Isolation and Characterization of C-4 Methyl Intermediates in Cholesterol Biosynthesis after Treatment of Rat Liver in Vitro with Cholestan-3β,5α,6β-triol

We have studied the effect in vitro of cholestan-3β,5α, 6β-triol upon the conversion of tritium-labeled mavalonic acid to cholesterol. An in vitro system is described which is capable of net sterol synthesis in milligram quantities. Thus it is possible to characterize accumulating intermediates by modern physical techniques such as infrared, ultraviolet, nuclear magnetic resonance, and mass spectrometry. By using these techniques two sterols were isolated and characterized for the first time: ( a ) 4,4-dimethyl-Δ 8(9) -cholesten-3β-ol and ( b ) 4β-methyl-Δ 8(9) -cholesten-3β-ol. In addition, a third compound was detected and is tentatively identified as 4,4-dimethyl-Δ 8(9) -cholesten-3-one. Our results are consistent with the hypothesis that the polar substituents of cholestantriol at C-5 and C-6 are responsible for the ability of this compound to interfere with the enzymatic demethylation at C-4 of C-4 methyl precursors in cholesterol biosynthesis.