Enantiomeric separation and spectrofluorometric detection of the racemic drugs, (±)-1-(2,6-dimethylphenoxy)-2-propamine (mexiletine) and (3RS)-4-amino-3-hydroxybutanoic acid (GABOB), derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole on a phenylcarbamylated cyclodextrin bonded stationary phase

Abstract

(±)-Mexiletine [(±)-1-(2,6-dimethylphenoxy)-2-propamine] and (3RS)-4-amino-3-hydroxybutanoic acid (GABOB) were derivatized with a fluorogenic reagent, 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). They were then separated on a phenylcarbamylated β-cyclodextrin [cyclomaltoheptaose] bonded stationary phase (Ultron ES-phCD) with a mobile phase of water–acetonitrile–methanol (50 + 10 + 40, v/v/v) for mexiletine and 50 mmol dm^–3 citric acid–acetonitrile (90 + 10, v/v) for GABOB and detected by spectrofluorimetry at 530 nm with excitation at 470 nm. The derivatives of the enantiomers were well separated from each other. The separation factors (α) for the NBD-(±)-mexiletine and -(RS)-GABOB derivatives were 1.08 and 1.07, respectively. The data suggest that the enantiomers of drugs having an amino group at the chiral centre but lacking the carboxy group and drugs having an amino moiety at the β-position from a chiral centre but bearing a carboxy moiety following derivatization with NBD-F are effectively separated on the modified cyclodextrin stationary phase. Using either Pirkle-type stationary phases (K. Imai, et. al., Biomed. Chromatogr., 1993, 7, 177) or the modified cyclodextrin bonded stationary phase (proposed here) and the derivatization with NBD-F, many chiral drugs having an amino functional group could be separated enantioselectively and sensitively detected.