Continued from 3S-3. Steroids with heterocyclic rings in the side chain
3S-4. Functional groups
4.0 GeneralReferences for this section
4.1 Acids, salts and esters
4.3 Esters of sterols and steroid alcohols
Nearly all biologically important steroids are derivatives of the parent hydrocarbons (cf. Table 1) carrying various functional groups. Their nomenclature follows the general recommendations of the nomenclature of organic compounds (Sections C and D in ). However, there are some special problems in the application of these recommendations to natural products like steroids. Therefore, and for the benefit of the biochemist not so familiar with the recommendations of substitutive nomenclature, these are outlined and exemplified here. For full details, the reader is referred to the IUPAC Recommendations .
Most substituents can be designated either as suffixes or prefixes; some, however, the commonest being halogens, alkyl groups (see 3S-2.7 and 3S-2.8) and alkoxy groups, can only be designated as prefixes. Lists of these two types are given in Tables I and II respectively section C-10 of .
When possible, one type of substituent must be designated as suffix. When more than one type is present that could be designated as suffix only one type may be so expressed and the other types must be designated as prefixes. The choice for suffix is made according to an order of preference that is laid down in ; the most important part of this order, for steroids, is as follows in decreasing preferences: onium salt, acid, lactone, ester, aldehyde, ketone, alcohol, amine.
Suffixes are added to the name of the saturated or unsaturated parent system (see 3S-2.5), the terminal e of -ane, -ene, -yne, -adiene etc. being elided before a vowel (presence or absence of numerals has no effect on such elisions).
The following recommendations are on these principles. In this section, the formulae of examples correspond to 2b, i.e. the methyl groups are indicated by a bond without lettering, and the hydrogen atoms at C-8, C-9 and C-14 are omitted.
3S-4.1. Acids, salts and esters
Acids, their salts and esters are generally named by use of suffixes.
(a) If a methyl group is changed into a carboxyl group, the suffix is -oic acid; it is preceded by the appropriate locant. In biochemical papers, these compounds are often named as anions, the counter-ion being unspecified; in this case, the suffix is -oate. Examples:
(b) If an acid is formed by substitution of a hydrogen atom in CH, >CH2 or -CH3 by a carboxyl group, i.e. C-COOH, >CH-COOH or -CH2-COOH the suffix is -carboxylic acid or, in the ion form, -carboxylate. Note that in this case the acid contains one more carbon atom than the parent compound. Examples:
Note Compound 48 was formerly called 5,17a(H)-etianic acid. This name, etianic acid, is now abandoned.
(c) Names of salts are formed by stating the cation and using, as a separate word, the ionic form of the name of the acid. Example:
(d) Esters are conveniently named in a similar way. Examples:
(a) Lactones, other than cardanolides and bufanolides, are named by changing the ending -ic acid or -carboxylic acid of the name of the hydroxy acid to -lactone or -carbolactone respectively, preceded by the locant of the acid group and then the locant of the hydroxyl group. The lactonised hydroxyl group is not stated separately. Examples:
Note In examples 53 and 54 the suffix carbolactone corresponds to a substituent with an additional carbon atom which is numbered accordingly (see 3S-2.7 ). If example 53 was called 3-hydroxy-23,24-dinorchol-5-eno-21,18-lactone (name not recommended), then the lactone carbonyl would be C-21 (see 3S-6.2 for use of nor). Similarly, if example 54 was called 7-acetylthio-3-oxo-21-homo-17-pregn-4-eno-21,17-lactone (name not recommended), then the lactone carbonyl would be C-21a (see 3S-6.1 for use of homo).
(b) Cardanolides and bufanolides. The -olide ending of these names denotes the lactone grouping, and substituents must be named as prefixes.
3S-4.3. Esters of steroid alcohols
Esters of steroid alcohols are named by the appropriate steroid substituent group followed by that of the acyloxy group in its anionic form. The steroid name is formed by replacing the terminal -e of the hydrocarbon name by -yl, -diyl, etc. and inserting this before the locant with a Greek letter to designate position and configuration. When necessary locants should be used with the anionic part of the name. Examples:
The prefix form acyloxy-, with the appropriate locants, is used if there is a preferred functional group as the suffix (e.g. an acid or lactone). Examples:
When the steroid has a trivial name that already specifies the hydroxyl group that is esterified, the prefix must be O-acyl-. Examples:
(1) If it is wanted to emphasize the unesterified form of the steroid (e.g. in an index) the polyol may be named with the ester groups indicated as in the example 55 5-cholestane-3,12-diol 12-acetate 3-benzoate. This style was recommended in the previous edition of these recommendations, but does not follow standard systematic nomenclature rules .
(2) In the case of simple sterols with trivial names, the substituent form of the trivial name may be used (e.g. cholesteryl linoleate). This form should not be used with polyols.
2. International Union of Biochemistry (1978) Biochemical nomenclature and related documents, The Biochemical Society, London.
3. International Union of Pure and Applied Chemistry, Nomenclature of organic chemistry, Sections A, B, C, D, E, F and H, 1979 Edition, Pergamon Press, Oxford, 1979. Section E appeared also in pp. 1-18 of , and section F in pp. 19-26 of  and in Eur. J. Biochem. 86, 1-8 (1978).
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