bluuebunny/crossref_metadata_2025 huggingface dataset:
Chiral discrimination and antipicornavirus activity of 6‐oxazolinylisoflavan
Authors: Quaglia M. Giovanna , Desideri Nicoletta , Bossù Elena , Sestili Isabella , Tomao Paola , Conti Cinzia , Orsi Nicola
Published: January 2005

Racemic 6‐oxazolinylisoflavan, a highly effective inhibitor of rhinovirus serotype 1B in vitro, was resolved by high‐performance liquid chromatography on a chiral stationary phase in order to study the activity of the enantiomers against picornaviruses. The absolute configuration of the two isomers was determined by circular dichroism curves. The antipicornavirus activity of each isomer, separately collected, was evaluated in vitro against human rhinovirus serotype 1B, enterovirus 71, echovirus 6, coxsackievirus B4, and poliovirus type 2 by means of the plaque reduction assay. Both enantiomers were inhibitors of picornavirus replication with the degree of their activity depending on virus and isomer tested. © 1993 Wiley‐Liss, Inc.
Racemization of chlorthalidone in the presence of liposomes
Authors: Lamparter Erich , Blaschke Gottfried , Schlüter Jürgen
Published: January 2005

The extent of racemization of (+)‐chlorthalidone as a function of pH is examined. The minimum of the log K/pH curve is pH 3. The reaction mechanism of inversion is postulated to involve a carbenium cation over the entire pH range and a ring opening reaction in the alkaline range. The influence of liposomes on the inversion rate is also studied, retardation of the racemization rate being observed with increasing liposome concentration. A model of drug distribution between liposome phase and aqueous phase based on the Nernst distribution principle is presented and reaction kinetic aspects are considered. © 1993 Wiley‐Liss, Inc.
Chirality of the γ‐lactones formed by Fusarium poae INRA 45
Authors: Latrasse Alain , Guichard Elisabeth , Piffaut Catherine , Fournier Nicole , Dufosse Laurent
Published: January 2005

A filamentous fungus, Fusarium poae INRA 45, was grown in two liquid Czapek‐type media (a Czapek medium, and a yeast extract plus casaminoacids‐enriched Czapek medium). Eight γ‐lactones, i.e., γ‐penta‐, γ‐octa‐, γ‐nona‐, γ‐deca‐, and γ‐dodecalactone, (6Z)‐γ‐ and (6E)‐γ‐dodecenolactones, and a di‐unsaturated γ‐dodecalactone, were tentatively, or conclusively, identified by capillary gas chromatography (GC) and coupled GC‐MS, in the volatile fractions of the cultures. Kinetics of the formation of γ‐decalactone, (6Z)‐γ‐ and (6E)‐γ‐dodecenolactones, (three major lactones), and γ‐dodecalactone (a minor lactone) were quantitatively studied by computerized GC integration. Variations of the (R/S) ratios of the lactone enantiomers were quantitatively studied by computerized multidimensional gas chromatography (MDGC) integration. The levels of the lactones were superior in the enriched Czapek‐type medium to those of the Czapek medium, but the compositions of these media did not influence significantly the (R/S) ratios of these lactones. Formation of the enantiomers is discussed in terms of metabolism of potential precursors. © 1993 Wiley‐Liss, Inc.
Chirality of amino acids of microorganisms used in food biotechnology
Authors: Brückner Hans , Becker Dieter , Lüpke Michael
Published: January 2005

Bacteria of the genera Acetobacter, Bifidobacterium, Brevibacterium, Lactobacillus, Micrococcus, Propionibacterium, and Streptococcus, which are used as so‐called starter cultures for the large‐scale production of fermented foods and beverages in food biotechnology, have been investigated for the chirality of their amino acids (AA) by gas chromatography (GC). Bacteria were grown in complex media, centrifuged, and washed with 0.85% aqueous NaCl. Aliquots were totally hydrolyzed (6 M HCl, 110°C, 18 h), or extracted with 70% aqueous ethanol in order to isolated free AA. The AA were adsorbed on Dowex WX 8 cation‐exchanger, eluted with 4 M ammonia and converted into their N(O)‐trifluoroacetyl(TFA) 2‐propyl esters or TFA methyl esters. The AA derivatives were investigated by capillary GC using the chiral stationary phases Chirasil‐L‐Val, Chirasil‐D‐Val, and Lipodex E. Besides L‐AA, in all bacteria D‐amino acids (D‐AA) were detected; those in the highest relative amounts were D‐Ala and D‐Asp (occurring in all bacteria) and, in several cases, D‐Glu. Lower, but significant amounts of other D‐AA such as D‐Ser, D‐Pro, D‐Val, D‐Thr, D‐Ile, D‐Leu, D‐Met, D‐Phe, D‐Tyr, D‐Orn, and D‐Lys were also detected in certain bacteria. These findings explain the origin of D‐AA found in all fermented foods and drinks produced with the aid of bacterial starter cultures. © 1993 Wiley‐Liss, Inc.
Enantioselective gallopamil protein binding
Authors: Gross Annette S. , Eser Claudia , Mikus Gerd , Eichelbaum Michel
Published: January 2005

