bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stereoisomeric flavour compounds XXXV: Chiral aroma compounds of sherry I. Optically pure stereoisomers of solerone and solerole
Authors: Mosandl Armin , Hollnagel Angelika 
Published: January 2005

AbstractThe enantioseparation of the sherry aroma components 5‐oxo‐4‐hydroxyhexanoic acid γ‐lactone (solerone) and 4,5‐dihydroxyhexanoic acid γ‐lactone (solerole) is achieved, using Chiraspher (Merck) as the chiral HPLC phase and the optical purity ascertained directly by HRGC with heptakis(3‐O‐acetyl‐2,6‐di‐O‐pentyl)‐β‐cyclodextrin (Lipodex D) as the chiral stationary phase. The absolute configurations of 4,5‐dihydroxyhexanoic acid γ‐lactones are assigned by 1H‐NMR spectral data of diastereomeric α‐methoxy‐α‐trifluoromethylphenylacetic acid (MTPA) esters, according to Mosher's model. Sensory qualities of the isomers are given.
Preparative resolutions of an α‐methyl carboxylic acid through selective transformations of readily epimerizable intermediates
Authors: Josef Kurt A. , D'Ambra Thomas E. , Rosi David , Philion Richard E. 
Published: January 2005

AbstractTwo preparations of the enantiomers of 2 are described. The first makes use of the chromatographic separation of the diastereomeric amides 6a and 6b. Standard hydrolysis of these amides caused racemization, so a milder sequence was developed which utilized carbonyldiimidazole and 1 equivalent of 1 N LiOH. The second preparation involved classical resolution of 9 with (−)‐cinchonidine. Subsequent transformations of this substrate involved ester formation, Friedel–Crafts acylation, and ester hydrolysis, all without racemization. The most notable of these reactions was the use of EtAlCl2 in the Friedel–Crafts step, which provided a mild acylation of 10. This second preparation affords a high yield, mild process for the potential preparation of kilogram quantities of (−)‐(R)‐2b.
Enantiomeric resolution of DNS‐amino acids by ligand exchange chromatography using l‐phenylalaninamide together with Cu(II) ions as chiral additives to the eluent
Authors: Carunchio V. , Girelli A. M. , Messina A. , Sinibaldi M. 
Published: January 2005

AbstractResolution of various α‐DNS DL‐amino acids by ligand exchange chromatography of L‐phenylalaninamide–copper(II) complexes on a conventional reversed‐phase packing is reported. Parameters of the mobile phase which control retention and enantioselectivity such as concentration of Cu(II) ion and L phenylalaninamide (PheNH2), pH, ionic strength, and acetonitrile content were examined. In order to obtain further information on the distribution and stability of the prevailing complex species formed between the metal ion and the chiral selector, spectrophotometric measurements in different media were also carried out.
Stereoselective pharmacokinetics of 3,4‐methylenedioxymethamphetamine in the rat
Authors: Fitzgerald Robert L. , Blanke Robert V. , Poklis Alphonse 
Published: January 2005

AbstractStudies to characterize the pharmacokinetics of the enantiomers of MDMA were conducted in rats using the iliac arterial cannulation. Two routes of administration, intravenous and subcutaneous, were evaluated at two dose levels for each route [20 and 40 mg/kg (±)‐MDMA for subcutaneous, 10 and 20 mg/kg (±)‐MDMA for intravenous administrations]. The average half‐life (±SD) for all dosing groups was 2.5 ± 0.8 h for (−)‐(R)‐MDMA and 2.2 ±0.8 h for (+)‐(S)‐MDMA. The more rapid clearnace of (+)‐(S)‐MDMA compared with (−)‐(R)‐MDMA is consistent with the area under the curve (AUC) data of the parent drug and its primary metabolite MDA. The mean (±SD) AUC S/R ratios of MDMA and MDA were 0.70 ± 0.05 and 3.1 ± 0.8, respectively. Following a 20 mg/kg dose of racemic MDMA iv the mean (±SD) of the percent dose excreted as (−)‐(R)‐MDMA, (+)‐(S)‐MDMA, (−)‐(R)‐MDA, and (+)‐(S)‐MDA were 20 ± 10, 12 ± 6, 3 ± 1, and 6 ± 2, respectively.
Enantioselective binding of mephobarbital to plasma proteins
Authors: O'shea Nerida J. , Hooper Wayne D. 
Published: January 2005

