Differentiation of Ergosterol from Cholesterol

Abstract

Ergosterol and cholesterol are sterols each containing in its molecule 3 benzene rings with the configuration found in phenanthrene, one 5-membered ring with a side chain and one secondary alcohol grouping. Ergosterol, however, has one more carbon atom than cholesterol, one hydrogen in the side chain being replaced by a methyl group, and it also has 3 double bonds instead of one double bond.

The greater degree of unsaturation of ergosterol argues for its greater reactivity. Heilbron and Spring 1 report that ergosterol yields a red color with antimony trichloride, but no reaction takes place with α- and β-dihydroergosterol, with α- and β-ergostenol (tetrahydroergosterol) with allo-α-ergostenol (hexahydroergosterol), or with cholesterol. They also report that the trichloracetic acid reaction with ergosterol, which is negative with cholesterol, is not given by partially or completely saturated derivatives of ergosterol.

Several other tests reported for ergosterol fail to give responses with cholesterol. Among these we may mention the reaction (1) with chloral hydrate, 2 (2) with a solution of bromine in chloroform (Tortelli-Jaffé reaction) 1 (3) with concentrated nitric acid or with a solution of mercuric acetate in nitric acid, 3 and (4) with a solution of selenium dioxide. 4 Montignie 4 and also Callow and Rosenheim 5 state that selenium dioxide is reduced to free selenium not only by ergosterol but also by dihydroergosterol. A test to differentiate ergosterol from cholesterol may be carried out by use of a reagent containing concentrated sulphuric acid with sodium selenite, the sterol being dissolved in chloroform. 6 The chloroform layer remains free from color in case of ergosterol, while the acid layer changes to dark red brown to light brown with no green fluorescence. In case of cholesterol a deep bluish purple develops in the chloroform layer, while the lower or acid layer is red brown without a display of green fluorescence.