The protein binding of the enantiomers of gallopamil has been investigated in solutions of human serum albumin, α1‐acid glycoprotein and serum. Over the range of concentrations attained after oral gallopamil administration, the binding of both enantiomers to albumin, α1‐acid glycoprotein, and serum proteins was independent of gallopamil concentration. The binding to both human serum albumin (40 g/liter) [range of fraction bound (fb) R: 0.624 to 0.699; S: 0.502 to 0.605] and α1‐acid glycoprotein (0.5 g/liter) (range of fb R: 0.530 to 0.718; S: 0.502 to 0.620) was stereoselective, favoring the (R)‐enantiomer (predialysis gallopamil concentrations 2.5 to 10,000 ng/ml). When the enantiomers (predialysis gallopamil concentration 10 ng/ml) were studied separately in drug‐free serum samples from six healthy volunteers the fraction of (S)‐gallopamil bound (fb: 0.943 ± 0.016) was lower (P < 0.05) than that of (R)‐gallopamil (fb: 0.960 ± 0.010). The serum protein binding of both (R)‐ and (S)‐gallopamil was unaffected by their optical antipodes (fb R: 0.963 ± 0.011; S: 0.948 ± 0.015) indicating that at therapeutic concentrations a protein binding enantiomer–enantiomer interaction does not occur. The protein binding of (R)‐ and (S)‐gallopamil ex vivo 2 h after single dose oral administration of 50 mg pseudoracemic gallopamil (fb R: 0.960 ± 0.010: predialysis [R] 6.9 to 35.3 ng/ml; S: 0.943 ± 0.016: predialysis [S] 9.5 to 30.7 ng/ml) was comparable to that observed in vitro in drug‐free serum. Gallopamil metabolites formed during first‐pass following oral administration, therefore, do not influence the protein binding of (R)‐ or (S)‐gallopamil. © 1993 Wiley‐Liss, Inc.
Stereoselectivity of biliary excretion of 2‐arylpropionates in rats
Authors: Menzel Sabine , Beck Winfried S. , Brune Kay , Geisslinger Gerd
Published: January 2005

To examine the stereoselectivity of biliary excretion, the optically pure enantiomers of ketoprofen (KT), ibuprofen (IBU), and flurbiprofen (FLU) were intravenously administered to normal and bile duct‐cannulated rats at 10 mg/kg. The recovery of total KT in bile was significantly higher after administration of (S)‐KT than after (R)‐KT [90.1 ± 3.5% vs 68.8 ± 8.2%, n =3, P < 0.05]. In normal rats the terminal half‐life of (R)‐KT was significantly shorter than that of (S)‐KT after administration of (R)‐KT (2.2 ± 0.6 h vs 14.3 ± 4.9 h, n = 3, P < 0.05). The terminal half‐life of both enantiomers was significantly shorter in rats with continuous bile drainage as compared to normal rats. No significant differences in pharmacokinetic parameters could be found between both enantiomers in bile duct‐cannulated animals. The total amount of IBU in bile was slightly higher after administration of (S)‐IBU than after (R)‐IBU administration. The percentage of (R)‐IBU after (R)‐IBU administration, however, was very low [(R)‐IBU: 1.5 ± 0.9%, (S)‐IBU: 23.4 ± 5.8%]. In normal rats the clearance of (R)‐IBU was significantly higher as compared to (S)‐IBU. Differences in pharmacokinetic parameters between normal and bile duct‐cannulated rats were not statistically significant due to high interindividual variability. The total recovery of FLU, which was excreted in bile to a lower extent than either KT or IBU, also tended to be greater after S‐enantiomer administration. Only small amounts of (S)‐FLU could be recovered in bile after (R)‐FLU administration. The pharmacokinetic parameters did not differ significantly between (R)‐ and (S)‐FLU or between normal and bile duct‐cannulated rats due to its low inversion rate and low excretion via bile. © 1993 Wiley‐Liss, Inc.
Selective antibodies to propranolol enantiomers produced from a new conjugate
Authors: Sahui‐Gnassi Albertine , Pham‐Huy Chuong , Galons Herve , Warnet Jean‐Michel , Claude Jean‐Roger , Duc Huynh‐Thien
Published: January 2005

A selective antibody to (S)‐propranolol enantiomer was produced in rabbits by immunization with a new conjugate of N‐aminopropylpropranolol‐albumin. A hapten was first prepared by condensing (S)‐propranolol or the racemate with 3‐bromopropylphthalimide followed by hydrazinolysis, and the resulting compound conjugated to serum albumin by means of a glutaraldehyde‐ or carbodiimide‐mediated reaction. Rabbits were immunized, and titres and specificity of antibodies were determined by ELISA. The antibodies obtained were tested with (S)‐, (R)‐, (R, S)‐propranolol, and other structural analogs. Selective (S)‐antibodies recognized (S)‐propranolol 20 times more avidly than (R)‐isomer while an antiserum against (R, S)‐propranolol recognized both (S)‐ and (R)‐isomers to about the same degree. ©1993 Wiley‐Liss, Inc.
Chiral‐recognition chromatography of β‐blockers on continuous polymer beds with immobilized cellulase as enantioselective protein
Authors: Mohammad Jamil , Li Yi‐Ming , El‐Ahmad Mostafa , Nakazato Ken'ichi , Pettersson Göouran , Hjertéean Stellan
Published: January 2005

Columns prepared by coupling cellulase as a chiral selector to silica beads are very efficient for the separation of enantiomers. In this paper we show that continuous polymer beds compete favorably with silica beads as chromatographic supports for such separations. The chiral stationary phase is prepared either by entrapment in and simultaneous covalent linkage of ally1 cellulase to the continuous beds during their preparation or by covalent immobilization of cellulase on an epoxy‐activated continuous bed. Enantiomers of β‐blockers were separated rapidly and with high resolution. The enantiomers of practolol were thus baseline resolved within 45 sec. The recognition center–or at least part of it—coincides with the active center of the enzyme, since the enantiomers could not be separated in the presence of the competitive enzyme inhibitors cellobiose and D‐glucose and the separation was also impaired upon addition of the substrate carboxymethyl cellulose to the eluent. Similar observations have been reported for silica columns derivatized with cellulase. The capacity factor and the separation selectivity could be tuned by the pH and the concentration of the mobile phase, a phosphate buffer. No modifier was required, as is sometimes the case with silica‐based supports. The continuous beds give faster enantiomer separations than do columns of silica and are more pH‐stable and cost effective to prepare. © 1993 Wiley‐Liss, Inc.
Direct enantiospecific HPLC bioanalysis of (R,S)‐atenolol on a chiral stationary phase
Authors: Kofahl Birgit , Henke Dorit , Mutschler Ernst
Published: January 2005

