Chiral ligand exchange capillary electrophoresis using borate anion as a central ion

Abstract

Native DL-pantothenic acid, having a 1,3-diol structure, was chirally resolved by ligand exchange capillary electrophoresis using (S)-3-amino-1,2-propanediol as a chiral selector and the borate anion as a central ion. The optimum conditions for both high resolution and short migration time of DL-pantothenic acid were found to be 200 mM (S)-3-amino-1,2-propanediol and 200 mM borate buffer (pH 9.2) containing 15% methanol with an applied voltage of +25 kV at 20 degrees C, using direct detection at 200 nm. With this system, the resolution (Rs) of racemic pantothenic acid was approximately 1.7. When (S)-1,2-propanediol, (S)-1,2,3-propanetriol, (S)-1,3-butanediol or (S)-1-amino-2-propanol were used as chiral ligand instead of (S)-3-amino-1,2-propanediol, DL-pantothenic acid was not enantioseparated. When borate was replaced with Tris or butylborate, no chiral separation was achieved. Therefore, the ionic interaction between the amino and carboxyl groups of the ternary complex may play an important role in the enantioseparation of DL-pantothenic acid by the proposed CE system.

Chiral separations by capillary electrophoresis: Recent developments and applications

“…A comprehensive overview of the selectands involved and the selectors used is given by Schmid et al [77] and Davankov [78]. Recently, Kodama et al [79] have described chiral ligand exchange CE using borate anion as a central ion.…”

Mechanism of enantioseparation of DL‐pantothenic acid in ligand exchange capillary electrophoresis using a diol–borate system

“…Figure 2 shows the 13 C NMR spectra of D-PTA and the D-PTA-borate-SAP ternary system. We adjusted pH of the solutions to 9.2 consistent with the CE experiments (vide supra) [18] by addition of aqueous NaOH, where carboxyl and amino groups in D-PTA and SAP are considered car- boxylate and ammonium groups, respectively (Fig. 1).…”

“…In the previous work, we introduced borate anion as the central ion of the chiral selector [18]. By using a 1,2-diol, (S)-3-amino-1,2-propanediol (SAP) (Fig.…”

Chiral resolution of monosaccharides as 1‐phenyl‐3‐methyl‐5‐pyrazolone derivatives by ligand‐exchange CE using borate anion as a central ion of the chiral selector

“…Further investigations with chiral ligand exchange CE have been described in recent reviews [3][4][5][6]. In these CE studies, copper(II) complexes with amino acids or their derivatives have been widely used as chiral selectors for the enantioseparation of amino acids, their derivatives and a-hydroxy acids, where the ternary copper(II) complexes are formed by the ligand-exchange reaction of the chiral selector with the racemic analyte [7,8].Recently, we found that some diols can be enantioseparated by ligand-exchange CE with borate anion as a central ion of the chiral selector [9,10] with the knowledge that 1,2-and 1,3-diols form considerably stable borate ester complexes in a moderately alkaline aqueous solution [11][12][13][14], where free borate ion, monocyclic and dicyclic (spirocyclic) complexes coexist in the solution [15,16]. By using a 1,2-diol, (S)-3-amino-1,2-propanediol (SAP), DL-pantothenic acid, which has a 1,3-diol structure, was successfully resolved by ligand-exchange CE [9] and the enantioseparation mechanism was also investigated [17].…”

“…By using a 1,2-diol, (S)-3-amino-1,2-propanediol (SAP), DL-pantothenic acid, which has a 1,3-diol structure, was successfully resolved by ligand-exchange CE [9] and the enantioseparation mechanism was also investigated [17]. Furthermore, neutral 1,2-diol compounds (1-phenyl-1,2-ethanediol, 3-phenoxy-1,2-propanediol and 3-benzyloxy-1,2-propanediol) were enantioseparated by ligand-exchange MEKC using (1S,2S,3R,5S)-pinanediol as a chiral selector ligand [10].…”