Continued from Appendix. Selected international non-proprietary names (INNs) of steroids
Pronunciation of pregn-4-ene
In the recently published recommendations on steroid nomenclature, the locant of a double bond is always inserted directly in front of the syllable(s) -ene, -diene, etc. This change results in a problem in the pronunciation of the names of compounds with one double bond when the parent has a consonant that is normally pronounced as part of the ending -ane. In particular, prenane and estrane pose this problem. To aid pronunciation, an additional 'a' is often inserted in speech, e.g. pregn(a)-4-ene. The 'a' in parenthesis is used only for pronunciation and should not be used in the written form. Similarly, estr-4-ene is pronounced estr(a)-4-ene.
This proposal is an extension of the existing form used for steroids with more than one double bond, e.g. pregna-4,6-diene.
Numbering of Steroid Side-chain Atoms
Additional alkyl substituents attached to a steroid skeleton are numbered using the locant of the attachment position and a superscript number indicating the number of atoms from the attachment position. Now that the numbers 28, 29 and 30 are assigned to the additional methyl groups at C-4 and C-14 in triterpenoids, such as lanosterol, the additional carbon atoms at C-24 of ergostane, campestane, poriferastane, stigmastane and gorgostane are also numbered using a subscript number, i.e. 241, 242. When it is necessary to identify these atoms in naming a steroid using one of these parents the appropriate locant is used. For example, fecosterol is 5-ergosta-8,24(241)-dien-3-ol [formerly 5-ergosta-8,24(28)-dien-3-ol]. It may alternatively be called 24-methylene-5-cholest-8-en-3-ol. In all other cases the use of a locant modified by a superscript number is intended for identification purposes, e.g. 13C-nmr, and not as a basis for further substitution. For example, oxymethalone (an international non-proprietary name) is 17-hydroxy-2-(hydroxymethylene)-17-methyl-5-androstan-3-one, not 21,17-dihydroxy-17-methyl-2-methylene-5-androstan-3-one.
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