bluuebunny/crossref_metadata_2025 huggingface dataset:
An approach to understand the complexation of supramolecular dye Congo red with immunoglobulin L chain λ
Authors: Król Marcin , Roterman Irena , Piekarska Barbara , Konieczny Leszek , Rybarska Janina , Stopa Barbara , Spólnik Paweł , Szneler Edward
Published: January 2005

Congo red, a dye of high self‐assembling tendency, has been found to form complexes with proteins by adhesion of the ribbon‐like supramolecular ligand to polypeptide chains of β‐conformation. Complexation is allowed by local or global protein instability, facilitating penetration of the dye to the locus of its binding. At elevated temperatures, L chain λ of myeloma origin was found to form two distinct complexes with Congo red, easily differentiated in electrophoresis as slow‐ and fast‐migrating fractions, bearing four‐ and eight‐dye‐molecule ligands, respectively, in the V domain of each individual chain. The slow‐migrating complex is formed after displacement of the N‐terminal polypeptide chain fragment (about 20 residues) from its packing locus, thereby exposing the entrance to the binding cavity. In this work the formation and stability of this complex was studied by molecular dynamics (MD) simulations. The effect of three‐ and five‐molecule ligands introduced to the site binding the dye was also analyzed in an attempt to understand the formation of fast‐migrating complexes. The wedging of the ligand containing five dye molecules, hence longer than established experimentally as the maximum for the slow‐migrating complex, was found to generate significant structural changes. These changes were assumed to represent the crossing of the threshold on the way to forming a fast‐migrating complex more capacious for dyes. They led to almost general destabilization of the V domain, making it susceptible to extra dye complexation. Theoretical studies were designed in close reference to experimental findings concerning the number of dye molecules in the ligand inserted to the site binding the dye, the location of the site in the domain, and the conditions of formation of the complexes. The results of the two kinds of studies appeared coherent. © 2005 Wiley Periodicals, Inc. Biopolymers, 2005
Total chemical synthesis and oxidative folding of δ‐conotoxin PVIA containing an N‐terminal propeptide
Authors: Buczek Pawel , Buczek Olga , Bulaj Grzegorz
Published: January 2005

Small disulfide‐rich peptides are translated as larger precursors typically containing an N‐terminal prepro sequence. In this study, we investigated the role of a propeptide in the oxidative folding of an extremely hydrophobic δ‐conotoxin, PVIA. δ‐Conotoxin PVIA (δ‐PVIA) is a 29‐amino acid neurotoxin stabilized by three disulfide bridges. Previous folding studies on δ‐conotoxins revealed that their poor folding properties resulted from their hydrophobicity. However, low folding yields of δ‐PVIA could be improved by the presence of a nonionic detergent, which acted as a chemical chaperone. δ‐PVIA provided an attractive model to investigate whether the hydrophilic propeptide region could function as an intramolecular chaperone. A 58‐amino acid precursor for δ‐PVIA (pro‐PVIA), containing the N‐terminal propeptide covalently attached to the mature conotoxin, was synthesized using native chemical ligation. Oxidative folding of pro‐PVIA resulted in a very low accumulation of the correctly folded form, comparable to that for the mature conotoxin δ‐PVIA. Our results are in accord with the relevant data previously observed for α‐ and ω‐conotoxins, indicating that conotoxin prepro sequences are so‐called class II propeptides, which are not directly involved in the oxidative folding. We hypothesize that these propeptide regions may be important for interactions with protein folding catalysts and sorting receptors during the secretory process. © 2005 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2005
Signal‐amplifying genetic circuit enables in vivo observation of weak promoter activation in the Rhl quorum sensing system
Authors: Karig David , Weiss Ron
Published: January 2005

Small changes in transcriptional activity often significantly affect phenotype but are not detectable in vivo by conventional means. To address this problem, we present a technique for detecting weak transcriptional responses using signal‐amplifying genetic circuits. We apply this technique to reveal previously undetectable log phase responses of several Rhl quorum sensing controlled (qsc) promoters from Pseudomonas aeruginosa. Genetic circuits with Rhl promoters and transcriptional amplification components were built and tested in Escherichia coli. This enabled us to isolate the behavior of the promoters under study from Las and quinolone interactions. To amplify qsc promoter responses to acyl‐homoserine lactones (AHL), the highly efficient λ repressor gene was placed downstream of several Rhl promoters and coupled to a fluorescent reporter under the control of the λ P(R) promoter. With amplification, up to ∼100‐fold differences in fluorescence levels between AHL induced and noninduced cultures were observed for promoters whose responses were otherwise not detectable. In addition, the combination of using signal amplification and performing experiments in E. coli simplified the analysis of AHL signal crosstalk. For example, we discovered that while a C4HSL/RhlR complex activates both qscrhlA and qscphzA1, a 3OC12HSL/RhlR complex activates qscphzA1 but not qscrhlA in our system. This crosstalk information is particularly important since one of the potential uses of amplification constructs is for the detection of specific quorum sensing signals in environmental and clinical isolates. Furthermore, the process of decomposing networks into basic parts, isolating these components in a well‐defined background, and using amplification to characterize both crosstalk and cognate signal responses embodies an important approach to understanding complex genetic networks. © 2004 Wiley Periodicals, Inc.
Cover Picture: Forced Intercalation Probes (FIT Probes): Thiazole Orange as a Fluorescent Base in Peptide Nucleic Acids for Homogeneous Single‐Nucleotide‐Polymorphism Detection (ChemBioChem 1/2005)
Authors: Köhler Olaf , Jarikote Dilip Venkatrao , Seitz Oliver
Published: January 2005

