Chiral ligand-exchange chromatography on an RP HPLC column coated with a new chiral selector derived froml-spinacine

Abstract

SummaryA commercial reversed-phase (RP) C18 HPLC column has been dynamically coated with the chiral selector N<n-decyI-L-spinacine and then loaded with copper(ll) ions. Several racemic mixtures of underivatized amino acids and oligopeptides were resolved on the column by chiral ligand-exchange chromatography. The most important experimental conditions affecting column efficiency, retention, and selectivity (temperature and mobile phase flow rate and composition) were extensively investigated.

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

“…The chiral discrimination method described here is simpler than that previously reported for the same chiral selector, based on the ligand‐exchange mechanism , because a pure aqueous buffer can be employed as mobile phase, without the addition of complexing metal ions. In addition, the retention times are much shorter for the aromatic and aliphatic amino acids as well as for oligopeptides, still maintaining a good enantioseparation.…”

“…It is doubtless that the separation of amino acids in their native form using the direct procedure is advantageous from many points of view . The most common chiral selectors working as active sites in CSPs employed for the optical recognition of amino acids are the following: ligand exchangers, requiring the presence of a complexing metal ion ; crown ethers ; ion exchangers ; polysaccharides ; cyclodextrins ; macrocyclic glycopeptide antibiotics (e.g. avoparcin, teicoplanin, vancomycin, or ristocetin) .…”

Chromatography of amino acids and short peptides. New advances

“…Column was thermostatted in the range 15 -60°C, and the influences of flow rate (0.2-1.0 mL/min), concentration of Cu acetate in the mobile phase and the pH on the mobile phase on the enantiomeric separation of free amino acids and some dipeptides were investigated in detail. It was found that the preparation of the dynamically coated column is easy and can be employed for the chiral separation of free amino acids and peptides (Remelli et al, 2002).…”

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

“…In order to evaluate the effect of mobile phase pH on retention and selectivity, a mixture of MeOH / acetate buffer solution 1 · 10 -2 mol dm -3 (adjusted at different pH values, in the range of 3.5-6.0) and copper perchlorate 1 · 10 -3 mol dm -3 30:70 was employed as eluent. The effect of pH was reported to be very important in the corresponding HPLC system, 33 where it is one of the most important parameters ruling the amino acid retention. Data reported in Table 3 show that, in the present system, the effect of pH on retention is rather low; in the case of Trp, the best enantioselectivity is observed at the lowest pH value, in agreement with the literature.…”

“…[30][31][32] In this molecule, the long alkyl chain acts as an anchor for the RP-18 silica support, while the His residue can form stationary ternary copper complexes with the enantiomers moving in the mobile phase. More recently, 33 the use in HPLC-CLEC of a new chiral selector, Spi(τ-dec), has been described; here the starting amino acid (and the chiral center) was L-spinacine ((4,5,6,7tetrahydro-1H-imidazo [4,5 -c] pyridine -6 -carboxylic acid), Spi). For both those chiral selectors the chromatographic results were encouraging.…”