Determination of the enantiomeric purity of oxfenicine by high-performance liquid chromatography

Summary Reaction of the methyl esters of the -amino acids, R-(–)-, and S-(+)-4-hydroxyphenylglycine (oxfenicine) with the enantiomerically pure acid anhydride of R-(+)-1-methoxy-1-trifluoromethyl-phenylacetic acid (i.e. R-(+)-MTPA) yields diastereoisomeric amides which are separable by high-performance liquid chromatography (HPLC). The ratios of the diastereoisomeric amides may be measured chromatographically and are shown to correspond to the enantiomeric purities of the amino acids. This method is particularly well suited for detecting low levels of an enantiomeric impurity in -amino acids which possess a base labile -methine hydrogen atom.     

Inclusion of Enantiomeric Carvones in β-Cyclodextrin: a Variable Temperature 1H NMR Study in Aqueous Solution

In aqueous solution, the apparent association constant at room temperature for the 1 : 1 inclusion of S-(+)-carvone in - cyclodextrin is double of that for R-(-)-carvone, whereas, at 45 °C, both enantiomers have association constants two orders of magnitude smaller, with the S-(+) inclusion being then slightly weaker than the R-(-) encapsulation. Calculations carried out at the molecular mechanics, AM1 and STO-3G levels confirm the preferential inclusion of the S-enantiomer and provide important clues for understanding chiral discrimination by -cyclodextrin.     

Heterogeneous catalytic oxidation of ethanol: A new process for acetic acid

ESR investigations on ZnO doped with various amounts of -Al₂O₃ thermally treated, are reported. Experimental data are related to the electronic structure of ZnO--Al₂O₃ and to desulfurization specific activity for natural gas.

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ZnO, -Al₂O₃. ZnO/-Al₂O₃ .

     

Effect of preparation method of nickel-zeolite catalysts on their catalytic properties

The effect of the carrier-gas (H₂, N₂, CO₂ and air) and the influence of additives (H₂S and water vapors) in the activation of Ni- and Cr-containing zeolites on their catalytic activity have been studied in toluene disproportionation.

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- (H₂, N₂, CO₂ ) (H₂S ) , Ni Cr, .

     

Chiral resolution of aminoalcohols by ion-pair chromatography

Summary Chiral resolution of aminoalcohols is performed by ionpair chromatography using (+)-10-camphorsulphonic acid in methylene chloride + 1-pentanol (1991) as mobile phase and LiChrosorb DIOL as adsorbing stationary phase. Change of the properties of the solid phase and the nonpolar solvent affects the retention and the separation efficiency but has no significant influence on the chiral selectivity. Studies of the structural requirements for the stereoselective separation have shown that a simultaneous electrostatic and hydrogen bonding between the two enantiomeric ions is of fundamental importance. Studies of equilibrium processes in the mobile phase indicate that the aminoalcohols are retained as ion pairs.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Effect of Surfactants on the Immobilization of 4-(2-Pyridylazo)resorcinol on Silochroms

The effect of cationic surfactants (cetyltrimethylammonium bromide, cetylpyridinium bromide, and tetrabutylammonium perchlorate) and a nonionic surfactant (OP-7) on the conditions of the immobilization of 4-(2-pyridylazo)resorcinol (PAR) on three types of silica gel (Silochrom S-120 (200–350 m), Silochrom S-120 (315–500 m), and Silochrom S-80 (200–350 m)) was studied. It was found that OP-7 does not affect the adsorption of surfactants. The effect of cationic surfactants increases in the order tetrabutylammonium perchlorate < cetyltrimethylammonium bromide < cetylpyridinium bromide. The adsorption activity of silica gels increases in the order Silochrom S-120 (315–500 m) < Silochrom S-80 (200–350 m) < Silochrom S-120 (200–350 m). Cetylpyridinium bromide provides full immobilization of PAR on silica gel Silochrom S-120 (200–350 m) in the pH range 2–9.     

Asymmetric reduction of prochiral arylketones with chiral 2,2′-dihydroxy-1,1′-binaphthyl — Borane complexes

Reduction of eight aryl ketones with borane complexes containing (–)(S)-2,2dihydroxy-1,1-binapthyl as a chiral auxiliary yielded (with one exception) (R)-alcohols with enantiomeric purities up to 54% (as determined with chiral NMR-shift reagents and/or by enantioselective chromatography on triacetyl-cellulose). In two cases addition of aromatic amines caused a significant increase of e.e. together with a reversal of the absolute chirality (fromR toS). Models for a possible transition state are discussed.Dedicated to Prof. Dr. Dr. mult. h. c.V. Gutmann on the occasion of the 65th anniversary of his birthday.     

