Direct high-performance liquid chromatography method with refractometric detection designed for stability studies of treosulfan and its biologically active epoxy-transformers

Treosulfan (TREO) is an alkylating agent registered for treatment of advanced platin-resistant ovarian carcinoma. Nowadays, TREO is increasingly applied iv in high doses as a promising myeloablative agent with low organ toxicity in children. Under physiological conditions it undergoes pH-dependent transformation into epoxy-transformers (S,S-EBDM and S,S-DEB). The mechanism of this reaction is generally known, but not its kinetic details. In order to investigate kinetics of TREO transformation, HPLC method with refractometric detection for simultaneous determination of the three analytes in one analytical run has been developed for the first time.The samples containing TREO, S,S-EBDM, S,S-DEB and acetaminophen (internal standard) were directly injected onto the reversed phase column. To assure stability of the analytes and obtain their complete resolution, mobile phase composed of acetate buffer pH 4.5 and acetonitrile was applied. The linear range of the calibration curves of TREO, S,S-EBDM and S,S-DEB spanned concentrations of 20–6000, 34–8600 and 50–6000 μM, respectively. Intra- and interday precision and accuracy of the developed method fulfilled analytical criteria. The stability of the analytes in experimental samples was also established. The validated HPLC method was successfully applied to the investigation of the kinetics of TREO activation to S,S-EBDM and S,S-DEB. At pH 7.4 and 37 °C the transformation of TREO followed first-order kinetics with a half-life 1.5 h.