Chromatographic separation of putative precursors of cholestanol
This paper describes convenient syntheses for labeled and unlabeled cholest-5-en-3-one, cholest-4-en-3-one, epicholesterol, cholest-4-en-3 beta-ol, and cholest-4-en-3 alpha-ol. The thin-layer chromatography, high-performance liquid chromatography, and gas-liquid chromatography of these compounds and of cholestanol and epicholestanol are also described. The synthesized compounds are potential precursors in the biosynthesis of cholestanol in mammals.
Catalytic β-stereospecific epoxidation of unsaturated steroids by trans-dioxoruthenium(VI)tetramesitylporphyrin. Stereochemical grounds for the β-diastereofacial selection
The catalytic epoxidation by dioxygen with trans-dioxoruthenium(VI)tetramesitylporphyrin [Ru(O)2(tmp)] of the acetic esters of cholesterol, 3-epicholesterol and isocholesterol,† as well as of the 7α-epimer of the latter, is β-stereospecific. Substitution by a methyl group on C-6 of pregnenolone acetate results in reduced reactivity towards catalytic epoxidation and lower β-stereoselectivity. 19-Norsterol esters bearing a double bond at C-8–C-14 or C-14–C-15 are inert towards O2–RU(O)2(tmp) epoxidation. The variable reactivity of these sterol ester substrates is explained by a transition state in which the steroid nucleus approaches the ruthenium–oxo bond approximately perpendicular to the porphyrin ring. The β-selectivity of Δ5-sterol ester epoxidation is accounted for in terms of this transition state geometry which provides a good fit between the porphyrin catalyst and the steroid substrate when the β-side faces the oxo ligand. On the other hand, reaction on the α-side involves unfavourable steric interactions between axial hydrogen atoms on C-3 and C-7 of the substrate and the porphyrin ring and a mesityl substituent of the catalyst, respectively. The crystal and molecular structures of cholesteryl ethyl carbonate and of its 5,6β-epoxide have been determined by single-crystal X-ray diffraction. The overall conformation of the steroid nucleus is nearly planar in the cholesteryl ester, while it is bent at the junction between rings A and B in the 5,6β-epoxide. This change from pseudo-trans- to cis-stereochemistry of the A–B ring junction upon epoxidation is proposed to amplify the β-diastereofacial selection. Variable temperature 1H NMR spectra indicate that in CD2Cl2 solution the 5,6β-epoxide (not the 5,6α-epoxide) of the cholesteryl acetate coordinates the ruthenium atom of Ru(CO)(tmp) with a nearly perpendicular geometry. These results corroborate the orthogonal substrate approach and the steric origin of the β-stereospecificity in Ru(O)2(tmp)-catalysed steroid epoxidations.
The Nature of the Action on a Photographic Plate of Sawdust and Cholesterol Irradiated by a Mercury Vapour Quartz Lamp.
THIS work was undertaken as the result of observations by Hume and Smith [1924] indicating that pine sawdust which had been irradiated by a mercury vapour quartz lamp developed anti-rachitic properties. For some time it was supposed by them that the activity of the irradiated sawdust might be due to secondary radiations or some emanations given out by the particles of wood exposed to ultra-violet rays. This view was countenanced by the statement of Kugelmass and McQuarrie [1924] that anti-rachitic substances, e.g. cod-liver oil, egg-yolk and sperm oil, were capable of fogging a photographic plate even when the plate was exposed through a quartz cover sealed in such a way as to preclude the action of a volatile substance. That certain animal and vegetable substances are capable of producing fog on a photographic plate is not new. Russell [1906] studied the phenomenon and showed that the action was intensified by a previous exposure of the substance to sunlight or a carbon arc. Temperature increased the effect. The substances with which Russell worked were woods of various kinds, coal, wool, fur and feathers. He observed an effect whether the plate was in contact with the substance or at a distance from it, or when air was drawn over the substance on to the plate. He also found that, given sufficient exposure of the plate, whatever produced the fogging could travel round the edges of an opaque mask, and that glass and mica prevented its passage. He believed the effect to be due to the evolution of hydrogen peroxide.