Gonadotropin releasing hormone antagonists: novel structures incorporating N omega-cyano modified guanidine moieties

A series of GnRH antagonists with substitutions at positions 1, 2, 3, 5 and 6 that included the recently reported homoArg-N omega-cyano-N omega'-alkyl- or Lysine-N epsilon-5'-(3-amino-1H-1,2,4-triazole) [Lys(atz)] amino acid derivatives was synthesized, characterized and tested for antiovulatory and anaphylactoid activities and binding affinity. Overall, these analogs were found to be considerably more soluble at neutral pH than their homologs Nal-Glu or Antide. The decapeptides with these substitutions in positions 5 and/or 6 retained high in vivo potency while those with similar substitutions at positions 1, 2 and 3 were significantly less potent than Nal-Glu or Antide. Of the 16 new analogs reported here, Azaline (Ac-DNal1, DCpa2, DPal3, Lys5(atz),DLys6(atz), ILys8,DA1a10]-GnRH) showed the most promising physico-chemical and biological properties [Lys(atz) = N epsilon-5'-(3-amino-1H-1,2,4-triazole) lysine]. Azaline is readily soluble in dilute buffers at pH 7.0, completely inhibits ovulation at 2.0 to 3.0 micrograms per rat, is equipotent to GnRH in releasing histamine in the rat and has a weaker anaphylactoid response in the rat than other analogs such as Nal-Glu or even Antide.