Antagonists of luteinizing hormone releasing hormone with novel unnatural amino acids at position six

Five new antagonists of luteinizing hormone releasing hormone (LHRH) containing novel unnatural amino acids at position six are reported. They are very effective in the rat antiovulatory assay. Using saline as vehicle, antagonist-[N- Ac-d -2-Nal¹, d -4-Cl-Ph², d -3-Pal³, Arg⁵, d -A2⁶,d -Ala¹⁰-LHRH inhibited ovulation completely at 1 μg/rat and three of the other antagonists showed some antiovulatory activity at μpg/rat.