Enantioseparation and recognition mechanisms of dinitrobenzoyl-derivatized amino acids and amino alcohols on chiral stationary phases consisting of cyanuric chloride with (S or R)-phenylalanyl-(S or R)-1-(1-naphthyl)ethylamide substituent

Chiral stationary phases (CSPs) derived from (S or R)-phenylalanyl-(S or R)-1-(1-naphthyl)ethylamide as a chiral selector were prepared by bending a chiral moiety onto 3-aminopropylsilane-modified silica gels through the s-triazine ring. These phases provide satisfactory recognition ability to separate most enantiomers of methyl esters of N-(3,5-dinitrobenzoyl) amino acids except phenylglycine. However, only the CSP with the (S,S) configuration provides satisfactory recognition ability to separate most enantiomers of N-(3,5-dinitrobenzoyl) amino alcohols except phenylglycinol and phenylalaninol. The CSPs with either (S,R) or (R,S) configuration provide no enantioseparation for most amino alcohols, except phenylglycinol. The chromatographic results also show that alteration of the absolute configuration of the CSP from the (S,S) to the (S,R) form decreases enantioseparation of most amino acids and amino alcohols. With the aid of AM1 calculations, elution orders of enantiomers of amino acids on SS-CSP and SR-CSP can be predicted. The calculations reveal that two mechanisms of chiral recognition for CSP bearing two chiral centers are involved in the phenylalanyl and 1-(1-naphthyl)ethylamido moieties of CSP. In the case of SS-CSP, the phenylalanyl moiety of CSP plays the dominant role in chiral recognition; in the case of SR-CSP, the 1-(1-naphthyl)ethylamido moiety of the CSP plays the dominant role. These theoretical predictions are consistent with the experimental observations in a high-performance liquid chromatograph.