The cover picture shows new PNA probes–FIT Probes–and their use in homogenous DNA detection and was designed by Elke Socher. In FIT Probes, the thiazole orange dye is forced to intercalate at a specific position of a probe–target complex. In their paper on p. 69 ff, O. Seitz et al. describe how the binding of FIT probes with DNA results in fluorescence enhancements due to the coplanarization of the two heterocyclic ring systems. The remarkable attenuation of fluorescence that is observed when forcing thiazole orange to intercalate next to a mismatched base pair allows a DNA target to be distinguished from its single‐base mutant under nonstringent hybridization conditions, a property that should be of advantage for real‐time quantitative PCR and nucleic acid detection within living cells.
Foundations of chemical microscopy. 3. derivatives of some chiral phenylalkylamines and phenylalkylamino acids with 5‐nitrobarbituric acid
Authors: Brittain Harry G. , Rehman Michael
Published: January 2005

At one time, 5‐nitrobarbituric acid (also known as dilituric acid) was extensively used as a chemical reagent for the qualitative identification of a variety of basic substances by light microscopy. This methodology was based on evaluation of observed crystal morphologies, because skilled observers could associate a unique crystal habit with the products formed with analytes when those were crystallized using standardized methods. As part of a study to understand the scientific foundations that permitted chemical microscopy to function as a useful analytical technique during its heyday, the products formed by dilituric acid with resolved and racemic phenylalkylamines and phenylalkylamino acids were characterized using a variety of physical analytical techniques. It was found that the different crystal morphologies associated with each of the crystalline adducts were derived from the ability of the systems to form differing structural types and/or hydrate crystal forms upon crystallization. Chirality 17:89–98, 2005. © 2005 Wiley‐Liss, Inc.
Determination of terbutaline enantiomers in biological samples using liquid chromatography with coupled columns
Authors: Walhagen Agneta , Edholm Lars‐Erick , Kened Brit‐Marie , Xiao Liu Chang
Published: January 2005

The purpose of this work was to develop and validate a method for the separation and determination of the enantiomers of terbutaline in plasma and intestinal juice. Terbutaline was extracted from plasma and intestinal juice by liquid‐solid extraction on small C18cartridges. The extract was then analyzed by coupled column liquid chromatography with amperometric detecton. For ciral separation a β‐cyclodextrin phase was used.

The within‐day variation (Cv) on spiked plasma samples was in the rane 0.8‐6.4% at 3.8‐33.8 nmol/liter for the (−)‐enantiomer, and 2.6‐23.0% at 1.3‐11.3 nmol/liter for the (+)‐enantiomer. The between‐day variation on spiked plasma samples was 5.5% at 10.7 nmol/liter and 13.6% at 4.3 nmol/liter for the (−)‐ and (+)‐enantiomers, respectively. The within‐day variation for inestinal juice was i the range 0.7‐1.5% at 5.6‐30.0 μmol/liter for the (+)‐enantiomer.
Liquid chromatographic separation of anomeric forms of saccharides with cyclodextrin bonded phases
Authors: Armstrong Daniel W. , Jin Heng L.
Published: January 2005

A brief review of sugar stereochemistry is given. The separation of 84 different pairs of anomers was accomplished on both α‐ and β‐cyclodextrin columns. Five different mobile phases were evaluated. The separation of anomers temperature, flow rate, and so on. The separation of anomers that mutarotate is somewhat more difficult than those that do not. Prior knowledge as to the rate of mutaroation is useful so that the chromatographic conditions can be arranged to minimize any deleterious effects on the separation.
Preparation of chiral statonary phase from an α‐amino phosphonate
Authors: Pirkle William H. , Burke John A.
Published: January 2005

A chiral statonary phase (CSP) derived from an N‐(3,5‐dinitrobenzoyl)‐α‐aminobenzylphosphonate has been prepared and evaluated for its utility in the direct separation of enantiomers. This CSP, 2, is structurally related to earlier N‐(3,5‐dinitrobenzoyl)‐α‐acids acid‐derived phases (e.g., CSP 1), but the mode of attachment to the support is different. In scope; CSP 2 is qualitaively similar to CSP 1. However, it differs quantitatively from CSP 1, showing either greater or lesser selectivity for different pairs of enantiomers.
Resolution of some β‐hydroxyphenethylamines as N‐(3,5‐dinitrobenzoyl) amides on chiral stationary phases derived from cinchona alkaloids
Authors: Salvadori Piero , Rosini Carlo , Pini Dario , Bertucci Carlo , Uccello‐Barretta Gloria
Published: January 2005

Three chiral stationary phases, obtained by derivatizing γ‐mercaptopropylsilanized silica gel with quinine, quinidine, and cinchonidine, have been employed in the resolution of N‐acyl derivatives of β‐hydroxyphenethylamines. The use of circular dichroism for detection and NMR analysis of analyte–selector mixtures provides an experimental basis for preliminary assignment of a recognition mechanism.
Pharmacokinetics of the enantiomers of terbutaline after repeated oral dosing with racemic terbutaline
Authors: Borgström Lars , Chang‐Xiao Liu , Walhagen Agneta
Published: January 2005

Terbutaline is a β2‐agonist and administered as the racemic mixture. The pharmacokinetics of the separate enantiomers differ with respect to degree of absorption and clearance. In the present study, repeated doses of racemic terbutaline were given to six healthy volunteers. Plasma was analyzed for the concentrations of the two enantiomers. The observed plasma concentrations at steady state differed from those predicted from the values observed after single dose administration of the separate enantiomers. The difference between the observed and predicted values can be tentatively explained by a combined influence of (−)‐terbutaline on the absorption of (+)‐terbutaline and the influence of (+)‐terbutaline on the elimination of (−)‐terbutaline. The results have implications for the interpretation of effect/concentration studies with terbutaline, but do not affect the doses used in clinical practice.
Stereochemical influences upon the opioid ligand activities of 4‐alkyl‐4‐arylpiperidine derivatives
Authors: Casy A. F. , Dewar G. H. , Al Deeb Omar A.A.
Published: January 2005

