SciCombinator

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Concept: Tartaric acid

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A highly sensitive, specific and enantioselective assay has been developed and validated for the estimation of TAK-700 enantiomers [(+)-TAK-700 and (-)-TAK-700] in rat plasma on LC-MS/MS-ESI in the positive-ion mode. Liquid-liquid extraction was used to extract (±)-TAK-700 enantiomers and IS (phenacetin) from rat plasma. TAK-700 enantiomers were separated using methanol and 5 mm ammonium acetate (80:20, v/v) at a flow rate of 0.7 mL/min on a Chiralcel OJ-RH column. The total run time was 7.0 min and the elution of (+)-TAK-700, (-)-TAK-700 and IS occurred at 3.71, 4.45 and 4.33 min, respectively. The MS/MS ion transitions monitored were m/z 308.2 → 95.0 for TAK-700 and m/z 180.2 → 110.1 for IS. The standard curves for TAK-700 enantiomers were linear (r(2)  > 0.998) in the concentration range 2.01-2015 ng/mL for each enantiomer. The inter- and intra-day precisions were in the ranges 3.74-7.61 and 2.06-8.71% and 3.59-9.00 and 2.32-11.0% for (+)-TAK-700 and (-)-TAK-700, respectively. Both the enantiomers were found to be stable in a battery of stability studies. This novel method was applied to the study of stereoselective oral pharmacokinetics of (+)-TAK-700 and it was unequivocally demonstrated that (+)-TAK-700 does not undergo chiral inversion to its antipode in vivo. Copyright © 2012 John Wiley & Sons, Ltd.

Concepts: Tartaric acid, Enantiomeric excess, Stereochemistry, Chirality, Enantiomer

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Equal and opposite: A chiral surfactant molecule was used to induce high enantioselectivity in the transformation from the achiral phase of mercury sulfide, probably through binding of the surfactant thiolate groups to Hg ions in the forming crystal. The generation of truly chiral inorganic NCs of tailored size and shape should be useful for many applications, such as enantioselective catalysis and sensing.

Concepts: Chemical bond, Cinnabar, Chemistry, Tartaric acid, Enantiomer, Electron, Atom, Chirality

28

The ligand exchange reaction between racemic Au38(2-PET)24 (2-PET: 2-phenylethylthiolate) clusters and enantiopure 1,1'-binapththyl-2,2'-dithiol (BINAS) was monitored in situ using a chiral HPLC approach. In the first exchange step, a clear preference of R-BINAS towards the left-handed enantiomer of Au38(2-PET)24 is observed (about four times faster than reaction with the right-handed enantiomer). The second exchange step is drastically slowed compared to the first step. BINAS substitution deactivates the cluster for further exchange, which is attributed to (stereo)electronic effects. The results constitute the first example of a ligand exchange reaction in a thiolate-protected gold cluster with directed enrichment of a defined species in the product mixture. This may open new possibilities for the design of nanomaterials with tailored properties.

Concepts: Racemic mixture, Tartaric acid, In situ, Stereochemistry, Chirality, Enantiomer

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We report the chiral diene ligated rhodium-catalyzed dynamic kinetic asymmetric transformation (DYKAT) of racemic secondary allylic trichloroacetimidates with a variety of N-methyl anilines, providing allylic N-methyl arylamines in high yields, regioselectivity, and enantiomeric excess. The rhodium-catalyzed DYKAT method addresses limitations previously associated with this particular class of aromatic nitrogen nucleophiles.

Concepts: Asymmetric synthesis, Tartaric acid, Asymmetric induction, Chirality, Racemic mixture, Enantiomeric excess, Stereochemistry, Enantiomer

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A good sort: A racemate is observed to segregate in situ upon diastereoselective adsorption on an achiral surface by surface-mediated complex formation in a liquid (see picture; yellow: enantiopure resolving agents, ovals: the enantiomers of the racemate to be resolved).

