What is "retroprogesterone"

Retroprogesterone, also known as 9β,10α-progesterone or as 9β,10α-pregn-4-ene-3,20-dione, is a synthetic steroid and stereoisomer of the natural progestogen, progesterone. It is the parent compound of a group of progestins consisting of dydrogesterone (6-dehydroretroprogesterone) and trengestone (1,6-bis-dehydro-6-chloro-retroprogesterone). Retroprogesterone itself binds with high affinity to the progesterone receptor as well.

Ro 6-3129 (6-16-ethylthioretroprogesterone) is a retroprogesterone derivative that was never marketed.