Reversal of elution order of urea and thiourea derivatives of propranolol enantiomers on ionically versus covalently bound pirkle phases

Abstract

AbstractThe chromatographic performance of a series of urea and thiourea derivatives of (±)‐propranolol has been evaluated on three different Pirkle stationary phases. Seven different isocyanate reagents were used to generate a range of both aliphatic and aromatic urea derivatives with the isothiocyanates yielding the corresponding thiourea analogues. The Pirkle phases employed consisted of 3,5‐dinitrobenzoylphenylglycine and 3,5‐dinitrobenzoylleucine, both ionically and covalently bound to aminopropyl silica as well as phenethylpropylurea (covalently attached only). The urea derivatives were consistently more strongly retained on covalently bound columns than their thiourea counterparts. This is in contrast to the situation observed for the ionic columns, where the thiourea derivatives were the more strongly retained on the phenylglycine column and the more strongly retained in four of seven instances on the leucine column. The underlying mechanisms giving rise to these differences in retention are as yet unidentified but appear to involve the urea group.