bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractSamples 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

AbstractRacemic 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractWe 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

AbstractTwo 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.
The absolute configuration of the enantiomers of 6‐chloro‐9‐(4′‐diethylamino‐1′‐methylbutyl)‐amino‐2‐methoxyacridine (quinacrine)
Authors: Craig J. Cymerman , Labelle Bruce , Ohnsorge Ulrich 
Published: January 2005

AbstractAbsolute configurations have been assigned to the enantiomers of the antimalarial drug quinacrine dihydrochloride. Condensation of (−)‐(R)‐4‐amino‐1‐diethylaminopentane (from L‐glutamic acid) with 6,9‐dichloro‐2‐methoxyacridine gave (−)‐(R)‐6‐chloro‐9‐(4′‐diethylamino‐1′‐methylbutyl) amino‐2‐methoxyacridine [(−)‐(R)‐quinacrine] while (+)−(S)‐quinacrine was obtained from the enantiomeric diamine.
Steric aspects of agonism and antagonism at β‐adrenoceptors: Synthesis of and pharmacological experiments with the enantiomers of formoterol and their diastereomers
Authors: Trofast Jan , ÖSterberg Kristina , Källström Britt‐Louise , Waldeck Bertil 
Published: January 2005

AbstractThe enantiomers of formoterol (R;R and S;S) and their diastereomers (R;S and S;R) were synthesized and purified using a new procedure which required the preparation of the (R;R)‐ and (S;S)‐forms of N‐(1‐phenylethyl)‐N‐(1‐(ρ‐methoxyphenyl)‐2‐propyl)‐amine as important intermediates. The enantiomeric purity obtained was greater than 99.3%, usually > 99.7%. The four stereoisomers were examined with respect to their ability to interact in vitro with β‐adrenoceptors in tissues isolated from guinea pig. The effects measured were (1) relaxation of the tracheal smooth muscle (mostly β2), (2) depression of subtetanic contractions of the soleus muscle (β2), and (3) increase in the force of the papillary muscle of the left ventricle of the heart (β1). All enantiomers caused a concentration‐dependent and complete relaxation of the tracheal smooth muscle which was inhibited by propranolol. The order of potency was (R;R) > > (R;S) = (S;R) > (S;S). There was a 1,000‐fold difference in potency between the most and the least potent isomer. The presence of the (S;S)‐isomer did not affect the activity of the (R;R)‐isomer on the tracheal smooth muscle. Also on the skeletal and cardiac muscles (R;R)‐formoterol was more potent than its (R;S)‐isomer. The selectivity for β2‐adrenoceptors appeared to be slightly higher for the (R;R)‐isomer than for the (R;S)‐isomer. The potency of the (S;R)‐ and (S;S)‐isomers on the papillary muscle was too low to be determined accurately. The present study shows that determination of enantiomeric ratios and conclusions regarding structure–effect relationships are critically dependent on a very high degree of stereochemical purity.
Stereoselective inhibition of diphenylhydantoin metabolism by p‐hydroxyphenyl‐phenylhydantoin enantiomers in rats
Authors: Huang Jin‐Ding , Hsieh Ching‐Yi 
Published: January 2005

AbstractDifferent doses of rac‐p‐HPPH (0.4 and 4 mg/h) were given repeatedly to rats infused with [14C]phenytoin. The serum levels of 14C‐labeled and unlabeled p‐HPPH, and [14C]phenytoin were measured by an HPLC method and radiometric analysis. The clearance of phenytoin and p‐HPPH was determined by rate of dosing divided by the steady‐state concentration. The phenytoin clearance was significantly lower in the high dose p‐HPPH injection group than in the low dose group (87 versus 262 ml/h), whereas p‐HPPH clearance showed no difference. The formation clearance of [14C]p‐HPPH was also significantly lower in rats injected with high dose of p‐HPPH (35 versus 169 ml/h). The clearance of other elimination pathways was also lower in rats with high dose of p‐HPPH (53 versus 89 ml/h). The serum protein binding of phenytoin was lower in rats injected with high dose of p‐HPPH. The result indicated that injections of rac‐p‐HPPH mainly inhibited on the formation of p‐HPPH itself. The formation of (R)‐p‐HPPH and (S)‐p‐HPPH in microsomal preparation was measured by a ligand‐exchange chromatographic method. The formation of (S)‐p‐HPPH or (R)‐p‐HPPH was not only inhibited by the enantiomer itself, but also cross‐inhibited by the other enantiomer. To the formation of either (S)‐p‐HPPH or (R)‐p‐HPPH, (S)‐p‐HPPH showed a higher inhibitory activity. The use of rac‐p‐HPPH to inhibit phenytoin metabolism in vivo involved several mechanisms. In addition to binding displacement on the serum proteins, one is the product inhibition by the respective p‐HPPH metabolite, the other is the competitive inhibition by the other p‐HPPH enantiomer.
Enantiomeric analysis of terfenadine in rat plasma by HPLC
Authors: Zamani Kaveh , Conner Dale P. , Weems Henri B. , Yang Shen K. , Cantilena Louis R. 
Published: January 2005