The simultaneous determination of the enantiomers of the β1‐selective adrenergic antagonist atenolol in human plasma and urine is described. After an alkaline preextraction atenolol is extracted from biological material at pH 12.3 using dichloromethane/propan‐2‐ol. The separation of the underivatized enantiomers is achieved by high‐performance liquid chromatography on a chiral stationary phase (Chiralcel OD, cellulose tris‐3, 5‐dimethylphenylcarbamate, coated on silica gel) with fluorimetric detection. (−)‐(S)‐Pindolol is used as an internal standard. The detection limits of 5 ng/ml enantiomer in plasma and 50 ng/ml enantiomer in urine are sufficient for pharmacokinetic studies after therapeutic doses. © 1993 Wiley‐Liss, Inc.
Rac‐Flurbiprofen is more ulcerogenic than its (S)‐enantiomer
Authors: Wechter William J. , Bigornia Annette E. , Murray E. David , Levine Barry H. , Young James W.
Published: January 2005

The most common, and sometimes life‐threatening, side‐effects associated with the human use of the analgesic, nonsteroidal antiinflammatory drugs (NSAIDs) are gastrointestinal. These include gastritis, ulceration, and severe bleeding. The aryl propionic acid class of NSAIDs are among the most widely used of these drugs in the world, including rac‐ibuprofen, rac‐flurbiprofen, and rac‐ketoprofen. Marketed as racemates, it was assumed that the “inactive” (R)‐enantiomers, having no cyclooxygenase inhibiting effect, also had no toxic effect. In a 30‐day dose response study of (S)‐, (R)‐, and rac‐flurbiprofen given daily over a range of doses the (R)‐isomer alone proved to be without apparent gastrointestinal (GI) toxicity. On the other hand the racemate proved to be 2 to 4 times as ulcerogenic in enantiomerically equivalent doses as the (S)‐enantiomer. These results have significant clinical implications. © 1993 Wiley‐Liss, Inc.
Stereoselective HPLC bioanalysis of atenolol enantiomers in plasma: Application to a comparative human pharmacokinetic study
Authors: Egginger Gabriele , Lindner Wolfgang , Kahr Sabine , Stoschitzky Kurt
Published: January 2005

An enantioselective HPLC bioassay has been developed relying on extraction of (R)‐ and (S)‐atenolol from alkalinized plasma or serum (pH > 12) into dichloromethane containing 5% (v/v) 1‐butanol followed by an achiral derivatization of the drug with phosgene leading to (R)‐ and (S)‐oxazolidine‐2‐one derivatives. Under these conditions there was quantitative conversion of the acetamido group to the corresponding nitrile. These stable derivatives were separated on a (R,R)‐diaminocylohexane‐dinitrobenzoyl chiral stationary phase [(R,R)‐DACH‐DNB] using dichloromethane/methanol 98/2 as mobile phase. Determination limits of 0.5 ng for (R)‐ and 0.6 ng for (S)‐atenolol could be achieved using fluorimetric detection. The assay was applied to a human pharmacokinetic study which was performed in a randomized cross‐over, double‐blind fashion in 12 healthy volunteers, administering single oral doses of 100 mg (R,S)‐, 50 mg (R)‐, and 50 mg (S)‐atenolol AUC0–24 and Cmax values of (R)‐atenolol were slightly but significant higher than those of (S)‐atenolol. The R/S ratios were 1.09 for AUC(R)/AUC(S) and 1.03 for Cmax (R)/Cmax(S) (P < 0.01) respectively after administration of the racemic drug. However, there were no differences between AUC, Cmax, and t½ values of each enantiomer, whether they were administered as single enantiometers or in the form of its racemic mixture. © 1993 Wiley‐Liss, Inc.
Estimation of the number of enantioselective sites of bovine serum albumin using frontal chromatography
Authors: Jacobson Stephen C. , Andersson Shalini , Allenmark Stig G. , Guiochon Georges
Published: January 2005

On a column with bovine serum albumin (BSA) immobilized covalently to silica, the adsorption isotherms of the enantiomers of mandelic acid, tryptophan, 2‐phenylbutyric acid, and N‐benzoylalanine are measured using a buffered mobile phase. Knowing the amount of BSA immobilized on the column (36 mg), the ratio of the number of enantiomer molecules needed to saturate the enantioselective retention mechanism to the number of BSA molecules is determined. The mean of the set of eight enantiomers is 0.28. These data confirm that at most one enantioselective site exists for each BSA molecule for the kind of enantiomers studied. © 1993 Wiley‐Liss, Inc.
Separation of the enantiomers of some racemic nonsteroidal aromatase inhibitors and barbiturates by capillary electrophoresis
Authors: Francotte Eric , Cherkaoui Samir , Faupel Michel
Published: January 2005

High‐performance capillary electrophoresis (HPCE) and micellar electrokinetic capillary chromatography (MECC) were applied to the resolution of racemic nonsteroidal antiaromatase drugs and intermediates. Successful results were obtained in both modes using α‐cyclodextrin (α‐CD), β‐cyclodextrin (β‐CD), γ‐cyclodextrin (γ‐CD), or 2,6‐di‐O‐methyl‐β‐cyclodextrin (DM‐β‐CD) as chiral selectors. Depending on the structure of the solute, one of the cyclodextrins was generally better suited for resolution of the racemate. The basic solutes were analyzed under HPCE conditions, whereas the nonionizable compounds such as glutethimide (Doriden®) were analyzed in MECC mode. For the azole‐type antiaromatase Fadrozole, both HPCE and MECC modes could be used to achieve the separation of the enantiomers. The influence of experimental factors such as pH, the presence of organic modifier, temperature, the micelle concentration, and the concentration of the chiral selector is also discussed on the basis of the results obtained with some chiral barbiturates. The possibility of analyzing the enantiomers directly in plasma samples was also demonstrated. © 1993 Wiley‐Liss, Inc.
Commonly used chiral drugs: A survey
Authors: Millership Jeffrey S. , Fitzpatrick Anne
Published: January 2005

