[Synthesis and analgesic activity of analogs of U-50488, an opiate kappa-agonist].

In this paper, we report the synthesis and analgesic activities in mouse hot plate test and writhing test of some analogs of U-50488, a kappa-agonist. Results showed that compounds in which the amino group was pyrrolinyl had higher kappa-agonist activity and the substitution of two chlorine atoms in 3 and 4-positions of the benzene nucleus was very important to kappa-activity. Furthermore, all of compounds in which the amino group was piperidyl, piperazinyl or morpholinyl exhibited very weak kappa-agonist activity.