Ligustrazine Metabolic Transformation And Structural Transformation

Stable isotope labelling, especially in conjunction with gas chromatography-mass spectrometry (GC/MS), plays an important role in the research and development of therapeutic agents. Labelled drugs may serve as internal standards for GC/MS assays and substrates for metabolism and biosynthesis studies.Tetramethylpyrazine (TMP), an active ingredient in the traditional Chinese herb, Chuanxiong (Ligusticum Wallichii Franch), has been widely used especially in the treatment of patients with cerebral ischemic diseases in China. It was reported that TMP has short half-life time because of its rapid metabolism in the liver and elimination mainly through the kidney, but there has been no report on its metabolites and metabolic pathway. In this paper we studied TMP metabolic transformation with the technique of stable isotope labelling to facilitate the characterization of its metabolites in urine and then modified TMP chemical structure in order to improve its pharmacokinetic properties and develope new drugs.Firstly, we designed and synthesized deuterium-labelled TMP (DTMP), starting from deuterated butanone which was obtained by exchange of butanone with deuterium oxide in the presence of anhydrous potassium carbonate. The resulting product exhibited characteristic isotopic ion clusters in its chemical ionisation mass spectrum and its average deuterium content was 3.3 D/mol, mainly located in 2,5-dimethyl groups.Secondly, we studied the metabolites in the urine(?) after i.g. admi-nistration of either TMP or DTMP or their equimolar mixture to male Wister rats at three doses of 30, 150 and 300mg/Kg. The metabolites were extracted with ammonium carbonate-ethyl acetate. The nonacidic (neutral and basic) fractions were subjected to GC/MS directly for analysis and the water soluble acidic ones derivatized with methanol solution saturated with hydrochloric acid before being subjected to GC/MS analysis. 12 components exhibiting the expected ion clusters in their mass spectra were found and so recognized as the metabolites of TMP. The structures of the main metabolites were deduced. It was found that the major metabolic pathways of TMP were the oxidation of methyl groups.a...