Initial results of a comparative survey of commonly used chiral drugs are presented. The survey considered the differences between drugs used in 1982 with those in use in 1991. Two major conclusions were reached: the use of single isomer chiral drugs had increased from 31.1% in 1982 to 34.3% in 1991 and the proportion of synthetic single isomer chiral drugs available in 1991 was considerably greater than in 1982. © 1993 Wiley‐Liss, Inc.
Microbial metabolism of 2‐arylpropionic acids: Chiral inversion of ibuprofen and 2‐phenylpropionic acid
Authors: Hutt Andrew J. , Kooloobandi Azam , Hanlon Geoffrey W.
Published: January 2005

The metabolism of (R,S)‐ibuprofen has been investigated in 24 microbial cultures. Of these Cunninghamella elegans, Mucor hiemalis, and Verticillium lecanii catalyzed the oxidation of the drug to 2‐[4‐(2‐hydroxy‐2‐methylpropyl)phenyl]propionic acid, a known mammalian metabolite. The extent of metabolism was greatest with V. lecanii, with some 47% of the substrate being consumed over a 7‐day incubation period. Enantiomeric analysis indicated stereoselective metabolism of (R)‐ibuprofen, the enantiomeric composition of the residual substrate being R/S = 0.25. Following a preparative scale incubation of (R,S)‐ibuprofen with V. lecanii, in which the reaction was allowed to go to completion, the metabolite was found to be predominantly of the S‐configuration (S/R = 2.1), suggesting that chiral inversion of either the drug and/or the metabolite had taken place. Analysis of extracts following incubation of (R,S)‐, (R)‐, and (S)‐2‐phenylpropionic acid with V. lecanii, for 21 days, indicated that chiral inversion of the (R)‐enantiomer to its optical antipode had taken place. The results of these investigations indicate that microorganisms, in addition to mammals, are able to mediate the chiral inversion of 2‐arylpropionic acids. This observation may have implications for the preparation of optically pure 2‐arylpropionic acids. © 1993 Wiley‐Liss, Inc.
Stereoselective sulfate conjugation of isoproterenol in humans: Comparison of hepatic, intestinal, and platelet activity
Authors: Pesola Gene R. , Walle Thomas
Published: January 2005

The stereochemistry of sulfate conjugation of isoproterenol (ISO) was examined with human liver, intestine, and platelets as the phenolsulfotransferase (PST) enzyme source and PAP35S as the cosubstrate. With the hepatic cytosol, two distinct sulfation reactions were identified, a high affinity reaction (Km 5 to 50 μM) and a low affinity reaction (Km 360 to 2,900 μM). The efficiency of sulfation (Vmax/Km) for both reactions was 5‐fold higher for (+)‐ than for (−)‐ISO. When the hepatic PSTs were resolved by ionexchange chromatography, it could be shown that the high affinity reaction was catalyzed by the monoamine (M) form and the low affinity reaction by the phenol (P) form of PST. Only the high affinity (M form) sulfation was detected in the jejunal cytosol with a Vmax/Km value 6.1‐fold higher for (+)‐ than for (−)‐ISO. Finally the platelet, as a potentially useful model tissue, also demonstrated only the high affinity M form reaction with a Vmax/Km value 5.7‐fold higher for (+)‐ than for (−)‐ISO. In summary, this study has shown that sulfation of ISO by PSTs in various human tissues is stereoselective and favors the inactive (+)‐enantiomer over the active (−)‐enantiomer by about 5‐fold, a finding which should be considered in the therapeutic use of chiral drugs cleared by sulfate conjugation. © 1993 Wiley‐Liss, Inc.
The temperature dependence of steady‐state kinetics: What can be learned about pig liver esterase stereospecificity?
Authors: Van Gelderen Hans , Mayer Joachim M. , Cellamare Saverio , Testa Bernard
Published: January 2005

The steady‐state kinetic parameters for pig liver carboxylesterase (PLE)‐catalyzed hydrolysis of the prochiral substrate dimethyl phenylmalonate (DMPM) (product enantioselectivity) and the separate enantiomers of three chiral 2‐phenylpropionic acid esters (substrate enantioselectivity) were measured at seven temperatures between 288 K and 312 K. Arrhenius plots of turnover numbers against the reciprocal of experimental temperatures yielded enthalpies and entropies of activation at enzyme saturation. (+)‐(S)‐methyl‐2‐phenylpropionate, (+)‐(S)‐4‐nitrophenyl 2‐phenylpropionate, and both enantiomers of phenyl 2‐phenylpropionate showed very similar activation enthalpies and entropies (approximately 50 kJ mol−1 and −50 J mol−1 K−1, respectively), but differences were observed for (−)‐(R)‐methyl 2‐phenylpropionate and (−)‐(R)‐4‐nitrophenyl 2‐phenylpropionate. Whereas the entropies of activation of all 2‐phenylpropionates were negative, positive entropies of activation were measured in the formation of monomethyl phenylmalonate enantiomers from DMPM. Enthalpy–entropy compensation analysis of the data indicates a common mechanism of PLE substrate and product enantiospecificity in the reactions studied here. © 1994 Wiley‐Liss, Inc.
Challenges and frustrations in the separation and analysis of chiral agrochemicals
Authors: Massey Peter R. , Tandy Michael J.
Published: January 2005

The development of chiral HPLC methods and isolation techniques within Zeneca Agrochemicals (formerly ICI Agrochemicals) is reviewed. The use of low temperature to improve chiral separations has been successfully applied to production analysis, but although useful for some compounds it is regrettably not a universal panacea for all poor separations. The need to isolate small quantities of individual enantiomers from new compounds for research evaluation has led us to devise a more universal and cheap chiral stationary phase (CSP) for Preparative‐LC. Joint academic research produced a CSP based on tartaric acid which was made commercially available and it was gratifying to find it was the only phase able to resolve a novel insecticide. However, as new CSPs emerged almost every month, our attention turned to using a universal chiral detector for analysis, rather than via separation of individual enantiomers. Diode laser‐based polarimeters offered the opportunity of cheap, sensitive chiroptical detectors for HPLC and the ability to move away from chiral columns in both research and production analysis. Jointly sponsored research with a university has successfully explored the versatility of chiroptical detectors in agrochemical and food analysis. Comparison of chiral SFC with chiral HPLC and an extensive evaluation of established and research agrochemicals on a wide range of commercial CSPs have led to a revised method development strategy. Current work with high load displacement chiral chromatography will be described as a potential means of isolating pure enantiomers from racemates. © 1994 Wiley‐Liss, Inc.
Isomeric‐Activity ratios of trimetoquinol enantiomers on β‐adrenergic receptor subtypes: Functional and biochemical studies
Authors: Fraundorfer Paul F. , Lezama Edwin J. , Salazar‐Bookaman M. Margarita , Fertel Richard H. , Miller Duane D. , Feller Dennis R.
Published: January 2005

