ABSTRACT
Steroids are a class of compounds that have a cyclopentanoperhydrophenanthrene skeleton, which occurs in nature and in synthetic products, and which can be classified into six groups according to the number of C-atoms: gonane (C-17), estrane (C-18), androstane (C-19), pregnane (C-21), cholane (C-24), and cholestane (C-27). These compounds are natural hormones or hormone precursors, except for cholane. In the naturally occurring steroids, the fusion of rings B and C is always trans and of the rings C and D usually trans (cis in the cardenolides and bufadienolides). Rings A and B are fused in cis and trans configurations with about equal frequency. Natural steroids possess either one or, more usually, two methyl groups at angular positions at which two rings meet. According to their function, steroid hormones can be divided into estrogen, androgen, glucocorticoids, and mineralocorticoids.
