Nomenclature of Steroids

Rule 2S-6 Shortening of Sidechains and Elimination of Methyl Groups

6.1 - Elimination of a methylene group from a steroid sidechain (including a methyl group) is indicated by the prefix "nor-", which in all cases is preceded by the number of the carbon atom that disappears. When alternatives are possible, the number attached to nor is the highest permissible. Elimination of two methylene groups is indicated by the prefix "dinor-".

Examples to Rule 2S-6.1



Exceptions: By Rules 2S-2.1 and 2S-2.2 the names gonane (for 18,19-dinorandrostane) and estrane (for 19-norandrostane) constitute exceptions to the above Rule 2S-6.1. The names gonane and estrane are used also as parent Names for their Derivatives.

However, 18-nor- and 19-nor- are used with other trivial names, as in 19-norpregnane, 18,19-dinorspirostan, 18-norestrone.

24-Nor-5b-cholan-23-oic acid

18,19-Dinor-5a-pregnane-20a-carboxylic acid

The compound produced by shortening the 17-sidechain of pregnane is named 17-methylandrostane rather than 21-norpregnane. See also Note to Rule 2S-2.2.

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