Sterols 3. Sterols and Their Conjugates from Plants and Lower Organisms

Plants contain a rather different range of sterols from animals. Like cholesterol, to which they are related structurally and biosynthetically, plant sterols form a group of triterpenes with a tetracyclic cyclopenta[a]phenanthrene structure and a side chain at carbon 17. The four rings (A, B, C, D) have trans ring junctions, and the side chain and two methyl groups (C-18 and C-19) are at an angle to the rings above the plane with β stereochemistry (as for the hydroxyl group on C-3 also). The basic sterol from which other sterol structures are defined is 5α-cholestan-3β-ol.