Pharmaceutical progestins' do not appear in the bio-synthetic pathway. They are not found in any living forms. Progestins effects are not the same as natural progesterone and never will be.
Progesterone is a hormone produced by the ovaries and the adrenal cortex.
Natural progesterone is chemically identical to progesterone found in the human body. In the body progesterone is synthesized from pregnenolone which is synthesized from cholesterol. Progesterone is not found in any plant. Natural progesterone is synthesized from fat saponins such as diosgenin from Mexican wild yam or from soy. What Your Doctor May Not Tell You About Menopause, by John R. Lee, M.D., Warner Books, 196.