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Enantioselective Process (enantioselective + process)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

Exploring Chiral Space en route to DPC 963: A Personal Account

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2003
William
Abstract DPC 961 and DPC 963 are non-nucleoside reverse transcriptase inhibitors (NNRTIs) for the treatment of HIV. These drug candidates contain a chiral quaternary center, which can be installed via addition of lithium cyclopropylacetylide to an N -acylketimine in the presence of a chiral moderator. This account describes our efforts to identify a cost-effective moderator by rapidly preparing, screening, and optimizing libraries of enantiopure ,-amino alcohols. The result is a highly enantioselective process that has been used to produce these NNRTIs on a metric ton scale. [source]

Thermodynamic origin of the chiral recognition of tryptophan on teicoplanin and teicoplanin aglycone stationary phases

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 5 2005
Mohamed Haroun
Abstract The D-, L-tryptophan binding and the chiral recognition properties of the teicoplanin and teicoplanin aglycone (TAG) chiral stationary phase (CSPs) were compared at various column temperatures. The solute adsorption isotherms (bi-Langmuir model) were determined for both the two CSPs using the perturbation method. It was demonstrated that the sugar units were involved in the reduction of the apparent enantioselectivity through two phenomena: (i) the inhibition of some enantioselective contacts with low-affinity binding regions of the aglycone and (ii) a decrease in the stereoselective properties of the aglycone high-affinity binding pocket. The phenomenon (ii) was governed by both a decrease in the ratio of the enantiomer adsorption constant and a strong reduction of the site accessibility for D- and L-tryptophan. In addition, a temperature effect study was performed to investigate the chiral recognition mechanism at the aglycone high-affinity pocket. An enthalpy-entropy compensation analysis derived from the Grunwald model as well as the comparison with the literature data demonstrated that the enantioselective binding mode was dependent on an interface dehydration process. The change in the enantioselective process observed between the TAG and teicoplanin CSP was characterized by a difference of ca. 2,3 ordered water molecules released from the species interface. [source]

Ruthenium-Catalyzed Synthesis of Allylic Alcohols: Boronic Acid as a Hydroxide Source

CHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2008
Asmae Bouziane
Abstract Secondary allylic alcohols were synthesized from linear allylic halides or carbonates using a catalytic amount of a ruthenium complex in the presence of boronic acid. The effects of solvent, base, ruthenium precursor, and boronic acid were fully explored, and the scope of the reaction was extended to various substrates. We also describe a preliminary investigation towards an enantioselective process. Les alcools allyliques secondaires ont été préparés à partir de chlorures ou de carbonates allyliques linéaires en présence d,acide boronique et d,une quantité catalytique de complexe de ruthénium. Les effets de la base, du solvant et du précurseur de ruthénium ont été étudiés. Cette nouvelle réaction a été étendue à différents chlorures de cinnamyle. Lors de cette étude, nous décrivons d,autre part les premiers résultats en catalyse énantiosélective. [source]

Investigations on the Iron-Catalyzed Asymmetric Sulfide Oxidation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2005
Julien Legros Dr.
Abstract The development of an enantioselective sulfide oxidation involving a chiral iron catalyst and aqueous hydrogen peroxide as oxidant is described. In the presence of a simple carboxylic acid, or a carboxylate salt, the reaction affords sulfoxides with remarkable enantioselectivities (up to 96,% ee) in moderate to good yields. The influence of the structure of the additive on the reaction outcome is reported. In the sulfoxide-to-sulfone oxidation a kinetic resolution (with s=4.8) occurs, which, however, plays only a negligible role in the overall enantioselective process. Furthermore, a positive nonlinear relationship between the ee of the product and that of the catalyst has been found. On the basis of these observations, a possible catalyst structure is proposed. [source]

Variations in ,-Hexachlorocyclohexane enantiomer ratios in relation to microbial activity in a temperate estuary

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2003
Tiruponithura V. Padma
Abstract Changes in the enantiomer ratios (ERs) of chiral pollutants in the environment are often considered evidence of biological alteration despite the lack of data on causal or mechanistic relationships between microbial parameters and ER values. Enantiomer ratios that deviate from 1:1 in the environment provide evidence for the preferential microbial degradation of one enantiomer, whereas ER values equal to 1 provide no evidence for microbial degradation and may mistakenly be interpreted as evidence that biodegradation is not important. In an attempt to link biological and geochemical information related to enantioselective processes, we measured the ERs of the chiral pesticide ,-hexachlorocyclohexane (,-HCH) and bacterial activity (normalized to abundance) in surface waters of the York River (VA, USA) bimonthly throughout one year. Despite lower overall ,-HCH concentrations, ,-HCH ER values were unexpectedly close to 1:1 in the freshwater region of the estuary with the highest bacterial activity. In contrast, ER values were nonracemic (ER , 1) and ,-HCH concentrations were significantly higher in the higher salinity region of the estuary, where bacterial activity was lower. Examination of these data may indicate that racemic environmental ER values are not necessarily reflective of a lack of biodegradation or recent input into the environment, and that nonenantioselective biodegradation may be important in certain areas. [source]