19-Norprogesterone is a close analogue of the steroid progesterone, lacking only the C-19 methyl group of that molecule. In 1953, it was discovered that a preparation of 19-Norprogesterone yielded results equivalent to progesterone in assays detecting inhibitors of ovulation. This discovery led to the birth of an industrial-academic program of medicinal chemistry-driven research into contraception. When preparation of synthetic 19-Norprogesterone was streamlined and crystalline material was obtained, the norsteroid proved 4-8 more active than the natural steroid. Today, it is the parent of a series of progestins that remain in use as drugs, including nomegestrol acetate, promegestone, trimegestone, gestonorone, and nestorone.
