Osaterone (developmental code name TZP-5258), also known as 17ñ-hydroxy-6-chloro-2-oxa-6-dehydroprogesterone, as well as 2-oxachloromadinone, is a steroidal antiandrogen and progestin that was never marketed. The C17ñ acetate ester of osaterone, osaterone acetate, in contrast, has been marketed.