Palladium catalysts for aerobic oxidative kinetic resolution of secondary alcohols based on mechanistic insight

The oxidative kinetic resolution of secondary alcohols has been accomplished using 1:1 complexes of PdCl(2) and N-heterocyclic carbenes. In these reactions, both achiral and chiral carbene ligands are used in conjunction with the chiral base (-)-sparteine. A general synthesis of 1:1 PdCl(2)-carbene complexes has been developed and is amenable to a wide range of carbene ligands. The potential of these complexes in aerobic oxidations is highlighted by the use of a chiral Pd(II) complex and the chiral base (-)-sparteine to enhance the kinetic resolution of a racemic alcohol. [reaction--see text]     

Evidence for a trigonal twist mechanism involving a phosphite ligand of Os3(CO)7,[P(OMe)3]5

The fluxional molecule Os₃(CO)₇[P(OMe)₃]₅ has been prepared from OS₃(CO)₁₂ and P(OMe)₃ by a combination of thermal and UV irradiation synthetic methods. An investigation by ³¹P and ¹³C NMR spectroscopy indicated that the mechanism of fluxionality in this compound probably involves the P(OMe)₃ ligand of the Os(CO)₃[P(OMe)₃] unit moving from one equatorial site to the other via a trigonal twist mechanism.     

Investigation of the metabolic fate of 2-, 3- and 4-bromobenzoic acids in bile-duct-cannulated rats by inductively coupled plasma mass spectrometry and high-performance liquid chromatography/inductively coupled plasma mass spectrometry/electrospray mass spectrometry

Inductively coupled plasma mass spectrometry (ICPMS) has been used to determine the rate and routes of excretion of bromine following the intraperitoneal administration (50 mg kg(-1)) of 2-, 3- and 4-bromobenzoic acids to male bile-duct-cannulated rats. Analysis of urine and bile for (79/81)Br using ICPMS showed that all three bromobenzoic acids were rapidly excreted (82-98%) within 48 h of dosing, primarily via the urine. High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) was then used to obtain metabolite profiles for bile and urine. These profiles revealed that extensive metabolism had taken place, with the unchanged bromobenzoic acids forming a minor part of the total of compound-related material detected. Concomitant MS studies, supplemented by alkaline hydrolysis, enabled the identification of the major metabolite of all three of the bromobenzoic acids as a glycine conjugate. Ester glucuronide conjugates were also identified, but formed only a small proportion of total.     

Supercritical fluid chromatography of petroleum products using flameless sulfur chemiluminescence detection

Supercritical fluid chromatography using flameless sulfur chemiluminescence detection has been investigated for the analysis of sulfur compounds in petroleum products. The chromatography and detection system was easy to implement and exhibited good precision, linearity, selectivity, and sensitivity. A minimum detectable limit of 0.3 pg sulfur/s was obtained, and response to sulfur in different sulfur species was nearly equimolar.     

Kinetic determination of magnesium and calcium by stopped-flow injection analysis

A kinetic method for the simultaneous determination of magnesium and calcium ions in solution is described. The method is based on the dissociation reactions of cryptand (2.2.2) complexes; a stopped-flow injection technique is used with spectrophotometric monitoring of the phthalein complexone complexes of the released metal ions. Analyses were done at a rate of 80 h^?1, with injected sample volumes of 80 μl. A microcomputer system for data acquisition and control of the system is described.     

In situ alkylation of cysteine residues in a hydrophobic membrane protein immobilized on polyvinylidene difluoride membranes by electroblotting prior to microsequence and amino acid analysis.

For identification of cysteine residues on microsequence analysis it is crucial to derivatize the sulfhydryl groups. This reaction requires a desalting step which often represents a major obstacle, especially if the sample consists of limited amounts of a hydrophobic membrane protein. An alkylation procedure is described, allowing efficient derivatization (greater than 90%) of cysteines and cystines even in low microgram quantities, as revealed by test analyses with lysozyme and a hydrophobic membrane protein. The modified protein is recovered in high yields in a form suitable for both microsequence analysis and amino acid analysis. The method involves electrophoretic desalting by miniaturized Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in situ alkylation after electro-transfer onto polyvinylidene difluoride membranes. Precautions against NH2-terminal blocking during sample preparations are provided. The general applicability of the method is illustrated by the structural characterization of the low abundance membrane receptor for human urokinase plasminogen activator.     