Trimetoquinol [1‐(3′,4′,5′‐trimethoxybenzyl)‐6,7‐dihydroxy‐1,2,3,4‐tetrahydroisoquinoline, TMQ] exists as two enantiomers, and the (−)‐(S)‐isomer is a potent β‐adrenergic receptor (β‐AR) agonist. Experiments were conducted to examine the functional and biochemical potencies of the (S)‐ and (R)‐enantiomers of TMQ for interaction with β‐AR subtypes in tissues, membrane fractions, and cell systems. The isomeric‐activity ratios (IARs) of the TMQ isomers [(S)‐isomer ≫ (R)‐isomer] for stimulation of β1‐ and β2‐AR of guinea pig right atria and trachea were 224 and 1585, respectively; these IARs were similar to those observed on atypical β‐AR systems of rat distal colon (575), rat brown adipocytes (398), but differed from that of rat esophageal smooth muscle (2884) in the presence of pindolol. In the absence of pindolol, the potencies for the TMQ enantiomers were slightly increased; however, the IARs remained unchanged in rat distal colon, rat brown adipocytes, and rat esophageal smooth muscle. Similarly, radioligand binding studies demonstrated that the TMQ isomer β‐AR affinities were stereoselective for the (−)‐(S)‐isomer in membranes of guinea pig left ventricle (β1) and lung (β2) giving IARs of 115 and 389, respectively; and in E. coli expressing human β1‐ and β2‐AR giving IARs of 661 and 724, respectively. Corresponding IARs of receptor affinities and stimulation of cAMP accumulation in Chinese hamster ovary cells expressing human β2‐AR and rat β3‐AR were 331 and 282, and 118 and 4678, respectively. These results indicate that the (−)‐(S)‐isomer of TMQ exhibits high affinity, and is a potent and highly stereoselective agonist for each β‐AR subtype, that the isomers generally fail to differentiate between the β‐AR subtypes, and that, based upon differences in IAR within β3‐AR containing systems, subtypes of atypical β (or β3)‐AR may exist in adipose tissue and smooth muscle. © 1994 Wiley‐Liss, Inc.
Asymmetric metabolic N‐oxidation of N‐ethyl‐N‐methylaniline by purified flavin‐containing monooxygenase
Authors: Hadley Mark R. , Oldham Harriet G. , Damani Lyaquatali A. , Hutt Andrew J.
Published: January 2005

The prochiral tertiary amine N‐ethyl‐N‐methylaniline (EMA) is known to be metabolically N‐oxygenated in vitro with microsomal preparations. This biotransformation is thought to be mediated predominantly by the flavin‐containing monooxygenase (FMO) enzyme system. Microsomal N‐oxygenation of EMA is known to be stereoselective and varies between species. In order to further characterise this metabolic transformation, we have examined the in vitro metabolism of EMA using purified porcine hepatic FMO. Following incubation of EMA with purified FMO, EMA N‐oxide, the only metabolite detected, was found to be produced stereoselectively [ratio (−)‐(S):(+)‐(R), ca. 4:1]. The enantiomeric ratio of the N‐oxide product did not change markedly with respect to time, enzyme or substrate concentration. Determination of the kinetics of formation of the N‐oxide indicated a single affinity for the prochiral substrate with differential rates of formation of the enantiomers. The extent of EMA N‐oxide formation was shown to be affected by activators and inhibitors of FMO and pH, but its stereoselectively was unaltered. © 1994 Wiley‐Liss, Inc.
Chiral HPLC with carbohydrate carbamates: Influence of support structure on enantioselectivity
Authors: Grieb Sally J. , Matlin Stephen A. , Phillips Joseph G. , Belenguer Ana M. , Ritchie Harald J.
Published: January 2005

The effect of particle size and pore size of the aminopropylated silica support for cellulose tris(phenylcarbamate) and tris(3,5‐dimethylphenylcarbamate) chiral HPLC phases was investigated. It was necessary to reduce phase loading below 20% w/w as pore size and particle size were reduced, but high efficiency columns could be prepared at a 15% w/w loading on 5 and 2.5 μm supports with 120‐Å‐diameter pores. The 2.5 μm phase permits the use of relatively high flow rates and very efficient enantioselective separations of a range of chiral compounds could be achieved in less than 3 min. © 1994 Wiley‐Liss, Inc.
Determination of the absolute configuration of secondary alcohols with Horeau's method including enantioselective gas chromatography
Authors: König Wilfried A. , Gehrcke Bärbel , Weseloh Gerald
Published: January 2005

The reaction of optically active secondary alcohols with excess of racemic 2‐phenylbutyric acid anhydride in pyridine proceeds at different rates to the diastereoisomeric esters (kinetic partial resolution). According to Horeau the (unknown) absolute configuration of the alcohol can be derived from the optical rotation of the remaining excess of 2‐phenylbutyric acid in the reaction mixture. Measuring the optical rotation may be very difficult in cases of small absolute rotation values and may be inaccurate due to the necessity to completely remove all chiral impurities. The application of Horeau's method is greatly facilitated by gas chromatographic determination of the enantiomeric ratio of the remaining 2‐phenylbutyric acid after methylation using a short capillary column with heptakis(2,6‐di‐O‐methyl‐3‐O‐pentyl)‐β‐cyclodextrin as a chiral stationary phase. Baseline resolution of the enantiomers is achieved after approximately 10 min of retention time. Due to the high selectivity of capillary gas chromatography the probability of impurities in the mixture to interfere with the measurement of the enantiomeric ratio is extremely low. © 1994 Wiley‐Liss, Inc.
Inversion of chiral α‐methylbenzylamine
Authors: Johansen Cecilie , Fiksdahl Anne
Published: January 2005