AbstractThe enantioselective protein binding of mephobarbital (MPB) was investigated in human plasma and human serum albumin solutions by equilibrium dialysis. A small but statistically significant difference was observed in the in vitro plasma protein binding of the enantiomers; (S)‐MPB was ∼59% bound and (R)‐MPB ∼67% bound. The binding to albumin [(S)‐MPB: ∼29% bound, and (R)‐MPB: ∼41% bound] was less than to plasma proteins but showed somewhat greater enantioselectivity, suggesting that albumin binding is a major source of the enantioselectivity in plasma. The effects of MPB concentration, of varying enantiomeric concentration ratio, and of phenobarbital on the enantioselective binding of MPB were studied. The effect of age was also investigated by measuring the binding in plasma from 8 young (18–25 yr) and 8 elderly (>60 yr) male subjects who took single doses of MPB. The results were in close agreement with the in vitro binding data, and the binding of both enantiomers was marginally but significantly lower in the young compared with the elderly subjects. These differences in binding were consistent with previously observed pharmacokinetic differences between the two subject groups.
Optical resolution and absolute configuration of a nonsteroidal antiinflammatory drug, 2‐(10,11‐Dihydro‐10‐oxodibenzo‐[b,f]thiepin‐2‐yl)propionic acid
Authors: Yamamoto Masao , Nohira Hiroyuki , Masaki Mitsuo 
Published: January 2005

AbstractThe title compound (±)‐1 (CN‐100) was efficiently resolved into a pair of enantiomers by fractional crystallization of the diastereomeric salts of (−)‐and (+)‐1‐phenylethylamine. The purity of the enantiomers was determined using the chiral cellulose column (CHIRALCEL OJ®) which allowed direct separation of the enantiomers. A separation factor (α) of 1.73 was obtained. X‐Ray crystallographic analysis of the (+)‐isomer [salt of (−)‐1‐(4‐bromophenyl)ethylamine] showed that this enantiomer has S‐configuration. Biological studies have shown that only the (+)‐isomer has antiinflammatory activity. Racemization of (−)‐isomer was carried out by heating its propionic acid solution in the presence of mineral acid, such as HBr.
Relative configuration of thioridazine enantiomers
Authors: Patrick Kennerly S. , Singletary Joan L. 
Published: January 2005

AbstractThe relative configuration of the enantiomers of thioridazine was defined to explore the stereochemistry associated with the selective binding of (−)‐thioridazine to dopamine D‐1 receptors and (+)‐thioridazine to D‐2 receptors. Using a seven‐step stereoconservative synthesis, (−)‐(S)‐2‐piperidinecarboxylic acid was converted to (−)‐(S*)‐2‐(2‐chloroethyl)‐1‐methylpiperidine, a literature (−)‐thioridazine synthetic precursor. Accordingly, (−)‐ and (+)‐thioridazine are the (S)‐ and (R)‐enantiomers, respectively.
Helix‐sense‐selective polymerization of diphenyl‐2‐pyridylmethyl methacrylate with chiral anionic initiators
Authors: Okamoto Yoshio , Mohri Haruhiko , Nakano Tamaki , Hatada Koichi 
Published: January 2005

AbstractPolymerization of diphenyl‐2‐pyridylmethyl methacrylate was carried out with the complexes of organolithium compounds with 22 chiral ligands. Helix‐sense‐selectivity of the polymerization was largely affected by a slight structural difference of chiral ligands. (+)‐(S)‐2‐(1‐Pyrrolidinylmethyl)pyrrolidine was the most effective ligand in producing a one‐handed helical polymer with narrow molecular weight distribution.
Iridium complexes of dehydroamino acids: The kinetic resolution of racemic diphosphines and their application in catalytic asymmetric hydrogenation
Authors: Brown John M. , Maddox Peter J. 
Published: January 2005

