Laureano Oliveros

Covalently bonded polysaccharide derivatives as chiral stationary phases in high-performance liquid chromatography

Polysaccharide derivatives have been extensively used as chromatographic chiral selectors in chiral stationary phases (CSPs) for the separation of enantiomers by HPLC. When coated onto a silica matrix, they represent nowadays one of the most popular type of CSPs. However, they are only compatible with a limited choice of solvents. The main drawback of these CSPs is related to the solubility of the chiral selector in a number of solvents, which limits their applicability. The different attempts which have been described up to now to overcome this problem by covalently fixing the chiral selector to a matrix are reviewed in this paper.

Chiral Chromatographic Discrimination Ability of a Cellulose 3,5-Dimethylphenylcarbamate/10-Undecenoate Mixed Derivative Fixed on Several Chromatographic Matrices

Abstract The properties as chiral selector in HPLC chiral stationary phases (CSPs) of a cellulose derivative bearing simultaneously 3,5-dimethylphenylamino carbonyl and 10-undecenoyl groups are described. This polysaccharide is reticulated (or bonded) on chromatographic supports such as silica gel, previously treated or not, graphite or alumina. The chiral stationary phases thus obtained are resistant to the usual solvents used in liquid chromatography and can be used on normal or reversed phase conditions. The results obtained on the resolution of racemic compounds with these stationary phases depend on the nature of the support. The best results were obtained with the chiral stationary phase in which the cellulose derivative is bonded on allyl silica gel.

Bonded cellulose-derived high-performance liquid chromatography chiral stationary phases I. Influence of the degree of fixation on selectivity

Four mixed 10-undecenoyl-3,5-dimethylphenylaminocarbonyl derivatives of cellulose, with an increasing proportion of alkenoyl groups, were synthesized and chemically bonded on allylsilica gel. The influence of the degree of fixation of the cellulose derivative on the matrix for the four resulting chiral stationary phases on their selectivity is discussed.

Ligand-exchange chromatography of enantiomeric amino acids on copper-loaded chiral bonded silica gel and of amino acids on copper(II)-modified silica gel

Abstract A method has been developed for the synthesis of a bonded phase that consists in attaching l -proline to triethoxypropylaminosilane and then bonding the final product to the silica gel microparticles. After treatment with copper(II) sulphate and elution with ammonia-water-acetonitrile mixtures, resolution of dl -tryptophan, phenylalanine and tyrosine is observed. A novel method has been found for ligand-exchange chromatography. Pure silica gel is treated with an ammoniacal solution of copper(II) sulphate; formation of copper(II) silicate occurs, the copper(II) ions being held strongly. A combined ligand-exchange and normal-phase partition mechanism was demonstrated and iso-capacity factor curves were determined for some amino acids. Example of separations of 20 common amino acids and of fragments of Metenkephalin are given, using isocratic elution and monitoring the column effluent at 210 nm with a UV detector.

3,5-Dimethylphenylcarbamates of amylose, chitosan and cellulose bonded on silica gel: Comparison of their chiral recognition abilities as high-performance liquid chromatography chiral stationary phases

Mixed 10-undecenoyl/3,5-dimethylphenylaminocarbonyl derivatives of amylose and chitosan were prepared and immobilized on allylsilica gel. The enantioselectivities of the resulting supports were compared to those of an analogous cellulose-derived chiral stationary phase previously prepared.

Chitosan derivatives as chiral selectors bonded on allyl silica gel: preparation, characterisation and study of the resulting high-performance liquid chromatography chiral stationary phases

Abstract Several mixed 10-undecenoyl/phenylaminocarbonyl or benzoyl derivatives of chitosan, differently substituted in the aromatic ring, were prepared, characterized and immobilized on allylsilica gel. The resulting high-performance liquid chromatography (HPLC) chiral supports were tested chromatographically. The influence of the starting polysaccharidic material, as well as that of the solvents used as mobile phase modifiers, on the preparation and performance of the resulting chiral stationary phases (CSPs) is discussed.

Solvent versatility of bonded cellulose-derived chiral stationary phases for high-performance liquid chromatography and its consequences in column loadability

The chromatographic behaviour of a 10-undecenoate/3,5-dimethylphenylcarbamate of cellulose bonded on allylsilica gel is tested using four organic mobile-phase modifiers (2-propanol, chloroform, tetrahydrofuran and ethyl acetate). The advantages of the broad choice of solvents offered by this kind of chiral stationary phases and their resistance are discussed. The loadability of the column and its dependence both on the racemate to be resolved and on the solvent used as mobile phase are also discussed.

Bonded cellulose-derived high-performance liquid chromatography chiral stationary phases: III. Effect of the reticulation of the cellulose derivative on performance

Abstract The influence of the reticulation of a mixed 10-undecenoyl/3,5-dimethylphenylaminocarbonyl derivative of cellulose on the enantioselectivity of several high-performance liquid chromatography (HPLC) chiral stationary phases (CSPs) was investigated. Three cellulose-derived chiral columns were obtained by reticulation of the same cellulose derivative on three end-capped silica gels of different pore size. The performance of the obtained supports was studied and compared with that of three bonded cellulose-derived CSPs prepared by fixation of the same cellulose derivative on allylsilica gel.

Bonded cellulose-derived high-performance liquid chromatography chiral stationary phases. II. Influence of the porosity of the silica gel matrix on performance.

Two cellulose derivatives bearing simultaneously 10-undecenoyl and 3,5-dimethylphenylaminocarbonyl groups in different ratios were chemically bonded on allylsilica gels of different porosity. The systematic study of the effect of the silica gel pore size on the bonding of the polysaccharide derivative and on the performance of the resulting chiral supports is presented.

Facile synthesis and highly efficient resolution of a constrained cyclopropane analogue of phenylalanine

Abstract Enantiomerically pure (2R,3R)- and (2S,3S)-1-(N-tert-butoxycarbonyl)amino-2,3-diphenyl-1-cyclopropanecarboxylic acids have been prepared by HPLC resolution of a racemic precursor. The complete stereoselectivity of the cyclopropanation process, together with the high efficiency of the subsequent transformations and the chromatographic resolution, allowed the preparation of optically pure compounds on a multigram scale.