More effective use of optical resolution processes can be obtained by increasing the overall yields after development of methods for inversion of the chiral centre of the unwanted isomer. The configuration of some optically active amines can be inverted in a three‐step synthesis via the N,N‐ditosylimides and a subsequent nucleophilic substitution by the azide ion. The azide product is reduced by hydrogenolysis. Low stereoselectivity caused by racemization to some extent was at first observed for the inversion of the benzylic substrate, (S)‐α‐methylbenzylamine (5a). However, modified reaction conditions allowed increased stereoselectivity, a more rapid and almost complete inversion of this substate as well. © 1994 Wiley‐Liss, Inc.
Acid‐catalyzed stereoselective heteronucleophilic substitution and racemization of 3‐O‐methyloxazepam and 3‐O‐ethyloxazepam
Authors: Yang Shen K.
Published: January 2005

Enantiomers of 3‐O‐methyloxazepam (MeOX) and 3‐O‐ethyloxazepam (EtOX) were resolved by chiral stationary phase high‐performance liquid chromatography (CSP‐HPLC). Reaction kinetics and deuterium isotope effects of acid‐catalyzed racemization of enantiomeric MeOX in ethanol and enantiomeric EtOX in methanol were studied by spectropolarimetry. The acid‐catalyzed heteronucleophilic substitution reactions of racemic MeOX in ethanol and racemic EtOX in methanol were studied by reversed‐phase HPLC. Thermodynamic parameters involved in the reactions were obtained by temperature‐dependent reaction rates. The effects of solvent's dielectric constant on the heteronucleophilic substitution reactions were also determined. A nucleophilically solvated and transient C3 carbocation intermediate resulting from an N4‐protonated enantiomer, derived from a 1,4‐benzodiazcpine either in M (minus) or P (plus) conformation, is proposed to be an intermediate and responsible for the acid‐catalyzed stereoselective nucleophilic substitution and the resulting racemization. © 1994 Wiley‐Liss, Inc.
The rabbit liver microsomal biotransformation of 1,1‐dialkylethylenes: Enantioface selection of epoxidation and enantioselectivity of epoxide hydrolysis
Authors: Bellucci Giuseppe , Chiappe Cinzia , Cordoni Antonio , Marioni Franco
Published: January 2005

The rabbit liver microsomal biotransformation of α‐methylstyrene (1a), 2‐methyl‐1‐hexene (1b), 2,4,4‐trimethyl‐1‐pentene (1c), and 2,3,3‐trimethyl‐1‐butene (1d) has been investigated with the aim at establishing the enantioface selection of the cytochrome P‐450‐promoted epoxidation of the double bond and the enantioselectivity of microsomal epoxide hydrolase (mEH)‐catalyzed hydrolysis of the resulting epoxides. GLC on a Chiraldex G‐TA (ASTEC) column was used to determine the enantiomeric composition of the products. The epoxides 2 first produced in incubations carried out in the presence of an NADPH regenerating system were not detected, being rapidly hydrolyzed by mEH to diols 3. The enantiomeric composition of the latter showed that no enantioface selection occurred in the epoxidation of 1c and 1d, and a very low (8%) ee of the (R)‐epoxide was formed from 1b. Incubation of racemic epoxides 2b–d with the microsomal fraction showed that the mEH‐catalyzed hydrolysis of 2c and 2d was practically nonenantioselective, while that of 2b exhibited a selectivity E = 4.9 favoring the hydrolysis of the (S)‐enantiomer. A comparison of these results with those previously obtained for linear and branched chain alkyl monosubstituted oxiranes shows that the introduction of the second alkyl substituent suppresses the selectivity of the mEH reaction of the latter and reverses that of the former substrates. © 1994 Wiley‐Liss, Inc.
Direct enantiomeric resolution of ibuprofen and flurbiprofen by packed column SFC
Authors: Wilson William H.
Published: January 2005

Packed column SFC is used to resolve the enantiomers of two nonsteroidal antiinflammatories. A Chiralpak AD column is used with a binary mobile phase of carbon dioxide/methanol to achieve resolution. The effects of composition, pressure, temperature, and flow on ibuprofen enantiomer separation are examined. In this instance, temperature affords the greatest change in resolution followed by pressure and composition. Baseline resolution of ibuprofen is achieved in less than 7 min and fluibiprofen is baseline resolved in less than 4 min. © 1994 Wiley‐Liss, Inc.
Evaluation of free D‐glutamate in processed foods
Authors: Rundlett Kimber L. , Armstrong Daniel W.
Published: January 2005

Monosodium glutamate (MSG) is added to many processed foods at significant levels for flavor enhancement. It is also naturally occurring at high levels in some foods. The enantiomeric composition of free glutamate in foods was examined and all foods analyzed were found to contain D‐glutamate. The relative percent of D‐glutamate in the food products studied depended on the origin of the glutamate. Foods to which MSG was added by the manufacturer had a high total level of MSG but a lower relative percentage of the D‐enantiomer (usually less than 0.8%). In comparison, fermented foods tend to have high relative levels of D‐glutamate but a lower total amount of the amino acid. The relative percent of D‐glutamate in nonfermented foods containing no added MSG was also found to be low compared to fermented products. In some cases the percent D‐glutamate could be related to the relative amounts of other food ingredients such as cheese. © 1994 Wiley‐Liss, Inc.
Determination of amphetamine and methamphetamine enantiomers by chiral derivatization and gas chromatography–mass spectrometry as a test case for an automated sample preparation system
Authors: Sievert Hans‐Jürgen P.
Published: January 2005

