DIRECT HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY DETERMINATION OF DIASTEREOMERIC OXPRENOLOL GLUCURONIDES

The beta-blocking agent oxprenolol is used therapeutically as the race mate. In humans and animals it is metabolized i.a. to ether glucuronid e diastereomers. A stereoselective HPLC assay was developed to determi ne directly, without hydrolysis to their parent enantiomers, the oxpre nolol glucuronides in biological samples. The glucuronide standards fo r this direct assay are prepared by incubation of rabbit liver microso mes with RS-oxprenolol. The glucuronides obtained are purified and con centrated with solid-phase extraction, and their concentration is meas ured by an indirect method, i.e. HPLC assay of the oxprenolol enantiom ers after enzymatic hydrolysis with beta-glucuronidase. The direct ass ay involves separation by HPLC using a C-18-reversed-phase column, wit h UV detection at 274 nm; nalorphine is used as internal standard. On injection onto the column, without previous hydrolysis, the limit of d etection is 20 ng for both glucuronides. The assay is sensitive, accur ate and reproducible. The method is suitable for the assay of glucuron ides in liver microsomal incubates and plasma.