19-去甲孕酮

19-Norprogesterone, also known as 19-norpregn-4-ene-3,20-dione, is a close analogue of the steroid progesterone, lacking only the C-19 methyl group of that molecule. The 1953 discovery that a preparation of 19-norprogesterone gave results equivalent to progesterone in assays detecting inhibitors of ovulation led to the birth of an ultimately successful industrial-academic program of medicinal chemistry-driven research into contraception; when arduous preparation of synthetic 19-norprogesterone was streamlined and crystalline material was obtained, the norsteroid proved 4- to 8-fold more active than the natural steroid. Chemistry used in 1938 to increase the bioavailability of ethisterone was cross-applied by Carl Djerassi and coworkers at Syntex in Mexico City in 1951 to prepare norethisterone, a synthetic norsteroid that was the first orally bioavailable progestin highly active in preventing ovulation. First human trials regarding contraceptive safety and efficacy were conducted using the related noretynodrel from G.D. Searle & Co.