An automated sample preparation system has been applied to the chiral analysis of amphetamine and methamphetamine using derivatization with trifluoracetyl‐L‐prolyl chloride (L‐TPC) and subsequent separation on a gas chromatography–mass spectrometry (GC‐MS) system. Tasks automated were the dilution of standards and the off‐line preparation of the diastereoisomer derivatives. Chromatographic performance, sensitivity, and reproducibility of the automated procedure were compared to the equivalent values obtained with two existing assays methods which employ manual derivatiation, either on‐column or off‐line. Chromatographic performance was unaffected by the derivatization procedure and sensitivity was better for both automated and manual off‐line derivatization. Qualitative reproducibility as based on enantiomeric composition was equivalent for all three approaches, while quantitative reproducibility as based on peak areas was best for the automated procedure. Considering the fact that the diastereoisomer derivatives are unstable over time, automated sample preparation with “just‐in‐time” derivatization can increase the overall precision of the analytical method. The procedures described here are general enough in nature that they could be applied to other chiral or even achiral analytes. © 1994 Wiley‐Liss, Inc.
Base‐catalyzed racemization of 3‐O‐acyloxazepam
Authors: Yang Shen K. , Bao Ziping
Published: January 2005

Enantiomers of 3‐O‐acyloxazepam (oxazepam 3‐acetate; OXA) underwent base‐catalyzed hydrolysis and racemization. Kinetics of reaction products formed from an OXA enantiomer in buffered and unbuffered alkaline solutions were analyzed by chiral stationary phase high‐performance liquid chromatography. Racemization occurred with varying rates in aqueous solutions with pH ranging from 7.5 to 14. Racemization mechanism was studied by the dependence of rates of hydrolysis and racemization on temperature and pH. Mass spectral analysis of racemization products derived from an OXA enantiomer in a deuterated solvent indicated that racemization was accompanied by a proton exchange with the solvent. The results indicated that a base‐catalyzed keto‐enol tautomerism between the C2‐carbonyl group and the C3 carbon was responsible for the observed racemization. © 1994 Wiley‐Liss, Inc.

This article is a US Goverment work and, as such, is in the public domain in the United States of America.
Improved synthesis and pharmacologic activity of the enantiomers of a new benzofurane type antiarrhythmic compound
Authors: Ecker Gerhard , Fleischhacker Wilhelm , Helml Thomas , Noe Christian R. , Scasny Sonja , Lemmens‐Gruber Rosa , Studenik Christian , Marei Hesham , Heistracher Peter
Published: January 2005

An improved synthesis of the enantiomers of the new benzofurane‐type antiarrhythmic compound 1 is described, which makes use of the enantiomerically pure mbe‐lactol. Thus, acylation of the benzofurane 4 with acetic anhydride and subsequent bromination gave the bromoacetyl‐derivative 6, which, after reduction with LiAlH4, was protected with mbe‐lactol to give a mixture of the diastereomers 8A and 8b. After separation via column chromatography assignment of absolute configuration was carried out using a well‐established NMR‐ method. Reaction with propylamine and cleavage of the protective group gave (R)‐1 and (S)‐1, respectively. Enantiomeric purity was confirmed using a direct HPLC method with rsp‐cyclodextrine as stationary phase. Pharmacological investigations on isolated guinea pig heart muscle preparations showed that GE 68 and its two enantiomers did not significantly differ from each other with regard to their negative inotropic, negative chronotropic, and lack of β‐adrenoceptor blocking action. In contrast, the reference drug propafenone was equally potent in its negative inotropic and chronotropic activity as GE 68, but additionally showed a weak β‐adrenoceptor blocking activity. © 1994 Wiley‐Liss, Inc.
Stereoselective distribution of hydroxychloroquine in the rabbit following single and multiple oral doses of the racemate and the separate enantiomers
Authors: Ducharme Julie , Wainer Irving W. , Parenteau Heli I. , Rodman John H.
Published: January 2005

Hydroxychloroquine (HCQ) stereoselective distribution was investigated in rabbits after 20 mg/kg po of racemic‐HCQ (rac‐HCQ) and 20 mg/kg po of each enantiomer, 97% pure (−)‐(R)‐HCQ and 99% pure (+)‐(S)‐HCQ. Concentrations were 4 to 6 times higher in whole blood than in plasma. Melanin did not affect plasma and whole blood levels since concentrations did not differ between pigmented and nonpigmented animals. After single and multiple doses of the separate enantiomers, only 5–10% of the antipode could be measured, in blood or plasma. Therefore, there was no significant interconversion from one enantiomer into the other. Following rac‐HCQ, plasma (+)‐(S)‐levels always surpassed (−)‐(R)‐ones while in whole blood, (−)‐(R)‐HCQ concentrations were always the highest. When the enantiomers were administered separately, blood concentrations achieved after (−)‐(R)‐HCQ were higher, especially after multiple doses. These observations suggest that (−)‐(R)‐HCQ is preferentially concentrated by cellular components of blood. This enantioselective distribution of HCQ could be secondary to a stereoselective protein binding to plasma proteins, although a more specific binding of (−)‐(R)‐HCQ to blood cells cannot be ruled out. Since in whole blood (−)‐(R)‐HCQ is retained in cellular components, metabolism would favour the more available (+)‐(S)‐enantiomer. © 1994 Wiley‐Liss, Inc.
Stereoisomeric flavour compounds LXVII. 2‐, 3‐, and 4‐Alkyl‐branched acids, part 1: General approach to the synthesis of the enantiopure acids
Authors: Karl Volker , Kaunzinger Astrid , Gutser Jutta , Steuer Petra , Angles‐Angel Jorge , Mosandl Armin
Published: January 2005

A general approach to the synthesis of 2‐, 3‐, and 4‐alkyl‐branched acids of high enantiomeric purity is described. The enantiopure 2‐alkyl‐branched acids are prepared via liquid chromatographic resolution of diastereomeric phenylglycinol amides and their absolute configuration is deduced from the 1H‐NMR data of the separated diastereomers. Chain elongation methods, by Arndt–Eistert synthesis, via 2‐alkylated alkyl carbonitrile or by malonic ester synthesis, are used to prepare 3‐ and 4‐alkyl‐branched acids of high configurational purity and known absolute configuration starting from the enantiomeric 2‐alkyl‐branched acids. © 1994 Wiley‐Liss, Inc.
Bidirectional chiral inversion of the enantiomers of the nonsteroidal antiinflammatory drug oxindanac in dogs
Authors: King Jonathan N. , Mauron Catherine , LeGoff Carmen , Hauffe Suzanne
Published: January 2005

