Chalcogen Bonding (ChB) as a Robust Supramolecular Recognition Motif of Benzisothiazolinone Antibacterials.

1,2-benzisothiazol-3(2H)-one derivatives are highly active against a broad spectrum of fungi as well as Gram positive and Gram negative bacteria. For this reason they are extensively used, for example, as additives in detergents, leather products, paper coatings, and antifouling paintings. In this paper experimental findings are reported proving that the sulfur atom of benzisothiazolinones have a remarkable tendency to form short and directional chalcogen bondings on the extension of the covalent N-S bond and, to a lesser extent, of the C-S bond. Analyses of the Cambridge Structural Database confirm the interaction as a primary recognition motif of these systems. The electrophilicity of sulfur is crucial in the chemical reactions initiating the cascade of events resulting in the biopharmacological activities of benzisothiazolinones. The reported results suggest that the electrophility of sulfur may play a role also at earlier stages than the reactive ones, namely it may pin the compounds at the active site of target enzymes via chalcogen bondings that preorganize the system in the conformation required for the bonds formation/cleavage determining the biopharmacological activity.

Synthesis and Conformational Analysis of Hydantoin-Based Universal Peptidomimetics.

The synthesis of a collection of enantiomerically pure, systematically substituted hydantoins as structural privileged universal mimetic scaffolds is presented. It relies on a chemoselective condensation/cyclization domino process between isocyanates of quaternary or unsubstituted α-amino esters and N-alkyl aspartic acid diesters followed by standard hydrolysis/coupling reactions with amines, using liquid-liquid acid/base extraction protocols for the purification of the intermediates. Besides the nature of the α carbon on the isocyanate moiety, either a quaternary carbon or a more flexible methylene group, conformational studies in silico (molecular modeling), in solution (NMR, circular dichroism (CD), Fourier transform infrared (FTIR)), and in solid state (X-ray) showed that the presented hydantoin-based peptidomimetics are able to project their substituents in positions superimposable to the side chains of common protein secondary structures such as α-helix and ß-turn, being the open α-helix conformation slightly favorable according to molecular modeling, while the closed ß-turn conformation preferred in solution and in solid state.

Multifunctional Neomycin-Triazine-Based Cationic Lipids for Gene Delivery with Antibacterial Properties.

Cationic lipids (CLs) have gained significant attention among nonviral gene delivery vectors due to their ease of synthesis and functionalization with multivalent moieties. In particular, there is an increasing request for multifunctional CLs having gene delivery capacity and antibacterial activity. Herein, we describe the design and synthesis of a novel class of aminoglycoside (AG)-based multifunctional vectors with high transfection efficiency and noticeable antibacterial properties. Specifically, cationic amphiphiles were built on a triazine scaffold, allowing for an easy derivatization with up to three potentially different substituents, such as neomycin (Neo) that serves as the polar head and one or two lipophilic tails, namely stearyl (ST) and oleyl (OL) alkyl chains and cholesteryl (Chol) tail. With the aim to shed more light on the effect of different types and numbers of lipophilic moieties on the ability of CLs to condense and transfect cells, the performance of Neo-triazine-based derivatives as gene delivery vectors was evaluated and compared. The ability of Neo-triazine-based derivatives to act as antimicrobial agents was evaluated as well. Neo-triazine-based CLs invariably exhibited excellent DNA condensation ability, even at a low charge ratio (CR, +/-). Besides, each derivative showed very good transfection performance at its optimal CR on two different cell lines, along with negligible cytotoxicity. CLs bearing symmetric two-tailed OL proved to be the most effective in transfection. Interestingly, Neo-triazine-based derivatives, used as either free lipids or lipoplexes, exhibited strong antibacterial activity against Gram-negative bacteria, especially in the case of CLs bearing one or two aliphatic chains. Altogether, these results highlight the potential of Neo-triazine-based derivatives as effective multifunctional nonviral gene delivery vectors.

Enzyme oxidation of plant galactomannans yielding biomaterials with novel properties and applications, including as delivery systems.

New biomaterials from renewable sources and the development of "functionalized biopolymers" are fields of growing industrial interest. Plant polysaccharides represent a valid alternative to traditional synthetic polymers, which are obtained from monomers of fossil, non-renewable origin. Several polysaccharides, either in their natural or chemically/biochemically modified forms, are currently employed in the biomedical, food and feed, and industrial fields, including packaging. Sustainable biochemical reactions, such as enzyme modifications of polysaccharides, open further possibilities for new product and process innovation. In the present review, we summarize the recent progress on enzyme oxidation of galactomannans (GM) from few leguminous plants (performed either with galactose oxidase or laccase) and we focus on the versatile and easily accessible laccase/TEMPO oxidative reaction. The latter causes a steep viscosity increase of GM water solutions and a transition of the gels from a viscous to an elastic form, due to formation of emiacetalic bonds and thus of internal cross-linking of the polymers. Following lyophilization of these hydrogels, stable aerogels can be obtained, which were shown to have good potential as delivery systems (DS) of actives. The active molecules tested and herewith described are polymyxin B, an antibiotic; nisin, an antimicrobial peptide; the enzymes lysozyme, protease and lipase; the mixture of the industrial microbiocides 5-chloro-2-methyl-4-isothiazolin-3-one (CIT) and 2-methyl-4-isothiazolin-3-one (MIT). The advantages of such aerogel systems and the possibilities they open for future developments, including as DS, are described.

Chiroptical phenomena in reverse micelles: the case of (1R,2S)-dodecyl (2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB).

(1R,2S)-Dodecyl(2-hydroxy-1-methyl-2-phenylethyl)dimethylammonium bromide (DMEB) aggregates dispersed in carbon tetrachloride have been investigated by Fourier transform infrared (FT-IR), vibrational circular dichroism (VCD) and (1)H nuclear magnetic resonance (NMR) spectroscopy at various surfactant concentration and water-to-surfactant molar ratio. Experimental data indicate that, even at the lowest investigated concentration and in absence of added water, DMEB molecules associate in supramolecular assemblies. At higher DMEB concentration the aggregates can confine water molecules, making it plausible to think that DMEB form reverse micelles and that water molecules are quite uniformly distributed among them and mainly located in the proximity of surfactant head groups. Moreover, the water state in DMEB reverse micelles has been found to be different from that in pure water, due to system-specific water/surfactant head group interactions. (1)H NMR diffusion measurements of both water and DMEB emphasize their joined translational motion characterized by a diffusion rate one order of magnitude lower than that of free molecules. Finally, VCD allowed us to show some characteristics of the association of optically active DMEB molecules as reverse micelles and water confinement inside; namely, we monitored the vibrational optical activity of deuterated hydroxyl bonds of the self-assembled DMEB molecules and their interaction with D(2)O molecules.

Design of a novel LOX-1 receptor antagonist mimicking the natural substrate.

The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), the major receptor for oxidized low-density lipoprotein (ox-LDL) in endothelial cells, is overexpressed in atherosclerotic lesions. LOX-1 specific inhibitors, urgently necessary to reduce the rate of atherosclerotic and inflammation processes, are not yet available. We have designed and synthesized a new modified oxidized phospholipid, named PLAzPC, which plays to small scale the ligand-receptor recognition scheme. Molecular docking simulations confirm that PLAzPC disables the hydrophobic component of the ox-LDL recognition domain and allows the interaction of the l-lysine backbone charged groups with the solvent and with the charged/polar residues located around the edges of the LOX-1 hydrophobic tunnel. Binding assays, in a cell model system expressing human LOX-1 receptors, confirm that PLAzPC markedly inhibits ox-LDL binding to LOX-1 with higher efficacy compared to previously identified inhibitors.

Peptidyl fluoro-ketones as proteolytic enzyme inhibitors.

Proteolytic enzymes are involved in many important physiological processes. Because of the critical roles played by these enzymes, aberrations in regulation of their activities can lead to pathological conditions. For this reason, finding inhibitors selective for a proteolytic enzyme that is contributing to a medical problem can be an effective therapeutic strategy. The introduction of fluorine in the backbone of proteolytic enzyme substrates can lead to active and selective inhibitors belonging to the peptidyl fluorinated ketone family. Fluorine not only can influence the mechanism of substrate/enzyme recognition events but also can modify the in vivo profile of the substrate. Although prediction of the total effects of fluorine on the pharmacokinetic parameters can be difficult, the pharmaceutical interest in the synthesis and biological evaluation of peptidyl fluorinated ketones highlights the potential of this family of molecules as therapeutically useful inhibitors.

Overexpression of a bacterial chymotrypsin: application for L-amino acid ester hydrolysis.

