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Cholecalciferol (vitamin D3), an example of a 9,10-secosteroid. The hydroxyl group (HO-) is in position C3 of the parent steroid A-ring. The triene substructure attached to the ring bearing the hydroxyl group is a result of the ring scission (cleavage) giving rise to this secosteroid.
The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield the vitamins D.

Secosteroids (sec·o·ster·oid, sek'ō-stēr'oyd) are a subclass of the tetracyclic steroid class that are structural relatives bearing a cleavage of one of the four rings of that parent class.[1] The subclass nomenclature derives from the verb Latin: secare meaning "to cut", and Latin: stere of steroid, meaning "solid, three-dimensional".[2] Subclasses are defined by the carbon atoms of the parent steroid skeleton where the ring cleavage has taken place, e.g., 9,10-secosteroids for derivatives deriving from cleavage between carbon atoms C9 and C10 of the steroid B-ring (similarly 5,6-secosteroids, 13,14-steroids, etc.).

The prototypical secosteroid is cholecalciferol, vitamin D3.[3]


  1. ^ See for instance, the [1], free (medical) dictionary [2], biology-online [3], and medilexicon [4] entries for this term.
  2. ^ Donald Ayers, 1972, Bioscientific Terminology, Tucson: University of Arizona Press, pp. 241, 129. ISBN 978-0-8165-0305-6. See, accessed 10 May 2014.
  3. ^ See, for instance, J.R. Hanson, 2010, "Steroids: partial synthesis in medicinal chemistry, Nat Prod Rep. 27(6):887-99. doi: 10.1039/c001262a, PMID: 20424788. See!divAbstract, accessed 10 May 2014.

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