SULPHUR CONTAINING HETERODIPOLAROPHILES. VARIABLE STEREOCHEMISTRY OF THE CYCLOADDITION OF THIOBENZOPHENONES TO KETENIMINES

Abstract

The thermal cycloaddition between thiobenzophenones (1) and ketenimines (2) takes place according to two reaction modes, the stereochemical course being determined by the type of substituent at nitrogen on the cumulene. Specifically, N-arylketenimines (2a) (X = H) react with (1) as a formal 4π system giving as final products 4H-3,1-benzothiazines (3) (1,4-cyclisation), whereas N-aryl ortho-disubstituted compounds (2b) (X = Me), as well as N-alkyl derivatives (2c), behave as 2π component to give 2-iminothietans (4) (1,2-cyclisation) (Scheme I). In the formation of the six membered ring compound (3), the ketenimine (2a) can be viewed to act as a 1,4-heterodiene to give the intermediate (3a) by addition of (1) across the C[dbnd]N bond and the C[dbnd]C of the N-aryl ring. Both reactions proved to be stereoselective.     

A New Alkaliphilic Cold-Active Esterase from the Psychrophilic Marine Bacterium Rhodococcus sp.: Functional and Structural Studies and Biotechnological Potential

The special features of cold-adapted lipolytic biocatalysts have made their use possible in several industrial applications. In fact, cold-active enzymes are known to be able to catalyze reactions at low temperatures, avoiding side reactions taking place at higher temperatures and preserving the integrity of products. A lipolytic gene was isolated from the Arctic marine bacterium Rhodococcus sp. AW25M09 and expressed in Escherichia coli as inclusion bodies. The recombinant enzyme (hereafter called RhLip) showed interesting cold-active esterase activity. The refolded purified enzyme displayed optimal activity at 30 °C and was cold-active with retention of 50 % activity at 10 °C. It is worth noting that the optimal pH was 11, and the low relative activity below pH 10 revealed that RhLip was an alkaliphilic esterase. The enzyme was active toward short-chain p-nitrophenyl esters (C2–C6), displaying optimal activity with the butyrate (C4) ester. In addition, the enzyme revealed a good organic solvent and salt tolerance. These features make this an interesting enzyme for exploitation in some industrial applications.     

Naphthoxazole‐Based Singlet Oxygen Fluorescent Probes

In this study, we report the synthesis and photochemical behavior of a new family of photoactive compounds to assess its potential as singlet oxygen (¹O₂) probes. The candidate dyads are composed by a ¹O₂ trap plus a naphthoxazole moiety linked directly or through an unsaturated bond to the oxazole ring. In the native state, the inherent great fluorescence of the naphthoxazole moiety is quenched; but in the presence of ¹O₂, generated by the addition and appropriate irradiation of an external photosensitizer, a photooxidation reaction occurs leading to the formation of a new chemical entity whose fluorescence is two orders of magnitude higher than that of the initial compound, at the optimal selected wavelength. The presented dyads outperform the commonly used indirect fluorescent ¹O₂ probes in terms of fluorescence enhancement maintaining the required specificity for ¹O₂ detection in solution.     

Spectrofluorimetric determination of pharmaceutical compounds with the cerium(IV)—cerium(III) system

The compounds to be determined are oxidised by cerium(IV). The concentration of cerium(III) formed is measured spectrofluorimetrically. The method has been used both in solution and, by fluorodensitometry, on t.l.c. plates. Detection limits of some substances are 15 ng ml^-1 for the solution method and 5 ng per spot for the t.l.c. method.     

Liquid chromatography of dansyl derivatives of some alkaloids and the application to the analysis of pharmaceuticals.

Derivatization of the alkaloids cephaeline, codeine, emetine, ephedrine, morphine, narcotine and others with dansyl chloride has been studied with the aim of developing a sensitive and specific liquid chromatographic method for these substances in complex pharmaceutical dosage forms. While codeine and narcotine do not react, the other compounds form completely substituted derivatives which possess maxima in their fluorescence emission spectra between 470 and 500 nm. The structure of the derivatives has been confirmed by nuclear magnetic resonance spectroscopy. The dansylated compounds have been separated by thin-layer chromatography and high-pressure liquid chromatography. The improved selectivity and sensitivity have permitted an analysis of these substances present in low concentrations in 10- 100-fold excesses of other drugs. Direct derivatization of syrups and aqueous slurries of capsules having a complex excipient and drug composition is feasible and time saving and serves as a pre-clean-up step. Detection limits are in the 1-10-ng range or better, depending on the efficiency of the detection device. The reproducibility of the method is limited by the derivatization step, but a relative standard deviation of less than 2% can be obtained. The analysis time for these pharmaceuticals may be reduced by at least one fifth of that required by conventional techniques.     

