Unusual resolution of N-(3,5-dinitrobenzoyl)-α-amino acids on a chiral stationary phase based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid

Abstract

While HPLC chiral stationary phases (CSPs) based on chiral crown ethers have been known useful for the resolution of only racemic primary amino compounds or some secondary amino compounds, in this study, we first demonstrated that the CSP based on (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid is also useful for the resolution of N-benzoyl-α-amino acids, which do not contain a primary or secondary amino group. Especially, N-(3,5-dinitrobenzoyl)-α-amino acids were resolved better than corresponding N-(3-nitrobenzoyl)- or N-benzoyl-α-amino acids, the separation ( α) and the resolution factors ( R S) for the resolution of eight N-(3,5-dinitrobenzoyl)-α-amino acids being in the range of 1.06–1.81 and 0.54–2.81, respectively. The optimum mobile phase condition was the mixture of acetic acid–triethylamine–acetonitrile with the ratio of 0.05/0.25/100 (v/v/v).