Concepts: Segregation, Tartaric acid, Racemic mixture, Stereochemistry, Enantiomer, Chirality

28

All enantiopure atropisomeric (atropos) ligands essentially require enantiomeric resolution or synthetic transformation from a chiral pool. In sharp contrast, the use of tropos (chirally flexible) ligands, which are highly modular, versatile, and easy to synthesize without enantiomeric resolution, has recently been the topic of much interest in asymmetric catalysis. Racemic catalysts bearing tropos ligands can be applied to asymmetric catalysis through enantiomeric discrimination by the addition of a chiral source, which preferentially transforms one catalyst enantiomer into a highly activated catalyst enantiomer. Additionally, racemic catalysts bearing tropos ligands can also be utilized as atropos enantiopure catalysts obtained via the control of chirality by a chiral source followed by the memory of chirality. In this feature article, our results on the asymmetric catalysis via the combination of various central metals and tropos ligands are summarized.

Concepts: Hydrogenation, Racemic mixture, Enantiomeric excess, Amino acid, Tartaric acid, Chirality, Stereochemistry, Enantiomer

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Herein, we report the enantio- and diastereoselective formation of trans-iodo- and trans-chlorocyclopropanes from α-iodo- and α-chlorozinc carbenoids by using a dioxaborolane-derived chiral ligand. The synthetically useful iodocyclopropane building blocks were derivatized by an electrophilic trapping of the corresponding cyclopropyl lithium species or a Negishi coupling to give access to a variety of enantioenriched 1,2,3-substituted cyclopropanes. The synthetic utility of this method was demonstrated by the formal synthesis of an HIV-1 protease inhibitor. In addition, the related stereoselective bromocyclopropanation was also investigated. New insights about the relative electrophilicity of haloiodomethylzinc carbenoids are also presented.

Concepts: Cyclopropane, Utility, Electrophile, Electrophilic addition, Tartaric acid, Chirality, HIV, Stereochemistry

28

Competition under control: A practical and efficient direct asymmetric vinylogous Michael reaction of deconjugated butenolides has been developed. Products of this reaction, highly functionalized chiral succinimides, are obtained in excellent yield with high diastereoselectivity (up to d.r.=18:1) and outstanding enantioselectivity (up to e.r.=99.5:0.5).

Concepts: Enantiomer, Michael reaction, Tartaric acid, Nucleophilic addition, Chirality, Stereochemistry

27

A novel and simple methodology for co-obtaining of enantiomerically pure α-hydroxyacids and α-ketoacids was developed by enantioselective oxidation of α-hydroxyacids bearing a substituent with an aryl group using α-hydroxyacid dehydrogenase (α-HADH). A high-throughput method was firstly established for screening of enantioselective α-HADHs. Sinorhizobium sp. ZJB1101 with high activity and excellent enantioselectivity of α-HADH for oxidation of α-hydroxyacids bearing a substituent with an aryl group was isolated and identified. This strain has potential for co-production of ®-α-hydroxyacids and α-ketoacids in near theoretical yields, while no consecutive oxidation of α-ketoacids was observed. The green conversion system appears promising for potential applications in industry.

Concepts: Methodology, Enantiomer, Aryl, Tartaric acid, Stereochemistry, Optics, Scientific method

27

Various optically active 2-hydroxy-γ-butyrolactone derivatives are produced via the kinetic resolution of racemic 2-hydroxy-γ-butyrolactones with diphenylacetic acid using pivalic anhydride and ®-benzotetramisole (®-BTM), a chiral acyl-transfer catalyst. Importantly, the substrate scope of this novel protocol is fairly broad (12 examples, s-value; up to over 1000). In addition, we succeeded in disclosing the reaction mechanism to afford high enantioselectivity using theoretical calculations and expounded on the substituent effects at the C-3 positions in 2-hydroxylactones.

Concepts: Tartaric acid, Optics, Enantiomer, Amino acid, Stereochemistry