Asymmetric halogenation and hydrohalogenation of styrene in crystalline cyclodextrin complexes

Asymmetric halogenation and hydrohalogenation of styrene in microcrystalline cyclodextrin complexes were studied in the gas-solid state, and compared with the homogenous reactions in aqueous or dimethyl sulfoxide solutions. The gas-solid brominations in the - and -cyclodextrin complexes produced predominantly (–)-1,2-dibromo-l-phenylethane. The chiral induction for the reaction of the -cyclodextrin complex rose to 9 times that of the -cyclodextrin complex. Brominations in the homogenous solutions containing the - or -cyclodextrin complexes gave no dibromide but racemic bromohydrin. In the gas-solid chlorination, the -cyclodextrin complex gave (–)-dichloride,S-(+)-2-chloro-l-phenylethanol (14% ee) and (+)-1,2,2-trichloro-l-phenylethane, and the -cyclodextrin complex produced (+)-dichloride,S-(+)-chlorohydrin (8% ee) and (+)-trichloride. The chiral induction of the gas-solid halogenation using the solid cyclodextrin complexes is attributed to the ability to hold rigidly a chiral conformation of the crystalline state. However, the gas-solid hydrohalogenation all gave racemic products.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986.     

Chiral separations by host-guest complexation with cyclodextrin and crown ether in capillary zone electrophoresis

Summary Capillary zone electrophoresis using cyclodextrins and a chiral crown ether as buffer constituents was studied for the enantiomeric separation of drugs and amino acids. Based on results obtained from separation of racemic -amino acids both chiral selectors are compared with respect to resolution, efficiency and retention time. For (±)-Quinagolide effects of buffer composition and temperature are examined using -cyclodextrin as chiral agent. Optimum conditions were pH 2.5 at 30 mmol L^–1 -cyclodextrin. A linear dependence of retention on -cyclodextrin concentration allowed calculation of formation constants of the host-guest complexes. Buffer concentration and temperature also influence resolution. The application of a chiral crown ether to the separation of optical isomers in capillary zone electrophoresis is described for the first time. Chiral recognition of solutes depends on the formation of protonated alkyl amines and separation is attributed to the formation of diastereomeric host-guest complexes with different interactions for each enantiomer. The effects of crown ether concentration on resolution are presented.     

Separation and identification of aliphatic amine derivatives with a new fluorescent reagent using high-performance liquid chromatography and thin-layer chromatography

Summary The use of 1,2-naphthoylenebenzimidazole-6-sulphochloride has been proposed as the reagent for derivatization of aliphatic amines prior to their separation, identification and quantitation both in HPLC and in TLC. The reaction of amines with this compound is quantitative and highly fluorescent derivatives are formed that provide favourable detection limits and sensitivity as compared to Dansyl derivatives of aliphatic amines. Actual detection limits achieved correspond to ca. 10^–10 mol of the amine in a spot after elution from the thin-layer plate and to ca. 5·10^–14 mol of the amine in a sample volume of 10 l injected into the liquid chromatograph. The use of this derivatization reagent offers good potential for the analysis of trace amounts of amines in environmental samples and in biological material.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Analysis of thiols by HPLC after fluorescent prelabelling with 4-(6-methylnaphthalen-2-yl)-4-oxobuten-2-oic acid

Summary The use of 4-(6-methylnaphthalen-2-yl)-4-oxobuten-2-oic acid as a fluorogenic reagent in pre-column derivatization for the high-performance liquid chromatography (HPLC) of biologically important thiols (L-cysteine, glutathione, N-acetylcysteine, homocysteine and mercaptopropionylglycine) was investigated. The aroylacrylic acid reacts selectively and rapidly (15 min. at room temperature) with the thiol compounds to give stable fluorescent adducts which can be separated by reversedphase HPLC and detected fluorometrically (_ex 300nm); _em 445nm). The experimental conditions for the thiol derivatization and chromatographic separation are discussed. Applications to the determination of N-acetylcysteine, mercaptopropionylglycine and cysteine are described.Presented in part at Bononiachem, XVI Congresso Nazionale di Chimica, Bologna, October 9–14, 1988.     