The synthesis and stereochemistry (configuration and preferred solute conformation) of some 4‐alkyl (methyl, n‐propyl, isobutyl)‐4‐(3‐hydrxyphenyl)‐1‐methylpiperidines and corresponding 3‐methyl diastereoisomeric pairs are reported, together with their in vivo and in vitro activities as opioid ligands. All potent agonists exhibit a preference for axial 4‐aryl chair conformations when protonated, and stereochemical analogies with rigid opioids of the benzomorphan class are discussed. Antagonist properties are found in compounds with preference for equatorial 4‐aryl chairs, notably the cis 3,4‐dimethyl derivative.
Optical resolution of β‐lactams by chiral HPLC on tris(phenylcarbamate)s of cellulose and amylose
Authors: Okamoto Yoshio , Senoh Toshiaki , Nakane Harumi , Hatada Koichi
Published: January 2005

Separation and optical resolution of 6 diastereomers and 25 racemates of β‐lactams were examined by HPLC on chiral stationary phases composed of six cellulose and one amylose tris(phenylcarbamate) derivatives. Most β‐lactams were optically resolved at least by one of the derivatives. The absolute configuration of β‐lactams was estimated by CD spectroscopy.
Metabolism of halazepam by rat liver microsomes: Stereoselective formation and n‐dealkylation of 3‐hydroxyhalazepam
Authors: Lu Xiang‐Lin , Yang Shen K.
Published: January 2005

Metabolism of halazepam [7‐chloro‐1,3‐dihydro‐5‐phenyl‐1‐(2,2,2‐trifluoroethyl)‐2H‐1,4‐benzodi epin‐2‐one, HZ] was studied by incubation with liver microsomes prepared from untreated, phenobarbital (PB)‐treated, and 3‐methylcholanthrene (3MC)‐treated male Sprague–Dawley rats. Metabolites of HZ were separated by normal‐phase HPLC. Relative rates of HZ metabolism by liver microsomes prepared from untreated and treated rats were PB‐treated ≫ untreated > 3MC‐treated at low concentration of microsomal enzymes (0.25 mg protein per ml of incubation mixture) and PB‐treated ≫ 3MC‐treated ≈ untreated at high concentration of microsomal enzymes (2 mg protein per ml of incubation mixture). The relative amounts of major metabolites were found to be 3‐hydroxy‐HZ (3‐OH‐HZ) > N‐desalkylhalazepam (NDZ, also known as N‐desmethyldiazepam and nordiazepam) ≫ oxazepam (OX) for all three rat liver microsomal preparations and the distribution of metabolites was independent of microsomal enzyme concentrations. Enantiomers of 3‐OH‐HZ were resolved by HPLC on a Chiralcel OC column (cellulose trisphenylcarbamate coated on silica gel, particle size 10 μm). 3‐OH‐HZ enantiomeres have racemization half‐lives of ∼ 150 min in pH 4,7.5, and 10 aqueous solutions. 3‐OH‐HZ formed in the metabolism of HZ by liver microsomes prepared from untreated and treated rats were found to have 3R/3S enantiomer rations of 37/63 (untreated), 55/45 (PB‐treated), and 36/64 (3MC‐treated), respectively. N‐dealkylation of 3‐OH‐HZ by liver microsomes from PB‐treated rats was substrate enantioselective; the 3R‐enantiomer was N‐dealkylated faster than 3S‐enantiomer. The results indicated that the stereoselective C3‐hydroxylation of HZ is dependent on the cytochromes P‐450 present in the rat liver microsomal preparations; pro‐R in liver microsomes from PB‐treated rats and pro‐S in liver microsomes from untreated and 3MC‐treated rats, respectively.
Stereoselective interaction of an azole antifungal agent with its target, lanosterol 14α‐demethylase (cytochrome p‐45014dm): A model study with stereoisomers of triadimenol and purified cytochrome p‐45014dm from yeast
Authors: Yoshida Yuzo , Aoyama Yuri
Published: January 2005

The effect of the four triadimenol stereoisomers on the purified yeast lanosterol 14α‐demethylase (cytochrome P‐45014DM), the primary target of azole antifungal agents, was studied. (1S,2R)‐Triadimenol was the most potent demethylase inhibitor and bound quantitatively to the enzyme below 0.05 μM. This isomer also interfered with the chemical reduction of cytochrome P‐45014DM and the binding of CO to the cytochrome. The other isomers showed a lower inhibitory effect on the enzyme, and the order of activity was (1R,2R) > (1R,2S) ≧ (1S,2S). Based on these findings and the reported preferred conformations for the triadimenol stereoisomers (Anderson, N.H. et al., Pestic. Sci. 15:310–316, 1984), it is predicted that orientation of the hydrophobic tert‐butyl and p‐chlorophenyl groups relative to the azole nitrogen is important to fit the antifungal agent in the active site of the demethylase.
Preparation of chiral building blocks and auxiliaries by chromatography on cellulose triacetate (CTA I): Indications for the presence of multiple interaction sites in CTA I
Authors: Francotte Eric , Wolf Romain M.
Published: January 2005

Due to the increasing demand for optically active compounds, the development of methods supplying optically pure isomers is intensively progressing. Among these methods the chromatographic resolution on chiral stationary phases is very promising, although only a limited number of preparative applications have been reported so far. In this work, we demonstrate that especially cellulose triacetate I (CTA I) as a chiral phase presents a number of advantages for this purpose. The broad applicability and the high loading capacity of CTA I are particularly important features for preparative chromatography. Nevertheless, slight structural modifications of the racemates to be resolved can often strongly improve the resolution. This strategy has been applied to numerous practical problems and is illustrated in this work taking as examples some chiral building blocks and auxiliaries. Moreover, a systematic investigation of the influence of a substituent in the para‐position of the phenyl ring for different series of aromatic compounds led to the conclusion that a large number of different interaction sites must be present in the chiral environment of CTA I.
Absolute configuration ofcis‐5,6‐dihydrodiol enantiomers derived from helical conformers of 1,12‐dimethylbenz[a]anthracene
Authors: Yang Shen K. , Mushtaq Mohammad , Fu Peter P.
Published: January 2005