AbstractThe reaction of chiral diphosphines with a configurationally pure cationic bis‐enamide complex of iridium, bis(menthyl (Z)‐α‐benzamidocinnamate)‐iridium tetrafluoroborate, is described. When the reactant ligand is racemic then kinetic resolution occurs with high specificity under the appropriate conditions. Since the iridium diphosphine complex is catalytically inactive in homogeneous hydrogenation, the residual enantiomer may be reacted with bis(norbornadiene)‐rhodium tetrafluoroborate to produce an active catalyst. This effects the hydrogenation of methyl (Z)‐α‐acetamidocinnamate in optical yields comparable with those obtained separately with the enantiomerically pure ligand rhodium complex. The reaction of pure (+)‐ or (‐)‐enantiomer of bis(menthyl (Z)‐α‐benzamidocinnamate)‐iridium tetrafluoroborate with enantiomerically pure diphosphines has been studied. Invariably one hand of the diphosphine reacts rapidly with a given enantiomer of the iridium complex to give a stable diphosphine iridium enamide complex in which the original configuration of the coordinated olefin is maintained. The other combination of enantiomers reacts much more slowly, in keeping with the kinetic resolution work, and produces an enamide complex which is unstable in solution, isomerising to a second diastereomer. Since the absolute configuration of the iridium bis‐enamide complex has been established by X‐ray crystallography, this experiment affords a method of determining the configuration of rhodium enamide complexes in asymmetric hydrogenation (assuming structural homology between Rh and Ir). In all cases the disfavoured enamide complex was the one involved in the catalytic pathway.
Chiral aspects of drug action at ion channels: A commentary on the stereoselectivity of drug actions at voltage‐gated ion channels with particular reference to verapamil actions at the Ca2+ channel
Authors: Kwon Yong‐Wha , Triggle David J. 
Published: January 2005

AbstractIon channels may be considered as pharmacological receptors possessing specific drug binding sites with defined structure‐activity relationships. Accordingly drug binding to ion channels is stereoselective. Interpretation of this stereoselectivity may be complex because of the existence of differences in affinity and access to different channel states. Such state‐dependent interactions may give rise to quantitative and qualitative differences in stereoselectivity. The implications of such differences are reviewed for drug action at Na+, K+ and Ca2+ channels. Detailed attention is paid to the actions of verapamil enantiomers in the cardiovascular system where activities differ in vascular and cardiac tissues because of state‐dependent interactions and stereoselective first‐oass metabolism.
The kinetics of diastereomeric amino acids with o‐phthaldialdehyde
Authors: Meyer Marc W. , Meyer Veronika R. , Ramseyer Stephan 
Published: January 2005

AbstractThe kinetics of the reaction of the amino acid epimers L‐isoleucine, D‐alloisoleucine, L‐threonine, and D‐allo‐threonine with o‐phthaldialdehyde and mercaptoethanol were determined at 25°C. L‐Isoleucine reacts faster than its D‐epimer whereas L‐threonine reacts slightly slower than its D‐epimer. In the case of isoleucine, the consequence can be an allo/iso ratio which in the worst case is 25% too low if these amino acids are quantified by liquid chromatography and o‐phthaldialdehyde fluorescence detection. The effect on dating of fossils by amino acid racemization is discussed.
Chiral resolution of α,α′‐bis[3‐(N,N‐diethylcarbamoyl)piperidino]‐p‐xylene, a novel antiplatelet compound
Authors: Gollamudi Ramachander , Feng Zixia 
Published: January 2005

