Enantioseparation of N-protected A-amino acids on a quinine-based stationary phase under anion exchange chromatographic conditions

KEUNCHKARIAN, SONIA; PADRÓ, JUAN M.; CASTELLS, CECILIA B.

Florianapolis, Brasil

Congreso; COLACRO XII - Latin American Congreso of Chromatography and Related Tecniques; 2008

International Institute of Chromatography (I.I.C.).

Several important chemical compounds are optically active molecules. The analysis of these enantiomers requires of highly efficient chiral separation methods, and high performance liquid chromatography (HPLC) using chiral stationary phases (CSPs) constitutes a good option. The use of CSPs with analytical purposes has many advantages over other strategies. For instance, previous reaction with highly a pure enantiomer to yield the diasteromers is not required, and no additional chiral additives into the mobile phase are needed, thus equilibration times are usually shorter. Several CSPs have been developed, and many of them are commercially available. However, the search of chiral materials that can be used to build CSPs with different and improved properties is permanent. The purpose of this work was to develop CSPs from the natural and accessible alkaloid quinine, which has been chemically attached to a modified silica support. Thereby, 3-mercaptopropylsilica was initially synthesized and then, quinine was linked to the surface by using AIBN as radical initiator. In order to obtain a chiral material with a satisfactory coverage density of chiral selector, several synthesis conditions have been evaluated. We studied different starting material (silica surface area), surface pretreatment, and different synthesis conditions. Elemental analysis was carried out on the prepared CSPs. Finally, the stationary phases were slurry packed into stainless steel columns. The enantiorecognition ability towards some racemic families, mainly ƒÑ-aminoacids, and the whole chromatographic performance of these columns has been tested. Moderate to high resolutions of optical isomers of natural ƒÑ-aminoacids, which were previously derivatized with a chromophore (Sanger¡¦s reagent: 2,4-dinitrofluorbenzene) and a fluorophore (9-fluorenylmethyl chloroformate, FMOC), respectively, by using these CSPs under ionic exchange condition were achieved. All the chromatographic variables that affect retention and selectivity have been extensively assessed: nature and percentage of organic solvent, pH of the mobile phase, ionic strength and temperature. The results were encouraging, since it could be optimized the separation of these analytes within reasonable analysis time.