Characterization of a cold-active and salt tolerant esterase identified by functional screening of Arctic metagenomic libraries

Background

The use of metagenomics in enzyme discovery constitutes a powerful approach to access to genomes of unculturable community of microorganisms and isolate novel valuable biocatalysts for use in a wide range of biotechnological and pharmaceutical fields.

Results

Here we present a novel esterase gene (lip3) identified by functional screening of three fosmid metagenomic libraries, constructed from three marine sediment samples. The sequenced positive fosmid revealed an enzyme of 281 amino acids with similarity to class 3 lipases. The 3D modeling of Lip3 was generated by homology modeling on the basis of four lipases templates [PDB ID: 3O0D, 3NGM, 3G7N, 2QUB] to unravel structural features of this novel enzyme. The catalytic triad of Lip3 was predicted to be Asp207, His267 and the catalytic nucleophile Ser150 in a conserved pentapeptide (GXSXG). The 3D model highlighted the presence of a one-helix lid able to regulate the access of the substrate to the active site when the enzyme binds a hydrophobic interface. Moreover an analysis of the external surface of Lip3 model showed that the majority of the surface regions were hydrophobic (59.6 %) compared with homologous lipases (around 35 %) used as templates. The recombinant Lip3 esterase, expressed and purified from Escherichia coli, preferentially hydrolyzed short and medium length p-nitrophenyl esters with the best substrate being p-nitrophenyl acetate. Further characterization revealed a temperature optimum of 35 °C and a pH optimum of 8.0. Lip3 exhibits a broad temperature stability range and tolerates the presence of DTT, EDTA, PMSF, β-mercaptoethanol and high concentrations of salt. The enzyme was also highly activated by NaCl.

Conclusions

The biochemical characterization and homology model reveals a novel esterase originating from the marine Arctic metagenomics libraries with features of a cold-active, relatively thermostable and highly halotolerant enzyme. Taken together, these results suggest that this esterase could be a highly valuable candidate for biotechnological applications such as organic synthesis reactions and cheese ripening processes.

     

Toward a global characterization of the phosphoproteome in prostate cancer cells: identification of phosphoproteins in the LNCaP cell line

Protein phosphorylation plays a major role in most cell-signaling pathways in all eukaryotic cells. Disruptions in phosphorylation-mediated cell-signaling events are associated with various diseases, including cancer. Here, we applied a fully non-gel-based methodology to obtain an initial panel of phosphoproteins from the LNCaP human prostate cancer cell line. The analytical strategy involved enrichment of phosphopeptides by immobilized metal ion affinity chromatography, the use of POROS Oligo R3 to capture phosphopeptides that were not retained with a C18 packing, and gas-phase fractionation in the m/z dimension to extend the dynamic range of the LC-MS/MS analysis. In this pilot investigation, 137 phosphorylation sites in 81 phosphoproteins were identified. The characterized phosphoproteins include kinases, co-regulators of steroid receptors, and a number of cancer-related proteins.     

Rational design and assembly of synthetic trimodular polyketide synthases

Type I polyketide synthases (PKSs) consist of modules that add two-carbon units in polyketide backbones. Rearranging modules from different sources can yield novel enzymes that produce unnatural products, but the rules that govern module-module communication are still not well known. The construction and assay of hybrid bimodular units with synthetic PKS genes were recently reported. Here, we describe the rational design of trimodular PKSs by combining bimodular units. A cloning-expression system was developed to assemble and test 54 unnatural trimodular PKSs flanked by the loading module and the thioesterase from the erythromycin synthase. Remarkably, 96% of them produced the expected polyketide. The obtained results represent an important milestone toward the ultimate goal of making new bioactive polyketides by rational design. Additionally, these results show a path for the production of customized tetraketides by fermentation, which can be an important source of advanced intermediates to facilitate the synthesis of complex products.     

Two New Chromanone Acid Derivatives from Calophyllum inophyllum

Chemistry of Natural Compounds - Two new chromanone acid derivatives, calophinophyllins A and B (1 and 2), together with a known one (3), were isolated from Calophyllum inophyllum. The structures...