The first synthesis of (-)-asperpentyn and efficient syntheses of (+)-harveynone, (+)-epiepoformin and (-)-theobroxide

A generally applicable strategy for the synthesis of a range of polyoxygenated cyclohexane natural products has been developed. The enantioselective syntheses of (-)-theobroxide, a polyoxygenated cyclohexane natural compound with potent growth inducing properties in potato microtubers has been achieved via a 1,2 O-silyl migration between trans-hydroxyl groups and a remote hydroxyl directed epoxidation of an enone derived from quinic acid. A thus derived alpha-iodoenone was subjected to Stille coupling with tetramethylstannane to afford the first title compound. A similar strategy enabled a route to the complete asymmetric synthesis of the acetylenic phytotoxin (+)-harveynone. By selective reduction of (-)-theobroxide, (+)-epiepoformin was also prepared in enantiopure form and similarly, stereoselective reduction of (+)-harveynone completed the first enantioselective synthesis of (-)-asperpentyn, another natural compound with antimicrobial activity.     

Characterization of dinitroporphyrin zinc complexes by electrospray ionization tandem mass spectrometry. Unusual fragmentations of beta-(1,3-dinitroalkyl) porphyrins

The zinc complexes of diaryl bis(p-nitrophenyl)porphyrins and beta-(1,3-dinitroalkyl)tetraphenylporphyrins were studied by electrospray ionization (ESI) tandem mass spectrometry (MS/MS). All porphyrins showed the protonated molecule under ESI conditions. The protonated molecules were induced to fragment and the corresponding ESI tandem mass spectra were analysed. Porphyrins with two p-nitrophenyl groups showed, as expected, characteristic fragmentations including either loss of one nitro group, as the major fragment of the tandem mass spectra, and loss of both nitro groups. In contrast, MS/MS of the beta-(1,3-dinitroalkyl)porphyrins provided interesting and unexpected results such as the absence (or in insignificant abundance) of the ions formed by loss of one nitro group. However, these porphyrins show an abundant fragment due to combined loss of the two nitro groups. Also, the typical beta-cleavage of the alkyl chain is not observed per se, only when combined with loss of HNO2 or *NO2. Instead, alpha-cleavage, with loss of the beta-pyrrolic substituent, is the most favourable process.     

Reductive Coupling Reactions of 2-Nitrochalcones and their β-Hydroxy-analogues: New Syntheses of 2-Arylquinoline and 2-Aryl-4-hydroxyquinoline Derivatives

Summary. A one-pot synthesis of novel 2-arylquinolines and 2-aryl-4-hydroxyquinolines was developed from the intramolecular reductive coupling reactions of 2-nitrochalcones and 3-hydroxy-1-phenyl-3-(2-nitrophenyl)-2-propen-1-ones. Depending on the reduction method and on the presence of electron donating substituents on the A ring of 2-nitrochalcones one can modulate the formation of 2-arylquinolines, their N-oxides, and of 2-aminochalcones. The reduction of 3-hydroxy-1-(2-hydroxyphenyl)-3-(2-nitrophenyl)-2-propen-1-ones with stannous chloride in hydrochloric acid gave 2′-aminoflavones and with ammonium formate and Pd/C yielded 2-(2-hydroxyaryl)-4-hydroxyquinolines.     

Organocatalysis of asymmetric epoxidation mediated by iminium salts under nonaqueous conditions

The first nonaqueous conditions are described for catalytic asymmetric epoxidation mediated by iminium salt organocatalysts, providing ee values of up to 67%.     

Highly stereoselective aldol reaction for the synthesis of gamma-lactones starting from tartaric acid

A simple stereoselective process for the synthesis of highly substituted gamma-lactones was developed based on aldol reactions between the enolate of dioxanes derived from tartaric acid and aldehydes. A range of aromatic and aliphatic aldehydes were reacted, in most cases achieving good yields and stereoselectivity. The limitations of this reaction were identified and a transition state is proposed.     

Detection and identification of quinonemethide triterpenes in Peritassa campestris by mass spectrometry

Analysis of tingenone and tingenol quinonemethide triterpenes was made by gas chromatography/mass spectrometry (GC/MS) of their trimethylsilyl (TMS) ethers. An extra TMS group, in addition to those predicted from the known structures, is added to these compounds during the derivatization process. The electron impact mass spectra showed base peaks at m/z 549 and 623, respectively, for the TMS derivatives of tingenone and tingenol, and electrospray (ES) and collision-activated dissociation (CAD) studies indicate that these ions correspond to losses of a methyl group from the derivatives studied. A mechanism, based on ES-MS/MS studies, is suggested for the derivatization and fragmentation pattern.     

Stereoselective radical reactions of some tartaric and glyceric acid derivatives

[reaction: see text] Free radicals generated by the decarboxylation of dimethoxydioxanecarboxylic acids derived from L-(+)-tartaric acid and L-glyceric acid added to some maleimides and acrylates with high stereoselectivity. This method provides easy access to some chiral building blocks.     

Validated method for determination of bromopride in human plasma by liquid chromatography--electrospray tandem mass spectrometry: application to the bioequivalence study

A simple, sensitive and specific liquid chromatography-tandem mass spectrometry method for the quantification of bromopride I in human plasma is presented. Sample preparation consisted of the addition of procainamide II as the internal standard, liquid-liquid extraction in alkaline conditions using hexane-ethyl acetate (1 : 1, v/v) as the extracting solvent, followed by centrifugation, evaporation of the solvent and sample reconstitution in acetonitrile. Both I and II (internal standard, IS) were analyzed using a C18 column and the mobile-phase acetonitrile-water (formic acid 0.1%). The eluted compounds were monitored using electrospray tandem mass spectrometry. The analyses were carried out by multiple reaction monitoring (MRM) using the parent-to-daughter combinations of m/z 344.20 > 271.00 and m/z 236.30 > 163.10. The areas of peaks from analyte and IS were used for quantification of I. The achieved limit of quantification was 1.0 ng/ml and the assay exhibited a linear dynamic range of 1-100.0 ng/ml and gave a correlation coefficient (r) of 0.995 or better. Validation results on linearity, specificity, accuracy, precision and stability, as well as application to the analysis of samples taken up to 24 h after oral administration of 10 mg of I in healthy volunteers demonstrated the applicability to bioequivalence studies.     

Polytetrafluoroethylene–iron oxide composite. Interactions with acrylic acid and vinyl acetate

Iron oxide finely dispersed on polytetrafluoroethylene (PTFE) affects the behavior of this polymer with regard to acrylic acid and vinyl acetate sorption. Acrylic acid photopolymerization and grafting onto x-ray preirradiated PTFE are also affected. Infrared, Mossbauer, and ESR spectroscopies show that PTFE-embedded iron oxide is not transformed to iron acrylate, although it is converted to iron acetate by exposure to acetic acid. X-ray-induced polytetra-fluoroethylene free radicals are longer lived in the polymer-oxide composite than in plain polytetrafluoroethylene.     

Time-reversal symmetry breaking and decoherence in chaotic Dirac billiards

In this work, we perform a statistical study on Dirac Billiards in the extreme quantumlimit (a single open channel on the leads). Our numerical analysis uses a large ensembleof random matrices and demonstrates the preponderant role of dephasing mechanisms in suchchaotic billiards. Physical implementations of these billiards range from quantum dots ofgraphene to topological insulators structures. We show, in particular, that the role offinite crossover fields between the universal symmetries quickly leaves the conductance tothe asymptotic limit of unitary ensembles. Furthermore, we show that the dephasingmechanisms strikingly lead Dirac billiards from the extreme quantum regime to thesemiclassical Gaussian regime.