title: Cyclic analogues of luteinizing hormone-releasing hormone with significant biological activities.
abstract: There is evidence that, in its receptor-binding conformation, the N and C terminus of LH-RH may be in close proximity and two cyclic analogues of the hormone were synthesized to test the hypothesis. Cyclic [beta-Ala1,D-Ala6,Gly10]- and [6-aminohexanoic acid1,D-Ala6,Gly10]-LH-RH were prepared by treatment of their linear precursor peptides with dicyclohexylcarbodiimide in the presence of 1-hydroxybenzotriazole in dilute dimethylformamide solution. Although the linear peptides possessed no detectable LH-releasing activity in ovariectomized rats, the cyclic beta-Ala analogue had 1.2% the activity of LH-RH, whereas the longer chain cyclic 6-aminohexanoic acid analogue had 0.65% activity. These results support the concept of an important interaction between the ends of the LH-RH molecule possibly involving hydrogen-bond formation between the pyrrolidone carbonyl group of pyroglutamic acid and the glycinamide group.
mesh_terms: D000818:Animals; D002369:Castration; D003500:Cyclization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone