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

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 beta-blockers. The reagent reacts with beta-blockers at 65 degrees C for 90 min in aqueous acetonitrile containing 0.05% triethylamine to produce the corresponding pair of diastereomers. No racemization occurs during the lagging reaction under these conditions. From results of the time-course study of oxprenolol the reactivities of the enantiomers of beta-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 beta-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 beta-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 beta-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. (C) 1997 Elsevier Science B.V.