Structure and Nomenclature of Steroids

A formula of a steroid compound is easily recognized by its four-membered hydrocarbon core (Fig. 1.1a). My little grand daughter called it “a little cottage”, more advanced beginners may recall the term “cyclopentenoperhydrophenanthrene”. All the thousands of natural and synthetic steroids are derivatives of that core. Ring A is the cyclohexane ring on the left; it is attached to another six-membered ring B. The C ring follows, the D ring is a cyclopentane system. Numbering of the core is shown in the most prolific steroid – cholesterol (Fig. 1.1b): it starts at the A ring, continues at B, C, and then D rings. Methyl groups at angular positions 13 and 10 are ascribed numbers 18 and 19, the numbering then continues in the side chain. The numbers are used to describe positions at which substituents or multiple bonds are attached in individual compounds. Most steroid compounds are derived from the following six basic hydrocarbons: