Participation of the nucleobases in the regioselective backbone fragmentation of nucleic acids. A molecular dynamics and tandem mass spectrometric investigation on a model dinucleoside phosphotriester

The anions (I–III) obtained from O-methyl 5′-O-(5′-deoxythymidine) 3′-O-(2′,3′-dideoxyuridine) phosphate by the competitive removal of the 3-N-H protons of the nucleobases and of the methyl group from the phosphotriester bond, assume in the gas phase stable conformations as a function of their charge site. The mass-analyzed ion kinetic energy (MIKE) spectra of I and III show that the regioselective backbone cleavage of the internucleotidic linkage is controlled by the 2′-H proton transfer to the nucleobase within the 5′-end nucleoside. Similar pathways are taken by species II when the nucleobase is eliminated as neutral from the 5′-end nucleoside.     

A Review on Coordination Properties of Al(III) and Fe(III) toward Natural Antioxidant Molecules: Experimental and Theoretical Insights

This review focuses on the ability of some natural antioxidant molecules (i.e., hydroxycinnamic acids, coumarin-3-carboxylic acid, quercetin, luteolin and curcumin) to form Al(III)- and Fe(III)-complexes with the aim of evaluating the coordination properties from a combined experimental and theoretical point of view. Despite the contributions of previous studies on the chemical properties and biological activity of these metal complexes involving such natural antioxidants, further detailed relationships between the structure and properties are still required. In this context, the investigation on the coordination properties of Al(III) and Fe(III) toward these natural antioxidant molecules might deserve high interest to design water soluble molecule-based metal carriers that can improve the metal’s intake and/or its removal in living organisms.     

Free radical-scavenging activity of indolic compounds in aqueous and ethanolic media

Indolic compounds are a broad family of substances present in microorganisms, plants and animals. They are mainly related with tryptophan metabolism, and present particularities that depend on their respective chemical structures. The most important members of the family are the plant hormone, indole-3-acetic acid, and the animal hormone, melatonin. An important characteristic of some indolic compounds is that they may be useful as chemical preventive agents against diseases such as cancer, oxidative stress, etc. For this reason, the possible antioxidant activities (free radical-scavenging activity) of several indoles were studied. The2,2'-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid /H(2)O(2)/HRP decoloration method was applied to determine both hydrophilic (in buffered media) and lipophilic (in organic media) antioxidant properties of the indolic compounds. Also, a study of the hydrophilic antioxidant activities of indoles at different pH values (between 4.5 and 8.5) was made. Finally, their possible role as diet plant antioxidants is discussed.     

Unexpected solid-state photochemistry of an alpha-thiophenyl-alpha'-thiophenyl-S,S-dioxo-substituted ketone

Samples of 2,4-dimethyl-2-(thiophen-3-yl)-4-(thiophen-3-yl-S,S-dioxo)pentan-3-one 2 were obtained by controlled MCPBA oxidation of 2,4-dimethyl-2,4-di(thiophen-3-yl)pentan-3-one 1. Rather than the expected photodecarbonylation, UV--vis irradiation of 2 led to the intramolecular 2 + 2 photocycloaddition product 5 in quantitative yields (by GC and NMR) both in solution and in crystalline solid state. Detailed X-ray powder diffraction analyses revealed that the solid-state reaction of sulfone 2 occurs with a loss of long-range order despite retaining some birefringence under polarized microscopy.     

Allylation of exocyclic N-Acyliminium ions generated from chiral N-[1-(phenylsulfonyl)alkyl]oxazolidin-2-ones

N-[1-(Phenylsulfonyl)alkyl]oxazolidin-2-ones are successfully prepared by condensation of the corresponding optically active oxazolidin-2-ones with aldehydes and benzenesulfinic acid. At low temperature, in the presence of titanium tetrachloride, these sulfones are converted into N-acyliminium ions, which react with allyltrimethylsilane with a variable degree of stereoselectivity. The best results are obtained with (R)-5,5-dimethyl-4-phenyloxazolidin-2-one as a chiral auxiliary. Cleavage of the oxazolidin-2-one ring with lithium/ammonia affords the corresponding homoallylamines, which reveal an absolute configuration opposite that expected on the basis of the usual steric effects. A complexation of the Lewis acid with the N-acyliminium ion may be responsible of this rather unusual stereochemical outcome.     