1,12‐Dimethylbenz[α]anthracene (1,12‐DMBA) cis‐5,6‐dihydrodiol was synthesized by oxidation of 1,12‐DMBA with osmium tetroxide in pyridine in low yield (⩽3%) and was purified by sequential use of reversed‐phase and normal‐phase HPLC. Two pairs of 1,12‐DMBA cis‐5,6‐dihydrodiol enantiomers, derived from P (right‐handed helix) and M (left‐handed helix) conformers, were eluted as a single chromatographic peak on both reversed‐phase and normal‐phase HPLC. However, these four enantiomers were resolved by sequential use of two chiral stationary phase (CSP) HPLC columns. CSP (Pirkle type I) columns were packed with either (R)‐N‐(3,5‐dinitrobenzoyl)phenylglycine or (S)‐N‐(3,5‐dinitrobenzoyl)leucine, which is ionically bonded to γ‐aminopropylsilanized silica. Absolute configurations of enantiomers were determined by comparing their circular dichroism spectra with those of conformationally similar cis‐5,6‐dihydrodiol enantiomers of 4‐methylbenz[α]anthracene and 7,12‐dimethylbenz[α]‐anthracene with known absolute stereochemistry.
Eudismic analysis of a series of muscarinic ligands carrying a 1,3‐oxathiolane nucleus
Authors: Gualtieri F. , Romanelli M. N. , Teodori E.
Published: January 2005

Eudismic analysis was performed on a set of 14 muscarinic ligands carrying a 1,3‐oxathiolane nucleus, in order to obtain information about both the existence of receptor subgroups and of agonist and competitive antagonist interaction sites. The results obtained were compared with those from a study of the enantioselectivity of the pairs of enantiomers. The two approaches do not appear to be completely equivalent and would seem to complement each other usefully.
2H‐NMR resolution of the methylenic isotopomers of ethanol applied to the study of stereospecific enzyme‐catalysed exchange
Authors: Rabiller Claude , Mesbahi Mahmoud , Martin Maryvonne L.
Published: January 2005

We have shown that site‐specific natural isotope fractionation of hydrogen studied by NMR (SNIF‐NMR) is an important source of information on the mechanistic and environmental effects which govern the photosynthesis of sugars and their fermentation into ethanol. Three isotope ratios associated with the methyl, methylene, and hydroxyl sites of ethanol are determined in achiral media. In this study we show that complementary information about possible stereospecific mechanisms involving the methylenic hydrogens is also rendered accessible by 2H‐NMR enantiomeric resolution. The synthesis of mandelate esters enables exchange between the pro‐R site of ethanol and water to be investigated. Simultaneous access to the three site‐specific isotope ratios of the ethyl group is obtained at isotopic dilutions close to the natural ones. Mediation of the exchange by the enzymic system alcohol dehydrogenase‐α‐lipoyldehydrogenase and by the yeast Saccharomyces cerevisiae are compared. The progress of the reaction can be followed quantitatively as a function of time and the occurrence of glycolytic metabolism of endogeneous materials by yeast can be substantiated in a one‐pot experiment.
Chemical synthesis, absolute configuration, and stereochemistry of formation of 10‐hydroxywarfarin: A major oxidative metabolite of (+)‐(r)‐warfarin from hepatic microsomal preparations
Authors: Lawrence Ross F. , Rettie Allan E. , Eddy A. Craig , Trager William F.
Published: January 2005

The synthesis of a diastereomerically pure 10‐hydroxywarfarin [4‐hydroxy‐3‐(2‐hydroxy‐3‐oxo‐1‐phenylbutyl)‐2H‐1‐benzopyran‐2‐one] was accomplished in three steps from racemic warfarin. The relative configuration of the synthetic product was established by conversion to a cyclic derivative followed by NMR and X‐ray diffraction analysis. Absolute stereochemistry was determined by enzymatic conversion of either of the pure enantiomers of warfarin to a 10‐hydroxy metabolite of known relative configuration. Metabolic formation of 10‐hydroxywarfarin was studied using hepatic microsomal preparations from female rats and man. The formation of 10‐hydroxywarfarin catalyzed by hepatic microsomes from both dexamethasone‐treated rats and man was highly stereoselective [(R)/(S): 3.4–9.0] for (R)‐warfarin. In contrast, little stereoselectivity was observed in reactions catalyzed by untreated rat liver microsomes. The resultant stereochemistry at the site of oxidation was also found to be highly dependent on substrate stereochemistry. (R)‐Warfarin gave (9R;10S)‐10‐hydroxywarfarin with only a trace of the (9R;10R) isomer irrespective of which enzyme preparation was used for catalysis, while (S)‐warfarin gave (9S;10R)‐10‐hydroxywarfarin with only a trace of the (9S;10S) isomer, again irrespective of which enzyme preparation was used for catalysis.
Reversal of elution order of urea and thiourea derivatives of propranolol enantiomers on ionically versus covalently bound pirkle phases
Authors: Dyas A. M. , Robinson M. L. , Fell A. F.
Published: January 2005

The chromatographic performance of a series of urea and thiourea derivatives of (±)‐propranolol has been evaluated on three different Pirkle stationary phases. Seven different isocyanate reagents were used to generate a range of both aliphatic and aromatic urea derivatives with the isothiocyanates yielding the corresponding thiourea analogues. The Pirkle phases employed consisted of 3,5‐dinitrobenzoylphenylglycine and 3,5‐dinitrobenzoylleucine, both ionically and covalently bound to aminopropyl silica as well as phenethylpropylurea (covalently attached only). The urea derivatives were consistently more strongly retained on covalently bound columns than their thiourea counterparts. This is in contrast to the situation observed for the ionic columns, where the thiourea derivatives were the more strongly retained on the phenylglycine column and the more strongly retained in four of seven instances on the leucine column. The underlying mechanisms giving rise to these differences in retention are as yet unidentified but appear to involve the urea group.
Racemates versus enantiomers in drug development: Dogmatism or pragmatism?
Authors: Testa Bernard , Trager William F.
Published: January 2005

No Absract.
Calmodulin discriminates between the two enantiomers of the receptor‐operated calcium channel blocker sk&f 96365: A study using 1H‐NMR and chiral HPLC
Authors: Reid David G. , MacLachlan Lesley K. , Robinson Simon P. , Camilleri Patrick , Dyke Catherine A. , Thorpe Christopher J.
Published: January 2005

