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

Abstract

As part of a program to prepare Δ 8(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 Δ 8(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 9 α-hydroxy- Δ 8(14)-15-ketosterols showed abundant M-62 or M-60 ions that appear to correspond to loss of ketene and HF or H 2O. The 9α-hydroxy-F 7-15-ketosterol IV, the 7α-fluoro-15-ketosterol VII and the 7α-fluoro-F 7-15-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-F 7-15-ketosterol VI showed high potency but appeared to be slightly less active than I.