Search results for "Enantiomer"
showing 10 items of 318 documents
Single Enantiomer’s Urge to Crystallize in Centrosymmetric Space Groups: Solid Solutions of Phenylpiracetam
2017
A detailed thermochemical and structural study of the phenylpiracetam enantiomer system was performed by characterizing the solid solutions, rationalizing the structural driving force for their formation, as well as identifying a common structural origin responsible for the formation of solid solutions of enantiomers. Enantiomerically pure phenylpiracetam forms two enantiotropically related polymorphs (enant–A and enant–B). The transition point (70(7) °C) was determined based on isobaric heat capacity measurements. Structural studies revealed that enant–A and enant–B crystallize in space groups P1 (Z′ = 4) and P212121 (Z′ = 2), respectively. However, pseudoinversion centers were present res…
Chiral and Racemic Spin Crossover Polymorphs in a Family of Mononuclear Iron(II) Compounds
2017
[EN] Understanding the origin of cooperativity and the equilibrium temperature of transition (T1/2) displayed by the spin-crossover (SCO) compounds as well as controlling these parameters are of paramount importance for future applications. For this task, the occurrence of polymorphism, presented by a number of SCO complexes, may provide deep insight into the influence of the supramolecular organization on the SCO behavior. In this context, herein we present a novel family of mononuclear octahedral FeII complexes with formula cis- [Fe(bqen)(NCX)2], where bqen is the chelating tetradentate ligand N,N¿-bis(8-quinolyl)ethane-1,2-diamine and X = S, Se. Depending on the preparation method, these…
A new chiral dimanganese(iii) complex: synthesis, crystal structure, spectroscopic, magnetic, and catalytic properties
2016
Two enantiomeric complexes of formula [MnIII2(μ-OCH3)2(R-valBINAM)2]·1.75DMF (1) and [MnIII2(μ-OCH3)2(S-valBINAM)2]·2DMF (2) [valBINAM = 1,1′-binaphthalene-2,2′-bis(3-methoxysalicylideneiminate)] have been synthesized using as a ligand the chiral Schiff bases resulting from the condensation reactions between o-vanillin and the chiral 1,1′-binaphthyl-2,2′-diamine. The structures of 1 and 2 which have been solved by single crystal X-ray diffraction consist of neutral dimers, the manganese(III) ions being bridged by two methoxido anions, arising from the solvent, and by two valBINAM2− ligands. Their circular dichroism spectra at room temperature emphasize the occurrence of the exciton coupling…
Enantiomeric Resolution of Asymmetric-Carbon-Free Binuclear Double-Stranded Cobalt(III) Helicates and Their Application as Catalysts in Asymmetric Re…
2018
A series of double-stranded binuclear helicates [Co2(H1)2]4+, [Co2(H2)2]4+, and [Co2(H3)2]4+, derived from monodeprotonated bis-pyridyl hydrazine-based ligands of H21, H22, and H23 with one, two, and three -CH2 spacers, were obtained. These asymmetric-carbon-free racemic helicates were separated into their ΔΔ and ΛΛ enantiomers. The resolved helicates were examined for the first time as enantioselective catalysts in asymmetric benzoylation and nitroaldol reactions.
Catalytic enantioselective aza-Reformatsky reaction with seven-membered cyclic imines dibenzo[b,f][1,4]oxazepines
2017
A catalytic enantioselective aza-Reformatsky reaction is reported with cyclic dibenzo[b,f][1,4]oxazepines and ethyl iodoacetate leading to the synthesis of chiral ethyl 2-(10,11-dihydrodibenzo[b,f][1,4]oxazepin-11-yl)acetate derivatives with excellent yields and high enantioselectivities (up to 98% yield and 97 : 3 er) using a readily available diaryl prolinol L4 as the chiral ligand and Me2Zn as the zinc source under an air atmosphere. Furthermore, different transformations were carried out with the corresponding chiral β-amino esters, preserving in all cases the optical purity.
Artemisia arborescens essential oil composition, enantiomeric distribution and antimicrobial activity from different wild populations from the Medite…
2016
International audience; Aerial parts of Artemisiaarborescens were collected from different sites of the Mediterranean area (southwestern Algeria and southern Italy) and the chemical composition of their essential oil (EO) extracted by hydrodistillation was studied by both gas chromatography (GC) equipped with an enantioselective capillary column and GC/mass spectrometry (GC/MS). The EOs obtained were tested against several Listeriamonocytogenes strains. Using GC and GC/MS, 41 compounds were identified, accounting for 96.0-98.8% of the total EO. All EOs showed a similar terpene profile, which was rich in chamazulene, -thujone, and camphor. However, the concentration of such compounds varied …
NMR structure determination of (11E)-trinervita-1(14),2,11-triene, a new diterpene from sexual glands of termites
2005
Graphical Abstract Full-size image; International audience; Female alates of Nasutitermes ephratae termites from Guadeloupe and Nasutitermes sp. from Brazil produce a diterpene hydrocarbon of the molecular formula C20H30 as the main component of their tergal gland secretion. Analysis of NMR, IR, and mass spectra of the diterpene led to a structure of (11E)-trinervita-1(14),2,11-triene. Based on a comparison with the published oxygenated trinervitane skeleton from termites we prefer the enantiomer with absolute configurations (4R,7S,8R,15S,16S). The suggested structure is supported by ab initio quantum chemical calculation of 1H and 13C chemical shifts for the optimized geometry of the molec…
Stereochemical features of the hydrolysis of 9,10-epoxystearic acid catalysed by plant and mammalian epoxide hydrolases
2002
cis-9,10-Epoxystearic acid was used as a tool to probe the active sites of epoxide hydrolases (EHs) of mammalian and plant origin. We have compared the stereochemical features of the hydrolysis of this substrate catalysed by soluble and membrane-bound rat liver EHs, by soluble EH (purified to apparent homogeneity) obtained from maize seedlings or celeriac roots, and by recombinant soybean EH expressed in yeast. Plant EHs were found to differ in their enantioselectivity, i.e. their ability to discriminate between the two enantiomers of 9,10-epoxystearic acid. For example, while the maize enzyme hydrated both enantiomers at the same rate, the EH from soybean exhibited very high enantioselecti…
Synthesis of disparlure and monachalure enantiomers from 2,3-butanediacetals
2020
2,3-Butanediacetal derivatives were used for the stereoselective synthesis of unsymmetrically substituted cis-epoxides. The procedure was applied for the preparation of both enantiomers of disparlure and monachalure, the components of the sex pheromones of the gypsy moth (Lymantria dispar) and the nun moth (Lymantria monacha) using methyl (2S,3R,5R,6R)-3-ethylsulfanylcarbonyl-5,6-dimethoxy-5,6-dimethyl-1,4-dioxane-2-carboxylate as the starting material.
Chiral Serum Pharmacokinetics of 4-Fluoroamphetamine after Controlled Oral Administration
2021
Abstract Over the last two decades, misuse of 4-fluoroamphetamine (4-FA) became an emerging issue in many European countries. Stimulating effects last for 4–6 hours and can impact psychomotor performance. The metabolism of amphetamine-type stimulants is stereoselective and quantification of (R)- and (S)-enantiomers has been suggested for assessing time of use. To date, no data on enantioselective pharmacokinetics is available for 4-FA in serum samples. An enantioselective liquid chromatography−tandem mass spectrometry (LC–MS-MS) method was developed using a chiral Phenomenex® Lux 3 μm AMP column. Validation of the method showed satisfactory selectivity, sensitivity, linearity (0.5–250 ng/mL…