Abstract
Some urea derivatives of chiral amino acids and amines have been developed as novel stationary phases for enantiomer separation by high performance liquid chromatography. The very large separation factors were obtained for separations of N-acetyl-DL-amino acid methylesters upon N- (t-butylaminocarbonyl)L-valyl-aminopropyl silica gel eluting with 2-propanolhexane (4:96), e. g. leucine 1.61, isoleucine 1.59, valine 1.49 etc. Excellent separations of N-3, 5- dinitrobenzoyl derivatives of racemic amines and amino acid methyl esters, and racemic carboxylic acid 3, 5- dinitroanilides were achieved upon (R)-1-(α-naphthyl)ethyl aminocarbonylaminopropyl silica gel eluting with hexane-dichloromethane-ethanol mixture (15:4:1) (separation factors:N-3, 5-dinitrobenzoyl-1-phenylethylamine 1.85, N-3, 5-dinitrobenzoyl valine methyl ester 2.02, 1-methylphenylacetic acid 3, 5-dinitroanilide 2.11 etc.). It should be emphasized that bonding of urea nitrogen to the chiral center is very responsible as the active sites for the diastereomeric hydrogen bond association in separation of enantiomers by high performance liquid chromatography.