Abstractα,α′‐Bis[3‐(N,N‐diethylcarbamoyl)piperidino]‐p‐xylene dihydrobromide, a novel antiplatelet agent, was resolved into three isomers A, B, and C, on a chiral α1‐acid glycoprotein analytical column using a mobile phase of 0.025 M phosphate buffer containing 0.025 M tetrabutylammonium hydrogen sulfate, at a pH of 6.5. The effect of molarity, temperature, pH, flow rate, and organic modifiers on the enantioselectivity was examined. Based on circular dichroic spectra at 220 nm, A and C appear to be the (−)‐ and (+)‐enantiomers, respectively, and B the meso diastereomer. Attempts at resolution using Pirkle type columns gave unsatisfactory results. It appears that both hydrophobic and polar interactions between the compound and the stationary phase are important determinants of resolution.
Some mechanistic aspects on chiral discrimination of organic acids by immobilized bovine serum albumin (BSA)
Authors: Allenmark Stig , Andersson Shalini 
Published: January 2005

AbstractAlthough chiral anionic compounds, notably a large number of organic acids, have been found to be readily separated into enantiomers on BSA‐based columns, the structural requirements for an efficient enantiomer discrimination by the protein is still not very well known. Since it is often observed that very hydrophobic acids, like many of the antiinflammatory “profens,” can be resolved with large separation factors for the enantiomers, a systematic study of a series of racemic α‐substituted alkanoic acids was made. The series of analytes was prepared from α‐amino acids, RCH(NH2)CO2H (where R = C1‐C6), by reaction with N‐(chloroformyl)‐carbazole. A rapid increase in the capacity ratios of both enantiomers was found with increasing length of R. The effect, however, was larger for the last eluted enantiomer, leading to a substantial increase in the separation factor; this being 7.3 for R = C6 in 20 mM phosphate buffer (pH 8.0) with 30% of acetonitrile. Further, the separation factor also increased with decreasing organic modifier content. Thus when the R = C6‐analyte was run at a mobile phase concentration of 20% acetonitrile and a flow rate of 1.5 ml/min, the time difference between the two eluted enantiomers exceeded 20 hr.A reasonable interpretation of our results seems to be that enantioselectivity is promoted by increased hydrophobic interaction. Since the anionic charge of the analyte is also taking part in the retention mechanism, a tight binding of the analyte will result from simultaneous electrostatic and hydrophobic interaction. When the latter is increased, less conformational freedom will be left for the analyte and the steric configuration at the α‐carbon atom will become more and more important. Steric hindrance by the α‐substituent in the first eluted enantiomer will counteract the tight binding caused by the combined binding interactions and lead to a smaller increase in the capacity ratio.
Enantioselective chromatography of the antimalarial agents chloroquine, mefloquine, and enpiroline on a α1 ‐acid glycoprotein chiral stationary phase: Evidence for a multiple‐site chiral recognition mechanism
Authors: Aubry Anne‐FrançCoise , Gimenez FrançCois , Farinotti Robert , Wainer Irving W. 
Published: January 2005

AbstractThe effect of mobile phase pH and dimethyloctylamine (DMOA) on the retention (k') and stereoselectivity (α) of antimalarial agents mefloquine, enpiroline, and chloroquine on the α1‐acid glycoprotein chiral stationary phase (AGP‐CSP) was investigated. An increase of k' with increasing pH was observed while the effect on α was a function of the solute. The magnitude and direction of changes induced by DMOA depended on pH and the structure of the solute.The results of this study are consistent with a change of the conformation of the AGP between pH 5 and 7. At pH 7, the effect of DMOA on mefloquine was relatively well described by a competitive displacement from one enantioselective site. The effect on chloroquine and enpiroline suggests a multiple‐site mechanism in which both competitive and allosteric interactions are involved.
4',6‐Dichloroflavan (BW683C): Enantiomeric separation by hplc/dad and antirhinovirus activity
Authors: Quaglia M.G. , Desideri N. , Bossù E. , Sestili I. , Conti C. 
Published: January 2005

