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West C.,CNRS Institute of Organic and Analytical Chemistry
Current Analytical Chemistry | Year: 2014

This paper presents a review of the literature covering separations of enantiomers achieved with supercritical fluids. Supercritical fluid chromatography (SFC) is the main technique represented but chiral extraction (chiral SFE) and simulated moving bed (SMB) are also present. First of all, a historical view of the technique is presented. Then stationary phases, mobile phases and operating conditions are discussed, with a particular focus on the effect of operating parameters on the resolution. Detection issues are presented. The interest of SFC for screening methods and for the preparative scale is demonstrated. Comparison with other chromatographic techniques, namely gaseous-phase chromatography (GC) and high-performance liquid chromatography (HPLC) is provided. While the pharmaceutical industry is the principal application area of enantioselective separations, other examples with agrochemicals or fragrances are also presented. © 2014 Bentham Science Publishers.


Lesellier E.,CNRS Institute of Organic and Analytical Chemistry | West C.,CNRS Institute of Organic and Analytical Chemistry
Journal of Chromatography A | Year: 2015

Packed column sub- and supercritical fluid chromatography (SFC) is a versatile separation method: on the one hand the number of parameters acting on the quality of a separation is very large, and the effects of these parameters can be complex (and not always fully understood). But on another hand, due to numerous advantageous properties of CO2-based mobile phases, method development is a fast task. This paper is a review of the main features of SFC, focusing essentially on achiral separations. However, several fundamental aspects discussed here are also relevant to chiral SFC separations. This is not intended to be an extensive review, as the way to practice SFC has somewhat evolved with time. We rather wished to provide an expert opinion on the characteristics of the method, pointing at the sources of difficulty and displaying the wide possibilities that it offers. A large number of selected applications concerning several different areas are also presented. © 2015 Elsevier B.V.


Gigant N.,CNRS Institute of Organic and Analytical Chemistry | Gillaizeau I.,CNRS Institute of Organic and Analytical Chemistry
Organic Letters | Year: 2012

A mild and efficient method for the direct alkenylation of nonaromatic enamides was achieved through a palladium(II)-catalyzed C-H functionalization. The reaction scope includes cyclic and acyclic enamides and a range of activated alkenes. This approach represents the first successful direct C(3)-functionalization of nonaromatic cyclic enamides. © 2012 American Chemical Society.


Lesellier E.,CNRS Institute of Organic and Analytical Chemistry
Journal of Chromatography A | Year: 2011

Numerous chromatographic tests are applied to study the C18 bonded phases, either to classify these phases, or to better determine their properties or their chromatographic behaviours. Because the carotenoid test is developed in supercritical fluid chromatography (SFC), many correlations with high performance liquid chromatography (HPLC) results have been necessary to ensure the trueness of the classification reached in these analytical conditions. Consequently, the analytical conditions of the carotenoid test were chosen to fit with the TbN/BaP values from the NIST 869a test, which describe the shape selectivity of the alkyl bonded phases. Additional studies performed in this paper by using well standardized silica (J'Sphere, YMC Pack ODS A, Wakosil II), which varied from their surface coverage (J'Sphere), their pore shape (YMC), or their bonding type and carbon content (Wakosil II). The use of these C18 stationary phases allows to reach more accurate conclusion on the comparison of the shape selectivity values provided either by the cis/. trans β-carotene selectivity or by the TRI/oTER or TbN/BaP ones. The extension of the studies to many other C18 stationary phases allows clarifying the relationships between the carotenoid test and the tests based on the use of PAH, as well as the usage limit of TRI/oTER and TBN/BaP selectivity in regards of the bonding density of the stationary phases for both monomeric and polymeric phases. By checking other aromatic compounds, another selectivity (anthracene/oTER) display greater correlation with the carotenoid test, that suggest an improvement of the relevance of this new compound couple for the steric selectivity study. © 2010 Elsevier B.V.


Gigant N.,CNRS Institute of Organic and Analytical Chemistry | Chausset-Boissarie L.,CNRS Institute of Organic and Analytical Chemistry | Gillaizeau I.,CNRS Institute of Organic and Analytical Chemistry
Organic Letters | Year: 2013

An efficient Pd-catalyzed decarboxylative cross-coupling reaction of simple enamides was achieved. Depending on the choice of the nitrogen-protecting group, a site-selective synthesis of mono- or diarylated framework(s) was performed under mild conditions. This unprecedented reactivity could be applied to the synthesis of a range of 2- or 2,4-diarylated nitrogen-containing bioactive derivatives. © 2013 American Chemical Society.