Mild and practical method for the alpha-arylation of nitriles with heteroaryl halides

[reaction: see text] A mild and transition-metal-free method for the alpha-arylation of aliphatic nitriles with activated heteroaryl halides was developed using NaHMDS or KHMDS as base at ambient temperature. The key to the success of this method is generation of the nitrile anion in the presence of the heteroaryl halide. The method is applicable to both primary and secondary carbonitriles and a wide range of heteroaryl halides. Selective monoarylation was observed with primary carbonitriles. The operational simplicity and the mild reaction conditions add to the value of this method as a practical alternative to the preparation of alpha-heteroaryl carbonitriles.     

muFKBP38: a novel murine immunophilin homolog differentially expressed in Schwannoma cells and central nervous system neurons in vivo

To better understand the process of multistage carcinogenesis in Schwann cells, we have attempted to isolate novel candidate genes involved in neoplastic progression of mouse malignant Schwannoma cells. The semi-differentiated Schwannoma cell line 56-24 and the less differentiated Schwannoma cell line 64-39 were established from peripheral nerve sheath tumors arising in transgenic mice of the MBP/SV40 large T strain Tg29. By using the chemical cross-linking subtraction technique, we have cloned a novel murine cDNA that detects pronounced expression in 56-24 cells but not in 64-39 cells. The longest open reading frame of the cDNA predicts a peptide showing 95% amino acid sequence homology to the recorded sequence of the human immunophilin homolog huFKBPr38, one of a family of proteins that are thought to interface with a wide range of intracellular signal transduction systems. The predicted open reading frame of the corresponding gene, named muFKBP38, encodes a 38 kDa protein that harbors an FK-binding protein (FKBP) domain that is 36% identical to that of muFKBP52, a three-unit tetratricopeptide repeat and a consensus leucine-zipper repeat. Although muFKBP38 mRNA was detected in both neurons and glial cells, pronounced expression of the immunophilin homolog appeared in various classes of neurons associated with the hippocampal formation, as shown by in situ hybridization analysis of adult mouse brains. Taken together, these data indicate that muFKBP38 is (i) a novel potential marker for semi-differentiated Schwannomas, (ii) may form homomultimers and/or interact with other proteins, and (iii) may have a role in neurons associated with memory function.     

Oxepinamides A-C and fumiquinazolines H--I: bioactive metabolites from a marine isolate of a fungus of the genus Acremonium

Three new oxepin-containing natural products (1-3) and two new fumiquinazoline metabolites (4-5) have been isolated from organic extracts of the culture broth and mycelia of an Acremonium sp., a fungus obtained from the surface of the Caribbean tunicate Ecteinascidia turbinata. The structures of the five compounds were determined through extensive analysis of 1D- and 2D-NMR data, and mass spectrometry. Compound 1 exhibited good anti-inflammatory activity in a topical RTX-induced mouse ear edema assay. Compounds 4 and 5 exhibited weak antifungal activity toward Candida albicans in a broth microdilution assay.     

MCSCF reaction-path energetics and thermal rate-constants for the reaction of3NH with H2

Summary The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (^3–)+H₂ (¹ _g ⁺ ) NH₂ (²B₁)+H (²S) involving the lowest triplet electronic state of NH₃ were calculated using multi-configuration (MC) SCF methods. The calculated change of internal energy for the reaction of 11.0 kcal mol^–1 agrees with the experimental value within 2 kcal mol^–1. The barrier to reaction is 23.4 kcal mol^–1 high. The harmonic MCSCF reaction-path potential was calculated and canonical variational transition state theory calculations of the rate constants performed over a temperature range from 400 to 2500 K. The computed rate constants are generally two orders of magnitude smaller than those of the comparable reaction of OH with H₂, whereas those of the reverse reaction are by a factor of 20 larger than those of OH₂ with H.