Inhibitors of sterol synthesis: Synthesis and spectral properties of derivatives of 3β-hydroxy-25,26,26,26,27,27,27-heptafluoro-5α-cholest-8(14)-en-15- one fluorinated at carbon 7 or carbon 9 and their effects on 3-hydroxy-3-methylglutaryl coenzyme a reductase activity in cultured mammalian cells

Article abstract of DOI:10.1016/0009-3084(94)90017-5

As part of a program to prepare Δ⁸⁽¹⁴⁾-15-ketosterols that cannot readily be metabolized to cholesterol or side-chain oxygenated species, we have prepared 3β-hydroxy-7α-fluoro-5α-cholest-8(14)-en-15-one (VII) and the 9α-hydroxy (IV), 9α-fluoro (VI) and 7α-fluoro (VIII) derivatives of 3β-hydroxy-25,26,26,26,27,27,27-heptafluoro-5α-cholest-8(14)-en-15- one (II). Sterol IV was prepared by oxidation of the Δ^8,14 dienol ethyl ether of the 3β-acetate of II with m-chloroperbenzoic acid, followed by mild alkaline hydrolysis of the 3β-acetate derivative of IV. Treatment of IV with hydrogen fluoride-pyridine gave VI. The 7α-fluoro-15-ketosterols VII and VIII were synthesized by treating the 3β,15-bis-trimethylsilyl Δ^7,14-dienol ether derivative of the appropriate Δ⁸⁽¹⁴⁾-15-ketosterol with N-fluoropyridinium triflate, followed by hydrolysis of residual trimethylsilyl ethers and purification by high-performance liquid chromatography. The combined results of ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts, ¹H-¹H coupling constants, ¹H-¹⁹F long-range coupling constants and molecular modeling indicated that a 7α-fluoro, 9α-fluoro or 9α-hydroxy substituent has negligible effect on the conformation of the 15-ketosterols. ¹H and ¹³C-NMR data are also given for Δ^6,8(14)- and δ^8(14),9(11)-15-ketosterols, synthetic byproducts that could not be detected readily in samples of the fluoro-15-ketosterols by chromatographic methods. Mass spectra of VI and of previously reported 9α-fluoro and 9α-hydroxy-Δ⁸⁽¹⁴⁾-15-ketosterols showed abundant M-62 or M-60 ions that appear to correspond to loss of ketene and HF or H₂O. The 9α-hydroxy-F₇-15-ketosterol IV, the 7α-fluoro-15-ketosterol VII and the 7α-fluoro-F₇-15-ketosterol VIII were of equivalent potency to the parent 3β-hydroxy-5α-cholest-8(14)-en-15-one (I) in lowering the levels of 3- hydrox-3-methylglutaryl coenzyme A reductase activity in CHO-K1 cells. The 9α-fluoro-F₇-15-ketosterol VI showed high potency but appeared to be slightly less active than I.