Pharmacognosy - medicinal plants (herbs)

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Theme XIV: Lipids


Sterols definition. Steroids, chemical formula.

What are sterols?

Sterols are steroid related structures found naturally in plants and animals and whose structures include partially or fully a hydrogenated core of 17H-cyclopentane-α-phenanthrene.


Besides the sterols, the steroids constitute part of other substances such as compounds of adrenal origin, certain alkaloids, antirachitic vitamins, bile acids, cardiac glycosides, saponins and sex hormones.

Steroid structure

The general structure of the steroid is:

Steroid structure

The rings are properly numbered and lettered as indicated. The fusion of the rings prevents the free rotation of the structure causing two different projections in the plane of symmetry which are designated as alpha and beta, which are also identified as stereochemical structures cis and trans respectively.


The hydrocarbon series of sterols gives rise to various active ingredients present in plants and animals.


Thus, for example, the ergosterol present in abundance in yeast and ergot which becomes ergocalciferol (vitamin D2).

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Sterols definition. Steroids, chemical formula.