Chiral Ligand‐Exchange Resolution of Underivatized Amino Acids on a Dynamically Modified Stationary Phase for RP‐HPTLC

Abstract

The synthesis of Spi(τ-dec), derived from the selective alkylation of L-spinacine (4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid) at the τ-nitrogen of its heteroaromatic ring, with a linear hydrocarbon chain of 10 carbon atoms, is described here for the first time. Spi(τ-dec) was successfully employed in the past to prepare home-made chiral columns for chiral ligand-exchange high-performance liquid chromatography. In the present article a new method is described, using Spi(τ-dec) as a chiral selector in high-performance thin-layer chromatography (HPTLC): commercial hydrophobic plates were first coated with Spi(τ-dec) and then treated with copper sulfate. The performance of this new chiral stationary phase was tested against racemic mixtures of aromatic amino acids, after appropriate optimization of both the conditions of preparation of the plates and the mobile phase composition. The enantioselectivity values obtained for the studied compounds were higher than those reported in the literature for similar systems. The method employed here for the preparation of chiral HPTLC plates proved practical, efficient, and inexpensive.

Direct chiral resolution of underivatized amino acids on a stationary phase dynamically modified with the ion‐exchanger Nτ‐decyl‐l‐spinacine

“…Eluent pH was adjusted by addition of suitable amounts of standard KOH or HClO 4 solutions, under potentiometric control. The synthesis and characterization of the chiral selector Spi(τ‐dec) are described elsewhere .…”

“…The chiral selector N τ ‐decyl‐ l ‐spinacine (Spi(τ‐dec)) (Scheme ), has been used in the past to prepare chiral stationary phases for chiral ligand‐exchange chromatography (CLEC), by means of the dynamic column coating procedure . Spi(τ‐dec) proved to be a good chiral selector for underivatized amino acid enantiomers, when a buffered mobile phase, containing the Cu 2+ ions, was used (CLEC mechanism).…”

Simultaneous separation of atenolol enantiomers and its acid/alkaline degradation impurities on mixed‐mode chiral ligand exchange stationary phases

“…12 Since Davankov and Rogozhin 13 successfully achieved the separation of amino acid enantiomers by CLEC in the 1960s, the ligand exchange stationary phase has developed rapidly in recent years. 14,15 A series of native and functionalized ligand exchange chiral stationary phases (CSPs) with different matrices have been developed. Davankov et al 16 bonded L-hydroxyproline on the styrene-divinylbenzene resin to achieve chiral separation of racemic amino acids with a relatively lower column efficiency.…”

“…The chiral selector and the analyte are adsorbed in the coordination sphere of the central metal ions, which makes it suitable for the separation of chiral compounds with two or more chelating sites 12 . Since Davankov and Rogozhin 13 successfully achieved the separation of amino acid enantiomers by CLEC in the 1960s, the ligand exchange stationary phase has developed rapidly in recent years 14,15 . A series of native and functionalized ligand exchange chiral stationary phases (CSPs) with different matrices have been developed.…”