In this work, a reliable protocol was designed to rapidly express and purify a microbial chymotrypsin(ogen) as a useful alternative to using animal proteases. The cDNA encoding for chymotrypsinogen from the deuteromycete Metarhizium anisopliae (chy1) was overexpressed in an Origami2(DE3) E. coli strain deficient in thioredoxin reductase and glutathione reductase activities, thus possibly allowing disulfide exchange. By using a quick purification protocol, in which the hexahistidine tag was added at the C-terminal end of the protease, the recombinant CHY1 protein could be purified in a single step on an Ni-NTA column as a mixture of 19.5- and 15-kDa mature active forms and did not require further activation/maturation steps. This expression and purification procedure offers an easier and faster means of producing recombinant CHY1 chymotrypsin than that previously described for Pichia pastoris. The kinetic properties could be characterized and CHY1 chymotrypsin was demonstrated to efficiently catalyze N-acetylated L-phenylalanine and L-tyrosine methyl ester hydrolysis.

Replacement of isobutyl by trifluoromethyl in pepstatin A selectively affects inhibition of aspartic proteinases.

Two bis-trifluoromethyl pepstatin A analogues, carboxylic acid 1 and its methyl ester 2, have been synthesised in order to probe the properties and size of the trifluoromethyl (Tfm) group and compare it to the "bigger" isobutyl that is present in pepstatin A. The results demonstrate that Tfm can effectively replace the isobutyl chain as far as inhibitory activity against plasmepsin II (PM II), an aspartic proteinase from Plasmodium falciparum, is concerned. On the other hand, replacement of isobutyl by Tfm selectively affected activity against other aspartic proteinases tested. Two lines of evidence led to these conclusions. Firstly, compounds 1 and 2 retained single-digit nanomolar inhibitory activity against PM II, but were markedly less active against PM IV, cathepsin D and cathepsin E. Secondly, the X-ray crystal structures of the three complexes of PM II with 1, 2 and pepstatin A were obtained at 2.8, 2.4 and 1.7 A resolution, respectively. High overall similarity among the three complexes indicated that the central Tfm was well accommodated in the lipophilic S1 pocket of PM II, where it was involved in tight hydrophobic contacts. The interaction of PM II with Phe111 appeared to be crucial. Comparison of the crystal structures presented here, with X-ray structures or structural models of PM IV and cathepsin D, allowed an interpretation of the inhibition profiles of pepstatin A and its Tfm variants against these three enzymes. Interactions of the P1 side chain with amino acids that point into the S1 pocket appear to be critical for inhibitory activity. In summary, Tfm can be used to replace an isobutyl group and can affect the selectivity profile of a compound. These findings have implications for the design of novel bioactive molecules and synthetic mimics of natural compounds.

The influence of fluorinated molecules (semiochemicals and enzyme substrate analogues) on the insect communication system.

Can the introduction of fluorine atoms affect the bioactivity of natural semiochemicals? Can fluorine contribute in the creation of specific enzyme inhibitors to interrupt or disrupt the insect communication system? The first step for the bioactivity of a molecule is interaction with the biological sensor. Hydrogen and fluorine are almost bioisosteric and the receptor site of the enzyme can still recognize and accept the fluoro analogue of its natural substrate. However, the peculiar electronegativity of the fluorine atom can affect the binding, absorption, and transport of the molecule. The differences in the molecule's electronic properties can lead to differences in the chemical interactions between the receptor and the fluorinated substrate. Fluorine introduction can modify the metabolic stability and pathway of the semiochemicals in many different ways. Fluorinated analogues can show synergism, inhibition, or hyperagonism effects on insect behaviors, that is, the activity of the nonfluorinated parent compounds can be mimicked, lost, or increased. In any case, the fluorinated molecules can interact with the bioreceptors in a new and disrupting way. The semiochemicals are olfactory substances: fluorine can affect their volatility or smell. Production of semiochemicals from exogenous substances, perception at antennal receptors, and processing of biological responses are the main steps of communication among insects. In the production step, the fluorinated molecules can interact with enzymes that catalyze the biosynthesis of the natural pheromones. In the perception step, fluorinated semiochemicals can interact with the olfactory receptor cells; this often leads to totally unpredictable behaviors. Fluorinated molecules have been developed as probes to elucidate the complex chemorecognition processes of insects. Many of these molecules have been tested to find highly effective behavior-modifying chemicals. New analogues have been synthesized to investigate the metabolic pathway of a pheromone molecule and many of them are promising disrupting agents. Despite such titanic research efforts, the results have often been random, rational trends in the induced behaviors have sometimes been impossible to find, and practical applications of the fluorinated semiochemicals are still uncertain.