1H nuclear magnetic resonance at 360 MHz shows that SK&F 96365 (1‐{β‐[3‐(p‐methoxyphenyl)‐propyloxy]‐p‐methoxyphenethyl}‐1H‐ imidazole hydrochloride), an antagonist of mammalian receptor‐operated calcium channels, interacts with the calcium‐binding regulatory protein calmodulin (CaM). This may be inferred by a number of chemical shift changes in the spectrum of the calcium‐saturated protein induced by addition of the compound. Moreover, two well‐resolved singlets corresponding to the 2‐proton of the SK&F 96365 imidazolium moiety are observed in the spectrum over a wide range of protein:compound ratios. Separation of rac SK&F 96365 into its two enantiomers by high‐performance liquid chromatography on a cellulose tris (4‐methylbenzoate) column enabled us to show that the doubling of this NMR signal in the presence of CaM is due to a propensity of the protein to distinguish between the two optical isomers of the compound.
Stereoselective inhibition of thromboxane‐induced coronary vasoconstriction by 1,4‐dihydropyridine calcium channel antagonists
Authors: Eltze Manfrid , Sanders Karl H. , Boss Hildegard , Boer Rainer , Ulrich Wolf‐Rüdiger , Flockerzi Dieter
Published: January 2005

The biological activity of the (+)‐S‐ and (−)‐R‐enantiomers of niguldipine, of the (−)‐S‐ and (+)‐R‐enantiomers of felodipine and nitrendipine, and of rac‐nisoldipine and rac‐nimodipine was investigated in vitro and in vivo. Inhibition of coronary vasoconstriction due to the thromboxane A2 (TxA2)‐mimetic U‐46619 in guinea pig Langendorff hearts, displacement of (+)‐[3H]isradipine from calcium channel binding sites of guinea pig skeletal muscle T‐tubule membranes, and blood pressure reduction in spontaneously hypertensive rats were determined. The enantiomers were obtained by stereoselective synthesis. Cross‐contamination was <0.5% for both S‐ and R‐enantiomers of niguldipine and nitrendipine and <1% for those of felodipine. From the doses necessary for a 50% inhibition of coronary vasoconstriction, stereoselectivity ratios for (+)‐(S)‐/(−)‐(R)‐niguldipine, (−)‐(S)‐/(+)‐(R)‐felodipine, and (−)‐(S)‐/(+)‐(R)‐nitrendipine of 28, 13, and 7, respectively, were calculated. The potency ratio racnisoldipine/rac‐nimodipine was 3.5. Ratios obtained from binding experiments and antihypertensive activity were (+)‐(S)‐/(−)‐(R)‐niguldipine = 45 and 35, (−)‐(S)‐/(+)‐(R)‐felodipine = 12 and 13, (−)‐(S)‐/(+)‐(R)‐nitrendipine = 8 and 8, and rac‐nisoldipine/rac‐nimodipine = 8 and 7, respectively. Highly significant correlations were found between the in vitro potency of the substances to prevent U‐46619‐induced coronary vasoconstriction and their affinity for calcium channel binding sites as well as their antihypertensive activity. The mechanism of TxA2‐induced coronary vasoconstriction in guinea pig Langendorff hearts can be readily explained by a transmembrane influx of extracellular Ca2+ susceptible to stereoselective blockade by 1,4‐dihydropyridine calcium channel antagonists.
Interindividual variability in the enantiomeric disposition of ibuprofen following the oral administration of the racemic drug to healthy volunteers
Authors: Avgerinos A. , Hutt A. J.
Published: January 2005

The plasma disposition of the enantiomers of ibuprofen has been investigated following the oral administration of the racemic drug (400 mg) to 24 healthy male volunteers. The plasma elimination of (R)‐ibuprofen was found to be more rapid than that of the S‐enantiomer [plasma half‐life: (R) 2.03 h; (S) 3.05 h; 2P < 0.001], resulting in a progressive enrichment in the plasma content of this isomer, some 64% of the total area under the plasma concentration time curves (AUC) being due to the pharmacologically active enantiomer. The influence of dose on the pharmacokinetic characteristics of the enantiomers of ibuprofen, over the range 200–800 mg, was investigated in three subjects. Examination of dosenormalized AUC values and oral clearance indicate the dose dependence of (R)‐ibuprofen disposition.
Immobilized serum albumin: Rapid HPLC probe of stereoselective protein‐binding interactions
Authors: Domenici Enrico , Bertucci Carlo , Salvadori Piero , Motellier Sylvie , Wainer Irving W.
Published: January 2005

A human serum albumin‐based HPLC chiral stationary phase (HSA‐CSP) has been examined as a tool to investigate binding of chiral drugs to HSA and drug–drug protein‐binding interactions. Rac‐oxazepam hemisuccinate (OXH) was used as a model compound and the chromatographic retention (k′) of its enantiomers was determined after addition of displacers to the mobile phase. Compounds known to bind at the same site as OXH and at different sites were tested for their displacing capacities. Competitive binding interactions between the OXH enantiomers and displacers in the mobile phase were reflected by decreases in the k′s of (R)‐ and (S)‐OXH. The results indicate that retention on the HSA‐CSP accurately reflects binding to native HSA and the technique can determine enantioselective and competitive binding interactions at specific sites on HSA. The HSA‐CSP was also able to recognize separate binding areas for (S)‐ and (R)‐OXH.
An HPLC procedure for the enantiomeric purity of an optically active cytosine analogue using ligand exchange
Authors: Pack Edward J. , Bleiberg Bonnie , Rosenberg Ira E.
Published: January 2005

An acylonucleotide analogue, 1‐[3‐hydroxy‐2‐(phosphonyl‐methoxy)propyl]cytosine (HPMPC), has shown activity against herpes simplex Type I and Type II viruses. An HPLC separation of the R‐ and S‐enantiomers of HPMPC by ligand exchange using a mobile phase containing phenylalanine as the chiral modifier and copper(II) as the metal ion is reported.
Metabolic enantiomeric interactions: The inhibition of human (S)‐warfarin‐7‐hydroxylase by (R)‐warfarin
Authors: Kunze Kent L. , Eddy A. Craig , Gibaldi Milo , Trager William F.
Published: January 2005

