The structural features of effective antagonists of the luteinizing hormone releasing hormone.

The structure-activity data of 6 years on 395 analogs of the luteinizing hormone releasing hormone (LHRH) have been studied to determine effective substituents for the ten positions for maximal antiovulatory activity and minimal histamine release. The numbers of substituents studied in the ten positions are as follows: (41)(1)-(12)(2)-(12)(3)-(5)(4)-(47)(5)-(52)(6)-(16)(7)-(18)(8)-(4)(9)-(8)(10). In position 1, DNal and DQal were effective with the former being more frequently the better substituent. DpClPhe was uniquely effective in position 2. Positions 3 and 4 are very sensitive to change. D3Pal in position 3 and Ser in position 4 of LHRH were in the best antagonists. PicLys and cPzACAla were the most successful residues in position 5 with cPzACAla being the better substituent. Position 6 was the most flexible and many substituents were effective; particularly DPicLys. Leu(7) was most often present in the best antagonists. In position 8, Arg was effective for both antiovulatory activity and histamine release; ILys was effective for potency and lesser histamine release. Pro(9) of LHRH was retained. DAlaNH2 (10) was in the best antagonists.