Enantioseparation of chiral aromatic amino acids by capillary electrophoresis in neutral and charged cyclodextrin selector modes

Abstract

Simultaneous enantioseparations of 15 racemic aromatic amino acids and L-mimosine for their chiral discrimination were achieved by neutral selector-modified capillary electrophoresis (CE) and by charged selector-modified CE. Among the diverse cyclodextrins (CDs) examined, hydroxypropyl (HP)-alpha-CD as the neutral selector and highly sulfated (HS)-gamma-CD as the charged selector provided best chiral environments of different enantioselectivities. Fairly good enantiomeric resolutions were achieved with the HP-alpha-CD mode except for racemic 6-hydroxy-3,4-dihydroxyphenylalanine, threo-3,4-dihydroxyphenylserine and homophenylalanine while high-resolution separations of all the enantiomeric pairs were achieved in the HS-gamma-CD mode except that L-mimosine was not detected and a partial resolution (0.6) for threo-3,4-dihydroxyphenylserine enantiomers. Relative migration times to that of internal standard under the respective optimum conditions were characteristic of each enantiomer with good precision (% RSD: 0.7-3.8), thereby enabling to cross-check the chemical identification of aromatic amino acids and also their chiralities. The method linearity was found to be adequate (r> 0.99) for the chiral assay of the aromatic amino acids investigated. When applied to extracts of three plant seeds, nonprotein amino acids such as L-mimosine (42 nug/g) from Mimosa pudica Linné, and L-3,4-dihydroxyphenylalanine (268 nug/g) from Vicia faba were positively detected along with L-tryptophan, L-phenylalanine and L-tyrosine.

Evaluation of enantioselective gas chromatography for the determination of minute deviations from racemic composition of α‐amino acids with emphasis on tyrosine: Accuracy and precision of the method

“…The buffer consisted of 50 mmol/l phosphate (KH 2 PO 4 /H 3 PO 4 ) at pH 2.5, plus either 1% (¼4.3 mmol/l) of highly sulfated g-cyclodextrin (HS-g-CD, Michigan Diagnostics, LLC, Troy, MI) or 30% (¼254 mmol/l) 2-hydroxypropyl-a-cyclodextrin (2-HP-a-CD, Fluka Chemie, Buchs, Switzerland). Between runs, the capillary was rinsed for 5 min with NaOH solution (0.1 mol/l) followed by backround electrolyt at 1 bar 48 .…”

Enantiomeric separation of ornithine in complex mixtures of amino acids by EKC with off-line derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate

“…Preliminary experiments were achieved with a group of six amino acids including Orn and other five protein amino acids usually present in fermented foods (Lys, Arg, Glu, Asp, and Gln). First, due to the good enantiomeric separations obtained for some compounds using highly anionic CDs as chiral selectors under acidic conditions [32,33], HS-␤-CD was selected as chiral selector. This CD was employed in an acidic buffer (50 mM phosphate buffer at pH 2.0) and with reverse polarity due to its high electrophoretic mobility towards the anode and the negligible EOF at pH 2.0.…”

Chiral Discrimination of Aromatic Amino Acids by Capillary Electrophoresis in (+)- and (-)-(18-Crown-6)-2,3,11,12-tetracarboxylic Acid Selector Modes

“…All analytes used in this study were available from prior studies. 8 (+)-and (−)-18C6H 4 were purchased from Fluka and Aldrich, respectively. A racemic mixture of baclofen, 3,4-dihydroxyphenylalanine and 3-hydroxyphenylglycine was enriched with enantiomerically pure (R)-baclofen, L-forms of 3,4-dihydroxyphenylalanine and 3-hydroxyphenylglycine in excess (3 : 1).…”

“…Based on this concept, simultaneous chiral discrimination of 15 racemic aromatic amino acids was achieved with chiral CE in neutral and charged cyclodextrin modes in our previous report. 8 The surest way of the accurate chiral discrimination is the reversal of enantiomer migration order (EMO). [9][10][11][12][13][14][15][16] It is especially desirable when peak tailing, fronting or overlapping is observed.…”