Enantiomeric separation of D/L-carnitine using HPLC and CZE after derivatization

Summary Carnitine is an essential component in tissues of animals, higher plants and many microorganisms. Whereas the L-carnitine enantiomer plays an important role in the metabolism of long chain fatty acids, D-carnitine has a considerable toxic influence on biochemical processes. The analytical separation of D-and L-carnitine depends upon derivatization with UV-or fluorescently active substances, e.g. FMOC and (+)/(–)-FLEC. The separation of diastereomeric (+)- and (–)-FLEC carnitine esters was performed successfully with capillary zone electrophoresis (CZE) and HPLC, after optimization of the derivatization process and of the composition and pH of the buffer, using UV- and fluorescence detection. With HPLC separation a detection limit of the carnitine esters of 5 mol/l when using fluorescence detection was achieved. With both separation systems baseline resolution and short analysis times could be obtained. The enantiomeric FMOC derivatives could be separated using the electrophoretic system and acidic buffers with high concentrations of an osmotic flow modifier together with -cyclodextrine as chiral selector. The applicability of the optimized separation conditions are demonstrated in the analysis of agar culture medium inoculated withPseudomonas putida and of pharmaceutical formulations. In all samples very low amounts of D- or L-carnitine could be determined in the presence of the other enantiomeric form. Problems caused by the impurity of the carnitine standards or the derivatization agent (+)/(–)-FLEC are discussed.     

Porphyrin Clathrates. Crystal Structures of Two Unexpected Products Obtained by Solvothermal Reactions of Pt-tetra(4-carboxyphenyl)porphyrin with Copper Acetate

The X-ray crystal structure of IX, perchlorate salt of R-(–-2-ethyl-N-benzyl-4,7,19,13-tetraoxa-8,9-benzo-1-azacyclopentadec-8-ene has been determined. In the molecule, the protonated nitrogen atom participates in two N-HO hydrogen bonds. The unusually high proton affinity of aza crown ether leads to the formation of diastreomer instead of complex formation with chiral R-(+)-1-phenyl ethyl ammonium perchlorate and S-(–)-1-phenyl ethyl ammonium perchlorate. The complex ability of host ethers was evaluated in terms of structural modification.     

Products of chlorination of 3-carene by N-chlorosuccinimide

Conclusions The chlorination of 3-carene by N-chlorosuccinimide gave (–)-4-chloro-3 (10)-carene, (–)-3,4-dichlorocarane, (+)-3,4-dichlorocarane, and 2,8-dichloro-p-mentha-1(7),5-diene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 206–209, January, 1987.     

Investigations in the field of acyl group carriers

Conclusions Two representatives of phosphate ester derivatives of pantothenonitrile have been obtained: the methyl ester of D-(+)-4-C-[2-O-mesylpantothenonitrilyloxy(phenoxy)phosphonyl]-N-benzyloxycarbonylserine and the ethyl ester of D-(+)-4-C-[2-O-mesylpantothenonitrilyl(phenoxy)phosphonyl]-N-benzyloxycarbonylserylglycine.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 3, pp. 174–176, 1969     

Synthesis and chiral-optical properties of (+)-3-methyl-3,4-dihydroisoquinoline-1-thione

(+)-3-Methyl-3,4-dihydroisoquinoline-1-thione was obtained by sulfuration of (+)-3-methyl-3,4-dihydroisoquinolone with phosphorus pentasulfide or by cyclization of (+)--benzylethyl isothiocyante under the influence of polyphosphoric acid. Measurements of the rotatory dispersion and circular dichroism showed the presence of two positive Cotton effects due to n^* and ^* transitions in the thioamide chromophore, as well as Cotton effects apparently due to ^* transitions in the aromatic chromophore.Communication XXXV from the series Stereochemical Investigations. See [11] for communication XXXIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 94–97, January, 1976.     

Interaction of cyclodextrins with drugs. Chromatographic investigation using a cyclodextrin bonded-phase and its application to chiral separations

Summary The interaction between cyclodextrin and the drug (1R,2S,3S,4S)-(5Z)-7-(3-((phenylsulfonyl)amino)bicyclo[2.2.1]hept-2-yl)hept-5-enoic acid ((+)-S-145), was studied using -, -, and -cyclodextrin bonded-phase columns. Retention behavior of (+)-S-145 on these columns revealed that the strength of inclusion was -cyclodextrin. Interaction between -cyclodextrin and (+)-S-145 was found to increase as the proportion of carboxylic ion in the (+)-S-145 molecule increased. Comparison of binding capacities of these bondedsilica gels obtained by frontal analysis and surface coverage indicated that availability of the immobilized - and -cyclodextrin was 20–25%. The synthesized -cyclodextrin bonded-phase column was superior to that of commercial columns in terms of chiral separation of (±)-S-145. A typical usage of the -cyclodextrin column is discussed for separation of (±)-S-145 in plasma samples.     

