[Metabolism of Etozolin in rat, dog and man]

Investigations on the metabolism of the new diuretic ethyl (Z)-(3-methyl-4-oxo-5-piperidino-thiazolidin-2-ylidene) acetate (Gö 687, etozolin, Elkapin) were carried out with urine of rat, dog and man as well as rat bile after enteral administration of the 14C-labelled substance. Seven metabolites were isolated with either the aid of high-pressure liquid chromatography (HPLC) or extraction and thin-layer chromatography. Mass spectroscopy was applied to determine the structures of the metabolites, partly by use of authentic reference substances. Because of the instability of most of the metabolites, some of them showing strong polarity, the described investigations on the metabolic profiles and the enrichment and purification of some metabolites could only be carried out with the HPLC-radioactivity detector system, which requires no clean-up for the samples. The metabolisation process of etozolin is qualitatively equal in rat, dog and man; it is characterized by 3 steps: 1. enzymatic cleavage of the ester group, which leads to the also diuretically active main metabolite (metabolite I) in the plasma of all 3 species; 2. glucuronidation of the resulting metabolite I, leading to metabolites II and III, which are diastereoisomeric esters of the two enantiomeric forms of metabolite I with beta-D-glucuronic acid. 50--60% of the urinary radioactivity can be described with these two metabolisation steps in all 3 species; 3. Oxidation of the piperidine moiety to metabolites IV--VII.