1. A thermodynamic study of the temperature-dependent elution order of cyclic alpha-amino acid enantiomers on a copper(II)-D-penicillamine chiral stationary phase
M Schlauch, A W Frahm Anal Chem. 2001 Jan 15;73(2):262-6. doi: 10.1021/ac0009999.
The reversal of the elution order of cyclic alpha-amino acid enantiomers as a function of the temperature on a copper(II)-N,S-dioctyl-D-penicillamine ligand-exchange column is described. The thermodynamic parameters accounting for the retention and the separation of analytes were determined by means of van't Hoff plots. The influence of different chromatographic conditions on these parameters was investigated, showing little effect of the Cu(II) concentration in the eluent but strong influence of the organic modifier content on the separation. Further, the pH of the mobile phase was found to be a determining factor for the retention of the analytes. Based on these findings, a separation mechanism is postulated comprising the importance of complex formation for primary docking at the stationary phase, while hydrophobic interactions are crucial for chiral discrimination.
2. Direct enantiomeric separation of platelet-activating factor receptor antagonist SM-10661 by ligand-exchange high-performance liquid chromatography with a copper (II) N,S-dioctyl-D-penicillamine complex
M Okamoto, Y Ueda, K Takahashi, H Nakazawa, T Doi Biosci Biotechnol Biochem. 1995 Sep;59(9):1740-1. doi: 10.1271/bbb.59.1740.
The enantiomeric separation of SM-10661, a platelet activating factor receptor antagonist, was investigated by HPLC using ligand-exchange chiral stationary phases. The stereoisomers of SM-10661 could all be separated by ligand-exchange HPLC with a Cu(II) N,S-dioctyl-D-penicillamine complex (Sumichiral OA-5000). The mechanism for the resolution includes the involvement of hydrophobic interactions between SM-10661 and Cu(II) D-penicillamine.
3. Direct HPLC separation of carnosine enantiomers with two chiral stationary phases based on penicillamine and teicoplanin derivatives
Laura Fumagalli, Lucia Pucciarini, Luca Regazzoni, Ettore Gilardoni, Marina Carini, Giulio Vistoli, Giancarlo Aldini, Roccardo Sardella J Sep Sci. 2018 Mar;41(6):1240-1246. doi: 10.1002/jssc.201701308. Epub 2018 Jan 2.
Carnosine is present in high concentrations in specific human tissues such as the skeletal muscle, and among its biological functions, the remarkable scavenging activity toward reactive carbonyl species is noteworthy. Although the two enantiomers show almost identical scavenging reactivity toward reactive carbonyl species, only d-carnosine is poorly adsorbed at the gastrointestinal level and is stable in human plasma. Direct methods for the enantioselective analysis of carnosine are still missing even though they could find more effective applications in the analysis of complex matrices. In the present study, the use of two different chiral stationary phases is presented. A chiral ligand-exchange chromatography stationary phase based on N,S-dioctyl-d-penicillamine resulted in the direct enantioseparation of carnosine. Indeed, running the analysis at 25°C and 1.0 mL/min with a 1.5 mM copper(II) sulfate concentration allowed us to obtain separation and resolution factors of 3.37 and 12.34, respectively. However, the use of a copper(II)-containing eluent renders it hardly compatible with mass spectrometry detectors. With the teicoplanin-based stationary phase, a mass spectrometry compatible method was successfully developed. Indeed, a water/methanol 60:40 v/v pH 3.1 eluent flowed at 1.0 mL/min and with a 25°C column temperature produced separation and resolution factors of 2.60 and 4.16, respectively.
