Determination of ML-1035 enantiomers in plasma by chiral high-performance liquid chromatography

ML-1035, is a gastroprokinetic agent structurally related to metoclopramide. Because ML-1035 contains an asymmetric chiral sulphoxide moiety, a chiral HPLC method has been developed to separate and quantitate its R- and S-enantiomers in plasma. The ML-1035 enantiomers present in plasma are extracted with dichloroethane under alkaline conditions, the extract evaporated to dryness and reconstituted in the mobile phase. Samples are chromatographed on a Chiralcel OD HPLC column with hexane-absolute ethanol (1% TEA) (1:1, v/v) as the mobile phase. The enantiomers of the unchanged drug are determined by fluorescence measurement (ex: 310 nm, em: 350 nm). The method provides a linear response for both enantiomers over a concentration range of 25 (limit of determination) to 2500 ng ml-1 with correlation coefficients of 0.9987 or greater. The inter-assay precision is 9.5% or less and the accuracy ranges from 93.9 to 103.4% of the theoretical value. The method is used to determine the plasma concentrations of the R- and S-enantiomers following oral and intravenous administration of R- or S-enantiomers to dogs. The method is also adapted to measure enantiomer levels from in vitro reaction mixtures so that the possibility of metabolic inversion may be assessed. The data suggest that no significant level of inversion between the enantiomers occurred either in vivo or in vitro.