Steroids are derivatives of cyclopentachyphanthrene hydrogenated phenanthrene. The number and position of double bonds in natural steroid molecules, the type, number and position of substituent groups, the configuration between subsiding groups and the ring nucleus, and the configuration between rings vary.
Its chemical structure is a cosmetic and looping compound composed of three six-carbon cyclohexane (A, B, C) and a five-carbon ring (D). Each carbon atom in the steroid molecule is numbered sequentially, and the number of the carbon atom is retained in the matrix structure of the steroid matrix, regardless of whether or not a carbon atom is present at any position.
The six-carbon rings A, B, and C in steroid molecules present in nature all have a "chair" conformation (ring structure), which is also the most stable conformation. The only exception is that the A-ring within the estrogen molecule is an aromatic ring with a planar conformation.
The junction between the A and B rings of steroids may be in either cis or trans configurations;
The junction of the C ring and the D ring is generally in trans configuration, with the exception of cardiac glycosides and toxins.