N-ARYLCARBAMOYL DERIVATIVES OF AMINO-ACIDS AS CHIRAL STATIONARY PHASES FOR OPTICAL RESOLUTION BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A series of twelve chiral stationary phases (CSPs) with arylcarbamoyl derivatives of amino acids bonded either ionically or covalently to 3-aminopropyltriethoxysilane-modified silica gel were prepared. These CSPs, except covalent CSP containing phenylcarbamoyl-(S)-phenylglycine, provide recognition ability for the separation of enantiomeric amide derivatives of amino-acids, amino alcohols, amines and acids by high-performance liquid chromatography. Generally, the ionic type of CSPs were observed to be more effective than the corresponding covalent type. Among the twelve CSPs, the ionic type of CSPs bearing (S)-phenylcarbamoyl-(S)- or -(R)-phenylglycine show the best chiral resolution performance for the four types of enantiomeric solutes. Especially for enantiomeric ibuprofen, the separation factor is the best among all reported values. Based on the chromatographic behaviour in this study, it is concluded that the stereoselectivity is due to the stereochemical elements of the CSPs, the hydrogen-bonding interaction on the urea linkage, and the pi-pi interactions of the aromatic rings. A chiral recognition model of these CSPs for enantiomer separations is proposed.