West C.,CNRS Institute of Organic and Analytical Chemistry | Lesellier E.,CNRS Institute of Organic and Analytical Chemistry
Journal of Chromatography A | Year: 2013

In supercritical fluid chromatography (SFC), the effects of adding a co-solvent to carbon dioxide are numerous. In this work, the changes in retention and selectivity occurring when the nature of the co-solvent (methanol, ethanol, isopropanol, acetonitrile) in the SFC mobile phase is varied, are studied on seven columns with different stationary phase chemistry (cyanopropyl-, pyridine-ethyl-, phenyl-oxypropyl-, phenyl-propyl-, phenyl-hexyl-, pentafluorophenyl-propyl- and octadecyl-bonded silica). Hierarchical cluster analysis and quantitative structure-retention relationships with the solvation parameter model are employed to evaluate these effects, based on the observed retention for over a hundred probe compounds. It appears that some columns are somewhat more affected than others by the change of solvent nature. Acetonitrile induces the strongest differences, essentially due to its poor capabilities as an eluent for bases and possibly because it does not adequately cover residual silanol groups. Ethanol appears to be a possible green alternative to the most-used methanol. Some hints on a possible partition-adsorption mixed mechanism are offered. Finally, sample applications with three different test mixtures relevant to cosmetic and pharmaceutical applications (flavanones, non-steroidal anti-inflammatory drugs and barbiturates) are presented. © 2013 Elsevier B.V.


Lesellier E.,CNRS Institute of Organic and Analytical Chemistry
Journal of Chromatography A | Year: 2015

Classification methods based on physico-chemical properties are very useful in analytical chemistry, both for extraction and separation processes. Depending on the number of parameters, several classification approaches can be used: by plotting two- or three-dimensional maps (triangles, cubes, spheres); by calculating comparison values for one system with reference to another one, i.e. the ranking factor F, or the Neue selectivity difference s2; or with chemometric methods (principal component analysis-PCA or hierarchical cluster analysis-HCA). All these methods display advantages and drawbacks: some of them are limited by the number of studied parameters (e.g. three for triangle or sphere plots); others require a new calculation when changing the reference point (F; s2), while for chemometric methods (PCA, HCA), the relationships between the clusters and the physico-chemical properties are not always easily understandable.From previous studies performed in supercritical fluid chromatography for stationary phase classification on the basis of linear solvation energy relationships (LSER) including five parameters, we developed a classification map called the σpider diagram. This diagram allows plotting in a two-dimensional map the location of varied systems, having as many parameters as the ones required getting a satisfactory classification. It can be three, five, eight, or any number.In the present paper, we apply this diagram, and the calculation mode to obtain this diagram, to different solvent classifications: Snyder triangle, solvatochromic solvent selectivity, Hansen parameters, and also to LSER Abraham descriptors and COSMO-RS parameters. The new figure based on Snyder data does not change the global view of groups, except by the use of corrected data from literature, and allows adding the polarity value onto the map. For the solvatochromic solvent selectivity, it leads to achieve a better view of solvents having no acidic character.For Hansen parameters, the "flattening" of the spherical view down to a single plane could be found easier to use. For COSMO-RS and with Abraham descriptor, a more subtle classification is achieved, mainly due to the use of five parameters instead of three. A strong reversed correlation is established between the Rohrschneider polarity P[U+02B9] and the normalized V (molecular volume) parameter.The study of the location of solvents used for reversed-phase liquid chromatography and the Arizona system for counter-current chromatography is discussed, as well as the replacement of unsafe solvents by greener ones, or the use of these classifications for the study of compound solubility.Besides, this paper also shows the ability to the spider diagram to plot on a single plane three axes from principal component analyses. © 2015 Elsevier B.V.


