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steroids (ster´oydz, ster-)
A large family of chemical substances, comprising many hormones, body constituents, and drugs, each containing the tetracyclic cyclopenta[a]phenanthrene skeleton. Formula I of the accompanying page of structures shows the numbering and lettering of the rings, which are retained even if, in a given compound, any of the atoms shown are absent or involved in ring closures, or if rings are expanded ("homo," see below) or contracted ("nor," see below). Stereoisomerism among s. is not only common but of critical biological significance, and the isomeric groups are usually represented as shown in II. The conventions are that the nucleus is presented as if projected onto the plane of the paper, with groups then lying above that plane being denoted by thickened bonds and called beta, those then lying below that plane by broken bonds and called a; the letter xi indicates unknown or unspecified orientation. Depending on the situation at C-5, the molecule is sometimes represented in perspective as in III and IV; 5a, 5beta, or 5xi should be included in the name. Unless otherwise stated, it is assumed that atoms or groups attached to the other ring-junctions (8, 9, 10, 13, 14) are as in II, i.e., 8beta, 9a, 10beta, 13beta, 14a.
The principal classes of steroids, with the names for the unsubstituted, saturated hydrocarbon forms that are clearly related to physiological functions or sources are: 1) gonanes (in which the methyl group in formula II, C-18 and C-19, have been replaced by H), 2) estranes (in which the C-19 methyl groups in formula II has been replaced by H), 3) androstanes (equivalent to formula II), 4) norandrostanes (in which one of the methyl groups, typically C-18, has been replaced by H), 5) cholanes (formula II with -CH(CH3)(CH2)2CH3 bonded to C-17), 6) cholestanes (with -CH(CH3)(CH2)3CH(CH3)2 at C-17, 7) ergostanes (with -CH(CH3)(CH2)2CH(CH3)CH(CH3)2 at C-17), and 8) stigmastanes (with -CH(CH3)(CH2)2CH(CH2CHCH3)CH(CH3)2 at C-17). In addition, each of the classes can be in a 5a- or 5beta-series.
The steroid derivatives known as cardanolides are androstanes with a 5-membered lactone linked to C-17. The squill-toad poisons known as the bufanolides are androstanes with a 6-membered lactone linked to C-17. Spirostans and furostans (the basic structures of many "genins," including the sapogenins) are androstanes having certain cyclic ether moieties.
The natural and synthetic derivatives are named by adding conventional chemical prefixes and suffixes for substituents; e.g., -ol for a hydroxyl group, -on(e) for a keto group, -al for an aldehyde group. "Nor" indicates loss of a -CH2- group; "homo," the addition of a -CH2- group; each is preceded by the letter indicating which ring is contracted or expanded, respectively, or, in the case where the -CH2- is lost from a methyl group, the number of the carbon atom lost. "Seco" indicates fission of a ring with addition of hydrogen atoms at the positions indicated by numerals preceding the term. Unsaturation is denoted, as usual, by substituting appropriate terms, e.g., -en(e), -yn(e), -adien(e), for the -ane or -an parts of the hydrocarbon or parent class names, with numerals indicating locations of the unsaturated bonds. The locations of double bonds are specified by the lower of the two (consecutive) numbers of the carbon atoms involved. When a double bond is formed between two nonconsecutive carbon atoms, the second is indicated in parentheses after the first; e.g., estriol and the estradiols possess three double bonds, between C-1 and C-2, between C-3 and C-4, and between C-5 and C-10, respectively.
Steroid alkaloids may be named from the steroid parent, as above, or from trivial family names usually ending in -anine if the steroid is saturated or in -enine, -adienine, etc., if it is not saturated (e.g., conanine, tomatanine).
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