Chemo-enzymatic approach to the synthesis of the antithrombotic clopidogrel

The (S)-2-chlorophenylglycine moiety is well recognized in the structure of (S)-clopidogrel, a known antithrombotic drug. We prepared an enantiomerically pure chiral building block via an enzyme-catalyzed resolution of (RS)-N-Boc-2-chlorophenylglycine methylester. The best results were obtained by means of an immobilized subtilisin, the cross-linked enzyme aggregate (Alcalase-CLEA®). The high enantiomeric excess of the synthon obtained remained the same over the course of clopidogrel synthesis; the simplicity of the process makes this pathway suitable for large-scale preparation.     

Reduction of Ozonides by Means of Polymeric Triphenylphosphine: Simplified Synthesis of Carbonyl Compounds from Alkenes

A classical system for the preparation of carbonyl compounds from alkenes relies upon ozonolysis of the double bond, followed by reductive cleavage of the ozonide so formed. Among the reagents of choice for such a reduction, triphenylphosphine certainly has enjoyed a widespread use.¹ However, in spite of the simplicity of the method, often one can face problems in the purification of the carbonyl compound from unreacted triphenylphosphine, especially if the polarities of both products are very similar. We have encountered such a problem during the preparation of the (20 S)-6β -ethoxy-3 α, 5-cyclo-5α -pregnane-20-carbaldehyde 4 from the suitably protected stigmasterol3². In this case, when triphenylphosphine was used for reduction of ozonide we never could isolate the aldehyde 2 uncontaninated by tripherylphosphine.     

Genotoxic potential of TiO2 on bottlenose dolphin leukocytes

Titanium dioxide is extensively used in a variety of products, including industrial materials and cosmetics. Studies mainly performed on human cell lines and in vivo exposure on experimental animals have raised concern about the toxic effects of ultrafine titanium dioxide; however, scarce information is available about its impact on aquatic life. The aim of this article was to assess the genotoxic potential of TiO₂ (anatase and rutile) on bottlenose dolphin leukocytes. Blood samples were obtained from four male and one female specimens reared at the Adriatic SeaWorld “Oltremare” (Riccione, Italy). Leukocytes were isolated by the lyses procedure and in vitro exposed to TiO₂ in RPMI. Experimental solutions were sonicated immediately before dosing the cells. Three exposure times (4, 24 and 48 h) and three doses (20, 50 and 100 μg/ml) were tested. Genotoxicity was detected by the single-cell gel electrophoresis (or comet assay) at pH ≥ 13, assessing single/double-strand breaks and alkali-labile sites. Cytotoxicity was also detected by the Trypan blue exclusion method. Results showed that both the crystalline forms of TiO₂ were genotoxic for bottlenose dolphin leukocytes, with a statistically significant increase of DNA fragmentation after exposure to 50 and 100 μg/ml for 24 and 48 h. Although preliminary, these are the first data regarding the genetic susceptibility of toothed cetaceans toward an “emerging” pollutant, such as TiO₂ particles.     

Multienzymatic preparation of 3-[(1R)-1-hydroxyethyl]benzoic acid and (2S)-hydroxy(phenyl)ethanoic acid

The use of two oxidoreductases (an aldoketo reductase from Escherichia coli JM109 and an alcohol dehydrogenase from Lactobacillus brevis) has demonstrated that it is possible to prepare enatiomerically pure diols in a one-pot operation. The reactions were applied to the synthesis of (1R)-1-[3-(hydroxymethyl)phenyl]ethanol and (1S)-1-phenylethane-1,2-diol, using a two-step procedure. The yield is nearly quantitative and the enantiomeric purity is greater than 95%. A third step has been introduced by adding a cell biocatalyst showing dihydrodiol dehydrogenase activity from Pseudomonas fluorescens N3. This allows for the preparation of 3-[(1R)-1-hydroxyethyl]benzoic acid and (2S)-hydroxy(phenyl)ethanoic acid.     

EQUILIBRIUM AMONG HEMATOPORPHYRIN DERIVATIVE COMPONENTSs—II. EFFECT OF ESTERASE ACTIVITY

Photofrin II is the hematoporphyrin-derivative fraction enriched in covalently-linked oligomers, characterized by a high degree of folding. Interaction with hydrophobic structures, such as biomolecules and cell structures, results in a modification of the equilibria among the different species, as a consequence of an unfolding effect exerted towards the electrostatic aggregates. The effect of esterase activity was evaluated, taking into account the nature suggested for the covalent linkage of the oligomers (ether and/or ester). The study was performed in Photofrin II aqueous solution by means of absorption and fluorescence spectral analysis. The results showed that the esterase is active only towards the unfold oligomers: that is, in Photofrin II solution supplemented with albumin. In these conditions, spectral analysis revealed the presence of a monomerization process, which is clearly evident during the first four hours of incubation. The monomerization effect induced by the enzyme was also proven by both equilibrium-dialysis measurements and zinc ion complexation. Zinc ion complexes with high affinity for monomeric species, giving rise to a very distinct emission band at 580 nm. The amount of ester linkage shown in the oligomers through enzyme hydrolysis appeared to be less than might have been expected, owing to the inhibiting effect of the monomer produced on the enzyme. The results are a step toward clarifying the intracellular and intratissue turnover of the drug observed after administration.     

Pillared layered structures versus zeolites as sorbents and catalysts. Part 8. Catalytic destruction of some chloro- and chlorofluoro-hydrocarbons in alumina-pillared clays

Summary Pillared clays have been monitored for catalytic destruction of halocarbons. In comparison with HZSM-5 zeolites, the catalysts tested give higher chlorohydrocarbons destruction with polymers formation. Fluorochlorohydro-carbons are destroyed as well.     

Finite elements for a prefractal transmission problem

In this Note we deal with the finite element approximation of a transmission problem across a prefractal curve approximating the von Koch fractal curve. We construct a mesh adapted to the geometric shape of the interface and we refine it consistently with some estimates in suitable weighted Sobolev spaces. In these spaces we also obtain an approximation error estimate. To cite this article: P. Bagnerini et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Natural estrogens in dairy products: Determination of free and conjugated forms by ultra high performance liquid chromatography with tandem mass spectrometry

Natural estrogens are synthesized by mammals in different amounts depending on the developmental stage and pregnancy/lactation period, and they may pass into milk, where they are mostly present as glucuronated and sulfated forms. In modern dairy practices, about 75% of milk is produced from pregnant cows; therefore, the amount of hormones that may pass into milk could be of concern. While estrogen determination in milk has been investigated in depth, the individual determination of estrogens and their conjugated forms in dairy products has not been fully addressed. The aim of this work was to develop and assess a sensitive method, using the peculiar retention properties of graphitized carbon black, to extract natural free estrogens and their major conjugated metabolites, without any enzymatic cleavage, from yogurt, cheese, and butter. The free and conjugated estrogens were eluted in two distinct fractions from the solid‐phase extraction cartridge and analyzed separately by ultra high performance liquid chromatography coupled to tandem mass spectrometry. Recoveries were higher than 80% for all the three sample typologies. The highest matrix effects were observed for butter, which was richest in lipid content, but was below 30%. A survey on some commercial dairy products suggests that production processes decreased estrogen content.