Inhibition of the metabolism of (S)‐warfarin, the more pharmacologically active enantiomer of the racemic drug, by (R)‐warfarin was investigated in microsomes obtained from three human livers. In each case the production of both (S)‐6‐ and (S)‐7‐hydroxywarfarin was found to be competitively inhibited by (R)‐warfarin. The Kis for inhibition of (S)‐6‐ and (S)‐7‐hydroxylation by (R)‐warfarin ranged from 7.0 to 8.4 μM and from 6.0 to 6.9 μM, respectively, while the Kms for the 6‐ and 7‐hydroxylation of (S)‐warfarin ranged from 3.6 to 3.8 μM and from 3.3 to 3.9 μM, respectively. In contrast, except for the 4′‐hydroxylation pathway (S)‐warfarin was found to be a weak inhibitor of the metabolism of (R)‐warfarin. Possible implications of these findings include the following: (1) the kinetic parameters defining the interactions of two enantiomers of a racemic drug with the cytochrome P‐450s or other macromolecular systems in the living organism can only be properly defined from experiments with the pure enantiomers, (2) an enantiomer of a racemic drug may contribute significantly to biological effect not by its inherent activity but by altering the pharmacokinetics of the eutomer, and (3) enantiomeric interactions are not easily detected unless directly sought and may be relatively common.
Interaction of propafenone enantiomers with human α1‐acid glycoprotein
Authors: Oravcová Jana , Lindner Wolfgang , Szalay Peter , Boháčik Ľubor , Trnovec Tomáš
Published: January 2005

The interaction of propafenone enantiomers with human α1‐acid glycoprotein was studied using high‐performance liquid chromatography. Each of the two optical antipodes interacted with one class of high‐affinity binding sites characterized by Ka(R) = (6.18 ± 0.93) × 105 M−1, n(R) = 1.34 ± 0.09 for the (R)‐isomer and Ka(S) = (8.93 ± 1.82) × 105 M−1, n(S) = 0.99 ± 0.08 for the (S)‐isomer. Nonspecific binding to secondary low‐affinity high‐capacity binding site(s) was only slightly greater in the case of the (S)‐enantiomer (n′k′(S) = (1.06 ± 0.09) × 104 M−1) compared to the (R)‐enantiomer (n′k′(R) = (6.87 ± 0.72) × 103 M−1). It was concluded that both enantiomers interact with common single class of high‐affinity binding sites on AAG (along with nonspecific binding) exhibiting only slight stereoselectivity for propafenone.
Pharmacologic antagonism of thromboxane A2 receptors by trimetoquinol analogs in vitro and in vivo
Authors: Shin Yangmee , Romstedt Karl J. , Doyle Kathrine , Harrold Marc W. , Gerhardt Mark A. , Miller Duane D. , Patil Popat N. , Feller Dennis R.
Published: January 2005

Although (−)‐(S)‐trimetoquinol [1‐(3,4,5‐trimethoxy‐benzyl)‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline; TMQ] is recognized as a potent bronchodilator, (+)‐(R)‐TMQ is a selective antagonist of human platelet aggregation and serotonin secretion induced by thromboxane A2 (TXA2) agonists. To confirm the pharmacological actions of TMQ analogs, the interaction of the drugs with TXA2 receptors was examined in human platelets and in a mouse sudden death model. The inhibitory potencies of TMQ analogs (pIC50 values) for displacement of [3H]SQ 29,548 binding to platelets showed excellent correlation with the respective pIC50 (−log IC50) values for U46619‐induced aggregation (r = 0.99, P < 0.01) and serotonin secretion (r = 0.99, P < 0.01) in human platelet‐rich plasma and for whole blood aggregation (r = 0.99, P < 0.01). In each system, the rank order of inhibitory potencies was rac‐iodoTMQ ⩾ (+)‐(R)‐TMQ > rac‐TMQ ≫ (−)‐(S)‐TMQ. Antithrombotic effects of TMQ analogs were evaluated in a mouse sudden death model. In vivo antithrombotic potencies of these compounds were consistent with the in vitro potencies as TXA2 receptor antagonists in platelet systems. Administration of rac‐iodoTMQ, (+)‐(R)‐TMQ and rac‐TMQ 15 min before the injection of U46619 (800 μg/kg, iv) protected mice against U46619‐induced sudden death. On the other hand, (−)‐(S)‐TMQ did not protect animals against death. Protection of U46619‐induced cardiopulmonary thrombosis by TMQ analogs was seen at doses of 3–100 mg/kg. Our findings show that these TMQ analogs act as potent and highly stereospecific TXA2 receptor antagonists in vitro and in vivo.
Stereoselectivity of (R)‐ and (S)‐hexahydro‐difenidol binding to neuroblastoma M1, cardiac M2, pancreatic M3, and striatum M4 muscarinic receptors
Authors: Waelbroeck M. , Camus J. , Tastenoy M. , Mutschler E. , Strohmann C. , Tacke R. , Lambrecht G. , Christophe J.
Published: January 2005

(R)‐Hexahydro‐difenidol has a higher affinity for M1 receptors in NB‐OK 1 cells, pancreas M3 and striatum M4 receptors (pKi 7.9 to 8.3) than for cardiac M2 receptors (pKi 7.0). (S)‐Hexahydro‐difenidol, by contrast, is nonselective (pKi 5.8 to 6.1). Our goal in the present study was to evaluate the importance of the hydrophobic phenyl, and cyclohexyl rings of hexahydro‐difenidol for the stereoselectivity and receptor selectivity of hexahydro‐difenidol binding to the four muscarinic receptors. Our results indicated that replacement of the phenyl ring of hexahydro‐difenidol by a cyclohexyl group (→ dicyclidol) and of the cyclohexyl ring by a phenyl moiety (→ difenidol) induced a large (4‐ to 80‐fold) decrease in binding affinity for all muscarinic receptors. Difenidol had a significant preference for M1, M3, and M4 over M2 receptors; dicyclidol, by contrast, had a greater affinity for M1 and M4 than for M2 and M3 receptors. The binding free energy decrease due to replacement of the phenyl and the cyclohexyl groups of (R)‐hexahydro‐difenidol by, respectively, a cyclohexyl and a phenyl moiety was almost additive in the case of M4 (striatum) binding sites. In the case of the cardiac M2, pancreatic M3, or NB‐OK 1 M1 receptors the respective binding free energies were not completely additive. These results suggest that the four (R)‐hexahydro‐difenidol “binding moieties” (phenyl, cyclohexyl, hydroxy, and protonated amino group) cannot simultaneously form optimal interactions with the M1, M2, and M3 muscarinic receptors. When each of the hydrophobic groups is modified, the position of the whole molecule, relative to the four subsites, was changed to allow an optimal overall interaction with the muscarinic receptor.
Synthesis of the [8] gingerol enantiomers
Authors: Martin Michel , Guibet Philippe
Published: January 2005

(+)‐(S)‐5‐Hydroxy‐1‐(4‐hydroxy‐3‐methoxyphenyl)‐3‐dodecanone 1a commonly named (+)‐(S)‐[8] gingerol is a natural product known to have cardiotonic activity.1–5 A total synthesis of both enantiomers is described with details for the first time using a general synthetic scheme which was recently outlined in the literature.6 This synthesis relies both on the separation of the diastereoisomers 4a and 4b by simple column chromatography on silica gel and on an HPLC analysis on a chiral phase to determine the optical purity of the enantiomers 8a and 8b of protected [8] gingerol. The gingerol isomers were thus obtained in good chemical yields in greater than 96% enantiomeric excess.
Optical resolution of two isomeric naphthylalanines by immobilized enyzmes
Authors: Pugnière Martine , Castro Bertrand , Previero Aldo
Published: January 2005

Optical resolution of β‐(1‐naphthyl)alanine and β‐(2‐naphthyl)alanine have been efficiently carried out through enzymatic hydrolysis of their methyl ester and/or N‐acetyl ester derivatives by immobilized enzymes. Difficulties related to the lipophilic character of these amino acids were overcome by using emulsions of n‐butyl acetate–water as reaction medium. The use of an automatic recirculating apparatus allowed reproducible and repetitive use of the immobilized biocatalysts.
N‐(n‐Butylamide) of (S)‐2‐(phenylcarbamoyloxy)propionic acid: A new chiral solvating agent, derived from L‐lactic acid, for the enantiomeric purity determination of derivatized amino acids
Authors: Pini Dario , Uccello‐Barretta Gloria , Rosini Carlo , Salvadori Piero
Published: January 2005

The N‐(n‐butylamide) of (S)‐2‐(phenylcarbamoyloxy)propionic acid, easily prepared starting from the inexpensive L‐ethyl lactate, can be used as convenient chiral solvating agent (CSA) to determine the enantiomeric composition of N‐(3,5‐dinitrobenzoyl)amino acid methyl esters.
New chiral fluoroanthryl derivatives: Resolution of the enantiomers by chromatography on cellulose esters and their evaluation as chiral solvating agents in NMR spectroscopy
Authors: Francotte Eric , Lang Robert W. , Winkler Tammo
Published: January 2005

2,2,2‐Trifluoro‐1‐(9‐anthryl)ethanol (TFAE) has now been widely used as a powerful chiral solvating agent for NMR spectroscopy. In connection with the development of a new general synthesis of halogenoalkylalkanols, starting from the corresponding ketone or aldehyde, we synthesized some halogenoalkyl‐1‐(9‐anthryl)methanol derivatives liable to work as chiral solvating agents. The racemic anthryl derivatives were preparatively resolved into their corresponding enantiomers by chromatography on triacetyl cellulose (CTA I) or on meta‐methylbenzoyl cellulose beads as chiral stationary phases. Their effectiveness as chiral solvating agents was measured as the magnitude of the splitting induced in the 1H‐NMR spectra of 1‐phenylethylamine and of (1‐phenylethyl)methyl ether in comparison with splitting caused by TFAE. While TFAE induced the largest splitting for 1‐phenylethylamine, 2,2,3,3,3‐pentafluoro‐1‐(9‐anthryl)propanol 2 was more effective in the case of (1‐phenylethyl)methyl ether, pointing out that depending on the substrate, other derivatives of the TFAE type can be very useful as chiral solvating agents.
A chiral stationary phase which affords unusually high levels of enantioselectivity
Authors: Pirkle William H. , Deming Kris C. , Burke John A.
Published: January 2005

A chiral stationary phase (CSP) derived from N‐(1‐naphthyl) leucine has been prepared. This CSP is conceptually similar to the CSP derived from N‐(2‐naphthyl)alanine and was expected to separate the enantiomers of the same clientele of analytes as does the latter. The magnitudes of the separation factors observed on the two CSPs may differ markedly for a given analyte, the new CSP often affording much greater enantioselectivity.
A new model to account for the order in which enantiomers of alkylarylcarbinols elute from a pirkle chiral HPLC column: Preparation, absolute stereochemistry, and chromatographic properties of (+)‐1,2‐benzocyclononen‐3‐ol and (+)‐1,2‐benzocyclodecen‐3‐ol
Authors: Hu Yulin , Ziffer Herman
Published: January 2005

Samples enriched in (−)‐ and (+)‐1,2‐benzocyclononen‐3‐ol were prepared by microbially mediated reactions. An enriched sample of (+)‐1,2‐benzocyclodecen‐3‐ol was prepared by fractional crystallization of the diastereoisomeric camphanates, followed by hydrolysis. The absolute stereochemistry of both alcohols was established by chemical transformations. The elution order of their enantiomers from a chiral Pirkle HPLC column [(R)‐N‐(3,5‐dinitrobenzoyl)phenyl glycine ionically bound to γ‐aminopropyl silanized silica] was determined. The information in conjunction with other data was used to formulate a rule to predict the configuration of an enantiomer of an alkylarylcarbinol from its elution order from this column.
Direct chromatographic resolution of racemic cyclohexylaminoglutethimide and its acetylated metabolite using cellulose‐based chiral stationary phase
Authors: Aboul‐Enein Hassan Y. , Bakr Soliman A.
Published: January 2005

