Abstract
25-Fluorocholesterol ( III) was prepared by treatment of 25-hydroxycholesterol ( IV) with hydrogen fluoride-pyridine. Compounds III, IV, and cholesterol ( I) were fully characterized by 1H and 13C NMR, and stereochemical assignments were established for the C-22 and C-23 protons. The side-chain proton assignments, which apply to most other sterols with a saturated eight-carbon side chain, were based on conformational analysis and comparison with NMR data for 25,26,26,26,27,27,27-heptafluorocholesterol ( II). The chromatographic behavior of I, II, and III were compared on thin-layer chromatography, high performance liquid chromatography, and gas chromatography. Major fragment ions in electron-impact mass spectra of III were analogous to ions of either cholesterol or desmosterol, and a similar analogy was observed for the trimethylsilyl ethers. The 25-hydroxysterol IV and the 25-fluorosterol III differed markedly in their effects on the levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in CHO-K1 cells. Whereas 25-hydroxycholesterol caused a ∼66% lowering of reductase activity in cells at 0.1 μM, the 25-fluorosterol III had no effect at this concentration.
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