Isolation and identification of new rapamycin dihydrodiol metabolites from dexamethasoneinduced rat liver microsomes |
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Authors: | M. J. M. NICKMILDER D. LATINNE R. K. VERBEECK W. JANSSENS D. SVOBODA G. J. J. LHOEST |
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Affiliation: | Department of Pharmaceutical Sciences-UCL, Pharmacokinetics and MetabolismUnit Laboratory of Mass Spectrometry, 7246, Av. E. Mounier, B-1200 Brussels, Belgium OE Experimental Immunology Unit-UCL, Clos Chapelle aux Champs, 3056, B-1200 Brussels, Belgium |
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Abstract: | 1. Rapamycin is metabolically transformed in rat liver microsomes to 3,4- and 5,6- dihydrodiol metabolites under the influence of the cytochrome P-450 mixed function oxygenase system. These metabolites were produced from dexamethasone-induced as well as from non-induced rat liver microsomes. The comparison of the ion spray mass spectra of the 5,6-dihydrodiol with the 3,4-dihydrodiol of rapamycin shows clearly that dihydrodiols were formed in two distinct positions of rapamycin. 2. FAB mass spectra as well as electrospray mass spectra of two additional peaks isolated from the same chromatographic run confirm the presence of a 3,4-dihydrodiol metabolite of rapamycin as also strongly suggested by UV spectra.Hplc reinjection of each individualpeak always resultedinchromatograms showing a combinationof thesame three peaks and therefore are to be considered as tautomers of the 3,4-dihydrodiol of rapamycin. 3. These tautomeric conformations were found to have no immunosuppressive potency, most probably due to important structural and stereochemical modifications of the rapamycin binding domain to the binding protein (FKBP-12) and or to important metabolic structural modifications of rapamycin effector domain. |
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