title: Liquid chromatographic enantioseparation of spin-labelled beta-amino acids.
abstract: Direct and indirect high-performance liquid chromatographic (HPLC) methods were developed for the enantioseparation of spin-labelled, cyclic, chiral beta-amino acids containing nitroxide free radicals, trans-3-amino- 1-oxyl-2,2,5,5-tetramethylpyrrolidine-4-carboxylic acid (trans-POAC), cis-4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylic acid (cis-beta-TOAC) and their N-Fmoc-protected analogues, synthesized in racemic and enantiomerically pure forms. The direct method involved the use of a Chiralcel OD-RH column, while indirect separation was carried out by application of either 2,3,4,6-tetra-O-acetyl-beta-D-glucopyranosyl isothiocyanate or (S)-N-(4-nitrophenoxycarbonyl)-phenylalanine methoxyethyl ester as chiral derivatizing agent. Use of 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide (Marfey's reagent) as chiral derivatizing agent failed because of the low of yield of the derivatization reaction. Selection and variation of the mobile phase was restricted by the sensitivity of the spin-labelled amino acids to acidic conditions. Conditions affording the best resolution were found and the differences in separation capability of the methods were noted. The sequence of elution of the enantiomers was determined by different methods and, in the case of the beta-TOAC analogues, the absolute configurations of the enantiomers corresponding to each peak were identified.
authors.affiliation: Department of Inorganic and Analytical Chemistry, University of Szeged, Dóm tér 7, H-6720 Szeged, Hungary. apeter@chem.u-szeged.hu
authors.forename: Antal
authors.initials: A
authors.lastname: Péter
authors.forename: Roland
authors.initials: R
authors.lastname: Török
authors.forename: Karen
authors.initials: K
authors.lastname: Wright
authors.forename: Michel
authors.initials: M
authors.lastname: Wakselman
authors.forename: Jean Paul
authors.initials: JP
authors.lastname: Mazaleyrat
mesh_terms: D000596:Amino Acids / Q000737:chemistry / Q000302:isolation & purification*; D002851:Chromatography, High Pressure Liquid; D013113:Spin Labels; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D013113:Spin Labels