Antagonists of the luteinizing hormone releasing hormone (LHRH) with emphasis on the TRP7 of the salmon and chicken II LHRH's.

The sequences of four naturally occurring luteinizing hormone releasing hormones (LHRH's) differ only in positions 5, 7 and 8. Salmon and chicken II LHRH's have Trp7; porcine/ovine (P/O) and chicken I LHRH's have Leu7. The receptor for P/O LHRH might effectively bind certain antagonists with Trp7. Thirteen antagonists having Trp7 and eight antagonists with other substitutions in position 7 were synthesized. One of the thirteen antagonists with the natural Trp7, [N-Ac-D-2-Nal1,D-pClPhe2,D-3-Pal3,D-Arg6,Trp7,D- Ala10]-LHRH, not only maintained activity, but had increased potency (ca. 58%; 90% antiovulatory activity/250 ng; rats) in comparison with the companion analog with the natural Leu7 of P/O LHRH. The other twelve Trp7-antagonists had lower potency.