title: A highly stereoselective synthesis of C-24 and C-25 oxysterols from desmosterol.
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.
authors.affiliation: College of Chemical and Biological Engineering, Zhejiang University; Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Zhejiang University, Hangzhou 310027, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: College of Chemical and Biological Engineering, Zhejiang University; Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Zhejiang University, Hangzhou 310027, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Qian
authors.affiliation: College of Chemical and Biological Engineering, Zhejiang University; Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Zhejiang University, Hangzhou 310027, China. Electronic address: xzchen@zju.edu.cn.
authors.forename: Xin-Zhi
authors.initials: XZ
authors.lastname: Chen
mesh_terms: D002384:Catalysis; D060326:Chemistry Techniques, Synthetic; D003897:Desmosterol / Q000737:chemistry*; D000072376:Oxysterols / Q000138:chemical synthesis* / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000072376:Oxysterols; D003897:Desmosterol
keywords: 2,2,6,6-Tetramethylpiperidine N-oxyl radical (TEMPO); Aerobic oxidation; Improved Sharpless asymmetric dihydroxylation reactions; Oxysterols; Stereoselective; Steroids