Search results for "Selectivity"
showing 10 items of 1148 documents
Aminoallenylidene complexes of ruthenium(II) from the regioselective addition of secondary amines to butatrienylidene intermediates: a combined exper…
2003
Aminoallenylidene complexes trans-[Cl(dppm)2RuC3(NRR )(CH3)] are obtained from the regioselective addition of secondary amines to trans-[Cl(dppm)2Ru C C C CH2] . Unsymmetrically substituted amines give rise to Z/E isomeric mixtures. Dynamic 31P NMR spectroscopy gave an energy barrier of about 85 kJ mol 1 for rotation around the CN-bond pointing to a large contribution of the iminium alkynyl resonance form trans-[Cl(dppm)2Ru–C C– C( NRR )(CH3)] . This is also indicated by the pronounced bond length alternation within the RuC3N-chain as is revealed by X-ray structure analysis of the Z isomer of the (benzylmethyl)methylamine derivative 2d. The issue of NR2 rotation was also addressed by DFT ca…
Influence of the Nature of the Ligand on Dirhodium(II) Carbene Species: A Theoretical Analysis
2008
The influence of three prototypic families of bridging ligands (carboxylate, carboxamidate, and ortho-metalated arylphosphines) on the electronic structure of dirhodium(II) carbene complexes was theoretically analyzed. The calculations indicated that the electron donation of the ligand to the Rh atom, rather than the chelating ability or the metal−ligand orbital mixing, was responsible for tuning carbene charge via back-donation, which can influence the reactivity and selectivity of the dirhodium complexes in catalytic carbene transfer reactions.
Stereochemistry of terpene derivatives. Part 3: Hydrolytic kinetic resolution as a convenient approach to chiral aminohydroxyiminocaranes with local …
2002
Abstract We have developed a stereoselective hydrolytic kinetic resolution process for diastereoisomeric mixtures of epoxyiminocarene intermediates in the presence of ( R , R )-(−)-(salen)Co(III)OAc catalyst, this was applied as the first step in the synthesis of novel chiral aminohydroxyiminocarane derivatives with local anaesthetic activity. The absolute configuration of the product was confirmed by X-ray crystallography.
The application of molecular imprinting technology to solid phase extraction
2001
In parallel to a long lasting search for universal multi-purpose sorbents, the area of solid phase extraction (SPE) is recently experiencing a rapid development of new types of tailor-made class specific or compound-specific sorbents which are designed to respond to the increasing demand for selectivity and efficiency in sample clean-up prior to quantification. An important issue here is the enrichment and clean-up of complex samples, such as environmental waters, sediments, biofluids and foodstuffs prior to detection. This because the analyte is often present in low concentration in a complex mixture of similar compounds and therefore needs to be isolated and enriched in order to be detect…
A Longitudinal Study on Social Development as an Impetus for School Reform Toward an Integrated School Day
2004
The Jyväskylä Longitudinal Study of Personality and Social Development, in which the same individuals have been studied from the age of 8 to age 42, has warranted the conclusion that children should be encouraged toward prosocial development at an early age, because it helps them to integrate into the school environment and saves them from the cycle of maladaptation. A project was designed at the invitation of a Finnish parliamentary group for the enhancement of children's socioemotional development at school. The project comprises seven subprojects including interventions at three levels: the child's behavior, school as a learning environment, and the school's relationships with the surro…
Use of Saccharomyces cerevisiae as a whole cell system for aldol condensation in organic medium: Study of the factors affecting the biotransformation
2011
Abstract Saccharomyces cerevisiae has been employed as a whole cell catalyst for a number of asymmetric transformations. This work explores the ability of this microorganism to carry out the asymmetric aldol condensation between 4-nitrobenzaldehyde and acetone. For this purpose, lyophilized cells of the FY86 laboratory strain from stationary phase cultures were employed. This reaction shows stereoselectivity, and its progress is affected by the water concentration in the medium, temperature and the growth stage of the yeast culture. Cell lysis experiments indicate that activity responsible for this biotransformation is located in the soluble fraction.
2-(6-Methoxy-7H-purin-7-yl)-1-phenylethanone monohydrate
2007
The crystal structure of the title compound, C14H12N4O2·H2O, was determined in the course of our studies of the synthesis and optimization of 7-aryl-7H-purines as inhibitors of the vascular endothelial growth factor receptor (VEGF-R), c-Jun NH2-terminal protein kinase 3 (JNK3) and the p38α mitogen-activated protein kinase (MAPK). In the title compound, two molecules are associated with each other through O—H⋯N hydrogen bonds to different N atoms in the purine ring system. The compound was prepared via a regioselective synthesis using the methyl(aqua)cobaloxime complex, CH3Co(DH)2OH2, as a temporary auxiliary. The X-ray crystallographic results confirmed the regioselective N-7 alkylation …
Structural Optimization of a Pyridinylimidazole Scaffold: Shifting the Selectivity from p38α Mitogen-Activated Protein Kinase to c-Jun N-Terminal Kin…
2018
Starting from known p38α mitogen-activated protein kinase (MAPK) inhibitors, a series of inhibitors of the c-Jun N-terminal kinase (JNK) 3 was obtained. Altering the substitution pattern of the pyridinylimidazole scaffold proved to be effective in shifting the inhibitory activity from the original target p38α MAPK to the closely related JNK3. In particular, a significant improvement for JNK3 selectivity could be achieved by addressing the hydrophobic region I with a small methyl group. Furthermore, additional structural modifications permitted to explore structure–activity relationships. The most potent inhibitor 4-(4-methyl-2-(methylthio)-1H-imidazol-5-yl)-N-(4-morpholinophenyl)pyridin-2-a…
Di- and Tetrairon(III) μ-Oxido Complexes of an N3S-Donor Ligand: Catalyst Precursors for Alkene Oxidations
2019
The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe 4 (μ-O) 4 (PTEBIA) 4 ](CF 3 SO 3 ) 4 (CH 3 CN) 2 ] (1a), [Fe 2 (μ-O)Cl 2 (PTEBIA) 2 ](CF 3 SO 3 ) 2 (1b), and [Fe 2 (μ-O)(HCOO) 2 (PTEBIA) 2 ](ClO 4 ) 2 (MeOH) (2) were prepared from the sulfur-containing ligand (2-((2,4-dimethylphenyl)thio)-N,N-bis ((1-methyl-benzimidazol-2-yl)methyl)ethanamine (PTEBIA). The tetrairon complex 1a features four μ-oxido bridges, while in dinuclear 1b, the sulfur moiety of the ligand occupies one of the six coordination sites of each Fe(III) ion with a long Fe-S distance of 2.814(6) A. In 2, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidati…
Acetylation of 5-Amino-1H-[1,2,4]triazole Revisited
2002
The products of the acetylation reactions of the common herbicide 5-amino-1H-[1,2,4]triazole were investigated using HPLC, GC-MS, 1H NMR, and FTIR spectroscopy. The conventional annular monoacetylation procedures with acetyl chloride are not regioselective and furnish a mixture of isomers. Traditional diacetylation in neat acetic anhydride under reflux produces a mixture of di-, mono-, and triacetylated derivatives. By using equivalent amounts of acetic anhydride in a dimethylformamide solution, a rapid and selective annular monoacetylation of 5-amino-1H-[1,2,4]triazole was achieved. The monoacetylation proceeds via the formation of the intermediate, 1-acetyl-3-amino-1H-[1,2,4]triazole, whi…