Determination of the absolute configuration of secondary alcohols with Horeau's method including enantioselective gas chromatography

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.     

Theoretical study of enantiodifferentiation in solid state cyclodextrins

A molecular mechanics investigation of R- vs. S-phenylethanol, R- vs. S-mandelic acid, R- vs. S-flurbiprofen, and R- vs. S-fenoprofen in their cyclodextrin crystal environments was undertaken. It was found that the dominant force responsible for guesthost complexation is the short-range London force; the enantiodiscriminating forces tend to be very small and are generally, but not always, dominated by long-range electrostatic contributions. Derivatized cyclodextrins are generally more enantiodiscriminating than native cyclodextrins, perhaps due to exterior rather than interior guest-host binding. © 1993 Wiley-Liss, Inc.     

γ-Cyclodextrin as chiral mobile phase additive in the HPLC separation of the atropisomers of some N-arylthiazoline-2-thiones and N-arylthiazoline-2-ones: Attempts to quantify the effect of selected structural parameters

The effect of the position and type of the substituent on the chromatographic separation of N-arylthiazoline-2-thione and arylthiazoline-2-one atropisomers are described in reversed-phase HPLC using β- or -β-cyclodextrin as chiral mobile phase additive. A quantitative approach to experimental design has been developed. © 1993 Wiley-Liss, Inc.     

Spectroscopic and computational exploration of hypoxanthine riboside interacting with plasma albumin

Hypoxanthine riboside (HXR) is a nucleoside essential for wobble base pairs to translate the genetic code. In this work, an absorption and luminescence study showed that HXR and human serum albumin (HSA) formed a new complex through hydrogen bonds and van der Waals forces at ground state. Fluorescence probe experiments indicated that HXR entered the first subdomain of domain II in HSA and was fixed by amino acid residues in site I defined by Sudlow, and after competing with a known site marker. The recognition interaction featured negative ΔH^?, ΔS^? and ΔG^? thermodynamic parameters. Fluorescence and circular dichroism spectra described the polarity of residues and α‐helix and β‐strand content changed because of HXR binding. The most rational structure for the HXR–HSA complex was recommended by the molecular docking method, in which the binding location, molecular orientation, adjacent amino acid residues, and hydrogen bonds were included. In addition, the influence of β‐cyclodextrin and some essential metal ions on the balance of the HSA–HXR system interaction was measured. The study gained comprehensive information on the transportation mechanism for HXR in blood, and was of great significance in understanding the theory of HXR biotransformation and in discussing its clinical in vivo half‐life.     

Evaluation of enantiomeric purity of selected amino acids in honey

Highly sensitive and accurate HPLC methods were used for the determination of total amounts of proline, leucine and phenylalanine and their enantiomeric ratios in a variety of different honey samples. Significant amounts of D -leucine and D -phenylalanine and relatively low concentrations of D -proline have been found in honeys of different botanical and geographical origins. It is suggested that the enantiomeric ratios of amino acids could be used to test for storage effects, age, and the quality of the processing of the honey. © 1994 Wiley-Liss, Inc.     

ESA Mission ROSETTA Will Probe for Chirality of Cometary Amino Acids

New crucial theoretical investigations on the origin of biomolecular chirality are reviewed briefly. With the goal to investigate these theories our team is going to perform the `chirality-experiment' in the near future with cometarymatter. In 2012 the robotical lander RoLand will detach fromthe orbiter of the ROSETTA spacecraft and set down on the surface of comet 46P/Wirtanen in order to separate andidentify cometary organic compounds via GC-MS in situ.Chiral organics will be separated into their enantiomers by application of 3 capillary columns coated with different kindsof stationary phases. Non-volatile compounds like amino acidswill be derivatized in especially developed gas phasealkylation steps avoiding reactions in the liquid phase. Theresults of these preliminary gas phase reactions are presentedin this article.     

Separation of the enantiomers of some racemic nonsteroidal aromatase inhibitors and barbiturates by capillary electrophoresis

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.