Isolation of brassicasterol from steam deodorizer distillate of rapeseed oil: Some properties of its acetate tetrabromide and its reduction to 22,23‐dihydrobrassicasterol

Abstract

Brassicasterol (5,22-ergostadien-3β-ol) was isolated from the steam deodorizer distillate of rapeseed oil and purified by acetylation, bromination, chromatography on 20% AgNO₃/SiO₂ columns and hydrolysis. Brassicasteryl and stigmasteryl (5,22-stigmastadien-3β-ol) acetates were brominated, and the yields of products and solubilities of the tetrabromides from the two steryl acetates were compared. Stigmasteryl acetate tetrabromide is less soluble than the corresponding brassicasteryl derivative; yet the latter precipitates selectively during bromination of a mixture of the two steryl acetates. This is explained on the basis of the stereochemistry of the bromine atoms in the side chains of the two steryl acetate tetrabromides. Hydrogenation of brassicasteryl acetate over Raney nickel gave the 22,23-dihydro derivative in excellent yield. The latter was separated from small amounts of ergostanyl acetate on a 20% AgNO₃/SiO₂ column.