Capillary gas chromatographic properties of three new mono-ester permethylated β-cyclodextrin derivatives

2^I-O-Methoxycarbonylmethyl-2^II–VII,3^I–VII,6^I–VII-eicosa-O-methyl-cyclodextrin (20Me/P2OCH₂COOMe), 6^I-O-methoxycarbonylmethyl-2^I–VII,3^I–VII,6^II–VII-eicosa-O-methyl-cyclodextrin (20Me/P6OCH₂COOMe), 6^I-O-methoxycarbonyl-6^I-deoxy-2^I–VII,3^I–VII,6^II–VII-eicosa-O-methyl-cyclodextrin (20Me/P6COOMe) have been evaluated as chiral stationary phases (CSPs) for capillary gas chromatography. General chromatographic properties of the corresponding columns have been investigated in terms of efficiency, polarity and inertness. More than 60 solutes have been used for studying their enantioselectivity by comparison with permethylated β-cyclodextrin as a reference. Similar enantioseparation ability was established for the four studied CSPs, the 20Me/P2OCH₂COOMe exhibiting in most cases a better enantioselectivity than the other selectors.     

Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part VI: Octakis (2,3,6-tri-O-pentyl)-γ-cyclodextrin

Perpentylated γ-cyclodextrin is a very hydrophobic liquid which exhibits enantioselectivity toward a number of non-polar chiral substrates including the saturated hydrocarbons cis- and trans-pinane, β-chiral olefins, iron(O) tricarbonyl complexes of prochiral olefins and 3,3,8,8-tetramethyl-trans-cyclooctene, a compound with planar chirality.     

Enantiomeric separation of 5-alkyl-5methylhydantion derivatives by capillary gas chromatography on permethylated β-cyclodextrin and molecular modeling

Permethylated β-cyclodextrin (hereafter designated perMe-β-CD), dililuted or not in polysiloxane, is an efficient chiral discriminant for native, 3-methylated, and 1,3-dimethylated series of 5-methyl-5-(C_nH_{2n + 1})hydantoins. From thermodynamic data obtained with pure perMe-β-CD and with the aid of molecular modeling, it is concluded that: (i) For native hydantoin derivatives having a carbon chain at the 5-position varying from ethyl to nonyl (2?n?9), the retention time is related to their H-bonding capability. The resolution is poor for derivatives with n?4. For n?5, the resolution is considerably improved and this increase in resolution is attributed to the long alkyl chain being capable of being buried inside the cyclodextrin cavity. (ii) For 1,3-dimethylhydantion derivatives having a carbon chain at the 5-position varying from ethyl to hexyl(2?n?6), the retention time is mainly determined by a steric fit between the solute and the inner volume of the macrocyclic cavity. For n = 2, a particular behavior is observed, consistent with a total inclusion of the solutes inside the cavity. By contrast with the native hydantoins, the selectively is high for light derivatives. Thus, the selectivity does not correlate with a strong docking energy (such as the presence of H-bonds postulated with native derivatives). (iii) For 3-methylhydantoin derivatives having a carbon chain at the 5-position varying from ethyl to octyl (2?n?8), as expected, retension time and selectivity are intermediate between that of native hydantoins and 1,3-dimethylhydantoins. For all three series, where n?5, the increase in chain length (n) does not bring about substantial changes in the chromatographic results. Therefore, for these long alkyl chain derivatives, similar dominant interactions with perMe-β-CD are postulated.     

γ(δ)-Thionolactones – Enantioselective Capillary GC and Sensory Characteristics of Enantiomers

The even numbered γ(δ)-thionolactones (C₆–C₁₂) were investigated, using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)- and heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as chiral stationary phases in capillary gas chromatography. The odor characteristics of γ(δ)-thionolactone enantiomers were investigated by enantioselective gas chromatography/olfactometry.     

Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part III: Hexakis(3-O-acetyl-2,6-di-O-pentyl)-α-cyclodextrin

The properties of hexakis(3-O-acetyl-2,6-di-O-pentyl)-α-cyclodextrin as a chiral stationary phase for capillary gas chromatography are described. For the first time the enantiomers of a series of different lactones are separated and their order of elution is assigned. Moreover, the enantiomers of trifluoroacetylated aldols and amino alcohols, the cyclic carbonates of 1,2-diols, 1,3-diols, O-alkylated glycerols, and some chiral pharmaceuticals are also separated on the new chiral phase. The modified α-cyclodextrin is stable above 200°C.     

Diluted modified cyclodextrins as chiral stationary phases – influence of the polysiloxane solvent: Heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin

The influence of different polysiloxane solvents on the efficiency and stereoselectivity of columns coated with mixtures of heptakis (2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin and the polysiloxanes was investigated. Generally, the enantioselectivity increased with decreasing polarity of the silicone solvent and/or increasing cyclodextrin concentration, with some exceptions. Thermodynamic investigations showed that a change of the diluting phase or the cyclodextrin concentration affects entropy as well as enthalpy differences between the diastereomeric cyclodextrin/solute complexes. As a consequence, a certain cyclodextrin/polysiloxane combination is superior to another only at a particular temperature.     

A Mild Isomerization Reaction for β,γ‐Unsaturated Ketone to α,β‐Unsaturated Ketone

A series of β,γ‐unsaturated ketones were isomerized to their corresponding α,β‐unsaturated ketones by the introduction of DABCO in iPrOH at room temperature. The endo‐cyclic double bond (β,γ‐position) on ketone was rearranged to exo‐cyclic double bond (α,β‐position) under the reaction conditions.     

Preparation of a permethylated β‐cyclodextrin chiral stationary phase by one‐pot hydrosilylation and immobilization at the C2 position for chiral high‐performance liquid chromatography

A novel cyclodextrin intermediate, mono‐2^A‐allylcarbamido‐2^A‐deoxy‐permethylated β‐cyclodextrin, was synthesized by reacting allylamine and newly prepared mono‐2^A‐azido‐2^A‐deoxy‐permethylated β‐cyclodextrin by the Staudinger reaction and anchored onto porous silica beads by a one‐pot hydrosilylation and immobilization procedure to afford a novel chiral stationary phase. This stationary phase acts as a new member of the previous chiral stationary phase series immobilized on the cyclodextrin C2 position. This stationary phase depicted enantiomeric separation abilities toward a series of bicyclic and tricyclic racemates under reversed‐phase conditions. The resolutions for hesperetin and naringenin achieved on the current phase reached 3.91 and 1.11, respectively, much higher than the previous permethylated β‐cyclodextrin with the linkage at the C6 position.     

Detection of β-blocking drugs in urine by capillary column gas chromatography-negative ion chemical ionization mass spectrometry

β-Blocking drugs present in commercial pharmaceutical products are determined in present urine of volunteers between 4 and 24 hours after the administration of a therapeutical dose. The drugs are extracted, hydrolysed, derivatized with pentafluoropropionic anhydride, and analyzed by capillary gas chromatography and electron capture detection. Metabolite identification and drug confirmation is by capillary gas chromatography–negative ion chemical ionization mass spectrometry (GC-NICIMS). This method is very specific and a sensitivity below 1 ng/ml is obtained.     

A brief study of the supercritical fluid chromatographic behavior of lanthanide β-diketonates

The chromatographic behaviors of lanthanide chelates of acetylacetone (ACAC), trifluoroacetylacetone (TFA), thenoyltrifluoroacetone (TTA), dipivaloylmethane (THD), 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (FOD), and the thenoyltrifluoroacetonepyridine (TTA·Py) adduct were investigated using packed column supercritical fluid chromatography. Mobile phases consisting of neat and alcohol modified CO₂ were used with a phenyl packed stationary phase. Lanthanide complexes of ACAC, THD, and FOD were shown to have better chromatographic performance compared to the corresponding chelates with TFA, TTA, and TTA·Py. In particular, TTA complexes such as Eu(TTA)₃ showed characteristic thermal decomposition in the mobile phase at elevated temperature. In addition, retention behavior was found to be a temperature dependent function of volatility and solubility for all chelates studied.