AbstractEnantiomeric pairs of the antihistaminic drug terfenadine and its carboxylic acid derivative were directly separated by HPLC using an ovomucoid protein column. Absolute configurations of terfenadine enantiomers were assigned by comparing their circular dichroism spectra with those of 1‐phenyl‐1‐butanol enantiomers of known absolute stereochemistry. Terfenadine and its major carboxylic acid metabolite extracted from blood plasma following an oral administration of a racemic terfenadine to rats were found to be enriched in the (S)‐ and (R)‐enantiomers, respectively. The results indicated that the (R)‐enantiomer of an orally administered racemic terfenadine was preferentially oxidized in rats to form a carboxylic acid metabolite enriched in the (R)‐enantiomer.
Living enantiosymmetric and enantioasymmetric polymerization of methylthiirane in homogeneous phase
Authors: Dumas PH. , Sigwalt P. 
Published: January 2005

AbstractThe polymerization of racemic methylthiirane in homogeneous phase, initiated by bis(isopropyl‐S‐cysteinato) cadmium is a living process. The resulting polymers are isotactic and optically active at partial conversion. The optical purity of the residual monomer may reach 27% at half conversion. The propagation occurs mainly on one valency of Cd, however oligomers grow slowly on the second valency. The stereoregularity of the polymer chain appears only when the length of the oligomer becomes high enough, making possible a bicoordination of the Cd counterions. The stereoregularity of the polymer is characterized by the molar fraction σ of isotactic diads which varies from 0.5 for atactic chains—formed at the beginning—to about one for isotactic segments formed for longer chains. The stereospecifictity also depends on temperature of propagation and on initiator concentration. The kinetics observed (zero order in monomer and one‐half in Cd) are explained by monomer coordination before insertion and dimeric association of the thiolate end groups. The enantioasymmetric process observed results from an unbalance in the number of the two different types of active sites and possibly from a difference in their reactivities. Enantioasymmetry has been found to decrease significantly when the dielectric constant ε of the medium increases.
Chiroptical properties of lecithin reverse micelles and organogels
Authors: Colombo Luca M. , Nastruzzi Claudio , Luisi Pier Luigi , Thomas Richard M. 
Published: January 2005