Lesellier E.,CNRS Institute of Organic and Analytical Chemistry
Journal of Chromatography A | Year: 2012

The chromatographic efficiency, in terms of plate number per second, was dramatically improved by the introduction of sub-two microns particles with ultra-high pressure liquid chromatography (UHPLC). On the other hand, the recent development of superficially porous particles, called core-shell or fused-core particles, appears to allow the achievement of the same efficiency performances at higher speed without high pressure drops. CO 2-based mobile phases exhibiting much lower viscosities than aqueous based mobile phases allow better theoretical efficiencies, even with 3-5μm particles, but with relative low pressure drops. They also allow much higher flow rates or much longer columns while using conventional instruments capable to operate below 400bar. Moreover, the use of superficially porous particles in SFC could enhance the chromatographic performances even more. The kinetic behavior of ODS phases bonded on these particles was studied, with varied flow rates, outlet (and obviously inlet) pressures, temperatures, by using a homologous series (alkylbenzenes) with 10% modifier (methanol or acetonitrile) in the carbon dioxide mobile phase. Results were also compared with classical fully porous particles, having different sizes, from 2.5 to 5μm. Superior efficiency (N) and reduced h were obtained with these new ODS-bonded particles in regards to classical ones, showing their great interest for use in SFC. However, surprising behavior were noticed, i.e. the increase of the theoretical plate number vs. the increase of the chain length of the compounds. This behavior, opposite to the one classically reported vs. the retention factor, was not depending on the outlet pressure, but on the flow rate and the temperature changes. The lower radial trans-column diffusion on this particle types could explain these results. This diffusion reduction with these ODS-bonded superficially porous particles seems to decrease with the increase of the residence time of compounds. © 2011 Elsevier B.V.


Lesellier E.,CNRS Institute of Organic and Analytical Chemistry
Journal of Chromatography A | Year: 2012

The recent introduction of new stationary phases for liquid chromatography based on superficially porous particles, called core-shell or fused-core, dramatically improved the separation performances through very high efficiency, due mainly to reduced eddy diffusion. However, few studies have evaluated the retention and selectivity of C18 phases based on such particles, despite some retention order change reported in literature between some of these phases. The carotenoid test has been developed a few years ago in the goal to compare the chromatographic properties of C18 bonded phases. Based on the analysis of carotenoid pigments by using Supercritical Fluid Chromatography (SFC), it allows, with a single analysis, to measure three main properties of reversed phase chromatography stationary phases: hydrophobicity, polar surface activity and shape selectivity. Previous studies showed the effect of the endcapping treatment, the bonding density, the pore size, and the type of bonding (monomeric vs. polymeric) on these studied properties, and described the classification map used for a direct column comparison. It was applied to ten ODS superficially porous stationary phases, showing varied chromatographic behaviors amongst these phases. As expected, due to the lower specific surface area, these superficially porous phases are less hydrophobic than the fully porous one. In regards of the polar surface activity (residual silanols) and to the shape selectivity, some of these superficially porous phases display close chromatographic properties (Poroshell 120, Halo C18, Ascentis Express, Accucore C18, Nucleoshell C18 on one side and Aeris Wide pore, Aeris peptide and Kinetex XDB on the other side), whereas others, Kinetex C18 and Halo peptide ES C18 display more specific ones. Besides, they can be compared to classical fully porous phases, in the goal to improve method transfer from fully to superficially porous particles. By the way, the paper also report the extension of the test to other ligands such as naphtyl, cholester, phenyl-hexyl, or to the new ODS bonded phases, such as charge surface hybrid phases, High Strength Silica, and Hybrid ones, and also presents results for identical brands using different particle size, such as Luna and Synergi phases. Phenyl-hexyl and napthyl ligands show rather close properties, low hydrophobicity, high polar surface activity and specific shape selectivity, whereas, at the opposite, the cholester phase display a polymeric behavior and a high hydrophobicity. Finally, additional classical (fully porous particles) C18 bonded phases are also reported to complete the data set presented in previous papers. © 2012 Elsevier B.V.


Gigant N.,CNRS Institute of Organic and Analytical Chemistry | Gillaizeau I.,CNRS Institute of Organic and Analytical Chemistry
Organic Letters | Year: 2012

An efficient domino approach for the diastereoselective synthesis of polyfunctionalized nitrogen-fused tetrahydroquinoline frameworks under mild conditions has been developed. The scope and limitation of this transformation were investigated by using a range of readily accessible enamides and benzyl azides. This method is also applicable to the formation of 2,3-functionalized enamides. © 2012 American Chemical Society.

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