SOME DERIVATIVES OF PREGNA-D-6'-PENTARANES AS POSSIBLE ANTAGONISTS OFPROGESTERONE

Some derivatives of progestins of the pregna-D-6'-pentarane series hav e been obtained and examined for their possible hormonal and antihormo nal activity in the Clauberg-McPhail assay as well as in the pregnancy maintenance test in ovariectomized rabbits. 16 alpha, 17 alpha-Cycloh exanoprogesterones of the 19-methyl and 19-nor series (1-4) saturated in ring A, which are inactive as progestins, exhibited a remarkable an tiprogesterone effect. They decreased the McPhail index under combined administration with progesterone in a dose-dependable manner and comp letely inhibited the action of the latter in the pregnancy maintenance test.