AbstractThe ultraviolet absorbance and circular dichroism (CD) spectra of lecithin reverse micelles and gels were investigated in order to establish whether the formation of these noncovalent macromolecular aggregates, which was induced by the addition of water to solutions of lecithin in organic solvents, was accompanied by specific spectroscopic changes. Systems containing the synthetic short‐chain lecithins, 1,2‐hexanoyl‐, 1,2‐diheptanoyl‐, 1,2‐dioctanoyl‐, and 1,2‐dinonaoyl‐sn‐glycero‐3‐phosphatidylcholines were used as models for the long‐chain lecithins, soybean phosphatidylcholine and palmitoyl‐oleoyl‐phosphatidylcholine. All the molecules studied had asymmetric centres, formed reverse micelles under appropriate conditions, and, while both the long‐chain lecithins also formed gels, none of the short‐chain molecules did. As well as having CD spectra that were simpler to interpret, spectroscopic observations on solutions of the short‐chain lecithins could be carried out over a large water content range. The ester chromophore of these compounds was shown to be highly sensitive to variation in both the solvent environment and the temperature, and components of both direct solvent effects and conformational change upon the addition of water were detected in the spectra.The spectra of the longer chain lecithins were complicated by the presence of double bonds although, here again, it was found that significant changes occurred as the water content increased, as monitored by the ester chromophore. However, no specific effect that could be ascribed to gelation alone was detected.The overall picture that emerged was that the ester chromophore of anhydrous micelles gave rise to a specific negative band in the CD spectrum (λmax ≈ 210 nm) whereas a positive CD signal (λmax ≈ 233 nm) was associated with the same chromophore in filled (i.e., hydrated) micelles. The two signals correspond to two different conformational states of the lecithin molecule, the hydrated state being not only more conformationally restricted but also providing a less polar environment for the ester groups, while the addition of water to the system shifts the conformational equilibrium. These observations have been interpreted as showing that only a limited range of lecithin conformation is compatible with the formation of the micellar structure and that it is this constraint, together with those introduced by the overall geometry of the aggregated state, that gives rise to the changes observed in the CD spectrum.
Racemization of the aqua‐{N‐salicylidene‐(S)‐alaninato}copper(II) by reaction with potassium cyanate
Authors: Krätsmár‐Šmogrovič J. , Blahová M. , Kettmann V. 
Published: January 2005

AbstractCopper(II) N‐salicylidene‐(S)‐alaninate trihydrate reacting as the S‐enantiomeric parent compound with KOCN in hot diluted methanol yielded by slow crystallisation from the cooled reaction mixture (in the course of 1 day) the racemic product K[Cu{sal‐(RS)‐ala}(NCO)]. The parameters of the axial type EPR spectrum in X‐band region and the LF band position in the electronic spectrum are typical of an axially distorted square pyramidal coordination of the Cu(II) atom in this complex. The spectral properties of the complex cuprate prepared and its basal crystallographic data are consistent with those of the earlier studied15 K2[Cu2{sal‐(RS)‐ala}2(μ‐NCO)2] synthetized by using [Cu{sal‐(RS)‐ala}(H2O)].H2O as the racemic parent complex in the reaction mixture with KOCN.
Stereoselective aliphatic hydroxylation of 6‐n‐propylchromone‐2‐carboxylic acid by female Dutch rabbits
Authors: Winter Steven M. , Caldwell John 
Published: January 2005

Abstract6‐n‐Alkylchromone‐2‐carboxylic acids are metabolized solely by aliphatic oxidation. In the rabbit, the 6‐n‐propyl congener (PCCA) undergoes ω‐1 hydroxylation exclusively. Following administration of PCCA to female Dutch rabbits (500 μmol/kg), some 77% of the dose was excreted in the urine, 41% as PCCA and 36% as 6‐(2'‐hydroxy‐n‐propyl)chromone‐2‐carboxylic acid. Since this metabolite is chiral, we have examined the stereochemistry of the excreted material. Diastereoisomeric (as camphanate and α‐methoxy‐α‐(trifluoromethyl)phenylacetate esters) and direct chiral HPLC and chiral lanthanide shift NMR have each shown the S:R ratio of the excreted metabolite to be 76:24. When rabbits were dosed with the racemic metabolite, excretion of the compound was not stereoselective. The regio‐ and stereo‐selectivity of the aliphatic hydroxylation of PCCA are thus reflections of the selectivities of the enzyme systems responsible for its formation and suggest PCCA to be an appropriate probe compound for the study of prochiral‐chiral hydroxylations.
Enantiospecificity of kappa receptors: Comparison of racemic compounds and active enantiomers in two novel series of kappa agonist analgesics
Authors: Colle Roberto , Clarke Geoffrey D. , Dondio Giulio , Giardina Giuseppe , Petrone Giuseppe , Sbacchi Massimo , Vecchietti Vittorio 
Published: January 2005

AbstractTwo novel series, Ia,b and IIa,b, of kappa opioid antinociceptive agents have recently been described. 2a,b,3a,b,c The biological activities of 16 racemic compounds and their corresponding (−) enantiomers are now compared in a battery of tests. Enantiomers of unsubstituted piperidines Ia were synthesized starting from S(−) pipecolic acid, whereas the enantiomerically pure substituted piperidines (Ib), tetrahydroisoquinolines (IIa), and thienopiperidines (IIb) were, in general, obtained after diastereomeric crystallization of the corresponding tartrate salts. The absolute stereochemistry of one representative enantiomer from series IIa was determined to be (1S) by X‐ray crystallographic analysis. Antinociceptive activity in the mouse abdominal constriction and tail‐flick tests following subcutaneous administration, and binding affinity for κ and μ receptors, were found to reside predominantly in the (−) enantiomers. Consequently, racemic compounds showed approximately half potency of the corresponding enantiomers. This potency difference was less clear after oral administration presumably due to small differences in bioavailability of the two corresponding enantiomers.For compounds with some affinity also for μ receptors (Ki <1,000 nM), the κ/μ selectivity was maintained within each enantiomeric pair, in contrast to results found for other κ agonists.
Stereoselectivity at α‐adrenoreceptor subtypes: observations with the enantiomers of WB 4101 separated through their amides of N‐Tosyl‐(S)‐proline
Authors: Andrisano Vincenza , Marucci Gabriella , Melchiorre Carlo , Tumiatti Vincenzo 
Published: January 2005

AbstractWe present a chromatographic method for the separation and determination of the optical purity of the enantiomers of WB 4101 [(±)‐1], one of the most potent and selective α1‐adrenoreceptor antagonists. (±)‐1 was converted into the amide of N‐tosyl‐(S)‐proline. The two diastereoisomers were separated on silica gel and analysed by HPLC reversed phase. The analytical method described is both accurate and sensitive and allows the optical purity to be determined at very low concentrations and to obtain WB 4101 enantiomers with a purity of more than 99.95%.
Use of cyclodextrins in capillary zone electrophoresis for the separation of optical isomers: Resolution of racemic tryptophan derivatives
Authors: Nardi Annalisa , Ossicini Luigia , Fanali Salvatore 
Published: January 2005

AbstractIn this study capillary zone electrophoresis has been used for the separation of racemic tryptophan derivatives in their enantiomers. The effect of cyclodextrins with different shape, added to the background electrolyte, on the migration time of 10 compounds, including methyl tryptophan, hydroxy tryptophan, and tryptophan ester derivatives, has been studied. Furthermore, the effect of cyclodextrins with different shape and that of the composition of the background electrolyte on the enantiomer resolution are discussed. Among different cyclodextrins used α‐cyclodextrin and heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin were found to possess the best complexing capacity and thus the resolution power toward analysed compounds.
The disposition of venlafaxine enantiomers in dogs, rats, and humans receiving venlafaxine
Authors: Paul Wang C. , Howell Stanley R. , Scatina Joann , Sisenwine Samuel F. 
Published: January 2005

AbstractA stereospecific high‐performance liquid chromatographic (HPLC) method was developed for the quantitation of the enantiomers of venlafaxine, an antidepressant, in dog, rat, and human plasma. The procedure involves derivatization of venlafaxine with the chiral reagent, (+)‐S‐naproxen chloride, and a postderivatization procedure. The method was linear in the range of 50 to 5,000 ng of each enantiomer per ml of plasma. No interference by endogenous substances or known metabolites of venlafaxine occurred. Studies to characterize the disposition of the enantiomers of venlafaxine were conducted in dog, rat, and human, following oral administration of venlafaxine. The Cmax, area under the curve (AUC) and (S)/(R) concentration ratios of the (R)‐ and (S)‐enantiomers were compared. In rats, the mean plasma ratio of (S)‐venlafaxine to that of (R)‐venlafaxine over 0.5 to 6.0 h varied from 2.97 to 8.50 with a mean value of 5.51 ± 2.45. The Cmax, AUC0—∞, and t1/2 values of the (R)‐ and (S)‐enantiomers in dogs were not significantly different from one another (P>0.1). The mean ratios [(S)/(R)] of enantiomers of venlafaxine in human over a 2 to 6 h interval ranged from 1.33 to 1.35 with an overall ratio of 1.34 ± 0.26 (n = 12). These ratios of the enantiomers [(S)/(R)] were not statistically different from unity (P>0.1) indicating that the disposition of venlafaxine enantiomers in humans is not stereoselective and is more similar to that in dogs than that in rats.