Aroonsiri Shitangkoon

Gas chromatographic separation of the enantiomers of volatile fluoroether anesthetics by derivatized cyclodextrins II. Preparative-scale separations for isoflurane

Abstract Preparative-scale gas chromatographic separation of the enantiomers of isoflurane, a volatile anesthetic, has been achieved with 2 m × 10 mm I.D. columns, packed with 80–100 mesh Chromosorb W AW, coated with up to 23% (w/w) trifluoroacetyl γ-cyclodextrin as stationary phase. The type and particle size of the support, the concentration of the stationary phase and the separation conditions were varied to improve product purity and the production rate under overloaded elution mode conditions. Using a sampling interface located between the exit of the preparative column and the fraction collector, effluent samples were directed onto a short, high-efficiency analytical capillary column every 30 s to achieve on-line enantiomeric analysis of the eluting bands, which allowed the calculation of purity, recovery and production rate for the separations.

Systematic modification of the separation selectivity of cyclodextrin-based gas chromatographic stationary phases by varying the size of the 6-O-substituents

Abstract Several heptakis(2,3-di-O-methyl)-β-cyclodextrin derivatives were synthesized in which the size of the primary 6-O-substituent was varied systematically from deoxy-fluoro, through methyl, n -pentyl, n -propyldimethylsilyl, tert. -butyldimethylsilyl, to triisopropylsilyl. The resulting solid cyclodextrin derivatives were dissolved at identical molal concentrations in OV-1701-vi to form useful gas chromatographic stationary phases for enantiomer separations. It was found that while all phases could be operated at temperatures as high as 250°C, the lower operating temperatures decreased greatly as the size of the substituent increased. Chiral selectivity also varied significantly with the size of the substituent: for almost all of the test compounds chiral selectivity had a local maximum when the substituent was the tert. -butyldimethylsilyl group.

Gas chromatographic separation of the enantiomers of volatile fluoroether anesthetics using derivatized cyclodextrin stationary phases. Part I

The capacity factors and chiral selectivity factors were determined as a function of temperature for the enantiomers of desflurane, enflurane and isoflurane on nine commercially available cyclodextrin derivative-coated GC capillary columns. The enantiomers could be separated with the trifluoroacetylcyclodextrin stationary phases which show good chiral selectivities coupled with modest column efficiencies. Very rapid enantiomeric trace determinations of desflurane, isoflurane and enflurane could be achieved with a trifluoroacetyl γ-cylodextrin-coated capillary column.

Determination of the gas-liquid partition isotherms of the enantiomers of methyl 2-chloropropionate on trichloroacetyl pentyl β-cyclodextrin using the elution by characteristic points method

The gas-liquid partition isotherms of the enantiomers of methyl 2-chloropropionate on a trichloroacetyl pentyl β-cyclodextrin stationary phase were determined at three different temperatures using the elution by characteristic points method. The isotherms were described using the single-component and competitive bi-Langmuir isotherm equations. The measured and calculated isotherms as well as the retention factor and separation selectivity data agree, indicating that these isotherms might be suitable for the modeling of the preparative-scale gas chromatographic separation of the enantiomers.

Preparative gas chromatographic separation of the enantiomers of methyl 2-chloropropionate using a cyclodextrin-based stationary phase

Abstract The enantiomers of methyl 2-chloropropionate, a volatile synthetic precursor, have been separated by preparative-scale gas chromatography using a 1 m × 22.5 mm I.D. column, packed with 20% (w/w) trichloroacetyl s-cyclodextrin-coated 60–80-mesh Chromosorb A. The preparative column was installed in a custom-designed preparative gas chromatograph and operated in the isothermal mode. An effluent-sampling interface valve, located between the exit of the preparative column and the fraction collector took 10-μl samples of the effluent gas every 20 s and sent the samples onto a short, efficient analytical capillary column to provide on-line enantiomeric analysis of the eluting bands. This near-real-time knowledge of the enantiomer composition of the effluent gas leads to aggressive, yet safe, fraction pooling schemes and permits the precise calculation of product purity, recovery and production rate. Results for the preparative separation of racemic as well as enantiomerically enriched (95% enantiomeric excess) feedstock are presented in this paper.

Libraries of opiate and anti-opiate peptidomimetics containing 2,3-methanoleucine.

A library of 96 peptides/peptidomimetics was prepared, in which half was based on the YGGFL-NH2 sequence, while the remainder were derivatives of a presumed anti-opiate peptide, YGGFLRF-NH2. Of the 48 compounds in each half of the library, 32 contained a stereoisomer of 2,3-methanoleucine substituted for Leu5. Binding of the YGGFL-NH2 derivatives to the mu- and delta-opioid receptors, and to the anti-beta-endorphin monoclonal antibody (clone 3E7), indicated any change at the Leu5 had little effect on the binding when compared with modifications to the YGGF-sequence. Conversely, cyclo-Leu residues did alter the binding of YGGFLRF-NH2 derivatives when substituted for Leu5. Of these 32 peptidomimetics, three derivatives of 2S,3S-cyclo-Leu had relatively low Ki values for binding to an NPFF receptor. Differences between the outcome of the screens were interpreted in terms of the position of the cyclo-Leu residue in the two sequences.

MALDI AND FAB MASS SPECTROMETRY OF NUCLEOSIDE TRIPHOSPHATES: A COMPARATIVE STUDY

Abstract Comparison of MALDI and FAB mass spectra of dATP, dTTP, dCTP, and dGTP shows that the former technique gives clear molecular ions with minimal fragmentation whereas the latter gives more fragment ions and weaker parent peaks.

Use of the equilibrium-dispersive model of nonlinear gas chromatography for the modelling of the elution band profiles in the preparative-scale gas chromatographic separation of enantiomers

Abstract The equilibrium-dispersive model of chromatography is applied to the study of enantioselective separations of methyl 2-chloropropionate in gas chromatography. The single-component and competitive bi-Langmuir isotherm equations that describe the sorption behavior of single enantiomers and racemates, respectively, are utilized by the equilibrium-dispersive model to predict the elution band profiles of single-component and binary mixture samples. The measured and the calculated band profiles are compared both for the analytical open tubular column used to acquire the isotherm data and for the 1 m×22.5 mm I.D. preparative packed column, followed by the comparison of the enantiomeric purity vs. production curves for both the measured and the simulated systems.