and Associated Occlusion by Biomimetic Glycocalyxlike Polymer in Central Venous Catheters

The use of catheters and other implanted devices is constantly increasing in modern medicine. Although catheters improve patients healthcare, the hydrophobic nature of their surface material promotes protein adsorption and cell adhesion. Catheters are therefore prone to complications, such as colonization by bacterial and fungal biofilms, associated infections, and thrombosis. Here we describe the in vivo efficacy of biologically inspired glycocalyxlike antiadhesive coatings to inhibit Staphylococcus aureus and Pseudomonas aeruginosa colonization on commercial totally implantable venous access ports (TIVAPs) in a clinically relevant rat model of biofilm infection. Although noncoated TIVAPs implanted in rats were heavily colonized by the 2 biofilm-forming pathogens with a high percentage of occlusion, coating TIVAPs reduced their initial adherence and subsequently led to 4-log reduction in biofilm formation and reduced occlusion. Our antiadhesive approach is a simple and generalizable strategy that could be used to minimize clinical complications associated with the use of implantable medical devices.

Structural and Immunological Characterisation of Heteroclitic Peptide Analogues Corresponding to the 600–612 Region of the HIV Envelope gp41 Glycoprotein

The conformational and immunological properties of different analogues corresponding to the 600-612 disulfide loop of the human immunodeficiency virus (HIV) gp41 glycoprotein envelope were studied. Fourteen analogues were designed and synthesised; namely, a series of seven analogues in which the disulfide bond was replaced by a lactam bridge and a series of seven analogues in which one residue of each analogue at a time, was replaced by its corresponding homologised alpha-amino acid (beta(3)-amino acid). In the case of the lactam analogues, the influence of the two possible CO-NH and NH-CO orientations of the lactam bridge as well as the size of the lactam ring was explored. The analogues were tested in ELISA with monoclonal antibodies raised against the 600-612 cyclic parent peptide as well as with sera from HIV-1 infected patients. A structural analysis of the parent and analogue peptides was carried out in dimethyl sulfoxide (DMSO-d(6)) using two-dimensional NMR techniques and molecular dynamics simulations. Comparison of the own conformation of the cyclic analogues with their either strong or weak reactivity with the antibodies reveals structural features that may be correlated with the antibody reactivity. Thus, a close structural similarity, particularly a characteristic orientation of the side-chains of residues Lys606, Leu607 and Ile608 in the loop, was found in certain beta(3)-analogues that were better recognised than the parent peptide by anti-peptide mouse monoclonal antibodies and patients antibodies.

SOLID-PHASE SYNTHESIS OF N, N'-UNSYMMETRICALLY SUBSTITUTED UREAS : APPLICATION TO THE SYNTHESIS OF CARBAZA PEPTIDES

The synthesis of Boc- or Fmoc-monoprotected propylenediamine derivatives is reported starting from N-protected α-amino acids. The introduction of these building blocks on solid support via the formation of a urea moiety leads to a new pseudopeptide family (Cαue5f8CH2ue5f8CH2ue5f8Nα(R)ue5f8COue5f8NHue5f8Cα). Two carbonylating reagents, i.e N,N′-carbonyldiimidazole and triphosgene, as well as different coupling procedures, have been tested to optimize the Boc and Fmoc solid-phase synthesis of a model peptide incorporating this isosteric replacement.

Root canal hydrophobization by dentinal silanization: Improvement of silicon-based endodontic treatment tightness†

A new strategy to improve silicon-based endodontic treatment tightness by dentine hydrophobization is presented in this work: root dentine was silanized to obtain a hydrophobic dentine-sealer interface that limits fluid penetration. This strategy was based on the grafting of aliphatic carbon chains on the dentine through a silanization with the silane end groups [octadecyltrichlorosilane (OTS) and octadecyltriethoxysilane]. Dentine surface was previously pretreated, applying ethylenediaminetetraacetic acid and sodium hypochlorite, to expose hydroxyl groups of collagen for the silane grafting. Collagen fibers exposure after pretreatment was visible with scanning electron microscopy, and Fourier transform infrared (FTIR) spectroscopy showed their correct exposition for the silanization (amide I and II, with 1630, 1580, and 1538 cm⁻¹ peaks corresponding to the vibration of C=O and C--N bonds). The grafting of aliphatic carbon chains was confirmed by FTIR (peaks at 2952 and 2923 cm⁻¹ corresponding to the stretching of C--H bonds) and by the increasing of the water contact angle. The most efficient hydrophobization was obtained with OTS in ethyl acetate, with a water contact angle turning from 51° to 109°. Gas and liquid permeability tests showed an increased seal tightness after silanization: the mean gas and water flows dropped from 2.02 × 10⁻⁸ to 1.62 × 10⁻⁸ mol s⁻¹ and from 10.8 × 10⁻³ to 5.4 × 10⁻³ µL min⁻¹, respectively. These results show clear evidences to turn hydrophilic dentine surface into a hydrophobic surface that may improve endodontic sealing.

Chemical treatment of the intra-canal dentin surface: a new approach to modify dentin hydrophobicity

Objective: This study evaluated the hydrophobicity of dentin surfaces that were modified through chemical silanization with octadecyltrichlorosilane (OTS). Material and Methods: An in vitro experimental study was performed using 40 human permanent incisors that were divided into the following two groups: non-silanized and silanized. The specimens were pretreated and chemically modified with OTS. After the chemical modification, the dentin hydrophobicity was examined using a water contact angle measurement (WCA). The effectiveness of the modification of hydrophobicity was verified by the fluid permeability test (FPT). Results and Conclusions: Statistically significant differences were found in the values of WCA and FPT between the two groups. After silanization, the hydrophobic intraradicular dentin surface exhibited in vitro properties that limit fluid penetration into the sealed root canal. This chemical treatment is a new approach for improving the sealing of the root canal system.

A New Transcutaneous Method for Breast Cancer Detection with Dogs

We developed a new transcutaneous method for breast cancer detection with dogs: 2 dogs were trained to sniff skin secretion samples on compresses that had been worn overnight by women on their breast, and to recognize a breast cancer sample among 4 samples. During the test, the dogs recognized 90.3% of skin secretion breast cancer samples. This proof-of-concept study opens new avenues for the development of a reliable cancer diagnostic tool integrating olfactory abilities of dogs.