Enantioseparation of β-blockers labelled with a chiral fluorescent reagent, R(−)-DBD-PyNCS, by reversed-phase liquid chromatography

Abstract

A fluorescent chiral tagging reagent, 4-(3-isothiocyanatopyrrolidin-1-yl)-7-( N, N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole [R(−)-DBD-PyNCS], has been used for the liquid chromatographic resolution of racemic pairs of β-blockers. The reagent reacts with β-blockers at 65°C for 90 min in aqueous acetonitrile containing 0.05% triethylamine to produce the corresponding pair of diastereomers. No racemization occurs during the tagging reaction under these conditions. From results of the time-course study of oxprenolol the reactivities of the enantiomers of β-blockers with R(−)-DBD-PyNCS are comparable. The optimum excitation and emission wavelengths of the resulting derivatives were ca. 460 and 550 nm, respectively. The derivatives of β-blockers were efficiently resolved by a reversed-phase column with water-acetonitrile containing 0.1% trifluoroacetic acid as the eluent. The resolution (Rs) values of the diastereomers derived from 10 β-blockers were in the range of 1.54–4.80. The Rs value for timolol was 0.643. The detection limits (signal-to-noise ratio of 2) were one or two orders of magnitude lower with β-blockers having the iso-propylamino structure (15–300 fmol) than with those having the tert-butylamino structure (1.25–8.00 pmol). The proposed procedure was applied to the determination of R(+)- and S(−)-propranolol in rat plasma and saliva after oral administration of R(+)-propranolol hydrochloride or S(−)-propranolol hydrochloride.