Determination of L-buthionin (SR)-sulfoximine, gamma-glutamylcysteine synthetase inhibitor in rat plasma with HPLC after prelabeling with dansyl chloride.

L-(SR)-Buthionin sulfoximine (L-(SR)-BSO) is a potent and specific inhibitor of gamma-glutamylcysteine synthetase, which catalyzes the first reaction of glutathione biosynthesis. A selective, sensitive, and simple high-performance liquid chromatographic method was developed for the determination of L-(SR)-BSO in rat plasma. After the compound was labeled with dansyl chloride (Dns-Cl) under optimal conditions, it was separated in a Zolbax-ODS column with a mobile phase that consisted of 0.01M phosphate buffer, methanol, and acetonitrile (8:1:3, v/v). The compound was detected with a fluorescence detector at an excitation wavelength of 335 nm and an emission wavelength of 525 nm using a xenon lamp. The coefficients of variation (DV) from the interassay in the low and high concentrations (10 and 500 micrograms/mL of L-(SR)-BSO in rat plasma) were 2.5 and 4.8%, respectively. The CVs from the intra-assay in the low and high concentrations were 3.2 and 5.6%, respectively. The minimum concentration of L-(SR)-BSO that could be determined was 10 micrograms/mL when 100-microL serum samples were used. The detection limit was 50 ng per injection volume. This method enables pharmacokinetic and pharmacodynamic studies in rats.