Search results for "Selectivity"
showing 10 items of 1148 documents
Regioselective Hydrogenation of a 60-Carbon Nanographene Molecule toward a Circumbiphenyl Core.
2019
Regioselective peripheral hydrogenation of a nanographene molecule with 60 contiguous sp2 carbons provides unprecedented access to peralkylated circumbiphenyl (1). Conversion to the circumbiphenyl core structure was unambiguously validated by MALDI-TOF mass spectrometry, NMR, FT-IR, and Raman spectroscopy. UV–vis absorption spectra and DFT calculations demonstrated the significant change of the optoelectronic properties upon peripheral hydrogenation. Stimulated emission from 1, observed via ultrafast transient absorption measurements, indicates potential as an optical gain material.
Anticoagulant Activity of the Enantiomers of Acenocoumarol in Man
1978
For the mono-coumarin derivatives warfarin and phen-procoumon it was shown that in man and rats the S(−) enantiomer is several times more potent as anticoagulant than the R(+) enantiomer. These stereoselective differences in the anticoagulant potency reflect differences in the affinity for the receptor site rather than differences in the pharmacokinetics.
Submicellar and micellar reversed-phase liquid chromatographic modes applied to the separation of beta-blockers.
2009
The behaviour of a reversed-phase liquid chromatographic (RPLC) system (i.e. elution order, resolution and analysis time), used in the analysis of β-blockers with acetonitrile-water mobile phases, changes drastically upon addition of an anionic surfactant (sodium dodecyl sulphate, SDS). Surfactant monomers cover the alkyl-bonded phase in different extent depending on the concentration of both modifiers, in the ranges 1 × 10-3-0.15 M SDS and 5-50% acetonitrile. Meanwhile, the surfactant is dissolved in the mobile phase as free monomers, associated in small clusters or forming micelles. Four characteristic RPLC modes are yielded, with transition regions between them: hydro-organic, micellar, …
Performance of different C18 columns in reversed-phase liquid chromatography with hydro-organic and micellar-organic mobile phases
2014
Column selection in reversed-phase liquid chromatography (RPLC) can become a challenge if the target compounds interact with the silica-based packing. One of such interactions is the attraction of cationic solutes to the free silanols in silica-based columns, which is a slow sorption-desorption interaction process that gives rise to tailed and broad peaks. The effect of silanols is minimised by the addition of a competing agent in the mobile phase, such as the anionic surfactant sodium dodecyl sulphate (SDS). In micellar-organic RPLC, the adsorption of an approximately fixed amount of SDS monomers gives rise to a stable modified stationary phase, with properties remarkably different from th…
Performance of a Chromolith RP-18e column for the screening of β-blockers
2009
The chromatographic performance of a monolithic column (Chromolith RP-18e) was comprehensively examined in the isocratic separation of ten beta-blockers, using ACN-water mobile phases, and compared with the performance of three microparticulate RP columns manufactured with different types of silica: Spherisorb ODS-2, Kromasil C18 and XTerra MS C18. The comparison considered the analysis time, selectivity, peak shape (column efficiency and asymmetry) and resolution, and was extended to a wide range of mobile phase compositions. The Chromolith column showed good performance for the analysis of beta-blockers with regard to the packed columns. In terms of selectivity and analysis time, the grea…
Acid-mediated reaction of bis(pyridine)iodonium(I) tetrafluoroborate with aromatic compounds. A selective and general iodination method
1993
Reaction of aromatic compounds with bis(pyridine)iodonium(I) tetrafluoroborate (IPy2BF4) in the presence of HBF4 or CF3SO3H in CH2Cl2 at room temperature furnishes monoiodo derivatives with excellent regioselectivity and yields. Use of either acid gives comparable results with activated aromatics, whereas CF3SO3H is much more effective in the iodination of deactivated aromatics. © 1993 American Chemical Society.
Six-Step Gram Scale Synthesis of the HIV Integrase Inhibitor Dolutegravir Sodium
2021
A short and practical synthesis for preparing the active pharmaceutical ingredient dolutegravir sodium was investigated. The convergent strategy developed herein starts from 3-(R)-amino-1- butanol and builds up the BC ring system in 76% isolated yield over four steps. Ring A was constructed by a one-pot 1,4-addition to diethyl-(2E/Z)-2-(ethoxymethylidene)-3-oxobutandioate and subsequent MgBr2·OEt2-mediated regioselective cyclization. Amide formation with 2,4- difluorobenzylamine was either performed from the carboxylic acid or through aminolysis of the corresponding ester precursor. Final salt formation afforded dolutegravir sodium in 48–51% isolated yield (HPLC-purity: 99.7–99.9%) over six…
Reaktionen von elektronenreichen Heterocyclen mit Orthocarbonsäure-Derivaten, 9. Acylierungsreaktionen von Indol und Methylindolen mit Dialkoxycarben…
1986
Indol und einige Methylderivate 1 lassen sich unter milden Bedingungen mit den Dialkoxycarbenium-tetrafluoroboraten 2 in meist guten Ausbeuten regioselektive acylieren. Mit dem Formylkation-Aquivalent 2a′ werden mit uberschussigem 1 auch die Bisindolycarbenium-tetrafluoroborate 13a – d erhalten. Reactions of Electron-rich Heterocycles with Orthocarboxylic Acid Derivatives, 9. – Acylation of Indole and Methylindoles with Dialkoxycarbenium Tetrafluoroborates Indole and some methylindoles 1 were acylated regioselectively with dialkoxycarbenium tetrafluoroborates 2 under mild conditions. The formyl cation equivalent 2a′ reacts with excess of indoles 1 to give the bisindolylcarbenium tetrafluoro…
Derivatisation of Pyrogallarenes
2005
Derivatisation of upper-rim hydroxy groups of pyrogallarenes produced completely acylated and tosylated pyrogallarene derivatives. Mesitylation of pyrogallarene, however, resulted in a regioselective derivatisation of hydroxy groups, i.e. eight OH groups out of 12 were mesitylated. Crystal structures of the synthesised pyrogallarene derivatives indicate that completely substituted pyrogallarenes exist in a distorted crown conformation despite of the lack of stabilising intramolecular hydrogen bonds. In contrast, the partially substituted pyrogallarene adopts a boat conformation and has an open cavity for the inclusion of small guest molecules. © Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinh…
Socioemotional behavior and school achievement in relation to extracurricular activity participation in middle childhood
2012
This 3-year longitudinal study investigated the associations of student (aged 9 to 10 years at the beginning of the study; n = 281; 51% girls) participation in extracurricular activities with teacher-rated socioemotional behavior and school achievement. MANOVA results showed that, after controlling for the grade level and the initial level of the outcome variables, participation in arts and crafts and music activities was related to higher adaptive behavior, academic attainments (i.e., reading, writing, arithmetic), and working skills (persistence, concentration, carefulness). Participation in performing arts was associated with higher academic working skills, and participation in academic …