Evaluation of different polymerase chain reaction methods for the identification of Vibrio parahaemolyticus strains isolated by cultural methods

Control of contamination by Vibrio parahaemolyticus in fishery products is often hampered by the lack of standardized methods and by the uncertainty associated with biochemical identification of the isolates. In this study, 5 polymerase chain reaction (PCR) methods for the identification of V. parahaemolyticus to the species level were evaluated by using 25 Vibrio reference strains and 163 isolates from fishery products, environmental sources, and clinical samples. Sequence targets of the methods were toxR, gyrB, and tlh genes (tested with 2 protocols), and the fragment pR72H. Isolate identification was confirmed by sequencing of the 16S rRNA gene and by PCR protocols for the identification of other Vibrio species. The PCR assay targeting the toxR gene achieved the highest performance (100% inclusivity and exclusivity). The 2 PCR protocols based on tlh gene detection, although showing the same inclusivity (100%), differed in the exclusivity (50 and 91%, respectively). Finally, the results provided by the PCR assays targeting the gyrB gene and pR72H fragment were less reliable and, in some cases, difficult to assess. According to the results of this study, the characteristics of accuracy expressed by the toxR identification method make it a suitable candidate as a reference method for the molecular identification of V. parahaemolyticus strains.     

Synthesis, X-ray diffraction and computational study of the crystal packing of polycyclic hydrocarbons featuring aromatic and perfluoroaromatic rings condensed in the same molecule: 1,2,3,4-tetrafluoronaphthalene, -anthracene and -phenanthrene

We have synthesised some planar polycyclic compounds, in which unsubstituted aromatic rings are condensed with perfluorinated aromatic rings, and have carried out a combined X-ray diffraction and computational study to analyse their self-recognition behaviour in crystalline phases. We compare our results with the parent hydrocarbons and with other compounds that have a variable degree of fluorination. Whereas the molecular planes in crystals of hydrocarbons with mono- or difluorinated aromatic rings or of perfluorinated compounds arrange themselves in V-shaped configurations, our present results show that perfluorinated rings tend to stack over unsubstituted rings even when these two moieties coexist in a condensed system, producing crystalline materials with parallel molecular layers with the arene-perfluoroarene recognition pattern. Our analysis shows that the packing energy of all these crystals is dispersion-dominated and that coulombic terms are selective rather than quantitatively predominant in crystals with arene-perfluoroarene interactions. No compelling proof of a special role of C-H...F interactions has been found.     

Chiral Lewis base promoted trichlorosilane reduction of ketimines. An enantioselective organocatalytic synthesis of chiral amines

The reduction of the carbon-nitrogen double bond is an important transformation. Here we report our studies on a family of chiral organic catalysts able to promote the stereoselective reduction of ketimines with trichlorosilane. The very cheap, metal-free catalysts were easily prepared in one step from commercially available products, namely a chiral aminoalcohol and picolinic acid derivatives. The catalyst structure was extensively modified in a study that allowed to identify an extremely active species, able to promote the reduction on a large variety of substrates with high efficiency (up to 95% ee). A three component methodology has been also developed, where the enantiomerically enriched amine was isolated after performing the reaction by mixing a ketone and an amine in the presence of trichlorosilane and the catalyst. Its synthetic potentiality was demonstrated by employing the present metal-free catalytic procedure in the preparation of (S)-metolachlor, a potent and widely used herbicide.     

A general stereoselective enamine mediated alkylation of α-substituted aldehydes

We herein present a general enamine-mediated α-alkylation of α-substituted aldehydes with carbenium ions for the stereoselective construction of quaternary stereogenic centers.     

1,3-dipolar cycloaddition reactions of azomethine ylides on enantiomerically pure (E)-γ-alkoxy-α,β-unsaturated esters.

Enantiomerically pure (E)-γ-alkoxy-α,β-unsaturated esters were reacted with azomethine ylides obtained from glycine imines in the presence of LiBr and diazabicycloundecene (DBU), to afford tetrasubstituted pyrrolidines with complete regiocontrol and fair to excellent diastereoselectivity (only two diastereoisomers formed in up to 96: 4 diastereoisomeric ratio). The results are compared with those of other 1,3-dipolar cycloadditions, and the origin of stereocontrol is discussed.     

Organocatalytic synthesis of dipyrromethanes by the addition of N-methylpyrrole to aldehydes

The reaction of aldehydes with N-methylpyrrole carried out in the presence of catalytic pyrrolidinium tetrafluoroborate at room temperature affords the corresponding dipyrromethanes and minor amounts of tripyrranes. This new, mild, and convenient process represents the first organocatalytic synthesis of dipyrromethanes. The products are obtained in chemical yields similar to those obtained with existing methods, which, however, require either a much larger excess of heterocycle (when aldehydes are employed as starting materials), or more drastic reaction conditions (when aldehyde equivalents are used as starting materials) than those employed here. A mechanism is proposed to explain the course of this reaction.