Pregnane
Pregnane , also known as 17β-ethylandrostane or as 10β , 13β-dimethyl-17β-ethylgonane , is a C21 steroid and , indirectly , a parent of progesterone . 
<triplet> Pregnane <subj> steroid <obj> subclass of <triplet> progesterone <subj> steroid <obj> instance of