Racemic cyclohexylaminoglutethimide (±ChAG) and its acetylated metabolite (±ChAG) were resolved by a direct chromatographic method using a Chiracel OD column without derivatization. Maximum resolutions (R) of 4.89 and 0.74 were obtained for the enantiomers of cyclohexylaminoglutethimide and its acetylated metabolite, respectively.
The effect of ethidium bromide on the liquid crystalline phases of aqueous DNA
Authors: Gottarelli Giovanni , Spada Gian Piero , Mariani Paolo , De Morais Monica Miranda
Published: January 2005

The influence of the intercalation of ethidium bromide (EB) on the characteristics of the DNA cholesteric and hexagonal mesophases is studied by optical microscopy, circular dichroism, and X‐ray diffraction. The distance between DNA rods in the hexagonal phase is not modified by the presence of EB whereas the pitch of the cholesteric mesophase is considerably shortened by the dye. This seems to be related to the stereochemical effect of the intercalation rather than to the presence of a random distribution of the positive charge of the dye.
The circular dichroism of tumor necrosis factor‐α: Measurement into the vacuum UV and analysis for secondary structure
Authors: Riazance‐Lawrence Jeannine H. , Toumadje Arazdordi , Johnson W. Curtis
Published: January 2005

The circular dichroism (CD) spectrum of tumor necrosis factor‐α has been measured into the vacuum UV to 168 nm. Analysis of the CD for secondary structure is in good agreement with X‐ray diffraction results, but the analysis is somewhat unstable. Adding the CD of this protein together with its X‐ray determined secondary structure to the basis set should improve subsequent analyses of CD spectra for other all‐β proteins.
Cooperativity of chirality in homogeneous catalysis: The gold(I)‐catalyzed aldol reaction and the vanadium(IV)‐catalyzed hetero Diels–Alder cycloaddition
Authors: Togni Antonio , Pastor Stephen D.
Published: January 2005

The notion of internal (or intramolecular) cooperativity of chirality is reviewed on the basis of various examples of diastereoisomeric ferrocenylphosphine ligands used in the gold(I)‐catalyzed aldol reaction. It was found that the stereochemical outcome of this reaction strongly depends on the specific combination of the absolute configuration of the different stereogenic centers present in the ligand. Thus, individual chirotopic segments in these ligand molecules can act either in a cooperative or noncooperative manner in determining both diastereo‐and enantioselectivity. Furthermore, several examples of application of the strategy of double stereodifferentiation (external, or intermolecular cooperativity of chirality) in the gold(I)‐catalyzed aldol reaction and the vanadium(IV)‐catalyzed hetero Diels–Alder condensation are presented. Based on our work it is apparent that, whether the diastereoselectivity of these two reactions is controlled by the catalyst or by a chiral substrate, cannot be predicted and very much depends on the nature of every individual reactant. Thus, it was found that in both reactions the chiral aldehyde substrate usually has a strong impact on the diastereoselectivity, leading to interesting patterns of double asymmetric induction. On the other hand, chiral isocyanoacetate and chiral‐activated dienes, respectively, showed little or no effect on the stereochemical outcome of the reactions.
Enantioselective carbonylation reactions of para‐substituted 2‐phenylpropenes
Authors: Consiglio Giambattista , Roncetti Lucia
Published: January 2005

The enantioselective hydroformylation catalyzed by [(R,R)‐Diop]Pt(SnCl3)Cl7 and the enantioselective hydroisopropoxycarbonylation catalyzed by [(R,R)‐Diop]PdCl28 or by [(R,R)‐Diop‐dbp]PdCl29 of some para‐substituted 2‐phenylpropenes (para substituents = NO2, H, CH3O, Cl, CF3) was investigated in order to recognize possible electronic influences on the regioselectivity and on the enantioface selection which take place in such carbonylation reactions. The catalytic systems used gave no carbonylation products when the nitro compound was the substrate. 7 and 8 show similar regioselectivities, the less branched isomer being exclusively formed for all substrates except p‐methoxy‐2‐phenylpropene which gave small amounts of the alternative regioisomer. The enantioselectivity depends on the σp effect of the substituent in both cases; the differences are, however, rather small and the trend is opposite in the two cases. The regioselectivity displayed by 9 is still in favour of the less branched isomer but it is high only in the case of p‐trifluoromethyl‐2‐phenylpropene. Larger differences with respect to the other catalytic systems were also observed for enantioselectivity but the trend for both regioselectivity and enantioselectivity is not linear.
Comments on a novel approach to the role of chirality in the origin of life
Authors: Chela‐Flores Julian
Published: January 2005

We review a recent paper20 in which a specific enhancement factor (i.e., a phase transition into a condensed Bose mode) is proposed to account for the observed amplification of the ground state energies of the L‐ and D‐amino acid enantiomers; the difference between these energies is assumed to be due to the neutral parity‐violating electroweak interaction. This physical effect initially shifts the enantiomer energies by about 3 × 10−19 eV. The proposed phase transition is characterized by a critical temperature Tc, which may be studied theoretically by enlarging the standard electroweak theory to include either the top quark or supersymmetry21. Possible experimental means of finding Tc are discussed.
Chiral separation of N‐aminoalkylsuccinimides on an α1 ‐ acid glycoprotein column: A quantitative structure—enantioselectivity relationship study
Authors: Norinder U. , Hermansson J.
Published: January 2005

Two quantitative structure–enantioselectivity models have been developed for a series of N‐aminoalkylsuccinimides using the statistical method PLS. The models permit the prediction of enantioselectivity on an α1‐acid glycoprotein column. The models are based on a physiocochemical description of the structures.