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CH3RE03-CATALYZED OXIDATION OF CHOLESTA-5, 7-DIEN-3B-YL ACETATE WITH THE UREA-HYDROGEN PEROXIDE ADDUCT UNDER VARIOUS CONDITIONS. SYNTHESIS OF THE NATURAL EPOXY STEROL 9A, 11A-EPOXY-5ACHOLEST-7-EN-3B,
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Secosteroids of marine origin
No full textThis review describes the isolation from marine organisms of all secosteroids reported in the literature from 1972 to 2004. Secosteroids are highly oxidized metabolites with bond cleavage in the rings of the steroid tetracyclic nucleus. All secosteroids are grouped in accordance with their ring joined to side chain as 5,6-, 9,11-, 9,10- 8,9-, 8,14- and 13,17-secosteroids and the structures and the synthetic works, where available, are reported. Furthermore, this review gives details on the biological activities of the isolated secosteroids (e.g. antiproliferative, antifouling, antiinflammatory, antimicrobial, ichthyotoxic and antiviral)
Chimica dei composti eterociclici farmacologicamente attivi
No full textQuesto testo esamina i composti eterociclici che permettono di sintetizzare nuovi farmaci. Particolare importanza è stata data ai meccanismi di reazione, all'analisi retrosintetica ed alla nomenclatura dei composti eterociclici
CH3ReO3-catalyzed oxidation of cholesta-5,7-dien-3beta-yl acetate with the urea-hydrogen peroxide adduct under various conditions. Synthesis of the natural epoxy sterol 9α,11α-epoxy-5α-cholest-7-en-3β,5,6β-triol
No full textThis article describes the oxidation of cholesta-5,7-dien-3β-yl acetate (4) with the urea-hydrogen peroxide adduct (UHP) using methyltrioxorhenium (MTO) as catalyst, under various conditions. Specifically, the effects of using different solvents (CHCl3 and ethers) and additives (EtOH and pyridine) on the course of the MTO-catalyzed oxidation of 4 were investigated. Some new steroids (6, 9, 10 and 11), obtained from this oxidation, were isolated and characterized on the basis of chemical evidence and interpretation of spectroscopic data including H-H COSY and HMBC experiments. The optimal solvent for the oxidation of 4 with MTO/UHP oxidizing system was diethyl ether. In this solvent the reaction is clean and gave as the main product 5,6β-dihydroxy-5α-cholest-7-en-3β-yl acetate (8, 65% yield), obtained with a more simple procedure and with a higher yield than that reported in literature. Sterol 8 is a key intermediate compound in the synthesis of many steroids of marine origin, biologically active, oxygenated at the B/C rings. In fact, starting from diol 8, we performed the synthesis of the natural cytotoxic epoxy sterol 9α,11α-epoxy-5α-cholest-7-en-3β,5,6β-triol (15, 21% yield) with an improvement in yield and number of steps over a synthesis of the same natural product previously reported. When the oxidation of 4 with the MTO/UHP system in diethyl ether was performed in the presence of pyridine as ligand, the unsaturated epoxide 5,6α-epoxy-5α-cholest-7-en-3β-yl acetate (10, 90% yield) was obtained after only 5 min in good yield. In fact, pyridine, besides having beneficial effect on the reaction rate, shuts down the ring opening reactions, as reported in literature
The oxidation of Delta2, Delta2,4 and Delta4,6 steroids with RuO4
No full textIn order to find new ways for the functionalization of the A and B rings of the steroid nucleus, the reaction of 5α-androst-2-en-17β-ol 17-acetate (1), cholesta-2,4-diene (4) and cholesta-4,6-dien-3β-ol 3-acetate (7) was examined using stoichiometric amounts of ruthenium tetraoxide to yield 1,2-cis diols and/or α-hydroxy ketones. The reaction of 5α-cholest-2-en-3-ol 3-acetate (9) with ruthenium tetraoxide was also carried out and afforded, apart from an α-hydroxy ketone, also a diketone and a seco-dicarboxylic acid. The structures of all new steroids, including stereochemical details, were deduced by analysis of spectral data
A new route to polyoxygenate C and D rings of steroids by oxidation of a D8,14-diene steroid with the methyltrioxorhenium-H2O2-urea system
No full textIn order to find new ways of introducing oxygenated functions in the 15-, 9- and 11-position on steroid rings and at the same time test the reactivity of a conjugated diene steroid toward methyltrioxorhenium (MTO)-catalyzed oxidation with the urea-hydrogen peroxide adduct (UHP), the reactions of 5α-cholesta-8,14-dien-3β-yl acetate 1 with the MTO-UHP system are performed in aprotic solvents. These oxidations are performed both at 0 °C and 25 °C in CHCl3 or diethyl ether as solvent and in the presence of pyridine ligand. From the reaction of diene 1 in CHCl3 we isolate two new sterols, 9β-hydroxy-15-oxo-5α-cholest-8(14)-en-3β-yl acetate 3 and 9α,11α,15α-trihydroxy- 5α-cholest-8(14)-en-3β-yl acetate 7, while oxidation in Et2O in the presence of pyridine ligand allows us to isolate the new epoxysteroid 9α,11α-epoxy-15α-hydroxy-5α-cholest-8(14)-en- 3β-yl acetate 13. The structure of all new steroids is secured on the basis of chemical evidence and interpretation of spectral data, which include H-H COSY, HMBC and NOESY experiments. These results represent a new and mild method for the functionalization of C and D rings from an 8,14-diene steroid, to give 15-oxygenated sterols, a class of compounds remarkable for their inhibitory action on sterol synthesis in animal cell culture systems
Oxidation of some conjugated diene steroids by hydrogen peroxide catalyzed by methyltrioxorhenium
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