The HPLC Enantioresolution of Phenyl Isocyanated Amino Acids, Peptides and Amino Alcohols on Cyclodextrin Bonded Phases Using the Acetonitrile-Based Mobile Phase

A variety of amino acids (primary and secondary), peptides and amino alcohols are pre-column phenyl isocyanated in alkaline medium and enantioresolved on the naphthylethylcarbamated β-cyclodextrin (i.e., RN- and SN-β-CD) bonded chiral phases (CSPs) using the acetonitrile-based mobile phase and on a native β-cyclodextrin (β-CD) phase for comparison. The resolution is believed to be a result of the hydrogen bonding between the secondary hydroxyl groups of cyclodextrin and the functional groups of analyte and is enhanced as the amino and the carboxyl groups are attached to the stereogenic center of analyte. Also, the enhancement is observed if the steric hindrance between the side-chain group of amino acid and the chiral selector exists. However, the resolution is deteriorated in the case that the side-chain group close to the stereogenic center of amino acid becomes bulky or is capable of forming hydrogen bonding with chiral selector. The aromatic moiety of the tagging reagent not only contributes the retention, but also benefits the resolution in some cases on the RN- and SN-β-CD phases through π-π interaction. The resolution is either not observed or unsatisfactory in the reversed-phase mode.