Mapping phosphorylation sites: a new strategy based on the use of isotopically labelled DTT and mass spectrometry

Phosphoproteomics, nowadays, represents a front line in functional proteomics as testified by the number of papers recently appearing in the literature. In an attempt to improve and simplify the methods so far suggested we have set up a simple isotope-coded approach to label and quantitate phospho-Ser/-Thr residues in protein mixtures. First of all, after appropriate oxidation of cysteine/cystine residues followed by tryptic hydrolysis, we have optimised and simplified the beta-elimination reaction to get the corresponding alkene moiety from the phosphate esters. This was achieved by (a) separating the elimination reaction from the addition reaction, (b) the use of Ba(OH)(2) as alkali reagent and (c) its further elimination by the simple addition of solid CO(2) to the peptide mixture. The Michael reaction was then performed, after the removal of BaCO(3) by centrifugation, by adding dithiothreitol (DTT) to the peptide mixture. Finally, the direct purification of the modified phosphopeptides was performed on a thiol-sepharose column. The availability of fully deuterated DTT, introducing a 6 Da difference with respect to the non-deuterated species, allows quantitation of the differential extent of signalling modification when analysed by matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS) and liquid chromatography/mass spectrometry. The entire procedure has been set up by using bovine alpha-casein, and resulted in the identification of all the phosphorylated tryptic peptides, including the tetraphosphorylated peptides, which escaped all previously reported procedures     

Antimicrobial activity and phenolic content of natural site and micropropagated Limonium avei (De Not.) Brullo & Erben plant extracts

This study reported the antimicrobial activity and phenolic content of natural site and micropropagated Limonium avei (De Not.) Brullo & Erben inflorescences. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ethanolic extracts were determined according to the Clinical Laboratory Standards Institute guidelines. Individual phenolic acids and flavonoids were detected by a high performance liquid chromatography (HPLC-DAD) method. The samples showed a comparable antimicrobial activity, although the natural site extract possessed the lower MIC values. The best activity was detected against Gram-positive bacteria, such as Staphylococcus aureus including methicillin resistant strains (MIC and MBC values ranging from 7.81 to 62.50?μg?mL(-1) and from 500 to 2000?μg?mL(-1) respectively). In contrast, a low activity was found on Gram-negative bacteria and Candida albicans. The HPLC-DAD analysis revealed ten phenolic acids and four flavonoids with a major amount of m-coumaric acid, naringin and quercetin in the natural site extract.     

Microwave-assisted oxidation of silibinin: a simple and preparative method for the synthesis of improved radical scavengers

A new and preparative oxidation of silibinin has been developed to give access to two different silibinin derivatives known for their enhanced antioxidant properties. Conventional heating methods were compared with results obtained from microwave (MW) heating. The base-catalysed oxidation of silibinin under MW heating is a very efficient method for the preparation of 2,3-dehydrosilybin and a related silybin rearrangement product. This latter compound shows enhanced radical scavenging properties. Optimised conditions were used to prepare 2,3-dehydrosilybins A and B from optically pure silybins A and B. An efficient, preparative purification method was also developed to enable isolation of different products in high purity.     

Application of an innovative matrix solid-phase dispersion–solid-phase extraction–liquid chromatography–tandem mass spectrometry analytical methodology to the study of the metabolism of the estrogenic mycotoxin zearalenone in rainbow trout liver and muscular tissue

The metabolic fate of the estrogenic mycotoxin zearalenone in rainbow trout is presently unknown. In this study, the tissue concentration of zearalenone and its principal metabolites (α-zearalenol and β-zearalenol) was determined. A known amount of zearalenone was administered as a single bolus to ten fish, and the biological tissue concentration was determined at various times following administration. The analytes were extracted from liver and muscular tissue using an on-line matrix solid-phase dispersion–solid-phase extraction sample preparation protocol, and their concentration determined by HPLC–Turboionspray–tandem mass spectrometry. The results showed that zearalenone is mainly metabolized into α-zearalenol in both liver and muscular tissues. The maximum concentrations of each analyte found in liver were 76.1, 211.2 and 63.7?ng/g respectively for zearalenone, α-zearalenol and β-zearalenol, while in muscular tissue they were 10.7, 8.2 and 6.5?ng/g. These values were reached after 2?h in liver tissue and 12?h in muscular tissue. Moreover the data obtained showed that the elimination rate in liver is quite fast since 48?h after the exposure less than 7% of the maximum concentration found is still present. In muscular tissue, however, about one-third of the maximum concentration found is still present after 48?h.     

Synthesis of fluoren-9-ones by the palladium-catalyzed cyclocarbonylation of o-halobiaryls

The synthesis of various substituted fluoren-9-ones has been accomplished by the palladium-catalyzed cyclocarbonylation of o-halobiaryls. The cyclocarbonylation of 4'-substituted 2-iodobiphenyls produces very high yields of 2-substituted fluoren-9-ones bearing either electron-donating or electron-withdrawing substituents. 3'-Substituted 2-iodobiphenyls afford 3-substituted fluoren-9-ones in excellent yields with good regioselectivity. This chemistry has been successfully extended to polycyclic fluorenones and fluorenones containing fused isoquinoline, indole, pyrrole, thiophene, benzothiophene, and benzofuran rings.