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  • Title: A facile synthesis of C-24 and C-25 oxysterols by in situ generated ethyl(trifluoromethyl)dioxirane.
    Author: Ogawa S, Kakiyama G, Muto A, Hosoda A, Mitamura K, Ikegawa S, Hofmann AF, Iida T.
    Journal: Steroids; 2009 Jan; 74(1):81-7. PubMed ID: 18996406.
    Abstract:
    Experiments were performed to compare the regioselective hydroxylation of the isopropyl C-H bond at C-25 in 5alpha-cholestan-3beta-yl acetate by in situ generated dimethyldioxirane, methyl(trifluoromethyl)dioxirane, hexafluoro(dimethyl)dioxirane or ethyl(trifluoromethyl)dioxirane (ETDO). The dioxiranes were generated from the corresponding ketones and potassium peroxymonosulfate in aq. NaHCO(3), pH 7.5-8.0. Of the four dioxiranes examined, partially fluorinated, sterically bulky ETDO displayed the highest reactivity and regioselectivity. Using in situ generated ETDO, a facile, synthesis was developed for two naturally occurring oxysterols, i.e., 25-hydroxycholesterol, as well as its 3-sulfate (overall yield of the sulfate, 24%) and 24-oxocholesterol (16%), starting from cholesterol.
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