Synthesis of conformationally restricted progestational 13-ethylsteroids

As 3-Ketodesogestrel and Gestodene differ in the conformation of the 13-ethyl group, a series of progestagens was devised in which this conformation is fixed. Thus, both epimers of a steroid with a methyl-substituted 11,13-ethano bridge were prepared and their biological activities compared. From the receptor binding activity, it was concluded that the “Desogestrel conformation” is the more active one.