AbstractRacemic 4',6‐dichloroflavan (BW683C), a highly effective inhibitor of rhinovirus serotype 1B in vitro, was resolved by high‐performance liquid chromatography on a chiral stationary phase. The enantiomers were separately collected and circular dichroism curves were obtained, in order to determine the absolute configuration of the two enantiomers. The activity of the isomers was studied on human rhinovirus serotype 1B multiplication in HeLa cell cultures, by means of the plaque reduction assay. Both enantiomers were potent inhibitors of virus replication; by comparing the IC50 values, the S form was 3.5 times more effective than the R form.
The effect of the enantiomers of ibuprofen and flurbiprofen on the β‐oxidation of palmitate in the rat
Authors: Zhao Bin , Geisslinger Gerd , Hall Iris , Day Richard O. , Williams Kenneth M. 
Published: January 2005

AbstractThe effects of the enantiomers of ibuprofen (0.25 and 0.50 mmol/kg b.w.) and flurbiprofen (0.01, 0.03, and 0.06 mmol/kg b.w.) on the β‐oxidation of palmitate were investigated in the rat. The mean cumulative exhalation of 14CO2 after ip administration of [U‐14C]palmitic acid was significantly reduced over 6 h by ibuprofen at the higher dose but not at the lower dose for either enantiomer. There was no difference between the enantiomers, the reduction over 6 h being 31.3 and 33.0% for (R)‐ and (S)‐ibuprofen, respectively. There was also a significant inhibition of β‐oxidation by flurbiprofen at all 3 doses. Again, there was no stereoselectivity evident in this inhibition. Flurbiprofen was much more potent than ibuprofen in eliciting this effect, the 0.01mmol/kg dose giving a similar reduction in β‐oxidation as observed for the 0.50 mmol/kg dose of ibuprofen. The data support the hypothesis that inhibition of the in vivo β‐oxidation of palmitate by ibuprofen and flurbiprofen is primarily via a nonstereoselective noncoenzyme A‐dependent mechanism. © 1992 Wiley‐Liss, Inc.
Enantio‐ and regioselectivity in the epoxide‐hydrolase‐catalyzed ring opening of aliphatic oxiranes: Part II: Dialkyl‐ and trialkylsubstituted oxiranes
Authors: Wistuba D. , Träger O. , Schurig V. 
Published: January 2005

AbstractThe extent of substrate enantioselectivity and regioselectivity of a series of aliphatic 2,3‐dialkyl‐ and trialkylsubstituted oxiranes in their in vitro epoxide‐hydrolase‐catalyzed hydrolysis depends on the size of the alkyl residues and on the substitution pattern of the oxirane ring. The enzyme‐catalyzed hydrolysis of cis‐oxiranes, containing at least one methyl substituent, shows complete or nearly complete substrate enantioselectivity and regioselectivity with nucleophilic attack by water occurring with inversion of configuration at the methylsubstituted ring carbon atom of (S)‐configuration. In the hydrolysis of the isomeric trans‐oxiranes, both enantiomers are metabolized with a higher rate for the (2S;3S)‐enantiomer. The conversion of trimethyloxirane occurs with high substrate enantioselectivity in favor of the (S)‐enantiomer and with complete regioselectivity at the monomethylsubstituted ring carbon atom. The differentiation of the enantiotopic ring carbon atoms (product enantioselectivity) in the smallest aliphatic meso‐oxirane, cis‐2,3‐dimethyloxirane, leads to (2R;3R)‐butane‐2,3‐diol with ee = 86%. cis‐2‐Ethyl‐3‐propyloxirane, possessing alkyl residues larger than methyl, represents an extremely poor substrate in the epoxide‐hydrolase‐catalyzed hydrolysis process. © 1992 Wiley‐Liss, Inc.
Short and simple synthesis of (R)‐ and (S)‐4‐hydroxypentylaminoacetamide: both enantiomers of the (ω‐1)‐hydroxylated metabolite of milacemide
Authors: Gorissen Hugo J. , Van Hoeck Jean‐Pierre , Mockel Anne M. , Journée Guido H. , Delatour Claude , Libert Valéry R. 
Published: January 2005

