The isolation of a second sterol from yeast-fat

Abstract

The crude sterol separating on saponification of yeast fat has been fractionally crystallized, ether, alcohol, and acetone being used as solvents. The less soluble laevo-rotatory ergosterol, melting in an open tube at 158.5[degree], was obtained, also a more soluble dextro-rotatory sterol melting at 108-109[degree], to which the name zymosterol has been given. The specific rotation of the latter in ether solution was +34.1. Examination of the absorption spectrum in the ultra violet region showed no characteristic selective absorption. If the alcoholic solution examined is sufficiently concentrated, the bands characteristic of ergosterol appear. The zymosterol appeared to be contaminated with rather less than 5% ergosterol. Zymosterol is quantitatively precipitated by digitonin. It gives an acetate melting at 115[degree], the iodine value of which, determined by Hubl''s reagent, indicated the presence of 3 ethylenic linkages. It gives a modified Salkowski reaction, the sulphuric layer being colored slightly yellow. The I value of the free sterol was compared with that of ergosterol by Hubl''s and Dam''s methods; the values obtained for the 2 sterols were in close agreement. Analysis showed the composition ef both sterols to be similar. The presence of a dextrorotatory sterol in yeast fat, isomeric with ergosterol, is therefore established.