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  • Title: A highly stereoselective synthesis of C-24 and C-25 oxysterols from desmosterol.
    Author: Zhao Q, Qian C, Chen XZ.
    Journal: Steroids; 2016 May; 109():16-21. PubMed ID: 26968128.
    Abstract:
    A new highly stereoselective construction of the side chain of the C-24 and C-25 oxysterols has been achieved by using desmosterol acetate as the starting material and an improved Sharpless catalytic asymmetric dihydroxylation with 100% d.e. (diastereomeric excess) as the key step. The result is much better than the usual asymmetric dihydroxylation procedure. t-Butyl nitrite/2,2,6,6-tetramethylpiperidine N-oxyl radical/FeCl3 catalyst system was developed to activate molecular oxygen for the aerobic oxidation of 24-hydroxycholesterol and the 24-ketocholesterol was obtained in 86.2% yield. The oxidation system has never been reported before. The mechanism for the catalytic aerobic oxidation was also proposed.
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