1. Dynamic ligand-exchange chiral stationary phase from S-benzyl-(R)-cysteine
B Natalini, R Sardella, A Macchiarulo, R Pellicciari Chirality. 2006 Aug;18(7):509-18. doi: 10.1002/chir.20280.
S-benzyl-(R)-cysteine (R-SBC) is a new chiral ligand-exchange stationary phase which has proved to be effective in the analytical separation of some natural and unnatural underivatized amino acids with fair to good separation and resolution factors. The dynamic coating of the RP-18 solid support with S-Benzyl-(R)-cysteine (R-SBC) gives rise to a stable and efficient chiral stationary phase (CSP) that has been successfully employed. The mechanism of chiral recognition is discussed and a molecular modeling study aimed at identifying molecular descriptors responsible for observed different behaviours of analytes upon different albeit closely related selectors is discussed.
2. Descriptive structure-separation relationship studies in chiral ligand-exchange chromatography
Benedetto Natalini, Antonio Macchiarulo, Roccaldo Sardella, Alberto Massarotti, Roberto Pellicciari J Sep Sci. 2008 Jul;31(13):2395-403. doi: 10.1002/jssc.200800102.
A new approach to model and interpret the separation of amino acid enantiomers is described. The descriptive structure-separation relationship (DSSR) study of a set of amino acid enantiomer couples analyzed with two chiral selectors S-benzyl-(R)-cysteine ((R)-SBC) and S-trityl-(R)-cysteine ((R)-STC) has been performed with the aim to highlight the molecular properties of the analyte affecting the enantiodiscrimination process. Although with some exceptions, the classification models obtained with (R)-STC indicate that the partial positive surface area (PPSA-1) is the suitable descriptor to account for the separation of both (R)- and (S)-enantiomers. On the other hand, two different descriptors characterize the separation process with (R)-SBC. While fractional negatively charged partial surface area (FNSA-3) results the discriminating descriptor for (R)-enantiomers, the relative polar surface area (RPSA) is able to best discriminate among (S)-enantiomers.
3. S-trityl-(R)-cysteine, a powerful chiral selector for the analytical and preparative ligand-exchange chromatography of amino acids
Benedetto Natalini, Roccaldo Sardella, Antonio Macchiarulo, Roberto Pellicciari J Sep Sci. 2008 Mar;31(4):696-704. doi: 10.1002/jssc.200700511.
S-trityl-(R)-cysteine [(R)-STC] is the new selector of a dynamically coated, chiral ligand-exchange stationary phase which proved to be highly effective in both analytical and preparative-scale separation of enantiomers of some natural and unnatural underivatized amino acids, with good separation and resolution factors. With the aim of identifying the best chromatographic conditions suitable for the preparative-scale separations, some parameters controlling retention, separation and resolution factors (such as the type and amount of cupric salt and the eluent pH) were investigated. The relatively easy removal of the Cu(II) ions renders this technique suitable for obtaining small amounts of enantiomerically pure samples for preliminary biological evaluations.