A thermodynamic study of enantiomeric recognition of organic ammonium cations by pyridino-18-crown-6 type ligands in methanol and a 1: 1 methanol-1,2-dichloroethane mixture at 25.0°C

LogK, H, andTS values for interactions of (R) and (S) enantiomers of -(1-naphthyl)ethylammonium perchlorate (NapEt), -phenylethylammonium perchlorate (PhEt), and the hydrogen perchlorate salt of 2-amino-2-phenylethanol (PhEtOH) with a series of chiral and achiral pyridino-18-crown-6 type ligands and 18-crown-6 (18C6) were determined from calorimetric titration data valid in methanol and in a 1: 1 (v/v) methanol-1,2-dichloroethane (MeOH-1,2-DCE) mixture at 25.0°C. In the MeOH-1,2-DCE solvent mixture, the chiral macrocyclic ligands exhibit excellent recognition for enantiomers of the three organic ammonium cations as shown by large differences in logK values ( logK) which range from 0.4 to 0.6 (2.5- to 4.0-fold difference in binding constants). The logK values in the solvent mixture MeOH-1,2-DCE are increased by 0.1–0.5 logK units over those in absolute methanol, indicating a favorable effect of 1,2-dichloroethane on enantiomeric recognition. In 1,2-dichloroethane, however, the interactions are too strong (logK>6) to observe the degree of recognition by a direct calorimetric method. Complexation of organic ammonium cations by these macrocyclic ligands is driven by favorable enthalpy changes. The entropy changes ure unfavorable in all cases. The thermodynamic origin of enantiomeric recognition for NapEt in 1:1 (v/v) MeOH-1,2-DCE is enthalpic, but those for PhEt and PhEtOH are entropic. Effects of the ligand structure and flexibility and of the organic cation structure on recognition and complex stability are discussed on the basis of the thermodynamic quantities. Different thermodynamic behaviors of achiral 5 and 18C6 from those of chiral macrocyclic ligands indicate a difference between chiral and achiral macrocycle interactions with the chiral organic ammonium cations. The different thermodynamic behavior of NapEt enantiomers compared to those of PhEt and PhEtOH enantiomers supports the idea that the solution complex conformation of NapEt is different from those of PhEt and PhEtOH. - interaction is absent for the PhEt and PhEtOH complexes with diesterpyridino-18-crown-6 ligands in solution. Therefore, the higher degree of enantiomeric recognition for NapEt than for either PhEt or PhEtOH by these chiral macrocyclic ligands is a result of the presence of - interaction in the NapEt system.     

Enantioselective Analyses of Antihistaminic Drugs by High-Performance Liquid Chromatography

High-performance liquid chromatographic methods have been developed for stereoselective separations of terfenadine and its active metabolite fexofenadine. Satisfactory enantioseparations of racemic terfenadine were achieved on a Chiralcel column by normal phase elution. Analysis of racemic fexofenadine, as such, took a very long time and achieved poor enantioselectivity on this column; nevertheless, the analyte when derivatised with diazomethane was well resolved. Racemic fexofenadine was also derivatised using a chiral agent: R-(+)-1-phenylethylisocyanate and subjected to achiral LC on a reversed-phase analytical column. Complete enantioseparations were achieved in short analysis times; excess reagent eluted before the diastereoisomeric pair and did not interfere.Part of this work was presented at the 10^th International Meeting on Recent Developments in Pharmaceutical Analysis RDPA03, Cogne, Valle d Aosta, Italy. June 28–July 1, 2003.     

Modification of the aluminium form of faujasite with fluorine

Aluminium-modified faujasites (AIY) were fluorinated with NH₄F solution. The AIY sample calcined before fluorine treatment shows poor crystallinity and low catalytic activity. The activity of the AIY sample fluorinated without calcination is significantly enhanced and crystallinity is well retained.

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(AIY) NH₄F. AIY, , . AIY, , , .