Mechanistic study on the palladium-catalyzed (3 + 2) intramolecular cycloaddition of alk-5-enylidenecyclopropanes

The intramolecular (3 + 2) cycloaddition of alkenylidenecyclopropanes to alkenes under palladium catalysis provides a practical and stereoselective entry into a variety of interesting bicycles. The reaction outcome and stereoselectivity of the process are somewhat dependent on the characteristics of the substrate and of the palladium ligand, which is not easy to justify on the basis of the current mechanistic understanding. We therefore decided to study the different mechanistic alternatives from a theoretical point of view. The energies of the reaction intermediates and transition states for different possible pathways have been explored at DFT level in a model system, and using PH(3) and P(OMe)(3) as ligands. The results obtained suggest that the most favourable reaction pathway involves an initial oxidative addition of Pd(0) at the distal position of the cyclopropane to afford a palladacyclobutane intermediate. The evolution of this intermediate into the final cycloadduct can occur following different paths, the most favorable depending on the configuration and substitution of the alkene cycloaddition partner, and the number of ancillary ligands coordinated to Pd. The computational results are consistent with the experimental observations and provide the basis for proposing which would be the operative mechanistic pathway in different cases. The results also allow us to explain the stereochemical divergences observed in some of the reactions.     

Highly homogeneous stereocontrolled construction of quaternary hydroxyesters by addition of dimethylzinc to α-ketoesters promoted by chiral perhydrobenzoxazines and B(OEt)3

A highly efficient enantioselective addition of Me(2)Zn to α-ketoesters, assisted by a chiral perhydro-1,3-benzoxazine ligand, is described. This novel catalytic system offers homogeneous elevated enantioselectivities in the preparation of α-hydroxyesters that bear a quaternary stereocenter, with a minor dependence on electronic and steric effects when aromatic, heteroaromatic, or aliphatic α-ketoesters are employed. The catalyst can be recovered and reused without loss of activity.     

MASPIT: three-hybrid trap for quantitative proteome fingerprinting of small molecule-protein interactions in mammalian cells

Organic small molecules generally act by perturbing the function of one or more cellular target proteins, the identification of which is essential to an understanding of the molecular basis of drug action. Here we describe the application of methotrexate-linked small molecule ligands to a mammalian three-hybrid interaction trap for proteome-wide identification of small molecule targets, quantification of the targeting potency of unmodified small molecules for such targets in intact cells, and screening for inhibitors of small molecule-protein interactions. During the course of this study we also identified the pyrido[2,3-d]pyrimidine PD173955, a known SRC kinase inhibitor, as a potent inhibitor of several ephrin receptor tyrosine kinases. This finding could perhaps be exploited in the design of inhibitors for this kinase subfamily, members of which have been implicated in the pathogenesis of various diseases, including cancer.     

Physicochemical Properties of a New Multicomponent Cosolvent System for the pKa Determination of Poorly Soluble Pharmaceutical Compounds

A mixture of cosolvents is described that significantly improves the solubility of most pharmaceutical compounds. The mixture consists of equal volumes of MeOH, 1,4‐dioxane, and MeCN, thereby containing polar and nonpolar solvents, and is referred to as MDM (from MeOH, dioxane, and MeCN). MDM is mixed with H₂O until the required composition is reached. The utility of this system is that it enables analytical measurements to be performed on a wide range of compounds where measurements would be impaired in aqueous solution. We present the physicochemical characteristics of MDM/H₂O mixtures (density, dielectric constant, p_sK_w) and the principles of pK_a measurement in this solvent/H₂O mixture. We also present pK_a values in H₂O of several drug compounds determined from values measured in MDM/H₂O mixtures.     

Modulation-frequency encoded multi-color fluorescent DNA analysis in an optofluidic chip

We introduce a principle of parallel optical processing to an optofluidic lab-on-a-chip. During electrophoretic separation, the ultra-low limit of detection achieved with our set-up allows us to record fluorescence from covalently end-labeled DNA molecules. Different sets of exclusively color-labeled DNA fragments-otherwise rendered indistinguishable by spatio-temporal coincidence-are traced back to their origin by modulation-frequency-encoded multi-wavelength laser excitation, fluorescence detection with a single ultrasensitive, albeit color-blind photomultiplier, and Fourier analysis decoding. As a proof of principle, fragments obtained by multiplex ligation-dependent probe amplification from independent human genomic segments, associated with genetic predispositions to breast cancer and anemia, are simultaneously analyzed.     

Thermodynamic analysis of polymerization-induced phase separation of a polystyrene in epoxy/monoamine–diamine systems. Effect of monoamine–diamine proportion on the phase diagram

Polymerization-induced phase separation of a polystyrene in various epoxy-amine systems where the amino groups were provided by a monoamine and a diamine mixed in different proportions was thermodynamically studied. A model based on the Flory–Huggins theory extended by Koningsveld and Staverman approach where the interaction parameter was dependent on temperature, composition and conversion, and polydispersity of the components was considered, was used. A general equation for the evolution during polymerization of the epoxy-amine species distributions according to the monoamine–diamine ratio was derived from the Stockmayer distribution. The interaction parameters continuously decreased with conversion. Phase diagrams of the blends were obtained and the critical composition was between 5 and 6 vol.% PS in all blends.     

Nucleophilic Additions to Coordinated 1,10‐Phenanthroline: Intramolecular,Intermolecular, Reversible,and Irreversible

KN(SiMe₃)₂ reacts with [Re(CO)₃(phen)(PMe₃)]OTf via reversible addition to the phen ligand and irreversible deprotonation of the PMe₃ ligand followed by intramolecular attack to phen by the deprotonated phosphane, whereas MeLi irreversibly adds to phen. The addition of MeLi has been shown to be intermolecular, unlike previously known nucleophilic additions to pyridines.     

A Molecular Imprinted Polymer Sensor for Biomonitoring of Fenamiphos Pesticide Metabolite Fenamiphos Sulfoxide

A new electrochemical method for the identification and quantification of Fenamiphos pesticide's major metabolite in biological samples – Fenamiphos Sulphoxide ( FNX ) was developed. Computational calculations, Density Functional Theory (DFT) and semi-empirical models (PM3) were performed to determine the best monomer, pyrrole, and a ratio of 1 : 5 (template: monomer) was chosen for the fabrication of the FNX− MIP sensor obtained by electropolymerization. The FNX− MIP sensor responded well to increasing FNX concentrations (range of 1–30 μM). Limit of detection and quantification (LOD=0.183 μM, LOQ=0.601 μM), respectively, selectivity, and repeatability were also investigated for the developed method. The obtained percentage of recovery showed good agreement compared to reference values obtained from GC-MS, which was used as a reference method. The FXN− MIP sensor proved selective in the presence of potential interferents. The developed sensor was successfully applied for the determination of FNX in spiked plasma and urine matrixes with acceptable recovery rates. The proposed method also proved successful in detecting FNX prepared from the in vitro metabolism of FNP using liver microsomes to metabolize it.