Effect of Enol Etherification on Antiestrual and Contraceptive Activity of Some Progestins in Rats

Summary Cyclopentyl enol ethers of 17a-acetoxyprogesterone, 6a-methyl-17a-acetoxy-progesterone and 17a-ethynyl-19-nortestos-terone acetate were tested for ability to inhibit estrus, mating and fertilization in female rats with the following results: The first compound showed no inhibitory effect; the second blocked the estrous cycle, without interfering with mating and fertilization; the third proved to be a potent antiestrual and contraceptive agent, although it did not disturb sexual receptivity or cause permanent sterility. Thus, enol etherification reduces the antifertility effects of 6a-methyl-17a-ace-toxyprogesterone, but strongly enhances those of 17a-ethynyl-19-nortestosterone acetate.