Chiral discrimination and antipicornavirus activity of 6-oxazolinylisoflavan

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.     

Chirality of amino acids of microorganisms used in food biotechnology

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.     

Direct enantiospecific HPLC bioanalysis of (R,S)-atenolol on a chiral stationary phase

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.     

Use of chiral β-lactones for the synthesis of chiral LC phases

Chiral β-lactones offer an easy and economic approach to novel chiral R- or S-configurated LC phases. The preferred method for their preparation is based on conventional ready-to-use aminopropyl-functionalized silicas, e.g., aminopropyl HPLC columns. The new stationary phases can be used for analytical and preparative separations and are particularly suitable for the resolution of rotatory and heterocyclic stereoisomers. Applications in the LC, SFC, and TLC mode are possible, including the use of β-lactone-based mobile phase additives in a “push–pull” combination. A large variety of organic solvents can be used as eluents. © 1993 Wiley-Liss, Inc.     

Optical resolution of glycerin sulfides and glycerin selenides on the chiral stationary phase of cellulose‐tris(3,5‐dimethylphenylcarbamate)

Cellulose‐tris(3,5‐dimethylphenylcarbamate) was prepared after a reported method and was coated onto an aminopropylated mesopore spherical silica gel. The final product was used as a chiral stationary phase of high performance liquid chromatography for the enantioseparation of a series of glycerin sulfides and glycerin selenides. Mixtures of hexane and 2‐propanol were used as mobile phases. The effects of 2‐propanol concentration in the mobile phase on the retention and resolution were investigated. Some enantiomers of the glycerin monosulfides and monoselenides could be separated satisfactorily, but none of the disulfides could be separated. The structural features of the solutes that influence chiral separation were discussed. Chirality 11:598–601, 1999. © 1999 Wiley‐Liss, Inc.     

Fluorenone 1,4-dihydropyridine derivatives with cardiodepressant activity: Enantiomeric separation by chiral HPLC and conformational aspects

The direct HPLC enantiomeric separation of five fluorenone-1,4-dihydropyridine-3,5-dicarboxylic diesters has been achieved using a Chiralpak AD stationary phase obtaining simultaneously good enantioselectivities, resolution factors, and elution times. CD spectra of the individual enantiomers for two compounds were measured. Thermodynamic parameters associated with the adsorption equilibria of the enantiomers with the chiral stationary phase were obtained from HPLC runs at various temperatures. The conformational preferences of the synperiplanar fluorenone group and of the cis/cis ester groups were obtained by ¹H NMR spectra, including NOE experiments. © 1996 Wiley-Liss, Inc.     

Proteome analysis to assess physiological changes in Escherichia coli grown under glucose-limited fed-batch conditions

Proteome analysis was used to compare global protein expression changes in Escherichia coli fermentation between exponential and glucose-limited fed-batch phase. Two-dimensional gel electrophoresis and MALDI-TOF mass spectrometry were used to separate and identify 49 proteins showing >2-fold difference in expression. Proteins upregulated during exponential phase include ribonucleotide biosynthesis enzymes and ribosomal recycling factor. Proteins upregulated during fed-batch phase include those involved in high-affinity glucose uptake, transport and degradation of alternate carbon sources and TCA cycle, suggesting an enhanced role of the cycle under glucose- and energy-limited conditions. We report the upregulation of several putative proteins (ytfQ, ygiS, ynaF, yggX, yfeX), not identified in any previous study under carbon-limited conditions.     

Chromatographic enantioseparation by cycloalkylcarbamate derivatives of cellulose and amylose

Cyclopentyl and (+/-)-exo-2-norbornylcarbamates of cellulose and amylose were prepared and their chiral recognition abilities as chiral stationary phases for high-performance liquid chromatography (HPLC) were evaluated. Among these carbamates, cellulose tris(cyclopentylcarbamate) and amylose tris((+/-)-exo-2-norbornylcarbamate) showed particularly high chiral recognition, which is comparable to that of several well-known phenylcarbamate derivatives. The chiral recognition mechanism of cellulose tris(cyclohexylcarbamate), which was previously found to be an effective chiral stationary phase for HPLC, was investigated using NMR spectroscopy. The derivative dissolved in chloroform exhibited the chiral discrimination of several enantiomers in NMR as well as in HPLC. For example, the 1,1'-bi-2-naphthol enantiomers were distinctly discriminated in the (1)H, (13)C, and 2D-NOESY spectra.     

Enantiomeric separation of a thiazolbenzenesulfonamide compound using packed-column subcritical fluid chromatography

Separation of enantiomers of a thiazolbenzenesulfonamide compound was performed on a Chiralpak AD column using subcritical fluid chromatography. Effects of alcohol modifier and temperature on the separations were studied. The results revealed that while the main adsorbing interactions were between the hydroxyl group of the analyte and the carbamate group of the stationary phase, chiral discrimination was achieved through an inclusion mechanism within the chiral cavity created along the amylose chains. Analogs and synthetic precursors of the thiazolbenzenesulfonamide studied were also investigated so as to understand the effect of functional groups and configuration of the analyte molecule upon chiral recognition.     

Monolithic stationary phases: Yesterday, today, and tomorrow

The history of the development of monolithic stationary phases in chromatography, the modern state of the art, and the prospects for their use are considered.