Secosteroid

The word secosteroid derives from the Latin verb secare meaning "to cut",[2]: 241  and 'steroid'.

Secosteroids are described as a subclass of steroids under the IUPAC nomenclature.

[4] Types or subclasses of secosteroids are defined by the carbon atoms of the parent steroid skeleton where the ring cleavage has taken place.

For example, 9,10-secosteroids are derived from cleavage of the bond between carbon atoms C9 and C10 of the steroid B-ring (similarly 5,6-secosteroids, 13,14-secosteroids, etc.).

[1]: §3S-8 Some nonsteroidal estrogens, like doisynolic acid (cleaved on the D ring)[6] and allenolic acid,[citation needed] are also secosteroids or secosteroid-like compounds.

Cholecalciferol , an example of a 9,10-secosteroid. IUPAC -approved carbon numbering and ring labeling is shown in the picture. Since secosteroids are derived from steroids, they retain the same labeling system as steroids. [ 1 ] : §3S-8
The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins.