547.926Metabolites of ecdysterone have been isolated from rat urine. By a combination of electron-impact and secondary-ion mass spectrometries and with the aid of accurate measurements of ion masses the molecular masses have been determined and structures have been proposed for three new metabolites, a common feature of which is the reduction of C~O to a methylene group. Ecdysterone metabolite (2) has the structure Steroids form one of the most important groups of organic compounds. Among the various metabolites produced by plants a not unimportant place is occupied ecdysteroids found in animals (invertebrata) and in plants. Structurally, these compounds are identical with or close to the hormones of the molting and metamorphosis of arthropods and, to all appearance, play an important role in the plant-insect ecological system. More than 150 ecdysteroids isolated from plants are known.Ecdysteroids possess a high biological activity and a wide range of pharmacological effects [1]. An original tonic preparation 6kdisten, the active principle of which is ecdysterone, has been created in the Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, under the direction of N. K. Abubakirov. The study of the metabolism of ecdysteroids is arousing particular interest among chemists and biologists.A general scheme of the metabolism in the organism of animals has been given in the literature [2][3][4]. Information on the metabolism of ecdysteroids is also given in a review by Lafont et al. [3], in which, together with diverse metabolic transformations, a specificity of the reactions for a given type of animals is noted. In particular, on the administration of 1 mg of a-ecdysone or ecdysterone to white mice the excrements collected during the 48 h after administration contained a certain amount of the initial substance. A whole series of metabolites, with the absence of polar conjugates, was determined by the reversed-phase HPLC method. Subsequent normal-phase analysis showed the predominant presence of metabolkes not absorbing at 254 nm, which can be explained by the reduction of the keto group in ring B. In the review [3] it is stated that the structures of various metabolites have been determined with the aid of NMR and mass spectra. However, no concrete details are given.In view of this, we have studied the metabolism of ecdysterone in the organism of white rats. The qualitative chromatography of an ethyl acetate fraction of the urine revealed five substances of ecdysteroid nature. Three of them formed the main components of the total ecdysteroids.The IR spectra of metabolites (2)-(4) did not contain the absorption bands at 1640-1670 cm -I that are characteristic for a AT-6-keto group. The peak of the molecular ion had a very low intensity or was even absent because of the instability of the molecular ions of ecdysteroids on electron impact. In spite of the absence in the majority of electron-impact (EI) mass spectra of the peak of the M + ion, this method plays an important role...