Preparation and evaluation of chiral high-performance liquid chromatographic stationary phases of mixed character (π-donor and π-acceptor) for the resolution of racemic compounds

Abstract

Up to now, most stationary phase have had either π-acceptor or π-donor characteristics. In this study, the behaviour of stationary phases having mixed characteristics (π-donor and π-acceptor) was investigated and compared with that of silicas bonded either with the same π-acceptor group or with the same π-donor group. The chiral selectors ( S)-1-(α-napthyl)ethylamine associated with ( S)-phenylalanine and ( S)-N-(3,5,-dinitrobenzoyl)phenylalanine, were bound to a γ-aminopropylsilanized silica gel. Stationary phases possessing mixed character were obtained either by bonding two chiral selectors on the same silica or by mixing two chiral silicas bonded with only one of two chiral selectors. The selectivity of these chiral stationary phases possessing π-donor and π-acceptor characters are similar; the α value are intermediate between those shown by two chiral stationary phases with only π-donor or π-acceptor character. The results obtained in the resolution of a series of racemic compounds with either π-donor or π-acceptor character show that the chiral recognition mechanism is probably more complex than the conventional face-to-face π-interactionss usually described.