A number of 2, 6-dimethyl-3, 5-bis (metho~ c~ bonyl)-4-substituted-l, 4-~ ydrop~ idines were synthesized and evaluated for pregnancy-interceptive activity in mated hamsters. Out of 24 compounds, 12, 15, 21, 22, 28, and 34 caused a marked reduction in the number of implantations when administered on days 3-8 postcoitum. In an in vitro competition assay, none of the compounds exhibited noticeable binding affinity for uterine progesterone ...