AbstractBoth (R)‐ and (S)‐4‐hydroxypentylaminoacetamide have been synthesized by reductive amination of glycinamide on the γ‐valerolactols corresponding to (R)‐ and (S)‐γ‐valerolactone, respectively. These enantiomeric lactones were readily obtained in high enantiomeric excess (ee) by enzymic porcine pancreatic lipase (PPL) kinetic resolution of rac‐methyl γ‐hydroxyvalerate. © 1992 Wiley‐Liss, Inc.
Preparation of α‐substituted α‐amino acids of high enantiomeric purity
Authors: Pirkle William H. , Heire Richard , Hyun Myung Ho 
Published: January 2005

AbstractRacemic 5,5‐dialkyl hydantoins derived from ketones are resolved by preparative liquid chromatography as the diastereomeric 1‐carboxamide derivatives afforded by the reaction with optically pure configurationally known α‐phenylethyl isocyanate. Hydrolysis of the resolved diastereomers affords α‐substituted α‐amino acids of high enantiomeric purity. The synthetic route is short, overall yields are high, and the absolute configuration of the amino acid enantiomers may be deduced from the chromatographic and NMR properties of the diastereomers. © 1992 Wiley‐Liss, Inc.
The influence of solute structure, temperature, and eluent composition on the chiral separation of 21 aminotetralins on a cellulose tris‐3,5‐dimethylcarbamate stationary phase in high‐performance liquid chromatography
Authors: Witte Dirk T. , Franke Jan‐Piet , Bruggeman Frank J. , Dijkstra Durk , De Zeeuw Rokus A. 
Published: January 2005

AbstractIn the present study 21 different chiral aminotetralins were used to investigate the mechanism behind their enantiomeric resolution (Rs) on a commercially available high‐performance liquid chromatography (HPLC) cellulose tris‐3,5‐dimethylcarbamate stationary phase. The differences in the chemical structures of the aminotetralins used were never directly located on the chiral carbon. Their chromatographic behavior was studied for two eluent compositions at six different temperatures. Hydrogen bonding and ππ interactions are two possible solute–chiral stationary phase (CSP) interactions. Differences between the enantiomers in their spatial arrangement of positions involved in solute–CSP interactions were the major forces behind enantiomeric separation.Lowering the temperature increased the Rs for the aminotetralins having π‐electrons not directly bonded to that part of the molecule where the hydrogen bonding with the CSP is located. Primary amines and secondary amines, with a sufficiently short N‐alkyl substituent, showed a decrease of Rs with lower temperatures, all other aminotetralins yielding an increase of Rs with lower temperatures. © 1992 Wiley‐Liss, Inc.
Cytochrome p‐455 nm complex formation in the metabolism of phenylalkylamines. XII. Enantioselectivity and temperature dependence in microsomes and reconstituted cytochrome p‐450 systems from rat liver
Authors: Jönsson Karl‐Henrik , Lindeke Björn 
Published: January 2005

AbstractFormation of metabolic intermediate (MI) complexes was studied with the enantiomers of amphetamine, 1‐phenyl‐2‐pentanamine, N‐hydroxyamphetamine, and 2‐nitroso‐1‐phenylpropane (the C‐nitroso analogue of amphetamine). Three different enzyme systems were used; liver microsomes from phenobarbital pretreated rats and two reconstituted systems containing the P450 2B1 and P450 2C11 forms of cytochrome P‐450. Enantioselective complex formation in microsomes was shown for the amines and the nitroso compound, but not for the hydroxylamine. The highly purified P450 2B1 system formed the MI complex with all substrates tested, and the enantioselectivity observed with the microsomal system was reproduced. In the P450 2C11 system the nitroso compounds were completely inactive, whereas the enantiomers of N‐hydroxyamphetamine still produced the complex at a high rate. Changes in temperature were shown to affect (R)‐2‐nitroso‐1‐phenylpropane more than its enantiomer. Both enantiomers showed biphasic Arrhenius plots for MI complex formation in microsomes (breaks around 22°C), but the activation energies of the (R)‐isomer were about five times higher than those of the (S)‐isomer. A theory is presented which suggests different modes of interaction with the active site of P‐450 to account for the different behaviour of the various substrates. © 1992 Wiley‐Liss, Inc.