The nonsteroidal antiinflammatory drug oxindanac exists as two enantiomers, with most of its pharmacological activity residing in the (S)‐isomer. The behavior of its enantiomers was investigated in dogs. Bidirectional inversion occurred in heparinised plasma and blood, with a ratio of enantiomers [S:R] of 7.3:1 being achieved at equilibrium after incubation for 24 h at 37°C. There was no detectable inversion of either isomer in plasma incubated at 4°C for up to 8 h or in aqueous solution at 37°C for up to 36 h. Bidirectional inversion also occurred in vivo, with a ratio of plasma AUC (0 ∞)s [S:R] of 8.1:1. The ratio of enantiomers reached equilibrium within 2 hr following (S)‐ or rac‐oxindanac, and within 8 h following (R)‐oxindanac. Elimination t½s of the isomers were the same (R, 12.1 h, S, 13.3 h). There were no differences in the ratio of enantiomers following oral or intravenous application, suggesting that a systemic site for inversion was predominant. Although concentrations of the respective isomers were similar at equilibrium following administration of either (R)‐, (S)‐, or rac‐oxindanac, AUC (0 ∞)s differed due to the delay in reaching equilibrium. The extent of inversion to the (S)‐isomer was 100, 73.2, and 60.7% after administration of (S)‐, rac‐, and (R)‐oxindanac, respectively. Although pharmacological activity might be equivalent at equilibrium following administration of either (R)‐, (S)‐, or rac‐oxindanac; efficacy at early time points should be superior in the order (S) > racemate > (R). In conclusion both enantiomers of oxindanac undergo conversion to their respective antipodes in dogs, although the inversion of R to S is more efficient than that of S to R. This bidirectional inversion occurred in vivo, and in vitro in plasma and blood. © 1994 Wiley‐Liss, Inc.
Implications of chirality on pharmacodynamic modeling
Authors: Wright Matthew R.
Published: January 2005

Although the implications of stereochemistry for pharmacokinetics are relatively well appreciated only recently has its influence on pharmacodynamics begun to be examined. The implications of different pharmacological interactions between enantiomers with similar and different kinetic properties are examined through the use of simulation of the pharmacological effect vs. time profile. The influences of assuming that the pharmacological effect is solely the result of the more active enantiomer are also discussed. The simulations demonstrate that the less pharmacologically active enantiomer may have a significant influence on the observed effect vs. time profile and that the assumption that all of the observed pharmacological activity arises from the more active enantiomer may lead to highly inaccurate prediction of the pharmacodynamic parameters. Finally, these observations suggest that the pharmacodynamic profiles of a drug administered as a racemate or as a “pure” formulation of the more active enantiomer may be significantly different. © 1994 Wiley‐Liss, Inc.
HPLC and NMR methods for the quantitation of the (R)‐enantiomer in (−)‐(S)‐timolol maleate drug raw materials
Authors: Lacroix Pauline M. , Dawson Brian A. , Sears Roger W. , Black D. Bruce
Published: January 2005

HPLC and 1H‐NMR methods for the quantitation of the (R)‐enantiomer in (−)‐(S)‐timolol maleate were developed and validated. The HPLC method requires a 25 cm × 4.6 mm 5 μm Chiracel OD‐H (cellulose tris‐3,5‐dimethylphenylcarbamate) column, a mobile phase of 0.2% (v/v) diethylamine and 4% (v/v) isopropanol in hexane at a flow rate of 1 ml/min and UV detection at 297 nm. A system suitability test was devised to verify the separation of the (R)‐ and (S)‐enantiomers of timolol from other drug‐related impurities. The NMR method requires the use of a high‐field NMR spectrometer (>360 MHz) and a chiral solvating agent, (−)‐(R)‐2,2,2‐trifluoro‐1‐(9‐anthrylethanol) (R‐TFAE). The limits of quantitation were 0.05% and 0.2% (m/m) for HPLC and NMR, respectively. The methods were applied to the determination of the (R)‐enantiomer in eight lots of raw material. The results for the two methods were in very good agreement, with results ranging from 0.1 to 4.1% (m/m) by HPLC and none detected to 4.3% (m/m) by NMR. The USP method for specific rotation was found to be unsuitable for detecting the presence of low levels of the (R)‐enantiomer in (−)‐(S)‐timolol maleate. © 1994 Wiley‐Liss, Inc.
Kinetics and stereochemistry of the microsomal epoxide hydrolase‐catalyzed hydrolysis of cis‐stilbene oxides
Authors: Bellucci Giuseppe , Chiappe Cinzia , Ingrosso Giovanni
Published: January 2005

The microsomal epoxide hydrolase (mEH)‐catalyzed hydrolysis of cis‐4,4′–dimethylstilbene oxide (1a), cis‐4,4′‐diethylstilbene oxide (1b), cis‐4,4′‐diisopropylstilbene oxide (1c), and cis‐4,4′‐dichlorostilbene oxide (1d) have been investigated using rabbit liver microsomal preparations. The kinetic parameters, Km and Vmax, and the absolute stereochemistry of the reactions have been determined and compared with those of cis‐stilbene oxide (1e). All epoxides 1a–d are hydrolyzed by mEH with high product enantioselectivity to give (R,R)‐(+)‐diols with ee ≥ 90%. The presence of the substituents on the phenyl rings markedly reduces the rates of mEH catalyzed hydrolysis with respect to cis‐stilbene oxide, by increasing Km and reducing Vmax in the cases of 1a, 1b, and 1d, or reducing only the Vmax in the case of 1c. The very low Vmax, together with a persistent ability to fit into the mEH active site, make all these epoxides, and particularly 1c, inhibitors of cis‐stilbene oxide hydrolysis. The kinetic and stereochemical results are interpreted on the basis of the proposed topology of the mEH active site. © 1994 Wiley‐Liss, Inc.