Zhao Q, Qian C, Chen XZ. A highly stereoselective synthesis of C-24 and C-25 oxysterols from desmosterol.
Steroids 2016;
109:16-21. [PMID:
26968128 DOI:
10.1016/j.steroids.2016.03.003]
[Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/08/2015] [Revised: 02/18/2016] [Accepted: 03/01/2016] [Indexed: 11/28/2022]
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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