The basic ring structures presented in Figure 1 can be subjected to a wide array of modifications by the introduction of hydroxyl or carbonyl substituents and unsaturation (double or triple bonds). In addition, heteroatoms such as nitrogen or sulfur can replace the ring carbons, and halogens and sulfhydryl or amino groups may replace steroid hydroxyl moieties. Furthermore, the ring size can be expanded or contracted by the addition or removal of carbon atoms. The consequences of these structural modifications are designated by application of the standard organic nomenclature conventions for steroids. The pertinent examples of this system are summarized in Table 1. Prefixes and suffixes are used to indicate the type of structural modification. Any number of prefixes may be employed (each with its own appropriate carbon number and specified in the order of decreasing preference of acid, lactone, ester, aldehyde, ketone, alcohol, amine, and ether); however, only one suffix is permitted.
Fig1. Family tree of the seven principal classes of steroids (bottom row) that are structurally derived from the parent cholestane (top row). Cholestane has 10 additional carbons added to sterane (see Figure 2); these include two methyl groups, C-18 and C-19, added respectively to C-13 and C-10 and an eight-carbon side chain (C-20 to C-27) attached to C-17 of the D-ring.
Fig2. Parent ring structures of steroids. The creation of the 5-carbon (pentano) ring on phenanthrene followed by reduction of all the aromatic double bonds creates the foundational, completely hydrogenated, cyclopentanoperhydrophenathrene, also known as sterane (the middle structure). The bottom structure is a different presentation of sterane that illustrates the numbering system or zip code for each of its 17 carbons and the convention for the A, B, C, and D labels for the 4 rings.
Table1. Steroid Nomenclature Conventions
Table 2 tabulates the systematic and trivial names of many common steroids. All of these formal names are devised in accordance with the official nomenclature rules for steroids laid down by the International Union of Pure and Applied Chemistry (IUPAC).
Table2. Trivial and Systematic Names of Some Common Steroids
