Chiral ion-pair chromatography on porous graphitized carbon using N-blocked dipeptides as counter ions

Surface-modified three-dimensional graphene nanosheets as a stationary phase for chromatographic separation of chiral drugs

Carbon-based stationary phases for chromatographic separation have been commercially available since the 1980s. Porous graphitic carbon liquid chromatography columns are known to be highly resistant to aggressive mobile phases and extreme pH values of solvents and eluents, an important advantage compared to conventional silica-based alternatives. In our work, we demonstrate a new variant of carbon-based stationary phases for liquid chromatography, specifically developed for chiral separation. Mesoporous three-dimensional graphene nanosheets (3D GNS), functionalized with tetracyanoethylene oxide (TCNEO) and (S)-(+)-2-pyrrolidinemethanol, demonstrate pharmaceutical-grade chiral separation of model ibuprofen and thalidomide racemic mixtures when used as Chiral Stationary Phases (CSPs), with performance parameters comparable to currently commercially available CSPs. Simple covalent attachment of functionalization groups to the surface of mesoporous three-dimensional graphene nanosheets makes these carbon-based CSPs chemically stable and up to an order of magnitude less expensive than standard silica-based analogues.

1,2,4-trisubstituted cyclopentanes as platforms for diversity

Despite their simplicity, relatively few examples of 1,2,4 (1,3,4)-amino-, azido-, and hydroxy-substituted cyclopentanes are reported in the literature. We found that cyclopent-3-en-1-ol can be transformed into a significant variety of compounds of this class by relatively common and efficient synthetic procedures. Stereochemical control of epoxidation of the cyclopentene double bond can be achieved by varying the substitutents at C4. The C4 substituent and epoxide functional group can be converted into a variety of intermediates with differential protection designed for use in applications requiring regiospecific control for further elaboration of the cyclopentane scaffold.

Supercritical Fluid Generated Stationary Phases for Liquid Chromatography and Capillary Electrochromatography

Chromatographic silica-bonded stationary phases have been prepared using supercritical CO(2) as the reaction medium. (29)Si solid-state NMR spectra of the generated bonded silica phases show unreacted silica species Q(3) and Q(4), alongside important resonances for surface-bound ligands, T(1), T(2), and T(3). Initially, a fluorinated octyl silica (C(8)) phase was produced, by reacting (1)H,(1)H,(2)H,(2)H-perfluorooctyltriethoxysilane with silica particles (3 microm) in sc-CO(2) at 60 degrees C and 450 atm for 3 h. In-house-packed LC columns of this fluorinated sc-C(8) silica phase yielded typical reversed-phase behavior when a standard test mix of benzamide (k' = 1.03), benzophenone (k' = 8.11), and biphenyl (k' = 14.92) was eluted. When packed into fused-silica capillaries for CEC, this fluorinated sc-C(8) silica phase gave linear plots of log k' versus percentage MeOH for benzophenone and biphenyl and, in contrast to octyl or octadecyl silica phases, displayed selectivity for aromatic thioureas when chromatographed among a series of synthetic organic thiourea test solutes. Similarily, an octadecyl silica phase (sc-C(18) silica) was prepared by reaction of n-octadecyltriethoxysilane in sc-CO(2), packed at 9500 psi and examined by LC. The sc-C(18) silica LC column yielded high column efficiency (up to 141 000 N/m (fluorene)) and excellent asymmetry factors (1.06, fluorene) without resource to end-capping. Following a second silylating or end-capping step using hexamethyldisilazane in sc-CO(2), sc-end-capped sc-C(18) silica phases elute N,N-DMA before toluene and the toluidine isomers as a single peak, indicating lowered silanol activity according to the Engelhardt test. A rapid separation of the important pharmaceutical substances, ketoprofen, naproxen, fentoprofen, and ibuprofen, on an sc-end-capped sc-C(18) silica phase is also shown.

Separation of polar compounds using carbon columns

The objective of this review with 122 references is to provide structure and retention mechanisms of porous graphitic carbon by chromatographic analysis and computational chemical analysis of retention mechanisms. Synthesis methods of porous graphitic carbon are described. Applications for use as matrix for dynamic coating on porous graphitic carbon and direct separation of polar compounds on porous graphitic carbon demonstrated that the physical and chemical stability of graphitic carbons performed in both chromatography and extraction, especially for polar compounds, those are difficult on both silica-based and organic polymer-based packing materials. The disadvantage is difficult desorption of non-polar compounds adsorbed on the surface. The development of 3.5-microm particles improves the separation power of graphitic carbon columns with the high theoretical plate number.

Stereoselective chromatography of cardiovascular drugs: an update

This review reports the latest achievements in chromatographic enantioseparations of various classes of cardiovascular drugs and selected applications of these methods in pharmaceutical and clinical analysis. The use of these drugs as test compounds for new chiral stationary phases and different parameters of chromatographic processes is also presented.

Enantiomeric separations of amino alcohols by packed-column SFC on Hypercarb with L-(+)-tartaric acid as chiral selector

The use of L-(+)-tartaric acid as a chiral mobile phase additive (CMPA) has been investigated in a packed-column SFC system. The CMPA, carbon dioxide, and methanol, containing a high concentration of aliphatic amine additive, were used as the mobile phase and Hypercarb as support [Gyllenhaal O., Karlsson A., SFC of metoprolol and other amino alcohols on Hypercarb (in preparation)]. Good enantioselectivities were obtained for tertiary amine homologues of 2-amino alcohols, used as beta-adrenoreceptor-blocking drugs. Moderate selectivities were observed for aromatic compounds having a second substituent in the ortho-position. The overall retention was influenced by the aromaticity of the analytes as well as the presence of free electron pairs in the molecule. Increased concentrations of CMPA gave higher retention and also increased the enantioselectivity. The practical utility of this present enantioselective system was demonstrated on one batch of (S)-metoprolol that was N-methylated with methyl iodide. The enantiomeric separation was accomplished within 10 min.